Method for regenerating waste lithium iron phosphate into lithium manganese iron phosphate positive electrode material under assistance of element doping

Abstract

The invention discloses a method for regenerating waste lithium iron phosphate into a lithium manganese iron phosphate positive electrode material under assistance of element doping. According to the method, the waste lithium iron phosphate is successfully regenerated into the lithium manganese iron phosphate material with excellent performance through solid-phase sintering and element doping. Compared with a traditional repairing and regenerating method, the method has the advantages that upgrading and regenerating of the waste lithium iron phosphate are realized, and the market competitiveness of regenerated products is improved. Compared with other methods, the method does not need an acid leaching step, and the recovery process is simpler and more environment-friendly. And an element doping modification means is introduced, so that the performance of the regenerated lithium manganese iron phosphate material is further improved. The invention aims to provide a green, efficient and high-valued method for upgrading and regenerating the waste lithium iron phosphate positive electrode material into the lithium iron manganese phosphate positive electrode material with industrial application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of recycling of waste lithium-ion batteries and recycling of electrode materials, and particularly relates to a method for regenerating waste lithium iron phosphate into lithium iron manganese phosphate cathode material assisted by element doping. Background Art

[0002] The new energy vehicle industry has developed rapidly. As its core power source, the output of lithium-ion power batteries has increased explosively. The LiFePO4 (LFP) battery has the advantages of low cost, good thermal stability, excellent cycle performance, etc., so its market share has exceeded that of nickel-cobalt-manganese ternary batteries. The LFP battery has a service life of only 5-8 years, and a large number of retired LFP batteries will be generated in the future. Reasonably recycling waste lithium-ion batteries can not only create economic benefits but also protect the environment. Industrially, waste lithium iron phosphate cathode material is generally recycled by hydrometallurgy. Hydrometallurgy has a high recovery rate, but has the disadvantages of long process, low efficiency, and the need to use chemical reagents such as strong acids and strong alkalis, which affect the environment. The structure of lithium iron phosphate is stable, and the main reason for the performance failure after cycling is the lack of active lithium. Therefore, direct lithium supplementation and repair regeneration of waste lithium iron phosphate cathode material have become a current research hotspot.

[0003] The methods for directly repairing and regenerating waste lithium iron phosphate cathode material mainly include high-temperature solid-phase method and hydrothermal method. The solid-phase method is to mix the waste lithium iron phosphate cathode material with an organic carbon source and a lithium salt evenly, and then realize the repair of waste lithium iron phosphate through calcination. The liquid-phase method is to disperse the waste lithium iron phosphate cathode material in a solution containing a reducing agent and lithium ions, and repair the waste lithium iron phosphate through hydrothermal treatment. The performance of the lithium iron phosphate cathode material repaired by the two methods has been significantly improved compared with that of the waste cathode material, but there may still be a gap compared with the brand-new lithium iron phosphate cathode material. At the same time, the disadvantage of the lithium iron phosphate cathode material in terms of energy density also limits its further development. The lithium iron manganese phosphate cathode material also has the advantages of low cost and excellent safety performance. Compared with the lithium iron phosphate cathode material, the addition of manganese increases the charge and discharge voltage of the material, improving the energy density, and is considered an upgraded version of lithium iron phosphate. Therefore, if the waste lithium iron phosphate cathode material can be directly repaired and regenerated into lithium iron manganese phosphate cathode material, it will not only greatly improve the competitiveness of the regenerated product in the market but also strongly promote the vigorous development of the waste lithium-ion battery recycling industry. The lithium iron manganese phosphate cathode material also has problems such as poor conductivity, poor rate performance, and poor stability, and the performance of the lithium iron manganese phosphate cathode material can be improved by element doping of the material.

[0004] The Chinese patent with the publication number CN11977038A in the prior art discloses a method for recycling waste lithium iron phosphate cathode materials into lithium manganese iron phosphate cathode materials. The waste lithium iron phosphate cathode materials are completely dissolved in an acid to obtain a leaching solution. Manganese salts, phosphoric acid, and lithium salts are added to the leaching solution and mixed evenly, followed by spray drying and solid-phase sintering under an inert atmosphere to obtain lithium manganese iron phosphate cathode materials. This method can successfully convert waste lithium iron phosphate cathode materials into lithium manganese iron phosphate cathode materials. However, this method has a long process. It is necessary to completely dissolve the waste powder in the leaching solution, which consumes a large amount of time. Moreover, the introduction of acid will also lead to an increase in cost and the generation of a large amount of wastewater, affecting the environment. Therefore, there is an urgent need to explore an efficient and green method that can convert waste lithium iron phosphate cathode materials into lithium manganese iron phosphate cathode materials. This method should have the advantage of low cost and does not require the use of acid chemical reagents during the conversion process.

