A method for upgrading and regenerating retired nickel-rich cathodes by high-temperature in-situ decomposition of Li6Zr2O7

Abstract

The present invention discloses a method for upgrading and regenerating retired nickel-rich cathodes by in-situ decomposition of Li6Zr2O7 at high temperature, which belongs to the technical field of cathode regeneration of lithium ion batteries. The retired lithium ion batteries are self-discharged, disassembled and separated to obtain positive electrode sheets; the retired positive electrode sheets are shredded, soaked and low-temperature calcined to obtain waste cathode powder that can be used for upgrading and regeneration; the pre-synthesized Li6Zr2O7 material is added. Since the Li6Zr2O7 material can be decomposed into Li2O, ZrO2 and Li2ZrO3 when calcined in an oxygen atmosphere at 800°C, the retired nickel-rich cathode can be repaired in-situ to achieve the purpose of lithium replenishment, bulk gradient doping and surface modification. The present invention improves the lithium replenishment material of retired nickel-rich cathodes, and uses a one-step upgrading and regeneration strategy of in-situ decomposition of lithium replenishment reagents to perform bulk repair and surface modification, thereby breaking the limitation of the nickel-rich cathode on the lithium salt requirement and avoiding the strong alkalinity brought by LiOH. The nickel-rich cathode modified by in-situ decomposition of lithium zirconate (Li6Zr2O7) has ultra-high temperature stability performance superior to commercial materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery positive electrode regeneration technology, and particularly relates to a method for upgrading and regenerating retired nickel-rich cathodes assisted by high-temperature in-situ decomposition of Li6Zr2O7. Background Art

[0002] The past few decades have witnessed rapid technological advancement and a surge in the market share of lithium-ion batteries (LIBs) in electric vehicles and portable electronics worldwide. However, retired LIBs are expected to reach 3TWh by 2030, with a compound annual growth rate (CAGR) of 25%. Therefore, solving the resource crisis and potential environmental pollution of the lithium supply chain largely depends on sustainable waste treatment of end-of-life batteries. So far, material recovery from retired LIBs has mainly relied on energy-intensive pyrometallurgical or hydrothermal methods, which necessarily involve laborious acid leaching, filtration, and precipitation treatments as well as hazardous chemical emissions. Therefore, direct cathode recycling, a new approach that aims to repair material composition and crystal defects without causing severe structural damage or component reorganization, has attracted widespread attention in recent years.

[0003] After long-term cycling, nickel-rich layered oxide cathodes, such as commercial LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811) materials, irreversibly produce excessive intrinsic defects on the entire scale, such as Li + / Ni 2+ Mixing, lithium vacancies, transition metal dissolution, secondary particle structure microcracks and surface impurities (Li2CO3 and rock salt phase), etc. + / Ni 2+ Mixing problems, although solid-state sintering, hydrothermal treatment or molten salt strategies have been proposed to repair them, chemical / electrochemical relithiation alone cannot completely solve the problem of microcracks or rock salt impurities on the particle surface, especially the problem of hindering ion diffusion inside / between particles. In addition, trace amounts of water can cause the hydrolysis of LiPF6 salt, and the generated product HF will etch the cathode in an oxidized and charged state, accelerating the migration of TM to the electrolyte.

[0004] Therefore, it is necessary to explore upgrading and recycling solutions that can solve all the above problems (including repairing large cracks, eliminating residual stress and supplementing missing elements, eliminating Li / Ni anti-sites, and removing interface impurities) at the same time, so that the value-added development of superior performance can offset the recycling cost. Summary of the invention

[0005] The purpose of the present invention is to provide a method for upgrading and regenerating retired nickel-rich cathodes by high-temperature in-situ decomposition of Li6Zr2O7. While removing impurities on the surface of the nickel-rich positive electrode material, the decomposition products of Li6Zr2O7, Li2O, ZrO2 and Li2ZrO3, are used to in-situ repair the retired nickel-rich ternary positive electrode, so as to achieve the purpose of lithium supplementation (Li2O), bulk gradient doping (ZrO2) and surface modification (Li2ZrO3). Thus, a positive electrode with high temperature stability is developed. Compared with the traditional method of adding lithium salt and zirconium salt separately, the positive electrode prepared by in-situ decomposition modification in the present invention has better long-cycle stability.

