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Johnson Matthey Technol. Rev., 2021, 65, (x), yyy-zzz Page 1 of 47 Doi: 10.1595/205651320X15899814766688

Recycling and Direct-Regeneration of Cathode Materials from

Spent Ternary Lithium-Ion Batteries by Hydrometallurgy: Status

Quo and Developing

Lizhen Duan

School of Metallurgical Engineering, Xi’an University of Architecture and Technology,

Xi’an 710055, China

Yaru Cui*



*Email: <[email protected]>

Qian Li



Juan Wang*

Xi’an Key Laboratory of Clean Energy, Xi’an University of Architecture and Technology,


*Email: <[email protected]>

Chonghao Man

College of Engineering, The University of New South Wales, Sydney, NSW 2052,

Australia

Xinyao Wang





ABSTRACT

The cathodes of spent ternary lithium-ion batteries (LIBs) are rich in non-ferrous

metals, such as lithium (Li), nickel (Ni), cobalt (Co)and manganese (Mn), which are

important strategic raw materials and also potential sources of environmental

pollution. How to extract these valuable metals cleanly and efficiently from spent

cathodes is of great significance for sustainable development of LIBs industry. In the

light of low energy consumption, green and high recovery efficiency, this paper

provides an overview on different recovery technologies to recycle valuable metals in

cathode materials of spent ternary LIBs. And the development trend and application

prospects on recovery strategies for cathode materials in spent ternary LIBs are simply

predicted also. It is proved that the high economic recovery system of “alkaline

solution dissolution/calcination pre-treatment → H2SO4 leaching → H2O2 reduction →

co-precipitation regeneration NCM” will be the dominant stream for recycling retired

NCM batteries soon. Furthermore, the emerging advanced technologies, such as deep

eutectic solvents (DESs) extraction and one–step direct regeneration/recovery of NCM

cathode materials are preferred methods to substitute conventional regeneration

system in the future.

Keywords: spent ternary LIBs, valuable metals, recovery technologies, direct

recovery/regeneration, deep eutectic solvents

1. Introduction

In 21st century, mankind is suffering increasingly severe crisis of energy scarcity

and ecological environment deterioration. The worldwide usage of fossil fuels account

for 84.7% of global energy consumption in 2018, which is equivalent to 11.7436 billion

tons of oil (1-2). That means the global CO2 emissions especially from fossil fuel will



continue to grow rapidly. It is crucial to explore green & renewable energy system,

such as wind energy, tidal energy and solar energy and energy storage batteries, etc.,

to replace fossil fuels. Among the popular new-energy sources, lithium-ion batteries

(LIBs), with excellent energy storage property, security and stability, are considered

as the most potential clean-sustainable energy storage equipment. LIBs are widely

used in energy storage fields such as zero-emission vehicles (mainly electric vehicles

(EVs), and plug-in electric vehicles (PHEVs)), computers and electronic communication

devices (3-6). The newly emerging model for super-performance LIBs, assembled with

specific complex 3D/porous/polyhedron geometric structure in cathode/anode

materials, is perfectly satisfied with the scale-up properties requirements for zero-

emission vehicles (3-5). The increasing requirement for new energy vehicles contribute

to the expansion of LIBs market. Statistics estimated that the world’s production of

LIBs will increase by 520% from 2016 to 2020 (7), and about 50 million electric buses

will run on the road by the end of 2027 (8). Therefore, as major electronic wastes, the

number of expired LIBs will increase inevitably. In China, the weight of retired LIBs

may even reach 500 thousand metric tons by the end of 2020 (9), and that of EU alone

will reach 13828 tons in 2020 (10). Since the harmful substances may damage

environment and the containing metals are precious resources, the recovery of retired

LIBs are bound to gain considerable social, economic and environmental benefit.

The cathodes of retired LIBs are rich in valuable non-ferrous metals such as lithium,

nickel, cobalt and manganese, which are secondary resources worth recycling.

Considering potential immense profit, researchers have been working hard to develop

various technologies to recycle precious metals in spent LIBs. The current recycling

technologies of valuable components from spent LIBs mainly include pyrometallurgy



and hydrometallurgy strategy. Although pyrometallurgical recovery processes have

the advantages of short process, high efficiency and easy to achieve industrial

application, high energy consumption and toxic gases generation still limits its

development (11-14). In contrast, hydrometallurgical recovery processes have

attracted extensive attention due to low energy consumption, environmental

friendliness and high recovery efficiency (15-19). Leaching valuable elements using

chemical reagents is the core of hydrometallurgical recovery strategy. After leaching

process, valuable metals in leachate are extracted by chemical precipitation, solvent

extraction and ion-exchange, etc. (20-25). The conventional hydrometallurgical

process for waste electrodes recovery can be illustrated as follows: 1) acid-reductant

leaching + selective chemical precipitation; 2) sulphuric roasting+ acid leaching +

selective chemical precipitation; 3) mechanochemical activation leaching + selective

chemical precipitation, as shown in Table 1 (26-34). Nevertheless, it seemed that

sulphuric roasting or mechanochemical activating before leaching may complicate the

recovery process and decrease overall leaching rate. Based on the point of “waste

substance + waste substance→ rebirth resources”, Li et al. (35) developed an in-situ

recovery model of graphite, Li2CO3 and Co by “oxygen-free roasting with anode

graphite + wet magnetic separation” process, without pretreating or adding any other

chemical regents. However, this technique is not suitable for complex electrode

materials recovery. Prabaharan et al. (36) investigated an electro-chemical leaching

system of “lead as anode + electrode scraps as cathode +H2SO4 as leachate”, in which

the leaching rate of Mn, Cu and Co exceeded 96％ through adjusting pH value.

Although it can perfectly achieve integrated recovery of valuable metals, the high

electricity consumption and recovery cost limits the spread of this method.



Surprisingly, Gomaa et al. (37, 38) explored a new-multifunctional recovery method

to recycle ultra-trace Co2+ (about 3.05/4.7X10-8M) with visible selective ion extraction-

separation-detection. It can almost extract 100％ Co2+ from leachate in only 10-15

min and the used ion-extractors after activation can regenerate and re-use in

repeated adsorption-desorption processes. Desorption by HCl eluting reagent, the

overall recovery rates of Co from waste LIBs or PCBs (printed circuit boards) are 98％

and 95.7％ respectively.