[0005] Currently, more and more researchers are focusing on how to repair and regenerate waste lithium iron phosphate cathode materials into lithium manganese iron phosphate cathode materials in a green and efficient manner. The Chinese patent with the publication number CN119284856A in the prior art discloses a method for rapidly upgrading and regenerating lithium manganese iron phosphate from waste lithium iron phosphate powder. By adding an oxidant during the leaching process, the acid leaching efficiency is improved, and the use of acid is reduced. However, acids and other reagents are still used in the regeneration process of this method, and the performance of the obtained lithium manganese iron phosphate is average. Summary of the Invention

[0006] The purpose of the present invention is to solve the deficiencies in the repair and regeneration of existing waste lithium iron phosphate. Specifically, for the main problems existing in the repair and regeneration of waste lithium iron phosphate, the present application provides a green, efficient, high-value, and industrially applicable method for upgrading and regenerating waste lithium iron phosphate cathode materials into lithium manganese iron phosphate cathode materials. In the present application, a self-made eluent is used to separate the electrode sheet. This eluent can react quickly with the surface of the current collector aluminum foil to generate Al 3+ and bubbles, causing the waste active material to lose adhesion to the current collector and achieving separation. Moreover, the eluent can passivate the material surface and inhibit the dissolution of the material. Compared with traditional separation methods, it can achieve separation in a green and efficient manner, and successfully obtain waste lithium iron phosphate cathode materials with less impurity content and complete structure. After the obtained waste lithium iron phosphate cathode materials are refined by ball milling, different from other methods, this method does not require the use of acid to leach the waste lithium iron phosphate cathode materials. Instead, it is directly mixed evenly with manganese salts, phosphorus sources, lithium salts, etc. by ball milling, and then regenerated lithium manganese iron phosphate cathode materials can be obtained through solid-phase sintering.

[0007] In addition, this method innovatively abandons the traditional step of leaching waste lithium iron phosphate cathode materials with reagents such as acids during the recycling and regeneration process, shortens the repair and regeneration process, and reduces the environmental impact of the recycling process. At the same time, the modification method of element doping is introduced during the repair and regeneration process. By means of element doping, the performance of recycled lithium manganese iron phosphate is improved, the market competitiveness of the recycled products is enhanced, and it provides the possibility of industrial application for the regeneration of waste lithium iron phosphate cathode materials into lithium manganese iron phosphate cathode materials.

[0008] To achieve the above object, the present invention is implemented by the following technical solutions:

[0009] A method for element doping to assist the regeneration of waste lithium iron phosphate into lithium manganese iron phosphate cathode materials, comprising the following steps:

[0010] S1. Place the waste lithium iron phosphate cathode plate in an eluent for elution, ball mill and refine it, and sieve to obtain waste active material powder;

[0011] S2. Mix the ball-milled and refined waste active material powder with a lithium source, a phosphorus source, a manganese source, a carbon source, and an element dopant evenly by ball milling to obtain a precursor powder;

[0012] S3. Sinter the precursor powder in two stages under a certain atmosphere condition, and cool it to room temperature to obtain the recycled lithium manganese iron phosphate cathode material.

[0013] Preferably, S1 is specifically: cut the waste lithium iron phosphate cathode plate and transfer it to an eluent for elution to separate the waste active material from the current collector, air-dry the separated waste active material, and then refine it by planetary ball milling to obtain waste active material powder.

[0014] Preferably, the eluent is made by diluting one or two of phytic acid, ferric phytate, and ferric acetate in deionized water to a pH between 6 and 7.

[0015] Preferably, the heating temperature of the elution is 60°C - 80°C, the soaking time of the elution is 2 - 5 min, the solid-liquid ratio of the waste lithium iron phosphate cathode plate to the eluent is 50 - 100 g / L, the drying temperature is 80 - 120°C, the drying time is 10 - 12 h, the ball-to-material ratio of the ball milling is 10 - 30:1, the ball milling speed is 250 - 400 rpm, and the ball milling time is 6 - 10 h.

[0016] Preferably, S2 is specifically as follows: The ball-milled and refined waste lithium iron phosphate powder is subjected to ICP-OES testing. According to the content of each element in the waste lithium iron phosphate powder and the required element molar ratio of the target product, the addition amounts of the lithium salt, manganese salt, phosphorus source, carbon source, and element dopant are determined. The waste lithium iron phosphate powder, lithium source, phosphorus source, manganese source, carbon source, and element dopant are added to a ball-milling tank, a grinding aid is added, and they are mixed evenly by wet ball milling. After air drying, a lithium iron manganese phosphate precursor powder is obtained.

