Method for repairing and regenerating lithium iron phosphate cathode material

Abstract

This invention discloses a method for repairing and regenerating lithium iron phosphate (LFP) cathode materials, belonging to the field of lithium-ion battery technology. The method involves: firstly, partially oxidizing the LFP cathode material obtained by stripping waste LFP electrode sheets; then, using excess carbon in the LFP cathode material to reduce the oxidized LFP at high temperature, resulting in decarbonized and regenerated LFP cathode material. By controlling the degree of oxidation to partially oxidize the LFP cathode material, and then using excess carbon in the LFP cathode material to reduce the oxidized LFP at high temperature, the decarbonization purpose is achieved, and pure LFP cathode material is obtained. This truly realizes the direct repair and regeneration of LFP cathode materials by decarbonization, ensuring the electrochemical performance of the recycled LFP repaired material.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a method for repairing and regenerating lithium iron phosphate cathode materials. Background Technology

[0002] With rapid global economic development, resource shortages and environmental damage are becoming increasingly severe. Lithium-ion batteries, due to their high voltage, high energy density, and long cycle life, are widely used in electric vehicles, communication base stations, and large-scale energy storage, reducing global dependence on non-renewable resources such as fossil fuels. Among them, lithium iron phosphate batteries stand out for their large capacity, good thermal stability, low toxicity, and low cost, and are widely used in mainstream electric vehicle battery systems. Thanks to the development of blade batteries and improvements in cell peak energy technology, the volumetric energy density of lithium iron phosphate batteries is now approaching that of ternary lithium batteries, and it is expected that lithium iron phosphate batteries will occupy a larger market share in the future.

[0003] As the development of lithium iron phosphate (LFP) batteries gains momentum, people are paying increasing attention to how to handle and recycle retired LFP batteries. Recycling and reusing used LFP batteries not only yields significant economic benefits but also plays a crucial role in energy conservation, emission reduction, and sustainable development. However, there is relatively little attention paid to the disposal of LFP battery waste generated by manufacturers during the production process.

[0004] Given the aforementioned problems, it is necessary to provide a method for repairing and regenerating lithium iron phosphate cathode materials. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a method for repairing and regenerating lithium iron phosphate cathode materials.

[0006] The technical problem solved by this invention is achieved by the following technical solution.

[0007] This invention provides a method for repairing and regenerating lithium iron phosphate cathode materials, comprising: reacting lithium iron phosphate cathode materials obtained by stripping waste lithium iron phosphate electrode sheets with an oxidant to partially oxidize the lithium iron phosphate cathode materials; and then using the excess carbon in the lithium iron phosphate cathode materials to reduce the oxidized lithium iron phosphate by reacting with the oxidized lithium iron phosphate to obtain carbon-removed repaired and regenerated lithium iron phosphate cathode materials.

[0008] The present invention has the following beneficial effects:

[0009] This invention provides a method for repairing and regenerating lithium iron phosphate (LFP) cathode materials. The LFP cathode material obtained by peeling off waste LFP electrode sheets is partially oxidized, and then the excess carbon in the LFP cathode material is used to reduce the oxidized LFP at high temperature, resulting in decarbonized and regenerated LFP cathode materials. By controlling the degree of oxidation to partially oxidize the LFP cathode material, over-oxidation of LFP is avoided. During subsequent high-temperature roasting, the excess carbon in the LFP cathode material is used to reduce the oxidized LFP, truly achieving direct decarbonization and regeneration of the LFP cathode material. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 The flowcharts are for the direct repair and regeneration experiments of lithium iron phosphate cathode materials in Examples 1-3.

[0012] Figure 2 The flowcharts are for the direct repair and regeneration experiments of lithium iron phosphate cathode materials in Examples 4-6.

[0013] Figure 3 The image shows the XRD pattern of lithium iron phosphate electrode powder I after calcination in Example 1.

[0014] Figure 4 The image shows the XRD pattern of the lithium iron phosphate electrode powder after two-stage calcination in Example 1.

[0015] Figure 5 The image shows the XRD pattern of lithium iron phosphate electrode powder I after oxidation with hydrogen peroxide in Example 4.

[0016] Figure 6 The image shows the XRD pattern of lithium iron phosphate electrode powder II after reduction and calcination in Example 4.

[0017] Figure 7 The image shows the XRD pattern of lithium iron phosphate electrode powder I after calcination in Comparative Example 1. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] The following is a detailed description of a method for repairing and regenerating lithium iron phosphate cathode material provided by an embodiment of the present invention.

[0020] This invention provides a method for repairing and regenerating lithium iron phosphate cathode material, comprising: reacting the lithium iron phosphate cathode material obtained by stripping waste lithium iron phosphate electrode sheets with an oxidant to partially oxidize the lithium iron phosphate cathode material; and then using the excess carbon in the lithium iron phosphate cathode material to reduce the oxidized lithium iron phosphate by reacting with the oxidized lithium iron phosphate to obtain carbon-removed repaired and regenerated lithium iron phosphate cathode material.

[0021] This invention provides a method for repairing and regenerating lithium iron phosphate (LFP) cathode materials. The method involves: stripping waste LFP electrode sheets to obtain LFP cathode materials; then reacting these materials with an oxidant to partially oxidize them; subsequently, using excess carbon from the LFP cathode materials, a reduction reaction is carried out with the oxidized LFP at high temperature to reduce the oxidized LFP cathode materials, resulting in carbon-removed and regenerated LFP cathode materials. This method employs an oxidation-reduction approach, using excess carbon from the roasting of the LFP cathode materials as the reducing agent. This eliminates the need for additional reducing agents and effectively removes carbon from the LFP cathode materials. Furthermore, the resulting LFP cathode materials contain only the LiFePO4 crystal form, free of other impurities, truly achieving direct repair and regeneration of LFP cathode materials.

