Direct regeneration method of positive electrode material of retired lithium ion battery

Abstract

The invention discloses a direct regeneration method of a positive electrode material of a retired lithium ion battery. The method comprises the following steps of: 1, discharging, disassembling, pyrolyzing, crushing and sorting the waste lithium ion battery, and sieving with a 60-mesh sieve to obtain positive electrode material black powder; 2, mixing the black powder with a solid reducing agent to obtain powder A; 3, mixing the powder A with a composite lithium salt to obtain powder B; 4, the powder B is subjected to ball milling in a ball mill, and powder C is obtained; and 5, roasting the powder C under a certain condition to obtain the regenerated positive electrode material. The decommissioned lithium ion battery positive electrode material is directly regenerated by utilizing a high-energy ball milling process and a multi-component molten salt synergistic solid reducing agent.

Description

Technical Field

[0001] The present invention relates to the technical field of recycling retired lithium-ion battery positive electrode materials, and in particular to a direct regeneration method for retired lithium-ion battery positive electrode materials. Background Art

[0002] Currently, retired lithium-ion battery recycling primarily involves pyrometallurgical and wet recycling processes. Pyrometallurgical recycling involves treating retired lithium-ion batteries at high temperatures through methods such as smelting, roasting, and calcining to obtain metals and soluble salts. This process suffers from high energy consumption and excessive solid waste and exhaust emissions. Wet recycling involves leaching and separating various elements in acidic, alkaline, or organic solutions to ultimately prepare battery materials. This method involves a lengthy process, consumes large amounts of chemical reagents, and generates significant amounts of wastewater.

[0003] Compared with the above processes, the direct regeneration method of using retired battery positive electrode material powder through various methods to replenish the lithium consumed during the battery cycle and restore its crystal structure to restore the performance of the battery material has attracted attention. This method has a short process, low reagent consumption, and important environmental and economic value. However, this method still faces the problem of increased energy consumption costs due to the high melting point (greater than 850°C) of the single lithium molten salt system, and its function is relatively single. There is a serious mixing of lithium and nickel in the recycled materials, low regeneration efficiency, and it is difficult to provide diversified characteristics to improve lithium replenishment efficiency. Summary of the Invention

[0004] In order to overcome the above technical problems, the purpose of the present invention is to provide a direct regeneration method for retired lithium-ion battery positive electrode materials, which directly regenerates retired lithium-ion battery positive electrode materials by using high-energy ball milling technology and multi-component molten salt in conjunction with a solid reducing agent.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] A direct regeneration method for retired lithium-ion battery positive electrode materials comprises the following steps:

[0007] Step 1: The discarded lithium-ion batteries are subjected to processes such as discharge, disassembly, pyrolysis, crushing and sorting, and are sieved through 60 mesh to obtain the positive electrode material black powder;

[0008] Step 2: mixing the black powder with a solid reducing agent to obtain powder A;

[0009] Step 3: mixing the powder A with a composite lithium salt to obtain powder B;

[0010] Step 4: milling the powder B in a ball mill to obtain powder C;

[0011] Step 5: calcining the powder C under certain conditions to obtain a regenerated positive electrode material.

[0012] The waste lithium-ion battery in step 1 includes a ternary lithium-ion battery (LiNi x Co y Mn 1-x-y O2, 0≤x, y<1, 0≤x+y<1), lithium nickel manganese oxide battery (LiNi x Mn 2-x O4, 0≤x<1.9), at least one of lithium cobalt oxide battery (LiCoO2), lithium manganese oxide battery (LiMn2O4), and lithium iron phosphate battery (LiFePO4).

[0013] In the first step, the mass of the active substance contained in the black powder is tested by ICP, chemical titration, atomic absorption spectroscopy, etc. and the ratio of each element is calculated. In the second step, the solid reducing agent is a solid reducing agent containing a reducing agent having a higher reducing power than Ni. 3+ 、Co 3+ 、Mn 4+ metals, metal compounds and solid organic matter; the mass of the positive electrode material active substance in the black powder is m1, the mass of the solid reducing agent is m2, m1:m2=1:0.01-0.4.