NCM batteries consist of more valuable metals that are worth recycling compared

with traditional LiCoO2 and LiFePO4 batteries. However, few reports have been made

to systematically clarify recovery techniques for waste NCM materials. In order to avoid

loss of valuable resources and risk of second pollution, it is urgent to construct a

sustainable recycling model for valuable metals in cathodes of spent LIBs. This review

is aiming to introduce the progress of hydrometallurgical recycling cathode materials

from spent NCM batteries. Hydrometallurgical recovery strategy of waste LIBs can be

classified as three steps: (a) pretreatment: separate active substances; (b) leaching:

extract valuable metals from active substances with appropriate solvents;(c)

separation of valuable metals: extract valuable metals existed in leachate selectively

by different methods to obtain their metals or metallic compounds. The conventional

process flow for recycling NCM materials from waste LIBs by hydrometallurgy is shown

in figure 1. And correspondingly, the advantages, disadvantages, existing problems

and application status of different treatment methods are analysed. Furthermore,

advanced recovery technologies, deep eutectic solvents (DESs) extraction and crystal

repair direct-regeneration/recovery technology are emphatically illustrated. The

challenge and potential prospects on valuable metals recovery from ternary cathode



materials of used LIBs by hydrometallurgy are prospected also. By comparing

advantages and disadvantages of different methods, it is expected that these

information will contribute to explore “economical-green-sustainable-high efficiency

leaching & separation & regeneration” recovery system for closed-circuit recycling of

LIBs.

2. NCM cathode materials for lithium-ion batteries

The LIBs are mainly divided into five types depending on the composition of cathode

materials: lithium iron phosphate battery (LiFePO4), lithium cobalt oxide battery

(LiCoO2), lithium manganese oxide battery (LiMn2O4), lithium nickel oxide battery

(LiNiO2), and lithium nickel cobalt manganese oxide battery (LiNixCoyMn1-x-yO2) (39-

43). Among them, layered LiNixCoyMn1-x-yO2 (NCM) materials become the leaders

because of excellent cycle/rate performance. Currently, there are five types of NCM

cathode materials that have been commercialized, NCM333 (LiNi1/3Co1/3Mn1/3O2),

NCM424 (LiNi0.4Co0.2Mn0.4O2), NCM523 (LiNi0.5Co0.2Mn0.3O2), NCM622

(LiNi0.6Co0.2Mn0.2O2) and NCM811 (LiNi0.8Co0.1Mn0.1O2) (44). It is predicted that the

NCM batteries will account for nearby 41% of the world’s LIBs market in 2025 (42).

The chemical characteristics and potential hazards of each component in ternary LIBs

are summarized in Table 2 (45-48). The NCM cathode materials are rich in lithium (Li),

nickel (Ni), cobalt (Co), manganese (Mn) and other strategic essential metals. The

heavy metals in waste LIBs will pose a huge threat to human health and ecological

environment (49). What’s more, the scarcity and high cost of nonferrous metals such

as Li and Co make it imperative to recycle ternary cathode materials from retired LIBs.

It is also reported that the global lithium resource reserves detected in 2018 are over

62 million tons, but China only account for 7%, about 4.5 million tons (50). As the



core raw material for LIBs industry, the value of cobalt is as high as $ AUD115,000

per tonne (51, 52). How to efficiently extract these valuable non-ferrous metals from

retired LIBs is of great significance for green and sustainable development of batteries

industry.

3. Metallurgical recycling strategies for NCM

3.1 Recovery process

The advantages and disadvantages of different technologies for recycling spent

ternary LIBs are shown in Table 3 (53-57). Considering low energy consumption and

high recovery rate, currently, hydrometallurical recycling process is considered as a

preferred strategy to recover valuable metals from used cathode materials. While,

pyrometallurgical processes are usually used as a pre-treatment for leaching in

hydrometallurgical recycling.

3.2 Recovery process of hydrometallurgical method

(a) Pre-treatment

To prevent short circuit, spontaneous combustion and explosion during dismantling

waste LIBs, a pre-discharge work must be carried out before (58-60). The cathodes

consist of active material, current collector (Al foil) and binder (PVDF). Separating

high-purity active material is the key of pre-treatment process step. Table 4 shows the

pre-treatment methods and corresponding recycling effects of retired NCM batteries

(61-66). Considering separation efficiency and purity of recovered products, the

ultrasonic treatment and solvent dissolution methods have distinct advantage

compared with other methods. But ultrasonic method has high recovery cost due to

special requirements on equipment; and most organic solvents used in the solvent

dissolution methods are toxic and expensive. On contrast, the mechanical separation



method has high degree of automatic operation and is easy to implement in industry.

However, it is difficult to avoid the components being mixed together, unable to be

separated fully in the next pulverization process, which may lower the purity of

recovered products. To improve extraction rate, reduction and roasting of cathode

materials are usually applied to convert the high valence metals of Co and Mn into low

ones that can be easily leached by chemical reagents. Considering recovery cost and

practical application, alkali dissolution and heat treatment are preferential pre-

treatment methods. The binders and current collectors of spent LIBs can be separated

simultaneously through heat calcination, and the obtained active materials even have

high purity and excellent crystal morphology and electrochemical performance.

(b) Leaching of valuable metals

Efficient leaching precious metals from active substances are the ultimate goal in

hydrometallurgical recovery process. Generally, acid leaching and bio-leaching are

applied to extract valuable metals (67), as shown in Figure 2.

The optimized process parameters and related leaching rate for extracting metals

from waste ternary LIBs are listed in Table 5 (68-75). It is proved that the leaching

ability of HCl in valuable metals is higher than that of other inorganic acid, such as

HNO3 and H2SO4 (68). And injecting suitable reducing agent into leaching system can

significantly strengthen the leaching efficiency. On compared, organic acids can

effectively increase the leaching rate of different metals while decrease the leaching

time. Due to environment-friendly and not introduce impurity ions, H2O2 is considered

as a popular candidate for reductants. However, H2O2 is easy to decompose under high

temperature, which weakens reduction effect (69). With better thermally stable,

NaHSO3 may be a favorable substitute.



