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DOI: 10.1039/D5GC02804C (Critical Review) Green Chem., 2025, Advance Article

From lithium-last technology to lithium-first technology: technical mapping and collaborative strategies for sustainable lithium-ion battery recycling

Jiefeng Xiao *af, Bo Niu b, Pengwei Li c, Weiqiang Chen d and Zhenming Xu e
aDepartment of Environmental Science and Engineering, College of Chemical Engineering, Huaqiao University, Xiamen 361021, China. E-mail: xiao_jiefeng@hqu.edu.cn
bCollege of Resources and Environmental Science, Hebei Agricultural University, Hebei, Baoding 071000, China
cCollege of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China
dKey Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China
eSchool of Environmental Science and Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240, China
fKey Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, School of Environment and Resource, Southwest University of Science and Technology, Mianyang 621010, China

Received 4th June 2025 , Accepted 31st July 2025

First published on 18th August 2025

Abstract

The lithium-ion battery (LIB) industry faces a critical challenge in achieving sustainable resource circularity amid surging global demand. While LIB recycling technologies have advanced, a disconnect persists between academia and industry: novel methods remain confined to labs, while industry relies on traditional hydrometallurgy with high pollution risks. This review redefines LIB recycling technologies as “lithium-last technology” (LLT) and “lithium-first technology” (LFT) paradigms, establishing a technical mapping to bridge this gap. LLT, driven by transition metal (TM) recovery, employs hydrogen-/nitrogen-based extractants or bio-extractants but suffers from inefficiency and environmental costs. LFT prioritizes selective lithium extraction via product- or process-oriented strategies, enhancing sustainability and shortening recycling routes. However, industrial adoption of LFT is hindered by operational complexity, impurity management, and scalability barriers. Life-cycle assessments reveal that emerging oxidative extraction and direct regeneration show promise for low-carbon development, yet traditional methods dominate due to rigid infrastructure and market immaturity. Future challenges include handling low-value LIBs (e.g., LFP), mitigating overcapacity, and integrating AI for pre-evaluation. This work provides actionable insights to align academic innovation with industrial needs, fostering eco-friendly and economically viable LIB recycling.

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Jiefeng Xiao

Jiefeng Xiao is a lecturer in the Department of Environmental Science and Engineering, Huaqiao University. He received his PhD from Shanghai Jiao Tong University in 2022, which was supervised by Prof. Zhenming Xu. He has been studying the resource recovery and pollution control of spent lithium-ion batteries. He has published 16 SCI papers in Environmental Science & Technology, Journal of Hazardous Materials, Journal of Cleaner Production, ACS Sustainable Chemistry & Engineering, etc. Among the papers, 4 articles on spent LIB processing were included in SI highly cited papers (1%).

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Bo Niu

Bo Niu is a Professor at the College of Resources and Environmental Science, Hebei Agricultural University. He received his PhD from Shanghai Jiao Tong University in 2019, which is supervised by Prof. Zhenming Xu. Then, he followed the Post-Doctoral Research Center in the School of Environmental Science and Engineering at Shanghai Jiao Tong University until 2021. He has published 29 SCI papers on resource recovery and pollution control about spent lithium-ion batteries (LIBs) and waste electronic components. Moreover, he also contributed to the in situ designing and construction of functional materials from spent LIBs through experimental and density functional theory calculations. The correlational research has been published in Chemical Review, PNAS, Environmental Science & Technology, Journal of Materials Chemistry A, Energy and environmental materials, Journal of Catalysis, Green Chemistry, etc. His recent research areas also include spent LIB treatment using machine learning.

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Pengwei Li

Pengwei Li is a lecturer in the Department of Materials Science and Chemical Engineering at Harbin Engineering University. He received his PhD from Northeastern University in 2024, with Professor Shaohua Luo as his supervisor. He mainly studies the high-value utilization of spent lithium-ion batteries and has published 22 SCI papers in journals such as Chemical Society Reviews, Journal of Energy Chemistry, Separation and Purification Technology, and ACS Applied Materials & Interfaces. One of his papers on the high-value utilization of spent lithium-ion batteries was included as an SI hot paper (0.1%).

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Weiqiang Chen

Weiqiang Chen is a professor of Urban and Industrial Sustainability at the Institute of Urban Environment, Chinese Academy of Sciences (CAS). He graduated from the School of Environment at Tsinghua University, Beijing, and worked at the Yale Center for Industrial Ecology during 2010–2015. His research focuses on (1) industrial ecology, (2) urban metabolism and sustainability, and (3) anthropogenic cycles and sustainable management of materials, especially metals, plastics, and chemicals. His studies have been published in PNAS, Nature Climate Change, Nature Geoscience, Nature Computational Science, Nature Communications, Environmental science and Technology, and other first-level journals. He is now associate editor for two journals: Resources, Conservation, and Recycling and Journal of Industrial Ecology.

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Zhenming Xu

Zhenming Xu is the Distinguished Professor in the School of Environmental Science and Engineering at Shanghai Jiao Tong University. He is the Most Cited Chinese Researcher according to Elsevier in 2020–2022. His group has been dedicated to the study of e-waste recycling. Over the past decade, his group has published more than 200 SCI papers on resource recovery and pollution control of e-waste, including spent lithium-ion batteries, waste printed circuit boards, waste electronic components, and waste liquid crystal panels. The findings are published in Chemical Review (1 paper), PNAS (2 papers), Environmental Science & Technology (39 papers), Journal of Hazardous Materials (60 papers), etc. The research results are reported and highly reviewed on more than 30 journal websites including Environmental Science & Technology News, The New York Times (Science), and New Scientist.


Green foundation

1. This review advances principle #1 (prevention) by redefining LIB recycling from traditional lithium-last technology to emerging lithium-first technology, systematically mitigating secondary pollution in conventional processes. It embodies principle #6 (energy Efficiency) through frameworks prioritizing low-energy pathways and AI-driven optimization.

2. The lithium-first paradigm significantly reduces hazardous chemical reliance and waste generation while circumventing energy-intensive purification. Selective extraction and direct regeneration routes collectively lower carbon footprint and resource consumption. By bridging academia-industry gaps, this work empowers global adoption of safer recycling systems.

3. Our roadmap integrating technical mapping with multi-stakeholder collaboration accelerates circular battery economies, supporting UN SDG 12 for sustainable resource management.


1. Introduction

Lithium-ion batteries (LIBs), the carrier of new energy, trigger energy evolution worldwide. The LIB industry has developed into a fiercely competitive global market. Global LIB shipment reached 1192 GWh in 2023, with a year-on-year increase of 25.6%.1 It is predicted that the shipment will reach 1[thin space (1/6-em)]926.0 GWh in 2025 and 5[thin space (1/6-em)]004.3 GWh in 2030.1 However, this prosperity hides a problem. Global critical resources such as about 60% lithium (Li), 30% cobalt (Co) and 10% nickel (Ni) were used for electric vehicle (EV) batteries in 2022.2 The potential shortages in the supply of critical resources may render the LIB industry unsustainable like fossil industry. To avoid this, it has become a consensus to recover critical resources from spent LIBs and realize the closed loop of the LIB industry.3 According to SNE research, global spent LIBs will reach 786[thin space (1/6-em)]000 tons in 2025 and 1[thin space (1/6-em)]436[thin space (1/6-em)]000 tons in 2030.4 In the future, spent LIBs will be the important source of critical resources for LIB manufacturing. As a result, LIB recycling has raised a new tide for the academia and industry worldwide.