[0014] The solid organic matter in step 2 is at least one of thiourea, ascorbic acid, citric acid, urea, oxalic acid, malic acid, thiomalic acid, glucose, catechol, resorcinol, hydroquinone, p-aminophenol, hydroxylamine hydrochloride, L-cysteine, gallic acid, tartaric acid, polyethylene glycol, tannic acid, thioacetamide, dithiothreitol, hydrazine benzoate, polyacrylic acid, lignin, and their compounds;

[0015] The present invention uses a solid reducing agent as a regeneration additive, which mainly provides a reducing environment in the subsequent roasting process, reduces the valence state of the transition metal elements, thereby replenishing the lithium lost in the active material contained in the black powder, reducing the degree of lithium-nickel mixing and lattice distortion, and optimizing the crystal structure; the solid reducing agent decomposes in the subsequent oxidation roasting process; the use of a solid ensures that the elements will not dissolve due to the presence of liquid in the subsequent ball milling process, resulting in element loss;

[0016] The ratio of black powder to solid reducing agent used in the present invention needs to be strictly controlled. If there is too much solid reducing agent, the crystal particles of the regenerated positive electrode material will be destroyed after calcination; if there is insufficient reducing agent, the degree of lithium-nickel mixing will be high after calcination and lithium replenishment will not be smooth.

[0017] The other lithium salt in step 3 is at least one of lithium sulfate, lithium phosphate, lithium hexafluorophosphate, lithium chloride, lithium hydroxide, lithium oxalate, and lithium dioxalatoborate.

[0018] In the step 3, the lithium salt ratio in the composite lithium salt is: 40-100 wt% of lithium carbonate, 0-50 wt% of lithium nitrate, and 0-30 wt% of other lithium salts;

[0019] The amount of lithium lost by the active material in the powder A in terms of chemical formula is n1, and the amount of lithium in the composite lithium salt is n2, where n1:n2=1:1-1.05.

[0020] The composition and ratio of the lithium salt used in the present invention need to be strictly controlled. The use of lithium carbonate can reduce the cost of the mixed lithium salt, and lithium nitrate can significantly reduce the melting point of the mixed lithium salt. The appropriate lithium salt ratio can be adapted to various solid reducing agents, reduce the roasting temperature, reduce the loss of solid reducing agent, and improve the regeneration efficiency.

[0021] The present invention can only replenish the lithium lost on a chemical basis. Therefore, the ratio of powder A and composite lithium salt used in the present invention needs to be strictly controlled. Too little lithium salt will lead to insufficient lithium content in the regenerated positive electrode material, thereby reducing material performance; too much lithium salt will lead to excessive residual lithium on the surface of the regenerated positive electrode material, thereby causing the electrolyte to decompose on the material surface during the battery cycle, causing changes in the material phase, aggravated lithium-nickel mixing, lattice distortion, and deterioration of battery performance.

[0022] In step 4, the ball-to-material ratio is 5-50:1; the ball diameter range is: 10mm and above accounts for 10-20%, 1-9mm accounts for 20-50%, and 1mm and below accounts for 40-70%;

[0023] The parameters of the ball milling beads in step 4 are: ball milling time 0.5-12h, rotation speed setting 100-1000r / min; irregular block structure is transformed into flaky nanoparticles with a thickness of about 100nm.

