Easily depolymerized lithium iron phosphate positive electrode material prepared by cross-linking polymerization and application of easily depolymerized lithium iron phosphate positive electrode material

Abstract

The invention discloses an easily depolymerized lithium iron phosphate positive electrode material prepared by cross-linking polymerization and application thereof, and belongs to the technical field of battery materials. The porosity tau of the easily depolymerized lithium iron phosphate positive electrode material is less than or equal to 0.8; wherein rho0 is the true density of the lithium iron phosphate positive electrode material before the pressing treatment, rho1 is the true density of the lithium iron phosphate positive electrode material after the pressing treatment under the first pressure P1, rho2 is the true density of the lithium iron phosphate positive electrode material after the pressing treatment under the second pressure P2, and P1 is less than P2; the units of P1 and P2 are both MPa, the unit of 0.1 is MPa, and the units of rho0, rho1 and rho2 are all g / cm < 3 >. The easily depolymerized lithium iron phosphate positive electrode material meeting the conditions is high in density and less in agglomeration among particles, so that a battery using the easily depolymerized lithium iron phosphate positive electrode material as the positive electrode material has relatively good rate capability and proper specific discharge capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of battery materials, and in particular to an easily depolymerized lithium iron phosphate positive electrode material prepared by cross-linking polymerization and an application thereof. Background Art

[0002] Lithium iron phosphate (LiFePO4) battery materials have become the mainstream material for power batteries and energy storage batteries due to their advantages such as high safety, good cycle stability, and low cost. However, compared with ternary batteries, LiFePO4 batteries have inferior rate performance.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The object of the present invention is to provide an easily depolymerized lithium iron phosphate positive electrode material prepared by cross-linking polymerization and its application, so as to solve or improve the above technical problems.

[0005] The present invention can be achieved like this:

[0006] In a first aspect, the present invention provides an easily depolymerized lithium iron phosphate positive electrode material, wherein the porosity of the easily depolymerized lithium iron phosphate positive electrode material is τ≤0.8;

[0007] in,

[0008] ρ0 is the true density of the easily depolymerized lithium iron phosphate positive electrode material before pressing, ρ1 is the true density of the easily depolymerized lithium iron phosphate positive electrode material after pressing at the first pressure P1, ρ2 is the true density of the easily depolymerized lithium iron phosphate positive electrode material after pressing at the second pressure P2, P1<P2; the units of P1 and P2 are both MPa, the unit of 0.1 is MPa, and the units of ρ0, ρ1 and ρ2 are all g / cm 3 .

[0009] In an optional embodiment, the easily decomposable lithium iron phosphate positive electrode material has at least one of the following characteristics:

[0010] Feature 1: τ≤0.5;

[0011] Feature 2: ρ0 ≥ 3.4 g / cm 3 ;

[0012] Feature 3: P1<P2<200MPa.

[0013] In a second aspect, the present invention provides a method for preparing an easily depolymerized lithium iron phosphate positive electrode material as described in the aforementioned embodiment, comprising the following steps: hydrothermally reacting a phosphorus source, an iron source, a lithium source, a solvent, and a dispersant in a reaction vessel to obtain a primary lithium iron phosphate product; cross-linking the primary lithium iron phosphate product with an organic matter and an acid in a solution environment to obtain a lithium iron phosphate having a coating layer; and calcining the lithium iron phosphate having the coating layer.

[0014] In an optional embodiment, the hydrothermal reaction comprises at least one of the following conditions:

[0015] Condition 1: The molar ratio of phosphorus in the phosphorus source, iron in the iron source, and lithium in the lithium source is (0.95-1.05):(0.90-1.05):(0.95-1.10);

[0016] Condition 2: The phosphorus source includes at least one of adenosine triphosphate, trimethyl phosphate and triethyl phosphate;

[0017] Condition 3: The iron source includes at least one of ferrous sulfate, ferrous chloride and ferrous nitrate;

[0018] Condition 4: The lithium source includes at least one of lithium carbonate and lithium hydroxide;

[0019] Condition 5: The amount of dispersant added is 0.5% to 5% of the total mass of the phosphorus source, iron source and lithium source;

[0020] Condition 6: The dispersant includes at least one of polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyethylene glycol and dodecyltrimethylammonium bromide;

[0021] Condition 7: The hydrothermal reaction is carried out at a pH of 5 to 8; preferably, the substance used to adjust the pH of the hydrothermal reaction includes an acid and / or a base, wherein the acid includes at least one of dilute sulfuric acid, dilute hydrochloric acid, acetic acid, and carbonic acid; and the base includes aqueous ammonia.

[0022] Condition 8: The solvent includes water and an organic solvent;

[0023] Condition 9: The temperature of the hydrothermal reaction is 150°C to 220°C, preferably 180°C;

[0024] Condition 10: The hydrothermal reaction time is 1 h to 8 h, preferably 2 h;

[0025] Condition 11: During the hydrothermal reaction, the pressure in the reaction vessel is 1 MPa to 10 MPa, preferably 5 MPa.

[0026] In an optional embodiment, the preparation of lithium iron phosphate with a coating layer includes: first mixing a primary lithium iron phosphate product with water to obtain a mixed solution; adding organic matter to the mixed solution, then adding acid to adjust the pH to 1 to 4, and allowing the organic matter to cross-link with the phosphate dissolved from the primary lithium iron phosphate product.

[0027] In an optional embodiment, the organic matter includes at least one of chitosan, polyethyleneimine, polylysine, quaternized cellulose, and polydiallyldimethylammonium chloride;

[0028] And / or, the amount of the organic matter added is 5 wt % to 50 wt % of the initial lithium iron phosphate product.

[0029] In an alternative embodiment, the acid comprises at least one of hydrochloric acid and sulfuric acid;

[0030] And / or, the standing time is 0.5h to 6h.

[0031] In an optional embodiment, the calcination temperature is 400°C to 800°C, preferably 500°C to 800°C, and more preferably 700°C;

[0032] and / or, the calcination time is 1 h to 6 h, preferably 4 h;

[0033] And / or, calcination is performed under an inert atmosphere.

[0034] In an optional embodiment, the method further comprises: post-processing the calcined product obtained by calcination;

[0035] The post-processing includes at least one of water washing, drying, crushing and demagnetization.