[0017] Preferably, the lithium salt is one or two of lithium hydroxide, lithium carbonate, and lithium oxalate; the manganese salt is one or two of manganese carbonate, manganese acetate, and manganese oxide; the phosphorus source is one or two of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid. The specific addition amounts of the lithium source, manganese source, and phosphorus source are related to the ICP-OES test results of the waste lithium iron phosphate. The added amounts need to ensure that the molar ratio of Li:Fe + Mn:P is 1:1:1. The carbon source is one or any combination of glucose, sucrose, and citric acid, and the addition amount is 2 - 8 wt%. The element dopant is one or any combination of zirconia, titanium oxide, nickel oxide, and alumina, and the addition amount is 1 - 3 mol%. The grinding aid is any one of ethanol, deionized water, and acetone.

[0018] Preferably, in S2, the ball-to-material ratio for ball milling is 10 - 20:1, the ball milling speed is 250 - 400 rpm, the ball milling time is 8 - 12 h, the temperature for air drying is 60 - 120 °C, and the drying time is 8 - 12 h.

[0019] Preferably, in S3, the sintering atmosphere is any one of argon, nitrogen, and hydrogen-argon mixture. The first-stage sintering temperature is 350 - 450 °C, the heat preservation time is 2 - 6 h, the second-stage sintering temperature is 650 - 750 °C, and the heat preservation time is 8 - 12 h.

[0020] The prepared recycled lithium iron manganese phosphate cathode material has excellent cycle stability and excellent rate performance.

[0021] After the present invention adopts the above method, compared with the prior art, the advantages are as follows:

[0022] 1) Compared with the traditional direct repair of waste lithium iron phosphate cathode materials, it can greenly and efficiently realize the upgrading and recycling of waste lithium iron phosphate, and the obtained lithium iron manganese phosphate material is more competitive in the market.

[0023] 2) Compared with other methods for recycling waste lithium iron phosphate cathode materials into lithium iron manganese phosphate cathode materials, acids are not required for leaching the waste cathode materials during the recycling process. The recycling process is short, the recycling efficiency is high, and acids are not needed, reducing the generation of wastewater and alleviating the environmental impact during the recycling process.

[0024] 3) In the recycling process, the modification method of element doping is introduced. By means of element doping, the electrochemical performance of the recycled lithium iron phosphate manganese cathode material is effectively improved, making it have more excellent rate performance and cycle stability. Description of the Drawings

[0025] Figure 1 It is a picture of the current collector aluminum foil and the flaky active powder obtained by soaking and separating the pole piece in Example 1 with an eluent.

[0026] Figure 2 It is a picture of the waste lithium iron phosphate powder before and after ball milling and refinement.

[0027] Figure 3 It is an XRD comparison chart of the XRD patterns of the recycled lithium iron phosphate manganese in Example 1, waste lithium iron phosphate, and standard lithium iron phosphate.

[0028] Figure 4 It is an SEM image of the recycled lithium iron phosphate manganese in Example 1.

[0029] Figure 5 It is the first charge-discharge curve graph of the lithium-ion battery made of the recycled lithium iron phosphate manganese material in Example 1 and waste lithium iron phosphate at a rate of 0.1C.

[0030] Figure 6 It is an XRD comparison chart of the XRD patterns of the recycled lithium iron phosphate manganese in Example 2 of the present invention, waste lithium iron phosphate, and standard lithium iron phosphate.

[0031] Figure 7 It is a comparison chart of the first charge-discharge curves of the lithium-ion batteries made of the recycled lithium iron phosphate manganese in Example 2 and waste lithium iron phosphate at a rate of 0.1C.

[0032] Figure 8 It is an XRD comparison chart of the XRD patterns of the recycled lithium iron phosphate manganese in Example 3 of the present invention, waste lithium iron phosphate, and standard lithium iron phosphate.

[0033] Figure 9 It is a comparison chart of the first charge-discharge curves of the lithium-ion batteries made of the recycled lithium iron phosphate manganese in Example 3 and waste lithium iron phosphate at a rate of 0.1C. Figure 10 It is an XRD comparison chart of the XRD patterns of the recycled lithium iron phosphate manganese in Comparative Example 1, waste lithium iron phosphate, and standard lithium iron phosphate.

[0034] Figure 11 It is a comparison chart of the rate performance of the lithium-ion batteries made of the recycled lithium iron phosphate manganese in Comparative Example 1 and the recycled lithium iron phosphate manganese in Example 1.

[0035] Figure 12XRD comparison chart of regenerated lithium iron manganese phosphate, waste lithium iron phosphate, and standard lithium iron phosphate spectra for Comparative Example 2.

[0036] Figure 13 Cycling performance chart of lithium-ion batteries made from regenerated lithium iron manganese phosphate of Comparative Example 2 and regenerated lithium iron manganese phosphate of Example 2 after 3 activation cycles at 0.1C rate and 100 cycles at 1C rate.