[0006] To achieve the above object, the present invention provides a method for upgrading and regenerating retired nickel-rich cathodes by high-temperature in-situ decomposition of Li6Zr2O7, comprising the following steps:

[0007] S1. Self-discharge the retired lithium-ion batteries, disassemble and separate them to obtain the positive electrode sheets to be recycled;

[0008] S2, placing the waste positive electrode sheet in N-methyl-2-pyrrolidone solvent for ultrasonic peeling, and then filtering and drying to obtain the waste positive electrode powder;

[0009] S3 heat-treats the waste cathode powder, and then obtains S-NCM811 powder after ball milling and sieving;

[0010] S4. Grind and mix the S-NCM811 powder obtained in S3 and the Li6Zr2O7 powder in a certain mass ratio, place the mixed powder in a tubular furnace in an oxygen atmosphere, calcine it, and then cool it naturally to obtain the regenerated positive electrode material R-NCM811-LZO.

[0011] Preferably, in step S1, the retired lithium-ion battery is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0012] Preferably, in step S1, the specific steps of self-discharging and disassembling the retired lithium-ion battery are as follows:

[0013] S11. Soak the retired 10 Ah lithium-ion battery in NaCl solution for 24-48 h until the voltage of the lithium-ion battery is lower than 1.4-1.5 V and then remove the used battery;

[0014] S12. Disassemble the used batteries in a glove box and separate the positive electrode sheet, the separator and the negative electrode sheet.

[0015] Preferably, in step S2, the following steps are included:

[0016] S21, placing the positive electrode sheet in N-methyl-2-pyrrolidone solvent and ultrasonicating for 4-6 h to remove the residual electrolyte;

[0017] S22. The filtered waste positive electrode powder is vacuum dried at 65-75°C for 8-12 h.

[0018] Preferably, in step S3, the waste positive electrode powder is heated to 400-500°C in a muffle furnace at a heating rate of 3°C / min, heat treated for 4-6 h to remove the binder and carbon black in the powder, finely ground in a ball mill at a speed of 400-600 r / min for 3-5 h, and then sieved with a 500-800 mesh sieve to obtain S-NCM811 powder.

[0019] Preferably, in step S4, 1-4 wt% of Li6Zr2O7 is added to the S-NCM811 powder, which is fully ground and then placed in a tubular furnace filled with oxygen and sintered at 700-900°C for 12 h.

[0020] Preferably, in step S4, the synthesis method of Li6Zr2O7 is to mix LiOH·H2O and ZrO2 in a molar ratio of 4:1, finely grind them in a ball mill at a speed of 400-600 r / min for 3-6 h, and calcine the ball-milled powder in a tubular furnace at 700-800°C to obtain Li6Zr2O7 powder.

[0021] Preferably, in step S4, the oxygen flow rate introduced into the tube furnace is 60-100 L / min, and the heating rate of the tube furnace is 2-5 °C / min.

[0022] Therefore, the present invention adopts the above-mentioned method of Li6Zr2O7 high temperature in-situ decomposition to assist the upgrading and regeneration of retired nickel-rich cathodes, and its beneficial effects are:

[0023] (1) Li6Zr2O7 is heated at high temperature and continuously decomposes when the temperature exceeds 700°C. The products of Li2O, ZrO2 and Li2ZrO3 produced by the high-temperature in-situ decomposition of Li6Zr2O7 are used to modify the waste positive electrode and the Li vacancies of waste NCM811 to reduce the diffusion energy barrier of Zr, making it easier for Zr to occupy the Li vacancies, thereby expanding the interlayer spacing and making it difficult for the structure to collapse when lithium ions are inserted / removed.

[0024] (2) In the present invention, Li6Zr2O7 is used instead of the traditional lithium salt LiOH, which can reduce the residual alkali on the surface of the regenerated positive electrode and improve the stability of the regenerated nickel-rich positive electrode.

