A method for directly regenerating positive electrode material of a waste lithium iron phosphate battery into lithium manganese iron phosphate by controlling iron lithium antisite defects

Abstract

The application relates to a method for directly regenerating a positive electrode material of a waste lithium iron phosphate battery into lithium manganese iron phosphate by controlling iron lithium anti-site defects. The positive electrode sheet of the waste lithium iron phosphate battery is calcined to remove a polymer binder and carbon coating, separated from an aluminum foil serving as a current collector, and ground to obtain a positive electrode material powder; the positive electrode material powder, a lithium source, a manganese source, a phosphorus source and a carbon source are mixed in a micro-lithium-rich molar ratio to obtain a precursor powder; the precursor powder is pre-fired under inert gas, calcined under inert gas at 650-700 DEG C for 10h, and the regenerated positive electrode powder material is obtained. The micro-lithium-rich molar ratio is Li:(Fe+Mn):P=(1.05-1.1):(0.9-0.95):1, the molar ratio of iron to manganese is Fe:Mn=(0.3-0.35):0.6, and the extra lithium occupies the iron site, which significantly improves the formation energy of iron lithium anti-site defects and effectively reduces the iron lithium anti-site defects.

Description

Technical Field

[0001] This invention belongs to the field of energy materials technology, specifically relating to a method for directly regenerating waste lithium iron phosphate battery cathode materials into lithium manganese iron phosphate by controlling the antisite defects of lithium iron phosphate. Background Technology

[0002] The widespread adoption of electric vehicles and the rapid development of lithium-ion batteries will lead to a large number of batteries needing to be retired in the future. Current research on the recycling of retired lithium-ion batteries focuses on recovering valuable metals. Progress in direct regeneration is slow. How to directly recycle or recycle retired batteries at high value remains a challenge.

[0003] Lithium iron phosphate (LiFePO4) has an olivine structure and belongs to the orthorhombic crystal system, space group Pnma. Lithium iron phosphate batteries are common cathode materials for energy storage / power batteries. This material has inherent lithium iron phosphate antisite defects (some iron atoms occupy lithium sites), which affect lithium-ion transport, leading to reduced ionic and electronic conductivity and impacting material usability. In retired lithium iron phosphate batteries, lithium deficiency during long-term cycling leads to the formation of the phosphate phase, which easily results in more lithium iron phosphate antisite defects, causing a decrease in specific capacity and discharge voltage. Therefore, how to achieve high-value recycling of lithium iron phosphate cathode materials and reduce lithium iron phosphate antisite defects during the recycling process has become a key and challenging aspect of lithium iron phosphate cathode material recycling. Summary of the Invention

[0004] To address existing challenges, this invention presents a method for directly recycling waste lithium iron phosphate battery cathode materials into lithium manganese iron phosphate. Through the design of a special micro-lithium-rich structure, waste lithium iron phosphate battery cathode materials can be recycled into micro-lithium-rich lithium manganese iron phosphate, effectively reducing the lithium iron phosphate antisite defect and significantly improving ionic and electronic conductivity. The capacity and discharge voltage of the recycled lithium manganese iron phosphate are significantly improved.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A method for directly regenerating spent lithium iron phosphate battery cathode materials into lithium manganese iron phosphate by controlling the antisite defects in lithium iron phosphate, comprising the following steps:

[0007] (1) The waste lithium iron phosphate battery positive electrode sheet was calcined at 400°C for 4 hours under inert gas to remove the polymer binder and carbon coating. After being separated from the current collector aluminum foil, it was ground to obtain positive electrode material powder.

[0008] (2) Dissolve the positive electrode material powder obtained in step (1) in aqua regia and microwave digest it, and measure its chemical composition by ICP-OES.

[0009] (3) The cathode material powder obtained in step (1) is ball-milled and mixed with lithium source, manganese source, phosphorus source and carbon source in a slightly lithium-rich molar ratio, and then dried to obtain precursor powder.

[0010] (4) The precursor powder obtained in step (3) is pre-calcined at 400°C for 2 hours under an inert gas.

