Positive electrode active material and preparation method therefor

Abstract

A positive electrode active material and a preparation method therefor. The positive electrode active material comprises secondary particles composed of primary particles; the primary particles comprise Li1+aFe1-x-yMnxAy(PO4), wherein -0.1≤a≤0.4, 0.5≤x≤0.7, 0≤y≤0.01, A comprises at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, and the crystallinity of the positive electrode active material is not less than 98%. The positive electrode active material has relatively high crystallinity, the ionic conductivity and the electronic conductivity of the positive electrode active material are relatively high, and when the positive electrode active material is applied to a lithium ion battery, the rate capability of the battery can be remarkably improved.

Description

A positive electrode active material and a preparation method thereof

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 14, 2023, with application number 202311729060.2 and application name “A positive electrode active material and its preparation method”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the field of lithium-ion batteries and relates to a positive electrode active material, and in particular to a positive electrode active material and a preparation method thereof. Background Art

[0003] Lithium-ion batteries, due to their high energy density, high safety, environmental friendliness, compact size, and light weight, are widely used in transportation power supplies, power storage, mobile communications, new energy storage power supplies, aerospace and military power supplies, and other fields. Furthermore, with the continuous development of lithium-ion batteries, the market has placed higher demands on their capacity and cycle life.

[0004] As an important component of lithium-ion batteries, positive electrode active materials account for a large proportion of them. Therefore, the performance of positive electrode active materials will greatly affect the performance of the battery. At present, the types of positive electrode active materials mainly include LiCoO2 positive electrode materials, LiNiO2 positive electrode materials, Li-Mn-O positive electrode materials, LiFePO4 positive electrode materials, conductive polymer positive electrode materials, etc. Among them, lithium iron phosphate positive electrode materials have attracted much attention in the industry due to their high theoretical capacity, low price, environmental friendliness, stable structure and long cycle life. However, their discharge voltage and energy density are still not ideal. Lithium manganese iron phosphate, as a composite solid solution of lithium manganese phosphate and lithium iron phosphate, has improved its energy density and discharge voltage, but its ionic conductivity and electronic conductivity are low, resulting in poor rate performance of the battery.

[0005] Therefore, there is an urgent need to develop a highly conductive lithium manganese iron phosphate positive electrode active material to improve the rate performance of the battery. Summary of the Invention

[0006] In response to the above-mentioned defects, the present application provides a positive electrode active material with high ionic conductivity and electronic conductivity, which can significantly improve the rate performance of lithium-ion batteries.

[0007] The present application provides a method for preparing a positive electrode active material. The positive electrode active material prepared by the preparation method has high ionic conductivity and electronic conductivity.

[0008] The present application provides a positive electrode sheet, comprising the above-mentioned positive electrode active material or the positive electrode active material prepared by the above-mentioned method for preparing the positive electrode active material. Since the positive electrode active material has high ionic conductivity and electronic conductivity, the positive electrode sheet is applied to a lithium-ion battery, which can enable the battery to have higher rate performance.

[0009] The present application provides a lithium-ion battery, comprising the above-mentioned positive electrode active material or the positive electrode active material prepared by the above-mentioned method for preparing the positive electrode active material or the above-mentioned positive electrode sheet, and the lithium-ion battery has high rate performance.

[0010] The present application provides a positive electrode active material, including secondary particles composed of primary particles, wherein the primary particles have a chemical composition shown in Formula 1, Li 1+a Fe 1-x-y Mn x A y (PO4) Formula 1

[0011] In formula 1, -0.1≤a≤0.4, 0.5≤x≤0.7, 0≤y≤0.01, and A includes at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y;

[0012] The positive electrode active material has a crystallinity of not less than 98%.

[0013] Furthermore, the positive electrode active material further includes a carbon coating layer covering the surface of the primary particles;

[0014] The mass percentage of carbon element in the positive electrode active material is 1.8-2.0 wt%.

[0015] Furthermore, the specific surface area of ​​the positive electrode active material is 17 to 22 m 2 / g, and / or the powder compaction density of the positive electrode active material is 2.1 to 2.4 g / cm 3 .