[0036] In an optional embodiment, the number of water washings is not less than 5 times.

[0037] In an optional embodiment, the drying is performed at 100° C. to 120° C. under an inert atmosphere for 2 h to 6 h.

[0038] In an optional embodiment, the magnetic field strength used for demagnetization is 5000 GS to 20000 GS.

[0039] In a third aspect, the present invention provides a battery, wherein the positive electrode material of the battery includes the easily decomposed lithium iron phosphate positive electrode material of the aforementioned embodiment.

[0040] The beneficial effects of the present invention include:

[0041] The porosity of the easily depolymerized lithium iron phosphate positive electrode material provided by the present invention is τ≤0.8; wherein, ρ0 is the true density of the easily depolymerized lithium iron phosphate positive electrode material before pressing, ρ1 is the true density of the easily depolymerized lithium iron phosphate positive electrode material after pressing at the first pressure P1, ρ2 is the true density of the easily depolymerized lithium iron phosphate positive electrode material after pressing at the second pressure P2, P1<P2; the units of P1 and P2 are both MPa, the unit of 0.1 is MPa, and the units of ρ0, ρ1 and ρ2 are all g / cm 3 The easily depolymerized lithium iron phosphate cathode material that meets the above conditions has high density and less agglomeration between particles, which can reduce the resistance of the material, and is conducive to the battery using it as the cathode material having good rate performance and suitable discharge specific capacity.

[0042] The present invention utilizes a hydrothermal reaction to prepare a high-density lithium iron phosphate primary product, then uses acid to etch away agglomeration interfaces and irregular particles in the lithium iron phosphate primary product, thereby reducing particle agglomeration. Simultaneously, phosphate groups dissolved under the action of the acid undergo cross-linking with organic matter to generate a complex that is coated on the surface of the lithium iron phosphate primary product. The lithium iron phosphate is then crystallized through calcination, and the complex is carbonized to form a carbon coating layer, ultimately obtaining low-agglomeration, carbon-coated lithium iron phosphate, which is beneficial to improving the rate performance of a battery further prepared from an easily depolymerized lithium iron phosphate positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 This is a flow chart for preparing the easily decomposable lithium iron phosphate positive electrode material provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0045] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0046] The easily depolymerized lithium iron phosphate positive electrode material prepared by cross-linking polymerization provided by the present invention and its application are described in detail below.

[0047] The present invention provides an easily depolymerized lithium iron phosphate positive electrode material, wherein the porosity of the easily depolymerized lithium iron phosphate positive electrode material is τ≤0.8;

[0048] in,

[0049] ρ0 is the true density of the easily depolymerized lithium iron phosphate positive electrode material before pressing, ρ1 is the true density of the easily depolymerized lithium iron phosphate positive electrode material after pressing at the first pressure P1, ρ2 is the true density of the easily depolymerized lithium iron phosphate positive electrode material after pressing at the second pressure P2, P1<P2; the units of P1 and P2 are both MPa, the unit of 0.1 is MPa, and the units of ρ0, ρ1 and ρ2 are all g / cm 3 .

[0050] In some optional embodiments, τ may be 0.15, 0.32, 0.33, 0.36, 0.49, 0.65, 0.8, etc., or other values ​​within the range of ≤0.8. In some typical embodiments, τ ≤ 0.5, such as τ is 0.15, 0.32, 0.33, 0.36, 0.49, etc.

[0051] In some optional embodiments, ρ0≥3.4 g / cm 3 .

[0052] Lithium iron phosphate powder used in batteries is typically nano- or micron-sized and prone to agglomeration. The resulting agglomerates contain numerous closed pores, resulting in a looser lithium iron phosphate cathode material. This, in turn, affects the conductivity and lithium ion diffusion rate of batteries made with this material. Generally, the more closed pores a material has, the lower its true density. However, by compressing the lithium iron phosphate cathode material to break up the agglomerates, the closed pores can be reduced, resulting in a higher true density.

[0053] In the present invention, the porosity is calculated using the true density indicator. The change in the true density of the lithium iron phosphate cathode material under different pressures can reflect the change in the closed pores of the material under different pressures, thereby reflecting the degree of agglomeration of the lithium iron phosphate cathode material. A small change in closed pores indicates a low degree of agglomeration of the lithium iron phosphate cathode material. In addition, a high pressure required to achieve a certain closed pore change indicates a low degree of agglomeration of the lithium iron phosphate cathode material. The relationship between the pressure change and the change in the true density of the lithium iron phosphate cathode material after the corresponding pressure treatment can reflect the porosity of the lithium iron phosphate cathode material. Lithium iron phosphate cathode materials with a porosity τ ≤ 0.8 have high density and low agglomeration between particles, which can reduce the material's resistance, which is beneficial for batteries using them as cathode materials to have good rate performance and suitable discharge capacity.

[0054] The true density of the easily decomposed lithium iron phosphate positive electrode material provided by the present invention before pressing is ≥3.4g / cm 3 , which can eliminate the situation of abnormally large agglomerated particles that do not meet the requirements of the present invention.

[0055] In some optional embodiments, the particle size D of the easily decomposed lithium iron phosphate positive electrode material provided by the present invention is10 100nm~1μm, D 90 3μm~50μm. 10 It is one of the key indicators of particle size distribution, indicating the particle size corresponding to the cumulative particle size distribution percentage reaching 10%, that is, the particles smaller than this particle size in the sample account for 10% of the total. 90 The easily depolymerized lithium iron phosphate cathode material provided by the present invention has low porosity, low powder agglomeration, is more uniform during the preparation of electrode slurry, and can exhibit good electrochemical performance.

[0056] In some optional embodiments, the method for destroying iron phosphate agglomeration adopted by the present invention is P1<P2<200MPa, which can avoid high pressure compaction of lithium iron phosphate, making it difficult to disperse the pressed blocks by ultrasonic means, thereby affecting the test of the true density of the powder.

[0057] As mentioned above, the easily decomposed lithium iron phosphate positive electrode material that meets the above conditions of the present invention has high density and less agglomeration between particles, which can reduce the resistance of the material, which is conducive to the battery using it as the positive electrode material having better rate performance and suitable discharge specific capacity.