[0022] In an optional implementation, the method includes: stripping waste lithium iron phosphate electrode sheets to obtain lithium iron phosphate cathode material; oxidizing the lithium iron phosphate cathode material in an air atmosphere using a first-stage roasting process to partially oxidize the lithium iron phosphate; and then reducing the oxidized lithium iron phosphate by using excess carbon in the lithium iron phosphate cathode material in a second-stage roasting process at high temperature, thereby achieving direct carbon removal and regeneration of the lithium iron phosphate cathode material.

[0023] From a technical standpoint, removing carbon (including conductive carbon black, PVDF, and NMP) from lithium iron phosphate (LFP) cathode materials typically relies on complete air roasting. However, during this air roasting process, the LFP is also completely oxidized. This invention, through ingenious design, controls the duration and temperature of the first stage of air roasting to prevent excessive oxidation of LFP during the carbon removal process. In the second stage of roasting, excess carbon in the LFP cathode material is used to reduce the oxidized LFP. After these two stages of roasting, some of the LFP is first oxidized and then reduced, truly achieving direct repair and regeneration of the LFP cathode material.

[0024] In an optional embodiment, the method for repairing and regenerating lithium iron phosphate cathode material includes: soaking waste lithium iron phosphate electrode sheets in a solvent to remove the current collector, drying and grinding them to obtain lithium iron phosphate electrode sheet powder I; placing lithium iron phosphate electrode sheet powder I in an air atmosphere and calcining it at 300-500℃ for 5-30 minutes, then replacing the air with an inert gas and continuing to calcine for 60-240 minutes to complete the first stage of calcination; taking out the product obtained from the first stage of calcination and grinding it to obtain lithium iron phosphate electrode sheet powder II; placing lithium iron phosphate electrode sheet powder II in an inert gas atmosphere and calcining it at 500-750℃ for 120-420 minutes to complete the second stage of calcination, and finally obtaining the repaired lithium iron phosphate cathode material.

[0025] In an optional embodiment, the method for repairing and regenerating lithium iron phosphate cathode material includes the following steps: soaking waste lithium iron phosphate electrode sheets in a solvent to remove the current collector, drying and grinding them to obtain lithium iron phosphate electrode sheet powder I; placing lithium iron phosphate electrode sheet powder I into a crucible and then placing it in a tube furnace, passing inert gas to remove air, and then heating it to 300-500°C. After heating, replacing the inert gas with air for roasting, and then replacing the air back with inert gas for roasting to complete the first stage of roasting; taking out the product obtained from the first stage of roasting and grinding it to obtain lithium iron phosphate electrode sheet powder II; placing lithium iron phosphate electrode sheet powder II into a crucible and placing it in a tube furnace, passing inert gas to remove air, heating it to 500-750°C for roasting to complete the second stage of roasting, and finally obtaining the repaired lithium iron phosphate cathode material.

[0026] In an optional embodiment, the method further includes: before calcination, lithium iron phosphate electrode powder I or lithium iron phosphate electrode powder II is first loaded into a crucible, the crucible is placed in a tube furnace and an inert gas is introduced, and after 60-120 minutes, the tube furnace is heated to the set temperature at a heating rate of 2-5℃ / min, and then calcination is carried out. The inert gas is one or any combination of two or more of nitrogen, argon, helium and neon.

[0027] In an optional embodiment, the method for repairing and regenerating lithium iron phosphate cathode material includes: stripping waste lithium iron phosphate electrode sheets to obtain lithium iron phosphate cathode material, oxidizing the lithium iron phosphate cathode material with hydrogen peroxide to partially oxidize the lithium iron phosphate, and then using excess carbon in the lithium iron phosphate cathode material to reduce the oxidized lithium iron phosphate at high temperature, thereby achieving carbon removal and repair regeneration of the lithium iron phosphate cathode material.

[0028] This invention also provides a method for repairing and regenerating lithium iron phosphate (LFP) cathode materials. By controlling the amount of hydrogen peroxide used, LFP is partially oxidized, and then excess carbon in the LFP cathode material is used to reduce the oxidized LFP at high temperature. Through oxidation with hydrogen peroxide followed by reduction by excess carbon in the system, the LFP cathode material achieves direct repair and regeneration of the LFP cathode material by removing carbon.

[0029] In an optional embodiment, the method for repairing and regenerating lithium iron phosphate cathode material includes the following steps: soaking waste lithium iron phosphate electrode sheets in a solvent to remove the current collector, then drying and grinding them to obtain lithium iron phosphate electrode powder I; adding hydrogen peroxide dropwise to lithium iron phosphate electrode powder I to partially oxidize the lithium iron phosphate, stopping the reaction after 20-40 minutes; taking out the product obtained from oxidation, washing and drying it, and then grinding it to obtain lithium iron phosphate electrode powder II; placing lithium iron phosphate electrode powder II in an inert gas atmosphere, pre-calcining it at 400-500℃ for 60-180 minutes, and then calcining it at 550-700℃ for 120-240 minutes to finally obtain the repaired lithium iron phosphate cathode material.

[0030] In an optional embodiment, the oxidation reaction temperature is 25-70°C, the molar ratio of hydrogen peroxide in hydrogen peroxide to lithium iron phosphate electrode powder I is 0.2-1.2:1, and preferably the mass fraction of hydrogen peroxide is 10%.

[0031] In an optional embodiment, the step of taking out the product obtained from the oxidation reaction, washing and drying it, and then grinding it into lithium iron phosphate electrode powder II is as follows: Take out the product obtained from the oxidation reaction, wash it with water, dry it at 50-80℃ for 5-24h, and grind it at 350-450rpm for 120-360min. The product is then obtained.

[0032] In an optional embodiment, lithium iron phosphate electrode powder I is prepared by the following steps: cutting waste lithium iron phosphate electrode sheets into fragments, soaking them in water to separate the lithium iron phosphate cathode material from the current collector, filtering the mixture of lithium iron phosphate cathode material after removing the current collector to obtain filtrate and filter residue, and then drying and grinding the filter residue to obtain lithium iron phosphate electrode powder I with a carbon content of 3-5 wt%.

