A modified deep eutectic solvent, a preparation method thereof, and a method for dissolving a cathode material of a lithium-ion battery

Abstract

The present invention relates to the technical field of solid waste recycling and resource utilization, and discloses a modified deep eutectic solvent, a preparation method thereof, and a method for dissolving and recovering valuable metals from a lithium-ion battery cathode material. It includes a deep eutectic solvent and ascorbic acid; the deep eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor is guanidine hydrochloride, and the hydrogen bond donor is lactic acid. In the present invention, chloride ions are coordinated by guanidine hydrochloride, acidity is provided by lactic acid, and the acidity and reducibility of the solvent are strengthened by ascorbic acid. The three act together to have a strong dissolving effect on the components of the lithium-ion battery cathode. It can take into account important parameters such as low solvent viscosity, high metal leaching rate, low dissolution temperature, and low operation energy consumption, reduce energy and material consumption during the recycling process, and provide ideas for the research and development of subsequent related solvents.

Description

Technical Field

[0001] The present invention relates to the technical field of solid waste recycling and resource utilization, and particularly relates to a modified deep eutectic solvent, a preparation method thereof, and a method for dissolving a lithium-ion battery cathode material. Background Art

[0002] To reduce carbon emissions and achieve sustainable development, new clean energy and large-scale energy storage systems have become new current development hotspots. Lithium batteries are an important part of the global realization of clean energy, and lithium batteries are required for both new electric vehicles and grid storage for balancing renewable energy.

[0003] Although lithium batteries avoid the pollution caused by the combustion of traditional fossil fuels, after hundreds of cycles of charge and discharge, the internal structure of the battery will undergo irreversible changes, resulting in the inactivation and scrapping of the battery. Therefore, the average life of lithium batteries is only 1-3 years. With the increasing demand and production of lithium batteries year by year, a large number of retired lithium batteries will be generated in a blowout manner. To solve the problems of large losses of precious metal elements in the hydrometallurgical recycling process of waste lithium battery electrode materials, large consumption of acids and alkalis, cumbersome steps, serious pollution caused by volatile organic compounds, and large wastewater discharge, and to achieve a green and clean resource recycling process, it is necessary to use a green solvent system to replace acids, alkalis, and volatile organic solvents in the process.

[0004] Deep eutectic solvents (DESs) are a type of new green solvents, usually composed of two to three components. The components interact with each other through hydrogen bonds to reduce the lattice energy, making the melting point of the system lower than that of any one component. They have the characteristics of low volatility, high conductivity, high stability, and non-flammability. At the same time, since deep eutectic solvents are obtained by simply heating and mixing two biocompatible components, they additionally have the characteristics of simple synthesis, non-toxic and harmless, easy to recycle and degrade, etc. Therefore, they have very broad application prospects in the fields of gas absorption, metal separation, biomass recovery, extraction, catalysis, etc., and are considered as green alternatives to molecular solvents and ionic liquids.

[0005] Currently, many domestic patents have reported methods for leaching and recycling lithium battery cathode components using deep eutectic solvents. For example, CN114122555A discloses a method for recycling lithium cobalt oxide, a lithium battery cathode material, using a ternary deep eutectic solvent system. By mixing choline chloride, ethylene glycol, and benzoic acid to prepare a ternary deep eutectic solvent system, cobalt and lithium in the battery cathode material can be efficiently and rapidly recovered, shortening the leaching time and improving the leaching efficiency of cobalt and lithium. However, the temperature required for its dissolution and recovery is relatively high, at 100-180°C, and the temperature used in its actual examples is about 140-180°C, resulting in high energy consumption.

