Lithium iron phosphate positive electrode material and preparation method thereof
By using iron oxide red as a raw material and forming a nitrogen-doped carbon-coated lithium iron phosphate matrix, the problems of complex lithium iron phosphate preparation process and poor electrical performance were solved, and low-cost, high-capacity lithium iron phosphate preparation was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-01-27
- Publication Date
- 2026-04-10
AI Technical Summary
In existing technologies, the preparation process of lithium iron phosphate is complex and costly, and the lithium iron phosphate prepared by the low-cost iron red method has poor electrical performance, especially low 1C discharge capacity.
A lithium iron phosphate matrix was prepared using iron oxide red as a raw material, and a nitrogen-doped carbon coating layer was formed by amine-modified alkyl glucoside. The preparation method included spray drying and tube furnace sintering to form a uniform carbon coating structure.
It reduced the preparation cost by 20-25%, increased the discharge capacity of lithium iron phosphate, enhanced electronic conductivity and lithium-ion diffusion rate, and improved electrical performance.
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Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the technical field of lithium ion battery cathode material lithium iron phosphate, and particularly relates to a high-capacity lithium iron phosphate cathode material. BACKGROUND
[0002] Lithium ion batteries have the characteristics of large discharge capacity, low price, non-toxicity and no environmental pollution. Since the early 1990s, industrial production has been fully realized. Lithium iron phosphate is considered to be an ideal cathode material that can be applied to electric vehicles due to its low cost, good reliability of lithium extraction and good thermal stability. With the adjustment of the state's subsidy policy for new energy vehicles, battery manufacturers are increasingly demanding cost control and lithium iron phosphate materials, especially the increasingly high requirements for the tap density of lithium iron phosphate. There are mainly three kinds of industrialized production processes for lithium iron phosphate in China, including high-temperature solid-phase method, carbon thermal reduction method and sol-gel method. The high-temperature solid-phase method mainly uses ferrous oxalate as a raw material to produce lithium iron phosphate; the carbon thermal reduction method mainly uses iron oxide and iron phosphate as a raw material to produce lithium iron phosphate; and the sol-gel method mainly uses iron nitrate as a raw material to produce lithium iron phosphate. The ferrous oxalate route is the earliest industrialized process technology route for lithium iron phosphate, and this process has the characteristics of large product particle hardness, difficult morphology control and poor processing performance; the iron phosphate route has the characteristics of simple process flow, high product tap density and high specific capacity; and the nitric acid route has the characteristics of good rate performance, good cycle performance, good low-temperature performance and low tap density. From the characteristics of each route, the iron phosphate route will become the mainstream process route; the material prepared by using divalent iron salt as an iron source has a relatively low tap density, and the cost of divalent iron salt is high. Trivalent iron salt has a low cost, and using the high-density iron trioxide (Fe2O3) as a raw material can improve the tap density of the product. Compared with other processes, the iron red method has the advantages of cheap and easily available raw materials, simple process and equipment, and easier realization of large-scale industrial production, but the lithium iron phosphate synthesized by the process has poor electrical performance.
[0003] In the prior art, CN110482515B discloses a preparation method of low-cost lithium iron phosphate. Waste iron sheet is added to a phosphoric acid solution to obtain a ferrous solution, lithium carbonate and iron trioxide are added, an oxidizing agent is added, oxidation is performed until the trivalent iron content of the material is less than 100 ppm, then glucose is added, then spray drying is performed to obtain a spray-dried material; the spray-dried material is placed in a roller furnace for calcination, the calcination time is 25-30 h, the calcination is divided into four stages, i.e., a heating stage, a first holding stage, a second holding stage and a cooling stage, and the material after cooling is subjected to crushing, mixing, screening and iron removal to obtain lithium iron phosphate, and the cost is more than 20% lower than that of the current lithium iron phosphate solid-phase method. However, the 1C discharge capacity of the lithium iron phosphate prepared by this method is 139-141 mAh / g, and the electrical performance is poor.