To date, great R&D efforts and finances have been invested toward developing effective technologies for recycling critical resources from spent LIBs.5 LIB recycling industry is booming and expanding, and its global market size amounted to $3.79 billion in 2023.6 For example, the number of registered LIB recycling enterprises in China reached over 42[thin space (1/6-em)]000 in 2022 alone, reflecting a substantial increase of 60.6%.7 However, we find that there is a new crisis behind this prosperity. Although LIB recycling has developed for decades, its widespread implementation in industry has only occurred in recent years. Within such a short time, substantial financial and human resources have been poured into LIB recycling, resulting in remarkable prosperity but also serious disorders. We conducted field research in major LIB recycling enterprises such as Bump and Green in China and found that industry was seriously out of step with academia. Although varieties of advanced technologies have been developed in academia, industry still applies the traditional technologies from decades ago.8,9 Therein, highly polluting hydrometallurgical technologies involving strong acids, reductants, and organic solvents were widely applied in these officially certified enterprises.10,11 In a way, these newly rising enterprises are much like the wet smelting plants. The apparent growth in academic research does not fully translate to practical progress. While over 10[thin space (1/6-em)]000 studies on battery recycling have been published since 2020, most lack industrial applicability. This disconnect stems from two key issues: insufficient industry-academia collaboration and an overemphasis on theoretical novelty over implementable solutions. The intricate operation, inaccessible equipment, and obscure mechanisms associated with the new technologies developed by academia make them challenging for industry to comprehend and implement. Relatively, most investors hastily pursue market opportunities, and haphazardly employ existing immature technologies for the recovery of spent LIBs, thereby giving rise to an underlying predicament. As a result, most of the studies are not devoted to industrial applications, and the innovation in academia is not driving progress in industry. It is highly significant to achieve the consistency of the development orientation in academia and industry by reviewing existing LIB recycling technologies and realize low-carbon development of LIB recycling industry.

Numerous reviews have been published regarding LIB recycling. These reviews either concentrate on certain part of recycling processes (pretreatment,12 metal leaching,13 and solvent extraction14), or focus on the specific LIB ingredient recycling (anode,15 cathode,16 and electrolyte17), or review specific technical advancements,18,19 or summarize some specific technology (hydrometallurgy,20 pyrometallurgy,21 and regeneration22). Previous reviews mostly emphasize on theoretic aspects such as reaction mechanisms, recycling efficiencies, and technical challenges, and neglect the analysis of future directions and underlying application potentials. Consequently, academia and industry are drifting apart. Academia lays more emphasis on fine regulations, complex operations, and special technologies, while industry has no efficient access to really applicable technologies. The main problem is that the current LIB recycling technology lacks a technical mapping, which can indicate clear directions for researchers and provide understandable guidance for practitioners.

To bridge the academia-industry disconnect in LIB recycling, this review redefines existing technologies as two paradigms: lithium-last technology (LLT, prioritizing transition metals) and lithium-first technology (LFT, targeting selective Li recovery). We construct a technical mapping framework to clarify their principles, advantages, and industrial scalability, highlighting their environmental trade-offs and economic feasibility. Critical gaps such as overreliance on hydrometallurgy, challenges in LIB recycling, and scalability barriers of emerging methods are systematically analyzed. We propose actionable strategies including AI-guided process optimization and life-cycle assessment integration to align innovation with industrial needs. This work aims to stimulate academia-industry collaboration toward sustainable, cost-effective LIB recycling systems.

2. What is the technical mapping for LIB recycling?

The evolution of lithium-ion battery (LIB) recycling reveals shifting material priorities in the battery industry. When LiCoO2 (LCO) batteries dominated consumer electronics starting in 1993,23 cobalt recovery formed the sole focus of recycling due to its high value. With minimal waste LIB production, recyclers blended LIBs with Ni–H hydride batteries to extract Co–Ni alloys.13,24 Early hydrometallurgical processes possessed lithium recovery capabilities. However, cobalt's substantially higher content in LCO cathodes (typically >8 times that of lithium), combined with its high recovery efficiency, characterized by technically feasible extraction into valuable forms (e.g., metal and salts) and high achievable yields, made it the dominant economic driver for recycling. Recyclers routinely discharged lithium into slag or wastewater after Co extraction.25 This established cobalt-first strategies known as “lithium-last technology” (LLT), where lithium recovery became a last consideration in multi-step purification processes, achieving only 60–90% efficiency.26 The introductions of NCA and NCM batteries maintained this pattern, as cobalt's economic dominance persisted through their limited market penetration. Recycling systems persistently optimized leaching and solvent extraction processes for Co/Ni/Mn sulfate refinement, while lithium recovery remained systematically deprioritized despite its technical feasibility.

Market forces eventually compelled technological transformation. As cobalt-low NCM and cobalt-free LFP batteries occupied the major EV market,27 recycling Co no longer serves as the sole focus in the LIB recycling. Meanwhile, increasing lithium prices created new economic imperatives. As a result, lithium recovery transitioned from cost burden to profit center. This economic shift gave rise to “lithium-first technology” (LFT), featuring innovative methods that prioritize lithium extraction before processing other materials. Modern LFT employs selective leaching to separate lithium at initial stages, achieving over 90% recovery rates by preventing cross-process losses.28,29 The remaining transition metal residues then feed cathode precursor production. More than technical refinement, this sequence inversion from LLT to LFT reflects fundamental restructuring of recycling economics, where recycling lithium now dictates process architecture. The industry's progression ultimately answers a critical challenge: maximizing lithium recovery as battery chemistry reduces cobalt dependence.

2.1 Lithium-last technology: focusing extracting reagents

During the “lithium-last” period, technological developments were driven by how to ensure efficient recovery of TMs. As shown in Fig. 1, the LLTs focus on the development of highly efficient extracting agents such as proton-based extractants (PbEs), non-protic extractants (NpEs), and bio-extractants.
image file: d5gc02804c-f1.tif
Fig. 1 Mapping of “lithium-last technology” for LIB recycling.
2.1.1 Proton-based extractants. PbE supplied hydrion (H+) to dissolve metals by seizing the structural oxygen in the cathode (Fig. 1). The anions could promote the dissolution via coordinating and chelating activities. In this process, the reducing agent was added to reduce the high-valence metals (Ni/Co/Mn), reducing reaction activation energy. Based on the sources of H+, we categorized PbE into three types: inorganic acid, organic acid, and inorganic acid generator.
Inorganic acid. Usually, it did need strong inorganic acid species such as HCl,30 H2SO4,31 and HNO3[thin space (1/6-em)]32 to produce enough H+ for dissolving metal. As shown in Fig. 2a, acid concentration, temperature, time, and reductant dosage have significant effects on metal leaching efficiencies. Always, the acid concentration of over 1 mol L−1 could leach over 80% of metals out within 30–60 min at 70–90 °C. In this process, active Li was more easily extracted from the cathode than TMs, resulting in a higher leaching rate. HCl showed a better performance than H2SO4 and HNO3, and this is because Cl− could act as the reductant in the leaching process.33 During dissolution, the reductant could greatly improve the leaching rate by lowering the reaction activation energy.34 The common reductant included H2O2[thin space (1/6-em)]34 and NaHSO3.35 Recently, the related research studies have focused on the application of organic reductants such as glucose,36 glutathione,37 ginkgo biloba,31 starch,38 and areca powder.39 However, organic reductants still had some limitations in scale application, such as high cost or second pollutant risk (high TOC in wastewater). At present, it is “H2SO4 + H2O2” rather than other reagents that is widely applied in industries. This is because H2SO4 would not cause serious acid smog like HCl and explosive risk like HNO3, and H2O2 has comprehensive advantages over other reductants, such as production, cost, and environmental friendliness. In addition, metal leaching efficiencies could be improved a lot assisted by ultrasound. For example, employing an ultrasound-assisted process could increase the leaching rates of both Li and Co by about 20% within 10 minutes.40 Notably, it is not economically feasible to leach all metals, particularly Fe, from the LFP cathode using inorganic acids, as the olivine structure of LFP is difficult to be completely destroyed.41,42 For instance, a significant amount of reagents (20 wt% HCl and 30.0 wt% H2O2) were highly demanded for leaching LFP.41 At present, how to effectively recover Fe resources in LFP in a cost-effective manner has been a problem plaguing researchers.
image file: d5gc02804c-f2.tif
Fig. 2 (a) Breakdown of proton-based extractant for LIB recovery. (b–d) Inorganic acid (b), organic acid (c), and inorganic acid generators (d).