[0006] CN114875243A discloses a deep eutectic solvent, a preparation method thereof, and a method for leaching a cathode material of a lithium battery. The hydrogen bond acceptors used include at least one of betaine, thiobetaine, and betaine hydrochloride; the hydrogen bond donors include reducing alcohols or organic acids; valuable metals in the waste lithium battery cathode material are leached using the above-mentioned deep eutectic solvent. However, its dissolution temperature is relatively high, and the viscosity of the deep eutectic solvent is large, making it difficult to carry out subsequent metal recovery and increasing the difficulty of industrialization. Summary of the Invention

[0007] Aiming at the problems of high viscosity and high dissolution temperature of the deep eutectic solvent in the method for recovering the active components of the lithium battery cathode, the present invention provides a deep eutectic solvent that can take into account important parameters such as low solvent viscosity, high metal leaching rate, low dissolution temperature, and low operation energy consumption, reduce energy consumption and material consumption in the recovery process, and provide ideas for the research and development of subsequent related solvents.

[0008] To achieve the above object, the technical solution adopted by the present invention is:

[0009] A modified deep eutectic solvent, comprising a deep eutectic solvent and ascorbic acid; the deep eutectic solvent comprises a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor is guanidine hydrochloride, and the hydrogen bond donor is lactic acid.

[0010] The deep eutectic solvent in the present invention reduces the system energy through the hydrogen bond interaction formed between guanidine hydrochloride and lactic acid, and the melting point of its mixture is much lower than that of any pure component. Ascorbic acid is dissolved therein as a solute. The solvent components are all small molecule organic compounds with low viscosity. Among them, guanidine hydrochloride provides chloride ion coordination, lactic acid provides acidity, and ascorbic acid strengthens the acidity and reducibility of the solvent. The three work together to have a strong dissolving effect on the cathode components of the lithium ion battery.

[0011] The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:2 - 8; the mass ratio of ascorbic acid to the deep eutectic solvent is 1 - 2:100. The higher the proportion of ascorbic acid, the better the leaching effect of the modified deep eutectic solvent.

[0012] The deep eutectic solvent further comprises water, and the mass of water does not exceed 40% of the total mass of the deep eutectic solvent. Water can be added to the deep eutectic solvent in the present invention to reduce its viscosity and use cost, but the dissolution effect and the leaching rate of valuable metals can be unaffected. If the water content exceeds 40%, the leaching effect will be reduced.

[0013] The viscosity of the modified eutectic solvent at 47 °C is below 50 mPa·s. The viscosity of common eutectic solvents is usually in the range of 100 - 200 mPa·s at 50 °C. The viscosity of the eutectic solvent of the present invention can be lower than 50 mPa·s, and even lower than 43 mPa·s, which is very beneficial for the precipitation and recovery of valuable metals in the later stage, and is also beneficial for reducing the heat transfer and mass transfer resistance of the solvent and reducing the transmission loss.

[0014] The preparation method of the modified eutectic solvent is to mix the hydrogen bond acceptor, hydrogen bond donor, ascorbic acid and water, and stir at 40 - 80 °C for more than 0.5 h to obtain the modified eutectic solvent. When water is not added, the usage amount and content of water are both 0. The stirring reaction time ends when the solution becomes a homogeneous phase state, which can usually be achieved after 0.5 h, but the time may be slightly longer.

[0015] The present invention also provides a method for dissolving a lithium-ion battery cathode material, which uses the modified eutectic solvent to dissolve the lithium-ion battery cathode material, and filters to obtain an enriched solution containing valuable metals.

[0016] In the present invention, the acidic lactic acid in the modified eutectic solvent destroys the layered structure of the lithium-ion battery cathode assembly, the reducing property of ascorbic acid reduces the transition metal therein to divalent, and the complexation of chloride ions of guanidine hydrochloride improves the solvation ability of metal ions. It can achieve a high dissolution rate of valuable metals under low-temperature conditions. The leaching rates of Li and Co in LCO can reach up to 100%, and the leaching rate of Li in NCM111 / 523 / 622 / 811 can reach 100%.

[0017] In some embodiments, when reacting at 50 °C for 6 h, more than 95% of each of LCO and NCM811 can be dissolved, and more than 85% of NCM111, NCM523, and NCM622 can be dissolved; the single extraction rate of Co in LCO by oxalic acid can reach 90%, and the single extraction rates of Co, Ni, and Mn in NCM are 70%, 89%, and 67% respectively.