[0004] In the prior art, coating lithium iron phosphate material with conductive substances is a key means to improve its rate and low-temperature performance, and carbon material is the simplest and most economical choice. Therefore, it is necessary to develop a new carbon coating technology to solve the problems of poor electrical performance in the process of preparing lithium iron phosphate by low-cost iron red method in the prior art. SUMMARY
[0005] The main purpose of the present application is to provide a lithium iron phosphate positive electrode material and a preparation method thereof, which has low manufacturing cost, high discharge capacity, simple process and is easy to realize industrialization, so as to solve the problems of complex process, high cost and low capacity of products prepared by low-cost iron red method in the prior art.
[0006] To achieve the above purposes, the technical solutions of the present application are as follows:
[0007] A lithium iron phosphate positive electrode material, comprising a lithium iron phosphate base and a carbon coating layer, wherein the lithium iron phosphate base is lithium iron phosphate particles prepared by using iron oxide red as raw material, and the carbon coating layer is a nitrogen-doped carbon coating layer formed by pyrolysis of amine-modified alkyl glucoside.
[0008] The preparation method of the lithium iron phosphate positive electrode material, comprising the following steps:
[0009] S1, dissolving a lithium source, iron oxide red and a phosphorus source in water to obtain a mixed slurry, adding a reducing agent to form a precursor slurry with a solid content of 25wt%-55wt%;
[0010] S2, sanding the precursor slurry to obtain a spray slurry, and preparing the spray slurry into a precursor powder by a spray drying method;
[0011] S3, placing the precursor powder in a tube furnace, obtaining a lithium iron phosphate base 1 under first sintering conditions in an inert atmosphere, and obtaining a lithium iron phosphate base 2 under second sintering conditions in an inert atmosphere;
[0012] S4, mixing the lithium iron phosphate base 1, amine-modified alkyl glucoside and water to form a lithium iron phosphate base slurry with a solid content of 40wt%-60wt%, sanding to obtain a lithium iron phosphate base sanding slurry 1 with a D50 of 1.6-2.5μm; mixing the lithium iron phosphate base 2, amine-modified alkyl glucoside and water to form a lithium iron phosphate base slurry with a solid content of 40wt%-60wt%, sanding to obtain a lithium iron phosphate base sanding slurry 2 with a D50 of 0.2-0.5μm; and mixing the lithium iron phosphate base sanding slurry 1 and the lithium iron phosphate base sanding slurry 2, and then spray drying to obtain a carbon-coated lithium iron phosphate precursor powder;
[0013] S5, placing the carbon-coated lithium iron phosphate precursor powder in a tube furnace, sintering and crushing.
[0014] Preferably, the amine-modified alkyl glucoside of the present application comprises one or more of N-alkanoyl-N-methyl glucosamine, N-dodecyl glucosamine, polyether amine methyl glucoside (Yangzhou Chenhua New Material Co., Ltd.), polyether amine ethyl glucoside (Yangzhou Chenhua New Material Co., Ltd.), more preferably one or more of N-dodecyl glucosamine, polyether amine methyl glucoside.
[0015] In S5, the nitrogen-doped carbon layer formed by pyrolysis of the amine-modified alkyl glucoside accounts for 1.5-2.4wt% of the mass of the lithium iron phosphate positive electrode material.
[0016] Preferably, in step S1, the molar ratio of the lithium source, red iron oxide, and phosphorus source is Li:Fe:P=(1.01-1.10):(0.95-0.99):1; for example, Li:Fe:P=1.02:0.95:1, 1.05:0.99:1, or 1.01:0.97:1, etc.; more preferably, Li:Fe:P=(1.01-1.06):(0.95-0.97):1.
[0017] Preferably, in step S1, the purity of the red iron oxide is 95wt% or higher, more preferably 99wt% or higher, and further preferably 99.5wt% or higher.
[0018] Preferably, in step S1, the phosphorus source comprises one or more of ammonium dihydrogen phosphate, phosphoric acid, and lithium dihydrogen phosphate, more preferably ammonium dihydrogen phosphate. Ammonium dihydrogen phosphate has good solubility in water and can be more uniformly dispersed in the reaction system, improving the uniformity of the reaction and the consistency of the product. During synthesis, ammonium dihydrogen phosphate can promote the stability of the crystal structure of lithium iron phosphate, helping to improve the cycle stability and capacity of the battery. Ammonium dihydrogen phosphate has a relatively low cost, which can reduce the production cost of lithium iron phosphate.