Organic acid. Compared with inorganic acids, organic acids have excellent environmental performances such as low corrosion and no toxic gas production. Notably, the organic anions can coordinate and chelate metal ions, greatly improving the metal dissolution. Relatively, organic acid differs from inorganic acid in two ways. One is that organic acid is suitable for all LIB chemistries such as LCO, NCM, and LFP. The other is that the reaction can be driven by both wet leaching and grinding. As shown in Fig. 2b, various organic acids such as ascorbic acid,43 formic acid,44 citric acid,45 lactic acid, oxalic acid,46 acetic acid,47 and methanesulfonic acid48 have been used for leaching spent LIBs. Commonly, the leaching conditions using organic acids are similar to those of inorganic acid. For example, 94.8% Co and 98.5% Li were extracted at 70 °C within 20 min using 1.25 M ascorbic acid as both acid species and reductant.43 It is noteworthy that the ligancy of organic acids exhibited strong positive correlation with the leaching efficiency. Choi et al.49 compared the performances of different organic acids at a fixed pH of 2 (using HNO3) without adding any reductant and found that the oxygen atoms in organic acids interacted with metal ions to promote the leaching rate. However, it is hard to efficiently leach metals by organic acids (chelation) alone. It is also necessary to add reductants (always H2O2) to lower the reaction activation energy, improving the leaching efficiency.44 Besides, organic reductants such as ethylene glycol (EG),45 orange peel,50 molasses,48 and bagasse pith51 can also be used to replace H2O2 for the leaching. Recently, ultra-leaching of spent LIB using mixed acids52,53 has attracted much attention. It was found that mixed HNO3 and ascorbic acid could completely leach metals from spent LIBs within 10 min.54 The use of mixed acids could gain higher profit than traditional “H2SO4 + H2O2”.55

Grinding is another driving way for recycling LIBs by organic acid. For example, by co-grinding with EDTA, 98% Co and 99% Li could be extracted from the LCO cathode.56 Besides, the leaching efficiencies of Li and Fe can be over 95% by co-grinding with citric acid.57 Currently, although mechanochemistry using organic acids have excellent performance for metal extraction, it is still far from scale application because of its high cost and limited handing capacity.


Inorganic acid generator. Different from inorganic and organic acids, inorganic acid generators such as Fe2(SO4)3,58,59 FeCl3,56 SiCl4,60 PVC,61 NH4Cl,62 and Na2SO4[thin space (1/6-em)]63 have been applied to indirectly leach metal from the spent LIBs, breaking the traditional idea of metal leaching from spent LIBs. Always, these generators possess the properties of easy hydrolysis, acidic product, and thermal instability, as shown in Fig. 2c. The driving methods include wet leaching (hydrolysis),58,64 mechano-chemistry (air-slake),56 roasting (decomposition),60,62 subcritical water (dehalogenation),61 and electrochemistry (electrolysis).63 For example, Fe3+ can hydrolyze to produce H+ for metal leaching. Using 0.2 mol L−1 Fe2(SO4)3, the leaching efficiencies of Ni, Co, Mn, and Li exceeded 96% at 90 °C within 40 min.59 Relatively, grinding was not conducive to the generation of H+, and the leaching rates of Li and Co were only 87% and 41%, respectively.56 Thus, it could be seen that the generation rate of H+ had a significant effect on metal leaching. For instance, NH4Cl, (NH4)2SO4,65 SiCl4,60 and copperas66 could effectively thermally decompose to produce HCl or H2SO4, achieving all metal leaching rates of over 95%.62,65 The suitable roasting temperature was 350–500 °C. In addition, by the dehalogenation, organic halides such as polyvinyl chloride (PVC)61 and chlorinated polyvinyl chloride (CPVC)67 could produce acids under subcritical water conditions (240–350 °C). The leaching efficiency of over 98% could be obtained.61 Recently, the electrolysis of salt solutions (NaCl,68 Na2SO4,63 and CuSO4[thin space (1/6-em)]69) has been applied for LIB recycling. By Na2SO4 electrolysis (2 mol L−1), the yielded concentration of H+ was 0.93 mol L−1 with a current efficiency of 78.2%.63 The leaching efficiencies for Al, Ni, Co, Mn, and Li all exceeded 99%. In summary, the utilization of inorganic acid generators effectively circumvents the necessity for strong acid. However, it still has the disadvantages of high temperature/pressure, limited handling capacity, complex operations, and unverified scalability.
2.1.2 Nitrogen-based extractants.
Inorganic nitrogen cations. NpE is always an alternative to dissolving the oxygen structure of the cathode. NpE includes inorganic NpE (i.e., NH4+) and organic NpE (i.e., NR4+). Therein, NH4+ is primarily derived from ammonia salts, while NR4+ is mainly derived from ionized organic nitride (quaternary ammonium salt). The driving methods include wet leaching and deep eutectic solvent (DES) way. However, due to the weak dissolving ability of NH4+, it was necessary to add coordinative NH3 to facilitate metal dissolving. Thus, the combination of ammonia salt and NH3·H2O could show an equivalent dissolving ability like H+, as shown in Table 1. In the NH3-(NH4)2SO4–Na2SO3 system, the optimal leaching efficiencies of Li, Co, and Ni were 96.2, 89.9, and 90.1%, respectively.70 It could be seen that the leaching rate of Mn was the lowest. This is because the Mn-coordinated complex was subsequently precipitated as a clathrate.71 It was found that the leaching efficiencies using inorganic NpE were much lower than that using acid species. This is because TMs were more difficult to reduce under an alkaline environment. To improve the leaching efficiencies, reductive roasting was applied to dissociate and transform metal oxides into simple substances. The results indicated that 97.7% Ni and 99.1% Co were leached out after reductive roasting.72 Besides, subcritical water (150–180 °C, 1.5–3.5 MPa)73 and electrochemical method74 had also been used to enhance the metal dissolution using inorganic NpE. In conclusion, compared with inorganic acid, inorganic NpE does not have obvious advantages in terms of environmental protection, economy, and efficiency. Therefore, it has not been used in industry.
Table 1 Summary of ammonia leaching
Reagents Reductants Conditions Efficiencies (%)
1 M NH3·H2O–1 M (NH4)2CO3 0.5 M (NH4)2SO3 80 °C, 1 h, 10 g L−1 94 Co, 37 Ni
4 M NH3·H2O–1.5 M (NH4)2SO4 0.5 M Na2SO3 90 °C, 3 h, 10 g L−1 89.9 Co, 90.1 Ni, 96.2 Li, 9.2 Mn
4 M NH3·H2O–1 M NH4HCO3 0.3 M Na2SO3 80 °C, 5 h, 10 g L−1 86.4 Co, 85.3 Ni, 79.1 Li, 1.45 Mn
4 M NH3·H2O–1.5 M NH4Cl 0.4 M Na2SO3 80 °C, 5 h, 10 g L−1 76.0 Co, 78.3 Ni, 74.7 Li


Organic nitrogen cation. Metal leaching using organic NpE and additives can be regarded as modified wet-leaching, which is called the DES method. In this case, organic NpE such as choline chloride,75,76 betaine hydrochloride,77 tetrabutylammonium chloride,78 and imidazolium chloride79 can ionize to a large number of organic nitrogen cations, as shown in Fig. 3a. These organic nitrogen cations would induce the formation of hydrogen bonds. Similarly, organic phosphorus80/sulfur81 cations could play the same role. Here, the acidity and reducibility of DES had significant effects on the metal leaching efficiencies. Always, under thermal conditions, the dissociated hydroxyl, carboxyl, and guanidyl of NpE embodied the weak acidity (Fig. 3b). Regarding nonacidic NpE, certain acids such as monochloroacetic acid78 and decanoic acid80 were incorporated to furnish appropriate acidity. The acidity of DES exhibited a significant correlation with the metal leaching efficiency. We discovered that a higher acidity would result in a more rapid leaching kinetics, as shown in Fig. 3c. For example, in the DES consisting of Choline Chloride (ChCl) and EG, to obtain the optimal Co leaching rate of 94%, it was a requisite to conduct the reaction at 220 °C for 24 h.75 Comparatively, when using p-toluenesulfonic acid instead of EG, nearly 100% leaching rates of Li and Co were achieved at 90 °C within 15 min.82 This was because higher acidity was conducive to the disruption of the oxygen structure, thereby leaving the crystal structure broken. Besides, auxiliary methods of grinding76 and microwave83 could be employed to facilitate the disruption of crystal structure. Wang et al.76 found that through mechanical pre-destruction of the crystal structure, the leaching rates of Ni, Co, and Mn were significantly improved from 65.8 to 99.0%, 71.2 to 98.2%, and 71.2 to 98.5% at 80 °C within 40 min, respectively.
image file: d5gc02804c-f3.tif
Fig. 3 (a) Chemical structures of typical organic NpE and others. (b–e) Key factors of metal leaching using organic NpE: source of acidity (b) and its effects on leaching efficiencies (c), source of reductant (d) and its effects on leaching efficiencies (e).

