Carbon source precursor, phosphate positive electrode material as well as preparation method and application of phosphate positive electrode material

Abstract

The invention belongs to the field of lithium ion battery materials, and discloses a carbon source precursor, a phosphate positive electrode material and a preparation method and application of the phosphate positive electrode material, the carbon source precursor comprises glutenin and gliadin, and the mass ratio of the glutenin to the gliadin is (0.65-1): 1. According to the present invention, glutenin and gliadin are subjected to dehydration decomposition and carbonization to form a ring, the three-dimensional network skeleton structure is converted into the uniformly distributed carbon network coating layer, and the phosphate positive electrode material particles dispersed in the three-dimensional network skeleton structure are coated in situ, such that the overgrowth during the grain high-temperature sintering can be easily limited; secondly, a carbon network coating layer formed by carbonization and cyclization of glutenin and gliadin is in a carbon film shape and a carbon filament shape, and the surfaces of crystal grains are uniformly coated with a carbon film; the carbon filaments are uniformly dispersed on the surfaces of the phosphate positive electrode material particles and among the particles to form a carbon network skeleton, so that the electronic conductivity of the phosphate positive electrode material is improved, and the electrochemical performance of the battery is further improved.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion battery materials, and relates to a cathode material for lithium-ion batteries, specifically to a carbon source precursor, a phosphate cathode material, and a preparation method and application thereof. Background Art

[0002] Phosphate cathode materials have attracted much attention in the research of cathode materials due to their excellent thermal stability, high safety, long cycle life, and low cost. However, due to the limitations of the material's own structure, compared with other cathode materials, their lower electronic conductivity and ion diffusion rate affect the rate performance and low-temperature performance of the material; in addition, it is difficult for phosphate cathode materials to balance characteristics such as high tap density, high capacity, high energy density, and cycle stability.

[0003] In the prior art, the commonly used preparation method for phosphate cathode materials is the solid-phase method. Generally, a carbon source, a lithium salt, a phosphate, and raw materials of other doped metal elements (iron salts, manganese salts, etc.) are ball-milled and mixed and then directly calcined to obtain a carbon-coated phosphate cathode material. In recent years, researchers have found that biomass carbon sources (such as sugars, cellulose, lignin, etc.) are widely used for coating modification of cathode materials due to their rich sources, low cost, and environmental friendliness. The commonly used biomass carbon sources have complex compositions, contain various functional groups and polymers, and are prone to uneven carbon layer deposition due to differences in local reaction rates during high-temperature pyrolysis, affecting the electrochemical stability of the cathode material. Summary of the Invention

[0004] Aiming at the defects and deficiencies existing in the prior art, on the first aspect, the present invention provides a carbon source precursor; on the second aspect, the present invention provides a preparation method for a phosphate cathode material; on the third aspect, the present invention provides a phosphate cathode material; on the fourth aspect, the present invention provides a battery.

[0005] On the first aspect, the present invention provides a carbon source precursor, which includes gluten and gliadin, and the mass ratio of gluten to gliadin is 0.65~1∶1.

[0006] On the second aspect, the present invention provides a preparation method for a phosphate cathode material, which includes the following steps: Step 1: Grind and mix an alkali metal source, a transition metal source, a non-metal source, and the above carbon source precursor to obtain a mixed powder A; Step 2: Add water to the mixed powder A, grind it evenly, and obtain a mixed material B after drying; Step 3: Pre-calcine, sinter, and crush the mixed material B in an inert atmosphere, and the obtained solid particles are the phosphate cathode material.

[0007] Preferably, the alkali metal source is any one or more than two of a lithium source, a sodium source, and a potassium source.

[0008] Preferably, the lithium source is any one or more than two of lithium carbonate, lithium hydroxide, lithium chloride, lithium dihydrogen phosphate, lithium acetate, lithium formate, lithium citrate, lithium nitrate, lithium benzoate, lithium tert-butoxide, lithium phosphate, and lithium oxalate.

[0009] Preferably, the sodium source is any one or more than two of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, sodium oxalate, sodium acetate, sodium citrate, sodium fluoride, sodium vanadate, and sodium metavanadate.

[0010] Preferably, the potassium source is any one or more than two of potassium carbonate, potassium bicarbonate, potassium hydroxide, potassium fluoride, potassium acetate, potassium oxalate, potassium citrate, potassium phosphate, potassium dihydrogen phosphate, and potassium hydrogen phosphate.

[0011] Preferably, the transition metal source is any one or more than two of an iron source, a manganese source, and a vanadium source.