[0019] Preferably, in step S1, the lithium source comprises one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium oxalate, more preferably lithium hydroxide.
[0020] Preferably, in step S1, the reducing agent comprises one or more of glucose, sucrose, carbon black, and polyethylene glycol. The reducing agent reduces the iron oxide to ferrous ions (Fe 2+ ), preferably glucose and / or sucrose; more preferably glucose, which has a good reduction effect and further improves the electrochemical performance of the carbon-coated lithium iron phosphate positive electrode material prepared subsequently.
[0021] Preferably, the reducing agent in step S1, in terms of element mass, the C:Fe in the reducing agent is preferably 1:(10-20).
[0022] Preferably, the precursor slurry in step S2 is sand-milled, and preferably the D50 of the slurry after sand-milling is 0.2-0.4 μm.
[0023] Preferably, the inlet air temperature for spray drying in steps S2 and S4 is preferably 180-250°C, and more preferably the inlet air temperature is 180-220°C, and the outlet air temperature is preferably 80-110°C, and more preferably the outlet air temperature is 80-100°C.
[0024] Preferably, the first sintering condition in step S3 comprises: heating to 180-220°C at a heating rate of 1-3°C / min, and holding for 1-3h, then heating to 750-800°C at a rate of 0.5-2°C / min, preferably 1°C / min, and holding for 2-10h, and more preferably the holding time is 6-10h.
[0025] Preferably, the second sintering condition in step S3 comprises: heating to 180-220°C at a heating rate of 1-3°C / min, and holding for 1-3h, then heating to 600-750°C at a rate of 0.5-2°C / min, preferably 1°C / min, and holding for 2-10h, and more preferably the holding time is 2-8h.
[0026] Preferably, in step S4, the mixing ratio of the lithium iron phosphate matrix sand-milling slurry 1 and the lithium iron phosphate matrix sand-milling slurry 2, in terms of the mass of the lithium iron phosphate matrix 1 and the lithium iron phosphate matrix 2, is (0.5-9):1, and more preferably the mixing ratio is (0.6-4):1.
[0027] Preferably, in step S5, the sintering comprises the following steps: first heating to 180-220°C at a rate of 2-5°C / min in an inert atmosphere, holding for 1-3h, then heating to 700-800°C at a rate of 0.5-2°C / min, and holding for 2-10h.
[0028] The beneficial effects of the present application include:
[0029] (1) Using a ferric salt as the iron source, the raw material cost is low, and compared with other processes, the iron red method has the advantages of inexpensive and readily available raw materials, simple process and equipment, and easier realization of large-scale industrial production, and the cost is reduced by 20%-25%;
[0030] (2) The nitrogen-doped carbon coating layer formed in-situ by pyrolysis of amine-modified alkyl glucoside has a higher electronegativity (3.04) than that of carbon atoms (2.55), and after doping, an area with uneven charge distribution is formed in the carbon skeleton, increasing the carrier concentration; the incorporation of nitrogen atoms may break the chemical inertness of the carbon material, promoting the transmission of electrons in the carbon network, significantly improving the electronic conductivity of the carbon coating; the nitrogen-doped carbon coating layer is more closely combined with the surface of the LFP particles, reducing the interface resistance and ensuring efficient transmission of electrons from the carbon network to the LFP active material. The porous structure (such as mesopores and micropores) of the nitrogen-doped carbon coating layer can provide additional diffusion channels for lithium ions, shortening the diffusion path; the introduction of nitrogen atoms may change the surface chemical properties of the carbon coating layer, enhancing its wettability with the electrolyte and promoting the migration of lithium ions at the solid-liquid interface; and part of the nitrogen atoms may be combined with the defect sites on the surface of the LFP particles, inhibiting the "bottleneck effect" during lithium ion diffusion and improving the overall diffusion rate. BRIEF DESCRIPTION OF DRAWINGS
[0031] Figure 1 TEM photograph of high-capacity lithium iron phosphate of Example 1 of the present application. DETAILED DESCRIPTION
[0032] In order to facilitate the understanding of the present application, the present application will be further described below in conjunction with examples. It should be understood that the following examples are only for better understanding of the present application, and do not mean that the present application is limited to the following examples only.