In addition to the acidity, the reducibility of DES was another key factor. The reductants could be organic cations or additives (Fig. 3d). In the leaching process, unstable high-valence M3+ (M = Co/Ni/Mn) was reduced as M2+. As a result, the lattice energy and stability of crystal structures decreased a lot after reduction.84 Always, extra reductants such as EG,75 urea,85 and L-ascorbic acid86 were added to avoid the loss of organic cations. As presented in Fig. 3e, the higher the reducibility, the faster the leaching efficiency. For example, when employing urea instead of EG, the optimal reaction conditions decreased from 220 to 180 °C, and from 24 to 12 h.75,85 Besides, the coordination and chelation of DES could facilitate the metal dissolution. In this process, the released TMs (i.e., Co) always coordinated with Cl− to form CoCl4− anions. Due to the existence of organic cations, high-valence CoCl4− could still exist. Under the action of reductive species, CoCl4− would be reduced into stable CoCl42−. In addition to Cl−, organic atoms such as O, S, and N could coordinate with TMs.

In summary, the key factors for metal leaching using organic NpE included cation type, acidity, and reducibility. Commonly, the leaching performances could be ordered as follows: ternary + auxiliary > ternary > binary. More specifically, the leaching ability were sequenced as ChCl/EG/lactic acid > ChCl/EG/urea > ChCl/EG.

2.1.3 Bio-extractant. Bio-extracting is a promising method for leaching metal, due to its low cost, simple operation, and environmental friendliness. The bio-extracting process was realized through bacteria and fungi, as shown in Fig. 4a. The common bacteria included Acidithiobacillus thiooxidans (A. thiooxidans), Acidithiobacillus ferrooxidans (A. ferrooxidans), and Leptospirillum ferriphilum (L. ferriphilum). Therein, the culture system had a significant impact on the leaching efficacy of bacteria. For example, in a single system (A. thiooxidans), the optimal leaching efficiencies were only 22% Li and 66% Co. Comparatively, leaching efficiencies of 90% Li, 90% Mn, 96% Co, and 97% Ni can be reached by mixed energy source-mixed culture system (A. thiooxidans and L. ferriphilum).87 This is because the mixed system could produce more biogenic acidic species (i.e., H2SO4) for metal dissolution.87 It has been proved that ascorbic acid88 and gallic acid89 could facilitate metal leaching from the spent LIBs. It showed that adding ascorbic acid realized 54% Co and 31% Li enhancement, obtaining leaching efficiencies of 94% Co and 95% Li.88 Besides, reductive species could improve the leaching efficiency. Liao et al.90 found that 99% of Co and 100% of Li were leached in a mixed system, with the assistance of Fe2+ as a reductant. Apart from bacteria, fungi were used for metal leaching from spent LIBs. Commonly used fungi included Aspergillus niger and Penicillium chrysogenum. Different from bacteria, heterotroph fungi primarily relied on the metabolites for metal leaching. Thus, the carbon source was much important. Naseri et al.91 compared the effects of carbon sources (molasses and sucrose) on the metabolites. The results indicated that the yield of organic acids in molasses media was higher than that in sucrose media, and the optimal leaching efficiencies of Mn and Li in the molasses media reached 87% and 100%, respectively.
image file: d5gc02804c-f4.tif
Fig. 4 (a) Diagram of the bioleaching method for spent LIB recovery. (b) Comparative results of bioleaching and chemical leaching (reproduced from ref. 92 with permission from the American Chemical Society, copyright 2018).

Under certain conditions, the metal leaching by fungi was highly comparable to or even better than that by bacteria or inorganic acid. As shown in Fig. 4b, a significant quantity of Co (82%) and Li (100%) dissolution was observed in fungi strain (MM1), while only 22% Co and 66% Li were solubilized in bacteria strain (80191).92 The reason might be that fungi could produce mixed acid species including citric acid, malic acid, and gluconic acid. Amongst them, citric acid showed excellent performance for metal leaching. For example, the optimal bio-production of citric acid by Penicillium citrinum reached 40.12 g L−1.93 In summary, bioleaching had the advantages of lower energy consumption and greater environmental friendliness over chemical leaching. However, the unstable operations had greatly limited its scale application.

2.2 Lithium-first technology: focusing lithium's selective extraction

As shown in Fig. 5, we classified LFT technologies into two categories: product-oriented technology (PtOT) and process-oriented technology (PsOT). Here, PtOT aimed to obtain the products with different solubilities, while PsOT focused on the selective release of Li elements from the cathode.
image file: d5gc02804c-f5.tif
Fig. 5 Mapping of the “lithium-first technology” for LIB recycling.
2.2.1 Product-oriented technology. Via the PtOT process, all metals were released non-selectively from the LIB cathode. Due to differences in solubility, lithium-containing products were transferred into the aqueous solution, while TM-containing products remained as sediment. For clarity, we further categorize PtOT into co-leaching/precipitation and reductive conversion for discussion.
Co-leaching/precipitation. Actually, co-leaching/precipitation is also a PbE leaching process. During the leaching process, however, the PbE anions would simultaneously react with leached TM cations to form new sediments, as depicted in Fig. 6a. As a result, only Li remained in the aqueous solution. To realize this, there is a special requirement for the species of PbE that its anions tend to precipitate with TM cations rather than Li cations. The common PbE includes H3PO4 and H2C2O4. For example, Zeng et al.96 treated LCO with H2C2O4 and found that Co was first leached as Co2+ and then precipitated into a CoC2O4 sediment, while leached Li+ still remained in the solution (Fig. 6b). Similarly, H3PO4 was also employed to convert >99% Co into Co3(PO4)2 sediments (97.1% purity).97 At present, there are two factors that limit the application of co-leaching/precipitation. One is the high cost of H3PO4 and H2C2O4, and the other is the separation of Co precipitates (the processing object in industry was always black mass including anode, cathode, Al, and Cu, rather than only cathode).
image file: d5gc02804c-f6.tif
Fig. 6 (a) Diagram of co-leaching/precipitation. (b) Flow chart of co-leaching/precipitation using H2C2O4. (c) Product properties of thermal reduction at different temperatures. (d) Li leaching efficiencies via mechanical reduction (reproduced from ref. 94 with permission from Elsevier, copyright 2023). (e) Hydrothermal reduction (reproduced from ref. 95 with permission from Elsevier, copyright 2023). (f) Diagram of electrochemical reduction.

Reductive conversion. Reductive conversion is primarily suitable for recycling LTMO-type battery. Following reduction, lithium is converted into water-soluble compounds (e.g., Li2O or Li2CO3), while TMs form water-insoluble species such as metals or oxides. Lithium can thus be selectively extracted via simple water leaching. The key to this process lies in the reducing power, derived from chemical reductants or electrical input. Based on the driving mechanism, we classify reductive conversion into four categories: thermal reduction, mechanical reduction, hydrothermal reduction, and electrochemical reduction.
Thermal reduction. Thermal reduction is one of the earliest technologies applied to recycling LIBs owing to its unique properties such as simple operation and low chemical consumption.98 The research focused on the development of reductants, as shown in Fig. 6c. The reductants could be classified into three types: metal reductant (Zn/Al), gaseous reductant (H2/NH3), and carbon-based reductant (C/CH4/organics). Among them, the carbon-based reductants have attracted much attention. Carbon-based reductants could be derived from wastes such as graphite,99 biomass,100,101 antibiotic bacterial residues,102 and plastics,103,104 achieving a win–win strategy of “waste + waste → resources”. During the reduction process, organics was first pyrolyzed to produce reductive gases such as CH4, H2, and CO, which then reduced the LTMO cathode.101,105

The disparities among these reductants were mainly manifested in the reaction temperature and products. Researchers endeavored to obtain a Li-containing product with high solubility and low energy consumption. Therein, highly water-soluble Li6ZnO4[thin space (1/6-em)]106 and Li2O107 could be obtained using Zn or gaseous reductants at 500–700 °C. Regarding Al-based reduction, NaOH solution was needed to recycle water-insoluble LiAlO2.108 When using carbon-based reductant, Li2O was further converted into slightly water-soluble Li2CO3, due to the existence of by-product CO2.109 Generally speaking, the reduced TM products exhibited a correlation with the reaction temperature. With the increase in temperature, TM was first reduced into oxides (CoO/NiO/MnO) and then metals (Co/Ni). Notably, metal Mn was hard to obtain due to its high Gibbs free energy.110 To obtain metal Mn, the reaction should be performed under vacuum and high-temperature (1450 °C) conditions.111 The recovery rate of Li depended largely on the type of product. The optimal recovery rate of Li2CO3 products always ranged from 80% to 90%,109 while that of Li2O products could readily exceed 90%.150 To improve the recycling rate of Li2CO3, carbonated water,112 grinding,113 and ultrasound113 have been applied. However, the concentration of Li liquor obtained was still low, which greatly increased the subsequent recycling cost.114 Thus, great efforts have been made to avoid the generation of Li2CO3. For example, Wang et al.115 added 10% NaOH to absorb CO2, effectively protecting Li2O. The results exhibited that over 93% Li was leached and the Li concentration was up to 14.99 g L−1. Recently, a flash Joule heating method116,117 has been applied to regulate the generation of Li-containing products. By this way, the temperature could rapidly exceed 2000 °C within 5 seconds. Due to the ultrashort reaction time, Li was controllably converted into Li2O.117 As a result, a Li liquor of 1.67 g L−1 could be obtained, which was higher than that of the traditional carbothermal process (0.86 g L−1 (ref. 99)).