[0016] Furthermore, the median particle size of the primary particles is 0.25 to 0.4 μm, and / or the median particle size of the secondary particles is 5 to 6 μm.

[0017] The present application also provides a method for preparing the positive electrode active material described in any one of the above, comprising the following steps:

[0018] (1) Adding the first raw material and deionized water to the second raw material to obtain a first mixed slurry; the second raw material includes a lithium source, an iron source, a manganese source, a phosphorus source, and a dopant, and the first raw material includes lithium manganese iron phosphate having a chemical composition shown in Formula 2, Li 1+b Fe1-c Mn c PO4 Formula 2

[0019] In formula 2, -0.1≤b≤0.4, 0.5≤c≤0.7;

[0020] (2) grinding the first mixed slurry to obtain a second mixed slurry; the median particle size of the second mixed slurry is 200 to 400 nm;

[0021] (3) granulating the second mixed slurry to obtain a third raw material having a median particle size of 3 to 4 μm;

[0022] (4) Sintering the third raw material in a protective atmosphere at a sintering temperature of 650-670° C., a sintering time of 6-8 h, and a heating rate of 3-8° C. / min to obtain the positive electrode active material.

[0023] Furthermore, in step (1), the first raw material also includes lithium iron phosphate Li3Fe2(PO4)3 and lithium manganese phosphate LiMnPO4;

[0024] The first raw material comprises, by weight percentage, 75-84 wt % of lithium manganese iron phosphate, 7-10 wt % of lithium iron phosphate, and 9-15 wt % of lithium manganese phosphate;

[0025] And / or, the first raw material accounts for 10-15% of the theoretically generated mass of the positive electrode active material.

[0026] Furthermore, in step (1), the second raw material further includes a carbon source; the carbon source accounts for 8 to 12% of the total mass of the theoretically generated mass of the positive electrode active material and the first raw material.

[0027] Furthermore, in step (2), the grinding includes a first grinding and a second grinding;

[0028] The first grinding process has a grinding speed of 1400 to 1700 r / min and a grinding time of 50 to 70 min;

[0029] The second grinding process has a grinding speed of 1600-2000 r / min and a grinding time of 50-70 min.

[0030] The present application also provides a positive electrode sheet, comprising any of the positive electrode active materials described above or comprising a positive electrode active material prepared by any of the methods for preparing the positive electrode active materials described above.

[0031] The present application also provides a lithium-ion battery, comprising any of the above-mentioned positive electrode active materials, or a positive electrode active material prepared by any of the above-mentioned methods for preparing the positive electrode active materials, or the above-mentioned positive electrode sheet.

[0032] The positive electrode active material in the present application includes secondary particles composed of primary particles, wherein the primary particles include the chemical composition of Formula 1, and the crystallinity is not less than 98%, and the content of the impurity phase (Li3Fe2(PO4)3 and LiMnPO4) is relatively small, which can effectively improve the ionic conductivity and electronic conductivity of the positive electrode active material, thereby effectively improving the rate performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1 is a SEM image of the positive electrode active material in Example 1 of the present application;

[0034] FIG2 is an XRD pattern of the first raw material in Example 1 of the present application;

[0035] FIG3 is an XRD diagram of the positive electrode active materials in Example 1 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0036] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0037] The first aspect of the present application provides a positive electrode active material, including secondary particles composed of primary particles, wherein the primary particles have a chemical composition shown in Formula 1, Li 1+a Fe 1-x-y Mn x A y (PO4) Formula 1

[0038] In formula 1, -0.1≤a≤0.4, 0.5≤x≤0.7, 0≤y≤0.01, and A includes at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y;

[0039] The crystallinity of the positive electrode active material is not less than 98%.