[0037] Figure 14 Process flow chart of the present invention. Detailed implementation manners

[0038] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0039] Unless otherwise specified, various reagents and raw materials used in the present invention are commercially available products purchased from the market or products that can be obtained by well-known methods.

[0040] Refer to Figure 14 As shown, a method for regenerating waste lithium iron phosphate into a lithium iron manganese phosphate cathode material assisted by element doping according to the present invention includes the following steps:

[0041] S1. Cut the waste lithium iron phosphate cathode plate and transfer it to an eluent for elution to separate the waste active material from the current collector. The separated waste active material is dried by blowing air, and then refined by planetary ball milling to obtain waste active material powder.

[0042] Among them, the eluent is prepared by diluting one or two of phytic acid, ferric phytate, and ferric acetate in deionized water to a pH between 6 and 7. The heating temperature of the elution is 60 - 80°C, the soaking time of the elution is 2 - 5 min, the solid-liquid ratio of the waste lithium iron phosphate cathode plate to the eluent is 50 - 100 g / L, the drying temperature is 80 - 120°C, the drying time is 10 - 12 h, the ball-to-material ratio of the ball milling is 10 - 30:1, the rotation speed of the ball milling is 250 - 400 rpm, and the ball milling time is 6 - 10 h.

[0043] S2. Perform ICP-OES testing on the obtained ball-milled and refined waste lithium iron phosphate powder. According to the content of each element in the waste lithium iron phosphate powder and the required element molar ratio of the target product, determine the addition amounts of lithium salt, manganese salt, phosphorus source, carbon source, and element dopant. This is common knowledge in the art and will not be elaborated here. Add the waste lithium iron phosphate powder, lithium source, phosphorus source, manganese source, carbon source, and element dopant into a ball-milling jar, add a grinding aid, and mix evenly by wet ball milling. After blowing and drying, obtain the lithium manganese iron phosphate precursor powder.

[0044] Among them, the lithium salt is one or two of lithium hydroxide, lithium carbonate, and lithium oxalate; the manganese salt is one or two of manganese carbonate, manganese acetate, and manganese oxide; the phosphorus source is one or two of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and phosphoric acid; the specific addition amounts of the lithium source, manganese source, and phosphorus source are related to the ICP-OES test results of the waste lithium iron phosphate, and the added amounts need to ensure that the molar ratio of Li:Fe+Mn:P is 1:1:1; the carbon source is one or any combination of glucose, sucrose, and citric acid, and the addition amount is 2-8 wt%; the element dopant is one or any combination of zirconia, titanium oxide, nickel oxide, and alumina, and the addition amount is 1-3 mol%; the grinding aid is any one of ethanol, deionized water, and acetone.

[0045] The ball-to-material ratio for ball milling is 8-20:1, the ball milling speed is 250-400 rpm, the ball milling time is 8-12 h, the temperature for blowing and drying is 60-120 °C, and the drying time is 8-12 h.

[0046] S3. Sinter the precursor powder in a certain atmosphere condition through two-stage sintering, and cool it to room temperature to obtain the regenerated lithium manganese iron phosphate cathode material.

[0047] Among them, in S3, the sintering atmosphere is any one of argon, nitrogen, and hydrogen-argon mixture; the first-stage sintering temperature is 350-450 °C, the holding time is 2-6 h, the second-stage sintering temperature is 650-750 °C, and the holding time is 8-12 h.

[0048] Example 1

[0049] The eluent used in this example is phytic acid, the lithium salt is lithium carbonate, the manganese salt is manganese carbonate, the phosphorus source is ammonium dihydrogen phosphate, the carbon source is glucose, and the element dopant is nano-zirconia. The performance of the regenerated lithium manganese iron phosphate cathode material is improved by zirconium element doping. The chemical formula of the regenerated lithium manganese iron phosphate cathode material obtained is LiMn 0.37 Fe 0.6 Zr 0.015 PO4, and the specific steps are as follows:

[0050] (1) Prepare the eluent. Take an appropriate amount of phytic acid, add deionized water until the pH of the solution is 6.5, then cut the waste lithium iron phosphate cathode sheet, place it in a beaker and add the eluent. The solid-liquid ratio is 80 g / L. Place the beaker in an oil bath and heat it to 80 °C for 2 minutes to completely separate the active material from the sheet, obtaining sheet-like active material.

[0051] (2) Place the sheet-like active material in a blast drying oven at 80 °C for 12 hours. After drying, place the waste lithium iron phosphate in a ball mill jar with a ball-to-material ratio of 20:1, a ball milling speed of 350 rpm, and a ball milling time of 8 hours to obtain the refined waste lithium iron phosphate cathode material.