[0018] The solid-liquid ratio of the lithium-ion battery cathode material to the modified eutectic solvent is 100 g / kg or less, preferably 0.2 - 100 g / kg, and more preferably 20 - 100 g / kg. As the solid-liquid ratio increases, the single dissolution amount of the lithium-ion battery cathode material gradually increases, and the highest can reach Li 2556 ppm and Co 29450 ppm.

[0019] The dissolution temperature is above 40°C, preferably 40 - 60°C, and more preferably 50 - 60°C; the present invention can dissolve the cathode material of lithium-ion batteries at low temperature, with good dissolution effect and high dissolution rate of valuable metals, achieving low-energy and high-efficiency recovery. The increase in temperature can reduce the viscosity of the modified deep eutectic solvent and enhance acidity, so the improvement effect on the leaching rate is significant. Experiments have shown that the leaching rates at 50°C have reached 97.42% for Li and 96.61% for Co. At this time, continuing to increase the temperature has limited effects on both the growth of the leaching rate and the decrease in viscosity.

[0020] The dissolution time is 2 h or more, preferably 6 h or more, and more preferably 6 - 24 h. The leaching rate increases with the increase of the dissolution time. When the dissolution time is 6 h, lithium cobaltate is basically completely dissolved under the set solid-liquid ratio, and the leaching rates reach 97.42% for Li and 96.61% for Co; when the dissolution is 24 h, it is completely dissolved, but the conditions are not economical.

[0021] When precipitating and recovering valuable metals from the enriched liquid containing valuable metals, the precipitant includes any one or more of oxalic acid, etc.; the addition amount of the precipitant is 1 - 3 times, preferably 1 - 1.5 times, and more preferably 1.2 times the equivalent of valuable metals in the enriched liquid; the temperature during the precipitation process is 40 - 60°C, and the precipitation time is 4 - 8 h; after filtration, the precipitate is washed with a mixture of one or more of water, ethanol, acetone, etc.; the calcination temperature is 800 - 100°C, and the calcination time is 1 - 6 h.

[0022] The cathode material of the lithium-ion battery includes any one or more of lithium cobaltate (LCO), lithium nickel cobalt manganese oxide (NCM111, NCM523, NCM622, NCM811).

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] (1) The present invention uses guanidine-based deep eutectic solvent as the main body, modifies the acidity and reducibility of the solvent with ascorbic acid, thereby improving the basic leaching rate of the solvent for the cathode active components, and using oxalic acid to precipitate the dissolved transition metals, leaving Li in the liquid phase to achieve the separation and recovery of different elements.

[0025] (2) The modified deep eutectic solvent of the present invention can dissolve the cathode material of lithium batteries at 50 - 60°C, with high dissolution efficiency. The viscosity of the system before and after adding the modifier and dissolution is less than 50 mPa·s, and it has broad application prospects in the field of energy material recovery. Description of the Drawings

[0026] Figure 1 It shows the influence of the amount of ascorbic acid on the leaching rate of lithium cobaltate dissolved by guanidine hydrochloride - lactic acid - ascorbic acid.

[0027] Figure 2Effect of water content on the leaching rate of lithium cobaltate dissolved by guanidine hydrochloride - lactic acid - ascorbic acid..

[0028] Figure 3 Effect of temperature on the leaching rate of lithium cobaltate dissolved by guanidine hydrochloride - lactic acid - ascorbic acid.

[0029] Figure 4 Effect of dissolution time on the leaching rate of lithium cobaltate dissolved by guanidine hydrochloride - lactic acid - ascorbic acid.

[0030] Figure 5 Effect of solid - liquid ratio on the leaching rate of lithium cobaltate dissolved by guanidine hydrochloride - lactic acid - ascorbic acid.

