Crosslinking polymerization prepared easily depolymerized lithium iron phosphate positive electrode material and application thereof

Abstract

The application discloses a cross-linking polymerization prepared easily-decomposable lithium iron phosphate positive electrode material and application thereof, and belongs to the technical field of battery materials. The easily-decomposable lithium iron phosphate positive electrode material has a looseness tau of 0.8 or less; wherein, p0 is the true density of the easily-decomposable lithium iron phosphate positive electrode material before compression treatment, p1 is the true density of the easily-decomposable lithium iron phosphate positive electrode material after compression treatment at a first pressure P1, p2 is the true density of the easily-decomposable lithium iron phosphate positive electrode material after compression treatment at a second pressure P2, P1 3 1 and P2 are both in MPa, 0.1 is in MPa, and p0, p1 and p2 are all in g / cm . The easily-decomposable lithium iron phosphate positive electrode material meeting the above conditions has high density and less aggregation between particles, which is beneficial to making the battery with the easily-decomposable lithium iron phosphate positive electrode material as the positive electrode material have better rate performance and proper discharge specific capacity.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to an easily degradable lithium iron phosphate cathode material prepared by crosslinking polymerization and its application. Background Technology

[0002] Lithium iron phosphate (LFP) 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 lithium batteries, LFP batteries have poorer rate performance.

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

[0004] The purpose of this invention is to provide an easily degradable lithium iron phosphate cathode material prepared by cross-linking polymerization and its application, so as to solve or improve the above-mentioned technical problems.

[0005] This invention can be implemented as follows:

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

[0007] in,

[0008] ρ0 is the true density of the easily degradable lithium iron phosphate cathode material before pressing; ρ1 is the true density of the easily degradable lithium iron phosphate cathode material after pressing under the first pressure P1; ρ2 is the true density of the easily degradable lithium iron phosphate cathode material after pressing under the second pressure P2, where 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 / cm³. 3 .

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

[0010] Feature 1: τ≤0.5;

[0011] Feature 2: ρ0 ≥ 3.4 g / cm³ 3 ;

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

[0013] Secondly, the present invention provides a method for preparing an easily degradable lithium iron phosphate cathode material as described in the foregoing embodiments, comprising the following steps: subjecting a phosphorus source, an iron source, a lithium source, a solvent, and a dispersant to a hydrothermal reaction in a reaction vessel to obtain a primary lithium iron phosphate product; crosslinking the primary lithium iron phosphate product with an organic compound and an acid in a solution environment to obtain a lithium iron phosphate with a coating layer; and calcining the lithium iron phosphate with the coating layer.

[0014] In an optional embodiment, the hydrothermal reaction includes 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 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 under conditions with a pH value of 5 to 8; preferably, the substances used to adjust the pH value of the hydrothermal reaction include acids and / or bases, wherein the acid includes at least one of dilute sulfuric acid, dilute hydrochloric acid, acetic acid and carbonic acid; and the base includes ammonia.

[0022] Condition 8: Solvents include water and organic solvents;

[0023] Condition 9: The temperature of the hydrothermal reaction is 150℃~220℃, preferably 180℃;

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

[0025] Condition 11: The pressure inside the reaction vessel during the hydrothermal reaction process 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 lithium iron phosphate primary product with water to obtain a mixture; adding organic matter to the mixture, then adding acid to adjust the pH to 1-4, and allowing it to stand so that the organic matter crosslinks with the phosphate ions dissolved from the lithium iron phosphate primary product.

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

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

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

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

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

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

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

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

[0035] The post-processing includes at least one of the following: washing, drying, crushing, and demagnetizing.

[0036] In an optional implementation, the number of water washes is not less than 5.

[0037] In an optional embodiment, drying is carried out at 100°C to 120°C in an inert atmosphere for 2 to 6 hours.

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

[0039] Thirdly, the present invention provides a battery in which the positive electrode material comprises the easily degradable lithium iron phosphate positive electrode material of the aforementioned embodiments.