[0040] Specifically, the crystallinity of the positive electrode active material can be obtained by XRD patterns to obtain the diffraction peak area A1 of the crystalline phase and the diffraction peak area A2 of the amorphous phase, and the crystallinity can be calculated by formula 2: Crystallinity (%) = A1 / (A1+A2)×100% Formula 2

[0041] The positive electrode active material in the present application includes secondary particles composed of primary particles, wherein the primary particles include the chemical composition shown in Formula 1 and have a crystallinity of not less than 98%. Since the positive electrode active material inevitably contains impurities, namely Li3Fe2(PO4)3 and LiMnPO4, which have low ionic and electronic conductivity, the lithium ions included in the impurities are difficult to deintercalate during the charge and discharge process, resulting in a decrease in the rate performance of the battery. The crystallinity of the positive electrode active material of the present application is not less than 98%, so the impurity content in the positive electrode active material is relatively low, which can effectively improve the overall ionic and electronic conductivity of the positive electrode active material, thereby enabling the lithium-ion battery to have a higher rate performance.

[0042] In addition, since part of the lithium ions in the positive electrode active material are distributed in the heterogeneous phase, the presence of the heterogeneous phase will result in a decrease in the number of lithium ions that can migrate freely. Therefore, the positive electrode active material of the present application also has a higher capacity.

[0043] Specifically, the content of the impurity phase in the positive electrode active material can be calculated by fitting the XRD measurement spectrum with the XRD standard card.

[0044] In a specific embodiment, the positive electrode active material also includes a carbon coating layer covering the surface of the primary particles; the mass percentage of carbon elements in the positive electrode active material is 1.8 to 2.0 wt%. Specifically, the mass percentage of carbon elements can be measured by a carbon-sulfur analyzer. By carbon coating the surface of the primary particles, the electronic conductivity can be further improved, so that the battery has a higher rate performance; at the same time, the carbon coating layer can also reduce the contact area between the positive electrode active material and the electrolyte, avoid side reactions with the electrolyte, and make the battery have better cycle performance. When the mass percentage of carbon elements in the positive electrode active material is within the above range, it can not only effectively improve the electronic conductivity of the positive electrode active material, but also have a shorter lithium ion migration path, will not hinder the deintercalation and insertion of lithium ions, and improve the specific capacity and rate performance. Specifically, the mass percentage of carbon elements here refers to the mass percentage of the total carbon elements included in the positive electrode active material.

[0045] In one embodiment, the specific surface area of ​​the positive electrode active material is 17 to 22 m 2 / g. Within this range, the positive electrode active material has a high specific surface area, which can increase the contact area between the electrode and the electrolyte to a certain extent, improve the electrochemical reaction rate, and thus enhance the battery's rate performance. At the same time, its specific surface area will not be too large, effectively reducing the occurrence of side reactions and lowering the initial irreversible lithium loss, thereby enabling the battery to have better cycle performance.

[0046] In one embodiment, the powder compaction density of the positive electrode active material is 2.1 to 2.4 g / cm 3Within this range, the positive electrode sheet has a higher compaction density and does not hinder the migration of lithium ions, so that the battery has a higher rate performance and a higher energy density.

[0047] In a specific embodiment, the median particle size of the primary particles is 0.25 to 0.4 μm. When the median particle size of the primary particles is within the above range, the migration path of lithium ions is shorter, which can further improve the rate performance of the positive electrode active material.

[0048] In one embodiment, the median particle size of the secondary particles is 5 to 6 μm. Within this range, the secondary particles have a suitable particle size, have a shorter lithium ion diffusion path, and further improve the rate performance of lithium ion batteries containing the positive electrode active material.

[0049] A second aspect of the present application provides a method for preparing any of the above-mentioned positive electrode active materials, comprising the following steps:

[0050] (1) Adding the first raw material and deionized water to the second raw material to obtain a first mixed slurry; the second raw material includes a lithium source, an iron source, a manganese source, a phosphorus source, and a dopant, and the first raw material includes lithium manganese iron phosphate having a chemical composition shown in Formula 2, Li 1+b Fe 1-c Mn c PO4 Formula 2

[0051] In formula 2, -0.1≤b≤0.4, 0.5≤c≤0.7;

[0052] (2) grinding the first mixed slurry to obtain a second mixed slurry; the median particle size of the second mixed slurry is 200 to 400 nm;

[0053] (3) granulating the second mixed slurry to obtain a third raw material having a median particle size of 3 to 4 μm;

[0054] (4) Sintering the third raw material in a protective atmosphere at a sintering temperature of 650-670° C., a sintering time of 6-8 h, and a heating rate of 3-8° C. / min to obtain a positive electrode active material.