[0031] Figure 6 Leaching rate of lithium cobaltate dissolved by guanidine hydrochloride - lactic acid - ascorbic acid in three - cycle dissolution.

[0032] Figure 7 Leaching rate of four kinds of lithium nickel cobalt manganate in guanidine hydrochloride - lactic acid - ascorbic acid.

[0033] Figure 8 Effect of the ratio of hydrogen - bond acceptor to hydrogen - bond donor on the dissolution rate.

[0034] Figure 9 Effect of temperature on the viscosities of modified deep eutectic solvents and different enrichment liquids. Detailed implementation manners

[0035] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further describes the present invention in detail with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Those skilled in the art who make modifications or equivalent replacements based on understanding the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall all be covered within the protection scope of the present invention.

[0036] Unless otherwise specified, the raw materials used in the following detailed implementation manners are all purchased from the market and used directly.

[0037] Example 1

[0038] Using guanidine hydrochloride and lactic acid in a molar ratio of 1:2 as the solvent, and the mass ratio of the solvent to ascorbic acid is 100:1 for reaction. Under the condition of magnetic stirring at 50 °C until a clear and transparent homogeneous liquid phase is formed, and the reaction time is 30 min to obtain a modified deep eutectic solvent.

[0039] Comparative example

[0040] Using the molar ratios of guanidine hydrochloride to lactic acid of 1:2, guanidine hydrochloride to glycolic acid of 1:2, choline chloride to lactic acid of 1:2, and choline chloride to glycolic acid of 1:2, common deep eutectic solvents were prepared as a control, and various deep eutectic solvents were obtained by stirring in an oil bath at 50 °C for 0.5 h.

[0041] The Hammett acidity, cyclic voltammetry, and viscosity of the obtained modified deep eutectic solvents and the deep eutectic solvents of Comparative Example 1 were tested and compared with other deep eutectic solvent systems, as shown in Table 1.

[0042] For the acidity test method of deep eutectic solvents, p-nitroaniline was used as the solute, and anhydrous ethanol, concentrated sulfuric acid, and deep eutectic solvents were used as solvents to prepare a solution with a concentration of 8.5 mg / L in a 25 mL volumetric flask. The ultraviolet absorbance at 377.5 nm and 25 °C was measured, and then the Hammett acidity was calculated according to the literature formula. The smaller the value, the greater the acidity.

[0043] For the viscosity test method of deep eutectic solvents: Take about 1.2 - 2 mL of the deep eutectic solvent to be tested on a flat plate. The test temperature is 20 - 60 °C, the temperature interval is 0.5 °C, the shear rate is 10 / s, and the shear stress at different temperatures is measured on a rotational rheometer to obtain the viscosity. γ in Table 1 50 represents the viscosity at 50 °C.

[0044] For the reducibility test method of deep eutectic solvents: Using platinum as the counter electrode and working electrode, silver as the reference electrode, and a scanning rate of 50 mV / s, the cyclic voltammogram at 20 - 60 °C was measured. The more negative the reduction peak potential appears on the reduction curve, the stronger the reducibility.

[0045] Application Example 1

[0046] Take the modified deep eutectic solvent prepared in Example 1 and the deep eutectic solvent of Comparative Example 1, dissolve the lithium cobaltate material, with a solid-liquid ratio of 1 g / 50 g, dissolve at 50 °C for 6 h. After the reaction, filter to collect the enriched solution of valuable metals, and test the dissolution rates of Co and Li in the enriched solution. The results are summarized in Table 1.

[0047]

[0048] Among them, D represents the leaching rate of valuable metals, %; w M,d represents the content of valuable metals in the enriched solution, ppm; m DES represents the mass of the enriched solution, g; m M,r represents the mass of the positive electrode component of the lithium-ion battery before dissolution, g.

[0049] Test method for metal ion content in the enriched solution: Take 0.5 g of the enriched solution, dilute it with 5 mL of concentrated nitric acid (68%), digest it in a microwave digestion instrument at a power of 800 w for 1 h, then dilute the digested enriched solution 1000 times with deionized water, conduct ICP-OES to test the metal ion concentration, and then calculate the dissolution rate by back-calculation using the formula above.