[0024] The process parameters of the spheroidal graphite used in the present invention need to be strictly controlled. After a suitable ball milling process, the active material in the black powder is transformed from an irregular block structure into flaky nanoparticles with a thickness of about 100nm, and the layered structure is peeled off, so that the black powder is fully activated and fully in contact with the lithium salt and the reducing agent, which is beneficial to replenishing lithium and restoring its structure; too large or too small a ball-to-material ratio will lead to an insufficient ball milling process; ball milling beads of different ball diameters have different effects, large balls crush particles in the material powder, and medium and small balls further pulverize the material, so that the layered structure is gradually peeled off; if the ball milling time is too short or the rotation speed is too low, it is only a mixture of several raw materials, and the advantages of ball milling cannot be brought into play; if the ball milling time is too long or the rotation speed is too high, the active material structure is easily completely damaged, resulting in poor performance of the regenerated positive electrode material.

[0025] The roasting conditions in step 5 are as follows: the heating rate in the high-temperature oxidation roasting stage is 1-10° C. / min, the holding time is 0.5-12 h; and the roasting atmosphere is air.

[0026] Among them, the roasting is divided into two stages. The first stage is low-temperature reduction roasting, the roasting temperature is 120-280℃, and the insulation time is 0-5h; the second stage is high-temperature oxidation roasting, the roasting temperature is 400-850℃; and finally the regenerated positive electrode material is obtained.

[0027] The roasting conditions used in the present invention need to be strictly controlled. If the roasting temperature in the reduction stage is too low, the reduction reaction efficiency will be reduced and the subsequent lithium replenishment efficiency will be low; if the roasting temperature is too high, the reducing agent will decompose and volatilize, and eventually become ineffective; if the holding time is too short, the reduction degree will be insufficient, and if the holding time is too long, it will lead to excessive reduction and damage to the microstructure of the active material; the oxidation roasting temperature should be determined according to the composition and ratio of the lithium salt. If the holding time is too long, the material will sinter, and if the holding time is too short, the lithium replenishment will be incomplete; if the heating rate during the roasting process is too fast, the reducing agent will be excessively decomposed and the molten salt composition will be unevenly distributed. If the heating rate is too slow, the reaction time will be too long, and the energy consumption of the production process will increase.

[0028] Beneficial effects of the present invention:

[0029] (1) The present invention utilizes high-energy ball milling technology and multi-component molten salt in conjunction with a solid reducing agent to directly regenerate retired lithium-ion battery positive electrode materials.

[0030] (2) The present invention utilizes a high-energy ball milling method to transform the active substances in the black powder from irregular block structures into flaky nanoparticles with a thickness of about 100 nm. The layered structure is peeled off, so that the black powder is fully activated and in full contact with the lithium salt and the reducing agent, which is beneficial to replenishing lithium and restoring its structure, effectively reducing the insulation time.

[0031] (3) The present invention adopts a low-temperature reduction + high-temperature oxidation roasting process, and uses a reducing agent to repair the crystal defects of the material in the low-temperature stage. Combined with a mixed molten salt system, it breaks through the thermodynamic limitations of a single lithium salt and reduces the lithium replenishment temperature in the oxidation roasting stage. In the high-temperature stage, the decomposition products of the reducing agent are used to optimize the surface properties of the positive electrode material and replenish the lost lithium, thereby realizing the directional repair of lattice defects and a direct regeneration process combined with efficient lithium replenishment.

[0032] (4) The present invention can reduce the amount of lithium added during the lithium replenishment process. The positive electrode material can be regenerated by only replenishing the lithium lost in chemical terms, thereby reducing the amount of residual lithium on the surface of the regenerated material and the consumption of chemical reagents. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a process flow chart of a direct regeneration method for retired lithium-ion battery positive electrode materials.

[0034] Figure 2 These are SEM images of the active material in (a) the black powder of the positive electrode material and (b) powder C prepared therefrom as described in Example 1.

[0035] Figure 3 This is the SEM image of the regenerated positive electrode material described in Example 1.

[0036] Figure 4 The cycling performance of the black powder and the regenerated positive electrode material described in Example 1 under 1C conditions. DETAILED DESCRIPTION

[0037] The present invention will be further described in detail below with reference to the embodiments.

