A method for preparing copper-aluminum co-doped modified lithium iron phosphate positive electrode material from waste lithium iron phosphate batteries

Abstract

The application discloses a method for preparing copper-aluminum co-doped modified lithium iron phosphate positive electrode material from waste lithium iron phosphate batteries, which comprises the following steps: firstly, obtaining waste positive electrode powder from the retired lithium iron phosphate batteries through a series of pretreatments, grinding and mixing the waste positive electrode powder, determining the element content of the mixed powder, taking trace copper and aluminum in the waste positive electrode powder as the copper source and the aluminum source for doping, appropriately supplementing lithium source, iron source, phosphorus source, copper source and aluminum source to make the elements in the waste positive electrode powder meet the stoichiometric ratio design requirements, and then performing acid immersion, adding carbon source and reducing agent and performing roasting to obtain the copper-aluminum co-doped modified lithium iron phosphate positive electrode material. The method can effectively solve the problems of short cycle life and poor rate performance of the recycled positive electrode material caused by copper impurities, and the problem that the solid-phase directly regenerated material is difficult to meet the commercial application requirements.

Description

TECHNICAL FIELD

[0001] The application relates to a method for preparing copper-aluminum co-doped modified lithium iron phosphate positive electrode material from waste lithium iron phosphate batteries, and belongs to the fields of lithium ion battery recycling and positive electrode material preparation. BACKGROUND

[0002] Lithium ion batteries are widely used in new energy vehicle power storage batteries due to their high energy density and low cost advantages. Due to capacity attenuation, lithium ion power batteries will face retirement after 3-5 years of use. It is estimated that the retired power lithium batteries will reach 134.49 GWh and the retired amount will reach 803,600 tons in 2025. The recycling and remanufacturing of lithium ion battery electrode materials of waste lithium batteries are important measures to realize the sustainable development of lithium ion batteries.

[0003] At present, the mainstream methods of lithium ion battery recycling include hydrometallurgy and pyrometallurgy. However, the hydrometallurgical recycling process is complex and produces a large amount of wastewater; the pyrometallurgical process consumes a large amount of energy, is difficult to remove metal impurities, emits toxic smoke, and the capacity, rate performance and cycle performance of the positive electrode material after recycling and regeneration are still different from those of the fresh material. The current research difficulty is how to reduce the impurity content in the waste positive electrode mixed powder on the basis of green environmental protection and how to improve the discharge specific capacity, rate and cycle performance of the regenerated positive electrode material by modifying the regenerated positive electrode material.

[0004] Most of the existing technologies for recycling waste lithium ion battery positive electrode materials to prepare new positive electrode materials by solid phase method are based on waste positive electrode materials obtained by manual or automatic fine sorting, and do not involve the treatment of metal impurities. After the retired lithium iron phosphate battery is discharged and disassembled, the battery cell is obtained, the residual electrolyte and binder in the battery cell are removed by 500 DEG C negative pressure pyrolysis treatment under inert atmosphere such as nitrogen, and then the waste positive electrode powder (mainly lithium iron phosphate positive electrode powder, a small amount of carbon and graphite powder, and a small amount of aluminum and copper) is obtained by crushing, screening, air separation and magnetic separation. When the recycled waste positive electrode powder is used as raw material to regenerate the positive electrode material by adding a proper amount of lithium source, iron source and phosphorus source, the trace metal impurities in the positive electrode material may tend to be in a metastable state during the charging and discharging process of the battery, thereby causing the performance of the battery to decay. Among them, the copper metal impurities have the most obvious influence. When the voltage of the battery reaches the redox potential of the copper metal impurities during the formation of the battery, the copper metal will be oxidized at the positive electrode and reduced at the negative electrode, and the copper metal deposition dendrites will pierce the separator after reciprocating accumulation, causing self-discharge of the battery. For the above reasons, the electrochemical performance of the lithium ion battery prepared by using the recycled and prepared positive electrode material cannot meet the demand of commercial application. SUMMARY

[0005] The purpose of the present application is to overcome the shortcomings of the prior art, and provide a method for preparing copper-aluminum co-doped modified lithium iron phosphate cathode material from waste lithium iron phosphate batteries, aiming to solve the problems of short cycle life and poor rate performance of the recycled cathode material caused by copper impurities. By converting copper into copper ions, the ions are doped into the lithium iron phosphate crystal cell during the subsequent calcination and preparation process, not only solving the shortcomings of copper impurities, but also improving the electrical conductivity of the material grain. The uniform dispersion and content optimization of the aluminum element can improve the intergranular conductivity of the material. The copper-aluminum co-doping modification can improve the rate performance and cycle stability of the recycled material, and is suitable for energy storage batteries.