[0012] Preferably, the iron source is any one or more than two of ferrous oxalate, ferrous sulfate, ferrous acetate, ferrous chloride, ferrous sulfate heptahydrate, ferrous nitrate, ferrous citrate, ferric chloride, ferric phosphate, ferric sulfate, ferric nitrate, and iron(III) oxide.

[0013] Preferably, the manganese source is any one or more than two of manganese oxalate, manganese carbonate, basic manganese carbonate, manganese hydroxide, manganese dioxide, manganese(III) oxide, manganese tetroxide, manganese acetate, manganese sulfate, and manganese chloride.

[0014] Preferably, the vanadium source is any one or more than two of ammonium metavanadate, sodium metavanadate, sodium vanadate, vanadium dioxide, vanadium(III) oxide, and vanadium pentoxide.

[0015] Preferably, the non-metal source is any one of a phosphorus source or a mixture of a phosphorus source and a fluorine source.

[0016] Preferably, the phosphorus source is any one or more than two of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, sodium hydrogen phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, potassium phosphate, and ferric phosphate.

[0017] Preferably, the fluorine source is any one or two of sodium fluoride and ammonium fluoride.

[0018] Preferably, when preparing the lithium vanadium fluorophosphate, sodium vanadium fluorophosphate, or potassium vanadium fluorophosphate cathode material, the non-metal source uses both a fluorine source and a phosphorus source.

[0019] Preferably, in step 1, in the mixed powder A, the stoichiometric ratios of the alkali metal ions in the alkali metal source, the metal ions in the transition metal source, the phosphate groups in the phosphorus source, and the chemical formula are the same.

[0020] Preferably, in step 1, the carbon source precursor is 6 wt.% to 25 wt.% of the sum of the masses of the carbon source precursor, the alkali metal source, the transition metal source, and the non-metal source.

[0021] Preferably, in step 1, the grinding speed is 200 to 450 rpm, and the grinding time is 1 to 8 h.

[0022] Preferably, in step 2, the grinding speed is 200 to 450 rpm, and the grinding time is 1 to 6 h.

[0023] Preferably, in step 2, the ratio of the volume of water to the mass of the mixed powder A added is (1.0 to 6.0) mL∶1.0 g.

[0024] Preferably, in step 2, the drying temperature is 60 to 100 °C, and the drying time is 3 to 6 h.

[0025] Preferably, in step 3, the pre-sintering temperature is 300 to 500 °C; the pre-sintering time is 1 to 6 h; the high-temperature sintering temperature is 600 to 850 °C; the high-temperature sintering time is 6 to 10 h.

[0026] Preferably, the gas providing the inert atmosphere is any one or more of argon, nitrogen, and helium.

[0027] In a third aspect, the present invention provides a phosphate cathode material prepared by the above preparation method.

[0028] In a fourth aspect, the present invention provides a battery including the phosphate cathode material prepared by the above preparation method.

[0029] Compared with the prior art, one or more technical solutions provided by the present invention have the following obvious beneficial effects: (1) Glutenin and gliadin are dehydrated, decomposed, and carbonized into rings, and the three-dimensional network skeleton structure is transformed into a uniformly distributed carbon network coating layer, which in-situ coats and disperses the phosphate cathode material particles in the three-dimensional network skeleton structure. First, it helps to limit the excessive growth of crystal grains during high-temperature sintering; second, the carbon network coating layer formed by the carbonization of glutenin and gliadin into rings is in the form of carbon films and carbon filaments. The carbon films are uniformly coated on the surface of the crystal grains; the carbon filaments are uniformly dispersed on the surface and between the phosphate cathode material particles, constituting a carbon network skeleton, which is beneficial to improving the electronic conductivity of the phosphate cathode material.

[0030] (1) Through sufficient grinding and mixing, other raw materials of the cathode material are evenly dispersed and adhered to the three-dimensional network skeleton structure, reducing the segregation phenomenon during the mixing and drying processes to a certain extent, achieving the replacement of multi-stage wet ball milling, sand milling, and spray drying, without the need to use the dispersing and grinding aid anhydrous ethanol, shortening the process flow, and thus reducing production energy consumption and costs.