[0038] Process flow such as Figure 1 As shown:

[0039] Example 1

[0040] (1) Dismantling, crushing, sorting, and pre-treating waste ternary lithium-ion batteries (LiNi5Co2Mn3O2) to obtain cathode material black powder;

[0041] (2) mixing the black powder obtained in step (1) with thiourea in a ratio of m1:m2=1:0.1 to obtain powder A;

[0042] (3) mixing the powder A obtained in step (2) with a mixed lithium salt (50% lithium carbonate, 40% lithium nitrate, and 10% lithium sulfate) in a ratio of n1:n2 = 1:1 to obtain powder B;

[0043] (4) The powder B obtained in step (3) was ball-milled in a ball mill with a ball-to-material ratio of 20:1, a ball diameter range of 10 mm and above accounting for 20%, 1-9 mm accounting for 30%, and 1 mm and below accounting for 50%, the ball milling time was 2 h, and the speed was set at 600 r / min to obtain powder C.

[0044] (5) The powder C obtained in step (4) was subjected to low-temperature reduction calcination at 210°C for 2 h at a heating rate of 5°C / min in an air atmosphere, and then was kept at 600°C for 4 h to obtain a regenerated positive electrode material.

[0045] Comparative Example 1

[0046] Compared with Example 1, the only difference is that the ratio of black powder to thiourea in step (2) is changed from m1:m2 to 1:0.

[0047] Comparative Example 2

[0048] Compared with Example 1, the only difference is that the ratio of black powder to thiourea in step (2) is changed from m1:m2 to 1:0.5.

[0049] Comparative Example 3

[0050] Compared with Example 1, the only difference is that the ratio of the mixed lithium salts in step (3) is changed to: lithium carbonate 100%, lithium nitrate 0%, lithium sulfate 0%).

[0051] Comparative Example 4

[0052] Compared with Example 1, the only difference is that n1:n2 in step (3) is changed to 1:0.8.

[0053] Comparative Example 5

[0054] Compared with Example 1, the only difference is that n1:n2 in step (3) is changed to 1:1.5.

[0055] Comparative Example 6

[0056] Compared with Example 1, the only difference is that the ball-to-material ratio in step (4) is changed to 1:1.

[0057] Comparative Example 7

[0058] Compared with Example 1, the only difference is that the ball-to-material ratio in step (4) is changed to 70:1.

[0059] Comparative Example 8

[0060] Compared with Example 1, the only difference is that the ball diameter range in step (4) is changed to 10 mm and above accounting for 30%, 1-9 mm accounting for 60%, and 1 mm and below accounting for 10%.

[0061] Comparative Example 9

[0062] Compared with Example 1, the only difference is that the ball diameter range in step (4) is changed to 10 mm and above accounting for 5%, 1-9 mm accounting for 10%, and 1 mm and below accounting for 85%.

[0063] Comparative Example 10

[0064] Compared with Example 1, the only difference is that the low-temperature reduction calcination temperature in step (5) is changed to 100°C.

[0065] Comparative Example 11

[0066] Compared with Example 1, the only difference is that the low-temperature reduction calcination temperature in step (5) is changed to 300°C.

[0067] Comparative Example 12

[0068] Compared with Example 1, the only difference is that the low-temperature reduction roasting holding time in step (5) is changed to 5 hours.

[0069] Comparative Example 13

[0070] Compared with Example 1, the only difference is that the holding time of high-temperature oxidation roasting in step (5) is changed to 900°C.

[0071] Comparative Example 14

[0072] Compared with Example 1, the only difference is that the holding time of the high-temperature oxidation roasting in step (5) is changed to 350°C.