[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The term "and / or" as can be used herein includes any and all combinations of one or more of the associated listed items.
[0034] Main raw material sources
[0035] Lithium carbonate, battery grade, GREEAMERICA ENERGY MATERIALS CO., LTD;
[0036] Ammonium dihydrogen phosphate, Jinzhengda Notart Chemical Co., Ltd.
[0037] Iron oxide red, Wuhu Xinda New Material Technology Co., Ltd.
[0038] Lithium hydroxide, battery grade, Tianqi Lithium Industry Co., Ltd.
[0039] Main test methods
[0040] TEM electron microscope: ThermoFisher Spectra 300 condenser spherical aberration correction transmission electron microscope is used in the present application to observe the atomic scale structure of the sample.
[0041] Preparation of lithium ion battery:
[0042] The lithium iron phosphate prepared in the example is mixed with PVDF and a conductive agent at a mass ratio of 96:2:2 to prepare a positive electrode slurry. An aluminum foil is used as a current collector, and the slurry is coated on the aluminum foil, which is then vacuum dried at 120°C for 12 hours. After thorough drying, the electrode sheet is cut into small pieces with a diameter of 16 mm to obtain the positive electrode sheet.
[0043] The battery is assembled in a glove box with high-purity argon (water and oxygen <0.1 ppm). 1M LiPF6 and ethyl carbonate (EC) / dimethyl carbonate (DMC) / diethyl carbonate (DEC) at a volume ratio of 1 / 1 / 1 are used as the electrolyte. The battery shell is CR2025, and lithium metal and Celgard2400 microporous membrane are used as the anode and the separator, respectively. The positive electrode sheet is obtained by drying at 105°C and rolling. The prepared positive electrode sheet, lithium sheet, separator, and electrolyte are assembled into a 2025 button cell.
[0044] Compaction density test:
[0045] A 1g sample of lithium iron phosphate powder is weighed to 0.0001g using a Shenzhen Sansi powder compaction density instrument. The powder sample is loaded into a compaction mold, which is then placed on the compaction density instrument. The instrument automatically applies pressure and records the volume change of the sample under different pressures. The compaction density is automatically calculated according to the formula ρ=m / V (mass / volume).
[0046] Example 1
[0047] Lithium carbonate 175.6g, iron oxide red 344g, and ammonium dihydrogen phosphate 504.8g (Li:Fe:P=1.08:0.98:1, molar ratio) are dissolved in 2000g of deionized water to form a mixed slurry with a solid content of 34wt%. 40.1g of glucose is added to the mixed slurry, which is stirred uniformly to obtain a precursor slurry.
[0048] The precursor slurry is ground using a sand mill, and the slurry D50=0.3μm. The spray drying inlet temperature is 180°C, and the outlet temperature is preferably 90°C. The ground precursor slurry is dried by spray drying to obtain a precursor powder.
[0049] The precursor powder is placed in a tube furnace and heated to 200°C at a rate of 3°C / min under an inert atmosphere, and then heated to 780°C at a rate of 1°C / min for 3h to obtain lithium iron phosphate matrix 1. The precursor powder is placed in a tube furnace and heated to 200°C at a rate of 3°C / min under an inert atmosphere, and then heated to 700°C at a rate of 1°C / min for 3h to obtain lithium iron phosphate matrix 2.