The leaching efficiency of valuable metals commonly depends on various factors,

including leaching methods/agents, pH value, composition of leaching system and

reductants, etc. To optimize leaching process and the subsequent separate and extract

process, researchers have made great efforts. Liu et al. (76) developed a new method

of pre-reduction roasting combined with two-step leaching to extract metals from

waste NCM cathodes. Transition metals ions of Mn4+ and Co3+ were converted into low-

valence ions of Mn2+ and Co through pre-reduction roasting, with 93.68% leaching

rate of Li in water leaching step and almost 99.6% leaching rate of Mn, Ni and Co in

H2SO4 leaching step. Zhuang et al. (77) studied the leaching property of mixed-acid

(phosphoric acid + citric acid) on valuable metals of used NCM materials. Without

adding any reductants, the leaching cost of raw materials is 37.81% lower than that

of the single acid leaching studied by Sun et al. (74,77). Under optimized conditions,

the leaching efficiency of Li, Ni, Co and Mn were up to 100%, 93.38%, 91.63% and

92.00%, respectively.

Besides conventional acid leaching, researchers have done a lot of works on

biological leaching (78-80). The leaching rates of waste NCM cathodes by bacteria in

literatures are summarized in Table 6 (81-86). Bioleaching technology mainly lies on

the organic/inorganic acids produced by decomposition of bacteria to leach valuable

metals. The bacteria leaching is characterized by extremely high selectivity for Li, with

leaching rate approaching 100%. Xin et al. (86) explored bio-leaching property on

different metals of three leaching system (as shown in Table 6). It was found that the

leaching rates of Li and Mn in MS-MC system were more than 95%, while that of Co

and Ni were only 40%. The bioleaching mechanism revealed that Li+ in NCM material

was released through biogenic acid dissolution, while transition metal ions Mn4+, Co3+



and Ni3+ must be reduced to Mn2+, Co2+ and Ni2+ before acid leaching. It was also

observed that Fe2+ in MS-MC system contributed to reduce insoluble transition metal

ions into soluble low valence ions. That means the high-valence transition metal ions

can be effective dissolved through interaction of reduction and acid leaching by

bacteria. Lowering pH value of the leaching system is an effective means to accelerate

the cells growth during bioleaching stage, which can ensure sufficient sulfuric acid and

normal circulation of Fe2+/Fe3+ (86). Through controlling the system’s pH, the leaching

efficiency of the above metals were all over 95%.

(c) Extraction of valuable metals

There are mainly three separation methods, including selective precipitation, solvent

extraction and ion-exchange, to extract valuable metals from leachate. Due to simple

and easy to achieve industrial application, chemical precipitation is widely used.

Element of Li in leachate is usually recycled in the form of Li2CO3 by selective

precipitation, while Co, Mn and Ni can be separated by chemical precipitation or solvent

extraction (87-89), which can be reused as raw materials in LIBs or other fields. And

the process parameters of chemical precipitation in literatures are summarized in Table

6 (90). Mreshram et al. (91) extracted valuable metals from H2SO4 leachate by

selective precipitation. The CoC2O4·2H2O was extracted from leaching solution by

oxalic acid, then precipitates of MnCO3, NiCO3, and Li2CO3 were obtained by controlling

pH to 7.5, 9, and 14, respectively. Granata et al. (92) found that the order of different

extractants affected the separation efficiency of metals in leachate. The best recovery

rates reached above 90% with P204 (D2EHPA) to extract manganese first, followed by

co-extraction of cobalt and nickel with Cyanex 272.



It was illustrated that reduction roasting is beneficial to improve the leaching rate of

non-ferrous metals. Zhang et al. (93) established a process of “reduction roasting →

H2O-CO2 leaching → H2SO4 leaching → evaporation and crystallization” to recover

valuable metals in waste NCM materials, as shown in Figure 3. The related leaching

mechanism and graphical illustration of recycling process are further illustrated in

Figure 4 (93). After reduction roasting, the phases in the cathode material were

converted into Li2CO3, Ni, Co and MnO, and corresponding leaching effect of different

metal was improved simultaneously (as the Figure 4(n) showed). For leaching system

containing gas, CO2 has significant influence on the leaching rate of Li. The solubility

of Li was improved by 47％after inputting CO2 to leaching system. Through controlling

the operation conditions of flow rate of CO2, pH and leaching temperature, Li was

selectively extracted as Li2CO3 by carbonic acid leaching combing evaporative

crystallization, while the elements of Ni, Mn and Co were deactivated and transformed

into leaching residues. The re-produced Li2CO3, possessing outstanding pureness and

submicron-scale stick morphology, can be directly used as lithium source to prepare

cathode materials of LIBs. After that, the other valuable metals in the leach residues

were recovered and extracted in the form of sulphate (MeSO4, Me=Mn, Ni and Co) by

H2SO4 leaching, with a high recovery rate of 96%.

In general, the leaching solution consists of complex components with different

properties. So combined separation methods are adopted to improve the overall

recovery efficiency (94). Chen et al. (94) developed an efficient process to extract

valuable metals from leachate based on two-step precipitation combined with solvent

extraction, as shown in Figure 5. The C4H8N2O2 was used to precipitate 98% nickel

from hydrochloric acid leachate firstly. And 97% cobalt was selectively precipitated as



CoC2O4·2H2O with (NH4)2C2O4. Then, 97% Mn2+ was recovered as MnSO4 by extracting

with D2EHPA solvent, and 89% of the lithium was precipitated by Na3PO4 to form

Li3PO4.

4. Regeneration technologies of NCM cathode materials

4.1 Regeneration of NCM from leachate

Sustainable recovery and regeneration of NCM materials from leaching solution is

current main trend for exhausted LIBs recovery. Common methods to synthesize

cathode materials include chemical co-precipitation, high temperature solid phase,

hydrothermal synthesis, sol-gel, microwave synthesis and electrostatic spinning

method, etc. (95-100). And the parameters of re-synthesis methods to regenerate

NCM cathode materials from leachate are summarized in Table 7(61, 101-107).

The NCM cathode materials regenerated by hydrometallurgical process hold superior

crystal morphology and rate/cycle performance, whose electrochemical performance

are comparable to that of commercial NCM materials (102,104). The conventional

hydrometallurgical regeneration process to prepare NCM materials is as follows:

leaching liquid → co-precipitation→ solid phase synthesis at high temperature, as

shown in Figure 6. In the regeneration process, appropriate amounts of cobalt salts,

manganese salts, nickel salts and lithium salts are added according to actual

stoichiometry composition of NCM materials.