[0006] To achieve the purpose of the present application, the following technical solutions are adopted:

[0007] A method for preparing copper-aluminum co-doped modified lithium iron phosphate cathode material from waste lithium iron phosphate batteries, comprising the following steps:

[0008] Step 1: Discharge and disassemble the waste lithium iron phosphate battery to obtain the battery cell, remove the residual electrolyte and decompose the binder under nitrogen or other inert atmosphere at 500 DEG C negative pressure pyrolysis, and then obtain the waste cathode powder (mainly lithium iron phosphate cathode powder, a small amount of carbon, graphite powder and trace amounts of aluminum and copper) by crushing, screening, air separation and magnetic separation;

[0009] Step 2: Using the waste cathode powder obtained in step 1 as raw material, the waste cathode powder is ground and mixed uniformly by solid phase ball milling method to obtain mixed powder A;

[0010] Step 3: Using inductively coupled plasma spectrometer to measure the content of each element in the mixed powder A obtained in step 2, adjusting the stoichiometric ratio of lithium, iron, phosphorus, copper and aluminum in the mixed powder A to be in the range of 1-1.05:1:1:0.001-0.02:0.001-0.02 by adding lithium source, iron source, phosphorus source, copper source and aluminum source, obtaining mixed powder B; using acetic acid containing hydrogen peroxide to acid leach the mixed powder B under the conditions of reaction temperature of room temperature-90 DEG C, reaction time of 10-120 min, solid-liquid ratio of 10-300 g / L, so as to realize the doping of copper ions into the lithium iron phosphate crystal cell, while the aluminum exists in the material in the form of single element to enhance the conductivity of the material, and the mixed powder C is obtained by evaporation drying;

[0011] Step 4: Adding 10-30% of glucose or sucrose as carbon source and reducing agent based on the mass of the mixed powder C, grinding and mixing, and calcining under nitrogen or argon inert atmosphere to obtain the copper-aluminum co-doped modified lithium iron phosphate cathode material.

[0012] Further, in step 1, the lithium iron phosphate content in the waste positive electrode powder is in the range of 85-95wt%, the carbon and graphite content is in the range of 1-15wt%, the copper content is in the range of 0-1wt%, and the aluminum content is in the range of 0-0.5wt%, based on the total mass of the waste positive electrode powder.

[0013] Further, in step 2, the ball milling speed is 150-1500rpm, and the ball milling time is 0.5-10h.

[0014] Further, in step 3: the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium oxalate, lithium phosphate, lithium acetate and lithium dihydrogen phosphate; the iron source is one or more of ferrous oxalate, iron oxide, iron acetate, iron phosphate, iron citrate and ammonium iron citrate; the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, iron phosphate, lithium phosphate and lithium dihydrogen phosphate; the copper source is one or more of copper acetate, copper oxalate, copper oxide and elemental copper; and the aluminum source is elemental aluminum powder with a particle size of less than 1 micron.

[0015] Further, in step 3, the mass concentration of hydrogen peroxide in the hydrogen peroxide-containing acetic acid used for acid leaching is 1-10%, and the concentration of acetic acid is 0.1-6mol / L.

[0016] Further, in step 4, the calcination is carried out in two steps: first, the temperature is raised to 300-450℃ at a heating rate of 1-6℃ / min, and the temperature is maintained for 2-8h; then the temperature is raised to 650-750℃ at a heating rate of 1-6℃ / min, and the temperature is maintained for 3-24h; finally, the temperature is naturally cooled to room temperature.

[0017] The method of the present application uses the copper and aluminum impurities generated in the pretreatment process of waste batteries as doping raw materials to regenerate the waste positive electrode material into a copper and aluminum co-doped modified positive electrode material, which can effectively solve the problems of short cycle life and poor rate performance of the recycled positive electrode material caused by metal copper impurities, and the problem that the solid-phase directly regenerated material is difficult to meet the demand of commercial application, thereby realizing the recycling of lithium, iron, phosphorus, copper and aluminum elements in the retired lithium ion batteries.