[0050] Lithium iron phosphate matrix 1 solid 510.7 g, 700 g of deionized water and 30.6 g of N-dodecyl glucosamine were mixed to form a lithium iron phosphate matrix 1 slurry with a solid content of 44 wt%, after stirring uniformly, the slurry was ground to D50 of 1.8 μm with a sand mill, lithium iron phosphate matrix 2 solid 170.3 g, 230 g of deionized water and 10.2 g of N-dodecyl glucosamine were mixed to form a lithium iron phosphate matrix 2 slurry with a solid content of 44 wt%, after stirring uniformly, the slurry was ground to D50 of 0.3 μm with a sand mill, to obtain a lithium iron phosphate matrix sand mill slurry 2; 600 g of lithium iron phosphate matrix 1 sand mill slurry and 200 g of lithium iron phosphate matrix 2 sand mill slurry were mixed, the inlet air temperature of spray drying was 180 ℃, and the outlet air temperature was preferably 90 ℃, the mixed slurry was dried by spray drying to obtain a carbon-coated lithium iron phosphate precursor powder;
[0051] The carbon-coated lithium iron phosphate precursor powder was placed in a tube furnace, first heated to 180 ℃ at a rate of 3 ℃ / min under an inert atmosphere, and then heated to 800 ℃ at a rate of 1 ℃ / min for 2 h, and the sintered product was crushed and refined to obtain a lithium iron phosphate positive electrode material A;
[0052] The obtained lithium iron phosphate positive electrode material was detected by microscope for micro-morphology, and a TEM diagram as shown in Figure 1 was obtained, and Figure 1 observation showed that the lithium iron phosphate particles were uniformly distributed, and the N-doped composite carbon layer was uniformly coated.
[0053] Example 2
[0054] Lithium carbonate 488 g, iron oxide red 1532 g, and ammonium dihydrogen phosphate 2300 g (Li:Fe:P=1.02:0.96:1, molar ratio) were dissolved in 4000 g of deionized water to form a mixed slurry with a solid content of 52 wt%, 152 g of sucrose was added to the mixed slurry, and after stirring uniformly, a precursor slurry was obtained.
[0055] The precursor slurry was ground by a sand mill, the slurry D50=0.3 μm, the inlet air temperature of spray drying was 180 ℃, and the outlet air temperature was preferably 90 ℃, the sand-milled precursor slurry was dried by spray drying to obtain a precursor powder.
[0056] The precursor powder was placed in a tube furnace, first heated to 200 ℃ at a rate of 3 ℃ / min under an inert atmosphere, and then heated to 750 ℃ at a rate of 1 ℃ / min for 10 h to obtain a lithium iron phosphate matrix 1, and the precursor powder was placed in a tube furnace, first heated to 200 ℃ at a rate of 3 ℃ / min under an inert atmosphere, and then heated to 700 ℃ at a rate of 1 ℃ / min for 2 h to obtain a lithium iron phosphate matrix 2.
[0057] The lithium iron phosphate matrix 1 solid 1723.1 g, 2410 g of deionized water and 117 g of polyether amine methyl glucoside were mixed to form a lithium iron phosphate matrix 1 slurry with a solid content of 45%, and after stirring uniformly, the slurry was ground to a D50 of 2.1 μm. The lithium iron phosphate matrix 2 solid 1148.7 g, 1608.2 g of deionized water and 78 g of polyether amine methyl glucoside were mixed to form a lithium iron phosphate matrix 2 slurry with a solid content of 45 wt%, and after stirring uniformly, the slurry was ground to a D50 of 0.23 μm to obtain a lithium iron phosphate matrix sand mill slurry 2. The lithium iron phosphate matrix 1 sand mill slurry 400 g was mixed with the lithium iron phosphate matrix 2 sand mill slurry 500 g, the inlet air temperature of spray drying was 180 ℃, and the outlet air temperature was preferably 90 ℃. The mixed slurry was dried by spray drying to obtain a carbon-coated lithium iron phosphate precursor powder.
[0058] The carbon-coated lithium iron phosphate precursor powder was placed in a tube furnace, first heated to 180 ℃ at a rate of 3 ℃ / min under an inert atmosphere, and then heated to 740 ℃ at a rate of 1 ℃ / min for 10 h. The sintered product was crushed and refined to obtain a lithium iron phosphate positive electrode material B.
