Composite additive and preparation method thereof, phosphate-based positive electrode material and preparation process thereof, and battery

Abstract

The invention provides a composite additive and a preparation method thereof, a phosphate-based positive electrode material and a preparation process thereof, and a battery, the composite additive comprises an organic additive and an inorganic additive, and the composite additive is a spherical solid with a D50 particle size of less than 1 [mu] m; the ratio of the mass of carbon generated after the organic additive in the composite additive is heated and decomposed to the mass of metal elements in the inorganic additive is (1.5-50): 1. The composite additive provided by the invention is more easily and uniformly dispersed in the positive electrode material, non-uniform performance caused by local agglomeration can be avoided, and composition segregation caused by size difference is reduced; when the composite additive is used for preparing the phosphate-based positive electrode material, the organic additive in the composite additive is decomposed to form a carbon coating layer with a proper thickness, and metal elements in the composite additive can be doped in a proper proportion, so that the electrochemical performance of the phosphate-based positive electrode material is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of batteries and relates to a composite additive for preparing a phosphate-based positive electrode material, and in particular to a composite additive and a preparation method thereof, a phosphate-based positive electrode material and a preparation process thereof, and a battery. Background Art

[0002] In the existing technology, the preparation process of lithium iron phosphate and lithium iron manganese phosphate is usually to directly mix multiple components such as iron source (ferric phosphate, ferrous oxalate, ferroferric oxide and ferromanganese phosphate, etc.), lithium source (lithium carbonate, lithium hydroxide and lithium dihydrogen phosphate, etc.), organic carbon source (glucose and polyethylene glycol, etc.), organic dispersant (polyethylene glycol, polyvinyl alcohol and polyvinyl pyrrolidone, etc.) and inorganic additives (titanium dioxide and magnesium oxide, etc.), and then prepare them through processes such as ball milling, sand milling, spray drying, calcination and crushing.

[0003] In the preparation process of phosphate-based positive electrode materials, the two types of components, organic additives (including organic carbon sources and organic dispersants) and inorganic additives, are quite different. During the grinding process, there are problems such as uneven dispersion, easy component segregation, and poor interface bonding. As a result, the lithium ion transmission resistance in the final prepared phosphate-based positive electrode material is relatively large, which is not conducive to the electrical performance of the phosphate-based positive electrode material (the theoretical gram capacity is 170mAh / g, and the actual maximum is only about 160mAh / g).

[0004] CN116936755A discloses a high-density lithium iron phosphate cathode material and a preparation method thereof, comprising an inorganic carbon source solvent and a lithium iron phosphate precursor, wherein the inorganic carbon source solvent is coated on the outside of the lithium iron phosphate precursor; S1, preparing a lithium iron phosphate precursor slurry; S2, preparing the inorganic carbon source solvent; S3, preparing the lithium iron phosphate precursor; S4, preparing the lithium iron phosphate material; the lithium iron phosphate precursor comprises an iron source, a lithium source, a carbon source, and an additive, wherein the iron source and the lithium source are added in a molar ratio of 1 to 1.02, and the amount of the carbon source added is 6 to 8% of the weight of the iron source; the inorganic carbon source solvent comprises water, an inorganic carbon source, sodium dodecylbenzene sulfonate or sodium dodecyl sulfate in a ratio of 94%:5%:1%; this document synthesizes lithium iron phosphate by combining a composite carbon source with an inorganic carbon source, overcoming the problem of poor performance of the lithium iron phosphate cathode material obtained by a single carbon source in the prior art, thereby enabling the lithium battery to have a higher energy density. However, in the process of preparing the high compact density lithium iron phosphate positive electrode material, there are problems such as uneven dispersion and poor interface bonding during the mixing and ball milling of the additives (inorganic matter) and the carbon source and the inorganic carbon source solvent, resulting in a large lithium ion transmission resistance in the high compact density lithium iron phosphate positive electrode material finally prepared.

[0005] CN112390241A discloses a lithium iron phosphate material and a method for preparing the lithium iron phosphate material using a mixed iron source and a mixed lithium source as raw materials. The method comprises the following steps: (1) using iron phosphate and iron oxide as iron sources, lithium carbonate and lithium phosphate as lithium sources, adding the iron source and lithium source to a dispersant, adding a carbon source and an additive to the dispersant, and ball milling to obtain a slurry; (2) spray drying the slurry obtained in step (1) to obtain a lithium iron phosphate precursor; (3) sintering the lithium iron phosphate precursor obtained in step (2) under an inert atmosphere, and crushing to obtain the lithium iron phosphate material. However, in the process of preparing the lithium iron phosphate material, the carbon source and the additive (inorganic additive) also have problems such as uneven dispersion during the ball milling process, and poor interfacial bonding of the obtained lithium iron phosphate material, resulting in a large lithium ion transmission resistance in the high compaction density lithium iron phosphate positive electrode material finally prepared.

[0006] The additives disclosed in the prior art for preparing phosphate-based cathode materials all have certain drawbacks. The significant differences between the organic and inorganic additives lead to uneven dispersion and easy component segregation during grinding, resulting in poor interfacial bonding in the resulting phosphate-based cathode materials. Furthermore, it is difficult to simultaneously form a carbon coating layer of appropriate thickness and dope with appropriate metal elements when preparing phosphate-based cathode materials. Therefore, the development and design of a novel composite additive for preparing phosphate-based cathode materials, a preparation method thereof, a phosphate-based cathode material, a preparation process thereof, and a battery are of vital importance. Summary of the Invention

[0007] In response to the deficiencies in the prior art, the present invention aims to provide a composite additive and a preparation method thereof, a phosphate-based positive electrode material and a preparation process thereof, and a battery. The composite additive provided by the present invention is a spherical solid with a D50 particle size of less than 1 μm. The organic additive and the inorganic additive in the composite additive are more easily and evenly dispersed in the positive electrode material, thereby avoiding uneven performance caused by local agglomeration and reducing component segregation caused by size differences. In addition, when the composite additive is used to prepare the phosphate-based positive electrode material, the mass ratio of the carbon produced by the organic additive in the composite additive upon thermal decomposition to the mass ratio of the metal element in the inorganic additive is (1.5-50):1. The composite additive can decompose to produce sufficient carbon source, thereby forming a carbon coating layer of suitable thickness. The metal elements in the composite additive can also be doped in appropriate proportions, thereby further improving the electrochemical performance of the phosphate-based positive electrode material prepared using the composite additive.

[0008] To achieve this object, the present invention adopts the following technical solutions:

[0009] In a first aspect, the present invention provides a composite additive for preparing a phosphate-based positive electrode material, wherein the composite additive comprises an organic additive and an inorganic additive, and the composite additive is a spherical solid with a D50 particle size of less than 1 μm;

[0010] The ratio of the mass of carbon generated by heating and decomposing the organic additive in the composite additive to the mass of the metal element in the inorganic additive is (1.5-50):1.

[0011] In the present invention, the ratio of the mass of carbon produced by thermal decomposition of the organic additive in the composite additive to the mass of the metal element in the inorganic additive is (1.5-50):1, for example, it can be 1.5:1, 2:1, 3:1, 5:1, 8:1, 10:1, 12:1, 15:1, 18:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1 or 50:1, but is not limited to the listed values, and other values ​​not listed within this numerical range are also applicable.

