Monocrystal lithium iron phosphate as well as preparation method and application thereof

Abstract

The invention discloses single-crystal lithium iron phosphate and a preparation method and application thereof, and belongs to the technical field of battery materials, the method comprises the following steps: S01, treating and recycling a lithium iron phosphate positive plate, a separation current collector and an active component feed liquid by using hydrogen peroxide, heating the active component feed liquid and phosphoric acid to react, and cooling to age iron phosphate crystals to obtain a lithium iron phosphate crystal; filtering, collecting solids and washing to obtain iron phosphate crystals; s02, mixing the iron phosphate crystals with glucose, and sintering the mixture for the first time at 400-680 DEG C in an inert gas atmosphere to obtain an iron phosphate precursor; and mixing the iron phosphate precursor, glucose, lithium carbonate and lithium fluoride, sanding, drying, and further sintering for the second time at 700-750 DEG C in an inert gas atmosphere to obtain the single-crystal lithium iron phosphate. The monocrystal lithium iron phosphate is uniform in particle size distribution, high in product purity and high in compaction density, and can be applied to the field of high-compaction high-performance long-circulation energy storage.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, specifically to a single-crystal lithium iron phosphate, its preparation method, and its applications. Background Technology

[0002] Lithium iron phosphate (LFP) is one of the most widely used and rapidly developing cathode materials in the fields of power batteries and energy storage batteries. Iron phosphate is a key precursor for preparing LFP cathode materials. Currently, the industrial large-scale production processes for LFP are mainly divided into three categories: sodium method, ammonia method, and iron method. The core difference between these three methods lies in the phosphorus source and the precipitant / reaction system used. Compared to polycrystalline materials, single-crystal materials have better particle structure stability and resistance to breakage under high compaction density, and are generally widely used in cathodes with high conductivity, such as lithium cobalt oxide and ternary cathode materials (NCM / NCA). In contrast, the application of single-crystal technology in LFP materials with lower intrinsic conductivity is relatively limited.

[0003] In the prior art, researchers have developed various methods for preparing single-crystal lithium iron phosphate. For example, Chinese patent document CN108321390A discloses a three-dimensional flower-like single-crystal lithium iron phosphate and its preparation method. This invention dissolves urea and sodium carbonate in ethylene glycol, adds a phosphorus source and an iron source, mixes them evenly, and then carries out a hydrothermal reaction. After the reaction is completed, the product is filtered, washed, and dried. Then, the obtained precursor and lithium source are mixed and calcined at high temperature under inert gas protection to obtain three-dimensional flower-like single-crystal lithium iron phosphate. The corresponding three-dimensional flower-like structure is composed of nanosheet lithium iron phosphate. Chinese patent document CN117377638A discloses a method for preparing sheet-like iron phosphate and a method for preparing sheet-like lithium iron phosphate. This invention uses an electrochemical method of electropulse to control the synthesis of sheet-like iron phosphate single crystals (particle size ~500nm) and sheet-like lithium iron phosphate with good electrical properties. However, the compaction density of the sheet-like structure is low, which does not meet the requirements of commercial production.

[0004] Chinese patent document CN119352158A discloses nanocrystalline lithium iron phosphate, its preparation method, and its applications. The method includes: ball milling a mixture containing lithium, iron, and phosphorus sources in a supercritical fluid, followed by calcination, impurity removal, and drying to obtain lithium iron phosphate; dispersing the lithium iron phosphate in glycerol and then sintering to obtain nanocrystalline lithium iron phosphate. This method requires sophisticated equipment and is difficult to industrialize.