[0033] In an optional embodiment, the solvent used for soaking the waste lithium iron phosphate electrode sheets is water, the soaking temperature is 25-100℃, and the soaking time is 10-60 min. The filter residue is dried at a temperature of 50-100℃ for 4-48 h. The filter residue is ground at a speed of 350-450 rpm for 120-360 min.

[0034] In an optional implementation, the method further includes: placing the repaired lithium iron phosphate cathode material obtained above in an 80-300 mesh sieve and sieving it through a vibrating sieve to collect the undersize material.

[0035] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0036] This invention provides a method for direct carbon removal, repair, and regeneration of lithium iron phosphate cathode materials. See the flowchart below. Figure 1 This includes the following steps:

[0037] (1) Cut the waste lithium iron phosphate electrode sheets into pieces of 2cm x 2cm using scissors.

[0038] (2) Put the broken electrode pieces cut in step 1 into a beaker, add water at 25-100℃ and soak for 10-60 minutes, then separate the lithium iron phosphate cathode material from the current collector.

[0039] (3) Filter the mixture of lithium iron phosphate cathode material from which the current collector was removed in step 2 using a Buchner funnel to separate the solid from the filtrate and collect the filter residue.

[0040] (4) Place the filter residue obtained in step 3 into an oven and dry it at 50-100℃ for 4-48 hours to obtain dried lithium iron phosphate fragments.

[0041] (5) The dried lithium iron phosphate fragments obtained in step 4 are loaded into a horizontal polytetrafluoroethylene ball mill jar, zirconium balls are added to the ball mill jar, and the jar is placed on a ball mill and milled at 350-450 rpm for 120-360 min to obtain lithium iron phosphate electrode powder I. The carbon content in the lithium iron phosphate electrode powder I is measured to be 3-5 wt% by a carbon-sulfur analyzer.

[0042] (6) The lithium iron phosphate electrode powder I after ball milling in step 5 is placed in a crucible and placed in a tube furnace and inert gas is introduced. After 60-120 min, the tube furnace is heated to 300-500℃ at a heating rate of 2-5℃ / min. After the heating is completed, the inert gas is replaced with air and introduced into the tube furnace to calcine the sample at 300-500℃ for 5-30 min. Then the air is replaced with inert gas and introduced into the tube furnace to continue calcining the sample at 300-500℃ for 60-240 min.

[0043] (7) After the roasting is completed, take out the lithium iron phosphate electrode powder I after roasting in step 6 and pour it into a horizontal polytetrafluoroethylene ball mill jar. Add zirconium balls into the ball mill jar and then place the ball mill jar on a ball mill and ball mill at 350-450 rpm for 120-360 min to obtain lithium iron phosphate electrode powder II. The carbon content in the lithium iron phosphate electrode powder II is less than 2% as measured by a carbon-sulfur analyzer. At the same time, the XRD test results show that Li3Fe2(PO4)3 and Fe2O3 are generated in the lithium iron phosphate electrode powder. Since the amount of Fe2O3 is very small, it is not obvious in the XRD pattern.

[0044] (8) The electrode powder II after ball milling in step 7 is placed in a crucible and placed in a tube furnace and inert gas is introduced. After 60-120 min, the tube furnace is heated to 500-750℃ at a heating rate of 2-5℃ / min and calcined for 120-420 min to obtain the repaired lithium iron phosphate cathode material.

[0045] (9) Place the repaired lithium iron phosphate cathode powder obtained in step 8 into an 80-300 mesh sieve and sieve it through a vibrating sieve to collect the sieve material.

[0046] (10) The carbon content of the sieved lithium iron phosphate cathode powder obtained in step 9 was found to be less than 1.3% by a carbon-sulfur analyzer.

[0047] This invention also provides a method for direct carbon removal, repair, and regeneration of lithium iron phosphate cathode materials, the flowchart of which can be found in the provided text. Figure 2 This includes the following steps:

[0048] (1) Cut the waste lithium iron phosphate electrode sheets into pieces of 2cm x 2cm using scissors.

[0049] (2) Put the broken electrode pieces cut in step 1 into a beaker, add water at 25-100℃ and soak for 10-60 minutes, then separate the lithium iron phosphate cathode material from the current collector.

[0050] (3) Filter the mixture of lithium iron phosphate cathode material from which the current collector was removed in step 2 using a Buchner funnel to separate the solid from the filtrate and collect the filter residue.

[0051] (4) Place the filter residue obtained in step 3 into an oven and dry it at 50-100℃ for 4-48 hours to obtain dried lithium iron phosphate fragments.

[0052] (5) The dried lithium iron phosphate fragments obtained in step 4 were placed into a horizontal polytetrafluoroethylene ball mill jar. Zirconium balls were added to the ball mill jar, and the jar was placed on a ball mill and milled at 350-450 rpm for 120-360 min to obtain lithium iron phosphate electrode powder. The carbon content in the lithium iron phosphate electrode powder was measured to be 3-5 wt% by a carbon-sulfur analyzer, and the Fe content in the lithium iron phosphate electrode powder was measured by titration. 3+ Content less than 1%.

[0053] (6) Take n mol of the lithium iron phosphate electrode powder I after ball milling in step 5 and put it into a beaker. Place the beaker in a water bath at 25-70℃ and slowly add 0.2n mol-1.2n mol of hydrogen peroxide with a mass fraction of 10%. Stop the reaction after 20-40 minutes.

[0054] (7) Filter the compound obtained in step 6 using a Buchner funnel, wash the filter residue with deionized water in small amounts several times, rinse the hydrogen peroxide in the lithium iron phosphate electrode powder and take filter residue II.

[0055] (8) Place the filter residue II obtained in step 7 into an oven and dry it at 50-80℃ for 5-24 hours. The Fe content in the filter residue II is determined by titration. 3+ Content greater than 3%.