[0011] (5) The powder obtained in step (4) is calcined at 650-700°C for 10 hours under an inert gas to obtain a regenerated positive electrode powder material.

[0012] In step (3), the designed micro-rich lithium molar ratio is Li:(Fe+Mn):P=(1.05~1.1):(0.9~0.95):1, and the iron to manganese molar ratio is Fe:Mn=(0.3~0.35):0.6, in which the extra lithium occupies the iron site.

[0013] Preferably, in step (3), the designed micro-rich lithium molar ratio is Li:Fe:Mn:P = 1.05:0.35:0.6:1, where the extra lithium occupies the iron sites, and the corresponding chemical formula of the resulting recycled cathode powder material is Li 1.05 Fe 0.35 Mn 0.6 PO4.

[0014] This invention presents a method for directly recovering lithium iron phosphate into lithium manganese iron phosphate. By simply adjusting the stoichiometric ratio, lithium iron phosphate can be recovered into lithium manganese iron phosphate with any manganese-iron ratio. Furthermore, by adjusting the lithium-iron ratio, the iron-lithium antisite defect in lithium manganese iron phosphate can be reduced, effectively improving ionic and electronic conductivity, specific capacity, and discharge voltage.

[0015] The inert gas is either argon or nitrogen.

[0016] In step (2), the aqua regia is a mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1.

[0017] In step (3), the lithium source can be a lithium-containing material used in the art to prepare lithium manganese iron phosphate, and can be selected from at least one of lithium carbonate, lithium acetate, lithium oxalate, lithium oxide, and lithium hydroxide.

[0018] Preferably, the lithium source is lithium acetate and / or lithium dihydrogen phosphate.

[0019] In step (3), the manganese source can be a manganese-containing substance used in the art to prepare lithium manganese iron phosphate, and can be at least one of manganese carbonate, manganese oxalate, manganese acetate, manganese oxide, manganese trioxide, and manganese tetroxide. Preferably, the manganese source is manganese oxalate.

[0020] In step (3), the phosphorus source can be a phosphorus-containing substance used in the art to prepare lithium manganese iron phosphate, and can be selected from at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium dihydrogen phosphate. Preferably, the phosphorus source is lithium dihydrogen phosphate.

[0021] In step (3), the carbon source can be any carbon-containing material used in the art to prepare carbon-coated lithium manganese iron phosphate, and can be at least one of starch, sucrose, glucose, cellulose, polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, citric acid, lactic acid, and succinic acid. Preferably, the carbon source is sucrose.

[0022] Compared with the prior art, the advantages of the present invention are as follows:

[0023] 1. This invention provides a method for directly regenerating spent lithium iron phosphate battery cathode materials into lithium manganese iron phosphate, which can control the antisite defects of lithium iron phosphate. This is achieved by designing a different material from currently used lithium manganese iron phosphate materials (chemical composition: Li). 1.0 Fe 0.4 Mn 0.6 The unique structure of PO4 (a slightly lithium-rich structure with a chemical composition of Li) 1.05 Fe 0.35 Mn 0.6 Lithium manganese iron phosphate (LiFePO4), in which some extra lithium occupies iron sites, increases the formation energy of anti-site defects in lithium iron phosphate, thereby reducing these defects, is obtained by ball milling a mixture of lithium, phosphorus, manganese, and carbon sources to obtain a lithium-rich LiFePO4 precursor. This precursor is then pre-calcined at 400°C for 2 hours under inert gas and followed by calcination at 650°C for 10 hours to obtain a lithium-rich LiFePO4 precursor. The LiFePO4 prepared by this method can be used as a cathode material for lithium-ion batteries, exhibiting significant improvements in specific capacity and median voltage compared to waste lithium iron phosphate. This recycling method is simple to operate, does not use any solvents, and the entire process is green, environmentally friendly, safe, and reliable.

[0024] 2. This invention pioneered the design of a micro-lithium-rich structure, unlike traditional lithium manganese iron phosphate materials. The chemical composition of this structure is Li... 1.05 Fe 0.35 Mn 0.6 PO4, in which some additional lithium occupies iron sites, significantly increases the formation energy of lithium iron phosphate antisite defects and can effectively reduce lithium iron phosphate antisite defects.