[0031] (2) The carbon source precursor composed of gluten and gliadin contains abundant nitrogen and sulfur elements. During the pre-burning process, on the one hand, nitrogen atoms and sulfur atoms of the carbon source precursor are introduced to the material surface, in-situ forming a nitrogen and sulfur-doped carbon coating layer. Nitrogen atoms and sulfur atoms can provide electron carriers and reduce the band gap, decreasing the internal resistance of the electrode; on the other hand, nitrogen atoms and sulfur atoms can destroy the ordered structure of graphite, inducing edge defects in the carbon layer, increasing the active lithium storage sites, and being conducive to the rapid diffusion of lithium ions, thereby improving the capacity of the material. Brief Description of the Drawings

[0032] Figure 1 It is a process flow schematic diagram of a preparation method of a phosphate cathode material provided by the present invention; Figure 2 It is a rate performance test chart of the battery assembled with the cathode material prepared in Example 1 at 0.1 - 5C; Figure 3 In which, a is the SEM test chart of the cathode material prepared in Example 1 observed at 2k times; Figure 3 In which, b is the SEM test chart of the cathode material prepared in Example 1 observed at 5k times; Figure 3 In which, c is the SEM test chart of the cathode material prepared in Example 1 observed at 30k times; Figure 4 It is the EDS test chart of the cathode material prepared in Example 1; Figure 5 It is the TEM test chart of the cathode material prepared in Example 1; Figure 6 It is the XRD test chart of the cathode material prepared in Example 1. Detailed Embodiments

[0033] The present invention provides the following specific technical solutions.

[0034] On the first aspect, the present invention provides a carbon source precursor, including gluten and gliadin, and the mass ratio of gluten to gliadin is 0.65 - 1:1.

[0035] The inventors have found through research that glutenin and gliadin, as environmentally friendly biomass macromolecular proteins, exist in crops such as wheat and barley, with low cost and wide sources. After adding water, glutenin and gliadin absorb water and swell, enhancing the cohesion and adhesion between protein molecules. Among them, the high-molecular-weight subunits (HMW-GS) and low-molecular-weight subunits (LMW-GS) of glutenin unfold in water, increasing the contact area between molecular chains; the high-molecular-weight subunits and low-molecular-weight subunits cross-link with each other through intermolecular disulfide bonds to form fibrous macromolecular aggregates, constituting the framework structure; gliadin gradually forms spherical aggregates through disulfide bonds between the frameworks, as well as non-covalent interactions such as hydrophobic interactions, hydrogen bonds, and electrostatic interactions to further improve the framework structure, forming a stable and viscous three-dimensional network framework structure. In the subsequent calcination process, glutenin and gliadin dehydrate, decompose, and carbonize into rings, and the three-dimensional network framework structure is transformed into a uniformly distributed carbon network coating layer, in-situ coating the phosphate cathode material particles dispersed in the three-dimensional network framework structure. On the one hand, it helps to limit the excessive growth during high-temperature sintering of the grains; on the other hand, the carbon network coating layer formed by the carbonization of glutenin and gliadin into rings is in the form of carbon films and carbon filaments. The carbon films are uniformly coated on the surface of the grains; the carbon filaments are uniformly dispersed on the surface and between the phosphate cathode material particles, constituting a carbon network framework, which is beneficial to improving the electronic conductivity and tap density of the phosphate cathode material.

[0036] In some preferred embodiments of the present invention, the mass ratio of glutenin to gliadin is 0.65~1∶1. The higher-molecular-weight glutenin cross-links through intermolecular disulfide bonds to form a three-dimensional network framework structure with more stable structure and higher elasticity; the lower-molecular-weight gliadin endows the three-dimensional network framework structure with viscosity through disulfide bonds and non-covalent interactions after absorbing water.

[0037] On the other hand, the present invention provides a method for preparing a phosphate cathode material, comprising the following steps: Step 1, grinding and mixing an alkali metal source, a transition metal source, a non-metal source, and the above carbon source precursor to obtain a mixed powder A; Step 2, adding water to the mixed powder A and grinding evenly, and then drying to obtain a mixed material B; Step 3, pre-calcining, sintering, and crushing the mixed material B in an inert atmosphere, and the obtained solid particles are the phosphate cathode material.

[0038] The inventor has discovered through research that using a mixture of glutenin and gliadin as a carbon source precursor, a three-dimensional network skeleton structure is constructed after the water absorption and cross-linking of glutenin and gliadin. The skeleton structure is evenly arranged in multiple honeycomb shapes. Through sufficient grinding and mixing, other raw materials of the cathode material are evenly dispersed and adhered to the three-dimensional network skeleton structure. The three-dimensional network skeleton structure can tightly bind the raw material particles, can reduce the segregation phenomenon during the mixing and drying processes to a certain extent, and can replace multi-stage wet ball milling, sand milling, and spray drying. There is no need to use the dispersion and grinding aid anhydrous ethanol, shortening the process flow, thereby reducing production energy consumption and costs. And after the particles are pre-sintered and high-temperature sintered, a phosphate cathode material with a larger particle size can be formed, and the tap density and bulk density of the cathode material can be improved without relying on spray granulation technology.