[0018] Compared with the prior art, the beneficial effects of the present application are:

[0019] The application discloses a method for preparing copper-aluminum co-doped modified lithium iron phosphate positive electrode material from waste lithium iron phosphate batteries. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 XRD pattern of the waste positive electrode powder obtained by pretreatment of the application example 1;

[0021] Figure 2 XRD pattern of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material obtained in the application example 1;

[0022] Figure 3 FESEM photo of the waste positive electrode powder obtained in the application example 1;

[0023] Figure 4 FESEM photo of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material obtained in the application example 1;

[0024] Figure 5 XPS spectrum of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material obtained in the application example 1;

[0025] Figure 6 EDS spectrum of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material obtained in the application example 1;

[0026] Figure 7The charge-discharge curves of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material obtained in Example 1 of the present application at current densities of 0.1C and 5C, respectively;

[0027] Figure 8 The charge-discharge curves of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material obtained in Example 1 of the present application at current densities of 0.1C and 5C, respectively;

[0028] Figure 9 The cycle performance diagram of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material obtained in Example 1 of the present application and the waste positive electrode powder at a current density of 5C. DETAILED DESCRIPTION

[0029] The embodiments of the present application are described in detail below, and the embodiments are implemented on the premise of the technical solutions of the present application, and detailed implementation manners and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0030] Example 1: Copper-aluminum co-doped modified lithium iron phosphate positive electrode material prepared from waste lithium iron phosphate battery

[0031] Step 1: After the retired lithium iron phosphate battery is discharged and disassembled, the battery cell is obtained, and the residual electrolyte and decomposed binder are removed by 500℃ negative pressure pyrolysis treatment under a nitrogen atmosphere, and then the waste positive electrode powder (mainly lithium iron phosphate positive electrode powder, a small amount of carbon, graphite powder and a small amount of aluminum and copper) is obtained by crushing, screening, air separation and magnetic separation.

[0032] Step 2: The waste positive electrode powder (lithium iron phosphate content is 94.5wt%, graphite content is 4.6wt%, copper content is 0.5wt%, and aluminum content is 0.2wt%) obtained in step 1 is used as raw material, and solid phase ball milling method is adopted to grind and mix the waste positive electrode powder uniformly under the conditions of rotation speed of 1200rpm and ball milling time of 6.5h, to obtain mixed powder A.

[0033] Step 3: The inductively coupled plasma spectrometer is used to measure the content of each element in the above mixed powder A, and the appropriate amount of lithium carbonate, iron oxide, ammonium dihydrogen phosphate, copper acetate and spherical aluminum powder with an average particle size of 600nm are added to adjust the stoichiometric ratio of lithium, iron, phosphorus, copper and aluminum in the mixed powder A to 1.05:1:1:0.003:0.003, to obtain mixed powder B; then the mixed powder B is subjected to acid leaching under the conditions of reaction temperature of 85℃, reaction time of 30min, solid-liquid ratio of 50g / L and 0.8mol / L acetic acid containing 5wt% hydrogen peroxide, so that the elemental copper is converted into copper acetate, so as to realize the doping of copper ions into the lithium iron phosphate crystal cell, and the aluminum exists in the material in the form of elemental aluminum, and the mixed powder C is obtained by evaporation drying.

[0034] Step 4: 30% of the mass of the mixed powder C was added as a carbon source and reducing agent, and after grinding and mixing, the mixture was calcined in two steps under a nitrogen atmosphere (first, the temperature was raised to 350°C at a rate of 4°C / min, and then the temperature was maintained for 4 h, and then the temperature was raised to 700°C at a rate of 2°C / min, and then the temperature was maintained for 10 h, and finally the temperature was naturally cooled to room temperature), to obtain a copper and aluminum co-doped modified lithium iron phosphate positive electrode material.

[0035] The waste positive electrode powder obtained in Step 1 of the present example and the copper and aluminum co-doped modified lithium iron phosphate positive electrode material obtained in Step 4 were respectively mixed with acetylene black and polyvinylidene fluoride (PVDF) at a ratio of 8:1:1 (mass ratio), and NMP (1-methyl-2-pyrrolidone) was added to make a paste, which was uniformly coated on an aluminum foil with a coating thickness of 75 μm. After drying at 80°C and rolling, the positive electrode sheet was cut into a 12 mm diameter positive electrode sheet, and then vacuum dried for use. A lithium metal sheet was used as the negative electrode, a Cellgard 2400 type polypropylene film was used as the separator, and lithium hexafluorophosphate was used as the electrolyte. The experimental battery was assembled in an argon glove box, and then the battery was subjected to constant voltage and constant current charge and discharge tests at 25°C.