[0012] The composite additive for preparing a phosphate-based positive electrode material provided by the present invention is a spherical solid having a D50 particle size of less than 1 μm obtained by compounding an organic additive with an inorganic additive. Since the D50 particle size of the spherical solid composite additive is less than 1 μm, the particles of the organic additive and the inorganic additive in the composite additive have a small particle size and a large specific surface area, making it easier to disperse evenly in the positive electrode material. This can avoid uneven performance caused by local agglomeration, reduce component segregation caused by size differences, enhance interfacial contact and electrochemical activity, shorten the ion / electron transmission path, and improve the reaction kinetics of the positive electrode material, thereby improving the electrochemical performance of the battery.

[0013] In the composite additive provided by the present invention, when the ratio of the mass of carbon produced after the organic additive is heated and decomposed to the mass of the metal element in the inorganic additive is (1.5-50):1, the positive electrode material and the battery have good performance. This is because at this ratio, the composite additive can decompose to produce sufficient carbon source, thereby forming a carbon coating layer of suitable thickness. The metal elements in the composite additive can also be doped in a suitable ratio to stabilize the olivine structure of the lithium iron phosphate. At the same time, the mixing ratio of lithium and iron elements can be effectively controlled, thereby improving the structural stability of the positive electrode material and ensuring that the battery has good electrochemical performance during charging and discharging.

[0014] Preferably, the organic additive includes an organic carbon source and an organic dispersant.

[0015] Preferably, the mass ratio of the organic carbon source to the organic dispersant in the organic additive is (5-10):3, for example, it can be 5:3, 5.5:3, 6:3, 6.5:3, 7:3, 7.5:3, 8:3, 8.5:3, 9:3, 9.5:3 or 10:3, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0016] Preferably, the organic carbon source comprises any one or a combination of at least two of glucose, polyethylene glycol, sucrose, citric acid, polyacrylonitrile or phenolic resin. Typical but non-limiting combinations include a combination of glucose and polyethylene glycol, a combination of polyethylene glycol and sucrose, a combination of citric acid and polyacrylonitrile, a combination of phenolic resin and glucose, or a combination of polyethylene glycol, citric acid and phenolic resin.

[0017] Preferably, the organic dispersant includes any one of polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, sodium lauryl sulfate, sodium dodecylbenzene sulfonate, cetyltrimethylammonium bromide, polyoxyethylene ether or sodium carboxymethyl cellulose, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of polyethylene glycol and polyvinyl alcohol, a combination of polyvinyl pyrrolidone and sodium lauryl sulfate, a combination of sodium dodecylbenzene sulfonate and cetyltrimethylammonium bromide, a combination of polyoxyethylene ether and sodium carboxymethyl cellulose, or a combination of polyvinyl alcohol, sodium lauryl sulfate and polyoxyethylene ether.

[0018] Preferably, the inorganic additive includes any one or a combination of at least two of TiO2, V2O5, BO3, NbO2, MgO or Al2O3, ZrO2, SiO2, CeO2, AlF3, MoS2 or LiBO3. Typical but non-limiting combinations include a combination of TiO2 and V2O5, a combination of V2O5 and BO3, a combination of NbO2 and MgO, a combination of Al2O3 and TiO2, a combination of BO3, NbO2 and MgO, or a combination of TiO2, V2O5, BO3 and Al2O3.

[0019] Preferably, the composite additive is formed by spray drying a slurry containing an organic additive and an inorganic additive at an inlet air temperature of 200-300°C and an outlet air temperature of 100-120°C.

[0020] The composite additive in the form of a spherical solid in the present invention is formed by spray drying at an inlet air temperature of 200-300°C and an outlet air temperature of 100-120°C; the inlet air temperature for spray drying is 200-300°C, for example, it can be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, 260°C, 270°C, 280°C, 290°C or 300°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable; the outlet air temperature for spray drying is 100-120°C, for example, it can be 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, 112°C, 114°C, 116°C, 118°C or 120°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] The composite additive in the present invention is a solid obtained by spray-drying a slurry containing an organic additive and an inorganic additive. Compared with vacuum oven drying, the spray drying in the present application converts the slurry into tiny droplets (10 to 100 μm) by atomization, ensuring uniform mixing of organic and inorganic components at the atomic / molecular level and avoiding local component segregation that occurs when the composite additive is formed. In addition, during spray drying, the droplets evaporate rapidly at high temperature and naturally shrink into spherical particles with good fluidity, which is more conducive to subsequent uniform mixing with a lithium source, an iron source, or a phosphorus source, thereby improving the uniformity of the positive electrode material prepared with the composite additive.

[0022] The present invention further limits the inlet and outlet temperatures of the spray drying process, thereby ensuring uniform mixing of organic and inorganic components at the atomic / molecular level during the spray drying process. It also improves the morphology of the composite additive and further enhances the fluidity of the composite additive, thereby improving the electrochemical performance of the positive electrode material and battery prepared using the composite additive.

[0023] In a second aspect, the present invention provides a method for preparing the composite additive according to the first aspect, the preparation method comprising:

[0024] The inorganic additive, the organic additive and the solvent are mixed to obtain a slurry, and the obtained slurry is spray-dried to obtain the composite additive.

[0025] In the preparation method provided by the present invention, a nanometer-scale spherical solid composite additive is prepared, which is more helpful in reducing the interfacial impedance of the phosphate-based positive electrode material and is more conducive to the transmission of lithium ions in the phosphate-based positive electrode material, thereby further improving the specific capacity and rate performance of the battery prepared with the phosphate-based positive electrode material.

[0026] Preferably, the preparation method further comprises pulverizing the inorganic additive before the mixing, and the pulverized inorganic additive having a D50 particle size of less than 1 μm is obtained after the pulverization.

[0027] The D50 particle size of the inorganic additive after crushing in the present invention is less than 1 μm, for example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0028] Preferably, the pulverization method includes air flow pulverization.

[0029] Preferably, the mixing method comprises: initially mixing the organic additive with a solvent to obtain an organic additive solution, and then mixing the inorganic additive with the obtained organic additive solution to obtain a mixed slurry.

[0030] Preferably, the solvent comprises water.

[0031] Preferably, the solid content of the organic additive solution is 5% to 20%, for example, it can be 5%, 6%, 8%, 10%, 12%, 14%, 16%, 18% or 20%, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0032] Preferably, the solid content of the mixed slurry is 15-25%, for example, it can be 15%, 16%, 18%, 20%, 21%, 22%, 23%, 24% or 25%, but it is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0033] Preferably, the preparation method further comprises sand milling the obtained mixed slurry between the mixing and the spray drying.

[0034] Preferably, after the sanding, a sanded slurry is obtained, and the D50 particle size of the particles in the sanded slurry is less than 1 μm, for example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0035] Preferably, the air inlet temperature of the spray drying is 200-300°C, and the air outlet temperature is 100-120°C.

[0036] The inlet air temperature of the spray drying in the present invention is 200-300°C, for example, it can be 200°C, 220°C, 240°C, 250°C, 260°C, 280°C, 290°C or 300°C, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0037] The outlet air temperature of the spray drying in the present invention is 100-120°C, for example, it can be 100°C, 105°C, 108°C, 110°C, 112°C, 115°C, 118°C or 120°C, but is not limited to the listed values. Other values ​​not listed within this numerical range are also applicable.

[0038] As a preferred technical solution of the preparation method of the present invention, the preparation method comprises:

[0039] (1) performing air flow pulverization on the inorganic additive to obtain a pulverized inorganic additive having a D50 particle size of less than 1 μm;

[0040] (2) preliminarily mixing an organic additive with water to obtain an organic additive aqueous solution having a solid content of 5 to 20%, and then mixing the obtained organic additive aqueous solution with the crushed inorganic additive obtained in step (1) to obtain a mixed slurry having a solid content of 15 to 25%;

[0041] (3) sand-milling the mixed slurry obtained in step (2) to obtain a sand-milled slurry, wherein the D50 particle size of the particles in the sand-milled slurry is less than 1 μm; and spray-drying the sand-milled slurry to obtain the composite additive, wherein the inlet air temperature of the spray drying is 200-300° C., and the outlet air temperature is 100-120° C.