[0025] 3. This invention differs from existing inventions that leach waste lithium iron phosphate into metal for recycling. Instead, it directly regenerates waste lithium iron phosphate into lithium manganese iron phosphate material without altering the crystal structure of the waste lithium iron phosphate.

[0026] 4. The process of this invention is simple, does not use any organic solvents, has virtually no environmental pollution, and is highly industrially operable.

[0027] 5. The lithium manganese iron phosphate material of the present invention has advantages such as high ionic and electronic conductivity, specific capacity and discharge voltage, and excellent cycle stability, and is suitable for widespread use. Attached Figure Description

[0028] Figure 1 The X-ray diffraction pattern of the lithium manganese iron phosphate material obtained in Example 1 of this invention.

[0029] Figure 2 The X-ray diffraction pattern of the lithium manganese iron phosphate material obtained in Example 2 of this invention.

[0030] Figure 3 The X-ray diffraction pattern of the lithium manganese iron phosphate material obtained in Example 3 of this invention.

[0031] Figure 4 The X-ray diffraction pattern of the lithium manganese iron phosphate material obtained in Comparative Example 1 of this invention is shown below.

[0032] Figure 5 The X-ray diffraction patterns and partial magnified views of the lithium manganese iron phosphate materials obtained in Examples 1 and 2 of this invention are shown.

[0033] Figure 6 The X-ray diffraction pattern of the lithium manganese iron phosphate material obtained in Example 1 of this invention is obtained by refining and fitting using the Retrieve method.

[0034] Figure 7 The X-ray diffraction pattern of the lithium manganese iron phosphate material obtained in Comparative Example 1 of this invention is obtained by refining and fitting using the Retrieve method.

[0035] Figure 8 Solid-state nuclear magnetic resonance (NMR) was performed on the lithium manganese iron phosphate materials obtained in Example 1 and Comparative Example 1 of this invention. 7 The spectrum obtained from Li spectrum testing.

[0036] Figure 9 This is a specific capacity / voltage curve obtained by assembling a half-cell using the lithium manganese iron phosphate material obtained in Example 1 of the present invention.

[0037] Figure 10 This is a specific capacity / voltage curve of a half-cell assembled with the lithium manganese iron phosphate material obtained in Comparative Example 1 of this invention. Detailed Implementation

[0038] To facilitate understanding of the present invention, a more comprehensive and detailed description of the invention will be provided below in conjunction with the accompanying drawings and preferred embodiments. However, the scope of protection of the present invention is not limited to the specific embodiments described below. Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, all raw materials, reagents, instruments, and equipment used in the present invention are commercially available or can be prepared by existing methods.

[0039] The above solution will be further described below with reference to specific embodiments. The preferred embodiments of the present invention are detailed below:

[0040] Example 1:

[0041] In this embodiment, a method for directly regenerating waste lithium iron phosphate battery cathode material into lithium manganese iron phosphate by controlling lithium iron phosphate antisite defects mainly includes the following steps:

[0042] (1) The waste lithium iron phosphate positive electrode sheet is calcined at 400°C for 4 hours under inert gas to remove the polymer binder and carbon coating. After separating it from the current collector aluminum foil, it is ground to obtain positive electrode material powder; the inert gas is argon.

[0043] (2) Weigh 0.0601g of the positive electrode material powder obtained in step (1), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times and obtain its chemical composition by ICP-OES method, which is approximately Li:Fe:P=0.83:1:1;

[0044] (3) Weigh 2.10g of the positive electrode material powder obtained in step (1), 3.58g of manganese oxalate dihydrate, 2.06g of lithium dihydrogen phosphate, 0.260g of lithium acetate, 0.640g of sucrose, 40.0g of agate grinding beads with a diameter of 6mm, and 20.0g of agate grinding beads with a diameter of 10mm. Add 10ml of anhydrous ethanol as a dispersant and mill the mixture in a planetary ball mill at 600r / min. -1 After ball milling at a certain speed for 8 hours, the precursor powder was dried to obtain the precursor powder.