[0025] (3) The Li2ZrO3 coating can prevent the positive electrode material from contacting with air and water, preventing the hydrolysis of LiPF6 and further destroying the positive electrode material.

[0026] (4) By designing and improving the lithium replenishment materials of waste nickel-rich cathodes, a one-step upgrading and regeneration strategy is developed through in-situ decomposition of lithium replenishment reagents for bulk repair and surface modification. This breaks the limitation of nickel-rich cathodes on lithium salt requirements and avoids the strong alkalinity brought by LiOH·H2O. The nickel-rich cathode modified by in-situ decomposition of lithium zirconate (Li6Zr2O7) has ultra-high temperature stability that is superior to commercial materials.

[0027] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a TEM image of the product prepared in Example 1 of the present invention;

[0029] Figure 2 TG diagram of Li6Zr2O7 of Example 1 of the present invention;

[0030] Figure 3 This is the XRD diagram of Li6Zr2O7 before and after heating according to Example 1 of the present invention;

[0031] Figure 4 The XRD diagrams of the products prepared in Example 1 and Comparative Example 1 of the present invention are shown below;

[0032] Figure 5 It is a comparison diagram of the charge and discharge curves of the products prepared in Example 1 and Comparative Example 1 of the present invention;

[0033] Figure 6 It is a comparison chart of the long cycle capacity retention rates of the products prepared in Examples 1, 2, 3 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0035] Unless otherwise defined, technical or scientific terms used in the present invention shall have the common meanings understood by one having ordinary skills in the field to which the present invention belongs.

[0036] In addition, it should be understood that although this specification is described according to the implementation modes, not every implementation mode includes only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation modes that can be understood by those skilled in the art. These other implementation modes are also covered within the protection scope of the present invention.

[0037] The present invention provides a method for upgrading and regenerating retired nickel-rich cathodes by high-temperature in-situ decomposition of Li6Zr2O7, comprising the following steps:

[0038] S1. Self-discharge the retired lithium-ion batteries, disassemble and separate them to obtain the positive electrode sheets to be recycled;

[0039] S2, placing the waste positive electrode sheet in N-methyl-2-pyrrolidone solvent for ultrasonic peeling, and then filtering and drying to obtain the waste positive electrode powder;

[0040] S3 heat-treats the waste cathode powder, and then obtains S-NCM811 powder after ball milling and sieving;

[0041] S4. Grind and mix the S-NCM811 powder obtained in S3 and the Li6Zr2O7 powder in a certain mass ratio, place the mixed powder in a tubular furnace in an oxygen atmosphere, calcine it, and then cool it naturally to obtain the regenerated positive electrode material R-NCM811-LZO.

[0042] In step S1, the retired lithium-ion battery is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0043] In step S1, the specific steps of self-discharging and disassembling the retired lithium-ion battery are as follows:

[0044] S11. Soak the retired 10 Ah lithium-ion battery in NaCl solution for 24-48 h until the voltage of the lithium-ion battery is lower than 1.4-1.5 V and then remove the used battery;

[0045] S12. Disassemble the used batteries in a glove box and separate the positive electrode sheet, the separator and the negative electrode sheet.

[0046] In step S2, the following steps are included:

[0047] S21, placing the positive electrode sheet in N-methyl-2-pyrrolidone solvent and ultrasonicating for 4-6 h to remove the residual electrolyte;

[0048] S22. The filtered waste positive electrode powder is vacuum dried at 65-75°C for 8-12 h.

[0049] In step S3, the waste positive electrode powder is heated to 400-500°C in a muffle furnace at a heating rate of 3°C / min, heat treated for 4-6 h to remove the binder and carbon black in the powder, finely ground in a ball mill at a speed of 400-600 r / min for 3-5 h, and then sieved with a 500-800 mesh sieve to obtain S-NCM811 powder.

[0050] In step S4, 1-4 wt% of Li6Zr2O7 is added to the S-NCM811 powder, which is fully ground and then placed in a tubular furnace with oxygen and sintered at 700-900°C for 12 h.