[0042] In a third aspect, the present invention provides a phosphate-based positive electrode material, wherein the composite additive described in the first aspect is added during the preparation of the phosphate-based positive electrode material.

[0043] Preferably, based on the mass of the phosphate-based positive electrode material, the mass fraction of carbon produced by carbonization of the organic additive in the phosphate-based positive electrode material is 1-5 wt %, and the mass fraction of the metal element in the inorganic additive in the phosphate-based positive electrode material is 0.1-0.6 wt %.

[0044] In the present invention, the mass fraction of the phosphate-based positive electrode material is expressed as 100%, and the mass fraction of carbon produced by carbonization of the organic additive in the phosphate-based positive electrode material is 1 to 5 wt%, for example, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt% or 5 wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] In the present invention, the mass fraction of the metal element in the inorganic additive in the phosphate-based positive electrode material is 0.1 to 0.6 wt%, for example, it can be 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt% or 0.6 wt%, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0046] Preferably, the phosphate-based positive electrode material includes a lithium iron phosphate positive electrode material and / or a lithium iron manganese phosphate positive electrode material.

[0047] In a fourth aspect, the present invention provides a process for preparing the phosphate-based positive electrode material according to the third aspect, the preparation process comprising:

[0048] When the phosphate-based positive electrode material is a lithium iron phosphate positive electrode material, an iron source, a lithium source and the composite additive of the first aspect are first mixed and then subjected to a first heat treatment to obtain the phosphate-based positive electrode material;

[0049] When the phosphate-based positive electrode material is a lithium manganese iron phosphate positive electrode material, the iron source, lithium source, manganese source and the composite additive of the first aspect are mixed for a second time and then subjected to a second heat treatment to obtain the phosphate-based positive electrode material.

[0050] Preferably, when the phosphate-based positive electrode material is a lithium iron phosphate positive electrode material, the molar ratio of the iron source to the lithium source in the first mixture is 1:(1-1.15), and the mass ratio of the lithium source to the composite additive is (3-10):1.

[0051] In the present invention, when the phosphate-based positive electrode material is a lithium iron phosphate positive electrode material, the molar ratio of the iron source to the lithium source in the first mixture is 1:(1 to 1.15), for example, it can be 1:1, 1:1.02, 1:1.04, 1:1.06, 1:1.08, 1:1.10, 1:1.12, 1:1.14 or 1:1.15, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0052] In the present invention, when the phosphate-based positive electrode material is a lithium iron phosphate positive electrode material, the mass ratio of the lithium source to the composite additive in the first mixture is (3 to 10):1, for example, it can be 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0053] Preferably, when the phosphate-based positive electrode material is a lithium manganese iron phosphate positive electrode material, the molar ratio of the iron source, lithium source and manganese source in the second mixture is (0.25-4):(1-1.15):1, and the mass ratio of the lithium source to the composite additive is (3-10):1.

[0054] When the phosphate-based positive electrode material in the present invention is a lithium manganese iron phosphate positive electrode material, the molar ratio of the iron source to the manganese source in the second mixture is (0.25-4):1, for example, it can be 0.25:1, 0.5:1, 0.75:1, 1:1, 1.25:1, 1.5:1, 1.75:1, 2:1, 2.5:1, 3:1, 3.5:1 or 4:1, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0055] When the phosphate-based positive electrode material in the present invention is a lithium iron manganese phosphate positive electrode material, the molar ratio of the lithium source to the manganese source in the second mixture is (1 to 1.15):1, for example, it can be 1:1, 1.02:1, 1.04:1, 1.06:1, 1.08:1, 1.10:1, 1.12:1, 1.14:1 or 1.15:1, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0056] When the phosphate-based positive electrode material in the present invention is a lithium iron manganese phosphate positive electrode material, the mass ratio of the lithium source to the composite additive in the second mixture is (3 to 10):1, for example, it can be 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, 9.5:1 or 10:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0057] Preferably, the first mixing and the second mixing methods independently comprise ball milling and sand milling performed sequentially.

[0058] Preferably, the D50 particle size of the materials after ball milling in the first mixture and the second mixture is independently less than 5 μm, for example, it can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0059] Preferably, the D50 particle size of the materials after sand grinding in the first mixture and the second mixture is independently less than 1 μm, for example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm or 1 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0060] Preferably, the iron source includes any one of ferric phosphate, ferrous oxalate, ferroferric oxide or ferromanganese phosphate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of ferric phosphate and ferrous oxalate, a combination of ferrous oxalate and ferroferric oxide, a combination of ferroferric oxide and ferromanganese phosphate, or a combination of ferric phosphate, ferrous oxalate and ferroferric oxide.

[0061] Preferably, the lithium source includes any one or a combination of at least two of lithium carbonate, lithium hydroxide or lithium dihydrogen phosphate. Typical but non-limiting combinations include a combination of lithium carbonate and lithium hydroxide, a combination of lithium hydroxide and lithium dihydrogen phosphate, or a combination of lithium carbonate, lithium hydroxide and lithium dihydrogen phosphate.

[0062] Preferably, the manganese source comprises any one of manganese sulfate, manganese chloride, manganese carbonate, manganese oxalate, manganese nitrate, manganese dioxide, manganese powder or trimanganese tetraoxide, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of manganese sulfate and manganese chloride, a combination of manganese carbonate and manganese oxalate, a combination of manganese nitrate and manganese dioxide, a combination of manganese powder and trimanganese tetraoxide, a ternary combination of manganese sulfate, manganese chloride and manganese carbonate, or a ternary combination of manganese oxalate, manganese nitrate and manganese dioxide.

[0063] Preferably, when the phosphate-based positive electrode material is a lithium iron phosphate positive electrode material, the preparation process further comprises spray drying between the first mixing and the first calcination.

[0064] Preferably, when the phosphate-based positive electrode material is a lithium manganese iron phosphate positive electrode material, the preparation process further includes spray drying between the second mixing and the second calcination.

[0065] Preferably, the first heat treatment comprises a first heating, a first heat preservation, a second heating and a second heat preservation performed in sequence in a protective atmosphere;

[0066] The temperature of the first insulation is 250-400° C., and the time is 2 hours to 4 hours; the temperature of the second insulation is 700-800° C., and the time is 5 hours to 12 hours.

[0067] The first heating rate in the present invention is 1 to 15°C / min, for example, it can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 12°C / min or 15°C / min, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable. The end temperature is the temperature of the first insulation.

[0068] The temperature of the first insulation in the present invention is 250-400°C, for example, it can be 250°C, 260°C, 280°C, 300°C, 320°C, 340°C, 350°C, 360°C, 380°C or 400°C, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable.

[0069] The first insulation time in the present invention is 2h to 4h, for example, it can be 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3h, 3.2h, 3.4h, 3.6h, 3.8h or 4h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0070] The second heating rate in the present invention is 1 to 15°C / min, for example, it can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 12°C / min or 15°C / min, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable. The end temperature is the temperature of the second insulation.

[0071] The temperature of the second insulation in the present invention is 700-800°C, for example, it can be 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C or 800°C, but is not limited to the listed values, and other unlisted values ​​within this numerical range are also applicable.