[0045] (4) Place the precursor powder in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 400℃ at a heating rate and held for 2 hours;

[0046] (5) Place the powder obtained in step (4) in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 650℃ at a heating rate and held for 10 hours. After cooling, approximately 3g of regenerated positive electrode powder material was obtained.

[0047] (6) Weigh 0.0601g of the positive electrode material powder obtained in step (5), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times, and obtain its chemical composition by ICP-OES method. The composition is approximately Li:Fe:Mn:P = 1.05:0.35:0.6:1, that is, the chemical formula of the obtained positive electrode powder material is Li 1.05 Fe 0.35 Mn 0.6 PO4.

[0048] Example 2:

[0049] In this embodiment, a method for directly regenerating waste lithium iron phosphate battery cathode material into lithium manganese iron phosphate by controlling lithium iron phosphate antisite defects mainly includes the following steps:

[0050] (1) The waste lithium iron phosphate positive electrode sheet is calcined at 400°C for 4 hours under inert gas to remove the polymer binder and carbon coating. After separating it from the current collector aluminum foil, it is ground to obtain positive electrode material powder; the inert gas is argon.

[0051] (2) Weigh 0.0601g of the positive electrode material powder obtained in step (1), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times and obtain its chemical composition by ICP-OES method, which is approximately Li:Fe:P=0.83:1:1;

[0052] (3) Weigh 2.10g of the positive electrode material powder obtained in step (1), 3.58g of manganese oxalate dihydrate, 2.06g of lithium dihydrogen phosphate, 0.260g of lithium acetate, 0.640g of sucrose, 40.0g of agate grinding beads with a diameter of 6mm, and 20.0g of agate grinding beads with a diameter of 10mm. Add 10ml of anhydrous ethanol as a dispersant and mill the mixture in a planetary ball mill at 600r / min. -1 After ball milling at a certain speed for 8 hours, the precursor powder was dried to obtain the precursor powder.

[0053] (4) Place the precursor powder in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 400℃ at a heating rate and held for 2 hours;

[0054] (5) Place the powder obtained in step (4) in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 700℃ at a certain rate and held for 10 hours. After cooling, approximately 3g of regenerated positive electrode powder material was obtained.

[0055] (6) Weigh 0.0601g of the positive electrode material powder obtained in step (5), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times, and obtain its chemical composition by ICP-OES method. The composition is approximately Li:Fe:Mn:P = 1.05:0.35:0.6:1, that is, the chemical formula of the obtained positive electrode powder material is Li 1.05 Fe 0.35 Mn 0.6 PO4.

[0056] Example 3:

[0057] In this embodiment, a method for directly regenerating waste lithium iron phosphate battery cathode material into lithium manganese iron phosphate by controlling lithium iron phosphate antisite defects mainly includes the following steps:

[0058] (1) The waste lithium iron phosphate positive electrode sheet is calcined at 400°C for 4 hours under inert gas to remove the polymer binder and carbon coating. After separating it from the current collector aluminum foil, it is ground to obtain positive electrode material powder; the inert gas is argon.

[0059] (2) Weigh 0.0601g of the positive electrode material powder obtained in step (1), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times and obtain its chemical composition by ICP-OES method, which is approximately Li:Fe:P=0.83:1:1;

[0060] (3) Weigh 1.57g of the positive electrode material powder obtained in step (1), 3.56g of manganese oxalate dihydrate, 2.54g of lithium dihydrogen phosphate, 0.33g of lithium acetate, 0.642g of sucrose, 40.0g of agate grinding beads with a diameter of 6mm, and 20.0g of agate grinding beads with a diameter of 10mm. Add 10ml of anhydrous ethanol as a dispersant and mill the mixture in a planetary ball mill at 600r / min. -1 After ball milling at a certain speed for 8 hours, the precursor powder was dried to obtain the precursor powder.