Li et al. (108) re-synthesized NCM333 (R-NCM) materials from cathode material’s

leaching liquids by one-step sol-gel method, and the related details and recycling

mechanism are showed in Figure 7 and Figure 8 (108). In the recovery system, the

H2O2 is used as reducing agent, and the lactic acid plays as leaching agent in leaching



stage and chelating agent in regeneration stage respectively. The mechanism of

leaching stage can be proved as follows:

3LNi1/3Co1/3Mn1/3O2 (s)+9C3H6O3(aq) +1/2H2O2(aq) →3C3H5O3Li(aq)+(C3H5O3)2 Ni(aq)

+ (C3H5O3)2 Co(aq)+ (C3H5O3)2 Mn(l)+5H2O+O2(g) (4-1)

Under the optimal conditions (lactic acid=1.5M, s/d=20g·L-1, H2O2=0.5vol%,

T=343K), the leaching efficiency of the metals reached 98％. Electrochemical results

proved that the re-synthesized NCM333 (R-NCM) cathode material held excellent

reversible discharge capacity of 138.2 mAh·g-1, whose capacity retention reached 96%

at 0.5 C after 100 cycles (105). Due to low charge-transfer resistance of regenerated

NCM333 (R-NCM, Rct=58.78Ω) compared with fresh NCM333 (F-NCM, Rct=70.02Ω),

which can provide higher lithium ion diffusion coefficient (DLi+) and faster Li+

intercalation/de-intercalation kinetic properties, the electrochemical performance

especially cycle capability of R-NCM is self-evident higher than that of F-NCM. It is

indicated that chelating agent of lactic acid can efficiently recycle and re-synthesize

NCM materials by sol-gel method with closed-loop recovery process.

4.2 Integrated high value utilization of electrode scraps

In industrial production of LIBs, a lot of cathode scraps are produced (89), and

difficult to be utilized. Since those cathode scraps are not assembled into batteries,

the active materials in them maintain superior electrochemical performance. Efficient

recycling valuable component in these electrode scraps embodies both economic and

environmental benefits.

Zhang et al. (109) developed a representative one-step recovery technology to

regenerate NCM material from electrode scraps. The main recovery process contains

detaching active materials from Al foil and direct re-preparing NCM cathode materials



by state solid reaction, as shown in Figure 9 (109). Pre-treated with direct calcination

(DC), solvent dissolution (SD) and basic solution dissolution (BD) methods, the re-

birth NCM samples presented diverse properties on electrochemical performance.

Interestingly, it was found that different quantity of LiF compound emerged on the

surface of regenerated NCM samples under pre-treated by DC/BD methods, as

resultants of HF released from PVDF reacted with Li element. It showed that the re-

prepared cathode materials directly calcined at 600°C (CD-600) exhibited uniform

spherical particles and superior cycle performance, with initial discharge capacity of

145.4 mAh·g-1 and capacity retention of 96.7% at 0.2C after100 cycles,

correspondingly. As the literatures proved that the emergence of suitable amount of

LiF contributes to hinder side reactions between NCM materials and electrolyte, which

could strengthen the structure stability of the recovered NCM materials (110-113).

4.3 Potential and challenge of mediate/direct regeneration method

The leaching-regeneration system, without intricate processes to remove impurities

and separate various metals, has caught researchers’ attention. With majority mature

technologies of co-precipitation, solvent dissolution and sol-gel, etc., the

hydrometallurgical recycle pattern is feasible to achieve industrial application. As

mentioned above, separation of active materials and leaching of valuable metals play

an important role in leaching-regeneration system. In fact, there are still low content

of impurities such as Al and Mg existed in the leachate. One recovery idea is employing

such impurities as doped metals to modify regeneration NCM materials, avoiding the

potential damage of impurities and purification treatment. And the excellent

electrochemical performance of regenerated Al/Mg-doped NCM materials (105,107)

are showed in Table 8. Furthermore, how to strictly control production conditions and



identify the optimal residual content of impurities is an imminent problem need to be

resolved. Thus, there is still a long way to go before building recycle system with

superior leaching rate and efficacious separation of overall metals.

Another interesting recovery idea is using smelting slag as coated material source to

enhance the electrochemical performance of regenerated NCM materials. For instance,

coating with V2O5 produced from vanadium-containing slag, the regenerated NCM

samples (106) presented high cycle performance, as shown in Table 8. Meanwhile,

the general acid-roasting process (15) combines with one-step or hierarchical leaching

technology is worth to be considered.

In addition, as a non-damaged restoration technology, the direct regeneration

technology, also named re-construction of crystal structure, is different from the

hydrometallurgical leaching-regeneration system. This integrated high value utilization

technology can efficaciously avoid attack of active materials from multiple chemical

reagents in leaching and extracting processes. Besides, this simple and sustainable

one-step recover technology is conductive to realize high value re-use and recycling

of secondary resources, effectively cutting down the recovery cost. Last but most

important, the directly regenerated NCM samples hold excellent charge/discharge

capacity, superior cycle/rate performance, even comparable to that of commercial NCM

materials. Accordingly, one-step recycling or direct re-synthesis NCM materials are

considered as most favourable and influential hydrometallurgical recycling strategies

for retired LIBs or cathode scarps, at present. However, there are still immense

challenges before successful industrial application. For example, the green-simple

technology is needed to be further explored for efficiently detaching active materials

from Al foils, without destructing both crystalline particles and Al foils. In addition, it



is high time that new methods should be developed for direct regeneration of different

types of NCM materials except high temperature solid phase method. Crucially, it is

imperative to build a closed-circuit recycling mode for all valuable components, such

as Al foils, PVDF and active materials via direct regeneration technology.

5. The latest recovery technologies of NCM cathode materials

5.1 Extractive methods based on deep eutectic solvents

Compared with the traditional extractants, deep eutectic solvents (DESs) have the

remarkable advantages of non-toxic, cheap and biodegradable, and extremely high

dissolution and reduction capability for metal oxides (114,115). However, there are

few reports on recycling electronic waste using deep eutectic solvents. As far as I see,

Tran et al. (116) first applied DESs to recycle cathode materials from waste LIBs. The

adopted DESs were synthesized by choline chloride and ethylene glycol, and the

possible synthesis reaction is as follows:

[HOC2H4N(CH3)3]++[Cl]-+n(HOCH2CH2OH)→[HOC2H4N(CH3)3]

++

(HOCH2CH2OH)n[Cl]- (5-1)

The Al foil and binder PVDF were recovered respectively while valuable metals were

extracted by DESs. The results showed that the leaching rate of cobalt in LiCoO2

cathode material was as high as 99.4% at 180°C, which was comparable to that of

traditional leaching agents such as sulfuric acid (99.70%) (70) and formic acid

(99.96%) (72). Cobalt in the DESs liquids can be recovered as Co3O4 by

electrodeposition and calcination.