[0072] The second insulation time in the present invention is 5 to 12 hours, for example, it can be 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0073] Preferably, the second heat treatment comprises a third heating step, a third heat preservation step, a fourth heating step and a fourth heat preservation step sequentially performed in a protective atmosphere;

[0074] The temperature of the third insulation is 250-400° C., and the time is 2 hours to 4 hours; the temperature of the fourth insulation is 650-800° C., and the time is 5 hours to 12 hours.

[0075] The third heating rate described in the present invention is 1 to 15°C / min, for example, it can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 12°C / min or 15°C / min, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable. The end temperature is the temperature of the third insulation.

[0076] The temperature of the third insulation in the present invention is 250-400°C, for example, it can be 250°C, 260°C, 280°C, 300°C, 320°C, 340°C, 350°C, 360°C, 380°C or 400°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0077] The third insulation time described in the present invention is 2h to 4h, for example, it can be 2h, 2.2h, 2.4h, 2.6h, 2.8h, 3h, 3.2h, 3.4h, 3.6h, 3.8h or 4h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0078] The fourth heating rate described in the present invention is 1 to 15°C / min, for example, it can be 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, 12°C / min or 15°C / min, but is not limited to the listed values. Other unlisted values ​​within this numerical range are also applicable. The end temperature is the temperature of the fourth insulation.

[0079] The temperature of the fourth insulation described in the present invention is 650-800°C, for example, it can be 650°C, 660°C, 680°C, 700°C, 720°C, 740°C, 750°C, 760°C, 780°C or 800°C, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0080] The fourth insulation time in the present invention is 5 to 12 hours, for example, it can be 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0081] In a fifth aspect, the present invention provides a battery comprising the phosphate-based positive electrode material described in the third aspect.

[0082] The numerical range described in the present invention includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0083] Compared with the prior art, the present invention has the following beneficial effects:

[0084] (1) The composite additive for preparing a phosphate-based positive electrode material provided by the present invention is a spherical solid having a D50 particle size of less than 1 μm obtained by compounding an organic additive with an inorganic additive. Since the D50 particle size of the spherical solid composite additive is less than 1 μm, the organic additive and the inorganic additive in the composite additive have a small particle size and a large specific surface area, and are more easily dispersed in the positive electrode material, thereby avoiding uneven performance caused by local agglomeration and reducing component segregation caused by size differences. It can also enhance interfacial contact and electrochemical activity, shorten the ion / electron transmission path, and improve the reaction kinetics of the positive electrode material, thereby improving the electrochemical performance of the battery;

[0085] (2) In the composite additive provided by the present invention, when the ratio of the mass of carbon produced after the organic additive is heated and decomposed to the mass of the metal element in the inorganic additive is (1.5-50):1, the positive electrode material and the battery have better performance. This is because under this ratio, the composite additive can decompose to produce sufficient carbon source, thereby forming a carbon coating layer of appropriate thickness. The metal elements in the composite additive can also be doped in a suitable ratio to stabilize the olivine structure of lithium iron phosphate. At the same time, it can also effectively control the mixing ratio of lithium and iron elements, improve the structural stability of the positive electrode material, and make the battery have better electrochemical performance during charging and discharging. DETAILED DESCRIPTION

[0086] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0087] Example 1

[0088] This embodiment provides a composite additive for preparing a lithium iron phosphate positive electrode material, wherein the composite additive comprises an organic additive (including an organic carbon source and an organic dispersant in a mass ratio of 8:3) and an inorganic additive, wherein the mass ratio of carbon produced by thermal decomposition of the organic additive to the mass ratio of the metal element in the inorganic additive is 10:1;

[0089] The composite additive is a spherical solid with a D50 particle size of 0.5 μm formed by spray drying a slurry containing organic additives and inorganic additives at an inlet air temperature of 250° C. and an outlet air temperature of 110° C.;

[0090] The preparation method of the composite additive comprises:

[0091] (1) performing air flow pulverization on the inorganic additive to obtain a pulverized inorganic additive having a D50 particle size of 0.5 μm;

[0092] (2) initially mixing the organic additive with water to obtain an organic additive aqueous solution having a solid content of 12%, and then mixing the obtained organic additive aqueous solution with the crushed inorganic additive obtained in step (1) to obtain a mixed slurry having a solid content of 20%;

[0093] (3) sand-milling the mixed slurry obtained in step (2) to obtain a sand-milled slurry, wherein the D50 particle size of the particles in the sand-milled slurry is 0.5 μm; and spray-drying the sand-milled slurry to obtain the composite additive, wherein the inlet air temperature of the spray drying is 250° C. and the outlet air temperature is 110° C.

[0094] This embodiment further provides a lithium iron phosphate positive electrode material, and the preparation process of the lithium iron phosphate positive electrode material includes:

[0095] The iron source, the lithium source and the composite additive provided in this embodiment are mixed by ball milling to obtain a ball-milled material with a D50 particle size of 3 μm, and then sand milled to obtain a sand-milled material with a D50 particle size of 0.5 μm; in a protective atmosphere, the obtained sand-milled material is heated to 320° C. at a rate of 8° C. / min and then kept warm for 3 h, and then heated to 750° C. at a rate of 8° C. / min and then kept warm for 8 h to obtain the lithium iron phosphate positive electrode material.

[0096] The molar ratio of the iron source to the lithium source is 1:1.08, and the mass ratio of the lithium source to the composite additive is 6:1.

[0097] Example 2

[0098] This embodiment provides a composite additive for preparing a lithium iron phosphate positive electrode material, wherein the composite additive comprises an organic additive (including an organic carbon source and an organic dispersant in a mass ratio of 7:3) and an inorganic additive, wherein the mass ratio of carbon produced by thermal decomposition of the organic additive to the mass ratio of the metal element in the inorganic additive is 25:1;

[0099] The composite additive is a spherical solid with a D50 particle size of 0.7 μm formed by spray drying a slurry containing organic additives and inorganic additives at an inlet air temperature of 280° C. and an outlet air temperature of 105° C.;

[0100] The preparation method of the composite additive comprises:

[0101] (1) performing air flow pulverization on the inorganic additive to obtain a pulverized inorganic additive having a D50 particle size of 0.7 μm;

[0102] (2) initially mixing the organic additive with water to obtain an organic additive aqueous solution having a solid content of 16%, and then mixing the obtained organic additive aqueous solution with the crushed inorganic additive obtained in step (1) to obtain a mixed slurry having a solid content of 18%;

[0103] (3) sand-milling the mixed slurry obtained in step (2) to obtain a sand-milled slurry, wherein the D50 particle size of the particles in the sand-milled slurry is 0.7 μm; and spray-drying the sand-milled slurry to obtain the composite additive, wherein the inlet air temperature of the spray drying is 280° C. and the outlet air temperature is 105° C.

[0104] This embodiment further provides a lithium iron phosphate positive electrode material, and the preparation process of the lithium iron phosphate positive electrode material includes:

[0105] An iron source, a lithium source, and the composite additive provided in this embodiment are mixed by ball milling to obtain a ball-milled material with a D50 particle size of 4 μm, which is then sand-milled to obtain a sand-milled material with a D50 particle size of 0.7 μm. In a protective atmosphere, the sand-milled material is heated to 360° C. at a rate of 12° C. / min and then held at that temperature for 2.5 hours. The temperature is then increased to 720° C. at a rate of 5° C. / min and then held at that temperature for 10 hours to obtain the lithium iron phosphate positive electrode material.

[0106] The molar ratio of the iron source to the lithium source is 1:1.12, and the mass ratio of the lithium source to the composite additive is 5:1.

