Comparison of the Ammoniacal Leaching Behavior of Layered

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Comparison of the ammoniacal leaching behavior of layered LiNixCoyMn1-x-yO2 (x=1/3, 0.5, 0.8) cathode materials Kui Meng, Yang Cao, Bao Zhang, Xing Ou, Dong-min Li, Jia-feng Zhang, and Xiaobo Ji ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b06675 • Publication Date (Web): 22 Mar 2019 Downloaded from http://pubs.acs.org on March 23, 2019

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ACS Sustainable Chemistry & Engineering

Comparison of the ammoniacal leaching behavior of layered LiNixCoyMn1-x-yO2 (x=1/3, 0.5, 0.8) cathode materials Kui Meng,a Yang Cao,b Bao Zhang,b Xing Ou,b Dong-min Li,b Jia-feng Zhang,b* Xiaobo Jia aSchool

of Chemistry and Chemical Engineering, Central South University, Changsha, 410083, PR China bSchool of Metallurgy and Environment, Central South University, Changsha, 410083, PR China *Corresponding

author. Tel :+86-0731-88836459; Email address: [email protected] (J.

Zhang) Lushan South Road 932, Changsha, Hunan Province, PR China

Abstract Recycling of spent lithium-ion batteries has received widespread concern on account of the high content of hazardous and valuable metals contained. In this research, ammonia leaching process is adapted to extract valuable metals selectively from LiNixCoyMn1-x-yO2 (x=1/3, 0.5, 0.8) cathode materials. By employing ammoniacal solution as the leaching agent and sodium sulfite as reductant, Ni, Co and Li are leached form lixivium either as complexes or metallic ion. Manganese is firstly leached from lixivium as Mn2+ and subsequently deposited from Mn3O4 to (NH4)2Mn(SO3)2·H2O as sodium sulfite added. Compared with the agglomerated (NH4)2Mn(SO3)2·H2O tightly wrapped on the surface of the unreacted material, loose and porous Mn3O4 is more favorable to ion diffusion and leaching reaction. 93.3% Li, 98.2% Co and 97.9% Ni can be leached out from LiNi1/3Co1/3Mn1/3O2 material by the introduced two-step leaching process, much higher than that the one-step process. Simultaneously, 94.4% Li, 99.7% Co and 99.5% Ni can be leached out from LiNi0.5Co0.2Mn0.3O2 material, while the

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leaching efficiency of Li, Ni, and Co reaches 95.0%, 98.4% and 96.9% for LiNi0.8Co0.1Mn0.1O2 material by a one-step leaching process. Keywords: Lithium-ion battery; Cathode; Recycling; (NH4)2Mn(SO3)2·H2O; Mn3O4. Introduction As a widely used energy source for power supplies from mobile phones to electric vehicles(EVs), lithium-ion batteries (LIBs), are experiencing an alarming increase in the number of wastes caused by the end of its use.1 LiNixCoyMn1-x-yO2 cathode materials have been highly favored in portable electronic applications including 3C digital products, energy storage devices, and electric vehicles because of their high energy density, long cycling life, and minimal memory effect.2 However, LIBs are consumables, meaning that they should be abandoned after some certain cycles.3-5 Recycling of spent lithium-ion batteries has received widespread concern on account of the high content of hazardous and valuable metals contained.6-7 According to the estimated date by the EV industry, the quantity and weight of spent LIBs will surpass 25 billion units and 500 thousand tons in 2020.8 Resource waste and environmental pollution will emerge if the spent LIBs are not handled properly. Recycling of spent LIBs can reduce dependence on mineral resources, and also accords with the concept of circular economy and sustainable development. Hydrometallurgy and pyrometallurgy processes are the primary methods for recovering valuable metals from spent LIBs.7 Characterized by high-temperature smelting, the products from pyrometallurgical are usually Co-Ni-Cu-Fe alloys and slags comprised by Al, Mn and Li.9 Even the process of pyrometallurgy is simple, and the