Wang et al. (117) developed a recycling process using DESs to detach active

substances and Al foil of retired LIBs, as the recovery flow shown in Figure 10. And

the specific synthesis reaction of DESs is as follows:



[HOC2H4N(CH3)3]++[Cl]-+n(CH2OHCHOHCH2OH)→[HOC2H4N(CH3)3]

++

(CH2OHCHOHCH2OH)n[Cl]- (5-2)

The DESs attacked the hydrogen atoms in PVDF molecular chain, forming

unsaturated double bonds, which were further oxidized into hydroxyl and carbonyl to

construct an unsaturated ketone structure on the molecular chain. Therefore, PVDF

was forced to deactivate and dissolve, the active materials and Al foil were separated

successfully. Hence, it can be indicated that DESs have great potential in regenerating

of cathode materials. High selectivity of valuable metals is the key to promote leaching

performance of DESs in recycling spent LIBs.

5.2 Technology of recovery NCM particles

Despite high recovery rates of R-NCM from leaching solution, electrochemical

performance is damaged to some extent due to inevitable contacting with organic

solvent during the treatment process. In the future, the recovery technologies that

show low efficiency must be avoided. Sieber et al. (118) directly recovered NCM

particles from used cathode scraps. The active material was detached from the Al foil

by strong stirring in water to maintain the electrochemical performance and

morphological characteristics of NCM particles. However, during the separation

process, side reactions occurred when the NCM cathode contacted with water, resulting

in a rapid increase in pH value and degradation of NCM particles followed by forming

of Al(OH)3 precipitate and LiAl(OH)4. The main chemical reactions during separation

stage are as follows:

2Al+2OH-+10H2O → 2[Al(OH)4(H2O)2]-+3H2 (5-3)

[Al(OH)4(H2O)2]- − H+ ⇄ [Al(OH)5(H2O)]2- − H+ ⇄ [Al(OH)6]3- (5-4)

2H++2Al + 2[Al(OH)4]-+4H2O → 4Al(OH)3 + 3H2 (5-5)



Li+ + [Al(OH)4]- → LiAl(OH)4 (pH＞ 11) (5-6)

Such side effects can be avoided by adjusting pH value with superior buffer solution,

aiming to detach active materials from Al foil and hinder degradation of NMC particles.

Under the control of buffer solution, the Al foil was successfully dissolved into solution

while NCM particles were well-preserved.

6. Conclusions and overlook

The waste cathode materials in LIBs contain valuable metals, which can be recycled

by hydrometallurgical process due to low energy consumption, environmental friendly

and excellent recovery efficiency. Based on the analysis and summary of

hydrometallurgical recycling process, the following conclusions are drawn:

(1) In view of economy and industrial application, the following flow is considered

as the most competitive process to recycle valuable metals from waste cathode

materials: alkaline solution dissolution/calcination treatment → reductant (H2O2) →

sulphuric acid leaching → co-precipitation → re-synthesis at high temperature.

(2) The leaching capability of reductant organic acid is greater than that of

inorganic acid leaching united with reductants. Bacterial leaching shows high selectivity

for lithium, which can be selected to recycle high purity lithium-containing products.

(3) In the stage of extracting valuable metals, the combination recovery process

can complement each other, which contributes to improve the quality of the recycled

products.

(4) The deep eutectic solvents (DESs) separation technology can achieve efficient

overall recovery of valuable components from spent LIBs, which is conducive to

sustainable development of society. The high efficient direct-regeneration or direct-



recovery of NCM materials will face to huge challenges and potential. In the future,

both of them will become research hotspots in exhausted LIBs recovery field.

Acknowledgements

This work was supported by Natural Science Foundation of China (No.51674186);

Natural Science Foundation of Shaanxi Province (No. 2020JQ-679); Key laboratory

project of education department of Shaanxi Province (No. 2018GY-166, 2019TD-019,

2019TSLGY07-04); Foundation of Xi’an Key Laboratory of Clean Energy (No.

2019219914SYS014CG036).

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The Authors

Lizhen Duan obtained her B.S. Degree in metallurgical engineering,

Xi’an University of Architecture and Technology, in 2018. She is

currently a candidate of M.D. at the School of Metallurgical

Engineering, Xi’an University of Architecture and Technology. Her

research interest is focused on cathode material for lithium-ion

batteries.

http://dx.doi.org/10.1016/j.nanoen.2015.04.013

http://dx.doi.org/10.1149/1.1793712

http://dx.doi.org/10.1016/j.electacta.2006.05.044

http://dx.doi.org/10.1039/C5GC03080C


http://dx.doi.org/10.1038/s41560-019-0368-4

http://dx.doi.org/10.1016/j.jhazmat.2019.120846

http://dx.doi.org/10.3390/nano9020246



Dr Yaru Cui, professor of School of Metallurgical Engineering in Xi’an

University of Architecture and Technology. She was conferred Ph.D.

degree in 2011, and was afforded the opportunity working in School of

Materials Science and Engineering, the University of New South Wales

of Australia, as a visiting fellow for one year. Her main research

interests covered metallurgical preparation of functional materials and

recycling technologies for metallurgical residues etc. At present, she

has authored or co-authored more than 70 journal publications.

Dr Qian Li obtained her PhD in Metallurgical Engineering, the Central

South University, in 2013. Then she worked as a lecturer in School of

Metallurgical Engineering at Xi’an University of Architecture and

Technology, China. She is mainly engaged in research and technology

of solar thin film cells, functional materials, sodium-ion battery and

lithium-ion battery. She has authored or co-authored more than 20

academic papers, 5 licensed patents.

Dr Juan Wang is a Distinguished Fellow and a Team Leader at

Shaanxi Key Laboratory of Nanomaterials & Nanotechnology,

China. She received her Ph.D. degree in materials science from

Xi’an University of Architecture & Technology, China, in 2009.

She is currently a professor and doctoral supervisor of the School

of Mechanical and Electrical Engineering, Xi’an University of

Architecture & Technology. She has authored or co-authored

over 50 papers in peer-reviewed journals related to the field of

energy and materials.

Chonghao Man obtained his B.S. Degree in condensed matter

physics, Southeast University of China, in 2018. Currently, he is

a MS candidate at the College of Engineering, the University of

New South Wales of Australia, major in information technology.