[0036] Figure 1 and Figure 2 The XRD patterns of the waste positive electrode powder obtained in Step 1 of the present example and the copper and aluminum co-doped modified lithium iron phosphate positive electrode material obtained in Step 4 are shown in FIGS. 1 and 2, respectively. As can be seen from the figures, both materials can be indexed to an orthorhombic olivine-type structure with a space group of Pnma. In the material, Fe 2+ occupies the 4a site of the octahedron, and Li + occupies the 4c site of the octahedron. The edge-shared LiO4 and corner-shared FeO6 octahedrons are both parallel to the c-axis and arranged along the b-axis direction.

[0037] Table 1 shows the unit cell parameters of the copper and aluminum co-doped modified lithium iron phosphate positive electrode material and the waste positive electrode powder.

[0038] Table 1

[0039]

[0040] As can be seen from Table 1, the unit cell parameters a, b, c and the unit cell volume of the co-doped sample are all reduced. This is because Cu 2+ doping may mainly occur Li + site substitution. The radius of Cu 2+ (0.073 nm) is smaller than the radius of Li + (0.076 nm), resulting in a decrease in the unit cell parameters, and the Cu-O bond energy is greater than the Li-O bond energy, resulting in a decrease in the unit cell volume. The decrease in the lattice parameter b can shorten the Li +The diffusion distance of lithium ions is reduced, the electronic conductivity of the lithium iron phosphate electrode material is improved, and the diffusion rate of lithium ions is improved.

[0041] Figure 3 and Figure 4 FESEM images of the waste positive electrode powder and the copper-aluminum co-doped modified lithium iron phosphate positive electrode material of the present embodiment, respectively. The particle size of the waste positive electrode powder is between 0.5 μm and 4 μm, while the particle size of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material is reduced and more uniform (particle size between 0.5 μm and 1 μm). The reduction of the particle size helps to reduce the diffusion path of lithium ions and increase the high-rate discharge performance of lithium iron phosphate.

[0042] Figure 5 XPS spectrum of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material of the present embodiment. In the figure, the 2p 3 / 2 and 2p 1 / 2 spin-splitting orbitals of Cu can be observed, and the satellite peak characteristic specific to divalent copper is observed, proving that copper is doped into the lithium iron phosphate material crystal cell in the form of a divalent ion.

[0043] Figure 6 EDS spectrum of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material of the present embodiment. The stoichiometric ratio Fe: P: Cu: Al: C ≈ 1: 1: 0.006: 0.012: 0.76, which is basically consistent with the design value within the error range.

[0044] Figure 7 Charge-discharge curves of the waste positive electrode powder of the present embodiment at 0.1C and 5C current densities, respectively. It can be observed that there is a smooth charge voltage platform at the constant current charging stage at 3.45V, and the discharge voltage platform is about 3.10V at 5C current density, the polarization voltage ΔV = 0.35V, and the 0.1C and 5C discharge specific capacities are 123.7 mAh / g and 89.9 mAh / g, respectively.

[0045] Figure 8 Charge-discharge curves of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material of the present embodiment at 0.1C and 5C current densities. It can be observed that there is a smooth charge voltage platform at the constant current charging stage at 3.45V, and the discharge voltage platform is about 3.25V at 5C current density, the polarization voltage ΔV = 0.20V, and the 0.1C and 5C discharge specific capacities are 151.5 mAh / g and 121.5 mAh / g, respectively. This indicates that the electrode polarization degree of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material is significantly smaller than that of the waste positive electrode powder during the high-rate charge-discharge process, and the discharge specific capacity is significantly higher than that of the waste positive electrode powder.