[0040] The beneficial effects of this invention include:

[0041] The porosity τ of the easily soluble lithium iron phosphate cathode material provided by this invention is ≤0.8; wherein, ρ0 is the true density of the easily degradable lithium iron phosphate cathode material before pressing; ρ1 is the true density of the easily degradable lithium iron phosphate cathode material after pressing under the first pressure P1; ρ2 is the true density of the easily degradable lithium iron phosphate cathode material after pressing under the second pressure P2, where 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 / cm³. 3 The easily degradable lithium iron phosphate cathode material that meets the above conditions has high density and less particle agglomeration, which can reduce the material's resistance and is beneficial for batteries using it as a cathode material to have better rate performance and suitable discharge specific capacity.

[0042] This invention utilizes a hydrothermal reaction to prepare a high-density lithium iron phosphate precursor. Then, acid etching removes agglomeration interfaces and irregular particles from the precursor, thereby reducing particle aggregation. Simultaneously, the phosphate ions dissolved under the acid react with organic matter to form a complex that coats the surface of the lithium iron phosphate precursor. Calcination then crystallizes the lithium iron phosphate and carbonizes the complex to form a carbon coating layer, ultimately yielding low-agglomeration, carbon-coated lithium iron phosphate. This improves the rate performance of batteries further prepared from easily decomposed lithium iron phosphate cathode materials. Attached Figure Description

[0043] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a flowchart illustrating the preparation process of the easily degradable lithium iron phosphate cathode material provided in an embodiment of the present invention. Detailed Implementation

[0045] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0046] The following is a detailed description of the easily degradable lithium iron phosphate cathode material prepared by crosslinking polymerization provided by the present invention and its applications.

[0047] This invention provides an easily degradable lithium iron phosphate cathode material, wherein the porosity τ of the easily degradable lithium iron phosphate cathode material is ≤0.8;

[0048] in,

[0049] ρ0 is the true density of the easily degradable lithium iron phosphate cathode material before pressing; ρ1 is the true density of the easily degradable lithium iron phosphate cathode material after pressing under the first pressure P1; ρ2 is the true density of the easily degradable lithium iron phosphate cathode material after pressing under the second pressure P2, where 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 / cm³. 3 .

[0050] In some alternative implementations, τ can 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 more typical implementations, τ≤0.5, such as τ being 0.15, 0.32, 0.33, 0.36, 0.49, etc.

[0051] In some alternative implementations, ρ0 ≥ 3.4 g / cm³ 3 .

[0052] Lithium iron phosphate powder used in batteries is typically nano- or micron-sized, making it prone to agglomeration. The resulting agglomerates contain numerous closed pores, leading to a relatively porous lithium iron phosphate cathode material. This, in turn, affects the conductivity and lithium-ion diffusion rate of the batteries made from lithium iron phosphate cathodes. Generally, the more closed pores, the lower the true density of the material. However, by pressing and breaking up the agglomerates in the lithium iron phosphate cathode material, the number of closed pores can be reduced, increasing the true density.

[0053] In this invention, porosity is calculated using the true density index. The change in true density of lithium iron phosphate cathode material under different pressures reflects the change in pore size under different pressures, thus reflecting the degree of agglomeration of the lithium iron phosphate cathode material. Less change in pore size indicates a low degree of agglomeration of the lithium iron phosphate cathode material. Furthermore, a higher pressure required to achieve a certain degree of pore size change indicates a low degree of agglomeration of the lithium iron phosphate cathode material. The relationship between pressure changes and the change in true density of the lithium iron phosphate cathode material after corresponding pressure treatment reflects the porosity of the lithium iron phosphate cathode material. Lithium iron phosphate cathode materials with a porosity τ≤0.8 have high density and less particle agglomeration, which can reduce the material's resistance and is beneficial for batteries using it as a cathode material to have better rate performance and suitable discharge specific capacity.

[0054] The easily degradable lithium iron phosphate cathode material provided by this invention has a true density ≥ 3.4 g / cm³ before pressing. 3 This can eliminate cases of abnormally large aggregated particles that do not meet the requirements of this invention.

[0055] In some optional embodiments, the particle size D of the easily degradable lithium iron phosphate cathode material provided by the present invention is...10 100nm~1μm, D 90 The range is from 3μm to 50μm. D 10 It is one of the key indicators of particle size distribution, representing the particle size corresponding to a cumulative particle size distribution percentage of 10%, that is, 10% of the particles in the sample are smaller than this size. Similarly, D 90 This indicates the particle size corresponding to a cumulative particle size distribution reaching 90%. The easily degradable lithium iron phosphate cathode material provided by this invention has low porosity and low agglomeration between powders, resulting in more uniformity during electrode slurry preparation and exhibiting excellent electrochemical performance.