[0050] Table 1 Physical property test table of several eutectic solvent systems and dissolution rates of Li and Co in lithium cobaltate

[0051]

[0052] As can be seen from Table 1, the guanidine hydrochloride-lactic acid-ascorbic acid modified eutectic solvent of the present invention has the characteristics of strong acidity, strong reducibility, and low viscosity. Among them, the eutectic solvent of choline chloride-glycolic acid also has a relatively low viscosity, but from the subsequent experimental results, its dissolution rate of valuable metals in the battery cathode material is poor. And the guanidine hydrochloride-lactic acid-ascorbic acid of the present invention has a dissolution rate of up to 97.42% for Li and 96.91% for Co after 6 h of dissolution at 50 °C, far higher than several other common eutectic solvents.

[0053] Application Example 2

[0054] According to the process conditions of Example 1, change the dosage of the modifier, adjust the mass ratio of the solvent to ascorbic acid to 100:0, 100:0.2, 100:0.6, 100:1.4, 100:2 respectively, and stir until a transparent, clear and homogeneous phase state is obtained to obtain eutectic solvents with different modifier contents.

[0055] Dissolve lithium cobaltate with the eutectic solvent according to the process conditions of Application Example 1, and test the dissolution rates of Li and Co. The results are as Figure 1 shown in Table 2.

[0056] The results show that the addition of ascorbic acid at a ratio of 100:1 can effectively improve the leaching rate of lithium cobaltate, increasing the leaching rate of the eutectic solvent for LCO from Li 61.09%, Co 34.72% to Li 97.42%, Co 96.91%.

[0057] Application Example 3

[0058] According to the process conditions of Example 1, keep the molar ratio of guanidine hydrochloride to lactic acid at 1:2, add water to form a solvent, and keep the mass ratio of the solvent formed by guanidine hydrochloride, lactic acid and water to ascorbic acid at 100:1. Adjust the water addition amount to 20%, 40%, 60%, 80%, 100% of the total modified eutectic solvent respectively to obtain eutectic solvents with different water contents. Dissolve lithium cobaltate with the eutectic solvent according to the process conditions of Application Example 1, and test the dissolution rates of Li and Co. The results are as Figure 2as shown in Table 2.

[0059] When the water content is lower than 40%, the leaching rates of Li and Co fluctuate within 80 - 100%. At this time, the leaching rates still remain at a relatively high level. Meanwhile, the viscosity of the modified deep eutectic solvent is greatly improved, and the material cost is reduced. When the water content is higher than 40%, the Co leaching rate drops rapidly (from 80% to 40%), and the Li% still remains at a relatively high level (above 90%), and then drops rapidly after the deep eutectic solvent completely disappears.

[0060] Application Example 4

[0061] According to the process conditions of Application Example 1, use the deep eutectic solvent prepared in Example 1 to dissolve lithium cobaltate, and adjust the dissolution temperatures to 20°C, 30°C, 40°C, 50°C, and 60°C respectively. Keep other processes unchanged, and test the dissolution rates of Li and Co. The results are as Figure 3 and shown in Table 2.

[0062] It can be seen from the data that when the temperature is 20°C, the dissolution rate of Li can reach nearly 50%, and the dissolution rate of Co can reach 57.56%, which is also close to or higher than the several deep eutectic solvents in the comparative example. As the temperature increases, the dissolution rate continuously increases. At 50°C, the dissolution rate of Li can reach 97.42% and the dissolution rate of Co can reach 96.81%. Further increasing the temperature to 60°C, the dissolution rate reaches 100%. Therefore, it shows that the deep eutectic solvent of the present invention can achieve excellent dissolution effects at 50 - 60°C, without further increasing the temperature and consuming more energy.