[0046] Figure 9The cycle performance chart of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material and the waste positive electrode powder at a current density of 5C. As can be seen from the figure, the initial discharge capacity of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material is 120.7 mAh / g, which is significantly higher than that of the waste positive electrode powder of 89.2 mAh / g. In addition, after 100 cycles of charge and discharge test, the discharge capacity of the copper-aluminum co-doped modified lithium iron phosphate positive electrode material almost does not decay. The electrochemical test results show that the appropriate copper and aluminum co-doping modification is beneficial to improve the discharge capacity and cycle performance of the regenerated lithium iron phosphate positive electrode material.

[0047] Example 2: Preparation of copper-aluminum co-doped modified lithium iron phosphate positive electrode material from waste lithium iron phosphate battery

[0048] Step 1: After discharging and disassembling the retired lithium iron phosphate battery, the battery cell is obtained, and the residual electrolyte and decomposed binder are removed by 500°C negative pressure pyrolysis treatment under inert atmosphere such as nitrogen. Then, the waste positive electrode powder (mainly lithium iron phosphate positive electrode powder, as well as a small amount of carbon, graphite powder and trace amounts of aluminum and copper) is obtained by crushing, screening, air separation and magnetic separation.

[0049] Step 2: The waste positive electrode powder (lithium iron phosphate content of 89.7wt%, graphite content of 8.5wt%, copper content of 1wt%, and aluminum content of 0.5wt%) obtained in step 1 is used as raw material, and solid phase ball milling method is adopted to grind and mix the waste positive electrode powder uniformly under the conditions of rotation speed of 1000 rpm and ball milling time of 4h, to obtain mixed powder A.

[0050] Step 3: The content of each element in the above mixed powder A is determined by using an inductively coupled plasma spectrometer, and the stoichiometric ratio of lithium, iron, phosphorus, copper and aluminum in the mixed powder A is adjusted to 1:1:1:0.01:0.01 by adding appropriate amounts of lithium oxalate, ferrous oxalate, diammonium hydrogen phosphate, copper oxide and spherical aluminum powder with an average particle size of 900 nm to obtain mixed powder B; then the mixed powder B is subjected to acid leaching under the conditions of reaction temperature of 70°C, reaction time of 60 min, solid-liquid ratio of 100 g / L, using 10wt% hydrogen peroxide and 1mol / L acetic acid, so that the elemental copper is converted into copper acetate, so as to realize the doping of copper ions into the lithium iron phosphate crystal cell, while the aluminum exists in the material in the form of elemental aluminum, and the mixed powder C is obtained by evaporation drying.

[0051] Step 4: 20% of the mass of the mixed powder C is added as a carbon source and a reducing agent, and after grinding and mixing, the calcination is carried out in two steps under argon atmosphere (firstly, the temperature is raised to 300°C at a heating rate of 1°C / min, and the temperature is maintained for 6h, then the temperature is raised to 650°C at a heating rate of 1°C / min, and the temperature is maintained for 20h, and finally the temperature is naturally cooled to room temperature), to obtain the copper-aluminum co-doped modified lithium iron phosphate positive electrode material.

[0052] Example 3: Preparation of copper-aluminum co-doped modified lithium iron phosphate cathode material from waste lithium iron phosphate battery

[0053] Step 1: The retired lithium iron phosphate battery was discharged and disassembled to obtain the battery cell, and the residual electrolyte and decomposed binder were removed by 500℃ negative pressure pyrolysis treatment under inert atmosphere such as nitrogen. Then, the waste positive electrode powder (mainly lithium iron phosphate positive electrode powder, a small amount of carbon, graphite powder and trace amounts of aluminum and copper) was obtained by crushing, screening, air separation and magnetic separation.

[0054] Step 2: The waste positive electrode powder obtained in step 1 (lithium iron phosphate content of 88.7wt%, graphite content of 10.5wt%, copper content of 0.2wt%, and aluminum content of 0.2wt%) was used as raw material, and solid phase ball milling method was adopted to grind and mix the waste positive electrode powder uniformly under the conditions of rotation speed of 800rpm and ball milling time of 10h, to obtain mixed powder A.

[0055] Step 3: The content of each element in the above mixed powder A was determined by inductively coupled plasma spectrometer, and the stoichiometric ratio of lithium, iron, phosphorus, copper and aluminum in the mixed powder A was adjusted to 1:1:1:0.02:0.02 by adding appropriate amounts of lithium hydroxide, ferric citrate, iron phosphate, elemental copper and spherical aluminum powder with an average particle size of 900nm, to obtain mixed powder B; then the mixed powder B was subjected to acid leaching under the conditions of 2.5wt% hydrogen peroxide, 0.5mol / L acetic acid, reaction temperature of 90℃, reaction time of 120min and solid-liquid ratio of 200g / L, so that the elemental copper was converted into copper acetate, so as to realize the doping of copper ions into the lithium iron phosphate crystal cell, while the aluminum existed in the material in the form of elemental substance, and the mixed powder C was obtained by evaporation drying.