[0056] (9) The dried filter residue II obtained in step 8 is loaded into a ball mill jar, zirconium balls are added into the ball mill jar, and the ball mill jar is placed on a ball mill and ball milled at 350-450 rpm for 120-360 min to obtain lithium iron phosphate electrode powder II.

[0057] (10) The lithium iron phosphate electrode powder II after ball milling in step 9 is placed in a crucible and placed in a tube furnace and inert gas is introduced. After 30-120 min, the tube furnace is heated to 400-500℃ at a heating rate of 5℃ / min for pre-calcination for 60-180 min, and then heated to 550-700℃ for calcination for 120-240 min to obtain the repaired and regenerated lithium iron phosphate powder.

[0058] Example 1

[0059] A method for direct repair and regeneration of lithium iron phosphate cathode materials after carbon removal includes the following specific steps:

[0060] (1) Cut the waste lithium iron phosphate electrode sheets into pieces of 2cm x 2cm using scissors.

[0061] (2) Put the broken electrode pieces cut in step 1 into a beaker, add water at 30°C and soak for 60 minutes, then separate the lithium iron phosphate cathode material from the current collector.

[0062] (3) Filter the mixture of lithium iron phosphate cathode material from which the current collector was removed in step 2 using a Buchner funnel to separate the solid from the filtrate and collect the filter residue.

[0063] (4) Place the filter residue obtained in step 3 into an oven and dry it at 50°C for 48 hours to obtain dried lithium iron phosphate fragments.

[0064] (5) The dried lithium iron phosphate fragments obtained in step 4 were loaded into a horizontal polytetrafluoroethylene ball mill jar, zirconium balls were added into the ball mill jar, and the ball mill jar was placed on a ball mill and ball milled at 400 rpm for 120 min to obtain lithium iron phosphate electrode powder I. The carbon content in the lithium iron phosphate electrode powder I was measured to be greater than 3% by a carbon-sulfur analyzer.

[0065] (6) The lithium iron phosphate electrode powder I after ball milling in step 5 is placed in a crucible and placed in a tube furnace and nitrogen is introduced. After 60 min, the tube furnace is heated to 500°C at a heating rate of 5°C / min. After the heating is completed, the nitrogen is replaced with air and introduced into the tube furnace to calcine the sample at 500°C for 5 min. Then the air is replaced with nitrogen and introduced into the tube furnace to continue calcining the sample at 500°C for 60 min.

[0066] (7) Take out the lithium iron phosphate electrode powder I after calcination in step 6 and pour it into a horizontal polytetrafluoroethylene ball mill jar. Add zirconium balls into the ball mill jar and then place the ball mill jar on a ball mill and ball mill at 400 rpm for 120 min to obtain lithium iron phosphate electrode powder. The carbon content in the lithium iron phosphate electrode powder II was measured to be 1.9% by a carbon-sulfur analyzer. At the same time, the XRD test results showed that Li3Fe2(PO4)3 and Fe2O3 were generated in the lithium iron phosphate electrode powder II. Since the amount of Fe2O3 was very small, it was not obvious in the XRD pattern.

[0067] (8) The lithium iron phosphate electrode powder II after ball milling in step 7 is placed in a crucible and placed in a tube furnace and nitrogen is introduced. After 60 min, the tube furnace is heated to 750°C at a heating rate of 5°C / min and calcined for 120 min to obtain the repaired lithium iron phosphate cathode material.

[0068] (9) Place the repaired lithium iron phosphate cathode powder obtained in step 8 into a 100-mesh sieve and sieve it through a vibrating sieve to collect the sieve material.

[0069] (10) The carbon content in the sieved lithium iron phosphate cathode powder obtained in step 9 was 1.3% as measured by a carbon-sulfur analyzer.

[0070] The products from the calcination process in Example 1 above were tested and analyzed: XRD tests were performed on the lithium iron phosphate electrode powder after a section of air calcination, and the XRD pattern is shown below. Figure 3 The lithium iron phosphate electrode powder after a first-stage air calcination exhibits the Li3Fe2(PO4)3 crystal form, indicating that some LiFePO4 was also oxidized during the first-stage air calcination oxidation and carbon removal process. XRD analysis was performed on the lithium iron phosphate electrode powder after a second-stage calcination; the XRD pattern is shown below. Figure 4 After two-stage air calcination, the lithium iron phosphate electrode powder only showed the LiFePO4 crystal form, while the Li3Fe2(PO4)3 crystal form disappeared. This indicates that the excess carbon in the lithium iron phosphate electrode powder reduced Li3Fe2(PO4)3 back to LiFePO4.

[0071] Example 2

[0072] A method for direct repair and regeneration of lithium iron phosphate cathode materials after carbon removal includes the following specific steps:

[0073] (1) Cut the waste lithium iron phosphate electrode sheets into pieces of 2cm x 2cm using scissors.

[0074] (2) Put the broken electrode pieces cut in step 1 into a beaker, add water at 50°C and soak for 40 minutes, then separate the lithium iron phosphate cathode material from the current collector.

[0075] (3) Filter the mixture of lithium iron phosphate cathode material from which the current collector was removed in step 2 using a Buchner funnel to separate the solid from the filtrate and collect the filter residue.

[0076] (4) Place the filter residue obtained in step 3 into an oven and dry it at 100°C for 4 hours to obtain dried lithium iron phosphate fragments.

[0077] (5) The dried lithium iron phosphate fragments obtained in step 4 were loaded into a horizontal polytetrafluoroethylene ball mill jar, zirconium balls were added to the ball mill jar, and the ball mill jar was placed on a ball mill and ball milled at 400 rpm for 240 min to obtain lithium iron phosphate electrode powder I. The carbon content in the lithium iron phosphate electrode powder I was measured to be greater than 3% by a carbon-sulfur analyzer.