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throughput is relatively high, but high energy consumption, secondary pollution and low recovery of Li still hinder its further application. In contrast, hydrometallurgical treatment could be a favored technology for recycling of valuable metals because of its low energy consumption, no emission of hazardous gases and high recycling efficiency.7 As a fundamental procedure in the hydrometallurgical recycling process, leaching is generally used to dissolve metals from the spent LIBs into a solution for further processing. Choosing a suitable system is especially important because it strongly influences the overall recycling of metals and determines the complexity of the subsequent purification and separation process. There are two types of leaching system: alkali leaching and acid leaching, the latter one attracts more attention due to its higher efficiency.7, 10 In the early stage of research, strong inorganic acids are often used for leaching, such as HCl, H2SO4, HNO3. Excess acid is usually used to ensure high efficiency during the leaching process, thus resulting in a large amount of spent acid that pollutes the environment. Besides, inorganic acid leaching usually leads to the emission of toxic gases (Cl2, SOx, and NOx). Compared with strong inorganic acids, organic acids have the advantages of biodegradability and complexation. Therefore, organic acids have subsequently been widely studied for extracting valuable elements from spent LIBs. However, acid leaching usually has a poor selectivity to different metals, thus leading to a complicated purification and separation process. Complex purification processes are costly and often resulted in excess wastewater emission. Therefore, alkali process would be more suitable for recycling of spent LIBs due to its good selectivity to different metals, which lied in the fact that valuable metal could



form stable metal ammine complexes, such as Ni, Co, Cu, Zn.11 According to our previous studies, although the ammoniacal leaching is less effective than acidic leaching, the simple purification and separation process makes it possible to extract valuable metals from low-grade ores.12 The principle of ammoniacal leaching lies in its leaching selectivity towards Ni, Co, and Li, resulting in products with different forms (complexes or metallic ion). Undesirable metals such as Mn can be precipitated out as hydroxide or oxide due to its poor complexation ability with ammonia. Moreover, ammonia is easy to be recycled. Based on the researches by Xiaohong Zheng et al., and Heesuk Ku et al., the kinetic parameter, dynamic equations as well as the activation energy of Li, Ni, Co have all been investigated and calculated, providing beneficial research basis of the ammoniacal leaching process to us.13-14 In general, most studies have focused on leaching kinetics in the ammoniacal process, but the leaching behavior of manganese elements, which form the solid phase due to the weak coordination with ammonia and may have a significant impact on leaching process, is rarely involved. In this paper, the ammoniacal leaching system is adapted to extract valuable metals from the LiNixCoyMn1-x-yO2 materials. The phase and morphology transformation of manganese in ammonia leaching process and its effect on the leaching of valuable elements have been studied in detail. Thermodynamics facilitates manganese elements to form a solid phase in an ammonia solution, and the leaching process is often affected by the formation of solid products based on hydrometallurgy principles. By investigating the chemical and structural changes of leaching product with different leaching conditions, it provides a new idea to improve the leaching rate of Li, Ni, and


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Co. Experimental Materials and methods LIB cathode materials were purchased from Shenzhen Kejing Star technology Co., LTD. The chemicals in the experiments were analytically pure. The experimental diagram is shown in Supporting Information (Fig. S1). First, 3 g powder was added to a 300 mL of ammoniacal solution at a stirring rate of 400 rpm at 80 °C. The ammoniacal solution was consisted of 4 M ammonia, 1.5M ammonium chloride and specified of sodium sulfite. The concentration of metallic ions in the solution was analyzed periodically by ICP-OES. After that, the slurry was filtered to separate the leachate and slag, and then the residue was dried overnight at 80 °C.

