Method for regenerating and modifying waste lithium iron phosphate positive electrode material and application

Abstract

The invention discloses a method for regenerating and modifying a waste lithium iron phosphate positive electrode material and application. According to the method, the waste lithium iron phosphate is directly regenerated by using the organic acid lithium without using a large amount of organic solvent and acid solution, so that the method is environment-friendly and low in cost; meanwhile, the organic acid lithium not only serves as a lithium source to supplement lithium element loss of the waste lithium iron phosphate, but also can be decomposed into carbon in the sintering process to repair carbon coating of the waste lithium iron phosphate, so that oxidation of the lithium iron phosphate and input of an extra carbon source in the regeneration process are avoided; besides, transition metal oxide is introduced to form a synergistic modification strategy of bulk phase doping and surface coating, so that the capacity and rate capability of the regenerated lithium iron phosphate material are improved, and the cycling stability of the regenerated lithium iron phosphate material in an all-solid-state lithium ion battery is improved; and a new thought is provided for regeneration and modification methods of the waste positive electrode material and realization of a high-energy-density solid-state battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion batteries, specifically relating to a method and application of regenerating and modifying waste lithium iron phosphate cathode materials. Background Technology

[0002] In recent years, lithium iron phosphate (LFP) batteries have been widely used in new energy vehicles, energy storage systems, and other fields due to their advantages such as high safety, long cycle life, and low cost. With the rapid expansion of the market, the amount of waste LFP batteries has also increased dramatically. Statistics show that by 2025, the annual amount of waste LFP batteries worldwide is expected to exceed one million tons. Effective recycling and reuse of waste LFP batteries can not only alleviate the shortage of lithium, iron, and phosphorus resources and reduce dependence on primary mineral resources, but also reduce environmental pollution, possessing significant economic value and environmental significance, and has become a key link in the sustainable development of the battery industry.

[0003] Currently, the main methods for regenerating spent lithium iron phosphate (LFP) materials include physical methods, chemical leaching, and pyrometallurgical methods. However, these traditional technologies generally have certain limitations. For example, simple physical repair is difficult to effectively improve the crystal structure defects and electrochemical performance of the material; although the acid-base leaching process in chemical leaching can extract valuable metals, it is complex, costly, and prone to generating large amounts of wastewater that pollute the environment; pyrometallurgical treatment suffers from high energy consumption and significant metal volatilization losses. In addition, during long-term use, spent LFP materials experience lithium loss, crystal structure collapse, damage to the carbon layer on the particle surface, and a decrease in electronic conductivity and lithium-ion diffusion capacity, resulting in poor electrical performance of the regenerated material, which is difficult to meet the high-performance requirements of batteries. Summary of the Invention

[0004] Objective of the Invention: The first objective of this invention is to provide a method for regenerating and modifying waste lithium iron phosphate cathode materials. Another objective of this invention is to provide applications for the materials obtained by this method.

[0005] Technical solution: The method for regenerating and modifying waste lithium iron phosphate cathode material according to the present invention includes the following steps: (1) Separate waste lithium iron phosphate powder from waste batteries and determine its lithium-iron molar ratio as n; weigh waste lithium iron phosphate powder, organic lithium acid and transition metal oxide and grind and mix them in a mortar, wherein the molar ratio of iron element in waste lithium iron phosphate, lithium element in organic lithium acid and metal element in transition metal oxide is 1:X:(0.2~1)X, 1*|1-n|≤X≤5*|1-n|; (2) Further ball mill the mixture from step (1) until it is evenly mixed; (3) Sinter the uniformly mixed mixture from step (2) at high temperature; (4) After taking out the sintered sample from step (3), transfer it to a glove box, cool it to room temperature, and then grind it to obtain the regenerated modified lithium iron phosphate cathode material.

[0006] Further preferably, the molar ratio of iron in waste lithium iron phosphate, lithium in organic lithium oxide, and metal in transition metal oxide is 1:X:X, where 1*|1-n|≤X≤5*|1-n|.