[0039] Preferably, the alkali metal source is any one or more of a lithium source, a sodium source, and a potassium source.

[0040] Preferably, the lithium source is any one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium dihydrogen phosphate, lithium acetate, lithium formate, lithium citrate, lithium nitrate, lithium benzoate, lithium tert-butoxide, lithium phosphate, and lithium oxalate.

[0041] Preferably, the sodium source is any one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, sodium oxalate, sodium acetate, sodium citrate, sodium fluoride, sodium vanadate, and sodium metavanadate.

[0042] Preferably, the potassium source is any one or more of potassium carbonate, potassium bicarbonate, potassium hydroxide, potassium fluoride, potassium acetate, potassium oxalate, potassium citrate, potassium phosphate, potassium dihydrogen phosphate, and potassium hydrogen phosphate.

[0043] Preferably, the transition metal source is any one or more of an iron source, a manganese source, and a vanadium source.

[0044] Preferably, the iron source is any one or more of ferrous oxalate, ferrous sulfate, ferrous acetate, ferrous chloride, ferrous sulfate heptahydrate, ferrous nitrate, ferrous citrate, ferric chloride, ferric phosphate, ferric sulfate, ferric nitrate, and iron(III) oxide.

[0045] Preferably, the manganese source is any one or more of manganese oxalate, manganese carbonate, basic manganese carbonate, manganese hydroxide, manganese dioxide, manganese(III) oxide, manganese(II,III) oxide, manganese acetate, manganese sulfate, and manganese chloride.

[0046] Preferably, the vanadium source is any one or more of ammonium metavanadate, sodium metavanadate, sodium vanadate, vanadium dioxide, vanadium(III) oxide, and vanadium pentoxide.

[0047] Preferably, the non-metal source is any one of a phosphorus source or a mixture of a phosphorus source and a fluorine source.

[0048] Preferably, the phosphorus source is any one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, sodium hydrogen phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, potassium phosphate and iron phosphate.

[0049] Preferably, the fluorine source is any one or both of sodium fluoride and ammonium fluoride.

[0050] Preferably, when preparing the lithium vanadium fluorophosphate, sodium vanadium fluorophosphate, and potassium vanadium fluorophosphate cathode materials, two kinds of non-metal sources, namely a fluorine source and a phosphorus source, are used.

[0051] Preferably, in step 1, in the mixed powder A, the stoichiometric ratios of the alkali metal ions in the alkali metal source, the metal ions in the transition metal source, the phosphate radicals in the phosphorus source and the chemical formula are the same.

[0052] Preferably, in step 1, the carbon source precursor is 6 wt.% to 25 wt.% of the sum of the masses of the carbon source precursor, the alkali metal source, the transition metal source, and the non-metal source.

[0053] Preferably, in step 1, the grinding speed is 200 - 450 rpm and the grinding time is 1 - 8 h.

[0054] Preferably, in step 2, the grinding speed is 200 - 450 rpm and the grinding time is 1 - 6 h.

[0055] Preferably, in step 2, the ratio of the volume of water added to the mass of the mixed powder A is (1.0 - 6.0) mL∶1.0 g.

[0056] Preferably, in step 2, the drying temperature is 60 - 100 °C and the drying time is 3 - 6 h.

[0057] Preferably, in step 3, the pre-sintering temperature is 300 - 500 °C; the pre-sintering time is 1 - 6 h; the high-temperature sintering temperature is 600 - 850 °C; the high-temperature sintering time is 6 - 10 h.

[0058] The inventor found through research that the carbon source precursor composed of glutenin and gliadin contains nitrogen and sulfur elements. During the pre-sintering process, on the one hand, the nitrogen atoms and sulfur atoms of the carbon source precursor are introduced to the material surface, in-situ forming a nitrogen and sulfur co-doped carbon coating layer. The nitrogen atoms and sulfur atoms can provide electron carriers and reduce the band gap, reducing the internal resistance of the electrode. On the other hand, the nitrogen atoms and sulfur atoms can destroy the ordered structure of graphite, induce the generation of carbon layer edge defects, increase the lithium storage active sites, and facilitate the rapid diffusion of lithium ions, thereby improving the capacity of the cathode material.

[0059] Preferably, the gas providing the inert atmosphere is any one or more of argon, nitrogen, and helium.

[0060] In a third aspect, the present invention provides a phosphate cathode material prepared by the above preparation method.