[0005] Chinese patent document CN113387339A discloses nanoscale iron phosphate, its preparation method, and its applications. The method involves first adding a surfactant and polymer microspheres to an iron salt solution to obtain a mixture. Then, a phosphate solution is added to the mixture to react and obtain an iron phosphate slurry. After removing the polymer microspheres from the slurry, solid-liquid separation is performed. The resulting solid is dried and calcined to obtain nanoscale iron phosphate. Although the single-crystal iron phosphate synthesized by this method has a particle size in the range of 10–100 nm, a higher tap density than conventional co-precipitation methods, and a smaller average particle size, its preparation process involves surfactants and polymer microspheres, making the process relatively complex. Summary of the Invention

[0006] To address the shortcomings of the existing technologies, this invention provides a single-crystal lithium iron phosphate and its preparation method. This method uses waste lithium iron phosphate cathode sheets as raw materials, combines the Fenton effect to convert them into single-crystal iron phosphate and lithium salt, and further controls the growth of single crystals. After mixing and sintering, single-crystal lithium iron phosphate is prepared. The corresponding single-crystal lithium iron phosphate has high compaction density and high product purity, and has good application prospects in the battery field, especially suitable for energy storage applications with low rate, long working time and small capacity.

[0007] The specific technical solution adopted is as follows: A method for preparing single-crystal lithium iron phosphate includes the following steps: S01 uses hydrogen peroxide to treat and recover lithium iron phosphate cathode sheets, separates current collector and active ingredient liquid, heats and reacts the active ingredient liquid with phosphoric acid, cools down to age iron phosphate crystals, filters and collects solids and washes them to obtain iron phosphate crystals. S02 mixes iron phosphate crystals and glucose and sintersects them for the first time at 400℃~680℃ in an inert gas atmosphere to obtain an iron phosphate precursor. The iron phosphate precursor, glucose, lithium carbonate and lithium fluoride are mixed, milled and dried, and then sintered for the second time at 700℃~750℃ in an inert gas atmosphere to obtain single crystal lithium iron phosphate.

[0008] Preferably, the recycled lithium iron phosphate cathode sheet is added to water, followed by hydrogen peroxide. The molar ratio of hydrogen peroxide to the theoretical lithium iron phosphate content in the recycled lithium iron phosphate cathode sheet, based on H2O2 content, is 1.05~1.1:1. Stirring causes the lithium iron phosphate to peel off from the current collector surface, separating the current collector and the active ingredient solution. In existing technologies, to reduce the charge transfer impedance between the cathode and the foil and the internal resistance of the cell, carbon-coated aluminum foil is typically used for lithium iron phosphate cathode sheets. This carbon-coated aluminum foil uses a mixture of water-based binders (polyacrylic acid, PMMA, CMC, and SBR, etc.) and conductive agents (conductive carbon black, carbon nanotubes, graphene, etc.) coated onto the aluminum foil. This mixture has good affinity and wetting properties for water. Furthermore, lithium iron phosphate itself has a theoretical expansion and contraction of 6.7% during battery cycling. Therefore, the above method facilitates the separation of the current collector and the active ingredient. A mixed solution of hydrogen peroxide and ferrous ions has strong oxidizing properties and can oxidize some organic compounds such as carboxylic acids, alcohols, and esters into inorganic forms, with a very significant oxidation effect.

[0009] Preferably, the heating reaction temperature of the active ingredient solution and phosphoric acid is 35℃~80℃, and the reaction time is 5-12 h.

[0010] Preferably, when the active ingredient solution and phosphoric acid are heated and reacted, the molar ratio of the amount of phosphoric acid used to the theoretical content of lithium iron phosphate in the recovered lithium iron phosphate cathode is 1.05~1.1:1; and the temperature is lowered to 5℃~30℃ and aged for 6-8 hours.

[0011] The reaction equation for the above process can be expressed as: H3PO4+LiFePO4+1 / 2 H2O2→FePO4+LiH2PO4+H2O; The active ingredient solution contains unreacted H2O2. Combined with the Fenton effect, a slightly excessive amount of phosphoric acid is used to dissolve lithium iron phosphate and oxidize it to form iron phosphate. The synthesis of single-crystal iron phosphate is controlled by adjusting the raw material ratio, aging temperature and stirring speed.