The residue was subjected to

the same leaching process one more time to increase the utilization of valuable metals (Li, Ni, Co). Materials characterization The crystal structure of the solid residues was identified by Powder X-ray diffraction measurement with Cu-Kα radiation (Rint-2000, Rigaku Corp.,). Morphology of powder was collected by scanning electron microscope equipped with an energy dispersive spectrometer (JSM-5612LV, JEOL Ltd.,). Leaching efficiencies of different metals were measured by plasma-atomic emission spectrometry (ICP-OES, IRIS Intrepid XSP, Thermo Electron Corp.,). The coefficient of variation of the experimental data is less than 0.3%. The concentration of sulfite was tested by HG/T



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2967-2010 (People’s Republic of China chemical industry standard). Results and discussion The following reaction occurs for LiNixCoyMn1-x-yO2 material during ammoniacal leaching process: 2LiNi x Co y Mn 1 - x - y O 2 +SO 3 2 - +(z1+z2)NH 3 +3H 2 O=2Li + +2x[Ni(NH 3 ) z 1 ] 2 + + 2y[Co(NH3)z2]2++2(1-x-y)Mn2++ SO42-+6OH-

(1)

Where z1 and z2 are determined by the concentration of ammonia in the system.13, 15-16 According to reaction (1), Li, Ni, and Co in LiNixCoyMn1-x-yO2 materials will be gradually dissolved during the leaching process, while Li is leached as metallic ion and Ni, Co is leached as complexes. Thermodynamics facilitates the formation of corresponding manganese hydroxide or oxide in an ammonia solution.17 M. Niinae et al. extracted Cu, Ni and Co from rich ferromanganese crusts with an ammoniacal solution and found the major phase of the residue was the ammonium manganese sulfite hydrate ((NH4)2Mn(SO3)2·H2O).18 The phase compositions of manganese-based precipitation under different leaching conditions will be discussed in detail later. All powders have spherical morphology with average particle sizes of 5~10 μm (Fig.1 a~c), and each spherical secondary particle is made up of agglomerated primary grains with estimated particle sizes of 0.6 to 1.5 μm (Fig.1 a1~c1). The leaching agent can infiltrate into the secondary particle along the gaps between primary grains and participate in the leaching reaction.19 The primary particle sizes decrease noticeably with increased Ni content, which is conducive to fast leaching speed due to the increase in the specific reaction area.


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The time dependency of leaching efficiency on different metals is given in Fig.1 a2~c2. Li, Ni, and Co exhibit similar leaching speeds and their leaching efficiency reach almost a constant after 5 h for LiNi1/3Co1/3Mn1/3O2, 3 h for LiNi0.5Co0.2Mn0.3O2 and 1 h for LiNi0.8Co0.1Mn0.1O2, respectively. The overall leaching rates of Li, Ni and Co can all reach around 80% for LiNi1/3Co1/3Mn1/3O2, 83% for LiNi0.5Co0.2Mn0.3O2 and 94% for LiNi0.8Co0.1Mn0.1O2, respectively. However, Mn exhibits an entirely different leaching behavior compared with other metals, namely, a peak could be observed after 1 h leaching, implying that Mn firstly dissolved in the solution and deposited in some forms as the reaction prolonging. The concentration of Me2+ (Me2+=Ni, Co, Mn) depends on the following two reactions in the lixivium. Me(OH)2=Me2++2OH-

(2)

c(Me2 + )

Kspθ= c(OH)2 , so c(Me2+)= Kspθ*c(OH-)2 Me2++nNH3=[Me(NH3)n]2+

(3)

{c[Me(NH3)𝑛]2 + }

Kfθ= c(Me2 + )c(NH )𝑛 3

so

c(Me2+)total=

c(Me2+)+c([Me(NH3)n]2+)=c(Me2+)+Kfθ*c(Me2+)*c(NH3)n=

c(Me2+)*(1+ Kfθ*c(NH3)n)= Kspθ*c(OH-)2*(1+ Kfθ*c(NH3)n) Since the equilibrium concentration in ammonia solution of Me2+ (Me2+=Ni, Co, Mn) is determined by stability constants (Supporting Information Table S1) and solubility constants (Supporting Information Table S2), thus the inconsistency behaviors of Mn and Ni/Co mainly resulted from their distinct stability constants, that is, Ni/Co can be leached into lixivium while most of the Mn will precipitate out as solid. It is worth noting that the leaching rate of Li is slightly lower than Ni and Co, especially