[0052] (3) Conduct ICP-OES testing on the waste lithium iron phosphate cathode material. ICP-OES is an inductively coupled plasma optical emission spectrometer. According to the test results and the stoichiometric ratios of the elements in the target product LiMn 0.37 Fe 0.6 Zr 0.015 PO4, add manganese carbonate, lithium carbonate, ammonium dihydrogen phosphate, zirconium oxide, and add 5 wt% of glucose as a carbon source. The addition amount of the dopant is 1.5 mol%. Add the raw materials to a planetary ball mill jar, use deionized water as a grinding aid, with a ball-to-material ratio of 15:1, a ball milling speed of 350 rpm, and a ball milling time of 10 hours. After ball milling, place the mixture in a blast drying oven at 80 °C for 10 hours to obtain the precursor powder.

[0053] (4) Place the dried precursor powder in a tube furnace, heat it to 400 °C at a rate of 5 °C / min under an argon atmosphere and hold for 4 hours, then heat it to 700 °C at a rate of 5 °C / min and hold for 10 hours to obtain the regenerated lithium manganese iron phosphate cathode material.

[0054] Figure 1 The results show that the use of the eluent can successfully separate the waste lithium iron phosphate from the current collector, and no impurities are introduced during the separation process. Figure 2 The results show that the waste lithium iron phosphate powder is significantly refined after ball milling, which is beneficial to improving the uniformity of subsequent mixing. Figure 3 This is the XRD diffraction pattern of Example 1 and the waste lithium iron phosphate. As shown in the figure, the regenerated lithium manganese iron phosphate material still maintains the olivine structure and there are no other impurity phases, successfully regenerating the waste lithium iron phosphate into lithium manganese iron phosphate. Figure 4 This is the SEM image of the regenerated lithium manganese iron phosphate in Example 1. As shown in the figure, the regenerated zirconium-doped lithium manganese iron phosphate particles are complete. Figure 5It is the first-cycle charge-discharge curve of the lithium-ion battery made of recycled lithium iron manganese phosphate material and waste lithium iron phosphate at a rate of 0.1C. As shown in the figure, the discharge specific capacity of waste lithium iron phosphate in the first cycle is 107 mAh / g, and the Coulomb efficiency is 93%. The discharge specific capacity of zirconium-doped recycled lithium iron manganese phosphate in the first cycle is 154 mAh / g, and the Coulomb efficiency is 93%. Moreover, charge-discharge platforms of manganese can be observed at 4.1V and 4.0V. The increase in charge-discharge voltage improves the energy density of the material.

[0055] Example 2

[0056] The eluent used in this example is ferric phytate, the lithium salt is lithium hydroxide, the manganese salt is manganese acetate, the phosphorus source is diammonium hydrogen phosphate, the carbon source is sucrose, and the element dopant is nano-titanium oxide. The performance of the recycled lithium iron manganese phosphate cathode material is improved by doping with titanium element. The chemical formula of the recycled lithium iron manganese phosphate cathode material obtained by repair is LiMn 0.38 Fe 0.6 Ti 0.01 PO4, and the specific steps are as follows:

[0057] (1) Prepare the eluent. Take an appropriate amount of ferric phytate, add deionized water until the pH of the solution is 6, then cut the waste lithium iron phosphate cathode plate and place it in a beaker with the eluent. The solid-liquid ratio is 50 g / L. Place the beaker in an oil bath and heat it to 70°C for 3 min to completely separate the active material from the plate, obtaining flaky active material.

[0058] (2) Place the flaky active material in a blast drying oven at 100°C for 10 h. After drying, place the waste lithium iron phosphate in a ball milling tank with a ball-to-material ratio of 10:1, a ball milling speed of 250 rpm, and a ball milling time of 10 h to obtain the refined waste lithium iron phosphate cathode material.

[0059] (3) Conduct ICP-OES testing on the waste lithium iron phosphate cathode material. According to the test results and the stoichiometric ratios of each element in LiMn 0.38 Fe 0.6 Ti 0.01 PO4, add manganese acetate, lithium hydroxide, diammonium hydrogen phosphate, and titanium oxide, and add 2 wt% of sucrose as the carbon source. The addition amount of the dopant is 1 mol%. Add the raw materials to a planetary ball milling tank, use ethanol as the grinding aid, with a ball-to-material ratio of 20:1, a ball milling speed of 250 rpm, and a ball milling time of 12 h. After ball milling, place the mixture in a blast drying oven at 60°C for 12 h to obtain the precursor powder.

[0060] (4) Place the dried precursor powder in a tubular furnace. Under a nitrogen atmosphere, heat it to 350 °C at a rate of 5 °C / min and hold for 6 h, then heat it to 650 °C at a rate of 5 °C / min and hold for 12 h to obtain the regenerated lithium iron manganese phosphate cathode material.