[0059] Example 3
[0060] Lithium carbonate 505 g, iron oxide red 1009 g, and phosphoric acid 1274 g (Li:Fe:P = 1.05:0.97:1, molar ratio) were dissolved in 4700 g of deionized water to form a mixed slurry with a solid content of 34.7 wt%. 50 g of glucose and 58 g of sucrose were added to the mixed slurry, and after stirring uniformly, a precursor slurry was obtained.
[0061] The precursor slurry was ground by a sand mill, and the slurry D50 = 0.5 μm. The inlet air temperature of spray drying was 180 ℃, and the outlet air temperature was preferably 90 ℃. The sand-milled precursor slurry was dried by spray drying to obtain a precursor powder.
[0062] The precursor powder was placed in a tube furnace, first heated to 200 ℃ at a rate of 3 ℃ / min under an inert atmosphere, and then heated to 790 ℃ at a rate of 1 ℃ / min for 2 h to obtain a lithium iron phosphate matrix 1. The precursor powder was placed in a tube furnace, first heated to 220 ℃ at a rate of 3 ℃ / min under an inert atmosphere, and then heated to 680 ℃ at a rate of 1 ℃ / min for 10 h to obtain a lithium iron phosphate matrix 2.
[0063] 1425.6g of lithium iron phosphate matrix 1 solid, 1996g of deionized water and 67g of polyether aminomethyl glucoside were mixed and stirred evenly to form a lithium iron phosphate matrix 1 slurry with a solid content of 45wt%. The slurry was ground to a D50 of 2.5μm using a sand mill. 1425.6g of lithium iron phosphate matrix 2 solid, 1996g of deionized water and 67g of polyether aminomethyl glucoside were mixed and stirred evenly to form a lithium iron phosphate matrix 2 slurry with a solid content of 45%. The slurry was ground to a D50 of 0.4μm using a sand mill to obtain lithium iron phosphate matrix sand mill slurry 2. 800g of lithium iron phosphate matrix 1 sand mill slurry and 600g of lithium iron phosphate matrix 2 sand mill slurry were mixed and spray-dried at an inlet air temperature of 180℃ and an outlet air temperature preferably of 90℃ to obtain carbon-coated lithium iron phosphate precursor powder.
[0064] Carbon-coated lithium iron phosphate precursor powder was placed in a tube furnace and heated to 180°C at a rate of 3°C / min under an inert atmosphere and held for 3 hours. Then, the temperature was increased to 740°C at a rate of 1°C / min and held for 10 hours. The sintered product was then pulverized and refined to obtain lithium iron phosphate cathode material C.
[0065] Comparative Example 1
[0066] The preparation method is the same as in Example 1, except that N-dodecylglucosamine is replaced with glucose to prepare lithium iron phosphate cathode material D.
[0067] The performance test data of the positive electrodes prepared in Examples 1-3 and Comparative Example 1 are shown in Table 1.
[0068] Table 1
[0069] Item Powder compaction (g / cm 3 )]]> 0.1 C discharge capacity (mAh / g) 1 C discharge capacity (mAh / g) Example 1 2.51 159.0 147.1 Example 2 2.52 157.8 145.7 Example 3 2.55 160.1 146.5 Comparative Example 1 2.51 160.0 141.2
[0070] Analysis of the results from the comparative examples and embodiments shows that the addition of N-dodecylglucosamine improves the electrical performance of lithium iron phosphate (LFP) products under the same compaction conditions. The main reason is that the nitrogen-doped carbon coating reduces the interfacial resistance, ensuring that electrons can be efficiently transferred from the carbon network to the LFP active material. Some nitrogen atoms may combine with defect sites on the surface of LFP particles, suppressing the "bottleneck effect" in the lithium-ion diffusion process and improving the overall diffusion rate.
[0071] Finally, it should be noted that the above embodiments are only used to describe preferred embodiments of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that various modifications and improvements made to the technical solutions of the present invention by means of modifications or equivalent substitutions should fall within the scope of protection defined by the claims of the present invention.
Claims
1. A lithium iron phosphate cathode material, comprising a lithium iron phosphate matrix and a carbon coating layer, wherein the lithium iron phosphate matrix is lithium iron phosphate particles prepared using iron oxide red as a raw material, and the carbon layer is a nitrogen-doped carbon coating layer formed by the pyrolysis of amine-modified alkyl glucoside.