[0061] (4) Place the precursor powder in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 400℃ at a heating rate and held for 2 hours;

[0062] (5) Place the powder obtained in step (4) in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 650℃ at a heating rate and held for 10 hours. After cooling, approximately 5g of regenerated positive electrode powder material was obtained.

[0063] (6) Weigh 0.0601g of the positive electrode material powder obtained in step (5), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times, and obtain its chemical composition by ICP-OES method. The composition is approximately Li:Fe:Mn:P = 1.1:0.3:0.6:1, that is, the chemical formula of the obtained positive electrode powder material is Li 1.1 Fe 0.3 Mn 0.6 PO4.

[0064] Example 4:

[0065] In this embodiment, a method for directly regenerating waste lithium iron phosphate battery cathode material into lithium manganese iron phosphate by controlling lithium iron phosphate antisite defects mainly includes the following steps:

[0066] (1) The waste lithium iron phosphate positive electrode sheet is calcined at 400°C for 4 hours under inert gas to remove the polymer binder and carbon coating. After separating it from the current collector aluminum foil, it is ground to obtain positive electrode material powder; the inert gas is argon.

[0067] (2) Weigh 0.0601g of the positive electrode material powder obtained in step (1), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times and obtain its chemical composition by ICP-OES method, which is approximately Li:Fe:P=0.83:1:1;

[0068] (3) Weigh 1.57g of the positive electrode material powder obtained in step (1), 3.56g of manganese oxalate dihydrate, 2.54g of lithium dihydrogen phosphate, 0.33g of lithium acetate, 0.642g of sucrose, 40.0g of agate grinding beads with a diameter of 6mm, and 20.0g of agate grinding beads with a diameter of 10mm. Add 10ml of anhydrous ethanol as a dispersant and mill the mixture in a planetary ball mill at 600r / min. -1 After ball milling at a certain speed for 8 hours, the precursor powder was dried to obtain the precursor powder.

[0069] (4) Place the precursor powder in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 400℃ at a heating rate and held for 2 hours;

[0070] (5) Place the powder obtained in step (4) in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 700℃ at a certain rate and held for 10 hours. After cooling, approximately 5g of regenerated positive electrode powder material was obtained.

[0071] (6) Weigh 0.0601g of the positive electrode material powder obtained in step (5), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times, and obtain its chemical composition by ICP-OES method. The composition is approximately Li:Fe:Mn:P = 1.1:0.3:0.6:1, that is, the chemical formula of the obtained positive electrode powder material is Li 1.1 Fe 0.3 Mn 0.6 PO4. Comparative Example 1:

[0072] In this embodiment, a method for directly regenerating waste lithium iron phosphate battery cathode material into lithium manganese iron phosphate mainly includes the following steps:

[0073] (1) The waste lithium iron phosphate positive electrode sheet is calcined at 400°C for 4 hours under inert gas to remove the polymer binder and carbon coating. After separating it from the current collector aluminum foil, it is ground to obtain positive electrode material powder; the inert gas is argon or nitrogen.

[0074] (2) Weigh 0.0601g of the positive electrode material powder obtained in step (1), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times and obtain its chemical composition by ICP-OES method, which is approximately Li:Fe:P=0.83:1:1;

[0075] (3) Weigh 1.57g of the positive electrode material powder obtained in step (1), 2.68g of manganese oxalate dihydrate, 1.64g of lithium dihydrogen phosphate, 0.110g of lithium acetate, 0.480g of sucrose, 40.0g of agate grinding beads with a diameter of 6mm, and 20.0g of agate grinding beads with a diameter of 10mm. Add 10ml of anhydrous ethanol as a dispersant and mill the mixture in a planetary ball mill at 600r / min. -1 After ball milling at a certain speed for 8 hours, the precursor powder was dried to obtain the precursor powder.

[0076] (4) Place the precursor powder in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 400℃ at a heating rate and held for 2 hours;

[0077] (5) Place the powder obtained in step (4) in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 650℃ at a heating rate and held for 10 hours. After cooling, approximately 4g of regenerated positive electrode powder material was obtained.