Xinyao Wang obtained his B.S. Degree in metallurgical

engineering, Xi’an University of Architecture and Technology in

2019. He is currently pursuing his M.D. at the School of

Metallurgical Engineering, Xi’an University of Architecture and

Technology under the supervision of Prof. Yaru Cui. His main

research is focused on recycling waste lithium-ion batteries.



<Tables>

Table I Summary of techniques for recovery and separation valuable metals from spent ternary lithium-ion

batteries [26-34]

Type of LIBs

Leaching system (reagents+ solid/Liquid/(g/L)+ temperature/K+time/min)

Leaching rate/% Extraction method(reagents) +Recovered products(recovery rate/purity/%)

Ref.

LiCoO2 acid + reductant leaching + selective chemical precipitation 1.5MH3Cit+0.4g/g tea waste+30+363+120

Co:96/Li: 98 selective precipitation(H2C2O4/H3PO4) + CoC2O4·2H2O(99/-)+ Li3PO4(93/-)

[26]

2MH3Cit+0.6g/g H2O2+50+343+80 Co:98/Li: 99 1.5MH3Cit+0.4g/g phytolacca americana+40+353+120 Co:83/Li: 96

NCM523 mechanochemical leaching + selective precipitation mechanochemical leaching Na2S·9H2O+15min+600rpm-water leaching+/+298+30

Li: 95.10 selective precipitation (Na2CO3) + Li2CO3 (-/99.96)+ Ni0.5Mn0.3Co0.2(OH)2

[27]

LiCoO2 mechanochemical activation leaching + selective precipitation mechanochemical activation (EDTA/600rpm/240min) +water leaching+/+298+/

Co:98/Li: 99 selective precipitation (NaOH/Na2CO3) + Co3O4 (about94/-)+ Li2CO3

[28]

LiCoO2 acid + reductant leaching + selective chemical precipitation 2% v/vH3PO4 & 2% v/vH2O2 +8+363+60

Co/Li: about 99 selective precipitation (H2C2O4/NaOH) + CoC2O4·2H2O (99/97.8)+ Li3PO4(88/98.3)

[29]

Mixed-type

sulphuric roasting+ acid leaching Before leaching: sulfuric acid baking:2MH2SO4+573k+30min Leaching step1: H2O+/+348+60 Leaching step1:1MH2SO4+0.5MHNO3+plus glucose+/+323+45

overall recovery efficiency: about Co:90.5/Li:93.2 Ni:82.8/Mn: 77.7

-- [30]

LiCoO2 acid + reductant leaching 1.0Mcitric acid+8v/v% H2O2+40+343+70

Co/Li: about 99 -- [31]

LiCoO2 acid + reductant leaching 3MH2SO4+0.4g/g plus glucose +25+368+120 3MH2SO4+0.4g/g cellulose+25+368+120 3H2SO4+0.4g/g sucrose +25+368+120

Co:98/Li: 96 Co:54/Li: 100 Co:96/Li: 100

-- -- --

[32]

Spent LIBs

acid + reductant leaching + selective chemical precipitation 1.5Mcitric+0.5g/g D-glucose+20+353+120

Co:92/Li:99 Ni:91/Mn:94

precipitation method(C4H8N2O2/H2C2O4/H3PO4) + Ni(C4H6N2O2)2+CoC2O4+ Li3PO4

[33]

LiFePO4 acid + reductant leaching + selective chemical precipitation 0.5H3PO4+/+273+60

Co/Li: over 95 evaporation and precipitation (ethanol) + FePO4·2H2O + LiH2PO4

[34]



Table 2 Chemical properties and potential environment pollution of

component materials from spent ternary lithium-ion batteries [45-48]

Material Constitute Content,% Chemical properties Potential environment pollution

Cathode material

LiNixMnyCo1-x-yO2 25-30 Reacting with acids and bases, and producing heavy metals

Heavy metals pollution

Anode material

Graphite/Carbon 14-19 Producing toxic gases such as CO and dust particles under combustion

Toxic gases and dust

Casing Stainless steel/Plastic

20-25 Hardly degradable White pollution

Electrolyte LiPF6、LiBF4 LiClO4、LiAsF6

10-15 Strongly corrosive, releasing toxic gases in contact with water or high temperatures

Produceing toxic gases, polluting the air and damaging human health

Electrolyte solvent

EC、EMC DMC、PC

- Producing CO under combustion

Harm to human health through skin and respiratory contact with organic compounds

Cu foil Cu 5-9 - Heavy metals pollution Al foil Al 5-7 - Heavy metals pollution Separator PP/PE - - Organic pollution Binder PVDF - - Fluorine pollution

Table 3 The advantages or disadvantages of pyrometallurgical and

hydrometallurgical method [53-57]

Item Pyrometallurgical method Hydrometallurgical method Process Calcination Leaching, purification, separation and

extraction Recycling methods

High temperature reduction/Sulfatizing roasting /Repair and regeneration

Acid leaching, bioleaching/ Chemical precipitation/ Solvent extraction/Ion exchange/ Repair and regeneration

Operating temperature

573-1273K 298-353K

Cost High Low Advantages High efficiency, large processing

scale, and easy to achieve industrial applications, no waste water and sludge

Low energy consumption, mild operating conditions, high recovery rate, multiple processing methods, high selectivity, low exhaust emissions

Disadvantages High energy consumption, producing toxic waste gas(CO/CO2/SO2/HF), low recovery rate and low selectivity, single processing method, high temperature operating system

Some chemicals are poisonous, waste liquid problem, long process, complex separation process



Table 4 Parameters and separation rate of pre-treatment methods for spent

LIBs in literature [61-66]

Type of LIBs Pretreatment methods

Reagents/ Temperature/K

Recovery rate of scrap materials/%

Separated substance /Purity/%

Ref.

LiNi1/3Co1/3Mn1/3O2 Solvent dissolution

Trifluoroacetic acid

- Al foil [61]

LiNi1/3Co1/3Mn1/3O2 Heat treatment Scraping+Water leaching

393 313

- PVDF Al foil

[62]

LiNi1/3Co1/3Mn1/3O2 Solvent dissolution

Dimethyl carbonate

99 Al foil ,PVDF

[63]

LiNi1/3Co1/3Mn1/3O2 Ultrasonic cleaning

N-methyl-2-pyrrolidone＆343

99 PVDF, Al foil

[64]

LiNixCoyMnzO2 Basic solution dissolution

1.5 M NaOH - Al foil [65]

Laptop LIBs Heat treatment 523-573 - Al foil [66]

Table 5 Optimal leaching parameters and corresponding leaching rate of

metals from active material by acid leaching [68-75]

Type of LIBs

Leaching reagents

Reducta-nts

Solid/L-iquid /(g/L)

Tempera-ture /K

Time /min

Leaching rate/% Ref.