[0007] Preferably, the transition metal oxide in step (1) is one or more of niobium pentoxide, molybdenum trioxide, tungsten trioxide, tantalum pentoxide, vanadium pentoxide, and titanium dioxide.

[0008] Preferably, the organic lithium acid in step (1) is one or a combination of lithium citrate, lithium formate, lithium acetate, and lithium oxalate.

[0009] Preferably, the ball milling in step (2) is carried out in a ball milling jar, which is a zirconia ball milling jar. The ball milling time is 4-12 h, the rotation speed is 300-500 rpm, and wet ball milling is used.

[0010] Preferably, the high-temperature sintering temperature in step (3) is 650-750℃ and the sintering time is 8-12 h.

[0011] Preferably, in step (1), the lithium-iron molar ratio is determined by ICP-OES testing, and the mortar is an agate mortar.

[0012] Preferably, in step (3), the mixture is placed in a corundum crucible and transferred to a tube furnace for high-temperature sintering in a hydrogen / argon mixed atmosphere; in step (4), the glove box is filled with argon. Preferably, the hydrogen / argon mixed atmosphere is 10% hydrogen and 90% argon.

[0013] More preferably, the grinding time in step (1) is not less than 30 min.

[0014] More preferably, the grinding time in step (4) is not less than 30 min.

[0015] Preferably, the method for separating lithium iron phosphate powder from waste batteries in step (1) is as follows: disassemble the waste lithium iron phosphate battery, separate the positive and negative electrode plates and the separator, first rinse the disassembled positive electrode plate with N-methylpyrrolidone (NMP) solution, then rinse with water, dry and calcine, and then peel off the lithium iron phosphate powder by high-speed oscillation.

[0016] More preferably, the concentration of the NMP solution is 0.01 mol / L to 0.5 mol / L.

[0017] The lithium iron phosphate material prepared by the method of regenerating and modifying waste lithium iron phosphate cathode material described in this invention.

[0018] The application of the lithium iron phosphate material described in this invention in the preparation of solid-state lithium-ion batteries.

[0019] Invention Principle: Lithium organic oxides, as a novel lithium source, possess low-temperature decomposition characteristics and chelating effects, enabling the release of active lithium ions at lower temperatures. This effectively repairs lithium defects in the lattice of spent lithium iron phosphate batteries, while the carbon source generated during decomposition repairs the conductive carbon layer on the particle surface. Furthermore, doping with transition metal elements optimizes the material's crystal structure, improves electronic conductivity and lithium-ion diffusion rate, and enhances the material's rate performance and cycle stability. Combining lithium organic oxides with transition metal oxides for the regeneration and modification of spent lithium iron phosphate batteries, through their synergistic effect, simplifies the process, reduces energy consumption, and significantly improves the overall performance of the recycled material, providing a new technological pathway for the high-value recycling and utilization of spent lithium iron phosphate batteries.

[0020] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. Lithium organic oxides possess the dual functions of lithium and carbon source. Their low-temperature decomposition characteristics allow lithium ions to rapidly diffuse to lattice defects in spent lithium iron phosphate at relatively low temperatures, replenishing lost lithium elements. The carbon produced during decomposition can repair damaged conductive carbon layers in situ, improving the electronic conductivity of the material. The introduction of metal oxides alters the crystal structure through doping, creating better channels for lithium ion diffusion. The synergistic effect of these two factors overcomes the limitations of traditional single-raw-source regeneration. 2. Compared with traditional pyrometallurgical and hydrometallurgical processes, which involve high-temperature smelting and acid-base leaching, this invention uses solid-state sintering, which significantly reduces the reaction temperature and energy consumption. The entire process generates no large amounts of wastewater or waste gas and does not require complex metal separation steps, simplifying the process, reducing production costs, and conforming to the concept of green and sustainable development. 3. This invention is applicable to waste lithium iron phosphate cathode materials from different sources and with different degrees of aging. It has high compatibility with raw materials. Whether the battery performance is slightly degraded or severely failed, the material can be effectively regenerated and its performance improved through this technology, which expands the scope of waste battery recycling and improves resource utilization. Attached Figure Description

[0021] Figure 1 The images show the XRD patterns of the waste lithium iron phosphate cathode materials repaired and regenerated in Examples 1, 1, and 2 of this invention.