[0056] Step 4: 25% of sucrose based on the mass of the mixed powder C was added as a reducing agent, and was ground and mixed, and was calcined in two steps under nitrogen atmosphere (firstly, the temperature was raised to 450℃ at a heating rate of 5℃ / min, and was kept for 4h, then the temperature was raised to 750℃ at a heating rate of 2℃ / min, and was kept for 5h, and finally was naturally cooled to room temperature), to obtain the copper-aluminum co-doped modified lithium iron phosphate cathode material.

[0057] The above only describes exemplary embodiments of the present application and does not limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for preparing copper-aluminum co-doped modified lithium iron phosphate cathode material from waste lithium iron phosphate batteries, characterized in that, The method comprises the following steps: Step 1: obtaining the battery cell by discharging and disassembling the waste lithium iron phosphate battery, removing the residual electrolyte and decomposing the binder in the battery cell by 500 DEG C negative pressure pyrolysis treatment under inert atmosphere, and then obtaining the waste positive electrode powder by crushing, screening, air separation and magnetic separation; Step 2: taking the waste positive electrode powder obtained in step 1 as raw material, grinding and mixing the waste positive electrode powder by solid phase ball milling to obtain mixed powder A; Step 3: determining the element content of the mixed powder A obtained in step 2, adjusting the stoichiometric ratio of lithium, iron, phosphorus, copper and aluminum in the mixed powder A in the range of 1-1.05:1:1:0.001-0.02:0.001-0.02 by adding lithium source, iron source, phosphorus source, copper source and aluminum source, obtaining mixed powder B; acid leaching the mixed powder B under the conditions of reaction temperature of room temperature-90 DEG C, reaction time of 10-120 min and solid-liquid ratio of 10-300 g / L by using acetic acid containing hydrogen peroxide, converting elemental copper into copper acetate, and obtaining mixed powder C by evaporation drying; wherein the mass concentration of hydrogen peroxide in the acetic acid containing hydrogen peroxide used for acid leaching is 1-10%, and the concentration of acetic acid is 0.1-6 mol / L; Step 4: adding 10-30% of glucose or sucrose based on the mass of the mixed powder C as carbon source and reducing agent, grinding and mixing, and calcining under inert atmosphere to obtain copper and aluminum co-doped modified lithium iron phosphate positive electrode material.

2. The method of claim 1, wherein: In step 1, the content of lithium iron phosphate in the waste positive electrode powder is in the range of 85-95 wt%, the content of carbon and graphite is in the range of 1-15 wt%, the content of copper is 0-1 wt%, and the content of aluminum is in the range of 0-0.5 wt% based on the total mass of the waste positive electrode powder.

3. The method of claim 1, wherein: In step 2, the ball milling speed is 150-1500 rpm, and the ball milling time is 0.5-10 h.

4. The method of claim 1, wherein: In step 3, the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium oxalate, lithium phosphate, lithium acetate and lithium dihydrogen phosphate.

5. The method of claim 1, wherein: In step 3, the iron source is one or more of ferrous oxalate, iron oxide, iron acetate, iron phosphate, iron citrate and ammonium iron citrate.

6. The method of claim 1, wherein: In step 3, the phosphorus source is one or more of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, iron phosphate, lithium phosphate and lithium dihydrogen phosphate.

7. The method of claim 1, wherein: In step 3, the copper source is one or more of copper acetate, copper oxalate, copper oxide and elemental copper.

8. The method of claim 1, wherein: In step 3, the aluminum source is elemental aluminum powder with particle size less than 1 micrometer.

9. The method of claim 1, wherein: In step 4, the calcination is carried out in two steps: first, heating to 300-450 DEG C at a heating rate of 1-6 DEG C / min, and holding for 2-8 h; then heating to 650-750 DEG C at a heating rate of 1-6 DEG C / min, and holding for 3-24 h; finally, naturally cooling to room temperature.

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