[0012] Preferably, in step S01, lithium hydroxide is added to the filtered filtrate to adjust the pH of the solution to 8-12, and further evaporation yields lithium dihydrogen phosphate crystals.

[0013] Preferably, iron phosphate crystals and glucose are mixed at a mass ratio of 100:0.5~3, and the inert gas atmosphere for the first sintering is nitrogen atmosphere, with a first sintering time of 3-5 h. The above sintering process can maintain the morphology of iron phosphate and control the growth of single crystals, which is beneficial to the morphology of the single crystal lithium iron phosphate product.

[0014] Preferably, a mixed powder is obtained by mixing an iron phosphate precursor, glucose, lithium carbonate, and lithium fluoride. The glucose content of the mixed powder is 3 wt% to 5 wt%, and the lithium fluoride content is 0.5 wt% to 1.5 wt%. The molar ratio of the iron phosphate precursor (based on its iron phosphate content) to lithium carbonate is 2:1 to 1.08. The purpose of adding lithium fluoride is to control the melting of the crystals and ensure the single crystal morphology through a molten salt solvothermal method. The addition of the complex salt can form a low-temperature eutectic solvent, reducing the reaction barrier and energy consumption. Simultaneously, the addition of LiF facilitates the formation of F... - Doping modification improves the electrochemical performance of the material. Preferably, the inert gas atmosphere for the second sintering is nitrogen atmosphere, and the second sintering time is 10-18 h.

[0015] The present invention also provides a single-crystal lithium iron phosphate prepared by the aforementioned method. Preferably, the single-crystal lithium iron phosphate has a grain size of 50nm~150nm, with regular morphology and uniform particle size distribution. Benefiting from its structural advantages, batteries prepared with single-crystal lithium iron phosphate as the positive electrode active component have high charge-discharge energy efficiency (energy efficiency ≥96.5%) and cycle performance (cycle life can reach 15,000 times at 0.25C charge-discharge) at relatively low rates (≤0.25C, i.e., 100% DOD charge-discharge time ≥4h).

[0016] The present invention also provides the application of the aforementioned single-crystal lithium iron phosphate in the preparation of batteries.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method of the present invention combines the Fenton effect to convert the recycled lithium iron phosphate cathode sheet into single crystal iron phosphate and lithium salt, and uses the corresponding single crystal iron phosphate to sinter with lithium carbonate, carbon source, etc. to prepare single crystal lithium iron phosphate. The obtained single crystal lithium iron phosphate product has high purity, grain size between 50nm and 150nm, regular morphology, uniform particle size distribution, and high compaction density, and can be applied to the field of high compaction, high performance, long cycle energy storage.

[0018] (2) Thanks to the structure of large single-crystal lithium iron phosphate, the battery prepared with single-crystal lithium iron phosphate as the positive electrode active component has high charge and discharge energy efficiency (energy efficiency ≥96.5%), cycle performance (cycle life can reach 15,000 times under 0.25C charge and discharge) and safety at a relatively low rate (≤0.25C, i.e. 100% DOD charge and discharge time ≥4h). Attached Figure Description

[0019] Figure 1 The image shows the XRD pattern of the iron phosphate crystals synthesized in Example 1.

[0020] Figure 2 The image shows the XRD pattern of the single-crystal lithium iron phosphate synthesized in Example 1.

[0021] Figure 3 This is a SEM image of the single-crystal lithium iron phosphate synthesized in Example 1.

[0022] Figure 4 Cycling curves of full cells prepared from single-crystal lithium iron phosphate synthesized in Example 1. Detailed Implementation

[0023] To make the objectives, features, and advantages of this invention more apparent and understandable, a detailed description is provided below through specific embodiments. Many specific details are set forth in the following description to provide a thorough understanding of the invention. However, the invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below. Technical features in various embodiments of the invention can be combined appropriately without mutual conflict.