[0056] In some optional embodiments, the method for breaking up iron phosphate agglomerates used in this invention uses P1 < P2 < 200 MPa, which can avoid the large pressure compaction of lithium iron phosphate causing the briquettes to be difficult to disperse by ultrasonication, thus affecting the test of the true density of the powder.

[0057] As mentioned above, the easily degradable lithium iron phosphate cathode material that meets the above conditions of the present invention has high density and less particle agglomeration, which can reduce the resistance of the material and is beneficial for batteries using it as cathode material to have better rate performance and suitable discharge specific capacity.

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

[0059] S1: Phosphorus source, iron source, lithium source, solvent and dispersant are subjected to hydrothermal reaction in a reaction vessel to obtain lithium iron phosphate primary product.

[0060] The hydrothermal method is a process in which crystals grow from a liquid phase. This invention utilizes the hydrothermal method to prepare easily degradable lithium iron phosphate cathode materials, achieving materials with good uniformity and high density. Furthermore, the particle size of the easily degradable lithium iron phosphate cathode material can be controlled by the temperature and time 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 added is not higher than the amount of phosphorus and lithium added. For example, the molar ratio of phosphorus, iron, and lithium is 0.95:0.90:0.95. Mixtures such as 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 can, to some extent, reduce the impact of magnetic foreign matter, such as iron, on battery safety performance when used as a positive electrode material.

[0062] In some alternative embodiments, the phosphorus source may, by way of example but not limitation, include at least one of adenosine triphosphate, trimethyl phosphate, and triethyl phosphate.

[0063] In some alternative embodiments, the iron source may, by way of example but not by way of limitation, include at least one of ferrous sulfate, ferrous chloride and ferrous nitrate.

[0064] In some alternative implementations, the lithium source may, by way of example but not limitation, 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%, 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 phosphorus, iron and lithium sources, an interface layer may form on the surface of the material, which is not conducive to the synthesis of lithium iron phosphate primary product.

[0067] In some alternative embodiments, the dispersant may, by way of example but not by way of limitation, include at least one of polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyethylene glycol, and dodecyltrimethylammonium bromide.

[0068] In some alternative embodiments, the hydrothermal reaction is carried out at a pH of 5 to 8; wherein the pH 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 result in a low yield of lithium iron phosphate primary product, and some raw materials cannot form a precipitate; if the pH value of the hydrothermal reaction is greater than 8, impurities are easily generated, resulting in insufficient purity of lithium iron phosphate primary product, which affects the electrochemical performance and safety performance of subsequent easily degradable lithium iron phosphate cathode materials.

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

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

[0072] In some alternative embodiments, the hydrothermal reaction temperature can be between 150°C and 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 more typical embodiments, the hydrothermal reaction temperature can be 180°C.

[0073] If the hydrothermal reaction temperature is below 150℃, the lithium iron phosphate crystal density is low and trivalent iron impurity ions are easily generated; if the hydrothermal reaction temperature is above 220℃, the lithium iron phosphate crystal will grow too fast, making it difficult to control the size of the lithium iron phosphate crystal.

[0074] In some optional embodiments, the hydrothermal reaction time can be from 1 hour to 8 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, or 8 hours, 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 less than 1 hour, the lithium iron phosphate particles are likely to be too small; if the hydrothermal reaction time is longer than 8 hours, the lithium iron phosphate particles are likely to be too large, making it difficult to control their size.

[0076] In some optional embodiments, the pressure inside the reaction vessel during the hydrothermal reaction process can be between 1 MPa and 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 other values ​​within the range of 1 MPa to 10 MPa. In some more typical embodiments, the pressure inside the reaction vessel during the hydrothermal reaction process can be 5 MPa.

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

[0078] S2: Crosslink lithium iron phosphate raw material with organic matter and acid in a solution environment to obtain lithium iron phosphate with a coating layer.