[0022] Figure 2 The images show SEM images of the waste lithium iron phosphate cathode materials repaired and regenerated in Examples 1, 1, and 2 of this invention.

[0023] Figure 3 The discharge capacity cycle curves of the waste lithium iron phosphate cathode materials repaired and regenerated in Examples 1, 1, and 2 of this invention are shown. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0025] The method for pretreating waste lithium iron phosphate powder in this invention is as follows: Waste lithium iron phosphate batteries are disassembled, and the positive and negative electrodes and separators are separated. The disassembled positive electrode is first rinsed with a 0.5 mol / L NMP solution, then rinsed with ultrapure water, and dried (100°C, 5 h) to obtain waste lithium iron phosphate positive electrode sheets with the surface electrolyte removed. The lithium iron phosphate positive electrode sheets are then calcined at 500°C for 3 h under a hydrogen / argon mixed gas atmosphere, cooled to room temperature, and placed in a vortex shaker for high-speed oscillation. After the lithium iron phosphate powder detaches from the electrode sheet, the collected waste lithium iron phosphate powder is ground and then sieved through a 40-mesh sieve to obtain pretreated waste lithium iron phosphate powder.

[0026] The specific method for assembling batteries with regenerated lithium iron phosphate material in this invention is as follows: The sample is transferred to a glove box filled with argon gas and ground for 30 min. Then, lithium iron phosphate cathode material, lithium phosphorus sulfur chlorine electrolyte, and conductive carbon (LFP: LPSCL: Super P) are ground in a mortar at a mass ratio of 60:30:10 for 30 min to prepare a mixed cathode material. Then, 5 mg of the mixed cathode material, 250 mg of LPSCL, and lithium indium alloy are added to a mold and pressed into a solid-state battery.

[0027] Example 1: Preparation process of lithium iron phosphate cathode material modified by regeneration of lithium citrate, tungsten trioxide and niobium pentoxide and its assembly into an all-solid-state battery.

[0028] (1) The pretreated waste lithium iron phosphate powder was subjected to ICP-OES test and the lithium iron molar ratio n was 0.9. Then |1-n| was 0.1 and X was 0.2 (the molar ratio of lithium element in organic lithium acid and metal element in transition metal oxide was 1:1). (2) Weigh 5 g of pretreated waste lithium iron phosphate, 0.44 g of lithium citrate, 0.73 g of tungsten trioxide and 0.42 g of niobium pentoxide into a mortar and grind and mix for 30 min; then transfer the ground mixture to a zirconia ball mill jar (ball-to-material ratio 8:1), add 15 mL of anhydrous ethanol as a dispersant, and ball mill at 400 rpm for 8 h; after ball milling, place the slurry in a vacuum drying oven at 60℃ and dry for 8 h to remove ethanol; (3) Place the dried product in a corundum crucible and sinter it at 700°C for 10 h in a hydrogen / argon atmosphere at a rate of 5°C / min. (4) After sintering, the regenerated lithium iron phosphate material is obtained and labeled as LCAW-LFP. It is assembled into a battery. The initial discharge capacity is 160.8 mAh / g. After 100 cycles, the capacity retention rate is 83.6%.

[0029] Example 2: Preparation process of lithium iron phosphate cathode material modified by regeneration of lithium oxalate, titanium dioxide and vanadium pentoxide.