Notably, thermal reduction was traditionally used to treat LTMO cathodes but not LFP, due to LFP’s stability and resistance to thermal decomposition. Until recently, salt-assisted thermal reduction has been proposed to treat LFP. Using Na2CO3 as the activating agent over 900 °C, LFP was reduced to Fe, NaLi2PO4, and LiNa5(PO4)2.118 Thus, salt-assisted roasting may be a promising way to treat refractory cathodes.


Mechanical reduction. Previously, when co-grinding PVC with LCO, it was found that the addition of reductants such as Al/Fe/Ni could facilitate metal release during grinding.119 In this process, LCO was mechanically reduced to CoFe4O6. Inspired by this, researchers have tried to use the reductant as the only additive to realize the mechanical reduction of the cathode. As shown in Fig. 6d, reducing reagents (RRs) such as Al, S, Ni, Fe, and Cu were tried for the mechanical reduction of LCO.94 The results indicated that LCO was reduced by Cu into Li2O and CoO at a rotary speed of 600 rpm within 90 min, achieving the optimal Li leaching rate of 94%. In addition, Li et al.120 co-grinded NaBH4 (strong reducibility) with LCO to successfully obtain Co, Li2O, and NaBO2. Although mechanical reduction could realize the selective extraction of Li, it should be noted that the introduction of metal impurity would increase the difficulty of subsequent TM recoveries. In view of this, developing impurity-free reductant was significant.
Hydrothermal reduction. Hydrothermal reduction integrated thermal reduction and water leaching processes. Under subcritical water conditions, Li within the LTMO cathode underwent reduction to form Li2O, which subsequently dissolves in water. However, the practical implementation of solid reductants has been hindered by inefficient solid–solid interfacial interactions between the reductant and cathode materials in aqueous environments. Recent advancements have introduced alcohol-mediated hydrothermal reduction as a promising strategy for recycling Li from LTMO cathodes.95,121 As illustrated in Fig. 6e, comparative investigations of alcohol reductants (methanol, ethanol, propanol, and EG) revealed EG as the most effective agent, achieving a remarkable Li extraction efficiency of 99%.95 Nevertheless, the relatively mild reducing capacity of EG necessitated prolonged processing durations (20 h) to achieve optimal recovery rates. This kinetic limitation highlights a critical research direction for process optimization, particularly through the development of catalytic enhancement strategies or hybrid reductant systems to accelerate the reaction kinetics while maintaining high extraction yields.
Electrochemical reduction. In addition to the above-mentioned reducing agents, the reducing force can stem from electrolysis in Fig. 6f.122 Conventional aqueous electrolytes are unsuitable for recovering metals from spent cathodes because the reduction potentials of target metals are typically higher than that of water. This leads to a competing reaction where water electrolysis occurs preferentially, consuming energy without effectively reducing the metals. To overcome this limitation, molten Na2CO3–K2CO3 at 750 °C was employed as the electrolyte. Notably, this method was suitable for treating all LIB cathodes such as LTMO and LFP. In this process, LCO was reduced first into CoO and then Co when the voltage increased from 1.0 V to 1.8 V. Here, the electrolyte played a crucial role for reduction. When employing an aqueous electrolyte, the working voltage increased to 3.5 V.123 Meantime, Li was transferred into the molten salts. As for LFP, the reduction products included Fe and Li3PO4. These findings breakthrough the idea of traditional reagent-dependent reduction, providing some inspirations for the reagent-free reduction. However, the problems of high energy consumption and massive waste salts have still limited the application of electrochemical reduction. We think some efforts can be made to seek an applicable electrolyte to reduce the conversion temperature, or reduce the cost of electrolyte.
2.2.2 Process-oriented technology. PsOT encompasses two distinct approaches: induced extraction and oxidative extraction. Unlike PtOT, PsOT focuses on regulating the metal release process, enabling controllable lithium extraction while retaining TMs in the cathode structure. This selective mechanism thereby allows targeted recycling of lithium from the cathode.
Induced extraction. Given that Li was more active than TMs and possessed a smaller ionic radius, it was easier to extract Li. Based on this, using proper extracting force could induce the priority release of Li. We defined the induced forces into squeezing force and pulling force, as shown in Fig. 7a. In a way, the cathode was similar to a water-absorbing sponge, where Li represented water and the TM-O structure represented the sponge. With the appropriate squeezing or pulling force, water (Li) could be released without damaging the sponge (TMs), thereby realizing the selective extraction of Li. Notably, in order to maintain the stability of the crystal structure, similar cations were used to replace Li.124,125 Fig. 7b shows the effects of replacement reagents on the leaching efficiencies of Li/Fe in LFP by grinding (1/2 mass ratio of LFP to NaCl, 500 rpm, and 6 h). The results indicated that NaCl showed a better replacement performance than Na2CO3 and KCl, achieving leaching efficiencies of 96.03% Li and <1% Fe. This is because Na possessed a smaller ionic radius than K, and Cl− did not chelate with Fe like CO32−. Relatively, grinding was found to be less suitable for layered LTMO compared to olivine LFP, as the former is significantly more susceptible to damage. As a result, the Li replacing rate (∼30%) was much low. This is because effective mechanical replacement was an induced extracting process but not a destructive process, thus the replacement reaction could not proceed effectively when the crystal structure of LTMO was damaged. To avoid the over-damage, SiO2 was added to protect the small-sized LCO particle, as shown in Fig. 7c. It was found that the best replacement result of 92.89% was achieved with the mass ratio of LCO and SiO2 as 1/2.125 In summary, mechanical replacement was an emerging technology that fitted the concept of “green chemistry”. However, the relevant mechanism was still unclear and more efforts should be made.
image file: d5gc02804c-f7.tif
Fig. 7 (a) Diagram of induced extraction. (b) Effects of replacement reagents on leaching efficiencies of Li/Fe in LFP by grinding (reproduced from ref. 124 with permission from American Chemical Society, copyright 2019). (c) Leaching rate of Li from LCO co-grinded with different dosages of SiO2 (reproduced from ref. 125 with permission from Elsevier, copyright 2021). (d) Potential mechanism of Li extraction by H+ in subcritical water, and the H+ source. (e) Redox potentials of different oxidants and their suitable driving methods. (f) Diagram of electrochemical reduction and its key factors. (g) Different electrolytes for electrolysis.

In addition to squeezing forces, pulling forces can also induce lithium release under subcritical water conditions. As illustrated in Fig. 7d, acid-assisted hydrothermal treatment exemplifies this pulling mechanism. In this process, when H+ adsorbs onto surface oxygen atoms, the metal–oxygen bonds weaken significantly, generating expanded lattice vacancies. Consequently, small-radius Li+ ions are gradually replaced by H+ to form HCoO2, while larger transition metal (TM) ions remain trapped. The unstable HCoO2 subsequently transforms into Co3O4. For instance, Lv et al.126 used a nearly stoichiometric amount of H2SO4 to provide H+ for the replacement of Li+. About 90% of Li was replaced from the high-Ni layered oxide cathode at 200 °C. Theoretically, Li+ in LFP could be substituted by H+. However, due to the strong binding affinity of PO43− to metal ions, a more substantial force was required to liberate these metal ions. To achieve an efficient liberation of Li (>99%), it was necessary to elevate the temperature to 280 °C.127 However, this caused 28.4% Fe and 40.5% P to be released together. In addition to acids, Lewis acids such as Co2+, Mn2+, and NH4+ could thermally hydrolyze to provide H+ for the replacement reaction.128,129 For example, with the addition of Co2+ or Mn2+, over 95% Li was replaced at 160 °C within 12 h.128 In this process, moderate acidity was crucial to the selective release of Li. Excessive acidity would led to the release of TMs, while the alkalinity (i.e., NH3·H2O130) could not provide an effective pulling force. Regarding the mechanism, researchers initially proposed that Co2+ could directly replace Li+ to form Co3O4. However, we consider this unlikely due to the significant difference in their ionic properties. Instead, we believed that the replacement reaction was mainly mediated by H+. Therefore, further investigation into the replacement mechanism was warranted.