2. The method for preparing the lithium iron phosphate cathode material according to claim 1, comprising the following steps: S1. Dissolve lithium source, iron oxide red and phosphorus source in water to obtain a mixed slurry, add reducing agent to form a precursor slurry with a solid content of 25wt%-55wt%; S2. The precursor slurry is milled to obtain a spray slurry, and the spray slurry is prepared into a precursor powder by spray drying. S3. The precursor powder is placed in a tube furnace and sintered under an inert atmosphere to obtain lithium iron phosphate matrix 1 under the first sintering condition. Under an inert atmosphere, the precursor powder is sintered under a second sintering condition to obtain lithium iron phosphate matrix 2. S4. Lithium iron phosphate matrix 1 is mixed with amine-modified alkyl glucoside and water to form a lithium iron phosphate matrix slurry with a solid content of 40wt%-60wt%. The slurry is then milled to a D50 of 1.6-2.5μm to obtain lithium iron phosphate matrix milled slurry 1. Lithium iron phosphate matrix 2 is mixed with amine-modified alkyl glucoside and water to form a lithium iron phosphate matrix slurry with a solid content of 40wt%-60wt%. The slurry is then milled to a D50 of 0.2-0.5μm to obtain lithium iron phosphate matrix milled slurry 2. Lithium iron phosphate matrix milled slurry 1 and lithium iron phosphate matrix milled slurry 2 are then mixed and spray-dried to obtain carbon-coated lithium iron phosphate precursor powder. S5. Place the carbon-coated lithium iron phosphate precursor powder in a tube furnace, sinter, and pulverize.
3. The method according to claim 2, characterized in that, In step S1, the molar ratio of lithium source, iron oxide red, and phosphorus source is calculated as Li:Fe:P = (1.01-1.10):(0.95-0.99):
1.
4. The method according to claim 2, characterized in that, The first sintering conditions described in step S3 include: heating to 180-220°C at a heating rate of 1-3°C / min, holding at that temperature for 1-3 hours, and then heating to 750-800°C at a rate of 0.5-2°C / min, preferably 1°C / min, holding at that temperature for 2-10 hours, and more preferably holding at that temperature for 6-10 hours.
5. The method according to claim 2, characterized in that, The second sintering conditions described in step S3 include: heating to 180-220°C at a heating rate of 1-3°C / min, holding at that temperature for 1-3 hours, and then heating to 600-750°C at a rate of 0.5-2°C / min, preferably 1°C / min, holding at that temperature for 2-10 hours, and more preferably holding at that temperature for 2-8 hours.
6. The method according to claim 2, characterized in that, The amine-modified alkyl glucosides include one or more of N-alkyl-N-methylglucosamine, N-dodecylglucosamine, polyether aminomethylglucosamine, and polyether aminoethylglucosamine.
7. The method according to claim 2, characterized in that, In step S4, the mixing ratio of lithium iron phosphate matrix slurry 1 and lithium iron phosphate matrix slurry 2 is (0.5-9):1, more preferably (0.6-4):1, based on the mass of lithium iron phosphate matrix 1 and lithium iron phosphate matrix 2.
8. The method according to claim 2, characterized in that, In step S5, the sintering includes the following steps: first, heating to 180-220℃ at a rate of 2-5℃ / min under an inert atmosphere, holding at that temperature for 1-3 hours, and then heating to 700-800℃ at a rate of 0.5-2℃ / min, holding at that temperature for 2-10 hours.
9. The method according to claim 2, characterized in that, In S5, the nitrogen-doped coated carbon layer formed by the pyrolysis of the amine-modified alkyl glucoside accounts for 1.5-2.4 wt% of the lithium iron phosphate cathode material by mass.
10. The method according to claim 2, characterized in that, The phosphorus source in step S1 includes one or more of ammonium dihydrogen phosphate, phosphoric acid, and lithium dihydrogen phosphate; and / or the lithium source includes one or more of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium oxalate; and / or the reducing agent includes one or more of glucose, sucrose, carbon black, and polyethylene glycol.