[0079] In some alternative embodiments, the preparation of lithium iron phosphate with a coating may include: first mixing lithium iron phosphate precursor with water to obtain a mixture; adding organic matter to the mixture, then adding acid to adjust the pH to 1-4, and allowing it to stand so that the organic matter crosslinks with the phosphate ions dissolved from the lithium iron phosphate precursor.

[0080] Before mixing with water, the initial lithium iron phosphate product can be washed.

[0081] In some alternative embodiments, the organic compound may, by way of example but not by way of limitation, include at least one of chitosan, polyethyleneimine, polylysine, quaternized cellulose and polydiallyldimethylammonium chloride, and other organic compounds that can be crosslinked with phosphate groups are also not excluded.

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

[0083] If too little organic matter is added, it will easily lead to low organic matter content, making it difficult to complete the coating of lithium iron phosphate raw material; if too much organic matter is added, it will easily cause the coating layer to be too thick, which will reduce the electrochemical performance of lithium iron phosphate.

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

[0085] In some alternative implementations, the settling time can be 0.5h to 6h, such as 0.5h, 1h, 2h, 3h, 4h, 5h or 6h, or other values ​​within the range of 0.5h to 6h.

[0086] This invention, by adding acid to adjust the pH value to 1-4, enables the slow dissolution of lithium iron phosphate (LFP) precursors during the standing process. Irregular, small, and agglomerated LFP particles in the precursors are dissolved first. The dissolved phosphate ions cross-link with organic matter to form complexes. These complexes coat the surface of undissolved LFP particles in the precursors, preventing the acid from further dissolving other LFP particles. This achieves the dual effect of reducing agglomeration and effectively controlling the particle size of LFP 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 raw material; if the pH value is greater than 4, it is easy to cause insufficient solubility and fail to achieve the etching effect; if the standing time is less 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 alternative implementations, the crosslinked material is subjected to solid-liquid separation (e.g., filtration), washing, and drying before subsequent calcination.

[0089] Continuing from the above, in the S2 process, phosphate ions dissolved from the lithium iron phosphate precursor undergo a cross-linking polymerization reaction with organic matter, generating flocculent complexes that coat the surface of the lithium iron phosphate particles, forming a uniform coating layer that facilitates particle size control. Furthermore, the uniform coating layer helps improve the conductivity of easily depolymerized lithium iron phosphate cathode materials; in addition, the coating also helps control the agglomeration of lithium iron phosphate particles, facilitating depolymerization and preventing anisotropic growth of the particles.

[0090] S3: Calcining lithium iron phosphate with a coating layer.

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

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

[0093] In some optional embodiments, the calcination time can be from 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 alternative embodiments, calcination is carried out in an inert atmosphere (such as a nitrogen atmosphere, an argon atmosphere, or a helium atmosphere).

[0095] The S3 process described above can crystallize lithium iron phosphate, making its crystal form better, and can also carbonize the organic matter in the coating layer, thereby enhancing the conductivity of the coating layer.

[0096] Furthermore, the preparation of the aforementioned easily degradable lithium iron phosphate cathode material also includes:

[0097] S4: Post-process the calcined product obtained from calcination.

[0098] In some alternative implementations, post-processing may include at least one of washing, drying, crushing, and demagnetizing.

[0099] The washing process can be performed once, twice, three times, or more. In some typical embodiments, the washing process is no less than five times. The purpose of this step is to remove phosphorus-containing compounds (such as metaphosphoric acid, pyrophosphoric acid, etc.) from the carbonized carbon coating layer.

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

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

[0102] In some alternative implementations, post-processing also includes packaging the demagnetized product.

[0103] One packaging method is vacuum packaging using aluminum-plastic film ton bags.

[0104] Continuing from the above, the method for preparing easily decomposed lithium iron phosphate cathode material provided by this invention utilizes a hydrothermal reaction to prepare a high-density lithium iron phosphate primary product. Then, acid etching is used to remove the agglomeration interfaces and irregular particles in the lithium iron phosphate primary product, thereby reducing particle agglomeration. At the same time, under the action of acid, the dissolved phosphate ions crosslink with organic matter to form a complex coating on the surface of the remaining lithium iron phosphate primary product. After calcination, the lithium iron phosphate is crystallized and the complex is carbonized to form a carbon coating layer. Then, water washing is used to remove the metaphosphoric acid and pyrophosphoric acid produced by the pyrolysis of phosphate ions, finally obtaining low-agglomeration, carbon-coated lithium iron phosphate. This can solve the problems of high internal resistance and low rate performance caused by lithium iron phosphate particle agglomeration in the prior art.