[0073] Example 2

[0074] (1) Dismantling, crushing, sorting, and pre-treating waste ternary lithium-ion batteries (LiNi5Co2Mn3O2) to obtain cathode material black powder;

[0075] (2) mixing the black powder obtained in step (1) with ascorbic acid in a ratio of m1:m2=1:0.05 to obtain powder A;

[0076] (3) mixing the powder A obtained in step (2) with a mixed lithium salt (60% lithium carbonate, 40% lithium nitrate) in a ratio of n1:n2=1:1 to obtain powder B;

[0077] (4) The powder B obtained in step (3) was ball-milled in a ball mill with a ball-to-material ratio of 25:1, a ball diameter range of 10 mm and above accounting for 15%, 1-9 mm accounting for 35%, and 1 mm and below accounting for 50%, the ball milling time was 2 h, and the speed was set at 500 r / min to obtain powder C.

[0078] (5) The powder C obtained in step (4) was subjected to low-temperature reduction calcination at 210°C for 1 h in an air atmosphere at a heating rate of 2°C / min, and then at 700°C for 3 h to obtain a regenerated positive electrode material.

[0079] Example 3

[0080] (1) Dismantling, crushing, sorting, and pre-treating waste ternary lithium-ion batteries (LiNi5Co2Mn3O2) to obtain cathode material black powder;

[0081] (2) mixing the black powder obtained in step (1) with glucose in a ratio of m1:m2=1:0.15 to obtain powder A;

[0082] (3) mixing the powder A obtained in step (2) with a mixed lithium salt (65% lithium carbonate, 30% lithium nitrate, and 5% lithium hydroxide) in a ratio of n1:n2 = 1:1.03 to obtain powder B;

[0083] (4) The powder B obtained in step (3) was ball-milled in a ball mill with a ball-to-material ratio of 3:1, a ball diameter range of 10 mm and above accounting for 15%, 1-9 mm accounting for 25%, and 1 mm and below accounting for 60%, the ball milling time was 5 h, and the speed was set at 800 r / min to obtain powder C.

[0084] (5) The powder C obtained in step (4) was subjected to low-temperature reduction calcination at 270°C for 4 h at a heating rate of 5°C / min in an air atmosphere, and then was kept at 800°C for 10 h to obtain a regenerated positive electrode material.

[0085] The properties of the black powder and regenerated positive electrode materials obtained in the above examples and comparative examples are shown in Table 1

[0086]

[0087] Figure 2 (a) is the black powder described in Example 1, Figure 2 (b) is the black powder after ball milling in Example 1. It can be seen that after appropriate ball milling process, the active material in the black powder is transformed from an irregular block structure into flaky nanoparticles with a thickness of about 100 nm. The layered structure is peeled off, making the black powder fully activated and in full contact with the lithium salt and reducing agent, which is beneficial to replenishing lithium and restoring its structure.

[0088] Figure 3 This is the SEM image of the regenerated positive electrode material described in Example 1. It can be seen that its size is basically consistent with the size of the active material after ball milling, and the primary particle structure is clear and the size is uniform.

[0089] Figure 4 The figure shows the cycling performance of the black powder and regenerated positive electrode material described in Example 1 under 1C conditions. The figure shows that the first-cycle capacity of the black powder in Example 1 is 41.8 mAh / g, the capacity retention rate after 200 cycles is 62.44%, and the charge-discharge efficiency at the 200th cycle is 90.82%. Under the same conditions, the regenerated positive electrode material obtained in Example 1 has a cycle capacity of 143.7 mAh / g, a capacity retention rate after 200 cycles is 95.24%, and a charge-discharge efficiency at the 200th cycle is 99.44%.

Claims

1. A direct regeneration method for retired lithium-ion battery positive electrode materials, characterized in that: The following steps are included: Step 1: The waste lithium-ion batteries are discharged, disassembled, pyrolyzed, crushed and sorted, and the cathode material black powder is obtained after being sieved through 60 mesh; Step 2: mixing the black powder with a solid reducing agent to obtain powder A; Step 3: mixing the powder A with a composite lithium salt to obtain powder B; Step 4: milling the powder B in a ball mill to obtain powder C; Step 5: calcining the powder C under certain conditions to obtain a regenerated positive electrode material.