[0024] Unless otherwise specified, the operating methods in the following examples are generally performed under conventional conditions or as recommended by the manufacturer. Contents not described in detail in this specification are prior art known to those skilled in the art. Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0025] Example 1 After the waste lithium iron phosphate batteries are discharged to empty (forced discharge to 1.8V), the lithium iron phosphate positive electrode is dissected and removed from the battery cell. The recycled lithium iron phosphate positive electrode is soaked in deionized water, and then hydrogen peroxide is added. The molar ratio of the amount of hydrogen peroxide added to the theoretical lithium iron phosphate content in the recycled lithium iron phosphate positive electrode is 1.05:1, based on the H2O2 content. The mixture is stirred for 8 hours to ensure that the active component lithium iron phosphate is fully soaked and peeled off from the current collector aluminum foil. After separating the current collector, the obtained active component solution is heated to 60°C, and then phosphoric acid is added (the molar ratio of the amount of phosphoric acid added to the theoretical lithium iron phosphate content in the above-mentioned lithium iron phosphate positive electrode is 1.05:1). The mixture is reacted for 10 hours, and then cooled to 5°C under stirring conditions for 6 hours to age the iron phosphate crystals. The mixture is filtered to obtain a filter cake, which is then vacuum filtered and washed with distilled water to obtain iron phosphate crystals. Lithium hydroxide is added to the filtrate to adjust the pH of the solution to 10, and then evaporated to obtain lithium dihydrogen phosphate crystals. The iron phosphate crystals obtained in the above steps were mixed with glucose at a mass ratio of 100:0.5. After mixing, the mixture was sintered for the first time under a nitrogen atmosphere at a temperature of 400°C for 5 hours to obtain an iron phosphate precursor. The iron phosphate precursor, glucose, lithium carbonate, and lithium fluoride were then mixed to obtain a mixed powder, wherein glucose accounted for 3 wt% of the mixed powder mass, lithium fluoride accounted for 1 wt% of the mixed powder mass, and the molar ratio of iron phosphate precursor to lithium carbonate was 2:1. The mixed powder was then milled, dried, and further sintered for the second time at 720°C under a nitrogen atmosphere for 12 hours to obtain single-crystal lithium iron phosphate.

[0026] Example 2 After the waste lithium iron phosphate batteries are discharged to empty (forced discharge to 1.8V), the lithium iron phosphate positive electrode is dissected and removed from the cell. The recycled lithium iron phosphate positive electrode is soaked in deionized water, and then hydrogen peroxide is added. The molar ratio of the amount of hydrogen peroxide added to the theoretical lithium iron phosphate content in the recycled lithium iron phosphate positive electrode is 1.1:1, based on the H2O2 content. The mixture is stirred for 8 hours to ensure that the active component lithium iron phosphate is fully soaked and peeled off from the current collector aluminum foil. After separating the current collector, the resulting active component solution is heated to 80°C, and then phosphoric acid is added (the molar ratio of the amount of phosphoric acid added to the theoretical lithium iron phosphate content in the above-mentioned lithium iron phosphate positive electrode is 1.1:1). The mixture is reacted for 8 hours, and then cooled to 20°C under stirring conditions for aging of iron phosphate crystals for 8 hours. The mixture is filtered to obtain a filter cake, which is then vacuum filtered and washed with distilled water to obtain iron phosphate crystals. Lithium hydroxide is added to the filtrate to adjust the pH of the solution to 8, and then evaporated to obtain lithium dihydrogen phosphate crystals. The iron phosphate crystals obtained in the above steps were mixed with glucose at a mass ratio of 100:1.5. After mixing, the mixture was sintered for the first time under a nitrogen atmosphere at a temperature of 620°C for 3 hours to obtain an iron phosphate precursor. The iron phosphate precursor, glucose, lithium carbonate, and lithium fluoride were then mixed to obtain a mixed powder, wherein glucose accounted for 4.5 wt% of the mixed powder mass, lithium fluoride accounted for 0.5 wt% of the mixed powder mass, and the molar ratio of iron phosphate precursor to lithium carbonate was 2:1. The mixed powder was then milled, dried, and further sintered for the second time at 714°C under a nitrogen atmosphere for 15 hours to obtain single-crystal lithium iron phosphate.