Oxidative extraction.
 
image file: d5gc02804c-t1.tif(1)
Oxidation extraction is an emerging method that simulates the charging process of LIBs, as illustrated in eqn (1). Under the action of oxidizing force, Li+ was de-intercalated from the cathode, thereby realizing the selective recovery of Li+.131,132 Thus, the key to oxidative extraction was how to provide the oxidizing force. As with the above-mentioned reduction conversion, the oxidizing force could derive from oxidants or electricity. Oxidant-based reaction could be driven by wet leaching, grinding, and roasting. Overall, the redox potential provided had a crucial impact on the de-intercalation of Li+. Fig. 7e presents the redox potentials of different oxidants, which were sorted as: φ(Fe3+/Fe2+) < φ(ClO−/Cl−) < φ(O2, H+/H2O) < φ(Cl2/Cl−) < φ(ClO−, H+/Cl−) < φ(H2O2, H+/H2O) ≈ φ(S2O82−/SO42−). It was summarized that LFP could effectively release Li+ under a lower redox potential than LTMO. For instance, using ferric salt,133 NaClO134/Ca(ClO)2,135 O2 (acidic),136,137 H2O2 (acidic),138 and persulfate,139,140 Li in LFP could all be leached out efficiently. In this process, the properly additive acids could enhance the redox potential, facilitating the release of Li from LFP.134 Relatively, the release of Li from LTMO demanded a higher redox potential.141,142 After releasing Li, LFP was converted into FePO4 while LTMO was converted into M3O4 (M = Co/Ni/Mn).

In addition to the redox potential, the driving method was another key factor. For instance, when roasting replaced wet leaching to drive the reaction, the combination of O2 and acids could successfully release Li from LTMO. According to the acid species, the roasting types could be classified into sulfation roasting,143–146 nitration roasting,147,148 and chlorination roasting.149,150 Therein, acidic species included concentrated acids (HNO3[thin space (1/6-em)]184 and H2SO4[thin space (1/6-em)]187) and inorganic acid generators (NH4Cl,149,151 S,146 FeS2[thin space (1/6-em)]29,145). It was noteworthy that there was no need to add acids when employing stronger oxidants.152,153 For example, by a NaS2O8-tuned roasting, >95% Li could be readily extracted at 300 °C.152 Besides, grinding was a widely applicable method for oxidative extraction.154 Its carbon emissions and economic gains were comparable to those of wet leaching.155 Notably, grinding was better suited to treat LFP than from LTMO,135,155,156 as the unstable LTMO crystal structure tended to mechanically collapse. In summary, oxidant-based extractions heavily depend on the reagents, thus recent studies have focused on seeking suitable oxidants.

Besides the oxidants, the electricity could furnish the oxidizing force for the de-intercalation of Li. As depicted in Fig. 7f, waste cathodes such as LTMO and LFP could all serve as the anode for the electrolysis reaction. Herein, the key factors included voltage and electrolyte. Recently, developing suitable electrolytes that guaranteed the efficient implementation of electrolysis has become the research focus. Thus, the development of electric oxidization could be seen as the change in electrolytes, from molten salts to composed organics, and finally to aqueous solutions, as shown in Fig. 7g. Early, molten Na2CO3–K2CO3 was used as the electrolyte for the de-intercalation of Li at 750 °C in an Ar atmosphere.157 LFP was oxidized into Fe3O4 and Li salts. Finally, 95.2% Li was recovered from the molten salts under 1 V for 5 h. However, high energy consumption and disposal of waste salts had emerged as the new problem. To address this, composited organics had attracted much attention to replace molten salts.158–160 For example, the working electrolyte of the LIB itself (LiPF6/carbonates) was directly used for the electrolysis, successfully recycling 90% Li as the metal after 4.4 V overcharge.159 Under an over-charging process (>4 V), Li was deposited on the Cu foil while LCO was converted into CoO2 (further decomposed into Co3O4).

To avoid the underlying organic pollution, researchers further developed more applicable and cost-effective aqueous solutions as the electrolyte. Common aqueous solutions included (NH4)2SO4,161 NaCl,162 Na2CO3,163 and K2SO4[thin space (1/6-em)]164 and acidic Na2SO4.165 Initially, Liu et al.161 directly used a waste cathode sheet as the anode for electrolysis in an (NH4)2SO4 solution. The results showed that >98% Li was extracted out, and the Al foil still remained as a metallic form after the electrolysis at 25 V for 3 h. Through optimization, the electrolysis voltage decreased to 2.5 V in a K2SO4 solution.164 Other aqueous solutions also demonstrated similar working voltages ranging from 2.5 to 4.2 V. In this case, the competitive reaction of water electrolysis (1.23 V) might result in a low energy conversion efficiency. However, this issue has not been well addressed yet. To improve the feasibility, researchers applied the photovoltaic-driven electrolysis for recycling Li, which greatly reduced the processing cost.166 Thus, future research could focus on the energy conversion of electrochemical oxidation. Interestingly, the de-lithiated materials showed good catalytic performances in the oxygen evolution reaction,162 and organics degradation.163 This might provide new insights for LIB recycling. Notably, the handling capacity of this method is still limited in the laboratory, and future research should focus on its pilot-scale test.

3. What are the main features of LIB recycling technologies?

In this section, we summarize the key factors, main advantages and disadvantages, and future directions of various LIB recycling technologies to further demonstrate their technical features, as shown in Table 2. LLT fundamentally adapts techniques from traditional mineral metallurgy. This allows direct use of existing metallurgical equipment for LIB recycling, enabling rapid scaling. Currently, LLT using PbE is widely adopted in industries. Other extractants with similar properties also show strong scalability. Essentially, LLT relies heavily on selecting the right combination of dissolving reagents, making PbE particularly reagent-dependent. Additionally, multiple processing stages are needed to ensure complete metal recovery. Consequently, current industrial PbE processes are operationally inflexible and carry risks of secondary pollution, such as acid mist and wastewater. To reduce reagent dependency, LIB recycling can be combined with processing other waste streams. For example, waste biomass such as orange peel50 and areca powder39 can serve as reductants for metal leaching. Furthermore, using mixed acids can significantly increase the leaching efficiency, potentially lowering chemical consumption.
Table 2 Features of different recycling technologies for spent LIBs
Technology Type Suitable objects Key factors Advantages Disadvantages Future directions
LLT Proton-based extractant LFP/LTMO Reagents Excellent scalability Heavily reagents dependency Mixed-use of acidic reagents
Small equipment investment Technical rigidity of recycling route Coupling with other waste disposal
Verified scale production Underlying secondary pollution risk  
Nitrogen-based extractant LTMO Reagents Excellent scalability Heavily reagents dependency Life-cycle assessment of DES-based recycling route
Small equipment investment Limited leaching kinetics  
Green process Unverified scale production test  
Bio-extractant LTMO Reagents Green process Poor operation stability Mixed culture system
Low running costs Limited handling capacity Pilot scale test
LFT Product-oriented technology LTMO Reagent Shortened recycling route Strict operation conditions Design of Li-containing product
Driving methods Low chemical consumption Limited Li separation Coupling with other waste disposal
  High Li selectivity   Specific device development
      Pilot scale test
Process-oriented technology LFP/LTMO Reagents Shortened recycling route Strict operation conditions Design of suitable oxidative reagents
Driving methods Low chemical consumption Limited Li separation Specific device development
  High Li selectivity Risk of oxidants Pilot scale test

Similarly, NpE technology is a hydrometallurgical process that uses natural organic compounds as dissolving reagents, replacing PbE. Consequently, it offers advantages such as excellent scalability and low investment costs. Natural NpE reagents are also non-toxic and environmentally friendly. However, NpE application in LIB recycling remains at the laboratory stage. Significant quantities of NpE reagents are required for effective metal leaching, and the leaching kinetics is typically slow. While the reusability of NpE reagents is claimed, this has not been demonstrated in large-scale production. Critically, Wang et al.167 demonstrated that NpE recycling routes incur a greater environmental burden and higher economic costs than conventional hydrometallurgy and pyrometallurgy. This finding underscores the necessity for the comprehensive life-cycle assessment (LCA) of NpE technology to establish evidence-based guidelines for its sustainable implementation.