[0061] In a fourth aspect, the present invention provides a battery comprising the phosphate cathode material prepared by the above preparation method.

[0062] To make the technical problems, technical solutions and technical advantages to be solved by the present invention clearer, the following will be described in detail with specific examples, but the protection scope of the present invention is not limited to the following specific embodiments.

[0063] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0064] Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0065] Example 1: A preparation method of a phosphate cathode material, as Figure 1 shown, includes the following steps: Step 1, mix 3.768 g of lithium carbonate, 15.082 g of iron phosphate, 1.047 g of gluten and 1.047 g of gliadin, grind for 4 h at 400 rpm, and obtain a mixed powder A.

[0066] Step 2, add 80 mL of water to the mixed powder A, grind for 2 h at 400 rpm, and dry at 80 °C for 3 h to obtain a mixed material B.

[0067] Step 3, sinter the mixed material B in an argon atmosphere at 400 °C for 2 h, then raise the temperature to 700 °C and sinter for 8 h. The solid particles obtained after crushing are the carbon-coated lithium iron phosphate cathode material Li 1.02 FePO4.

[0068] Comparative Example 1: A preparation method of a phosphate cathode material includes the following steps: Step 1, mix 3.768 g of lithium carbonate, 15.082 g of iron phosphate, 2.094 g of glucose, grind for 4 h at 400 rpm, and obtain a mixed powder A.

[0069] Step 2, add 80 mL of water to the mixed powder A, grind for 2 h at 400 rpm, and spray granulate to obtain a mixed material B.

[0070] Step 3: Place mixture B in an argon atmosphere and sinter at 400 °C for 2 h, then raise the temperature to 700 °C and sinter for 8 h. The solid particles obtained after crushing are the carbon-coated lithium iron phosphate cathode material Li 1.02 FePO4.

[0071] Comparative Example 2: Step 1: Mix 3.768 g of lithium carbonate, 15.082 g of iron phosphate, and 2.094 g of glucose, and grind at 400 rpm for 4 h to obtain mixed powder A.

[0072] Step 2: Add 80 mL of water to mixed powder A, grind at 400 rpm for 2 h, and dry at 80 °C for 3 h to obtain mixture B.

[0073] Step 3: Place mixture B in an argon atmosphere and sinter at 400 °C for 2 h, then raise the temperature to 700 °C and sinter for 8 h. The solid particles obtained after crushing are the carbon-coated lithium iron phosphate cathode material Li 1.02 FePO4.

[0074] Example 2: A method for preparing a phosphate cathode material, comprising the following steps: Step 1: Mix 3.768 g of lithium carbonate, 24.186 g of iron nitrate, 11.504 g of ammonium dihydrogen phosphate, 1.949 g of gluten, and 2.436 g of gliadin, and grind at 200 rpm for 1 h to obtain mixed powder A.

[0075] Step 2: Add 20 mL of water to mixed powder A, grind at 200 rpm for 1 h, and dry at 60 °C for 1 h to obtain mixture B.

[0076] Step 3: Place mixture B in an argon atmosphere and sinter at 300 °C for 1 h, then raise the temperature to 600 °C and sinter for 6 h. The solid particles obtained after crushing are the carbon-coated lithium iron phosphate cathode material Li 1.02 FePO4.

[0077] Example 3: A method for preparing a phosphate cathode material, comprising the following steps: Step 1: Mix 2.517 g of lithium hydroxide, 14.431 g of ferrous sulfate, 11.504 g of ammonium dihydrogen phosphate, 1.978 g of gluten, and 3.043 g of gliadin, and grind at 450 rpm for 8 h to obtain mixed powder A, then grind at 450 rpm for 1 h and dry at 100 °C for 6 h to obtain mixture B.

[0078] Step 2: Add 150 mL of water to mixed powder A, grind at 450 rpm for 1 h, and dry at 100 °C for 6 h to obtain mixture B.

[0079] Step 3: Place mixture B in an argon atmosphere and sinter at 500 °C for 6 h, then raise the temperature to 850 °C and sinter for 10 h. The solid particles obtained after crushing are the carbon-coated lithium iron phosphate cathode material Li 1.05 Fe 0.95 PO4.

[0080] Example 4: A method for preparing a phosphate cathode material, comprising the following steps: Step 1: Mix 3.768 g of lithium carbonate, 15.082 g of iron phosphate, 1.047 g of gluten, and 1.047 g of gliadin. After grinding at 400 rpm for 4 h, a mixed powder A is obtained.

[0081] Step 2: Add 80 mL of water to the mixed powder A, grind at 400 rpm for 2 h, and dry at 80 °C for 3 h to obtain mixture B.