[0055] Specifically, in step (1), a lithium source, an iron source, a manganese source, a phosphorus source, and a dopant are mixed to obtain a second raw material, and then a first raw material and deionized water are added to the second raw material, wherein the first raw material includes lithium manganese iron phosphate having a chemical composition shown in Formula 2, to obtain a first mixed slurry, and the solid-liquid ratio of the first mixed slurry is preferably 1:3 to 1:5.

[0056] The lithium source of the present application refers to the raw material for providing lithium element, and iron source refers to the raw material for providing iron element, and manganese source refers to the raw material for providing manganese element, and phosphorus source refers to the raw material for providing phosphorus element, and dopant refers to the compound including at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y, as long as containing the target element (lithium, iron, manganese, phosphorus), it is within the scope of the present application, and a kind of target element can be introduced into the reaction system by one or more raw materials. Exemplarily, the lithium source can be selected from at least one of lithium carbonate, lithium hydroxide, lithium dihydrogen phosphate, and lithium oxalate, and the iron source can be selected from at least one of ferric phosphate, ferric oxide, ferric nitrate, and ferric oxalate, and the manganese source can be selected from at least one of manganese carbonate, manganese tetraoxide, manganese nitrate, manganese chloride, and manganese sulfate, and the phosphorus source can be selected from at least one of lithium dihydrogen phosphate, ammonium dihydrogen phosphate, phosphoric acid, ammonium phosphate, and ammonium monohydrogen phosphate. It should be explained that when two or more elements in the target element are included in the raw material simultaneously, the raw material can be understood as the element source of two target elements. For example, when the raw material is lithium dihydrogen phosphate, it serves as both a lithium source and a phosphorus source.

[0057] The present application does not impose any specific restrictions on the molar ratios of the lithium source, iron source, manganese source, phosphorus source, and dopant, as long as the chemical formula of the prepared positive electrode active material satisfies Formula 1.

[0058] The present application does not limit the specific sources of the lithium source, iron source, manganese source, phosphorus source, and dopant, for example, they can be obtained through commercial sources or conventional preparation methods.

[0059] The present application does not specifically limit the mixing method. It is only necessary to fully mix the second raw material and the first raw material in deionized water. For example, any one of mechanical stirring, liquid stirring, and gas stirring can be used.

[0060] In step (2), the first mixed slurry is ground to obtain a second mixed slurry, and the median particle size of the second mixed slurry is 200 to 400 nm, so that the second raw material and the first raw material included in the second mixed slurry are small and uniform, with a smooth surface, and the first raw material is evenly dispersed in the second mixed slurry, which is conducive to the formation of more uniform positive electrode active material particles in the subsequent sintering process and improves the crystallinity of the positive electrode active material.

[0061] In step (3), the second mixed slurry after grinding is granulated and reshaped. Preferably, a spray dryer is selected for granulation and reshaping, with an inlet temperature of 200-210°C and an outlet temperature of 90-95°C to obtain a third raw material with a particle size of 3-4 μm.

[0062] In step (4), the temperature of the third raw material is raised from room temperature to a sintering temperature of 650-670°C at a heating rate of 3-8°C / min under a protective atmosphere, and the heat preservation sintering is carried out for 6-8 hours to obtain a sintered product; during this process, the first raw material decomposes at high temperature to form crystal nuclei, which can induce the metal ions in the second raw material to grow rapidly along the active crystal surface of the first raw material, effectively inhibiting the formation of impurity phases; the sintered product is crushed and sieved through a sieve to obtain a positive electrode active material with a higher degree of crystallinity.

[0063] The present application does not make any specific limitation on the protective atmosphere. For example, the protective atmosphere can be any one of argon, nitrogen, and helium.

[0064] The present application does not make any specific limitation on the crushing method and screen. For example, it can be crushed by jaw crusher rollers, mechanical grinding, air flow grinding and graded crushing, and the screen mesh number is preferably 280 mesh.