[0027] Example 3 After the waste lithium iron phosphate batteries are discharged to empty (forced discharge to 1.8V), the lithium iron phosphate positive electrode is dissected and removed from the battery cell. The recycled lithium iron phosphate positive electrode is soaked in deionized water, and then hydrogen peroxide is added. The molar ratio of the amount of hydrogen peroxide added to the theoretical lithium iron phosphate content in the recycled lithium iron phosphate positive electrode is 1.08:1, based on the H2O2 content. The mixture is stirred for 6 hours to ensure that the active component lithium iron phosphate is fully soaked and peeled off from the current collector aluminum foil. After separating the current collector, the obtained active component solution is heated to 45°C, and then phosphoric acid is added (the molar ratio of the amount of phosphoric acid added to the theoretical lithium iron phosphate content in the above-mentioned lithium iron phosphate positive electrode is 1.06:1). The mixture is reacted for 10 hours, and then cooled to 25°C under stirring conditions for 7 hours to age the iron phosphate crystals. The mixture is filtered to obtain a filter cake, which is then vacuum filtered and washed with distilled water to obtain iron phosphate crystals. Lithium hydroxide is added to the filtrate to adjust the pH of the solution to 12, and the solution is evaporated to obtain lithium dihydrogen phosphate crystals. The iron phosphate crystals obtained in the above steps were mixed with glucose at a mass ratio of 100:1. After mixing, the mixture was sintered for the first time under a nitrogen atmosphere at a temperature of 680℃ for 4 hours to obtain an iron phosphate precursor. The iron phosphate precursor, glucose, lithium carbonate, and lithium fluoride were then mixed to obtain a mixed powder, wherein glucose accounted for 4 wt% of the mixed powder mass, lithium fluoride accounted for 1.5 wt% of the mixed powder mass, and the molar ratio of iron phosphate precursor to lithium carbonate was 2:1. The mixed powder was then milled, dried, and further sintered for the second time at 708℃ under a nitrogen atmosphere for 15 hours to obtain single-crystal lithium iron phosphate.

[0028] Example 4 After the waste lithium iron phosphate batteries are discharged to empty (forced discharge to 1.8V), the lithium iron phosphate positive electrode is dissected and removed from the battery cell. The recycled lithium iron phosphate positive electrode is soaked in deionized water, and then hydrogen peroxide is added. The molar ratio of the amount of hydrogen peroxide added to the theoretical lithium iron phosphate content in the recycled lithium iron phosphate positive electrode is 1.05:1, based on the H2O2 content. The mixture is stirred for 10 h to ensure that the active component lithium iron phosphate is fully soaked and peeled off from the current collector aluminum foil. After separating the current collector, the resulting active component solution is heated to 70°C, and then phosphoric acid is added (the molar ratio of the amount of phosphoric acid added to the theoretical lithium iron phosphate content in the above-mentioned lithium iron phosphate positive electrode is 1.1:1). The mixture is reacted for 10 h, and then cooled to 10°C under stirring conditions for 6 h of iron phosphate crystal aging. The mixture is filtered to obtain a filter cake, which is then vacuum filtered and washed with distilled water to obtain iron phosphate crystals. Lithium hydroxide is added to the filtrate to adjust the pH of the solution to 9, and then evaporated to obtain lithium dihydrogen phosphate crystals. The iron phosphate crystals obtained in the above steps were mixed with glucose at a mass ratio of 100:1. After mixing, the mixture was sintered for the first time under a nitrogen atmosphere at a temperature of 550°C for 3 hours to obtain an iron phosphate precursor. The iron phosphate precursor, glucose, lithium carbonate, and lithium fluoride were then mixed to obtain a mixed powder, wherein glucose accounted for 4.5 wt% of the mixed powder mass, lithium fluoride accounted for 1.5 wt% of the mixed powder mass, and the molar ratio of iron phosphate precursor to lithium carbonate was 2:1. The mixed powder was then milled, dried, and further sintered for the second time at 750°C under a nitrogen atmosphere for 10 hours to obtain single-crystal lithium iron phosphate.