In fact, bio-extractant technology is the most environmentally friendly and economic method for metal leaching. The main reagents it consumes are cheap Fe/S additives and carbon sources. Due to the outstanding advantages, bio-extractant technology has been applied for Cu/Zn mineral metallurgy in industry. However, due to the disadvantages of unstable operation and low handling capacity (typically <1 ton per day scale), its practical application for LIB recycling is limited. To address this, we think that mixed culture systems may be promising to improve the leaching efficiency and system stability.

In contrast to LLT, LFT focuses not only on reagents but also on driving methods to achieve controlled lithium release from cathodes. Its selective extraction capability streamlines recycling processes and reduces chemical consumption. Nevertheless, its stringent operating conditions limit practical application. For LFT specifically, the primary limitations are associated with the separation of lithium-containing products. For example, the Li-containing products tend to further transform into insoluble or slightly soluble species such as Li2CO3, Li3PO4, and LiAlO2. Other metal impurities such as Na, K, and Fe are always introduced in the reaction. These limitations make the subsequent separation and purification challenging. Consequently, optimizing the product design to enhance lithium recovery remains critical for PtOT. Recent studies have demonstrated that coupling LIB recycling with waste streams such as organic residues102 and plastics104,168 can significantly reduce chemical consumption and improve economic viability. In contrast, the core challenge of PsOT lies in generating effective oxidizing power. Significant research efforts have focused on developing diverse driving methods. Among these, certain PsOT approaches (e.g., oxidative leaching) exhibit high compatibility with existing hydrometallurgical equipment, enabling limited industrial pilot-testing. However, safety concerns regarding oxidant usage, including combustion, explosion, and corrosion risks, must be addressed. Meanwhile, other driving methods (subcritical water, grinding, and electrolysis) lack commercially viable implementations. Consequently, developing specialized equipment and conducting pilot-scale validation are critical for industrializing these emerging technologies.

A comparative schematic of conventional LLT and emerging LFT process flows is presented in Fig. S1, highlighting the intrinsic route-shortening advantage of LFT.169 The diagram demonstrates the elimination of two critical LLT steps—reductive leaching and precipitation filtration—resulting in a >40% reduction in processing stages. This structural simplification enables substantially lower chemical consumption and dramatically reduced energy inputs, translating to ∼20% higher carbon mitigation efficiency and near-complete elimination of energy-related emissions relative to conventional routes. The streamlined material loops further enhance environmental performance across key impact categories including freshwater ecotoxicity and fossil resource scarcity.

In addition to the above-mentioned recycling technologies, direct cathode regeneration offers a transformative approach to sustainable battery recycling, showing clear economic and environmental benefits over traditional methods. Direct regeneration delivers >23% higher revenue per kilogram of spent NCM cathodes compared to conventional pyrometallurgical and hydrometallurgical routes.170 Critically, its carbon emissions are >40% lower than pyro-/hydrometallurgical routes,171 making it the lowest-emission recycling option. These advantages stem from preserving cathode crystal structures while avoiding energy-heavy decomposition steps.172 Recent breakthroughs are enhancing this potential: specially designed organic lithium salts now simultaneously refill missing lithium, prevent unwanted phases, and add conductive carbon coatings to degraded cathodes;173 spontaneous room-temperature lithiation techniques eliminate energy-intensive heating;174 and ultrafast methods such as Joule heating enable cathode repair within seconds.175 Anode-to-cathode lithium transfer strategies further reduce material-specific sorting needs.171 Despite these advances, scaling this technology faces persistent challenges. Strict sorting requirements for different cathode types, particularly degraded Ni-rich/NCM blends, remain critical barriers. Regenerating LFP cathodes is particularly critical, as the low economic value of recovered iron renders conventional recycling methods financially unsustainable. These developments position direct regeneration as vital for closed-loop systems, but real-world deployment requires better supply chains and universal cathode methods. We must now address a pivotal question: can new regeneration techniques handle mixed cathode waste while maintaining the significant emission reductions seen with single materials? Emerging traceability solutions like QR-code battery passports offer one practical pathway to resolve this challenge.22

4. Whether advanced LIB recycling technologies applicable?

As mentioned above, we have discussed the focus, definition, mapping, and features of LIB recycling technologies. In this section, we try to further answer another important question that “whether these technologies are applicable in industry?”. Fig. 8a first summarizes the main processing routes for spent LIBs. Always, by traditional hydro-/pyrometallurgy or emerging technologies, spent LIBs can be processed to recover high-purity products such as TM products and Li2CO3 (type 1). These recovered products can be further processed to synthesize a fresh cathode (type 2). In addition, by proper repairing treatments, spent LIBs can be directly regenerated (type 3).
image file: d5gc02804c-f8.tif
Fig. 8 Applicability comparisons of LIB recycling technologies: (a) flow charts of different LIB recycling technologies. (b) Hydrometallurgy and pyrometallurgy, the functional unit (FU) was 1 t spent electric vehicle LIB pack (reproduced from ref. 176 with permission from MDPI under the Creative Commons Attribution (CC BY) license, copyright 2021). (c) Newly developed technologies (reproduced from ref. 169 with permission from Elsevier, copyright 2024). (d) Direct regeneration of LTMO170 and LFP177 batteries (reproduced from ref. 170 with permission from the American Chemical Society, copyright 2021; reproduced from ref. 177 with permission from Elsevier, copyright 2020).

On this basis, traditional hydro- and pyrometallurgical methods are compared in Fig. 8b.176 Here, hydrometallurgical methods use H2SO4 (HM-SA) and citric acid (HM-CA), while pyrometallurgical methods include smelting and reduction roasting (N2 or vacuum). The results indicated that N2 roasting exhibited the lowest energy consumptions (4833 MJ FU−1) and greenhouse gas (GHG) emissions (1525 kg CO2-eq per FU), which only accounted for ∼23% and ∼64% of those for HM-CA. The high energy use and GHG emissions of HM were attributed to the heavy utilization of chemicals. However, it should be noted that the comparison is a bit idealistic. It is unrealistic to assume that all products obtained by different methods can be recycled for LCO production. Recently, Xiao et al.169 have included the impacts of recovered products to perform the evaluation for five typical newly developed technologies (Fig. 8c). It was found that PbE technology (i.e., HM-SA) was more economically and environmentally balanced than other technologies. PtOTs such as co-leaching/precipitation thermal reduction (vacuum) did not show advantages over HM-SA. Notably, oxidizing extraction (i.e., oxidative leach) had high application potential in pursuit of low-carbon development. The above findings were consistent with the practice.

Recently, direct regeneration of cathode has attracted much attention due to its excellent economic and environmental advantages.173,178,179 For example, as shown in Fig. 8d, when processing 1 kg of spent LTMO battery (i.e., NCM), the revenues for regeneration, pyro- and hydrometallurgy were $6.90, $5.20 and $5.60, respectively.170 Besides, only 0.6 kg of GHG emissions were released during the direct regeneration process, which were significantly lower than those of hydrometallurgy (2.27 kg) and pyrometallurgy (2.16 kg). Similar comparative results were obtained when processing 1 kg of LFP battery. Direct regeneration yielded a profit of $1.1, whereas pyrometallurgy and hydrometallurgy exhibited profits of −$2.6 and −$1.4.177 It can be concluded that the LIB type has significant impacts on their economic returns, and recycling LFP is not profitable. However, it should be noted that the direct regeneration is much complex, and the presorting of LIB ingredients is very strict.180 Due to such strict conditions, current objects of direct regeneration are predominantly residual materials or defective products from fresh LIB manufacturing, which account for less than 1% of the LIB recycling market.