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for LiNi0.8Co0.1Mn0.1O2 material. LiNixCoyMn1-x-yO2 material can be readily reacted with air, resulting in LiOH and Li2CO3 formed on the material surface and the amount of Li2CO3 will increase with the Ni content in LiNixCoyMn1-x-yO2 material.2 Thus it is reasonable that the leaching rate of Li is slightly lower since Li2CO3 is almost insoluble in ammoniacal solution. However, even the leaching efficiencies of Li, Ni, and Co are all higher than 80%, it is still not satisfactory when used in industry field, while it is necessary to find possible reasons for the low efficiencies. As seen in Fig. 2a, the residue obtained after leaching is mainly unreacted LiNi1/3Co1/3Mn1/3O2 and (NH4)2Mn(SO3)2·H2O, meaning that the incomplete leaching maybe the cause of the low leaching rate. Fig. 2b shows that the original morphology of raw material is severely damaged after 5 h leaching, while the residue is made up of both primary particles and secondary particles. According to XRD and EDS results (Fig. 2c~d), the dense irregular primary particle at position 1 should be ascribed to (NH4)2Mn(SO3)2·H2O, While the bulk material at is the

unreacted

LiNi1/3Co1/3Mn1/3O2.

It

might

indicate

that

a

part

of

(NH4)2Mn(SO3)2·H2O grown on the surface of LiNi1/3Co1/3Mn1/3O2 material acts as a coating layer nucleates The dense (NH4)2Mn(SO3)2·H2O is not beneficial for the leaching process because it might hinder the internal diffusion path of leaching agent. Therefore, the key to improving the leaching rate of valuable metals is to avoid the growth of (NH4)2Mn(SO3)2·H2O. Since SO32- is one of the necessary ingredients for the formation of (NH4)2Mn(SO3)2·H2O. According to the reaction (1), the amount of SO32- is 961% of


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the theoretical amount when the concentration of SO32- is 0.5 M, that means reducing the usage amount of Na2SO3 may be helpful to avoid the formation of (NH4)2Mn(SO3)2·H2O. The concentration of SO32- in fresh leaching agent is slightly less than 0.5 M, indicating that raw Na2SO3 is oxidized lightly (Fig. 3a). The concentration of SO32increases slightly over time due to the volatilization of leaching agent at 80 °C in the blank test, demonstrating that SO32- oxidized in the air can be neglected from 0 to 5 h. Compared with the blank test, some SO32- can be consumed by the high valence state metal ions in LiNi1/3Co1/3Mn1/3O2 material, but a considerable SO32- still exists in the lixivium after 5 h. The excessed SO32- not only causes a waste of Na2SO3 but also promotes the formation of (NH4)2Mn(SO3)2·H2O. Fig. 3b shows the effect of SO32- concentration on extraction rates of Li, Ni, and Co, where n/n0 represents the ratio between the actual amount and the theoretical amount of SO32-. As shown in Fig. 3b, the addition of SO32- significantly improves the leaching efficiency of Li, Ni, and Co when n/n0 is lower 8. However, this effect seems very little when n/n0 exceeds 8. The extraction rates of Li, Ni, and Co are 74.7%, 78.3%, and 76.0%, respectively when n/n0 is equal to 8. It is noteworthy that the leaching rate of Li, Ni, and Co decreases abruptly as n/n0 increase from 3 to 4. Results from XRD patterns (Fig. 3c~e) indicate that the leaching product is Mn3O4 when n/n0 is equal to 3, while some diffraction peaks can be assigned to (NH4)2Mn(SO3)2·H2O when n/n0 equal to 4, and these peaks become much more apparent as the n/n0 value increase from 4 to 5, the chemical reactions of manganese might be described as follows based on



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thermodynamic analysis. If C(Mn2+) ≤

K𝑠𝑝((N𝐻4)2Mn(S𝑂3)2·𝐻2O) C(NH4+ )2·C(S𝑂23 ― )2

,

Mn2++2OH- = Mn(OH)2

(4)

6Mn(OH)2+O2 = 2Mn3O4+6H2O

(5)