[0063] Application Example 5

[0064] According to the process conditions of Application Example 1, use the deep eutectic solvent prepared in Example 1 to dissolve lithium cobaltate, and adjust the dissolution times to 0.5 h, 1 h, 2 h, 6 h, and 8 h respectively. Keep other processes unchanged, and test the dissolution rates of Li and Co. The results are as Figure 4 and shown in Table 2.

[0065] It can be seen from the data that after dissolution for 1 h, the dissolution rate of Li can reach 76.53% and the dissolution rate of Co can reach 82.25%. Further prolonging the time, the dissolution rate gradually increases, and it can reach 100% at 8 h.

[0066] Application Example 6

[0067] According to the process conditions of Application Example 1, use the deep eutectic solvent prepared in Example 1 to dissolve lithium cobaltate, and adjust the solid - liquid ratios of lithium cobaltate and the deep eutectic solvent to 2:50, 3:50, 4:50, and 5:50 respectively. Keep other processes unchanged, and test the dissolution rates and dissolution amounts of Li and Co. The results are as Figure 5 and shown in Table 2.

[0068] As can be seen from the results, the dissolution rate gradually decreases as the solid-liquid ratio increases. Therefore, after the solid-liquid ratio is further increased, the dissolution amount is still increasing, and the improvement effect is obvious. It has a larger dissolution amount compared to the eutectic solvents in the prior art, which is very beneficial for industrial use.

[0069] Table 2 Dissolution rate and dissolution amount data under different conditions

[0070]

[0071]

[0072] Application Example 7 Extraction of transition metals

[0073] For the metal elements dissolved in the eutectic solvent, chemical precipitation is mostly used to obtain products. Here, oxalic acid is used as a precipitating agent to extract the transition metals in the solvent respectively. First, in a round-bottom flask, add solid oxalic acid according to 1.2 times the equivalent of the dissolution amount of lithium cobaltate in the enriched solution (the dissolution amount of lithium cobaltate in the enriched solution can be directly measured by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometer) to obtain the concentration of each metal ion in the enriched solution, and multiplying by the mass of the enriched solution can get the dissolution amount). Place it in an oil bath at 50 °C and react at 400 rpm for 6 h. After the reaction, centrifuge the obtained solid-liquid mixture to separate the phases, and calcine the solid phase in a muffle furnace at 900 °C for 3 h to obtain cobalt tetroxide products. The purity of cobalt element is above 99%, and the overall recovery rate is above 90%.

[0074] The guanidine hydrochloride-lactic acid eutectic solvent after the reaction can be used for secondary recycling to dissolve lithium cobaltate, or dissolve lithium cobaltate after supplementing ascorbic acid according to the initial liquid-solid ratio.

[0075] Application Example 8

[0076] The eutectic solvent after recovering cobalt in Application Example 7 was recycled, and the cases of direct recycling and supplementing ascorbic acid at a ratio of 100:1 were tested. Add LCO at a ratio of 1:50 and react with stirring at 50 °C for 6 h; for the reaction mixture, perform the same operation as in Application Example 7 to extract Co, and repeat this process three times.

[0077] The results are as Figure 6 shown in Table 3. L1 refers to the content of metal elements in the enriched solution after the first dissolution during recycling, and S1 refers to the content of metal elements in the enriched solution after using oxalic acid to precipitate Co for the first time during recycling. L2, S2, L3, and S3 refer to the situations of the second and third times of recycling respectively.

[0078] Table 3 Dissolution effect of recycled modified eutectic solvent

[0079]

[0080] Application Example 9

[0081] According to the process of Application Example 1, the modified eutectic solvent prepared in Example 1 was used to dissolve four kinds of lithium nickel cobalt manganese oxides (NCM111, NCM523, NCM622, NCM811). The dissolution rates of Li, Ni, Co, and Mn are as Figure 7 shown. It can be seen that in the lowest NCM523, the dissolution rate of Mn can reach 85%, and the other dissolution rates are more excellent. This shows that the modified eutectic solvent of the present invention is applicable to various cathode materials for lithium-ion batteries.