[0030] (1) The pretreated waste lithium iron phosphate powder was subjected to ICP-OES test and the lithium iron molar ratio n was 0.92. Then |1-n| was 0.08 and X was 0.4 (the molar ratio of lithium element in organic lithium acid and metal element in transition metal oxide is 1:1). (2) Weigh 5 g of pretreated waste lithium iron phosphate, 0.65 g of lithium oxalate, 0.51 g of titanium dioxide and 1.16 g of vanadium pentoxide into a mortar and grind and mix for 30 min; then transfer the ground mixture to a zirconia ball mill jar (ball-to-material ratio 8:1), add 15 mL of anhydrous ethanol as a dispersant, and ball mill at 500 rpm for 12 h; after ball milling, place the slurry in a 60 ℃ vacuum drying oven and dry for 8 h to remove ethanol; (3) The dried product was placed in a corundum crucible and sintered at 750°C for 12 h in a hydrogen / argon atmosphere at a rate of 5 °C / min. (4) After sintering, the regenerated lithium iron phosphate material can be obtained. After assembling into a battery, the initial discharge capacity was tested to be 160.4 mAh / g. After 100 cycles, the capacity retention rate was 83.2%.

[0031] Example 3: Preparation process of lithium iron phosphate cathode material modified by regeneration of lithium acetate, lithium formate, and tantalum pentoxide.

[0032] (1) The pretreated waste lithium iron phosphate powder was subjected to ICP-OES test and the lithium iron molar ratio n was 0.98. Then |1-n| was 0.02, and X was 0.02 (the molar ratio of lithium element in organic lithium acid and metal element in transition metal oxide is 1:1). (2) Weigh 5g of waste lithium iron phosphate, 0.02g of lithium formate, 0.02g of lithium acetate and 0.14g of tantalum pentoxide into a mortar and grind and mix for 30 min; then transfer the ground mixture to a zirconia ball mill jar (ball-to-material ratio 8:1), add 15 mL of anhydrous ethanol as a dispersant, and ball mill at 300 rpm for 4 h; after ball milling, place the slurry in a vacuum drying oven at 60 ℃ and dry for 8 h to remove ethanol; (3) The dried product was placed in a corundum crucible and sintered at 750°C for 12 h in a hydrogen / argon atmosphere at a rate of 5 °C / min. (4) After sintering, the regenerated lithium iron phosphate material can be obtained. After assembling into a battery, the initial discharge capacity is 160.1 mAh / g. After 100 cycles, the capacity retention rate is 83.4%.

[0033] Example 4: Preparation process of lithium iron phosphate cathode material modified by lithium oxalate and titanium dioxide regeneration.

[0034] (1) The pretreated waste lithium iron phosphate powder was subjected to ICP-OES test and the lithium iron molar ratio n was 0.94. Then |1-n| was 0.06 and X was 0.18 (the molar ratio of lithium element in organic lithium acid and metal element in transition metal oxide was 1:0.5). (2) Weigh 5g of pretreated waste lithium iron phosphate, 0.29g of lithium oxalate and 0.23g of titanium dioxide into a mortar and grind them together for 30min. Then transfer the ground mixture to a zirconia ball mill jar (ball-to-material ratio 8:1), add 15mL of anhydrous ethanol as a dispersant, and ball mill at 500rpm for 12h. After ball milling, place the slurry in a 60℃ vacuum drying oven and dry for 8h to remove the ethanol. (3) Place the dried product in a corundum crucible and sinter it at 750°C for 12 h in a hydrogen / argon atmosphere at a rate of 5°C / min. (4) After sintering, the regenerated lithium iron phosphate material is assembled into a battery. The initial discharge capacity is 159.1 mAh / g, and after 100 cycles, the capacity retention rate is 81.1%.

[0035] Example 5: Preparation process of lithium iron phosphate cathode material modified by regeneration of lithium citrate, lithium acetate, titanium dioxide and tungsten trioxide.