NCA 4 M HCl 50 363 1080 Li, Ni, Co, Al: About100

[68]

Mixed-type batteries

1M H2SO4 - 50 368 240 Li:93.40/Ni: 96.30 Co:66.20/Mn:50.2

[69]

5vol% H2O2

50 368 240 Li:93.40/Ni:96.30 Co:79.20/Mn:84.60

0.075M NaHSO3

20 368 240 Li:96.70/Ni: 96.40 Co:91.60/Mn:87.90

NCM311 1M H2SO4 1vol% H2O2

40 313 60 Li, Ni , Co, Mn: About 99.70

[70]

NCM311 2 M L-Tartaric acid

4vol% H2O2

17 343 30 Li: 99.70/Ni :99.31 Co:98.64/Mn:99.31

[71]

NCM311 2 M Formic acid

6vol% H2O2

50 333 10 Li:98.22/Ni:99.96 Co:99.96/Mn:99.95

[72]

NCM311 3 M Tricarbox-ylic acid

4vol% H2O2

50 333 30 Li: 99.70/Ni: 93.00 Co:91.80/Mn:89.80

[73]

LiNi1/3Co1/3Mn1/3O2

1.2 M DL-malic acid

1.5vol% H2O2

40 353 30 Li:98.90/Ni:95.10 Co:94.30/Mn:96.40

[74]

NCM 3.5 M Acetic acid

4vol% H2O2

40 333 60 Li: 99.97/Ni: 92.67 Co:93.62/Mn:96.32

[75]

Table 6 Leaching rate of metals from active material in spent LIBs with

biological bacteria [81-86]

Type of LIBs

Leaching reagents Decomposing acids Leaching rate/% Ref.

NCM batteries

Aspergilus niger (PTCC 5210)

gluconic, citric, malic and oxalic acid

Li:100/Ni:54/Co:64/Mn:77 [81]

Spent coin

A. thiooxidans (PTCC 1717)

H2SO4 Li: 99/Co: 60/Mn: 20 [82]



cells Laptop batteries

A.thiooxidans, A.ferrooxidans

H2SO4 Li:99.20/Ni:89.4/Co:50.4 [83]

NCM batteries

Aspergilus niger gluconic, citric, malic and oxalic acid

Li:100/Ni:45/Co:38/Mn:72 [84]

NCM batteries

Aspergilus niger gluconic, citric, malic and oxalic acid

Li: 95/Ni:38/Co:45/Mn:70 [85]

NCM batteries

Sulfur-oxidizing bacteria (SOB) Iron-oxidizing bacteria (IOB)

Sulfur-A.t system, Pyrite-L.f system MS-MC system

NCM: >95 [86]

LiFePO4 Li: 98 LiMn2O4 Li: 95/Mn:96

Table 7 Summary of the chemical precipitation parameters investigated in the

literature [90]

Elements Precipitates Precipitants pH Ref. Li Li2CO3 Na2CO3 - 137, 157 and 187

LiF NH4F - 136 Li3PO4 H3PO4/Na3PO4 - 102, 159 and 188

Co Co(OH)2 NaOH 10 114 CoCO3 Na2CO3 9–

10 157 and 212

Co2O3·3H2O NaClO 3 182 CoC2O4·2H2O H2C2O4/(NH4)2C2O4 1.5,

2 136, 186 and 187

Ni Ni(OH)2 NaOH 8,11 114 and 182 NiCO3 Na2CO3 9 160 NiC8H14N4O4 C4H8N2O2 5,9 114 and 201

Mn Mn(OH)2 NaOH 12 114 MnCO3 Na2CO3 7.5 160 MnO2 KMnO4 2 114

Ni/Co/Mn co-precipitation

NixCoyMnz(OH)2 NaOH 11 73, 74 and 208 (NixCoyMnz)CO3 Na2CO3 7.5–

8 213

Fe/Al/Cu impurities Fe(OH)3 NaOH 3–6 113, 157, 186, 201 and 214

Al(OH)3 Cu(OH)2

Table 8 Regeneration preparation and electrochemical properties of cathode

materials from leaching solution [61,101-107]



Regenerated NCM materials

NCM 333

NCM523 NCM 333

NCM 333

Li-riched NCM

Mg-doped NCM333

V2O5-coated NCM333

Al-doped NCM333

Resynthesis method High temperature solid-state method

Co- precipitation

Co-precipitation

Co-precipitation

Hydrothermal method

Co-precipitation

Solid-state reaction

Co-precipitation

Reagent - NaOH NaOH NH3·H2O

Na2CO3 Na2CO3

NH3·H2O - NH4VO3

Calcination temperature/k

723→1173 773→1123 1173 773→1173 723→1173 - 623

Initial charge capacity/(mAh·g-1)

201 198.4 178 198.9 About 330 175.4 - About 230

Initial discharge capacity/(mAh·g-1)

155.4 172.9 158 163.5 258.8 152.7 172.4 170

Cycles 30 50 100 50 50 50 100 50 Capacity retention /%

83.01 93.8 80 94.01 87 94 90.6 About 88

Rate performance: current density/(C) //Discharge capacity/(mAh·g-1) (approximation) Back to original current density

- 0.2C //180-170 0.5C //170-168 1C //162-161 2C //158-159 168-170

0.1C //149-150 0.2C //149-146 1/3C //131-138 0.5C //139-177 C //130-131 -

0.2C //156-154 0.5C //150-144 1C //139-135 2C //130-127 148-152

0.1C //245-262 0.2C //240-235 0.5C //220-200 1C //190-175 2C //160-150 230-222

- 0.1C //178-160 0.2C //175-173 0.5C //160-152 1C //135-131 2C //110-100 173-175

0.1C //165-147 0.2C //145-132 0.5C //134-120 1C //117-115 2C //107-98 132-155

Ref. [61] [101] [102] [103] [104] [105] [106] [107]



<Figure captions>



Fig. 1. Process flow of hydrometallurgical recovery method for waste NCM cathode materials.