[0051] In step S4, the synthesis method of Li6Zr2O7 is to mix LiOH·H2O and ZrO2 in a molar ratio of 4:1, finely grind them in a ball mill at a speed of 400-600 r / min for 3-6 h, and calcine the ball-milled powder in a tubular furnace at 700-800°C to obtain Li6Zr2O7 powder.

[0052] In step S4, the oxygen flow rate into the tube furnace is 60-100 L / min, and the heating rate of the tube furnace is 2-5 °C / min.

[0053] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0054] Embodiment 1

[0055] This embodiment provides a method for upgrading and regenerating retired nickel-rich cathodes by high-temperature in-situ decomposition of Li6Zr2O7, comprising the following steps:

[0056] S1, 10 Ah retired LiNi 0.8 Co 0.1 Mn 0.1 The O2 lithium-ion battery was immersed in a NaCl solution for 48 h and self-discharged until the voltage of the lithium-ion battery was lower than 1.4 V. The battery was then disassembled and separated to obtain the positive electrode sheet that needed to be recycled.

[0057] S2. Place the waste positive electrode sheet in N-methyl-2-pyrrolidone solvent and perform ultrasonic treatment for 4 h to remove the residual electrolyte, and then filter and vacuum dry at 70°C to obtain the waste positive electrode powder.

[0058] S3: The waste positive electrode powder was heated to 400℃ at a heating rate of 5℃ / min and calcined for 4 hours to remove the binder and carbon black in the powder. Then it was finely ground in a ball mill at a speed of 500 r / min for 3 hours, and then sieved with a 500-mesh screen to obtain S-NCM811 powder.

[0059] S4. After grinding and mixing 5 g of S-NCM811 powder and 100 mg of Li6Zr2O7, the mixed powder was placed in a tubular furnace with oxygen and calcined at 800°C for 10 h, and then cooled naturally to obtain the regenerated positive electrode material R-NCM811-LZO; the oxygen flow rate was 60 L / min. The heating rate of the tubular furnace was 3°C / min.

[0060] Embodiment 2

[0061] S1, 10 Ah retired LiNi 0.8 Co 0.1 Mn 0.1 The O2 lithium-ion battery was immersed in a NaCl solution for 48 h and self-discharged until the voltage of the lithium-ion battery was lower than 1.4 V. The battery was then disassembled and separated to obtain the positive electrode sheet that needed to be recycled.

[0062] S2. Place the waste positive electrode sheet in N-methyl-2-pyrrolidone solvent and perform ultrasonic treatment for 4 h to remove the residual electrolyte, and then filter and vacuum dry at 70°C to obtain the waste positive electrode powder.

[0063] S3: The waste positive electrode powder was heated to 400℃ at a heating rate of 5℃ / min and calcined for 4 hours to remove the binder and carbon black in the powder. Then it was finely ground in a ball mill at a speed of 500 r / min for 3 hours, and then sieved with a 500-mesh screen to obtain S-NCM811 powder.

[0064] S4. After grinding and mixing 5 g of S-NCM811 powder and 40 mg of LiOH·H2O, the mixed powder was placed in a tubular furnace with oxygen and calcined at 800°C for 10 h, and then cooled naturally to obtain the regenerated positive electrode material R-NCM811-LZO; the oxygen flow rate was 60 L / min. The heating rate of the tubular furnace was 3°C / min.

[0065] Embodiment 3

[0066] S1, 10 Ah retired LiNi 0.8 Co 0.1 Mn 0.1 The O2 lithium-ion battery was immersed in a NaCl solution for 48 h and self-discharged until the voltage of the lithium-ion battery was lower than 1.4 V. The battery was then disassembled and separated to obtain the positive electrode sheet that needed to be recycled.

[0067] S2. Place the waste positive electrode sheet in N-methyl-2-pyrrolidone solvent and perform ultrasonic treatment for 4 h to remove the residual electrolyte, and then filter and vacuum dry at 70°C to obtain the waste positive electrode powder.