[0078] (6) The lithium iron phosphate electrode powder I after ball milling in step 5 is placed in a crucible and placed in a tube furnace and nitrogen is introduced. After 90 min, the tube furnace is heated to 350°C at a heating rate of 5°C / min. After the heating is completed, the nitrogen is replaced with air and introduced into the tube furnace to calcine the sample at 350°C for 30 min. Then the air is replaced with nitrogen and introduced into the tube furnace to continue calcining the sample at 350°C for 90 min.

[0079] (7) Take out the lithium iron phosphate electrode powder I after calcination in step 6 and pour it into a horizontal polytetrafluoroethylene ball mill jar. Add zirconium balls into the ball mill jar and then place the ball mill jar on a ball mill and ball mill at 400 rpm for 240 min to obtain lithium iron phosphate electrode powder II. The carbon content in the lithium iron phosphate electrode powder II was measured to be 1.9% by a carbon-sulfur analyzer. At the same time, the XRD test results showed that Li3Fe2(PO4)3 and Fe2O3 were generated in the lithium iron phosphate electrode powder II. Since the amount of Fe2O3 was very small, it was not obvious in the XRD pattern.

[0080] (8) The electrode powder II after ball milling in step 7 is placed in a crucible and placed in a tube furnace and nitrogen is introduced. After 90 min, the tube furnace is heated to 500℃ at a heating rate of 5℃ / min and calcined for 420 min to obtain the repaired lithium iron phosphate cathode material.

[0081] (9) Place the repaired lithium iron phosphate cathode powder obtained in step 8 into a 200-mesh sieve and sieve it through a vibrating sieve to collect the sieve material.

[0082] (10) The carbon content in the sieved lithium iron phosphate cathode powder obtained in step 9 was 1.1% as measured by a carbon-sulfur analyzer.

[0083] Example 3

[0084] A method for direct repair and regeneration of lithium iron phosphate cathode materials after carbon removal includes the following specific steps:

[0085] (1) Cut the waste lithium iron phosphate electrode sheets into pieces of 2cm x 2cm using scissors.

[0086] (2) Put the broken electrode pieces cut in step 1 into a beaker, add water at 80°C and soak for 20 minutes, then separate the lithium iron phosphate cathode material from the current collector.

[0087] (3) Filter the mixture of lithium iron phosphate cathode material from which the current collector was removed in step 2 using a Buchner funnel to separate the solid from the filtrate and collect the filter residue.

[0088] (4) Place the filter residue obtained in step 3 into an oven and dry it at 70°C for 18 hours to obtain dried lithium iron phosphate fragments.

[0089] (5) The dried lithium iron phosphate fragments obtained in step 4 were loaded into a horizontal polytetrafluoroethylene ball mill jar, zirconium balls were added, and the ball mill jar was placed on a ball mill and milled at 400 rpm for 360 min to obtain lithium iron phosphate electrode powder I. The carbon content in the lithium iron phosphate electrode powder I was measured to be greater than 3% by a carbon-sulfur analyzer.

[0090] (6) The lithium iron phosphate electrode powder I after ball milling in step 5 was placed in a crucible and placed in a tube furnace and nitrogen was introduced. After 120 min, the tube furnace was heated to 450 °C at a heating rate of 5 °C / min. After the heating was completed, the nitrogen was replaced with air and introduced into the tube furnace to calcine the sample at 450 °C for 20 min. Then the air was replaced with nitrogen and introduced into the tube furnace to continue calcining the sample at 450 °C for 240 min.

[0091] (7) Take out the lithium iron phosphate electrode powder I after calcination in step 6 and pour it into a horizontal polytetrafluoroethylene ball mill jar. Add zirconium balls and place the ball mill jar on a ball mill. Mill at 400 rpm for 360 min to obtain lithium iron phosphate electrode powder II. The carbon content in the lithium iron phosphate electrode powder II was measured to be 1.8% by a carbon-sulfur analyzer. At the same time, the XRD test results showed that Li3Fe2(PO4)3 and Fe2O3 were generated in the lithium iron phosphate electrode powder II. Since the amount of Fe2O3 was very small, it was not obvious in the XRD pattern.

[0092] (8) The electrode powder II after ball milling in step 7 is placed in a crucible and placed in a tube furnace and nitrogen is introduced. After 120 min, the tube furnace is heated to 600℃ at a heating rate of 5℃ / min and calcined for 240 min to obtain the repaired lithium iron phosphate cathode material.

[0093] (9) Place the repaired lithium iron phosphate cathode powder obtained in step 8 into an 80-mesh sieve and sieve it through a vibrating sieve to collect the sieve material.

[0094] (10) The carbon content in the sieved lithium iron phosphate cathode powder obtained in step 9 was 1.2% as measured by a carbon-sulfur analyzer.

[0095] Example 4

[0096] A method for direct repair and regeneration of lithium iron phosphate cathode materials after carbon removal includes the following specific steps:

[0097] (1) Cut the waste lithium iron phosphate electrode sheets into pieces of 2cm x 2cm using scissors.

[0098] (2) Put the broken electrode pieces cut in step 1 into a beaker, add water at 60°C and soak for 30 minutes, then completely separate the lithium iron phosphate cathode material from the current collector.

[0099] (3) The mixture of lithium iron phosphate cathode material from which the current collector was removed in step 2 was filtered by Buchner funnel to separate the solid from the filtrate and take filter residue I.

[0100] (4) Place the filter residue I obtained in step 3 into an oven and dry it at 50°C for 24 hours to obtain dried lithium iron phosphate fragments.

[0101] (5) The dried lithium iron phosphate fragments obtained in step 4 were placed into a ball mill jar, and zirconium balls with a ball-to-material ratio of 5:1 were added to the ball mill jar. The jar was then placed on a planetary ball mill and milled at 400 rpm for 120 min to obtain lithium iron phosphate electrode powder I. The carbon content in the lithium iron phosphate electrode powder I was found to be greater than 3% by a carbon-sulfur analyzer, and the Fe content in the lithium iron phosphate electrode powder I was determined by titration. 3+ Content less than 1%.