[0058] Accordingly, the present invention also provides a method for preparing the above-mentioned easily depolymerized lithium iron phosphate cathode material, such as Figure 1 , including the following steps:

[0059] S1: hydrothermally reacting a phosphorus source, an iron source, a lithium source, a solvent, and a dispersant in a reaction vessel to obtain a primary lithium iron phosphate product.

[0060] The hydrothermal method is a process in which crystals grow from a liquid phase. The present invention utilizes this method to prepare readily depolymerizable lithium iron phosphate cathode materials, resulting in readily depolymerizable lithium iron phosphate cathode materials with good uniformity and high density. The particle size of the readily depolymerizable lithium iron phosphate cathode material can be controlled by the temperature and duration of the hydrothermal reaction.

[0061] In some optional embodiments, the molar ratio of phosphorus in the phosphorus source, iron in the iron source, and lithium in the lithium source can be (0.95-1.05):(0.90-1.05):(0.95-1.10). Preferably, the molar ratio of phosphorus, iron, and lithium is controlled so that the amount of iron input is not higher than the amount of phosphorus and lithium input. For example, the molar ratio of phosphorus, iron, and lithium is: 0.95:0.90:0.95 , 0.95:0.90:1, 0.95:0.90:1.1, 1:0.90:0.95, 1:0.90:1, 1:0.90:1.1, 1.05:0.90:0.95, 1.05:0.90:1, 1.05:0.90:1.1 or 1.05:1:1.1, etc., can reduce the impact of iron as a magnetic foreign matter in the positive electrode material of the battery on the safety performance of the battery to a certain extent.

[0062] In some optional embodiments, the phosphorus source may illustratively but not limitatively include at least one of adenosine triphosphate, trimethyl phosphate, and triethyl phosphate.

[0063] In some optional embodiments, the iron source may illustratively but not limitatively include at least one of ferrous sulfate, ferrous chloride, and ferrous nitrate.

[0064] In some optional embodiments, the lithium source may illustratively but not limitatively include at least one of lithium carbonate and lithium hydroxide.

[0065] In some optional embodiments, the amount of dispersant added can be 0.5% to 5% of the total mass of the phosphorus source, iron source and lithium source, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, etc., or other values ​​within the range of 0.5% to 5%.

[0066] If the amount of dispersant added exceeds 5% of the total mass of the phosphorus source, iron source and lithium source, an interface layer may be formed on the surface of the material, which is not conducive to the synthesis of the initial lithium iron phosphate product.

[0067] In some optional embodiments, the dispersant may illustratively but not limitatively include at least one of polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyethylene glycol, and dodecyltrimethylammonium bromide.

[0068] In some optional embodiments, the hydrothermal reaction is carried out at a pH value of 5 to 8; wherein the pH value of the hydrothermal reaction can be 5, 5.5, 6, 6.5, 7, 7.5 or 8, or other values ​​within the range of 5 to 8.

[0069] If the pH value of the hydrothermal reaction is less than 5, it is easy to cause low yield of the initial lithium iron phosphate product and some raw materials cannot form precipitation; if the pH value of the hydrothermal reaction is greater than 8, impurities are easily generated, resulting in insufficient purity of the initial lithium iron phosphate product, affecting the electrochemical performance and safety performance of the subsequent easily decomposed lithium iron phosphate positive electrode material.

[0070] In some optional embodiments, the substance used to adjust the pH value of the hydrothermal reaction may include an acid and / or a base. The acid may illustratively include at least one of dilute sulfuric acid, dilute hydrochloric acid, acetic acid, and carbonic acid. The base may illustratively include aqueous ammonia.

[0071] In some optional embodiments, the solvent includes water and an organic solvent. The organic solvent may include alcohol or acetonitrile. For example, the alcohol may include ethanol, glycerol, or isobutanol. The volume ratio of water to alcohol may be 6:4 to 9:1.

[0072] In some optional embodiments, the temperature of the hydrothermal reaction may be 150° C. to 220° C., such as 150° C., 160° C., 170° C., 180° C., 190° C., 200° C., 210° C., or 220° C., or other values ​​within the range of 150° C. to 220° C. In some typical embodiments, the temperature of the hydrothermal reaction may be 180° C.

[0073] If the temperature of the hydrothermal reaction is lower than 150°C, the density of the lithium iron phosphate crystals is low and trivalent iron impurity ions are easily generated; if the temperature of the hydrothermal reaction is higher than 220°C, the lithium iron phosphate crystals will grow too fast, making it difficult to control the size of the lithium iron phosphate crystals.

[0074] In some optional embodiments, the hydrothermal reaction time can be 1 hour to 8 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours or 8 hours, etc., or other values ​​within the range of 1 hour to 8 hours. In some more typical embodiments, the hydrothermal reaction time can be 2 hours.

[0075] If the hydrothermal reaction time is shorter than 1 hour, the lithium iron phosphate particles may be too small; if the hydrothermal reaction time is longer than 8 hours, the lithium iron phosphate particles may be too large and the size may be difficult to control.

[0076] In some optional embodiments, the pressure in the reaction vessel during the hydrothermal reaction process may be 1 MPa to 10 MPa, such as 1 MPa, 2 MPa, 3 MPa, 4 MPa, 5 MPa, 6 MPa, 7 MPa, 8 MPa, 9 MPa, or 10 MPa, or may be other values ​​within the range of 1 MPa to 10 MPa. In some typical embodiments, the pressure in the reaction vessel during the hydrothermal reaction process may be 5 MPa.

[0077] By controlling the pressure in the reaction vessel, lithium iron phosphate is more likely to nucleate and easily generate high-density particles.

[0078] S2: cross-linking the initial lithium iron phosphate with an organic substance and an acid in a solution environment to obtain lithium iron phosphate with a coating layer.

[0079] In some optional embodiments, the preparation of lithium iron phosphate with a coating layer may include: first mixing a primary lithium iron phosphate product with water to obtain a mixed solution; adding organic matter to the mixed solution, then adding acid to adjust the pH to 1 to 4, and allowing the organic matter to cross-link with the phosphate dissolved from the primary lithium iron phosphate product.