Otherwise, Mn2++2NH4++2SO32-+H2O = (NH4)2Mn(SO3)2·H2O

(6)

Therefore, the leaching products of LiNi1/3Co1/3Mn1/3O2 material can be changed by changing the amount of Na2SO3 used in the leaching process. By comparing the SEM images of the two leaching products (Fig. 3f~f1, g~g1), it can be seen that the submicron particles dispersed on the surface of the unreacted material when n/n0 is equal to 3. However, leaching residue is tightly wrapped on the surface of the unreacted material, and the particles are severely agglomerated as n/n0 increase from 3 to 4. Since the thermodynamically stable condition of (NH4)2Mn(SO3)2·H2O is just fulfilled as n/n0 increase from 3 to 4, the supersaturation of SO32- is small. According to the Von Weimarn equation, it is beneficial to the growth of the crystal under this condition.20 Moreover, Ostwald ripening is also benefiting to the (NH4)2Mn(SO3)2·H2O growth during the leaching process.13 Dense coating layer and particle agglomeration would inhibit the leaching process, which explains why the leaching rate of Li, Ni, and Co decreases as n/n0 increase from 3 to 4. Hence, the formation of (NH4)2Mn(SO3)2·H2O should be avoided during the leaching process. Even EDS spectra show that there is no sulfur when n/n0 is equal to 3, but the black box exhibit the peak of sulfur when n/n0 is equal to 4, which is consistent with XRD


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analysis (Fig. 3f2~g2). Based on the above discussions, the one-step leaching process cannot achieve satisfactory leaching rate of Li, Ni, and Co under excess SO32-. Therefore, we are trying to further improve the leaching rate by employing a two-step leaching process with no (NH4)2Mn(SO3)2·H2O exists in the residue. The first-step leaching is carried out for 5 h with n/n0 equal to 3, and the leaching residue is used as raw material for the second-step leaching process which is also carried out with n/n0 equal to 3. The second-step leaching can effectively extract the rest of Li, Ni, and Co from the residue (Fig. 4a). Compared with the first-step leaching, the second-step leaching is slower, which is mainly due to the nano-Mn3O4 coating on the surface of the unreacted core and hindering the diffusion of reactants and products. The leaching rate of lithium is slightly lower than that of nickel and cobalt during the second-step leaching process, which further confirms our previous inference that there are some kinds of insoluble lithium salt on the surface of the LiNi1/3Co1/3Mn1/3O2 material. The total leaching rate of Li, Ni, and Co reaches 93.3%, 98.2% and 97.9%, which is much higher than one-step leaching with an excess of SO32-. Compared with the XRD pattern of the one-step leaching residue, the two-step leaching residue exhibits only the diffraction peaks of Mn3O4, without the diffraction peaks of the LiNi1/3Co1/3Mn1/3O2 material, indicating that the rest of Li, Ni, and Co in the first-step leaching residue have been wholly leached out (Fig. 4b). It can be seen from Fig. 4c~c1 that the two-step leaching residue inherits some characteristics of the LiNi1/3Co1/3Mn1/3O2 material. The volume of primary particles



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decreases after leaching, so the two-step leaching residue is composed of loose and porous secondary spherical Mn3O4 particles. The shape of the nano-Mn3O4 primary particles may be due to rapid nucleation in the ammoniacal solution. Besides, the OHion is a strong capping agent on the surface of the nanoparticles, which usually hinders crystal growth by Ostwald ripening. Therefore, the size of the nano-Mn3O4 particles could not increase significantly.17, 21 The EDS spectra show peaks of Mn and O, without peaks of Ni and Co, which is consistent with the XRD analysis (Fig. 4c2). The leaching process of LiNi1/3Co1/3Mn1/3O2 material is represented by the schematic diagram (Fig. 4d). When C(Mn2+) is less than


, the loose

and porous nano-Mn3O4 covers the surface of the unreacted core. Since the amount of SO32- is insufficient for complete leaching, it is an unreacted core in the particle. The rest of Li, Ni, and Co in the unreacted core can be effectively leached by second-step leaching.