[0107] Example 3

[0108] This embodiment provides a composite additive for preparing a lithium iron phosphate positive electrode material. The composite additive comprises an organic additive (including an organic carbon source and an organic dispersant in a mass ratio of 9:3) and an inorganic additive. The mass ratio of carbon produced by thermal decomposition of the organic additive to the mass ratio of the metal element in the inorganic additive is 5:1.

[0109] The composite additive is a spherical solid with a D50 particle size of 0.3 μm formed by spray drying a slurry containing organic additives and inorganic additives at an inlet air temperature of 220° C. and an outlet air temperature of 115° C.;

[0110] The preparation method of the composite additive comprises:

[0111] (1) performing air flow pulverization on the inorganic additive to obtain a pulverized inorganic additive having a D50 particle size of 0.3 μm;

[0112] (2) initially mixing the organic additive with water to obtain an organic additive aqueous solution having a solid content of 8%, and then mixing the obtained organic additive aqueous solution with the crushed inorganic additive obtained in step (1) to obtain a mixed slurry having a solid content of 22%;

[0113] (3) sand-milling the mixed slurry obtained in step (2) to obtain a sand-milled slurry, wherein the D50 particle size of the particles in the sand-milled slurry is 0.3 μm; and spray-drying the sand-milled slurry to obtain the composite additive, wherein the inlet air temperature of the spray drying is 220° C. and the outlet air temperature is 115° C.

[0114] This embodiment further provides a lithium iron phosphate positive electrode material, and the preparation process of the lithium iron phosphate positive electrode material includes:

[0115] An iron source, a lithium source, and the composite additive provided in this embodiment are mixed by ball milling to obtain a ball-milled material with a D50 particle size of 2.5 μm, which is then sand-milled to obtain a sand-milled material with a D50 particle size of 0.3 μm. In a protective atmosphere, the sand-milled material is heated to 280° C. at a rate of 5° C. / min and then held at that temperature for 3.5 hours. The temperature is then increased to 780° C. at a rate of 12° C. / min and then held at that temperature for 7 hours to obtain the lithium iron phosphate positive electrode material.

[0116] The molar ratio of the iron source to the lithium source is 1:1.04, and the mass ratio of the lithium source to the composite additive is 8:1.

[0117] Example 4

[0118] This embodiment provides a composite additive for preparing a lithium iron phosphate positive electrode material, wherein the composite additive comprises an organic additive (including an organic carbon source and an organic dispersant in a mass ratio of 10:3) and an inorganic additive, wherein the mass ratio of carbon produced by thermal decomposition of the organic additive to the mass ratio of the metal element in the inorganic additive is 50:1;

[0119] The composite additive is a spherical solid with a D50 particle size of 0.9 μm formed by spray drying a slurry containing organic additives and inorganic additives at an inlet air temperature of 300° C. and an outlet air temperature of 120° C.;

[0120] The preparation method of the composite additive comprises:

[0121] (1) performing air flow pulverization on the inorganic additive to obtain a pulverized inorganic additive having a D50 particle size of 0.9 μm;

[0122] (2) initially mixing the organic additive with water to obtain an organic additive aqueous solution having a solid content of 20%, and then mixing the obtained organic additive aqueous solution with the crushed inorganic additive obtained in step (1) to obtain a mixed slurry having a solid content of 22%;

[0123] (3) sand-milling the mixed slurry obtained in step (2) to obtain a sand-milled slurry, wherein the D50 particle size of the particles in the sand-milled slurry is 0.9 μm; and spray-drying the sand-milled slurry to obtain the composite additive, wherein the inlet air temperature of the spray drying is 300° C. and the outlet air temperature is 120° C.

[0124] This embodiment further provides a lithium iron phosphate positive electrode material, and the preparation process of the lithium iron phosphate positive electrode material includes:

[0125] An iron source, a lithium source, and the composite additive provided in this embodiment are mixed by ball milling to obtain a ball-milled material with a D50 particle size of 4.5 μm, which is then sand-milled to obtain a sand-milled material with a D50 particle size of 0.9 μm. In a protective atmosphere, the sand-milled material is heated to 250° C. at a rate of 1° C. / min and then held for 4 hours, and then heated to 700° C. at a rate of 1° C. / min and then held for 12 hours to obtain the lithium iron phosphate positive electrode material.

[0126] The molar ratio of the iron source to the lithium source is 1:1.15, and the mass ratio of the lithium source to the composite additive is 3:1.

[0127] Example 5

[0128] This embodiment provides a composite additive for preparing a lithium iron phosphate positive electrode material, wherein the composite additive comprises an organic additive (including an organic carbon source and an organic dispersant in a mass ratio of 5:3) and an inorganic additive, wherein the mass ratio of carbon produced by thermal decomposition of the organic additive to the mass ratio of the metal element in the inorganic additive is 1.5:1;

[0129] The composite additive is a spherical solid with a D50 particle size of 0.1 μm formed by spray drying a slurry containing organic additives and inorganic additives at an inlet air temperature of 200° C. and an outlet air temperature of 100° C.;

[0130] The preparation method of the composite additive comprises:

[0131] (1) performing air flow pulverization on the inorganic additive to obtain a pulverized inorganic additive having a D50 particle size of 0.1 μm;

[0132] (2) initially mixing the organic additive with water to obtain an organic additive aqueous solution having a solid content of 5%, and then mixing the obtained organic additive aqueous solution with the crushed inorganic additive obtained in step (1) to obtain a mixed slurry having a solid content of 25%;

[0133] (3) sand-milling the mixed slurry obtained in step (2) to obtain a sand-milled slurry, wherein the D50 particle size of the particles in the sand-milled slurry is 0.1 μm; and spray-drying the sand-milled slurry to obtain the composite additive, wherein the inlet air temperature of the spray drying is 200° C. and the outlet air temperature is 100° C.

[0134] This embodiment further provides a lithium iron phosphate positive electrode material, and the preparation process of the lithium iron phosphate positive electrode material includes:

[0135] An iron source, a lithium source, and the composite additive provided in this embodiment are mixed by ball milling to obtain a ball-milled material with a D50 particle size of 2 μm, which is then sand-milled to obtain a sand-milled material with a D50 particle size of 0.1 μm. In a protective atmosphere, the sand-milled material is heated to 400° C. at a rate of 15° C. / min and then held at that temperature for 2 h, and then heated to 800° C. at a rate of 15° C. / min and then held at that temperature for 5 h, thereby obtaining the lithium iron phosphate positive electrode material.

[0136] The molar ratio of the iron source to the lithium source is 1:1, and the mass ratio of the lithium source to the composite additive is 10:1.

[0137] Example 6

[0138] This embodiment provides a composite additive for preparing a lithium manganese iron phosphate positive electrode material. The composite additive comprises an organic additive (including an organic carbon source and an organic dispersant in a mass ratio of 8:3) and an inorganic additive. The mass ratio of carbon produced by thermal decomposition of the organic additive to the mass ratio of the metal element in the inorganic additive is 10:1.