[0036] The pretreated waste lithium iron phosphate powder was subjected to ICP-OES testing, and the lithium iron molar ratio n was found to be 0.96. Therefore, |1-n| was 0.04, and X was taken as 0.12 (the molar ratio of lithium element in organic lithium acid and metal element in transition metal oxide is 1:0.2). Weigh 5g of pretreated waste lithium iron phosphate, 0.13g of lithium citrate, 0.12g of lithium acetate, 0.03g of titanium dioxide, and 0.09g of tungsten trioxide into a mortar and grind them together for 30 min. Then, transfer the ground mixture to a zirconia ball mill jar (ball-to-material ratio 8:1), add 15 ml of anhydrous ethanol as a dispersant, and ball mill at 500 rpm for 12 h. After ball milling, place the slurry in a 60℃ vacuum drying oven and dry for 8 h to remove the ethanol. The dried product was placed in an alumina crucible and sintered at 750°C for 12 h in a hydrogen / argon atmosphere at a rate of 5°C / min. After sintering, the regenerated lithium iron phosphate material is assembled into a battery. The initial discharge capacity is 158.6 mAh / g, and after 100 cycles, the capacity retention rate is 81.3%.

[0037] Comparative Example 1: Preparation process of lithium iron phosphate cathode material regenerated from lithium citrate and its assembly into an all-solid-state battery.

[0038] (1) The pretreated waste lithium iron phosphate powder was tested by ICP-OES and the lithium iron molar ratio n was 0.9. Then |1-n| was 0.1 and X was 0.2. (2) Weigh 5 g of pretreated waste lithium iron phosphate and 0.44 g of lithium citrate into a mortar and grind and mix for 30 min; then transfer the ground mixture to a zirconia ball mill jar (ball-to-material ratio 8:1), add 15 mL of anhydrous ethanol as a dispersant, and ball mill at 400 rpm for 8 h; after ball milling, place the slurry in a vacuum drying oven at 60℃ for 8 h to remove ethanol; (3) Place the dried product in a corundum crucible and sinter it at 700°C for 10 h in a hydrogen / argon atmosphere at a rate of 5°C / min. (4) After sintering, the regenerated lithium iron phosphate material is obtained and designated as LCA-LFP, which is then assembled into a battery.

[0039] from Figure 1 It can be seen that the recycled lithium iron phosphate material in Comparative Example 1 is not significantly different from that in the examples; the XRD pattern peaks match the standard card, and there are no obvious impurities or heterogeneous phases. Figure 2 It can be seen that the recycled lithium iron phosphate material in Comparative Example 1 is not significantly different from that in the examples; the particles are uniform and rounded, with no abnormal carbon coating. However, from... Figure 3 It can be seen that the capacity of the recycled lithium iron phosphate material in Comparative Example 1 is 50 mAh / g lower than that in Example 1, and it decays rapidly after 3 charge-discharge cycles, proving that its cycle performance is much lower than that of Example 1.

[0040] Comparative Example 2: Preparation process of waste lithium iron phosphate cathode material recycled from lithium carbonate and sucrose and its assembly into an all-solid-state battery.

[0041] (1) The pretreated waste lithium iron phosphate powder was tested by ICP-OES and the lithium iron molar ratio n was 0.9. Then |1-n| was 0.1 and X was 0.2. (2) Weigh 5g of waste lithium iron phosphate, 0.12g of lithium carbonate and 0.12g of sucrose into a mortar and grind and mix for 30 min; then transfer the ground mixture to a zirconia ball mill jar (ball-to-material ratio 8:1), add 15 mL of anhydrous ethanol as a dispersant, and ball mill at 500 rpm for 6 h; after ball milling, place the slurry in a vacuum drying oven at 60 ℃ and dry for 8 hours to remove ethanol; (3) Place the dried product in a corundum crucible and sinter it at 700°C for 10 h in a hydrogen / argon atmosphere at a rate of 5°C / min. (4) After sintering, the regenerated lithium iron phosphate material is obtained and designated as S-LFP, which is then assembled into a battery.