[0078] (6) Weigh 0.0601g of the positive electrode material powder obtained in step (5), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times, and obtain its chemical composition by ICP-OES method. The composition is approximately Li:Fe:Mn:P = 1.0:0.4:0.6:1, that is, the chemical formula of the obtained positive electrode powder material is Li 1.0 Fe0.4 Mn 0.6 PO4. Comparative Example 2:

[0079] In this embodiment, a method for directly regenerating waste lithium iron phosphate battery cathode material into lithium manganese iron phosphate mainly includes the following steps:

[0080] (1) The waste lithium iron phosphate positive electrode sheet is calcined at 400°C for 4 hours under inert gas to remove the polymer binder and carbon coating. After separating it from the current collector aluminum foil, it is ground to obtain positive electrode material powder; the inert gas is argon or nitrogen.

[0081] (2) Weigh 0.0601g of the positive electrode material powder obtained in step (1), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times and obtain its chemical composition by ICP-OES method, which is approximately Li:Fe:P=0.83:1:1;

[0082] (3) Weigh 1.57g of the positive electrode material powder obtained in step (1), 2.68g of manganese oxalate dihydrate, 1.64g of lithium dihydrogen phosphate, 0.110g of lithium acetate, 0.480g of sucrose, 40.0g of agate grinding beads with a diameter of 6mm, and 20.0g of agate grinding beads with a diameter of 10mm. Add 10ml of anhydrous ethanol as a dispersant and mill the mixture in a planetary ball mill at 600r / min. -1 After ball milling at a certain speed for 8 hours, the precursor powder was dried to obtain the precursor powder.

[0083] (4) Place the precursor powder in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 400℃ at a heating rate and held for 2 hours;

[0084] (5) Place the powder obtained in step (4) in a tube furnace and heat it at 3°C ​​for 3 minutes under an argon atmosphere. -1 The temperature was increased to 650℃ at a heating rate and held for 10 hours. After cooling, approximately 4g of regenerated positive electrode powder material was obtained.

[0085] (6) Weigh 0.0601g of the positive electrode material powder obtained in step (5), add 2ml of aqua regia and microwave digest, make up to 25ml, dilute 100 times, and obtain its chemical composition by ICP-OES method. The composition is approximately Li:Fe:Mn:P = 1.0:0.4:0.6:1, that is, the chemical formula of the obtained positive electrode powder material is Li 1.0 Fe 0.4 Mn 0.6 PO4.

[0086] Performance testing experiment

[0087] The equipment used in the performance testing experiments, embodiments, and comparative examples of this invention is shown in Appendix Table 1.

[0088] Table 1

[0089]

[0090] Specific testing methods:

[0091] The lithium manganese iron phosphate cathode material powders (Li) obtained in Examples 1, 2, 3 and Comparative Example 1 were used. 1.05 Fe 0.35 Mn 0.6 PO4, Li 1.1 Fe 0.3 Mn 0.6 PO4, Li 1.0 Fe 0.4 Mn 0.6 After grinding, PO4 was analyzed on a Bruker D8 X-ray diffractometer in Germany at 1°min. -1 The rate tests were conducted, and the test results are as follows: Figure 1 , 2 As shown in Figures 3 and 4. Enlarged comparison images of Example 1 and Example 2 are shown below. Figure 5 As shown. The X-ray diffraction patterns of the lithium manganese iron phosphate materials obtained in Example 1 and Comparative Example 1, refined and fitted using the Retrieve method, are shown below. Figure 6 , 7 As shown in Tables 2 and 3, the unit cell parameters of the X-ray diffraction patterns of the lithium manganese iron phosphate materials obtained in Example 1 and Comparative Example 1, refined and fitted using the Retrieve method, are shown in Tables 2 and 3.