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

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

[0107] The present invention also provides a battery comprising the above-described battery cells. This battery 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. As examples, the electrical device may include, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys may include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

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

[0110] Example 1

[0111] This embodiment provides an easily degradable lithium iron phosphate cathode material, such as... Figure 1 Its preparation method includes:

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

[0113] The phosphorus source is adenosine triphosphate (ATP), the iron source is ferrous sulfate, and the lithium source is lithium hydroxide. The molar ratio of phosphorus, iron, and lithium in the phosphorus source is 1:1:1.05. The solvent consists 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℃, the reaction time is 2 hours, and the pressure inside the reactor during the hydrothermal reaction is 5 MPa.

[0114] S2: Crosslink lithium iron phosphate raw material with organic matter and acid in a solution environment to obtain lithium iron phosphate with a coating layer.

[0115] Specifically, the lithium iron phosphate primary product is first washed and then mixed with water at a solid-liquid ratio of 10g:50mL to obtain a mixture. Organic matter is added to the mixture, and then acid is added to adjust the pH to 1. The mixture is allowed to stand so that the organic matter cross-links with the phosphate ions dissolved from the lithium iron phosphate primary product. Then, the mixture is filtered, washed, and dried to obtain lithium iron phosphate with a coating layer.

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

[0117] S3: Calcining lithium iron phosphate with a coating layer.

[0118] The calcination is carried out under a nitrogen atmosphere at a temperature of 700℃ for 4 hours.

[0119] S4: The calcined product obtained by calcination is washed 5 times with deionized water, then dried at 120°C in a nitrogen atmosphere for 2 hours, then crushed by air jet milling, then demagnetized under a 10000GS magnetic field, and finally vacuum packaged with aluminum-plastic film.

[0120] Example 2

[0121] This embodiment provides an easily degradable lithium iron phosphate cathode material, the preparation method of which includes:

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

[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 consists 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 ammonia to the reactor. The hydrothermal reaction temperature is 200℃, the reaction time is 2 hours, and the pressure inside the reactor during the hydrothermal reaction is 3 MPa.

[0124] S2: The lithium iron phosphate primary product is cross-linked with organic matter and acid in a solution environment, followed by filtration, washing and drying to obtain lithium iron phosphate with a coating layer.

[0125] Specifically, the lithium iron phosphate primary product is first washed and then mixed with water at a solid-liquid ratio of 10g:100mL to obtain a mixture. Organic matter is added to the mixture, and then acid is added to adjust the pH to 3. The mixture is allowed to stand so that the organic matter cross-links with the phosphate ions dissolved from the lithium iron phosphate primary product to obtain lithium iron phosphate with a coating layer.

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

[0127] S3: Calcining lithium iron phosphate with a coating layer.

[0128] The calcination is carried out under a nitrogen atmosphere at a temperature of 700℃ for 4 hours.

[0129] S4: The calcined product obtained by calcination is washed 5 times with deionized water, then dried at 100℃ in an argon atmosphere for 6 hours, then crushed by air jet milling, then demagnetized under a 5000GS magnetic field, and finally vacuum packaged with aluminum-plastic film.

[0130] Example 3

[0131] This embodiment provides an easily degradable lithium iron phosphate cathode material, the preparation method of which includes:

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

[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 consists 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℃, the reaction time is 1 hour, and the pressure inside the reactor during the hydrothermal reaction is 8 MPa.

[0134] S2: The lithium iron phosphate primary product is cross-linked with organic matter and acid in a solution environment, followed by filtration, washing and drying to obtain lithium iron phosphate with a coating layer.

[0135] Specifically, the lithium iron phosphate primary product is first washed and then mixed with water at a solid-liquid ratio of 10g:50mL to obtain a mixture. Organic matter is added to the mixture, and then acid is added to adjust the pH to 2. The mixture is allowed to stand so that the organic matter cross-links with the phosphate ions dissolved from the lithium iron phosphate primary product to obtain lithium iron phosphate with a coating layer.