[0102] (6) Take 158g of the lithium iron phosphate electrode powder I after ball milling in step 5 and put it into a beaker. Place the beaker in a water bath at 25°C and slowly add 68g of hydrogen peroxide with a mass fraction of 10%. Stop the reaction after 20 minutes.

[0103] (7) Filter the compound obtained in step 6 using a Buchner funnel, wash the filter residue with deionized water in small amounts several times, rinse the hydrogen peroxide in the lithium iron phosphate electrode powder and take filter residue II.

[0104] (8) Place the filter residue II obtained in step 7 into an oven and dry it at 80°C for 8 hours. The Fe content in the filter residue II is then determined by titration. 3+ Content greater than 3%.

[0105] (9) The dried filter residue II obtained in step 8 is loaded into a ball mill jar, zirconium balls with a ball-to-material ratio of 5:1 are added into the ball mill jar, and the ball mill jar is then placed on a planetary ball mill and ball milled at 400 rpm for 60 min to obtain lithium iron phosphate electrode powder II.

[0106] (10) The lithium iron phosphate electrode powder II after ball milling in step 9 is placed in a crucible and placed in a tube furnace and inert gas is introduced. After 30 minutes, the tube furnace is heated to 400°C at a heating rate of 5°C / min for 60 minutes, and then heated to 550°C for 120 minutes to obtain the repaired and regenerated lithium iron phosphate powder.

[0107] XRD analysis was performed on lithium iron phosphate electrode powder treated with hydrogen peroxide. The XRD pattern is shown below. Figure 5 The lithium iron phosphate electrode powder treated with hydrogen peroxide showed only the LiFePO4 crystal form, with no other crystal forms appearing. However, titration tests indicated that the lithium iron phosphate electrode powder contained Fe. 3+ The content increased significantly, indicating that the trivalent iron in the lithium iron phosphate electrode powder treated with hydrogen peroxide exists in an amorphous form. XRD analysis was performed on the lithium iron phosphate electrode powder after reduction calcination; the XRD pattern is shown below. Figure 6 As shown, the lithium iron phosphate electrode powder after reduction and calcination only showed the LiFePO4 crystal form, with no other impurity crystal forms appearing.

[0108] Example 5

[0109] A method for direct repair and regeneration of lithium iron phosphate cathode materials after carbon removal includes the following specific steps:

[0110] (1) Cut the waste lithium iron phosphate electrode sheets into pieces of 2cm x 2cm using scissors.

[0111] (2) Put the broken electrode pieces cut in step 1 into a beaker, add water at 40°C and soak for 80 minutes, then completely separate the lithium iron phosphate cathode material from the current collector.

[0112] (3) The mixture of lithium iron phosphate cathode material from which the current collector was removed in step 2 was filtered by Buchner funnel to separate the solid from the filtrate and take filter residue I.

[0113] (4) Place the filter residue I obtained in step 3 into an oven and dry it at 60°C for 18 hours to obtain dried lithium iron phosphate fragments.

[0114] (5) The dried lithium iron phosphate fragments obtained in step 4 were loaded into a ball mill jar, and zirconium balls with a ball-to-material ratio of 10:1 were added to the ball mill jar. The jar was then placed on a planetary ball mill and milled at 400 rpm for 60 min to obtain lithium iron phosphate electrode powder I. The carbon content in the lithium iron phosphate electrode powder I was found to be greater than 3% by a carbon-sulfur analyzer, and the Fe content in the lithium iron phosphate electrode powder I was found to be greater than 3% by titration. 3+ Content less than 1%.

[0115] (6) Take 79g of the lithium iron phosphate electrode powder I after ball milling in step 5 and put it into a beaker. Place the beaker in a water bath at 70°C and slowly add an appropriate amount of 85g of hydrogen peroxide with a mass fraction of 10%. Stop the reaction after 25 minutes.

[0116] (7) Filter the compound obtained in step 6 using a Buchner funnel, wash the filter residue with deionized water in small amounts several times, rinse the hydrogen peroxide in the lithium iron phosphate electrode powder and take filter residue II.

[0117] (8) Place the filter residue II obtained in step 7 into an oven and dry it at 80°C for 5 hours. The Fe content in the filter residue II is then determined by titration. 3+ Content greater than 3%.

[0118] (9) The dried filter residue II obtained in step 8 is loaded into a ball mill jar, zirconium balls with a ball-to-material ratio of 10:1 are added into the ball mill jar, and the ball mill jar is then placed on a planetary ball mill and ball-milled at 400 rpm for 360 min to obtain lithium iron phosphate electrode powder II.

[0119] (10) The lithium iron phosphate electrode powder II after ball milling in step 9 is placed in a crucible and placed in a tube furnace and inert gas is introduced. After 90 min, the tube furnace is heated to 450°C at a heating rate of 5°C / min for 120 min, and then heated to 600°C for 180 min to obtain the repaired and regenerated lithium iron phosphate powder.

[0120] Example 6

[0121] A method for direct repair and regeneration of lithium iron phosphate cathode materials after carbon removal includes the following specific steps:

[0122] (1) Cut the waste lithium iron phosphate electrode sheets into pieces of 2cm x 2cm using scissors.

[0123] (2) Put the broken electrode pieces cut in step 1 into a beaker, add water at 100°C and soak for 10 minutes, then completely separate the lithium iron phosphate cathode material from the current collector.

[0124] (3) The mixture of lithium iron phosphate cathode material from which the current collector was removed in step 2 was filtered by Buchner funnel to separate the solid from the filtrate and take filter residue I.

[0125] (4) Place the filter residue I obtained in step 3 into an oven and dry it at 90°C for 10 hours to obtain dried lithium iron phosphate fragments.