[0092] Table 2

[0093]

[0094] Table 3

[0095]

[0096] The lithium manganese iron phosphate cathode materials (Li) obtained in Example 1 and Comparative Example 1 were used... 1.05 Fe 0.35 Mn 0.6 PO4, Li 1.0 Fe 0.4 Mn 0.6 PO4 was subjected to solid-state nuclear magnetic resonance spectroscopy (magnetic field strength 14.1 T) on a nuclear magnetic resonance spectrometer. 7 Li dipole decoupled magic angle rotation (DD / MAS) experiment, such as Figure 8 As shown. The instrument's 7The Li Larmor frequency was 233.08 MHz, and proton decoupling (TPPM) was performed during acquisition. The powder sample was placed in a 4.0 mm pencil-shaped zirconia rotor. Spectra were obtained at a rotation speed of 8 kHz, with a 3 s cycle delay, approximately 90° pulses (3.8 μs), and 128 scans. The Li signal of LiCl was used as... 7 Reference for Li chemical shift.

[0097] The lithium manganese iron phosphate cathode materials (Li) obtained in the examples and comparative examples are compared. 1.05 Fe 0.35 Mn 0.6 PO4, Li 1.1 Fe 0.3 Mn 0.6 PO4, Li 1.0 Fe 0.4 Mn 0.6 PO4 was mixed with polyvinylidene fluoride binder and carbon black conductive agent in a mass ratio of 8:1:1 to obtain corresponding mixtures. These mixtures were then added to NMP (N-methylpyrrolidone) solvent to obtain mixed slurries. The mixed slurries were then coated onto the surface of an aluminum substrate and dried to obtain the corresponding positive electrode sheets at a drying temperature of 120°C. The obtained positive electrode sheets and lithium sheets were used as the positive and negative electrodes of a battery. A coin cell was assembled using a Celgard 2500 battery separator, LB-878 electrolyte, and a CR2032 battery case.

[0098] The above half-cell was tested using a Land CT 2001A blue battery tester at 0.2C / 1C rates (1C = 170mAh g). -1 Under the conditions of charging and discharging, the test results are as follows: Figure 9 , 10 (Specific capacity / voltage curves of half-cells assembled with lithium manganese iron phosphate materials obtained in Example 1 and Comparative Example 1) and Table 4 are shown.

[0099] The charge / discharge capacity and coulombic efficiency of the lithium manganese iron phosphate materials obtained in Examples 1-4 and Comparative Examples 1-2 are shown in Table 4.

[0100] Table 4

[0101]

[0102] Test Result Analysis:

[0103] (1) By Figure 1 , 2As can be seen from examples 1, 2, 3 and comparative example 1, the characteristic peaks of the cathode materials prepared in examples 1, 2, 3 and comparative example 1 are compared with the lithium iron phosphate standard card. The characteristic peaks of the cathode materials are one-to-one, and all of them are shifted to a smaller angle due to the addition of manganese. This indicates that lithium manganese iron phosphate cathode materials were prepared. The sharp XRD characteristic peaks indicate good crystallinity. In example 1, the ratio of the (020) peak to the (111) peak is 1.019, which is slightly greater than the 0.955 of comparative example 1. This indicates that it is a slightly lithium-rich structure. In example 3, there is an impurity phase Li3PO4, indicating that the lithium content in the slightly lithium-rich structure should be less than 1.1, otherwise impurities will be generated.

[0104] (2) By Figure 5 It can be seen that the micro-lithium-rich structure in Example 1 can only be formed below 650°C. At 700°C, the micro-lithium-rich structure is destroyed and partially converted into a lithium phosphate structure.

[0105] (3) By Figure 6 , 7 As shown in Tables 2 and 3, the cathode material prepared in Example 1 has a slightly lithium-rich structure, in which some lithium occupies iron sites and there are fewer antisite defects, which is one of the reasons for the excellent performance of the material.

[0106] (4) By Figure 8 It can be seen that the cathode material prepared in Example 1 has lithium in two different chemical environments, which fully demonstrates that it has a slightly lithium-rich structure, unlike the conventional lithium manganese iron phosphate material (i.e., Comparative Example 1).

[0107] (5) By Figure 9 , 10 It can be seen that the cathode material prepared in Example 1 has a discharge specific capacity of approximately 155 mAh g at a 0.2C rate. -1 The discharge specific capacity at 1C rate is approximately 137 mAh g. -1 The 1C discharge voltage is approximately 3.73V, which is better than that of Comparative Example 1, indicating that the material has a high capacity and excellent rate performance.