[0029] Sample Analysis The XRD pattern of the iron phosphate crystals synthesized in Example 1 (without glucose sintering) is as follows: Figure 1 As shown in the figure, the iron phosphate crystal exhibits diffraction peaks of monoclinic iron phosphate dihydrate, which are basically consistent with the peak position at PDF#00-65-0258. In particular, the 101 crystal plane near 2theta≈20° shows that it is a large single crystal structure, while the diffraction peaks on the (020) crystal plane show that it is a Fe(PO)4 structure.

[0030] Figure 2 The XRD pattern of the single-crystal lithium iron phosphate synthesized in Example 1 shows sharp diffraction peaks and no Fe. 3+ The appearance of impurity peaks indicates that the synthesized lithium iron phosphate cathode material has good crystallinity. Its position is basically consistent with the peak position at PDF#81-1173. The main peak at 2theta≈30° corresponds to the (110) main peak of LiFePO4, indicating high purity.

[0031] Figure 3 The image shows a SEM image of the single-crystal lithium iron phosphate synthesized in Example 1. As can be seen from the image, the crystal size is between 50 nm and 150 nm, with regular morphology and uniform particle size distribution.

[0032] The performance of the monocrystalline lithium iron phosphate synthesized in Example 1 was further tested, and a coin cell was prepared. The coin cell structure consists of a positive electrode shell + positive electrode + separator + negative electrode + gasket + spring sheet + negative electrode shell. The cathode composition is 96% monocrystalline lithium iron phosphate, 2% PVDF binder, and 2% Super S conductive carbon black (by weight), with an areal density of 460 g / m³. 2 ; The electrolyte concentration was 1 mol / L, the solute was LiPF6 (Capchem, Shenzhen, China 99.9%), the solvent was ethylene carbonate (EC, Capchem, <20ppm H2O) and diethyl carbonate (DEC, Capchem, <20ppm H2O) in a mass ratio of 1:1, and the additives were 2.5% VC, 1% PS, 2% DTD, and 0.5% FEC. The separator used is the Celgard 20u battery separator; The negative electrode is a lithium sheet; Tests showed that the coin cell capacity of this single-crystal lithium iron phosphate reached over 160 mAh / g, and the compaction density reached 2.55 g / cm³. 3 The product purity reaches electronic grade and can be applied to high-pressure, high-performance, long-cycle energy storage.

[0033] The performance of the monocrystalline lithium iron phosphate synthesized in Example 1 was further tested, and a full cell was prepared. The preparation method of the full cell was as follows: monocrystalline lithium iron phosphate, SP, and PVDF were mixed and stirred in an NMP stirring tank at a mass ratio of 94.5%:3%:2.5% to obtain a solid content of 65%. This slurry was then coated on both sides of a 12+1+1 carbon-coated foil using a coating machine, and the double-sided areal density was 360 g / m². 2 After rolling, the thickness of the positive electrode sheet after rolling is 156±2mm; for the negative electrode, BTR artificial graphite:SP:CMC:SBR:PAA adhesive is mixed in an H2O mixing tank at a mass ratio of 95%:1.5%:0.5%:2%:1%, with a solid content of 45%. This slurry is then coated onto both sides of a 6 μm copper foil using a coating machine, with a double-sided surface density of 178g / m². 2 After rolling, the negative electrode sheet thickness is 129±2mm. Then, the positive and negative electrodes are cut to form a certain stack size. The separator is Enjie 9+3+1+1 (9μm wet PE base film, 3μm alumina ceramic, and 1μm PVDF adhesive on both sides). The separator-negative electrode-separator-positive electrode stack (roll) forms a single core. The core is shaped after hot pressing. The core tabs are ultrasonically welded and then laser welded to the top cover. After the core is wrapped, it is placed in the shell and laser-sealed once. After vacuum baking, it enters the liquid injection process. The liquid injection volume is calculated at 3.8 g / Ah. The first liquid injection volume accounts for 95% of the total liquid injection volume. Then, it enters the formation negative pressure process at 45℃ for 48h. After the formation is completed, a second liquid injection (remaining 5%) is performed and a second sealing is performed. Then, the discharge capacity test and cell screening are carried out to obtain the full cell.