[0139] The composite additive is a spherical solid with a D50 particle size of 0.5 μm formed by spray drying a slurry containing organic additives and inorganic additives at an inlet air temperature of 250° C. and an outlet air temperature of 110° C.;

[0140] The preparation method of the composite additive comprises:

[0141] (1) performing air flow pulverization on the inorganic additive to obtain a pulverized inorganic additive having a D50 particle size of 0.5 μm;

[0142] (2) initially mixing the organic additive with water to obtain an organic additive aqueous solution having a solid content of 12%, and then mixing the obtained organic additive aqueous solution with the crushed inorganic additive obtained in step (1) and the obtained organic additive aqueous solution to obtain a mixed slurry having a solid content of 20%;

[0143] (3) sand-milling the mixed slurry obtained in step (2) to obtain a sand-milled slurry, wherein the D50 particle size of the particles in the sand-milled slurry is 0.5 μm; and spray-drying the sand-milled slurry to obtain the composite additive, wherein the inlet air temperature of the spray drying is 250° C. and the outlet air temperature is 110° C.

[0144] This embodiment further provides a lithium manganese iron phosphate positive electrode material, and the preparation process of the lithium manganese iron phosphate positive electrode material includes:

[0145] An iron source, a lithium source, a manganese source, and the composite additive provided in this embodiment are mixed by ball milling to obtain a ball-milled material with a D50 particle size of 3 μm, which is then sand-milled to obtain a sand-milled material with a D50 particle size of 0.5 μm. In a protective atmosphere, the sand-milled material is heated to 320° C. at a rate of 8° C. / min and then held at that temperature for 3 hours, and then heated to 750° C. at a rate of 8° C. / min and then held at that temperature for 8 hours to obtain the lithium manganese iron phosphate positive electrode material.

[0146] The molar ratio of the iron source, the lithium source and the manganese source in the second mixture is 0.89:1:1, and the mass ratio of the lithium source to the composite additive is 6:1.

[0147] Example 7

[0148] This embodiment provides a composite additive for preparing a lithium iron phosphate positive electrode material. Except that spray drying is replaced by vacuum oven drying, the rest is the same as that of Example 4.

[0149] This embodiment further provides a lithium iron phosphate positive electrode material, which is the same as that of Example 4 except that the composite additive in the preparation process of the lithium iron phosphate positive electrode material is the composite additive provided in this embodiment.

[0150] Example 8

[0151] This embodiment provides a composite additive for preparing a lithium iron phosphate positive electrode material. Except that the composite additive is a spherical solid with a D50 particle size of 0.6 μm formed by spray drying a slurry containing organic additives and inorganic additives at an inlet air temperature of 400°C and an outlet air temperature of 150°C, the rest is the same as Example 4.

[0152] This embodiment further provides a lithium iron phosphate positive electrode material, which is the same as that of Example 4 except that the composite additive in the preparation process of the lithium iron phosphate positive electrode material is the composite additive provided in this embodiment.

[0153] Example 9

[0154] This embodiment provides a composite additive for preparing a lithium manganese iron phosphate positive electrode material. Except that the composite additive is a spherical solid with a D50 particle size of 0.5 μm formed by spray drying a slurry containing organic additives and inorganic additives at an inlet air temperature of 400°C and an outlet air temperature of 150°C, the rest is the same as Example 6.

[0155] This embodiment further provides a lithium manganese iron phosphate positive electrode material, which is the same as that of Example 6 except that the composite additive in the preparation process of the lithium manganese iron phosphate positive electrode material is the composite additive provided in this embodiment.

[0156] Example 10

[0157] This embodiment provides a composite additive for preparing a lithium iron phosphate positive electrode material. Except that in step (1) of the preparation method of the composite additive, a crushed inorganic additive having a D50 particle size of 1.5 μm is obtained, the rest is the same as that of Example 5.

[0158] This embodiment further provides a lithium iron phosphate positive electrode material, which is the same as that of Example 5 except that the composite additive in the preparation process of the lithium iron phosphate positive electrode material is the composite additive provided in this embodiment.

[0159] Example 11

[0160] This embodiment provides a composite additive for preparing a lithium iron phosphate positive electrode material. Except that in step (1) of the preparation method of the composite additive, a crushed inorganic additive having a D50 particle size of 2 μm is obtained, the rest is the same as that of Example 5.

[0161] This embodiment further provides a lithium iron phosphate positive electrode material, which is the same as that of Example 5 except that the composite additive in the preparation process of the lithium iron phosphate positive electrode material is the composite additive provided in this embodiment.

[0162] Example 12

[0163] This embodiment provides a composite additive for preparing a lithium iron phosphate positive electrode material. Except that in step (2) of the preparation method of the composite additive, the organic additive and water are initially mixed to obtain an organic additive aqueous solution with a solid content of 3%, and the solid content of the mixed slurry obtained by mixing the obtained inorganic additive and the obtained organic additive aqueous solution is 10%, the rest is the same as Example 5.

[0164] This embodiment further provides a lithium iron phosphate positive electrode material, which is the same as that of Example 5 except that the composite additive in the preparation process of the lithium iron phosphate positive electrode material is the composite additive provided in this embodiment.

[0165] Example 13

[0166] This embodiment provides a composite additive for preparing a lithium iron phosphate positive electrode material. Except that in step (2) of the preparation method of the composite additive, the organic additive and water are initially mixed to obtain an organic additive aqueous solution with a solid content of 25%, and the solid content of the mixed slurry obtained by mixing the obtained inorganic additive and the obtained organic additive aqueous solution is 35%, the rest is the same as Example 5.

[0167] This embodiment further provides a lithium iron phosphate positive electrode material, which is the same as that of Example 5 except that the composite additive in the preparation process of the lithium iron phosphate positive electrode material is the composite additive provided in this embodiment.

[0168] Comparative Example 1

[0169] This comparative example provides a composite additive for preparing a lithium iron phosphate positive electrode material, which is the same as Example 4 except that the composite additive is a spherical solid with a D50 particle size of 2 μm formed by spray drying a slurry containing an organic additive and an inorganic additive, that is, in step (3) of the preparation method of the composite additive, the D50 particle size of the particles in the obtained sand-milled slurry is 2 μm.

[0170] This comparative example also provides a lithium iron phosphate positive electrode material, which is the same as Example 4 except that the composite additive in the preparation process of the lithium iron phosphate positive electrode material is the composite additive provided in this comparative example.

[0171] Comparative Example 2

[0172] This comparative example provides a composite additive for preparing a lithium iron phosphate positive electrode material. Except that the composite additive is a spherical solid with a D50 particle size of 1.5 μm formed by spray drying a slurry containing organic additives and inorganic additives at an inlet air temperature of 250°C and an outlet air temperature of 80°C, the rest is the same as Example 4.

[0173] This comparative example also provides a lithium iron phosphate positive electrode material, which is the same as Example 4 except that the composite additive in the preparation process of the lithium iron phosphate positive electrode material is the composite additive provided in this comparative example.

[0174] Comparative Example 3

[0175] This comparative example provides a composite additive for preparing a lithium iron phosphate positive electrode material, which is the same as Example 4 except that the composite additive is a slurry containing an organic additive and an inorganic additive, i.e., the spray drying in step (3) of the preparation method of the composite additive is omitted.

[0176] This comparative example also provides a lithium iron phosphate positive electrode material, which is the same as Example 4 except that the composite additive in the preparation process of the lithium iron phosphate positive electrode material is the composite additive provided in this comparative example.

[0177] Comparative Example 4

[0178] This comparative example provides a composite additive for preparing a lithium manganese iron phosphate positive electrode material, which is the same as Example 6 except that the composite additive is a spherical solid with a D50 particle size of 2 μm formed by spray drying a slurry containing an organic additive and an inorganic additive, that is, in step (3) of the preparation method of the composite additive, the D50 particle size of the particles in the obtained sand-milled slurry is 2 μm.

[0179] This comparative example also provides a lithium iron manganese phosphate positive electrode material, which is the same as Example 6 except that the composite additive in the preparation process of the lithium iron manganese phosphate positive electrode material is the composite additive provided in this comparative example.