[0080] The lithium iron phosphate product may be washed before being mixed with water.

[0081] In some optional embodiments, the organic matter may illustratively but not limitatively include at least one of chitosan, polyethyleneimine, polylysine, quaternized cellulose and polydiallyldimethylammonium chloride. In addition, other organic substances that can be cross-linked with phosphate groups are not excluded.

[0082] The amount of organic matter added can be 5wt% to 50wt% of the initial lithium iron phosphate product, such as 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt% or 50wt%, etc., or it can be other values ​​within the range of 5wt% to 50wt%.

[0083] If the amount of organic matter added is too little, it is easy to cause the organic matter to be low, making it difficult to complete the coating of the initial lithium iron phosphate product; if the amount of organic matter added is too much, it is easy to cause the coating layer to be too thick, which in turn reduces the electrochemical performance of the lithium iron phosphate.

[0084] In some optional embodiments, the acid may illustratively include at least one of hydrochloric acid and sulfuric acid.

[0085] In some optional embodiments, the standing time may be 0.5 h to 6 h, such as 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h or 6 h, etc., or other values ​​within the range of 0.5 h to 6 h.

[0086] The present invention adjusts the pH value to 1-4 by adding acid, so that the primary lithium iron phosphate product can be slowly dissolved during standing. Irregular lithium iron phosphate particles, small lithium iron phosphate particles and agglomerated lithium iron phosphate particles contained in the primary lithium iron phosphate product are dissolved first, and the dissolved phosphate radicals are cross-linked with organic matter to form complexes. These complexes are coated on the surfaces of undissolved lithium iron phosphate particles in the primary lithium iron phosphate product, and can prevent the acid from further dissolving other lithium iron phosphate particles, thereby playing the dual role of reducing agglomeration and effectively controlling the particle size of the lithium iron phosphate particles through coating.

[0087] It should be noted that if the pH value in S2 is less than 1, it is easy to cause excessive acid solubility and excessive loss of lithium iron phosphate product; if the pH value is greater than 4, it is easy to cause insufficient solubility and no etching effect; if the standing time is shorter than 0.5h, it is easy to cause the complex formed after cross-linking to fail to form a stable coating on the lithium iron phosphate particles, resulting in poor coating effect.

[0088] In some optional embodiments, the material after the cross-linking reaction is subjected to solid-liquid separation (such as filtration), washed and dried, and then subjected to a subsequent calcination process.

[0089] Continuing from the above, during the S2 process, the phosphate groups dissolved from the initial lithium iron phosphate product undergo a cross-linking polymerization reaction with organic matter, forming a flocculent complex that coats the surface of the lithium iron phosphate particles, forming a uniform coating that facilitates size control of the lithium iron phosphate particles. Furthermore, the uniform coating improves the conductivity of the easily depolymerized lithium iron phosphate cathode material. Furthermore, the coating helps control the agglomeration of the lithium iron phosphate particles, facilitates their depolymerization, and prevents their anisotropic growth.

[0090] S3: calcining the lithium iron phosphate with the coating layer.

[0091] In some optional embodiments, the calcination temperature may be 400° C. to 800° C., such as 400° C., 450° C., 500° C., 550° C., 600° C., 650° C., 700° C., 750° C., or 800° C., or other values ​​within the range of 400° C. to 800° C. In some more typical embodiments, the calcination temperature may be 500° C. to 800° C.; in some more typical embodiments, the calcination temperature may be 700° C.

[0092] If the calcination temperature is lower than 400°C, it is easy to cause poor crystal form and chemical properties of lithium iron phosphate; if the calcination temperature is higher than 800°C, impurities such as Fe2P that affect the electrochemical performance are likely to appear.

[0093] In some optional embodiments, the calcination time can be 1 hour to 6 hours, such as 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, or other values ​​within the range of 1 hour to 6 hours. In some more typical embodiments, the calcination time can be 4 hours.

[0094] In some optional embodiments, calcination is performed under an inert atmosphere (such as a nitrogen atmosphere, an argon atmosphere, or a helium atmosphere).

[0095] The above-mentioned S3 process can, on the one hand, crystallize and transform lithium iron phosphate to make the crystal form of lithium iron phosphate better, and on the other hand, carbonize the organic matter in the coating layer, thereby enhancing the conductivity of the coating layer.

[0096] Furthermore, the preparation of the above-mentioned easily decomposable lithium iron phosphate positive electrode material further includes:

[0097] S4: post-treating the calcined product obtained by calcination.

[0098] In some optional embodiments, post-processing may include at least one of water washing, drying, crushing, and demagnetization.

[0099] The number of water washings may be 1, 2, 3 or more times. In some typical embodiments, the number of water washings is not less than 5 times. This step is used to remove phosphorus-containing compounds (such as metaphosphoric acid, pyrophosphoric acid, etc.) in the carbonized carbon coating layer.

[0100] Drying can be carried out at 100°C to 120°C (such as 100°C, 105°C, 110°C, 115°C or 120°C, etc.) and an inert atmosphere (such as a nitrogen atmosphere, an argon atmosphere or a helium atmosphere, etc.) for 2h to 6h (such as 2h, 3h, 4h, 5h or 6h, etc.).

[0101] The magnetic field strength used for demagnetization may be 5000GS to 20000GS, such as 5000GS, 10000GS, 15000GS or 20000GS, or other values ​​within the range of 5000GS to 20000GS.

[0102] In some optional embodiments, the post-processing further includes packaging the demagnetized product.

[0103] Among them, the packaging method can be, for example, vacuum packaging using aluminum-plastic film ton bags.

[0104] Continuing from the above, the preparation method of the easily depolymerized lithium iron phosphate positive electrode material provided by the present invention utilizes a hydrothermal reaction to prepare a high-density lithium iron phosphate primary product, and then uses acid to etch away the agglomeration interface and irregular particles in the lithium iron phosphate primary product, thereby reducing the agglomeration of the particles. At the same time, the phosphate groups dissolved under the action of the acid are cross-linked with organic matter to form a complex coated on the surface of the remaining lithium iron phosphate primary product. The lithium iron phosphate is then crystallized by calcination and the complex is carbonized to form a carbon coating layer. The metaphosphoric acid and pyrophosphoric acid generated by the thermal decomposition of the phosphate groups are then removed by water washing, and finally low-agglomeration, carbon-coated lithium iron phosphate is obtained, which can solve the problems of large internal resistance and low rate performance of the product caused by the agglomeration of lithium iron phosphate particles in the prior art.