[0061] Figure 6 is the XRD diffraction pattern of Example 2 and waste lithium iron phosphate. As shown in the figure, the regenerated lithium iron manganese phosphate material still maintains the olivine structure and there are no other impurity phases, successfully regenerating waste lithium iron phosphate into lithium iron manganese phosphate. Figure 7 is the first charge-discharge curve of the lithium-ion battery made of the regenerated lithium iron manganese phosphate material and waste lithium iron phosphate at a rate of 0.1C. As shown in the figure, the initial discharge specific capacity of titanium-doped regenerated lithium iron manganese phosphate is 151 mAh / g, and the Coulomb efficiency is 93.23%. And charge-discharge platforms of manganese can be observed at 4.1V and 4.0V. The increase in charge-discharge voltage improves the energy density of the material.

[0062] Example 3

[0063] The eluent used in this example is iron acetate, the lithium salt is lithium hydroxide, the manganese salt is manganese acetate, the phosphorus source is diammonium hydrogen phosphate, the carbon source is sucrose, and the element dopant is nano-titanium oxide. The performance of the regenerated lithium iron manganese phosphate cathode material is improved by doping with titanium element. The chemical formula of the regenerated lithium iron manganese phosphate cathode material obtained is LiMn 0.37 Fe 0.6 Ni 0.03 PO4, and the specific steps are as follows:

[0064] (1) Prepare the eluent. Take an appropriate amount of iron phytate, add deionized water until the pH of the solution is 7, then cut the waste lithium iron phosphate cathode plate, place it in a beaker and add the eluent. The solid-liquid ratio is 100 g / L. Place the beaker in an oil bath and heat to 60 °C and hold for 5 min until the active material is completely separated from the plate to obtain flaky active material.

[0065] (2) Place the flaky active material in a blast drying oven at 120 °C and dry for 11 h. After drying, place the waste lithium iron phosphate in a ball milling tank. The ball-to-material ratio is 30:1, the ball milling speed is 400 rpm, and the ball milling time is 6 h to obtain the refined waste lithium iron phosphate cathode material.

[0066] (3) Conduct ICP-OES testing on the waste lithium iron phosphate cathode material. According to the test results and LiMn 0.37 Fe 0.6 Ni 0.03The stoichiometric ratios of the elements in PO4, manganese acetate, lithium hydroxide, diammonium hydrogen phosphate, nickel oxide were added, and 8 wt% of citric acid was added as the carbon source, and the doping amount of the dopant was 3 mol%. The raw materials were added to a planetary ball milling tank, acetone was used as the grinding aid, the ball-to-material ratio was 8:1, the ball milling speed was 400 rpm, and the ball milling time was 8 h. After ball milling, the mixture was placed in a blast drying oven at 120 °C for 8 h to obtain the precursor powder.

[0067] (4) The dried precursor powder was placed in a tube furnace and heated to 450 °C at a rate of 5 °C / min under an argon-hydrogen mixed gas atmosphere and held for 2 h, then heated to 750 °C at a rate of 5 °C / min and held for 8 h to obtain the regenerated lithium manganese iron phosphate cathode material.

[0068] Figure 8 is the XRD diffraction pattern of Example 3 and waste lithium iron phosphate. As shown in the figure, the regenerated lithium manganese iron phosphate material still maintains the olivine structure, there are no other impurity phases, and the waste lithium iron phosphate is successfully regenerated into lithium manganese iron phosphate. Figure 9 is the first charge-discharge curve of the lithium ion battery made of the regenerated lithium manganese iron phosphate material and waste lithium iron phosphate at a rate of 0.1C. As shown in the figure, the discharge specific capacity of the nickel-doped regenerated lithium manganese iron phosphate in the first cycle is 152 mAh / g, and the Coulomb efficiency is 92.7%. And charge-discharge platforms of manganese can be observed at 4.1V and 4.0V. The increase in the charge-discharge voltage improves the energy density of the material.

[0069] Comparative Example 1

[0070] Corresponding to Example 1 above, lithium carbonate was used as the lithium salt, manganese carbonate as the manganese salt, ammonium dihydrogen phosphate as the phosphorus source, and glucose as the carbon source. No element dopant was added, and the chemical formula of the directly repaired and regenerated lithium manganese iron phosphate cathode material is LiMn 0.37 Fe 0.6 Zr 0.015 PO4, and the specific steps are as follows:

[0071] (1) Prepare the eluent. Take an appropriate amount of phytic acid, add deionized water until the pH of the solution is 6.5, then cut the waste lithium iron phosphate cathode plate, place it in a beaker and add the eluent, the solid-liquid ratio is 100 g / L, place the beaker in an oil bath, heat to 80 °C and hold for 2 min, and the active material is completely separated from the plate to obtain flaky active material.