[0180] Comparative Example 5

[0181] This comparative example provides a composite additive for preparing a lithium manganese iron phosphate positive electrode material. Except that the composite additive is a spherical solid with a D50 particle size of 1.2 μm formed by spray drying a slurry containing organic additives and inorganic additives at an inlet air temperature of 250°C and an outlet air temperature of 80°C, the rest is the same as Example 6.

[0182] This comparative example also provides a lithium iron manganese phosphate positive electrode material, which is the same as Example 6 except that the composite additive in the preparation process of the lithium iron manganese phosphate positive electrode material is the composite additive provided in this comparative example.

[0183] Comparative Example 6

[0184] This comparative example provides a composite additive for preparing a lithium manganese iron phosphate positive electrode material. Except that the composite additive is a slurry containing an organic additive and an inorganic additive, that is, the spray drying in step (3) of the preparation method of the composite additive is omitted, the rest is the same as Example 6.

[0185] This comparative example also provides a lithium iron manganese phosphate positive electrode material, which is the same as Example 6 except that the composite additive in the preparation process of the lithium iron manganese phosphate positive electrode material is the composite additive provided in this comparative example.

[0186] Comparative Example 7

[0187] This comparative example provides a composite additive for preparing a lithium iron phosphate positive electrode material. Except that the ratio of the mass of carbon produced by the thermal decomposition of the organic additive in the composite additive to the mass of the metal element in the inorganic additive is 1:1, the rest is the same as Example 1.

[0188] This comparative example also provides a lithium iron phosphate positive electrode material, which is the same as Example 5 except that the composite additive in the preparation process of the lithium iron phosphate positive electrode material is the composite additive provided in this comparative example.

[0189] Comparative Example 8

[0190] This comparative example provides a composite additive for preparing a lithium iron phosphate positive electrode material. Except that the ratio of the molar amount of carbon produced by the thermal decomposition of the organic additive in the composite additive to the molar amount of the metal element in the inorganic additive is 60:1, the rest is the same as Example 1.

[0191] This comparative example also provides a lithium iron phosphate positive electrode material, which is the same as Example 5 except that the composite additive in the preparation process of the lithium iron phosphate positive electrode material is the composite additive provided in this comparative example.

[0192] The lithium iron phosphate positive electrode material / lithium iron manganese phosphate positive electrode material (90% by mass), conductive carbon black (7% by mass), and PVDF binder (3% by mass) provided in the above embodiments and comparative examples were mixed with NMP solvent to prepare a slurry, coated on aluminum foil, vacuum dried at 120° C. for 12 hours, compacted, and cut to obtain a positive electrode sheet; the obtained positive electrode sheet / polyethylene separator / lithium sheet were assembled, injected with electrolyte, and packaged into CR2032 button batteries (lithium iron phosphate batteries were prepared in Examples 1 to 5 and 7 to 12 and Comparative Examples 1 and 2, and lithium iron phosphate batteries were prepared in Example 6 and Comparative Examples 3 and 4); after the assembly was completed, the obtained CR2032 button batteries were allowed to stand in an insulated box at a test temperature of 25±2° C. for 2 hours;

[0193] The obtained CR2032 button batteries were charged at a constant current and constant voltage of 0.1C using a Blue Electric test system, with a charge cut-off current of 0.05C; and then discharged at a constant current of 0.1C to obtain the charge specific capacity, discharge specific capacity, 0.5C rate performance, and 1C rate performance, as shown in Tables 1 and 2.

[0194] Table 1

[0195]

[0196] Table 2

[0197]

[0198] From Table 1 and Table 2, we can get:

[0199] (1) After preparing a lithium iron phosphate positive electrode material using the composite additive provided in Examples 1 to 5 of the present invention, a lithium iron phosphate battery prepared using the obtained lithium iron phosphate positive electrode material has a high charge and discharge specific capacity and good rate performance;

[0200] After the lithium iron manganese phosphate positive electrode material is prepared using the composite additive provided in Example 6 of the present invention, the lithium iron manganese phosphate battery prepared using the obtained lithium iron manganese phosphate positive electrode material has a high charge and discharge specific capacity and good rate performance;

[0201] (2) By comparing Example 4 with Example 7, it can be seen that the composite additive in the present invention is a solid obtained by spray-drying a slurry containing an organic additive and an inorganic additive; compared with vacuum oven drying, the spray drying in the present application converts the slurry into tiny droplets (10 to 100 μm) by atomization, ensuring uniform mixing of organic and inorganic components at the atomic / molecular level, avoiding local component segregation when forming the composite additive; in addition, during spray drying, the droplets evaporate rapidly at high temperature and naturally shrink into spherical particles with good fluidity, which is more conducive to subsequent uniform mixing with the lithium source, iron source, and phosphorus source, thereby improving the uniformity of the positive electrode material prepared with the composite additive;

[0202] (3) By comparing Example 4 with Example 8, and Example 6 with Example 9, it can be seen that the present invention further limits the inlet and outlet air temperatures of the spray drying, thereby further ensuring the uniform mixing of organic and inorganic components at the atomic / molecular level during the spray drying, and further improving the morphology of the composite additive, further enhancing the fluidity of the composite additive, thereby improving the electrochemical performance of the positive electrode material and battery prepared using the composite additive;

[0203] (4) By comparing Example 5 with Examples 10 and 11, it can be seen that the D50 particle size of the inorganic additive after pulverization in step (1) of the preparation method of the composite additive will affect the performance of the prepared positive electrode material and battery; when the D50 particle size of the inorganic additive after pulverization is less than 1 μm, the positive electrode material and the battery have better performance. This is because after pulverizing the inorganic additive, the bonding state of the inorganic additive can be opened, the dispersibility of the inorganic additive can be improved, and thus the uniformity of the negative electrode additive can be improved; in addition, when the D50 particle size of the inorganic additive after pulverization is less than 1 μm, the particle size of the inorganic additive is small, the specific surface area is large, and it is easier to be evenly dispersed in the positive electrode material, which can avoid uneven performance caused by local agglomeration, reduce component segregation caused by size difference, and enhance interface contact and electrochemical activity, shorten the ion / electron transmission path, and improve reaction kinetics;

[0204] (5) By comparing Example 5 with Examples 12 and 13, it can be seen that in step (2) of the preparation method of the composite additive of the present invention, the solid content of the organic additive aqueous solution and the solid content of the mixed slurry will affect the performance of the prepared positive electrode material and battery; when the solid content of the organic additive aqueous solution is 5-20%, and the solid content of the mixed slurry is 15-25%, the positive electrode material and the battery have better performance. This is because within this solid content range, the spray drying process is not prone to equipment clogging, and the spray material particle size is moderate, which is conducive to the preparation of nano-scale lithium iron phosphate / lithium manganese iron phosphate positive electrode materials, thereby improving the lithium ion / electron conductivity of the positive electrode material;

[0205] (6) By comparing Example 4 with Comparative Examples 1-2, and Example 6 with Comparative Examples 4-5, it can be seen that the D50 particle size of the spherical solid composite additive in the present invention affects the performance of the prepared positive electrode material and battery; when the D50 particle size of the spherical solid composite additive is less than 1 μm, the positive electrode material and the battery have better performance. This is because when the D50 particle size of the spherical solid composite additive is less than 1 μm, the particle size of the organic additive and the inorganic additive in the composite additive is small, the specific surface area is large, and it is easier to be evenly dispersed in the positive electrode material, which can avoid uneven performance caused by local agglomeration, reduce component segregation caused by size difference, enhance interface contact and electrochemical activity, shorten the ion / electron transmission path, and improve reaction kinetics;