When

C(Mn2+)

is

larger

than


,

the

dense

(NH4)2Mn(SO3)2·H2O will form on the surface of the unreacted core. The (NH4)2Mn(SO3)2·H2O becomes thicker and thicker by prolonging the reaction time. Finally, it is subject to the internal diffusion process, resulting in incomplete leaching of valuable metals. Fig. 5a shows that the leaching rates of Li, Ni, and Co reach its maximum when n/n0 is equal to 2.25, which is 85.1%, 87.6%, and 87.2%, respectively. The Gibbs free energy of the LiNixCoyMn1-x-yO2 material increases with the nickel content, so the leaching rate of Li, Ni, and Co at leaching equilibrium is enhanced under the same leaching conditions.22-23 Fig. 5b shows that the leaching product is Mn3O4 when n/n0 is


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equal to 2.25. The diffraction peaks of (NH4)2Mn(SO3)2·H2O and (NH4)2Mn(SO3)2 can be found when n/n0 is equal to 9.66. The drying of residue leads to dehydration of (NH4)2Mn(SO3)2·H2O. By comparing the SEM images of the two leaching products (Fig. 5c~d), it can be seen that the leaching residue is submicron primary particle when n/n0 is equal to 2.25. Fewer residues make it unable to keep loose and porous secondary particles because the amount of leaching residue from LiNi0.5Co0.2Mn0.3O2 material is less than LiNi1/3Co1/3Mn1/3O2 material. In contrast, the leaching residue is much larger and denser when n/n0 is equal to 9.66. The peaks of Ni and Co in EDS spectra indicate that both residues have unreacted materials (Fig. 5c1~d1). EDS spectra show that there is no sulfur when n/n0 is equal to 2.25, however, a large amount of sulfur appears while n/n0 is equal to 9.96, which is consistent with XRD analysis. Similarly, a two-step leaching process is carried out to improve the leaching rate of valuable metals. The first-step leaching is carried out for 3 h with n/n0 equal to 2.25, and the leaching residue is used as raw material for the second-step leaching process which is also carried out with n/n0 equal to 2.25. The second-step leaching can effectively extract the rest of Li, Ni, and Co from the residue (Fig. 6a). Compared with the first-step leaching, the second leaching speed is faster, since that the submicron leaching residue help increase the reaction area and speed up the reaction. The leaching rate of lithium is slightly lower than that of nickel and cobalt during the second-step leaching, further confirming our previous inference that there some kinds of insoluble lithium salt formed on the surface of the LiNi0.5Co0.2Mn0.3O2 material. The total leaching rate of Li, Ni, and Co reaches 94.4%, 99.7%, and 99.5%, which is much higher



than one-step leaching with an excess of SO32-. Compared with XRD pattern of the onestep leaching residue, the two-step leaching residue shows only the diffraction peaks of Mn3O4, without the diffraction peaks of the LiNi0.5Co0.2Mn0.3O2 material, indicating that the rest of Li, Ni, and Co in the first-step leaching residue have been wholly leached out (Fig. 6b). Fig. 6c shows that the particles from the second-step leaching residue are smaller than the first-step leaching residue because the rest of Li, Ni, and Co in the residue is leached out. The EDS spectra show peaks of Mn and O, without the peaks of Ni and Co, which is consistent with the XRD analysis (Fig. 6d). Fig. 7a shows that the leaching rate of Li, Ni, and Co reaches its maximum, which is 95.0%, 98.4%, and 96.9%, respectively. A satisfactory overall leaching rate is achieved due to the comparative larger Gibbs free energy of the LiNi0.8Co0.1Mn0.1O2 material. Fig. 7b shows that the leaching product is MnOOH when n/n0 is equal to 2.25. The increased valence of manganese in the one-step leaching of the LiNi0.8Co0.1Mn0.1O2 material could be caused by the weaker reducibility of the leaching condition. The diffraction peaks of (NH4)2Mn(SO3)2·H2O can be found when n/n0 is equal to 9.73. By comparing the SEM images of the two leaching products (Fig. 7c~d), it can be seen that the leaching residue is submicron primary particle when n/n0 is equal to 2.25. Similarly, fewer residues make it unable to keep loose and porous secondary particles because the amount of leaching residue from LiNi0.8Co0.1Mn0.1O2 material is less than LiNi1/3Co1/3Mn1/3O2 material. In contrast, the leaching residue is much larger and denser when n/n0 is equal to 9.73. The EDS spectra have peaks of Mn and O, without the peaks of Ni and Co when n/n0 is equal to 2.25, indicating that Li, Ni, and Co have