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

[0137] S3: Calcining lithium iron phosphate with a coating layer.

[0138] The calcination is carried out under a nitrogen atmosphere at a temperature of 800℃ for 2 hours.

[0139] S4: The calcined product obtained by calcination is washed 5 times with deionized water, then dried at 110℃ in a nitrogen atmosphere for 4 hours, then crushed by air jet milling, then demagnetized under a 20000GS magnetic field, and finally vacuum packaged with aluminum-plastic film.

[0140] Example 4

[0141] This embodiment provides an easily degradable lithium iron phosphate cathode material, the preparation method of which includes:

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

[0143] The phosphorus source is adenosine triphosphate (ATP), 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 consists 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℃, the reaction time is 8 hours, and the pressure inside the reactor during the hydrothermal reaction is 1 MPa.

[0144] S2: Crosslink lithium iron phosphate raw material with organic matter and acid in a solution environment to obtain lithium iron phosphate with a coating layer.

[0145] Specifically, the lithium iron phosphate primary product is first washed and then mixed with water at a solid-liquid ratio of 10g:100mL to obtain a mixture. Organic matter is added to the mixture, and then acid is added to adjust the pH to 4. The mixture is allowed to stand so that the organic matter cross-links with the phosphate ions dissolved from the lithium iron phosphate primary product. Then, the mixture is filtered, washed, and dried to obtain lithium iron phosphate with a coating layer.

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

[0147] S3: Calcining lithium iron phosphate with a coating layer.

[0148] The calcination is carried out under a nitrogen atmosphere at a temperature of 800℃ for 1 hour.

[0149] S4: The calcined product obtained by calcination is washed 5 times with deionized water, then dried at 110℃ in a nitrogen atmosphere for 4 hours, then crushed by air jet milling, then demagnetized under a 15000GS magnetic field, and finally vacuum packaged with aluminum-plastic film.

[0150] Example 5

[0151] This embodiment provides an easily degradable lithium iron phosphate cathode material, the preparation method of which includes:

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

[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 consists 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 ammonia water to the reactor. The hydrothermal reaction temperature is 200℃, the reaction time is 2 hours, and the pressure inside the reactor during the hydrothermal reaction is 10 MPa.

[0154] S2: The lithium iron phosphate primary product is cross-linked with organic matter and acid in a solution environment, followed by filtration, washing and drying to obtain lithium iron phosphate with a coating layer.

[0155] Specifically, the lithium iron phosphate primary product is first washed and then mixed with water at a solid-liquid ratio of 10g:50mL to obtain a mixture. Organic matter is added to the mixture, and then acid is added to adjust the pH to 2. The mixture is allowed to stand so that the organic matter cross-links with the phosphate ions dissolved from the lithium iron phosphate primary product to obtain lithium iron phosphate with a coating layer.

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

[0157] S3: Calcining lithium iron phosphate with a coating layer.

[0158] The calcination is carried out under a nitrogen atmosphere at a temperature of 500℃ for 6 hours.

[0159] S4: The calcined product obtained by calcination is washed 5 times with deionized water, then dried at 110℃ in a nitrogen atmosphere for 4 hours, then crushed by air jet milling, then demagnetized under a 15000GS magnetic field, and finally vacuum packaged with aluminum-plastic film.

[0160] Example 6

[0161] This embodiment provides an easily degradable lithium iron phosphate cathode material, the preparation method of which includes:

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

[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 consists 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 ammonia water to the reactor. The hydrothermal reaction temperature is 200℃, the reaction time is 4 hours, and the pressure inside the reactor during the hydrothermal reaction is 5 MPa.

[0164] S2: The lithium iron phosphate primary product is cross-linked with organic matter and acid in a solution environment, followed by filtration, washing and drying to obtain lithium iron phosphate with a coating layer.

[0165] Specifically, the lithium iron phosphate primary product is first washed and then mixed with water at a solid-liquid ratio of 10g:50mL to obtain a mixture. Organic matter is added to the mixture, and then acid is added to adjust the pH to 2. The mixture is allowed to stand so that the organic matter cross-links with the phosphate ions dissolved from the lithium iron phosphate primary product to obtain lithium iron phosphate with a coating layer.