[0105] In addition, the present invention also provides a battery cell, the positive electrode material of which includes the above-mentioned easily depolymerized lithium iron phosphate positive electrode material.

[0106] For example, the battery cells can be used in, but are not limited to, electrical devices such as vehicles, ships, or aircraft.

[0107] The present invention also provides a battery comprising the above battery cell, which has high rate performance and suitable discharge specific capacity.

[0108] The present invention also provides an electrical device comprising the aforementioned battery cell and / or battery. For example, the electrical device may include, but is not limited to, a mobile phone, a tablet, a laptop computer, an electric toy, an electric tool, a battery-powered vehicle, an electric car, a ship, a spacecraft, and the like. The electric toy may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys. The spacecraft may include airplanes, rockets, space shuttles, and spacecraft.

[0109] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0110] Example 1

[0111] This embodiment provides a lithium iron phosphate cathode material that is easily decomposed, such as Figure 1 , the preparation method thereof comprises:

[0112] S1: a phosphorus source, an iron source, a lithium source, a solvent and a dispersant are subjected to a hydrothermal reaction in a reaction vessel (reactor) to obtain a primary product of lithium iron phosphate.

[0113] The phosphorus source is adenosine triphosphate, the iron source is ferrous sulfate, and the lithium source is lithium hydroxide. The molar ratio of phosphorus in the phosphorus source, iron in the iron source, and lithium in the lithium source is 1:1:1.05. The solvent is composed of water and ethanol in a volume ratio of 8:2, and the mass of the solvent is 50% of the total mass of the phosphorus source, iron source, lithium source, solvent, and dispersant. The dispersant is dodecyltrimethylammonium bromide, and the amount of dispersant added is 1% of the total mass of the phosphorus source, iron source, and lithium source. The hydrothermal reaction is carried out at a pH of 7, which is adjusted by adding dilute sulfuric acid to the reactor. The hydrothermal reaction temperature is 180°C, the reaction time is 2 hours, and the pressure in the reactor during the hydrothermal reaction is 5 MPa.

[0114] S2: cross-linking the initial lithium iron phosphate with an organic substance and an acid in a solution environment to obtain lithium iron phosphate with a coating layer.

[0115] Specifically, the lithium iron phosphate product is first washed and then mixed with water at a solid-liquid ratio of 10g:50mL to obtain a mixed solution; organic matter is added to the mixed solution, and then acid is added to adjust the pH to 1, and the mixed solution is allowed to stand to allow the organic matter to cross-link with the phosphate dissolved from the lithium iron phosphate product, and then filtered, washed, and dried to obtain lithium iron phosphate with a coating layer.

[0116] The organic material is chitosan, the amount of the organic material added is 20 wt % of the initial lithium iron phosphate product, the acid is dilute sulfuric acid, and the standing time is 2 hours.

[0117] S3: calcining the lithium iron phosphate with the coating layer.

[0118] The calcination was carried out in a nitrogen atmosphere at a temperature of 700° C. and for 4 h.

[0119] S4: The calcined product was washed with deionized water five times, dried at 120° C. in a nitrogen atmosphere for 2 h, crushed by jet milling, demagnetized under a 10,000 GS magnetic field, and finally vacuum-packaged with aluminum-plastic film.

[0120] Example 2

[0121] This embodiment provides an easily decomposable lithium iron phosphate positive electrode material, and the preparation method thereof includes:

[0122] S1: a phosphorus source, an iron source, a lithium source, a solvent and a dispersant are subjected to a hydrothermal reaction in a reaction vessel (reactor) to obtain a primary product of lithium iron phosphate.

[0123] The phosphorus source is trimethyl phosphate, the iron source is ferrous sulfate, and the lithium source is lithium carbonate. The molar ratio of phosphorus in the phosphorus source, iron in the iron source, and lithium in the lithium source is 1:1:1.06. The solvent is composed of water and ethanol in a volume ratio of 6:4, and the mass of the solvent is 50% of the total mass of the phosphorus source, iron source, lithium source, solvent, and dispersant. The dispersant is dodecyltrimethylammonium bromide, and the amount of dispersant added is 0.5% of the total mass of the phosphorus source, iron source, and lithium source. The hydrothermal reaction is carried out at a pH of 8, which is adjusted by adding aqueous ammonia to the reactor. The hydrothermal reaction temperature is 200°C, the reaction time is 2 hours, and the pressure in the reactor during the hydrothermal reaction is 3 MPa.

[0124] S2: cross-linking the initial lithium iron phosphate with an organic substance and an acid in a solution environment, followed by filtering, washing, and drying to obtain lithium iron phosphate with a coating layer.

[0125] Specifically, the lithium iron phosphate product is first washed and then mixed with water at a solid-liquid ratio of 10g:100mL to obtain a mixed solution; organic matter is added to the mixed solution, and then acid is added to adjust the pH to 3, and the mixed solution is allowed to stand to allow the organic matter to cross-link with the phosphate dissolved from the lithium iron phosphate product to obtain lithium iron phosphate with a coating layer.

[0126] The organic material is chitosan, the amount of the organic material added is 5 wt % of the initial lithium iron phosphate product, the acid is dilute sulfuric acid, and the standing time is 6 hours.

[0127] S3: calcining the lithium iron phosphate with the coating layer.

[0128] The calcination was carried out in a nitrogen atmosphere at a temperature of 700° C. and for 4 h.

[0129] S4: The calcined product was washed with deionized water five times, dried at 100° C. in an argon atmosphere for 6 h, crushed by jet milling, demagnetized under a 5000 GS magnetic field, and finally vacuum-packaged with aluminum-plastic film.

[0130] Example 3

[0131] This embodiment provides an easily decomposable lithium iron phosphate positive electrode material, and the preparation method thereof includes:

[0132] S1: a phosphorus source, an iron source, a lithium source, a solvent and a dispersant are subjected to a hydrothermal reaction in a reaction vessel (reactor) to obtain a primary product of lithium iron phosphate.