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been completely leached out (Fig. 7c1). The EDS spectra have peaks of S, and Ni when n/n0 is equal to 9.73, indicating that the residue has little unreacted material and the formation of (NH4)2Mn(SO3)2·H2O, which is consistent with the XRD analysis (Fig. 7d1). Conclusion In this research, the ammonia leaching process is adapted to selectively extract valuable metals (Ni, Co, and Li) from LiNixCoyMn1-x-yO2 (x=1/3, 0.5, 0.8) cathode materials. Manganese is primarily leached into lixivium as Mn2+ and then subsequently precipitates out. The phase of residue is changed from Mn3O4 to (NH4)2Mn(SO3)2•H2O with the increase of sodium sulfite. Compared with dense and agglomerated (NH4)2Mn(SO3)2•H2O tightly wrapped on the surface of the unreacted material, loose and porous Mn3O4 is more favorable to ion diffusion and leaching reaction. Low leaching rate of Li, Ni and Co can be solved by a two-step leaching process. We will focus on studying the crystal growth mechanism of (NH4)2Mn(SO3)2•H2O and controlling the crystal growth of (NH4)2Mn(SO3)2•H2O, which will help to allow LiNi1/3Co1/3Mn1/3O2 and LiNi0.5Co0.2Mn0.3O2 material to be leached by a one-step leaching process. Acknowledgments This work was financially supported by National Natural Science Foundation of China (51778627). Supporting Information Schematic diagram of the reactor for leaching experiments, critical stability constants



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Fig. 1 SEM images of LiNixCoyMn1-x-yO2 powders: (a) x=1/3, (b) x=0.5, (c) x=0.8, where a1~c1 indicates the magnified images of the corresponding sample; Effect of time from 0 to 8 h on extraction efficiency of metals: (a2) x=1/3, (b2) x=0.5, (c2) x=0.8.


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Fig. 2 XRD pattern (a) and SEM/EDS (b~d) of leaching residue of LiNi1/3Co1/3Mn1/3O2 material (5 h leaching, 0.5 M Na2SO3)



Fig. 3 (a) Effect of time from 0 to 5 h on concentration of SO32-; (b) effect of SO32concentration on the leaching efficiency of Li, Ni and Co; (c~e) XRD pattern and enlarged XRD patterns in selected 2θ of different residues; SEM/EDS of residue with n/n0 equal to3 (f~f2) and 4 (g~g2)


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Fig. 4 (a) Effect of time on the extraction of Li, Ni, and Co during the second-step leaching; XRD pattern (b) and SEM/EDS (c~c2) of the leaching residue (6 h leaching, n/n0=3 Na2SO3); (d) schematic diagram of the leaching process



Fig. 5 (a) Effect of SO32- concentration on the extraction of Li, Ni, and Co; (b) XRD pattern of different residues; SEM/EDS of the residue with n/n0 equal to2.25 (c~c1) and 9.96 (d~d2)


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Fig. 6 (a) Effect of time on the extraction of Li, Ni, and Co at the second-step leaching; XRD pattern (b) and SEM/EDS (c~d) of the leaching residue



Fig. 7 (a) Effect of SO32- concentration on extraction of Li, Ni, and Co; (b) XRD pattern of different residue; SEM/EDS of residue with n/n0 equal to2.25 (c~c1) and 9.73 (d~d1)


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An efficient method and the mechanism for extracting valuable elements from spent lithium-ion batteries are presented.


Comparison of the Ammoniacal Leaching Behavior of Layered

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