At present, traditional LLT (i.e., PbE technology) has been extensively utilized in the industry, whereas the implementation of the novel LFL is scarce. To the best of our knowledge, PtOT (i.e., thermal reduction) has been employed for recycling LTMO. Specifically, enterprises adopt customized tunnel furnaces for the continuous operation, and realize a 92% comprehensive recycling rate of Li. The residual TM oxides are subsequently recovered through hydrometallurgy. Recently, enterprises have initiated the application of PsOT (i.e., oxidative leach) to recover LFP and gradually accomplished economies of scale. Nevertheless, the mainstream technology remains traditional hydrometallurgy. Hence, the adoption of new technologies still has a long way to go.

In summary, the applicability evaluation is the last mile of emerging technologies to industrial application. However, many technologies are still limited to the lab and current industrial technologies are still traditional pyro-/hydrometallurgical methods that have been used for decades. The model-based LCA can offer a guide to the likelihood of commercial viability for these technologies.181 However, it is hard to provide a precise economic judgment for immediate industry implementation without careful examination in a real operation, as the above recycling technologies have not been used in a large industry scale. To address this, artificial intelligence (AI) can be applied to help obtain the reliable results without the vast experiments.182,183 Besides, AI can effectively predict the future change and improve the management effectiveness in LIB recycling.184 In the future, it is of great significance to construct an effective pre-evaluation model of ex-ante assessment of emerging technologies appropriately combined with actual data to promote the industrialization of emerging technologies.

5. What future challenges will reshape lithium-ion battery recycling?

To sum up, the market of LIB recycling is changing rapidly, LIB recycling technologies are emerging, and the corresponding challenges it faces are constantly changing. In view of this, we discuss the future challenges from the following aspects.

5.1 Evolving battery chemistries in LIB recycling

The application landscape of LIB has undergone a fundamental transformation since 1990, evolving from portable electronics to large-scale electric vehicles and energy storage systems. This transition has triggered two significant changes in the characteristics of spent LIBs. First, the exponential growth in LIB consumption has led to a dramatic increase in end-of-life battery volumes. In the early stages, LIB recycling received minimal attention as small quantities were typically co-processed with nickel-metal hydride batteries. Current projections indicate that spent LIB volumes will reach 786[thin space (1/6-em)]000 tons by 2025, transforming battery recycling from a niche environmental issue into a major societal priority. Second, the economic model of LIB recycling has shifted dramatically. Initially, cobalt-rich LCO batteries provided substantial profits for pioneers such as Green and Umicore. However, strategies to reduce cobalt content have driven the widespread adoption of lower-cost alternatives (LFP), which contain fewer valuable metals. This shift is evident in China's 2023 recycling data, where LFP batteries accounted for 68% of recovered materials. As a result, modern LIB recycling must address dual challenges: managing exponentially growing volumes while ensuring economic viability for low-value chemistries. The industry's ultimate challenge lies in developing cost-effective processes to sustainably manage these abundant yet marginally profitable battery streams.

5.2 Shifting paradigms in LIB recycling economics

Traditional LIB recycling thrived on recovering cobalt, nickel, and lithium from high-value batteries. However, two disruptive trends now redefine industry priorities. First, severe structural overcapacity plagues recycling infrastructure. China's 156 government-certified recyclers (as of 2023) possess 3.79 million tons annual capacity – exceeding global spent LIB generation – yet operate at 16.4% utilization. This imbalance prompted regulatory intervention: suspended new certifications in 2024 and proposed stringent standards prioritizing low-carbon, high-quality operations. Second, market dominance of lithium iron phosphate (LFP) batteries coupled with lithium price volatility has eroded profitability. While lithium recovery remains critical for LFP recycling, emerging seawater extraction technologies have driven lithium carbonate prices from CNY 600[thin space (1/6-em)]000/tons (2022) to CNY 80[thin space (1/6-em)]000/tons (2024). This over 85% price collapse necessitates innovative value-creation strategies beyond metal recovery. The industry now confronts dual imperatives: implementing energy-efficient processes to meet stricter environmental standards while developing alternative revenue streams through material upcycling or closed-loop integrations. Recent studies highlight critical needs in byproduct valorization185,186 and pollution mitigation technologies to address emerging regulatory and economic constraints. Successfully navigating these challenges requires reimagining recycling economics through technological breakthroughs and strategic circular economy alignments.

5.3 Market transformation in LIB recycling dynamics

The LIB recycling sector has transitioned from explosive growth to hypercompetition within three years. China's enterprise registrations skyrocketed from 5925 (2020) to 45[thin space (1/6-em)]949 (2023),187 reflecting rushed market entry strategies. This gold-rush mentality forced adoption of legacy metallurgical processes to accelerate production launch, creating systemic technological lock-in. Current recyclers face dual pressures: serious capacity underutilization and collapsing margins due to lithium carbonate price inversion. Three structural shifts redefine market rules: (1) transition from blue-ocean to red-ocean competition with low industry-wide gross margins; (2) emergence of technology-driven cost leadership as a key differentiator; (3) regulatory emphasis on advanced process integration over mere certification compliance. The 2023 price collapse has exposed fundamental vulnerabilities – most recyclers now operate below break-even thresholds. Surviving this consolidation phase requires replacing energy-intensive pyrometallurgy with selective hydrometallurgical processes and direct recycling innovations. Recent studies demonstrate a cost reduction potential through cathode healing technologies, though scalability remains unproven.174 This technological pivot, while critical for competitiveness, presents formidable capital and R&D challenges for entrenched operators. The sector's sustainability now hinges on strategic alliances between recyclers and battery manufacturers to develop closed-loop material ecosystems.

Based on the above discussion, the best way to address these challenges is the popularization and application of advanced technologies that can achieve the economic and environmental coupling. Hence, it is of great significance and urgency to establish an easily understandable technical mapping for industrial stakeholders.

6. Conclusions and perspectives

This study establishes a groundbreaking “lithium last-first” technical mapping framework to bridge the academia-industry gap in LIB recycling. By redefining technologies into LLT and LFT paradigms, we reveal their distinct operational logics: LLT prioritizes transition metal recovery through extractant optimization, while LFT enables lithium-first extraction via process innovation. This classification clarifies three critical insights: (1) traditional hydrometallurgy dominates industry due to infrastructure compatibility despite high pollution risks; (2) emerging LFT shortens recycling routes but faces scalability barriers from impurity management and energy intensity; (3) direct regeneration and oxidative extraction show the strongest low-carbon potential but require industrial validation. The technical mapping provides actionable guidance for academia to align research with industrial needs while helping enterprises evaluate technology upgrade paths.

To accelerate sustainable LIB recycling, three collaborative pathways are proposed:

(1) Joint R&D Platforms: Establish cross-sector innovation hubs combining academic expertise in selective extraction mechanisms with industry's process engineering capabilities. Focus on pilot-scale verification of LFT and impurity control solutions.

(2) AI-Driven Process Optimization: Develop shared databases integrating material properties, recycling parameters, and economic/environmental metrics. Use machine learning to predict optimal technology combinations for specific battery types.

(3) Policy-Industry-Academia Synergy: Create certification systems rewarding low-carbon technologies (e.g., oxidative leaching), coupled with fiscal incentives for enterprises adopting LFT. Implement “Green Process Credits” to offset initial upgrade costs.

To advance battery recycling technologies, herein, four key priorities can be addressed. First, modular systems should be designed to efficiently process low-value LFP materials. Second, extraction methods need improvement to maintain selectivity despite impurity interference. Third, establishing battery-to-precursor partnerships will help create circular material flows. Fourth, adopting real-time life cycle assessment tools enables adaptive process optimization.

This study demonstrates the critical need to bridge academic research with industrial applications. Our findings highlight the feasibility of developing sustainable recycling systems through stakeholder collaboration. Using technical mapping as an analytical framework allows different parties to jointly design solutions that meet both economic and environmental requirements. Specifically, this approach helps balance production costs with ecological impacts across the battery life cycle.

Data availability

No primary research results, software or code have been included and no new data were generated or analysed as part of this review. The SI accompanying this article contains a schematic diagram comparing material flows in conventional LLT versus streamlined LFT processes. See DOI: https://doi.org/10.1039/d5gc02804c.

Conflicts of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

This work was supported by Natural Science Foundation of Xiamen, China (3502Z202372038), the Opening Project of Key Laboratory of Solid Waste Treatment and Resource Recycle, Ministry of Education, 23kfgk04, and the Scientific Research Funds of Huaqiao University (20221XD053).

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