Spent LiNixMnyCo1-x-yO2 barreries

Anode material、Shell and separator

Leaching residue

Leachate

Purification• Chemical precipitation• Ion exchange• Solvent extraction• Deep eutectic solvent (DESs)• Chemical precipitation• Evaporation

In NaCl solutionCryogenic freezingDischarge

Dismanlting

Cathode material

Anode material

Electrolyte

Sepa-rator

Shell

Manual dismantlc

Mechanical dismantlc

Pretreatment

Cathode electrode

Leaching

Adjusting solution composition

Nickel sourceManganese sourceCobalt source

Re-synthesis

Calcination

• Inorganic acid leaching• Organic acid leaching• Bioleaching• Mechanochemical

leaching

• Heat treatment• Solvent dissolution • Mechanical separation• Ultrasonic treatment• Alkali dissolving

Li source(LiOH/Li2CO3)

Regenerated NCM materials

Separation and extraction of

metals

Pure metal or metal compound

• Co-precipitation• Sol-gel• Hydrothermal method• High temperature

solid-state method

Direct regenerationof NCM materials



Fig. 2 Separation methods for leaching metals from active materials.



Fig. 3 Process of chemical precipitation for hydrometallurgical recycling NCM material

from spent LIBs.

Cathode powder

Roasted products

Planetary ball milling

Lignite

Cathode material of spent LIBs

Pretreatment

Reduction roasting

Water CO2

Carbonated water leaching

650℃，3h

300rpm1h

20% carbon dosage

Filtrate(LiHCO3) Residue

Evaporation

Li2CO3

Acid leaching

Filtrate(Ni,Co,Mn) Residue

Purification

Solvent extraction and evaporation

NiSO4 ·6H2O CoSO4 ·7H2O NiSO4 ·6H2O

100℃ 1.15 times H2SO4 T=2.5 h,T=55 °C,Liquid/solid=3.5 mL·g−1

NaOH

Flow rate=30mL·min-1

T=1 h, T=65 °C,Liquid/solid=10mL·g−1

Roasting-Leaching-Single Method Seperation System



Fig. 4 Details and mechanism of recycle of previous metals in spent NCM cathode

materials by reduction roasting combined acid leaching: Backscattering SEM and EDS

mapping results of the cathode scrap after reduction roasting(a-i); Effect of CO2 flow

rate (k: L/S ratio 7.5 mL·g−1, t=2 h, T=25 °C); XRD and SEM of LiCO3 (l) and residue

(m) after the carbonation water leaching; The comparasion of leaching efficiency

between roasted cathode scrap and unroasted cathode scrap(n). (93)

Cathode scrap of LIBS

Leaching

Muffle furnace(In argon

atmosphere)

Reduction Roasting

Carbonated Water

Leaching

2LiHCO3（aq) → Li2CO3（s)+H2O（aq)+CO2（g)Selective

Separation of Li

Evaporation

Separation of Ni、Mn

and Co

Acid Leaching

2Ni+2H2SO4+O2 → 2NiSO4+2H2O

2Co+2H2SO4+O2 → 2CoSO4+2H2O

MnO+H2SO4+O2 → MnSO4+H2O

a b

d e

c

f

g h i

k l

m n



Fig. 5 Metals recovery process from the leachate of spent lithium-ion batteries by

combined solvent extraction and selective chemical precipitation.

Leachate

Cathode material

Filtration

Chemical precipitation（pH=6,t=30min)

Leaching Citric acid、H2O2

HCl

NiCl2

Filter cake Filtrate

Precipitation (NH4)2C2O4

Filtration CoC2O4·2H2O

Solvent extraction

Mn-loaded organic phase

MnSO4

Solvent(Li)

Na3PO4 Precipitation

Li3PO4

FiltrationStrippingH2SO4

C4H8N2O2

Saponified D2EHPA

Acid Leaching- Combined Methods Seperation System



Fig. 6 Regeneration flow of LiNi1/3Co1/3Mn1/3O2 cathode material from leaching liquid

by co-precipitation.

Co-extraction

Extract liquor

Feed liquor

Extract liquor Raffinate

Stripping Purification

Adjusting composition(Ni:Mn:Co=1:1:1)

HydroxideCo-precipitation

Organic phase

MnSO4

NiSO4

CoSO4

Carbonate precipitation

NaOHNa2CO3

Na2CO3

Ni1/3Co1/3Mn1/3(OH)2 Li2CO3

Solid state reaction

LiNi1/3Co1/3Mn1/3O2

Conventional Leaching-Regeneration System by Co-precipitation



Fig. 7 Re-synthesis flow of LiNi1/3Co1/3Mn1/3O2 cathode material from leachate of

spent LIBs by sol-gel method.

Diamanlting


Steel Anode electrode

Basic solvent

Cathode electrode

Discharging

Drying

5％ NaOH

Calcination

NaOH

Acid leaching Lactic acid、H2O2

Filtration

Adjusting composition(Ni:Mn:Co=1:1:1) Acetate

Sol-gel method

Calcination

LiNi1/3Co1/3Mn1/3O2

Leaching-Regeneration System By Sol-gel



Fig. 8 Possible products and mechanism in the lactic acid leaching process (a); XRD

and SEM patterns of R-NCM and F-NCM samples(b); Electrochemical performances of

R-NCM and F-NCM samples: charge/discharge profiles at 0.2 C(c); cycling

performances at 1 C(d); rate performances at different currents(e); and Nyquist plots

in the frequency range of 100 kHz to 0.01 Hz(f). (108)

F-NCM

R-NCM

a

c d

e f

b



Fig. 9 Diagram illustration of recycle and regeneration of NCM111cathode materials under

three different routes (a); SEM images of DC-600(b), SD-800(c)and BD-800(d) samples;

rate performances of DC(e) samples at 0.2 C; cycling performances of DC(f) samples. (109)

b

c

a

d

fe

Direct Regeneration Mechanism



Fig. 10 The separation of cathode materials and Al foil from spent LIBs by using choline

chloride-glycerol DESs.

Choline Chloride+Glycerol(DES)

Manual diamanlting


Organic separators

Anode electrode

Cutting、Stripping

Cathode electrode

Discharging

Metal shell

Deep-eutectic solvent dissolution

5％ NaOH

Manual separation

Al foil Cathode material

DESs pretreatment system

Documents

· ************Accepted Manuscript*********** Johnson Matthey’s international journal of research exploring science and technology in industrial

· **Accepted Manuscript* Johnson Matthey’s international journal of research exploring science and technology in industrial