2. The direct regeneration method of retired lithium-ion battery positive electrode materials according to claim 1, characterized in that: The waste lithium-ion battery in step 1 includes a ternary lithium-ion battery (LiNi x Co y Mn 1-x-y O2, 0≤x, y<1, 0≤x+y<1), lithium nickel manganese oxide battery (LiNi x Mn 2-x O4, 0≤x<1.9), at least one of lithium cobalt oxide battery (LiCoO2), lithium manganese oxide battery (LiMn2O4), and lithium iron phosphate battery (LiFePO4).

3. The direct regeneration method of retired lithium-ion battery positive electrode material according to claim 1, characterized in that: In the step 1, ICP, chemical titration, atomic absorption spectroscopy, etc. are used to test the mass of the active substance contained in the black powder and calculate the ratio of each element.

4. The direct regeneration method of retired lithium-ion battery positive electrode materials according to claim 1, characterized in that: In the step 2, the solid reducing agent comprises a reducing agent having a higher reducing power than Ni 3+ 、Co 3+ 、Mn 4+ metals, metal compounds and solid organic matter; the mass of the positive electrode material active substance in the black powder is m1, the mass of the solid reducing agent is m2, m1:m2=1:0.01-0.

4.

5. The direct regeneration method of retired lithium-ion battery positive electrode materials according to claim 4, characterized in that: The solid organic matter in step 2 is at least one of thiourea, ascorbic acid, citric acid, urea, oxalic acid, malic acid, thiomalic acid, glucose, catechol, resorcinol, hydroquinone, p-aminophenol, hydroxylamine hydrochloride, L-cysteine, gallic acid, tartaric acid, polyethylene glycol, tannic acid, thioacetamide, dithiothreitol, hydrazine benzoate, polyacrylic acid, lignin and their compounds.

6. The direct regeneration method of retired lithium-ion battery positive electrode materials according to claim 1, characterized in that: In the step 3, the lithium salt ratio in the composite lithium salt is: 40-100 wt% of lithium carbonate, 0-50 wt% of lithium nitrate, and 0-30 wt% of other lithium salts; The amount of lithium lost by the active material in the powder A in terms of chemical formula is n1, and the amount of lithium in the composite lithium salt is n2, where n1:n2=1:1-1.

05.

7. The direct regeneration method of retired lithium-ion battery positive electrode materials according to claim 6, characterized in that: The other lithium salt in step 3 is at least one of lithium sulfate, lithium phosphate, lithium hexafluorophosphate, lithium chloride, lithium hydroxide, lithium oxalate, and lithium dioxalatoborate.

8. The direct regeneration method of retired lithium-ion battery positive electrode materials according to claim 1, characterized in that: In step 4, the ball-to-material ratio is 5-50:1; the ball diameter range is: 10mm and above accounts for 10-20%, 1-9mm accounts for 20-50%, and 1mm and below accounts for 40-70%; The parameters of the ball milling beads in step 4 are: ball milling time 0.5-12h, rotation speed setting 100-1000r / min; irregular block structure is transformed into flaky nanoparticles with a thickness of about 100nm.

9. The direct regeneration method of retired lithium-ion battery positive electrode materials according to claim 1, characterized in that: The roasting conditions in step 5 are as follows: the heating rate in the high-temperature oxidation roasting stage is 1-10° C. / min, the holding time is 0.5-12 h; and the roasting atmosphere is air.

10. The direct regeneration method of retired lithium-ion battery positive electrode materials according to claim 9, characterized in that: in, The calcination is divided into two stages. The first stage is low-temperature reduction calcination, the calcination temperature is 120-280℃, and the insulation time is 0-5h; the second stage is high-temperature oxidation calcination, the calcination temperature is 400-850℃; and finally the regenerated positive electrode material is obtained.

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