[0072] (2) Place the flaky active material in a blast drying oven at 80 °C for 12 h. After drying, place the waste lithium iron phosphate in a ball milling tank, the ball-to-material ratio is 20:1, the ball milling speed is 350 rpm, and the ball milling time is 6 h to obtain the refined waste lithium iron phosphate cathode material.

[0073] (3) The spent lithium iron phosphate cathode material was tested by ICP - OES. According to the test results and the stoichiometric ratio of the target product elements, manganese carbonate, lithium carbonate, ammonium dihydrogen phosphate, and zirconium oxide were added, and 5 wt% glucose was added as the carbon source. The raw materials were added to a planetary ball - milling jar, with ethanol as the grinding aid, a ball - to - material ratio of 15:1, a ball - milling speed of 300 rpm, and a ball - milling time of 8 h. After ball - milling, the mixture was dried in a forced - air drying oven at 70 °C for 10 h to obtain the precursor powder.

[0074] (4) The dried precursor powder was placed in a tube furnace. Under an argon atmosphere, it was heated to 450 °C at a rate of 5 °C / min and held for 4 h, then heated to 700 °C at a rate of 5 °C / min and held for 12 h to obtain the regenerated lithium manganese iron phosphate cathode material.

[0075] Figure 10 Figure 1 is the XRD diffraction pattern of Comparative Example 1 and the spent lithium iron phosphate. As shown in the figure, the regenerated lithium manganese iron phosphate material still maintains the olivine structure and there are no other impurity phases, successfully regenerating the spent lithium iron phosphate into lithium manganese iron phosphate. Figure 11 Figure 2 is the comparison chart of the rate performance of the lithium - ion batteries made of the regenerated lithium manganese iron phosphate in Comparative Example 1 and Example 1. As shown in the figure, under the condition that the other regeneration steps are the same, zirconium element doping can significantly improve the rate performance of the regenerated lithium manganese iron phosphate material. During the regeneration process, the performance of the regenerated material can be improved by element doping.

[0076] Comparative Example 2

[0077] Corresponding to Example 2, in Example 1, the eluent used was phytic acid, the lithium salt was lithium hydroxide, the manganese salt was manganese acetate, the phosphorus source was diammonium hydrogen phosphate, the carbon source was sucrose, and the element dopant was nano - titanium oxide. The difference was that the spent lithium iron phosphate powder used was obtained from industrial production and had a higher content of impurity elements. The chemical formula of the regenerated lithium manganese iron phosphate cathode material obtained by repair and regeneration was LiMn 0.37 Fe 0.6 Ti 0.015 PO4, and the specific steps are as follows:

[0078] (1) Prepare the eluent. Take an appropriate amount of iron phytic acid, add deionized water until the pH of the solution is 6.7, then cut the spent lithium iron phosphate cathode plate, place it in a beaker and add the eluent, with a solid - to - liquid ratio of 80 g / L. Place the beaker in an oil - bath pot, heat it to 70 °C and hold for 3 min until the active material is completely separated from the plate to obtain flaky active material.

[0079] (2) Place the flaky active material in a forced - air drying oven at 100 °C for 10 h. After drying, place the spent lithium iron phosphate in a ball - milling jar, with a ball - to - material ratio of 15:1, a ball - milling speed of 350 rpm, and a ball - milling time of 8 h to obtain the refined spent lithium iron phosphate cathode material.

[0080] (3) The waste lithium iron phosphate cathode material was tested by ICP - OES. According to the test results and the stoichiometric ratio of the target product elements, manganese acetate, lithium hydroxide, diammonium hydrogen phosphate, and titanium oxide were added, and 5 wt% of sucrose was added as the carbon source. The raw materials were added to a planetary ball - milling tank, with ethanol as the grinding aid, a ball - to - material ratio of 20:1, a ball - milling speed of 280 rpm, and a ball - milling time of 10 h. After ball - milling, the mixture was dried in a forced - air drying oven at 80 °C for 8 h to obtain the precursor powder.

[0081] (4) The dried precursor powder was placed in a tube furnace. Under an argon atmosphere, it was heated to 400 °C at a rate of 5 °C / min and held for 6 h, and then heated to 700 °C at a rate of 5 °C / min and held for 10 h to obtain the regenerated lithium manganese iron phosphate cathode material.