[0082] Step 3: Place mixture B in an argon atmosphere and sinter at 450 °C for 3 h and at 700 °C for 8 h. The solid particles obtained after crushing are the lithium iron phosphate cathode material Li 1.02 FePO4.

[0083] Example 5: Step 1: Mix 15.899 g of sodium carbonate, 23.396 g of ammonium metavanadate, 23.008 g of ammonium dihydrogen phosphate, 11.115 g of ammonium fluoride, 4.079 g of gluten, and 4.079 g of gliadin. After grinding at 400 rpm for 4 h, a mixed powder A is obtained.

[0084] Step 2: Add 80 mL of water to the mixed powder A, grind at 400 rpm for 2 h, and dry at 80 °C for 3 h to obtain mixture B.

[0085] Step 3: Place mixture B in an argon atmosphere and sinter at 400 °C for 2 h, then raise the temperature to 700 °C and sinter for 8 h. The solid particles obtained after crushing are the carbon-coated sodium vanadium fluorophosphate cathode material Na3V2(PO4)2F3.

[0086] Example 6: Step 1: Mix 12.597 g of sodium fluoride, 18.188 g of vanadium pentoxide, 23.008 g of ammonium dihydrogen phosphate, 6.724 g of gluten, and 6.724 g of gliadin. After grinding at 300 rpm for 4 h, a mixed powder A is obtained.

[0087] Step 2: Add 80 mL of water to the mixed powder A, grind at 400 rpm for 2 h, and dry at 80 °C for 3 h to obtain mixture B.

[0088] Step 3: Place mixture B in an argon atmosphere and sinter at 400 °C for 2 h, then raise the temperature to 850 °C and sinter for 10 h. The solid particles obtained after crushing are the carbon-coated sodium vanadium fluorophosphate cathode material Na3V2(PO4)2F3.

[0089] Comparative Example 3: Step 1: Mix 15.899 g of sodium carbonate, 23.396 g of ammonium metavanadate, 23.008 g of ammonium dihydrogen phosphate, 11.115 g of ammonium fluoride, and 8.158 g of glucose. Grind at 400 rpm for 4 h to obtain mixed powder A.

[0090] Step 2: Add 80 mL of water to mixed powder A, grind at 400 rpm for 2 h, and dry at 80 °C for 3 h to obtain mixture B.

[0091] Step 3: Place mixture B in an argon atmosphere and sinter at 400 °C for 2 h, then raise the temperature to 700 °C and sinter for 8 h. The solid particles obtained after crushing are the carbon-coated sodium vanadium fluorophosphate cathode material Na3V2(PO4)2F3.

[0092] Respectively, add the lithium iron phosphates prepared in Examples 1-6 and Comparative Examples 1-3, acetylene black, and PVDF to an appropriate amount of N-methylpyrrolidone (NMP) solution in a ratio of 8:1:1, adjust the viscosity of the slurry and mix and stir evenly, and coat on the current collector aluminum foil at a loading of 2-4 mg / cm 2 Dry at 80 °C under vacuum for 12 h; cut out a 12-mm circular electrode sheet and assemble a CR2025 coin cell in a glove box with an argon atmosphere; use lithium metal as the negative electrode, Celgard 2500 microporous polypropylene membrane as the separator, and the electrolyte is 1 M LiPF6 (volume ratio of diethyl carbonate (DEC): fluoroethylene carbonate (FEC) is 1:1); use a BlueTEC battery test system to test the rate performance of the batteries assembled with the cathode materials prepared in Examples 1-6 and Comparative Examples 1-3 at different rates (1C = 170 mAh / g). The test data are shown in Table 1.

[0093] Table 1 Rate performance of the batteries assembled in Examples 1-6 and Comparative Examples 1-3 (unit: mAh / g) Figure 2 It is the rate performance test chart of the battery assembled with the cathode material prepared in Example 1 at 0.1-5C.

[0094] By comparing the rate performance and capacity retention rate of the batteries assembled with the cathode materials prepared in Comparative Example 1 and Comparative Example 1, it can be seen that the preparation method provided by the present invention does not require spray granulation, and the batteries assembled with the cathode materials prepared by it still have a relatively high level of rate performance and capacity retention rate, even higher than those of the batteries assembled with the cathode materials prepared in Comparative Example 1.

[0095] By comparing the rate performance and capacity retention rate of the batteries assembled with the cathode materials prepared in Comparative Example 1 and Comparative Example 2, it can be seen that the rate performance and cyclic capacity retention rate of the cathode materials prepared by the direct mixing and roasting process in the prior art are relatively poor, while the preparation method provided by the present invention can also prepare cathode materials with good rate performance and cyclic capacity retention rate without spray granulation.