[0068] S3: The waste positive electrode powder was heated to 400℃ at a heating rate of 5℃ / min and calcined for 4 hours to remove the binder and carbon black in the powder. Then it was finely ground in a ball mill at a speed of 500 r / min for 3 hours, and then sieved with a 500-mesh screen to obtain S-NCM811 powder.

[0069] S4. After grinding and mixing 5 g of S-NCM811 powder, 40 mg of LiOH·H2O and 60 mg of ZrO2, the mixed powder was placed in a tubular furnace with oxygen and calcined at 800°C for 10 h, and then cooled naturally to obtain the regenerated positive electrode material R-NCM811-LZO; the oxygen flow rate was 60 L / min. The heating rate of the tubular furnace was 3°C / min.

[0070] Comparative Example 1

[0071] S1, 10 Ah retired LiNi 0.8 Co 0.1 Mn 0.1 The O2 lithium-ion battery was immersed in a NaCl solution for 48 h and self-discharged until the voltage of the lithium-ion battery was lower than 1.4 V. The battery was then disassembled and separated to obtain the positive electrode sheet that needed to be recycled.

[0072] S2. Place the waste positive electrode sheet in N-methyl-2-pyrrolidone solvent and perform ultrasonic treatment for 4 h to remove the residual electrolyte, and then filter and vacuum dry at 70°C to obtain the waste positive electrode powder.

[0073] S3: The waste positive electrode powder was heated to 400℃ at a heating rate of 5℃ / min and calcined for 4 hours to remove the binder and carbon black in the powder. Then it was finely ground in a ball mill at a speed of 500 r / min for 3 hours, and then sieved with a 500-mesh screen to obtain S-NCM811 powder.

[0074] Product testing

[0075] (1) Transmission electron microscopy (TEM) characterization

[0076] The R-NCM811-LZO of Example 1 was characterized by TEM. Figure 1 It can be seen that the regenerated NCM811 obtained in Example 1 has a crystalline coating layer on its surface.

[0077] (2) Thermogravimetric analysis (TG) characterization

[0078] The Li6Zr2O7 in Example 1 was subjected to TG test, and the test results are as follows: Figure 2 It was found that Li6Zr2O7 began to decompose continuously when the temperature exceeded 700℃.

[0079] (3) X-ray diffractometer (XRD) characterization

[0080] XRD test was performed on the material before and after thermal decomposition of Li6Zr2O7 in Example 1. The test results are as follows: Figure 3 As shown, the product of Li6Zr2O7 heated at 800℃ for 10 h is Li2ZrO3.

[0081] The products of Example 1 and Comparative Example 1 of the present invention were subjected to XRD tests respectively. Figure 4 As shown, it can be seen that the R-NCM811-LZO in Example 1 and the S-NCM811 in the comparative example have the same crystal structure, and the increase in the peak intensity ratio of (003) and (104) of R-NCM811-LZO indicates that the crystal structure is well restored. The separation of peaks (006) / (102) and (108) / (110) indicates that R-NCM811-LZO has restored a highly crystalline layered structure.

[0082] (4) Electrochemical performance test

[0083] Figure 5 The first cycle (0.1C) charge-discharge curves of the regenerated R-NCM811-LZO in Example 1 of the present invention and the S-NCM811 in Comparative Example 1; Figure 6 It is a comparison chart of the cycle curves of R-NCM811-LZO in Example 1 of the present invention, R-NCM811-LiOH in Example 2, R-NCM811-LiOH-ZrO2 in Example 3 and S-NCM811 in the comparative example.

[0084] Will Figure 5 as well as Figure 6 A comprehensive analysis of the test results shows that the first cycle (0.1C) discharge capacity of the R-NCM811-LZO battery prepared in Example 1 is as high as 202 mAh g -1 Compared with the test results of S-NCM811 in Comparative Example 1 which has not undergone the lithium replenishment process, it is shown that the lithium replenishment effect of Example 1 is excellent, and the specific capacity retention rate is still 93.2% after 200 cycles at 1 C, showing better cycle stability than the products prepared in Examples 2 and 3. The capacity retention rate of the regenerated R-NCM8111-LZO after 200 cycles at a high temperature of 55°C is still 84.7%.