[0166] The organic compound is polydiallyl dimethylammonium chloride, and its addition amount is 50 wt% of the initial lithium iron phosphate product. The acid is dilute sulfuric acid. The standing time is 6 hours.

[0167] S3: Calcining lithium iron phosphate with a coating layer.

[0168] The calcination is carried out under a nitrogen atmosphere at a temperature of 400℃ for 6 hours.

[0169] S4: The calcined product obtained by calcination is washed 5 times with deionized water, then dried at 120°C in a nitrogen atmosphere for 2 hours, then crushed by air jet milling, then demagnetized under a 5000GS magnetic field, and finally vacuum packaged with aluminum-plastic film.

[0170] Comparative Example 1

[0171] This comparative example is a lithium iron phosphate cathode material prepared by the carbothermal reduction method, the preparation method of which includes:

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

[0173] S2: The wet-milled material is calcined at 750℃ for 2 hours in an inert atmosphere (nitrogen atmosphere);

[0174] S3: The calcined product obtained by calcination is washed 5 times with deionized water, dried in a nitrogen atmosphere at 110℃ for 4 hours, then sent to an air jet mill for pulverization, demagnetized under a magnetic field strength of 15000GS, and finally vacuum packaged in aluminum-plastic film.

[0175] Comparative Example 2

[0176] This comparative example is a carbon-coated lithium iron phosphate cathode material prepared by a hydrothermal method, the preparation method of which includes:

[0177] S1: Weigh the sample of phosphoric acid, ferric nitrate, lithium hydroxide and glucose in a molar ratio of 1.05:1:1.05:0.1, add it to the hydrothermal reactor, adjust the pH value to 7 with ammonia water, and carry out the hydrothermal reaction in the reactor at 180℃ for 2 hours.

[0178] S2: The hydrothermally heated material is calcined in an argon atmosphere at a temperature of 750℃ for 2 hours.

[0179] S3: The calcined product obtained by calcination is washed 5 times with deionized water, dried in a nitrogen atmosphere at 110℃ for 4 hours, then sent to an air jet mill for pulverization, demagnetized under a magnetic field strength of 15000GS, and finally vacuum packaged in 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 case

[0189] The easily degradable lithium iron phosphate cathode materials obtained in Examples 1-6 and Comparative Examples 1-6 were subjected to the following tests:

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

[0191] (2) Looseness: According to Calculations were performed using a tablet press with a holding time of 10 seconds. P1 was 23 MPa and P2 was 39 MPa. The final values ​​were rounded to the nearest whole number.

[0192] (3) Rate performance and discharge specific capacity test: assembled into button cells according to GB / T 42161-2022 for testing.

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

[0194] Table 1 Test Results

[0195]

[0196] Table 1 shows that the synthesis method of lithium iron phosphate, the amount of organic matter coating, and the choice of calcination temperature affect the porosity and electrochemical performance of lithium iron phosphate cathode materials. Lithium iron phosphate cathode materials with lower porosity exhibit more uniform slurry preparation, resulting in excellent electrochemical performance at both low and high rates. For example, the lithium iron phosphate cathode material in Example 1 has the lowest porosity, and the corresponding battery prepared has a higher discharge specific capacity compared to other examples. Among these, the hydrothermal method has better porosity and electrochemical performance than the carbothermal reduction method. Too low an amount of organic matter coating affects the conductivity of the lithium iron phosphate cathode material, while too thick a coating layer affects rate performance and the lithium-ion insertion / extraction rate. The calcination temperature determines the crystal form and purity of the lithium iron phosphate cathode material. Too low a temperature makes it difficult to form a good crystal structure, and the organic matter is not completely carbonized, resulting in insufficient conductivity; too high a temperature introduces impurities into the lithium iron phosphate, affecting electrochemical performance.

[0197] In summary, the easily disintegrating lithium iron phosphate cathode material provided by this invention has high density and less particle agglomeration, which is beneficial for batteries using it as cathode material to have better rate performance and suitable discharge specific capacity.