[0034] Figure 4 The results show that the full cell retains 97.8% of its capacity after 470 cycles at 0.25C, and the curve indicates that its cycle life can reach more than 15,000 cycles.

[0035] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing single-crystal lithium iron phosphate, characterized in that, Includes the following steps: S01 uses hydrogen peroxide to treat and recover lithium iron phosphate cathode sheets, separates current collector and active ingredient liquid, heats and reacts the active ingredient liquid with phosphoric acid, cools down to age iron phosphate crystals, filters and collects solids and washes them to obtain iron phosphate crystals. S02 mixes iron phosphate crystals and glucose and sintersects them for the first time at 400℃~680℃ in an inert gas atmosphere to obtain an iron phosphate precursor. The iron phosphate precursor, glucose, lithium carbonate and lithium fluoride are mixed, milled and dried, and then sintered for the second time at 700℃~750℃ in an inert gas atmosphere to obtain single crystal lithium iron phosphate.

2. The method for preparing single-crystal lithium iron phosphate according to claim 1, characterized in that, Based on H2O2 content, the molar ratio of added hydrogen peroxide to the theoretical lithium iron phosphate content in the recovered lithium iron phosphate cathode sheet is 1.05~1.1:

1.

3. The method for preparing single-crystal lithium iron phosphate according to claim 1, characterized in that, The heating reaction temperature of the active ingredient solution and phosphoric acid is 35℃~80℃, and the reaction time is 5-12 h.

4. The method for preparing single-crystal lithium iron phosphate according to claim 1, characterized in that, When the active ingredient solution and phosphoric acid are heated and reacted, the molar ratio of the amount of phosphoric acid used to the theoretical content of lithium iron phosphate in the recovered lithium iron phosphate cathode is 1.05~1.1:1; then the temperature is lowered to 5℃~30℃ and aged for 6-8 hours.

5. The method for preparing single-crystal lithium iron phosphate according to claim 1, characterized in that, Ferric phosphate crystals and glucose were mixed at a mass ratio of 100:0.5~3. The first sintering was carried out under a nitrogen atmosphere and the first sintering time was 3-5 hours.

6. The method for preparing single-crystal lithium iron phosphate according to claim 1, characterized in that, A mixed powder was obtained by mixing iron phosphate precursor, glucose, lithium carbonate and lithium fluoride. The mass of glucose accounted for 3 wt% to 5 wt% of the mixed powder, the mass of lithium fluoride accounted for 0.5 wt% to 1.5 wt% of the mixed powder, and the molar ratio of iron phosphate precursor to lithium carbonate was 2:1 to 1.

08.

7. The method for preparing single-crystal lithium iron phosphate according to claim 1, characterized in that, The second sintering is performed under a nitrogen atmosphere as the inert gas, and the second sintering time is 10-18 h.

8. Single-crystal lithium iron phosphate prepared by any one of the methods described in claims 1-7.

9. The single-crystal lithium iron phosphate according to claim 8, characterized in that, The grain size of single-crystal lithium iron phosphate is 50nm~150nm.

10. The application of single-crystal lithium iron phosphate according to claim 8 or 9 in the preparation of batteries.

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