[0133] The phosphorus source is triethyl phosphate, the iron source is ferrous chloride, and the lithium source is lithium carbonate. The molar ratio of phosphorus in the phosphorus source, iron in the iron source, and lithium in the lithium source is 1:1:1.04. The solvent is composed of water and glycerol in a volume ratio of 9:1, and the mass of the solvent is 50% of the total mass of the phosphorus source, iron source, lithium source, solvent, and dispersant. The dispersant is polyethylene glycol, and the amount of dispersant added is 1% of the total mass of the phosphorus source, iron source, and lithium source. The hydrothermal reaction is carried out at a pH of 5, which is adjusted by adding dilute sulfuric acid to the reactor. The hydrothermal reaction temperature is 220°C, the hydrothermal reaction time is 1 hour, and the pressure in the reactor during the hydrothermal reaction is 8 MPa.

[0134] S2: cross-linking the initial lithium iron phosphate with an organic substance and an acid in a solution environment, followed by filtering, washing, and drying to obtain lithium iron phosphate with a coating layer.

[0135] Specifically, the lithium iron phosphate product is first washed and then mixed with water at a solid-liquid ratio of 10g:50mL to obtain a mixed solution; organic matter is added to the mixed solution, and then acid is added to adjust the pH to 2, and the mixed solution is allowed to stand to allow the organic matter to cross-link with the phosphate dissolved from the lithium iron phosphate product to obtain lithium iron phosphate with a coating layer.

[0136] The organic material is polyethyleneimine, the amount of the organic material added is 10 wt % of the initial lithium iron phosphate product, the acid is dilute sulfuric acid, and the standing time is 2 hours.

[0137] S3: calcining the lithium iron phosphate with the coating layer.

[0138] The calcination was carried out in a nitrogen atmosphere at a temperature of 800° C. for 2 h.

[0139] S4: The calcined product was washed with deionized water five times, dried at 110° C. in a nitrogen atmosphere for 4 h, crushed by jet milling, demagnetized under a 20,000 GS magnetic field, and finally vacuum-packaged with aluminum-plastic film.

[0140] Example 4

[0141] This embodiment provides an easily decomposable lithium iron phosphate positive electrode material, and the preparation method thereof includes:

[0142] S1: a phosphorus source, an iron source, a lithium source, a solvent and a dispersant are subjected to a hydrothermal reaction in a reaction vessel (reactor) to obtain a primary product of lithium iron phosphate.

[0143] The phosphorus source is adenosine triphosphate, the iron source is ferrous nitrate, and the lithium source is lithium carbonate. The molar ratio of phosphorus in the phosphorus source, iron in the iron source, and lithium in the lithium source is 1:0.95:1.06. The solvent is composed of water and ethanol in a volume ratio of 8:2, and the mass of the solvent is 60% of the total mass of the phosphorus source, iron source, lithium source, solvent, and dispersant. The dispersant is polyethylene glycol, and the amount of dispersant added is 5% of the total mass of the phosphorus source, iron source, and lithium source. The hydrothermal reaction is carried out at a pH of 7, which is adjusted by adding dilute sulfuric acid to the reactor. The hydrothermal reaction temperature is 150°C, the reaction time is 8 hours, and the pressure in the reactor during the hydrothermal reaction is 1 MPa.

[0144] S2: cross-linking the initial lithium iron phosphate with an organic substance and an acid in a solution environment to obtain lithium iron phosphate with a coating layer.

[0145] Specifically, the lithium iron phosphate product is first washed and then mixed with water at a solid-liquid ratio of 10g:100mL to obtain a mixed solution; organic matter is added to the mixed solution, and then acid is added to adjust the pH to 4, and the mixed solution is allowed to stand to allow the organic matter to cross-link with the phosphate dissolved from the lithium iron phosphate product, and then filtered, washed, and dried to obtain lithium iron phosphate with a coating layer.

[0146] The organic material is polylysine, the amount of the organic material added is 5 wt % of the initial lithium iron phosphate product, the acid is dilute sulfuric acid, and the standing time is 2 hours.

[0147] S3: calcining the lithium iron phosphate with the coating layer.

[0148] The calcination was carried out in a nitrogen atmosphere at a temperature of 800° C. for 1 h.

[0149] S4: The calcined product was washed with deionized water five times, dried at 110° C. in a nitrogen atmosphere for 4 h, crushed by jet milling, demagnetized under a 15,000 GS magnetic field, and finally vacuum-packaged with aluminum-plastic film.

[0150] Example 5

[0151] This embodiment provides an easily decomposable lithium iron phosphate positive electrode material, and the preparation method thereof includes:

[0152] S1: a phosphorus source, an iron source, a lithium source, a solvent and a dispersant are subjected to a hydrothermal reaction in a reaction vessel (reactor) to obtain a primary product of lithium iron phosphate.

[0153] The phosphorus source is trimethyl phosphate, the iron source is ferrous sulfate, and the lithium source is lithium carbonate. The molar ratio of phosphorus in the phosphorus source, iron in the iron source, and lithium in the lithium source is 1:1:1.06. The solvent is composed of water and isobutanol in a volume ratio of 8:2, and the mass of the solvent is 70% of the total mass of the phosphorus source, iron source, lithium source, solvent, and dispersant. The dispersant is dodecyltrimethylammonium bromide, and the amount of dispersant added is 5% of the total mass of the phosphorus source, iron source, and lithium source. The hydrothermal reaction is carried out at a pH of 7, which is adjusted by adding aqueous ammonia to the reactor. The hydrothermal reaction temperature is 200°C, the reaction time is 2 hours, and the pressure in the reactor is 10 MPa during the hydrothermal reaction.

[0154] S2: cross-linking the initial lithium iron phosphate with an organic substance and an acid in a solution environment, followed by filtering, washing, and drying to obtain lithium iron phosphate with a coating layer.

[0155] Specifically, the lithium iron phosphate product is first washed and then mixed with water at a solid-liquid ratio of 10g:50mL to obtain a mixed solution; organic matter is added to the mixed solution, and then acid is added to adjust the pH to 2, and the mixed solution is allowed to stand to allow the organic matter to cross-link with the phosphate dissolved from the lithium iron phosphate product to obtain lithium iron phosphate with a coating layer.