[0206] (7) By comparing Example 4 with Comparative Example 3, and Example 6 with Comparative Example 6, it can be seen that the composite additive in the present invention is a spherical solid particle formed by natural shrinkage after drying, has good fluidity and strong temperature resistance, is not prone to the problem of re-separation of organic additives and inorganic additives during storage and transportation, and can more accurately control the amount of organic additives and inorganic additives added in the composite additive, thereby being more conducive to subsequent uniform mixing with the lithium source, iron source, and phosphorus source, thereby improving the uniformity of the positive electrode material prepared using the composite additive;

[0207] (8) By comparing Example 5 with Comparative Examples 7 and 8, it can be seen that the ratio of the molar amount of carbon produced after the organic additive in the composite additive of the present invention is heated and decomposed to the molar amount of the metal element in the inorganic additive will affect the performance of the prepared positive electrode material and battery; when the ratio of the mass of carbon produced after the organic additive is heated and decomposed to the mass of the metal element in the inorganic additive is (1.5 to 50):1, the positive electrode material and the battery have better performance. This is because the positive electrode material has a better carbon coating layer ratio and a more appropriate metal doping ratio under this ratio, which can stabilize the olivine structure of lithium iron phosphate and effectively control the mixing ratio of lithium and iron elements, thereby improving the structural stability of the positive electrode material and making the battery have better electrochemical performance during charging and discharging.

[0208] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A composite additive for preparing a phosphoric acid-based positive electrode material, characterized in that: The composite additive comprises an organic additive and an inorganic additive, and the composite additive is a spherical solid with a D50 particle size of less than 1 μm; The ratio of the mass of carbon generated by heating and decomposing the organic additive in the composite additive to the mass of the metal element in the inorganic additive is (1.5-50):

1.

2. The composite additive according to claim 1, characterized in that The organic additives include an organic carbon source and an organic dispersant; Preferably, the mass ratio of the organic carbon source to the organic dispersant in the organic additive is (5-10):3; Preferably, the organic carbon source comprises any one or a combination of at least two of glucose, polyethylene glycol, sucrose, citric acid, polyacrylonitrile or phenolic resin; Preferably, the organic dispersant comprises any one or a combination of at least two of polyethylene glycol, polyvinyl alcohol, polyvinyl pyrrolidone, sodium lauryl sulfate, sodium dodecylbenzenesulfonate, cetyltrimethylammonium bromide, polyoxyethylene ether or sodium carboxymethyl cellulose; Preferably, the inorganic additive includes any one or a combination of at least two of TiO2, V2O5, BO3, NbO2, MgO or Al2O3, ZrO2, SiO2, CeO2, AlF3, MoS2 or LiBO2.

3. The composite additive according to claim 1 or 2, characterized in that The composite additive is formed by spray drying a slurry containing an organic additive and an inorganic additive at an air inlet temperature of 200-300° C. and an air outlet temperature of 100-120° C.

4. A method for preparing the composite additive according to any one of claims 1 to 3, characterized in that: The preparation method comprises: The inorganic additive, the organic additive and the solvent are mixed to obtain a slurry, and the obtained slurry is spray-dried to obtain the composite additive.

5. The preparation method according to claim 4, characterized in that The preparation method further comprises pulverizing the inorganic additive before the mixing, wherein the pulverizing obtains a pulverized inorganic additive having a D50 particle size of less than 1 μm; Preferably, the mixing method comprises: initially mixing the organic additive and the solvent to obtain an organic additive solution, and then mixing the inorganic additive with the obtained organic additive solution to obtain a mixed slurry; Preferably, the solid content of the organic additive solution is 5 to 20%; Preferably, the solid content of the mixed slurry is 15-25%; Preferably, the preparation method further comprises sand milling the obtained mixed slurry between the mixing and the spray drying; Preferably, the sand-milled slurry is obtained after the sand-milling, and the D50 particle size of the particles in the sand-milled slurry is less than 1 μm; Preferably, the preparation method comprises: (1) performing air flow pulverization on the inorganic additive to obtain a pulverized inorganic additive having a D50 particle size of less than 1 μm; (2) preliminarily mixing an organic additive with water to obtain an organic additive aqueous solution having a solid content of 5 to 20%, and then mixing the obtained organic additive aqueous solution with the crushed inorganic additive obtained in step (1) to obtain a mixed slurry having a solid content of 15 to 25%; (3) sand-milling the mixed slurry obtained in step (2) to obtain a sand-milled slurry, wherein the D50 particle size of the particles in the sand-milled slurry is less than 1 μm; and spray-drying the sand-milled slurry to obtain the composite additive, wherein the inlet air temperature of the spray drying is 200-300° C., and the outlet air temperature is 100-120° C.

6. A phosphate-based positive electrode material, characterized in that: The composite additive according to any one of claims 1 to 3 is added during the preparation of the phosphate-based positive electrode material.

7. The phosphate-based cathode material according to claim 6, characterized in that Based on the mass of the phosphate-based positive electrode material, the mass fraction of carbon produced by carbonization of the organic additive in the phosphate-based positive electrode material is 1-5wt%, and the mass fraction of the metal element in the inorganic additive in the phosphate-based positive electrode material is 0.1-0.6wt%.

8. A process for preparing the phosphate-based cathode material according to claim 6 or 7, characterized in that: The preparation process comprises: When the phosphate-based positive electrode material is a lithium iron phosphate positive electrode material, an iron source, a lithium source and the composite additive according to any one of claims 1 to 3 are first mixed and then subjected to a first heat treatment to obtain the phosphate-based positive electrode material; When the phosphate-based positive electrode material is a lithium manganese iron phosphate positive electrode material, the iron source, lithium source, manganese source and the composite additive according to any one of claims 1 to 3 are mixed for a second time and then subjected to a second heat treatment to obtain the phosphate-based positive electrode material.

9. The preparation process according to claim 8, characterized in that: When the phosphate-based positive electrode material is a lithium iron phosphate positive electrode material, the molar ratio of the iron source to the lithium source in the first mixture is 1:(1-1.15), and the mass ratio of the lithium source to the composite additive is (3-10):1; Preferably, when the phosphate-based positive electrode material is a lithium iron manganese phosphate positive electrode material, the molar ratio of the iron source, the lithium source and the manganese source in the second mixture is (0.25-4):(1-1.15):1, and the mass ratio of the lithium source to the composite additive is (3-10):1; Preferably, the first mixing method and the second mixing method each independently comprise ball milling and sand milling performed sequentially; Preferably, the D50 particle size of the materials in the first mixture and the second mixture after ball milling is independently less than 5 μm; Preferably, the D50 particle size of the materials in the first mixture and the second mixture after sand grinding is independently less than 1 μm; Preferably, the first heat treatment comprises a first heating, a first heat preservation, a second heating and a second heat preservation performed in sequence in a protective atmosphere; The temperature of the first insulation is 250-400°C, and the time is 2h-4h; the temperature of the second insulation is 700-800°C, and the time is 5-12h; Preferably, the second heat treatment comprises a third heating step, a third heat preservation step, a fourth heating step and a fourth heat preservation step sequentially performed in a protective atmosphere; The temperature of the third insulation is 250-400° C., and the time is 2 hours to 4 hours; the temperature of the fourth insulation is 650-800° C., and the time is 5 hours to 12 hours.

10. A battery, characterized in that: The battery comprises the phosphate-based positive electrode material according to claim 6 or 7.

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