[0082] Previous research work

[0083] Example 2

[0084] Only guanidine hydrochloride and lactic acid were used for preparation according to the process of Example 1, without adding ascorbic acid, but the ratio of the two was changed to 1:4, 1:6, and 1:8 respectively to dissolve lithium cobalt oxide. The solid-liquid ratio was 1 g / 50 g, and it was dissolved at 50 °C for 6 h. After the reaction, the enriched solution of valuable metals was collected by filtration, and the dissolution rates of Co and Li in the enriched solution were tested. The results are as Figure 8 shown. It was found that for the eutectic solvent, there is no obvious rule for the influence of the ratio of hydrogen bond acceptor to hydrogen bond donor on the dissolution rate, and the change in the dissolution rate is not significant. Therefore, 1:2 with the least amount of lactic acid was used for subsequent exploration because the less lactic acid, the weaker the corrosion of the equipment and the more beneficial to production.

[0085] Example 3

[0086] Lithium cobalt oxide was dissolved according to the solid-liquid ratios of 0.5:50, 1:50, and 5:50, and the viscosity of the mixed solution was tested. The results are as Figure 9 shown. The modified eutectic solvent of the present invention has a low viscosity, and the viscosity increase at 50 °C under different conditions is also relatively small.

[0087] Generally speaking, the modified eutectic solvent of the present invention has strong dissolution ability, can quantitatively leach extremely insoluble cathode active powders for lithium-ion batteries, and efficiently recover the transition metals therein. This type of eutectic solvent-modifier system has broad application prospects in the application of lithium-ion battery transition metal recovery.

Claims

1. A method for dissolving a cathode material of a lithium-ion battery, characterized in that, Dissolve the cathode material of the lithium-ion battery using a modified eutectic solvent, and filter to obtain an enriched solution containing valuable metals; the dissolution temperature is 40 - 60 °C; the dissolution time is more than 6 h; The modified eutectic solvent includes a eutectic solvent and ascorbic acid; the eutectic solvent includes a hydrogen bond acceptor and a hydrogen bond donor; the hydrogen bond acceptor is guanidine hydrochloride, and the hydrogen bond donor is lactic acid; the mass ratio of ascorbic acid to the eutectic solvent is 1.4 - 2:100; The eutectic solvent further includes water, and the mass of water is less than 40% of the mass of the eutectic solvent; The viscosity of the modified eutectic solvent at 47 °C is below 50 mPa·s; The cathode material of the lithium-ion battery includes any one or more of LCO, NCM111, NCM523, NCM622, NCM811.

2. The method for dissolving a cathode material of a lithium-ion battery according to claim 1, wherein, The molar ratio of the hydrogen bond acceptor to the hydrogen bond donor is 1:2 - 8.

3. The method for dissolving the cathode material of a lithium-ion battery according to claim 1, wherein The preparation method of the modified eutectic solvent is: mix the hydrogen bond acceptor, hydrogen bond donor, ascorbic acid and water, and stir at 40 - 80 °C for more than 0.5 h to obtain the modified eutectic solvent.

4. The method for dissolving a cathode material of a lithium ion battery according to claim 1, wherein The solid-liquid ratio of the cathode material of the lithium-ion battery to the modified eutectic solvent is below 100 g / kg.

5. The method for dissolving a cathode material of a lithium ion battery according to claim 1, characterized in that, It further includes the step: adding a precipitant to the enriched solution, and recovering the valuable metals through filtration, washing, drying, and calcination.

6. The method for dissolving a cathode material of a lithium ion battery according to claim 1, wherein The precipitant includes oxalic acid; the addition amount of the precipitant is 1 - 3 times the equivalent of the valuable metals in the enriched solution, the temperature during the precipitation process is 40 - 60 °C, and the precipitation time is 4 - 8 h; the precipitate after filtration is washed with a mixture of one or more of water, ethanol, and acetone; the calcination temperature is 800 - 100 °C, and the calcination time is 1 - 6 h.

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