[0156] The organic material is quaternized cellulose, the amount of the organic material added is 10 wt % of the initial lithium iron phosphate product, the acid is dilute sulfuric acid, and the standing time is 0.5 h.

[0157] S3: calcining the lithium iron phosphate with the coating layer.

[0158] The calcination was carried out in a nitrogen atmosphere at a temperature of 500° C. and for 6 h.

[0159] S4: The calcined product was washed with deionized water five times, dried at 110° C. in a nitrogen atmosphere for 4 h, crushed by jet milling, demagnetized under a 15,000 GS magnetic field, and finally vacuum-packaged with aluminum-plastic film.

[0160] Example 6

[0161] This embodiment provides an easily decomposable lithium iron phosphate positive electrode material, and the preparation method thereof includes:

[0162] S1: a phosphorus source, an iron source, a lithium source, a solvent and a dispersant are subjected to a hydrothermal reaction in a reaction vessel (reactor) to obtain a primary product of lithium iron phosphate.

[0163] The phosphorus source is triethyl phosphate, the iron source is ferrous chloride, and the lithium source is lithium carbonate. The molar ratio of phosphorus in the phosphorus source, iron in the iron source, and lithium in the lithium source is 1:1:1.06. The solvent is composed of water and acetonitrile in a volume ratio of 8:2, and the mass of the solvent is 80% of the total mass of the phosphorus source, iron source, lithium source, solvent, and dispersant. The dispersant is dodecyltrimethylammonium bromide, and the amount of dispersant added is 5% of the total mass of the phosphorus source, iron source, and lithium source. The hydrothermal reaction is carried out at a pH of 7, which is adjusted by adding aqueous ammonia to the reactor. The hydrothermal reaction temperature is 200°C, the reaction time is 4 hours, and the pressure in the reactor during the hydrothermal reaction is 5 MPa.

[0164] S2: cross-linking the initial lithium iron phosphate with an organic substance and an acid in a solution environment, followed by filtering, washing, and drying to obtain lithium iron phosphate with a coating layer.

[0165] Specifically, the lithium iron phosphate product is first washed and then mixed with water at a solid-liquid ratio of 10g:50mL to obtain a mixed solution; organic matter is added to the mixed solution, and then acid is added to adjust the pH to 2, and the mixed solution is allowed to stand to allow the organic matter to cross-link with the phosphate dissolved from the lithium iron phosphate product to obtain lithium iron phosphate with a coating layer.

[0166] The organic material is polydiallyldimethylammonium chloride, the amount of the organic material added is 50 wt% of the initial lithium iron phosphate product, the acid is dilute sulfuric acid, and the standing time is 6 hours.

[0167] S3: calcining the lithium iron phosphate with the coating layer.

[0168] The calcination was carried out in a nitrogen atmosphere at a temperature of 400° C. and for a time of 6 h.

[0169] S4: The calcined product was washed with deionized water five times, dried at 120° C. in a nitrogen atmosphere for 2 h, crushed by jet milling, demagnetized under a 5000 GS magnetic field, and finally vacuum-packaged with aluminum-plastic film.

[0170] Comparative Example 1

[0171] This comparative example is a lithium iron phosphate positive electrode material prepared by a carbon thermal reduction method, and its preparation method includes:

[0172] S1: iron phosphate, lithium carbonate, and glucose were sampled at a molar ratio of 1:1.05:0.3 to obtain a raw material; the raw material was mixed with alcohol at a solid-liquid ratio of 10 g:50 mL, and then wet-milled for 6 h;

[0173] S2: The wet-ground material was calcined at 750 °C for 2 h in an inert atmosphere (nitrogen atmosphere);

[0174] S3: The calcined product was washed with deionized water five times, dried in a nitrogen atmosphere at 110° C. for 4 h, and then crushed in a jet mill. It was demagnetized at a magnetic field strength of 15,000 GS and finally vacuum-packed with aluminum-plastic film.

[0175] Comparative Example 2

[0176] This comparative example is a carbon-coated lithium iron phosphate positive electrode material prepared by a hydrothermal method, and its preparation method includes:

[0177] S1: Weigh phosphoric acid, ferric nitrate, lithium hydroxide, and glucose in a molar ratio of 1.05:1:1.05:0.1, add them to a hydrothermal reactor, adjust the pH to 7 with ammonia water, and perform a hydrothermal reaction at 180°C in the reactor for 2 h;

[0178] S2: calcining the hydrothermal material under argon atmosphere at a temperature of 750°C for 2 h;

[0179] S3: The calcined product was washed with deionized water five times, dried in a nitrogen atmosphere at 110° C. for 4 h, and then crushed in a jet mill. It was demagnetized under a magnetic field strength of 15,000 GS and finally vacuum-packed with aluminum-plastic film.

[0180] Comparative Example 3

[0181] The difference between this comparative example and Example 1 is that in S2, the amount of organic matter added is 2 wt % of the initial lithium iron phosphate product.

[0182] Comparative Example 4

[0183] The difference between this comparative example and Example 1 is that in S2, the amount of organic matter added is 60 wt % of the initial lithium iron phosphate product.

[0184] Comparative Example 5

[0185] The difference between this comparative example and Example 1 is that in S3, the calcination temperature is 300°C.

[0186] Comparative Example 6

[0187] The difference between this comparative example and Example 1 is that in S3, the calcination temperature is 900°C.

[0188] Test example

[0189] The easily depolymerized lithium iron phosphate positive electrode materials obtained in Examples 1 to 6 and Comparative Examples 1 to 6 were subjected to the following tests:

[0190] (1) ρ0, ρ1 and ρ2: Tested according to the method of GB / T 24586-2009.

[0191] (2) Porosity: According to Calculation. The compression was performed using a tablet press, the holding time was 10s, P1 was 23MPa, P2 was 39MPa, and the final values ​​were rounded off.

[0192] (3) Rate performance and discharge capacity test: The battery was assembled into a button cell and tested in accordance with GB / T 42161-2022.

[0193] The test results are shown in Table 1.