[0082] Figure 12 XRD diffraction patterns of Comparative Example 2 and waste lithium iron phosphate are shown in the figure. The regenerated lithium manganese iron phosphate material still maintains the olivine structure and there are no other impurity phases, successfully regenerating waste lithium iron phosphate into lithium manganese iron phosphate. Figure 13 The figure shows the comparison of the cycling performance at 1C rate of lithium - ion batteries made from the regenerated lithium manganese iron phosphate of Comparative Example 1 and the regenerated lithium manganese iron phosphate of Example 1. Using the waste lithium iron phosphate obtained with the eluent as the raw material, the discharge specific capacity of the regenerated lithium manganese iron phosphate at 1C rate after 100 cycles is 116.6 mAh / g, and the capacity retention rate is 99%. For the regenerated lithium manganese iron phosphate material obtained with industrial black powder as the raw material, the discharge specific capacity at 1C rate after 100 cycles is 99 mAh / g, and the capacity retention rate is 95%. The performance of Example 2 is more excellent. This is because compared with the waste cathode material eluted with the eluent, there are more impurities in the black powder, which will affect the regeneration effect and lead to poor performance of the regenerated material. Therefore, introducing an eluent to elute and separate the waste electrode sheet is beneficial to the regeneration of the waste lithium iron phosphate cathode material.

[0083] The technical features of the above - mentioned embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above - mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0084] The above - mentioned embodiments only represent several implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

[0085] The above has elaborated in detail the embodiments of a method for regenerating waste lithium iron phosphate into a lithium manganese iron phosphate cathode material with the assistance of element doping. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the core idea of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A method for regenerating waste lithium iron phosphate into lithium iron manganese phosphate positive electrode material by element doping, characterized in that: The steps include: S1. Place the waste lithium iron phosphate positive electrode sheet in an eluent for elution, ball-mill and sieve to obtain waste active material powder; S2, mixing the ball-milled waste active material powder with a lithium source, a phosphorus source, a manganese source, a carbon source and an element dopant by ball milling to obtain a precursor powder; S3. Sintering the precursor powder in two stages under certain atmosphere conditions and cooling it to room temperature to obtain a regenerated lithium manganese iron phosphate positive electrode material.

2. The preparation method according to claim 1, characterized in that: The S1 specifically comprises: cutting the waste lithium iron phosphate positive electrode sheets and transferring them to an eluent for elution to separate the waste active materials from the current collector, air-drying the separated waste active materials, and then refining the waste active material powder by planetary ball milling.

3. The preparation method according to claim 2, characterized in that: The eluent is prepared by diluting one or two of phytic acid, phytic acid iron and ferric acetate in deionized water until the pH value is between 6 and 7.

4. The preparation method according to claim 2, characterized in that: The heating temperature of the elution is 60-80°C, the soaking time of the elution is 2-5min, the solid-liquid ratio of the waste lithium iron phosphate positive electrode sheet to the eluent is 50-100g / L, the drying temperature is 80-120°C, the drying time is 10-12h, the ball-to-material ratio of the ball milling is 10-30:1, the ball milling speed is 250-400rpm, and the ball milling time is 6-10h.

5. The preparation method according to claim 1, characterized in that: The S2 specifically comprises: performing an ICP-OES test on the obtained ball-milled waste lithium iron phosphate powder, determining the addition amount of lithium salt, manganese salt, phosphorus source, carbon source and element dopant according to the content of each element in the waste lithium iron phosphate powder and the element molar ratio required by the target product, adding the waste lithium iron phosphate powder and the lithium source, phosphorus source, manganese source, carbon source and element dopant into a ball mill, adding a grinding aid, mixing evenly by wet ball milling, and obtaining lithium manganese iron phosphate precursor powder after air drying.

6. The preparation method according to claim 5, characterized in that: The lithium salt is one or two of lithium hydroxide, lithium carbonate, and lithium oxalate; the manganese salt is one or two of manganese carbonate, manganese acetate, and manganese oxide; the phosphorus source is one or two of diammonium phosphate, diammonium hydrogen phosphate, and phosphoric acid; the specific addition amount of the lithium source, manganese source, and phosphorus source is related to the ICP-OES test result of the waste lithium iron phosphate, and the added amount needs to ensure that the molar ratio of Li:Fe+Mn:P is 1:1:1; the carbon source is one or a combination of any two of glucose, sucrose, and citric acid, and the addition amount is 2-8wt%; the element dopant is one or a combination of any two of zirconium oxide, titanium oxide, nickel oxide, and aluminum oxide, and the addition amount is 1-3mol%; the grinding aid is any one of ethanol, deionized water, or acetone.

7. The preparation method according to claim 5, characterized in that: The ball-to-material ratio of ball milling is 8-20:1, the ball milling speed is 250-400rpm, the ball milling time is 8-12h, the blast drying temperature is 60-120℃, and the drying time is 8-12h.

8. The preparation method according to claim 1, characterized in that: In S3, the sintering atmosphere is any one of argon, nitrogen, and hydrogen-argon mixed gas; the sintering temperature in the first stage is 350-450°C, and the holding time is 2-6h; the sintering temperature in the second stage is 650-750°C, and the holding time is 8-12h.

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