[0126] (5) The dried lithium iron phosphate fragments obtained in step 4 were loaded into a ball mill jar, and zirconium balls with a ball-to-material ratio of 20:1 were added to the ball mill jar. The jar was then placed on a planetary ball mill and milled at 400 rpm for 240 min to obtain lithium iron phosphate electrode powder I. The carbon content in the lithium iron phosphate electrode powder I was found to be greater than 3% by a carbon-sulfur analyzer, and the Fe content in the lithium iron phosphate electrode powder I was determined by titration. 3+ Content less than 1%.

[0127] (6) Take 316g of the lithium iron phosphate electrode powder I after ball milling in step 5 and put it into a beaker. Place the beaker in a water bath at 50°C and slowly add 170g of hydrogen peroxide with a mass fraction of 10%. Stop the reaction after 40 minutes.

[0128] (7) Filter the compound obtained in step 6 using a Buchner funnel, wash the filter residue with deionized water in small amounts several times, rinse the hydrogen peroxide in the lithium iron phosphate electrode powder and take filter residue II.

[0129] (8) Place the filter residue II obtained in step 7 into an oven and dry it at 70°C for 10 hours. The Fe content in the filter residue II is then determined by titration. 3+ Content greater than 3%.

[0130] (9) The dried filter residue II obtained in step 8 is loaded into a ball mill jar, zirconium balls with a ball-to-material ratio of 20:1 are added into the ball mill jar, and the ball mill jar is then placed on a planetary ball mill and ball-milled at 400 rpm for 360 min to obtain lithium iron phosphate electrode powder II.

[0131] (10) The lithium iron phosphate electrode powder II after ball milling in step 9 is placed in a crucible and placed in a tube furnace and inert gas is introduced. After 120 min, the tube furnace is heated to 500°C at a heating rate of 5°C / min for 60 min, and then heated to 700°C for 240 min to obtain the repaired and regenerated lithium iron phosphate powder.

[0132] Comparative Example 1

[0133] The difference from Example 1 is as follows:

[0134] The lithium iron phosphate electrode powder after ball milling in step 5 was placed in a crucible and placed in a tube furnace and nitrogen was introduced. After 120 min, the tube furnace was heated to 600 °C at a heating rate of 5 °C / min. After the heating was completed, the nitrogen was replaced with air and calcined for 120 min. After the experiment, the carbon-sulfur analyzer did not detect the presence of carbon in the calcined lithium iron phosphate electrode powder.

[0135] XRD analysis was performed on lithium iron phosphate electrode powder that had been air-calcined for 120 min. The XRD pattern is shown below. Figure 7 As shown, the lithium iron phosphate electrode powder calcined in air for 120 min exhibits Li3Fe2(PO4)3 and Fe2O3 crystal forms, with no LiFePO4 crystal form detected. This indicates that during the carbon removal process of air calcination for 120 min, LiFePO4 was completely oxidized and decomposed into Li3Fe2(PO4)3 and Fe2O3.

[0136] Comparative Example 2

[0137] Similar to the steps in Example 1, the only difference is that the air roasting temperature during the first stage of roasting is 600°C, resulting in the lithium iron phosphate electrode powder being over-oxidized after the first stage of roasting.

[0138] Comparative Example 3

[0139] Similar to the steps in Example 1, the only difference is that the air roasting time during the first stage of roasting is 35 minutes, resulting in the lithium iron phosphate electrode powder being over-oxidized after the first stage of roasting.

[0140] Comparative Example 4

[0141] Similar to the steps in Example 1, the only difference is that the calcination temperature during the second stage of calcination is 450°C. As a result, a small amount of Li3Fe2(PO4)3 in the lithium iron phosphate electrode powder after the second stage of calcination was not reduced back to LiFePO4.

[0142] Comparative Example 5

[0143] Similar to the steps in Example 1, the only difference is that the calcination temperature during the second stage of calcination is 800°C, and the result is that some LiFePO4 in the lithium iron phosphate electrode powder after the second stage of calcination decomposes into Li3PO4 and Fe2P.

[0144] Comparative Example 6

[0145] Similar to the steps in Example 1, the only difference is that the roasting time in the second stage is 90 minutes. The result is that a small amount of Li3Fe2(PO4)3 in the lithium iron phosphate electrode powder after the second stage roasting was not reduced back to LiFePO4.

[0146] Comparative Example 7

[0147] The difference from Example 4 is that in step (6), the beaker is placed in a water bath at 25°C and 10g of hydrogen peroxide with a mass fraction of 10% is slowly added to it, and the reaction is stopped after 20 minutes.

[0148] Comparative Example 8

[0149] The difference from Example 4 is that in step (6), the beaker is placed in a water bath at 25°C and 340g of hydrogen peroxide with a mass fraction of 10% is slowly added to it, and the reaction is stopped after 60 minutes.

[0150] Test Results

[0151] Finished product quality of Examples 1-6 and Comparative Examples 1 and 7-8

[0152] Table 1 shows the main element content (specific data obtained by ICP-AES equipment), ferric iron content (specific data obtained indirectly by titrating total iron content and ferrous iron content), and carbon content (specific data obtained by carbon-sulfur analyzer equipment) of the lithium iron phosphate cathode material products prepared in Examples 1-6 and Comparative Examples 1 and 7-8.

[0153] Table 1 Elemental Content

[0154]

[0155]

[0156] As shown in Table 1, the main elements, ferric iron and carbon content, in the lithium iron phosphate prepared in the examples are all normal, meeting the industrial production standards for lithium iron phosphate batteries. In Comparative Example 1, during the carbon removal process of air calcination for 120 min, LiFePO4 was completely oxidized and decomposed into Li3Fe2(PO4)3 and Fe2O3, with almost all iron existing in the form of ferric iron. Simultaneously, the carbon content detected by the carbon-sulfur analyzer was less than 0.1%. In Comparative Example 7, the amount of hydrogen peroxide used was small, resulting in less oxidation of the lithium iron phosphate cathode material and less carbon consumption during subsequent reduction. The repaired lithium iron phosphate cathode material still contained a large amount of carbon, failing to achieve the purpose of carbon removal. In Comparative Example 8, when the amount of hydrogen peroxide was too high, most of the lithium iron phosphate cathode material was oxidized, requiring a large amount of reducing agent. Therefore, the repaired lithium iron phosphate cathode material contained a small amount of carbon, but because most of the lithium iron phosphate cathode material was oxidized into other compounds, its electrochemical performance was significantly reduced accordingly.