[0194] Table 1 Test results

[0195]

[0196] It can be seen from Table 1 that the selection of the synthesis method of lithium iron phosphate, the coating amount of organic matter, and the calcination temperature will affect the porosity and electrochemical performance of the lithium iron phosphate positive electrode material. The slurry of lithium iron phosphate positive electrode material with low porosity is more uniform, which is reflected in the electrochemical performance. Both low rate and high rate show excellent electrochemical performance. For example, the lithium iron phosphate positive electrode material in Example 1 has the lowest porosity, and the corresponding battery prepared has a higher discharge specific capacity compared with other embodiments. Among them, compared with the carbon thermal reduction method, the hydrothermal method has better porosity and electrochemical performance. Too low an organic coating amount will affect the conductivity of the lithium iron phosphate positive electrode material. Too thick a coating layer will affect the rate performance and the deintercalation speed of lithium ions. The calcination temperature determines the crystal form and purity of the lithium iron phosphate positive electrode material. If the temperature is too low, it is difficult to generate a good crystal structure and the organic matter is not completely carbonized, resulting in insufficient conductivity. If the temperature is too high, the lithium iron phosphate will produce impurities, affecting the electrochemical performance.

[0197] In summary, the easily depolymerized lithium iron phosphate positive electrode material provided by the present invention has high density and less agglomeration between particles, which is conducive to making the battery using it as the positive electrode material have better rate performance and suitable discharge specific capacity.

[0198] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. An easily depolymerized lithium iron phosphate cathode material prepared by cross-linking polymerization, characterized in that: The porosity of the easily depolymerized lithium iron phosphate positive electrode material is τ≤0.8; in, ρ0 is the true density of the easily depolymerized lithium iron phosphate positive electrode material before pressing, ρ1 is the true density of the easily depolymerized lithium iron phosphate positive electrode material after pressing at the first pressure P1, ρ2 is the true density of the easily depolymerized lithium iron phosphate positive electrode material after pressing at the second pressure P2, P1<P2; the units of P1 and P2 are both MPa, the unit of 0.1 is MPa, and the units of ρ0, ρ1 and ρ2 are all g / cm 3 .

2. The easily decomposable lithium iron phosphate positive electrode material according to claim 1, characterized in that The easily decomposable lithium iron phosphate positive electrode material has at least one of the following characteristics: Feature 1: τ≤0.5; Feature 2: ρ0 ≥ 3.4 g / cm 3 ; Feature 3: P1<P2<200MPa.

3. A method for preparing the easily decomposable lithium iron phosphate positive electrode material according to claim 1 or 2, characterized in that: The following steps are involved: A phosphorus source, an iron source, a lithium source, a solvent and a dispersant are hydrothermally reacted in a reaction container to obtain a primary lithium iron phosphate product; the primary lithium iron phosphate product is cross-linked with an organic matter and an acid in a solution environment to obtain a lithium iron phosphate with a coating layer; and the lithium iron phosphate with the coating layer is calcined.

4. The preparation method according to claim 3, characterized in that The hydrothermal reaction includes at least one of the following conditions: Condition 1: The molar ratio of the phosphorus element in the phosphorus source, the iron element in the iron source, and the lithium element in the lithium source is (0.95-1.05):(0.90-1.05):(0.95-1.10); Condition 2: The phosphorus source includes at least one of adenosine triphosphate, trimethyl phosphate and triethyl phosphate; Condition 3: The iron source includes at least one of ferrous sulfate, ferrous chloride and ferrous nitrate; Condition 4: The lithium source includes at least one of lithium carbonate and lithium hydroxide; Condition 5: The added amount of the dispersant is 0.5% to 5% of the total mass of the phosphorus source, the iron source and the lithium source; Condition 6: The dispersant includes at least one of polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyethylene glycol and dodecyltrimethylammonium bromide; Condition 7: The hydrothermal reaction is carried out at a pH of 5 to 8; preferably, the substance used to adjust the pH of the hydrothermal reaction includes an acid and / or a base, wherein the acid includes at least one of dilute sulfuric acid, dilute hydrochloric acid, acetic acid, and carbonic acid; and the base includes aqueous ammonia. Condition 8: The solvent includes water and an organic solvent; Condition 9: The temperature of the hydrothermal reaction is 150°C to 220°C, preferably 180°C; Condition 10: The hydrothermal reaction time is 1 h to 8 h, preferably 2 h; Condition 11: During the hydrothermal reaction, the pressure in the reaction vessel is 1 MPa to 10 MPa, preferably 5 MPa.

5. The preparation method according to claim 3, characterized in that The preparation of the lithium iron phosphate with a coating layer includes: first mixing the lithium iron phosphate product with water to obtain a mixed solution; adding the organic matter to the mixed solution, then adding the acid to adjust the pH to 1-4, and allowing the organic matter to cross-link with the phosphate dissolved from the lithium iron phosphate product.

6. The preparation method according to claim 5, characterized in that The organic matter comprises at least one of chitosan, polyethyleneimine, polylysine, quaternized cellulose and polydiallyldimethylammonium chloride; And / or, the amount of the organic matter added is 5wt% to 50wt% of the initial lithium iron phosphate product.

7. The preparation method according to claim 6, characterized in that The acid comprises at least one of hydrochloric acid and sulfuric acid; And / or, the standing time is 0.5h to 6h.

8. The preparation method according to claim 3, characterized in that The calcination temperature is 400°C to 800°C, preferably 500°C to 800°C, and more preferably 700°C; and / or, the calcination time is 1 h to 6 h, preferably 4 h; And / or, calcination is performed under an inert atmosphere.

9. The preparation method according to any one of claims 3 to 8, characterized in that: Also includes: post-processing the calcined product obtained by calcination; Wherein, the post-processing includes at least one of washing, drying, crushing and demagnetization; Preferably, the number of water washings is not less than 5 times; Preferably, the drying is carried out at 100° C. to 120° C. under an inert atmosphere for 2 h to 6 h; Preferably, the magnetic field strength used for demagnetization is 5000 GS to 20000 GS.

10. A battery, characterized in that: The positive electrode material of the battery includes the easily decomposed lithium iron phosphate positive electrode material according to claim 1 or 2.

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