[0096] By comparing the rate performance and cyclic capacity retention rate of the batteries assembled with the cathode materials prepared in Example 5 and Comparative Example 3, it can be seen that the rate performance and cyclic capacity retention rate of the cathode materials prepared in Example 5 are more excellent, which can prove that the carbon source precursor provided by the present invention can also improve the rate performance and cyclic capacity retention rate when applied to sodium phosphate cathode materials.

[0097] Compared with sodium vanadium fluorophosphate prepared using glucose as a carbon source, the sodium vanadium fluorophosphate prepared in Examples 5-6 of the present invention contains a carbon coating layer doped with nitrogen and sulfur elements, has more active sites for lithium storage, is beneficial to promoting the transmission and insertion / extraction process of lithium ions, and thus improves the rate performance.

[0098] The physical and chemical properties of the lithium iron phosphate cathode materials prepared in Examples 1-4 and Comparative Examples 1-2 of the present invention are shown in Table 2.

[0099] Table 2 Physical and chemical properties of the lithium iron phosphate cathode materials prepared in Examples 1-4 and Comparative Examples 1-2 The lithium iron phosphate cathode materials prepared in Examples 1-4 and Comparative Examples 1-2 were all crushed at 200 rpm for 1 h.

[0100] By comparing the batteries assembled with the cathode materials prepared in Example 1 and Comparative Example 1, the tap density and compression density of the cathode materials prepared with the carbon source precursor provided by the present invention are similar to those of the cathode materials after spray granulation, which can further prove that the carbon source precursor provided by the present invention can also prepare cathode materials with high tap density and compression density without spray granulation, simplify the process flow, and reduce the production cost. Comparative Example 2 is the cathode material prepared without spray drying and using glucose as a carbon source, which has smaller particle size, tap density and compression density, and higher resistance, which can further prove the superiority of the cathode materials prepared with the carbon source precursor and preparation process provided by the present invention.

[0101] Figure 3 In [a], a is the SEM test image of the positive electrode material prepared in Example 1 observed at 2k times magnification; Figure 3 In [b], b is the SEM test image of the positive electrode material prepared in Example 1 observed at 5k times magnification; Figure 3 In [c], c is the SEM test image of the positive electrode material prepared in Example 1 observed at 30k times magnification. Combining Figure 3 a, b, and c in [a], it can be seen that the average particle size of the positive electrode material prepared by the preparation method provided by the present invention is about 500 nm, the crystal particles grow sufficiently, the primary particles aggregate to form secondary particles, showing an oval particle shape, and there is less agglomeration phenomenon. From Figure 3 c in [c], it can be clearly observed that there is a carbon filament network structure between the particles. Figure 3 Combining c in [c] with Table 1, it can be proved from the side that the carbon source precursor provided by the present invention can uniformly disperse and adhere other raw materials of the positive electrode material in the three-dimensional network skeleton structure, to a certain extent reducing the segregation phenomenon during the mixing and drying processes, achieving the replacement of multi-stage wet ball milling, sand milling and spray drying, without the use of the dispersion and grinding aid anhydrous ethanol, shortening the process flow, thereby reducing the production energy consumption and cost, and the prepared positive electrode material still has good rate performance and cycle capacity retention rate.

[0102] Figure 4 is the EDS test image of the positive electrode material prepared in Example 1. From Figure 4 it can be seen that the material contains Fe, P, O, C, N, S species elements, indicating that the surface of the lithium iron phosphate positive electrode material prepared by the present invention contains a carbon coating layer doped with nitrogen atoms and sulfur atoms. Figure 4 Combining with Table 1, it can be proved from the side that compared with the positive electrode material prepared using glucose as the carbon source, the carbon source precursor provided by the present invention contains a small amount of nitrogen and sulfur elements after calcination, increasing the active sites for lithium storage in the positive electrode material, which is beneficial to promoting the transmission and insertion / extraction processes of lithium ions, and thus improving the rate performance.

[0103] Figure 5 is the TEM test image of the positive electrode material prepared in Example 1. From Figure 5 it can be seen that the dotted area represents a carbon coating layer with a thickness of about 3 nm, and below the dotted area is the positive electrode matrix material, indicating that the prepared positive electrode material is coated with a carbon coating layer with uniform thickness, improving the electronic conductivity of the material, and thus promoting the electrochemical capacity of the material.