[0085] Therefore, the present invention adopts the above-mentioned method of upgrading and regenerating retired nickel-rich cathodes by in-situ decomposition of Li6Zr2O7 at high temperature. The pre-synthesized Li6Zr2O7 material is added to the waste cathode powder. Since the Li6Zr2O7 material can be decomposed into Li2O, ZrO2 and Li2ZrO3 when calcined in an oxygen atmosphere at 800°C, the retired nickel-rich ternary positive electrode can be repaired in-situ. The purpose of lithium replenishment, bulk gradient doping and surface modification is achieved by using Li2O, ZrO2 and Li2ZrO3 respectively. The one-step upgrading and regeneration strategy of bulk repair and surface modification by in-situ decomposition of lithium replenishment reagent breaks the limitation of nickel-rich cathode on lithium salt requirements and avoids the strong alkalinity brought by LiOH·H2O. The nickel-rich cathode modified by in-situ decomposition of lithium zirconate (Li6Zr2O7) has ultra-high temperature stability performance superior to commercial materials.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for upgrading and regenerating retired nickel-rich cathodes by high-temperature in-situ decomposition of Li6Zr2O7, characterized in that: The following steps are involved: S1. Self-discharge the retired lithium-ion batteries, disassemble and separate them to obtain the positive electrode sheets to be recycled; S2, placing the waste positive electrode sheet in N-methyl-2-pyrrolidone solvent for ultrasonic peeling, and then filtering and drying to obtain the waste positive electrode powder; S3 heat-treats the waste cathode powder, and then obtains S-NCM811 powder after ball milling and sieving; S4. Grind and mix the S-NCM811 powder obtained in S3 and the Li6Zr2O7 powder in a certain mass ratio, place the mixed powder in a tubular furnace in an oxygen atmosphere, calcine it, and then cool it naturally to obtain the regenerated positive electrode material R-NCM811-LZO.

2. The method for upgrading and regenerating retired nickel-rich cathodes by high-temperature in-situ decomposition of Li6Zr2O7 according to claim 1, characterized in that: In step S1, the specific steps of self-discharging and disassembling the retired lithium-ion battery are as follows: S11. Soak the retired 10 Ah lithium-ion battery in NaCl solution for 24-48 h until the voltage of the lithium-ion battery is lower than 1.4-1.5 V and then remove the used battery; S12. Disassemble the used batteries in a glove box and separate the positive electrode sheet, the separator and the negative electrode sheet.

3. The method for upgrading and regenerating retired nickel-rich cathodes by high-temperature in-situ decomposition of Li6Zr2O7 according to claim 1, characterized in that: In step S2, the following steps are included: S21, placing the positive electrode sheet in N-methyl-2-pyrrolidone solvent and ultrasonicating for 4-6 h to remove the residual electrolyte; S22. The filtered waste positive electrode powder is vacuum dried at 65-75°C for 8-12 h.

4. The method for upgrading and regenerating retired nickel-rich cathodes by high-temperature in-situ decomposition of Li6Zr2O7 according to claim 3, characterized in that: In step S3, the waste positive electrode powder is heated to 400-500°C in a muffle furnace at a heating rate of 3°C / min, heat treated for 4-6 h to remove the binder and carbon black in the powder, finely ground in a ball mill at a speed of 400-600 r / min for 3-5 h, and then sieved with a 500-800 mesh sieve to obtain S-NCM811 powder.

5. The method for upgrading and regenerating retired nickel-rich cathodes by high-temperature in-situ decomposition of Li6Zr2O7 according to claim 4, characterized in that: In step S4, 1-4 wt% of Li6Zr2O7 is added to the S-NCM811 powder, which is fully ground and then placed in a tubular furnace with oxygen and sintered at 700-900°C for 12 h.

6. The method for upgrading and regenerating retired nickel-rich cathodes by high-temperature in-situ decomposition of Li6Zr2O7 according to claim 4, characterized in that: In step S4, the oxygen flow rate into the tube furnace is 60-100 L / min, and the heating rate of the tube furnace is 2-5 °C / min.

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