[0042] from Figure 1 It can be seen that the recycled lithium iron phosphate material in Comparative Example 2 is not significantly different from that in the examples; the XRD pattern peaks match the standard card, and there are no obvious impurities or heterogeneous phases. Figure 2 It can be seen that the recycled lithium iron phosphate material in Comparative Example 2 is not significantly different from that in the examples; the particles are uniform and rounded, with no abnormal carbon coating. From Figure 3 It can be seen that the capacity of the recycled lithium iron phosphate material in Comparative Example 2 is 80 mAh / g lower than that in Example 1, and it decays rapidly after 3 charge-discharge cycles, proving that its cycle performance is much lower than that of Example 1.

[0043] Data analysis shows that, in terms of electrical performance, Examples 1, 2, and 3 are significantly better than Examples 4 and 5. This indicates that when the molar ratio of lithium in the organic lithium oxide to the metal in the transition metal oxide is 1:1, the prepared material exhibits the best performance.

Claims

1. A method for recycling modified waste lithium iron phosphate cathode material, characterized in that, The method comprises the following steps: (1) separating waste lithium iron phosphate powder from waste batteries, determining the lithium-iron molar ratio of the waste lithium iron phosphate powder as n, and grinding and mixing the waste lithium iron phosphate powder, lithium organic acid and transition metal oxide in a mortar, wherein the molar ratio of iron in the waste lithium iron phosphate, lithium in the lithium organic acid and metal in the transition metal oxide is 1:X:(0.2-1)X, and 1*|1-n|≤X≤5*|1-n|; (2) further ball milling the mixture ground in step (1) to mix uniformly; (3) high-temperature sintering the mixture mixed uniformly in step (2); (4) taking out the sintered sample in step (3) and transferring it to a glove box, grinding after cooling to room temperature to obtain a regenerated modified lithium iron phosphate positive electrode material.

2. The method for regenerating modified waste lithium iron phosphate cathode material according to claim 1, characterized in that, In step (1), the molar ratio of iron in the waste lithium iron phosphate, lithium in the lithium organic acid and metal in the transition metal oxide is 1:X:X, and 1*|1-n|≤X≤5*|1-n|. 3.The method of claim 1, wherein the modified spent lithium iron phosphate cathode material is regenerated. In step (1), the transition metal oxide is one or a combination of niobium pentoxide, molybdenum trioxide, tungsten trioxide, tantalum pentoxide, vanadium pentoxide and titanium dioxide.

4. The method of regenerating modified spent lithium iron phosphate cathode material according to claim 1, wherein, In step (1), the lithium organic acid is one or a combination of lithium citrate, lithium formate, lithium acetate and lithium oxalate.

5. The method of regenerating modified spent lithium iron phosphate cathode material according to claim 1, wherein, In step (2), the ball milling is carried out in a zirconia ball mill jar, the ball milling time is 4-12 h, the rotation speed is 300-500 rpm, and wet ball milling is adopted.

6. The method of regenerating modified spent lithium iron phosphate cathode material according to claim 1, wherein, In step (3), the high-temperature sintering temperature is 650-750°C, and the sintering time is 8-12 h.

7. The method of regenerating modified spent lithium iron phosphate cathode material according to claim 1, wherein, In step (1), the lithium-iron molar ratio is determined by ICP-OES testing, and the mortar is an agate mortar.

8. The method of regenerating modified spent lithium iron phosphate cathode material according to claim 1, wherein, In step (3), the mixture is placed in a corundum crucible and transferred to a tube furnace for high-temperature sintering in a hydrogen / argon mixed atmosphere; in step (4), the glove box is filled with argon.

9. A lithium iron phosphate material prepared by the method of claim 1-8.

10. Use of the lithium iron phosphate material of claim 9 in the preparation of a solid-state lithium ion battery.

Images