[0104] Figure 6 is the XRD test image of the positive electrode material prepared in Example 1. From Figure 6 it can be seen that the lithium iron phosphate positive electrode material has a pure phase and high crystallinity.

[0105] The above-described embodiments are only preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope of the present invention, according to the technical solution and its concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A carbon source precursor, characterized in that It includes glutenin and gliadin, and the mass ratio of glutenin to gliadin is 0.65~1:

1.

2. A method for preparing a phosphate positive electrode material, characterized in that: The steps include: Step 1, grinding and mixing an alkali metal source, a transition metal source, a non-metal source and the carbon source precursor according to claim 1 to obtain a mixed powder A; Step 2, adding water to the mixed powder A and grinding it evenly, and then drying it to obtain a mixed material B; Step 3, pre-sintering, sintering and crushing the mixed material B in an inert atmosphere in sequence, and the obtained solid particles are the phosphate positive electrode material.

3. The method for preparing a phosphate positive electrode material according to claim 2, characterized in that: The alkali metal source is any one or more of a lithium source, a sodium source, and a potassium source; the lithium source is any one or more of lithium carbonate, lithium hydroxide, lithium chloride, lithium dihydrogen phosphate, lithium acetate, lithium formate, lithium citrate, lithium nitrate, lithium benzoate, lithium tert-butoxide, lithium phosphate, and lithium oxalate; the sodium source is any one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, sodium phosphate, sodium dihydrogen phosphate, sodium hydrogen phosphate, sodium oxalate, sodium acetate, sodium citrate, sodium fluoride, sodium vanadate, and sodium metavanadate; the potassium source is any one or more of potassium carbonate, potassium bicarbonate, potassium hydroxide, potassium fluoride, potassium acetate, potassium oxalate, potassium citrate, potassium phosphate, potassium dihydrogen phosphate, and potassium hydrogen phosphate; The transition metal source is any one or more of an iron source, a manganese source, and a vanadium source; the iron source is any one or more of ferrous oxalate, ferrous sulfate, ferrous acetate, ferrous chloride, ferrous sulfate heptahydrate, ferrous nitrate, ferrous citrate, ferric chloride, ferric phosphate, ferric sulfate, ferric nitrate, and ferric oxide; the manganese source is any one or more of manganese oxalate, manganese carbonate, basic manganese carbonate, manganese hydroxide, manganese dioxide, manganese trioxide, manganese tetraoxide, manganese acetate, manganese sulfate, and manganese chloride; the vanadium source is any one or more of ammonium metavanadate, sodium metavanadate, sodium vanadate, vanadium dioxide, vanadium trioxide, and vanadium pentoxide; The non-metallic source is a phosphorus source or a mixture of a phosphorus source and a fluorine source; the phosphorus source is any one or more of phosphoric acid, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, lithium dihydrogen phosphate, sodium dihydrogen phosphate, sodium phosphate, sodium hydrogen phosphate, potassium dihydrogen phosphate, potassium hydrogen phosphate, potassium phosphate and iron phosphate; the fluorine source is any one or two of sodium fluoride and ammonium fluoride.

4. The method for preparing a phosphate positive electrode material according to claim 2, characterized in that: In step 1, in the mixed powder A, the alkali metal ions in the alkali metal source, the transition metal ions in the transition metal source, the non-metal source and the chemical formula have the same stoichiometric ratio.

5. The method for preparing a phosphate positive electrode material according to claim 2, characterized in that: In step 1, the carbon source precursor is 6 wt.% to 25 wt.% of the sum of the mass of the carbon source precursor, the alkali metal source, the transition metal source, and the non-metal source.

6. The method for preparing a phosphate positive electrode material according to claim 2, characterized in that: In step 2, the ratio of the volume of water added to the mixed powder A to the mass of the mixed powder A is (1.0-6.0) mL: 1.0 g.

7. The method for preparing a phosphate positive electrode material according to claim 2, characterized in that: In step 3, the pre-firing temperature is 300-500°C; the pre-firing time is 1-6 hours; The high temperature sintering temperature is 600~850℃; the high temperature sintering time is 6~10h.

8. The method for preparing a phosphate positive electrode material according to claim 2, characterized in that: In step 1, the grinding speed is 200-450 rpm, and the grinding time is 1-8 h; in step 2, the grinding speed is 200-450 rpm, and the grinding time is 1-6 h.

9. A phosphate positive electrode material, characterized in that: A positive electrode material prepared by the preparation method according to any one of claims 2 to 8.

10. A battery, characterized in that: A positive electrode material comprising the preparation method described in any one of claims 2 to 8.

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