[0198] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A readily degradable lithium iron phosphate cathode material prepared by cross-linking polymerization, characterized in that, The porosity τ of the easily soluble lithium iron phosphate cathode material is ≤0.8; in, , The true density of easily decomposed lithium iron phosphate cathode material before pressing. The true density of easily degradable lithium iron phosphate cathode material after pressing under the first pressure P1. The true density of easily degradable lithium iron phosphate cathode material after pressing under a second pressure P2, where P1 < P2; both P1 and P2 are in MPa, and 0.1 is in MPa. , as well as The units are all g / cm³ 3 .

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

3. A method for preparing the easily degradable lithium iron phosphate cathode material as described in claim 1 or 2, characterized in that, Includes the following steps: Phosphorus source, iron source, lithium source, solvent and dispersant are subjected to hydrothermal reaction in a reaction vessel to obtain lithium iron phosphate primary product; the lithium iron phosphate primary product is crosslinked with organic matter and acid in a solution environment to obtain lithium iron phosphate with a coating layer; the lithium iron phosphate with the coating layer is calcined. The organic compound includes at least one of chitosan, polyethyleneimine, polylysine, quaternized cellulose, and polydiallyldimethylammonium chloride; the amount of the organic compound added is 5 wt% to 50 wt% of the lithium iron phosphate precursor. The calcination temperature is 400℃~800℃.

4. The preparation method according to claim 3, characterized in that, Hydrothermal reactions include at least one of the following conditions: 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); 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 amount of the dispersant added is 0.5% to 5% of the total mass of the phosphorus source, the iron source, and the lithium source; Condition 6: The dispersant comprises at least one of polyethylene, polypropylene, polystyrene, polyvinyl alcohol, polyethylene glycol, and dodecyltrimethylammonium bromide; Condition 7: The hydrothermal reaction is carried out under conditions where the pH value is 5-8; Condition 8: The solvent includes water and organic solvents; Condition 9: The temperature of the hydrothermal reaction is 150℃~220℃; Condition 10: The hydrothermal reaction time is 1 hour to 8 hours; Condition 11: The pressure inside the reaction vessel during the hydrothermal reaction process is 1 MPa to 10 MPa.

5. The preparation method according to claim 4, characterized in that, Substances used to adjust the pH value of the hydrothermal reaction include acids and / or bases, wherein the acid includes at least one of dilute sulfuric acid, dilute hydrochloric acid, acetic acid, and carbonic acid; and the base includes ammonia.

6. The preparation method according to claim 4, characterized in that, The hydrothermal reaction temperature is 180℃.

7. The preparation method according to claim 4, characterized in that, The hydrothermal reaction time is 2 hours.

8. The preparation method according to claim 4, characterized in that, The pressure inside the reaction vessel during the hydrothermal reaction process is 5 MPa.

9. The preparation method according to claim 3, characterized in that, The preparation of the coated lithium iron phosphate includes: first mixing the primary lithium iron phosphate with water to obtain a mixture; adding the organic matter to the mixture, then adding the acid to adjust the pH to 1-4, and allowing it to stand so that the organic matter crosslinks with the phosphate ions dissolved from the primary lithium iron phosphate.

10. The preparation method according to claim 9, characterized in that, The acid includes at least one of hydrochloric acid and sulfuric acid; And / or, the settling time is 0.5h to 6h.

11. The preparation method according to claim 3, characterized in that, The calcination temperature is 500℃~800℃; And / or, the calcination time is 1h~6h; And / or, calcination is carried out under an inert atmosphere.

12. The preparation method according to claim 11, characterized in that, The calcination temperature is 700℃.

13. The preparation method according to claim 11, characterized in that, The calcination time is 4 hours.

14. The preparation method according to any one of claims 3 to 13, characterized in that, Also includes: The calcined product obtained from calcination is then subjected to post-processing. The post-processing includes at least one of the following: washing, drying, crushing, and demagnetizing.

15. The preparation method according to claim 14, characterized in that, Wash at least 5 times.

16. The preparation method according to claim 14, characterized in that, Drying is carried out at 100℃~120℃ in an inert atmosphere for 2h~6h.

17. The preparation method according to claim 14, characterized in that, The magnetic field strength used for demagnetization is 5000GS~20000GS.

18. A battery, characterized in that, The positive electrode material of the battery includes the easily degradable lithium iron phosphate positive electrode material as described in claim 1 or 2.

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