[0108] (6) As shown in Table 4, the cathode material prepared in Example 1 has a better discharge specific capacity and first-cycle coulombic efficiency at a 0.2C rate than other examples and comparative examples. The material prepared in Example 2 had its slightly lithium-rich structure destroyed due to heating at 700 degrees Celsius, resulting in the formation of lithium phosphate, which led to a decrease in discharge specific capacity and coulombic efficiency. The material prepared in Example 3 had a lower specific capacity due to a decrease in iron in the stoichiometric ratio, which led to a decrease in the redox couple. The reason for the decrease in specific capacity in Example 4 is the same as in Example 2. Comparative Examples 1 and 2 had lower specific capacities due to higher iron-lithium antisite defects.

[0109] In summary, this invention provides a method for directly regenerating waste lithium iron phosphate battery cathode materials into lithium manganese iron phosphate. The method is simple and convenient to operate, does not use any solvents, is virtually pollution-free, and is highly practical. It can be quickly promoted to industrial production and has significant practical implications in the field of waste battery recycling.

Claims

1. A method for directly regenerating waste lithium iron phosphate battery cathode material into lithium manganese iron phosphate by controlling lithium iron phosphate antisite defects, characterized in that: It includes the following steps: (1) The waste lithium iron phosphate battery positive electrode sheet was calcined at 400°C for 4 hours under inert gas to remove the polymer binder and carbon coating. After being separated from the current collector aluminum foil, it was ground to obtain positive electrode material powder. (2) Dissolve the positive electrode material powder obtained in step (1) in aqua regia and microwave digest it, and measure its chemical composition by ICP-OES. (3) The cathode material powder obtained in step (1) is ball-milled and mixed with lithium source, manganese source, phosphorus source and carbon source in a slightly lithium-rich molar ratio, and then dried to obtain precursor powder; (4) The precursor powder obtained in step (3) is pre-calcined at 400°C for 2 hours under an inert gas. (5) The powder obtained in step (4) is calcined at 650-700°C for 10 hours under an inert gas to obtain regenerated positive electrode powder material; In step (3), the designed micro-rich lithium molar ratio is Li:(Fe+Mn):P = (1.05~1.1):(0.9~0.95):1, where the molar ratio of iron to manganese is Fe:Mn=(0.3~0.35):0.6, and the extra lithium occupies the iron site.

2. The method according to claim 1, characterized in that: In step (3), the designed micro-rich lithium molar ratio is Li: Fe: Mn: P = 1.05: 0.35: 0.6:1, where the extra lithium occupies the iron sites, and the corresponding chemical formula of the resulting recycled cathode powder material is Li 1.05 Fe 0.35 Mn 0.6 PO4.

3. The method according to claim 1, characterized in that: The inert gas is either argon or nitrogen.

4. The method according to claim 1, characterized in that: In step (2), the aqua regia is a mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:

1.

5. The method according to claim 1, characterized in that: In step (3), the lithium source is at least one of lithium carbonate, lithium acetate, lithium oxalate, lithium oxide, and lithium hydroxide.

6. The method according to claim 1, characterized in that: In step (3), the manganese source is at least one of manganese carbonate, manganese oxalate, manganese acetate, manganese oxide, manganese trioxide, and manganese tetroxide.

7. The method according to claim 1, characterized in that: In step (3), the phosphorus source is at least one of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium dihydrogen phosphate.

8. The method according to claim 1, characterized in that: In step (3), the carbon source is at least one of starch, sucrose, glucose, cellulose, polyvinyl alcohol, polyethylene glycol, sodium carboxymethyl cellulose, citric acid, lactic acid, and succinic acid.

9. A positive electrode powder material prepared by the method of claim 2, characterized in that: It is directly recycled from waste lithium iron phosphate battery cathode materials, and its chemical formula is Li. 1.05 Fe 0.35 Mn 0.6 PO4.

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