[0157] Electrochemical performance:

[0158] Table 2 shows the electrochemical performance of lithium iron phosphate batteries prepared in Examples 1-6 and Comparative Examples 1 and 7-8. The specific data were obtained by testing with equipment such as an electrochemical workstation.

[0159] Table 2 Electrochemical Performance

[0160]

[0161]

[0162] As shown in Table 2, the lithium iron phosphate products obtained through two-stage roasting in Examples 1-3, after carbon removal and regeneration, have a charging capacity of 159.7 mAh / g and an initial charge-discharge efficiency of 94.9%. The lithium iron phosphate products obtained through hydrogen peroxide oxidation followed by roasting in Examples 4-6, after carbon removal and regeneration, have a charging capacity of 158.6 mAh / g and an initial charge-discharge efficiency of 94.5%. It is evident that the lithium iron phosphate cathode materials recovered using the two methods provided in the embodiments of this invention both exhibit excellent electrochemical performance.

[0163] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for repairing and regenerating lithium iron phosphate cathode materials, characterized in that, include: Lithium iron phosphate (LiFePO4) cathode material is obtained by stripping waste LiFePO4 electrode sheets. In an air atmosphere, the LiFePO4 cathode material is oxidized through a single-stage roasting process to partially oxidize the LiFePO4. The single-stage roasting process includes: placing the stripped LiFePO4 cathode material in an air atmosphere and roasting it at 300-500°C for 5-30 minutes; then replacing the air with an inert gas and continuing the roasting process for 60-240 minutes. The process involves: 1) Reducing the oxidized lithium iron phosphate by using excess carbon in the lithium iron phosphate cathode material in a two-stage high-temperature roasting process (500-750℃), thereby achieving carbon removal, repair, and regeneration of the lithium iron phosphate cathode material; or 2) Obtaining lithium iron phosphate cathode material by peeling off waste lithium iron phosphate electrode sheets, oxidizing the lithium iron phosphate cathode material with hydrogen peroxide to partially oxidize the lithium iron phosphate, and then reducing the oxidized lithium iron phosphate by using excess carbon in the lithium iron phosphate cathode material in a high-temperature process (the reduction includes: placing the oxidized lithium iron phosphate in an inert gas atmosphere, pre-calcining at 400-500℃ for 60-180 min, and then roasting at 550-700℃ for 120-240 min), thereby achieving carbon removal, repair, and regeneration of the lithium iron phosphate cathode material.

2. The method according to claim 1, characterized in that, Includes the following steps: After soaking the waste lithium iron phosphate electrode sheets in solvent to remove the current collector, they are dried and ground to obtain lithium iron phosphate electrode sheet powder I. The lithium iron phosphate electrode sheet powder I is placed in an air atmosphere and calcined at 300-500℃ for 5-30 min. Then the air is replaced with an inert gas and calcined for another 60-240 min to complete the first stage of calcination. The product obtained from the first stage of calcination is taken out and ground to obtain lithium iron phosphate electrode powder II. The lithium iron phosphate electrode powder II is placed in an inert gas atmosphere and calcined at 500-750℃ for 120-420 min to complete the second stage of calcination, and finally the repaired lithium iron phosphate cathode material is obtained.

3. The method according to claim 2, characterized in that, Also includes: Before calcination, either lithium iron phosphate electrode powder I or lithium iron phosphate electrode powder II is first loaded into a crucible, the crucible is placed in a tube furnace and inert gas is introduced. After 60-120 minutes, the tube furnace is heated to the set temperature at a heating rate of 2-5℃ / min, and then calcination is carried out.

4. The method according to claim 1, characterized in that, Includes the following steps: After soaking and removing the current collector from the waste lithium iron phosphate electrode sheets in a solvent, the sheets are dried and ground to obtain lithium iron phosphate electrode powder I. Hydrogen peroxide is added dropwise to the lithium iron phosphate electrode powder I to partially oxidize the lithium iron phosphate. The reaction is stopped after 20-40 minutes. The oxidized product is taken out, washed, dried, and then ground to obtain lithium iron phosphate electrode powder II. The lithium iron phosphate electrode powder II is placed in an inert gas atmosphere and pre-calcined at 400-500℃ for 60-180 minutes, and then calcined at 550-700℃ for 120-240 minutes to finally obtain the repaired lithium iron phosphate cathode material.

5. The method according to claim 4, characterized in that, The oxidation reaction temperature is 25-70℃, and the molar ratio of hydrogen peroxide in the hydrogen peroxide solution to lithium iron phosphate electrode powder I is 0.2-1.2:

1.

6. The method according to claim 5, characterized in that, The hydrogen peroxide has a mass fraction of 10%.

7. The method according to claim 2 or 4, characterized in that, The grinding speed is 350-450 rpm, and the time is 120-360 min.

8. The method according to claim 2 or 4, characterized in that, The lithium iron phosphate electrode powder I is obtained through the following steps: cutting waste lithium iron phosphate electrode sheets into fragments, soaking them in water to separate the lithium iron phosphate cathode material from the current collector, filtering the mixture of lithium iron phosphate cathode material after removing the current collector to obtain filtrate and filter residue, drying and grinding the filter residue to obtain lithium iron phosphate electrode powder I with a carbon content of 3-5 wt%.

9. The method according to claim 8, characterized in that, The lithium iron phosphate fragments were soaked in water at a temperature of 25-100℃ for 10-60 min, the filter residue was dried at a temperature of 50-100℃ for 4-48 h, and the filter residue was ground at a speed of 350-450 rpm for 120-360 min.

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