[0065] The method for preparing the positive electrode active material in the present application is to react the lithium manganese phosphate and lithium iron phosphate included in the first raw material with the second raw material to generate new lithium manganese iron phosphate, while the metal elements in the second raw material rapidly grow along the active crystal planes of the lithium manganese iron phosphate in the first raw material, thereby effectively reducing the content of the impurity phase in the positive electrode active material and improving its crystallinity so that the crystallinity is within the above range. At the same time, since the first raw material can be directly decomposed into crystal nuclei during the heating process, the preparation method can accelerate the crystallization of the system, shorten the reaction time, and lower the reaction temperature, thereby achieving the purpose of reducing costs and increasing efficiency.

[0066] In a specific embodiment, in step (1), the first raw material further comprises lithium iron phosphate Li3Fe2(PO4)3 and lithium manganese phosphate LiMnPO4;

[0067] The first raw material comprises, by weight percentage, 75-84 wt% lithium iron manganese phosphate, 7-10 wt% lithium iron phosphate, and 9-15 wt% lithium manganese phosphate. When the lithium iron manganese phosphate, lithium iron phosphate, and lithium manganese phosphate included in the first raw material are within the aforementioned ranges, the resulting positive electrode active material can have a lower content of impurities, resulting in a higher degree of crystallinity and, in turn, a higher rate capability for the lithium-ion battery.

[0068] In one embodiment, the first raw material accounts for 10-15% of the theoretical mass of the positive electrode active material. Within this range, the crystallinity can be further significantly improved, thereby making the positive electrode active material have higher ionic conductivity and electronic conductivity, thereby improving the rate performance of the lithium ion battery.

[0069] The calculation method of the theoretical generated mass of the positive electrode active material in this application is as follows:

[0070] Assuming that the molar ratio of the lithium source, iron source, manganese source, phosphorus source, and dopant in the first raw material is (1+a):(1-xy):x:1:y, the theoretical generated mass of 1 mol of positive electrode active material is calculated by formula 3:

[0071] Theoretical generated mass of 1 mol of positive electrode active material (g) = (1 + a) × M1 + (1 - xy) × M2 + x × M3 + M4 + y × M5 Formula 3

[0072] In formula 3, M1 is the molar mass of Li, M2 is the molar mass of Fe, M3 is the molar mass of Mn, and M4 is the molar mass of PO4 － The molar mass of M5 is the molar mass of A.

[0073] In one embodiment, in step (1), the second raw material further comprises a carbon source; the carbon source accounts for 8-12% of the total mass of the theoretically generated mass of the positive electrode active material and the mass of the first raw material. During the sintering process, the carbon source decomposes at high temperature, forming a coating layer on the surface of the primary particles, which improves the conductivity of the positive electrode active material while effectively inhibiting the excessive growth of the primary particles. Within this range, the ionic conductivity and electronic conductivity of the positive electrode active material can be effectively improved while not hindering the insertion and extraction of lithium ions, thereby enabling the battery to have a higher specific capacity and rate performance.

[0074] The carbon source of this application refers to a raw material that provides carbon. As long as it contains the target element, it falls within the definition of this application, and a target element can be introduced into the reaction system through one or more raw materials. For example, the carbon source can be selected from at least one of glucose, sucrose, starch, polyvinyl alcohol, polyethylene glycol, citric acid, and ascorbic acid.

[0075] In one embodiment, in step (2), the grinding includes a first grinding and a second grinding;

[0076] The grinding speed of the first grinding is 1400-1700 r / min, and the grinding time is 50-70 min;

[0077] The second grinding process is performed at a grinding speed of 1600 to 2000 r / min and a grinding time of 50 to 70 min. When the grinding speeds and grinding times for the first and second grinding processes are within the above ranges, the first and second raw materials can be made finer and more uniform, and the first raw material can be more evenly distributed in the second mixed slurry, further improving the uniformity and crystallinity of the positive electrode active material.

[0078] The present application does not specifically limit the grinding methods of the first grinding and the second grinding. For example, any one of a basket mill, a ball mill, and a sand mill can be selected for the first grinding, and any one of a sand mill and a ball mill can be selected for the second grinding.

[0079] In a third aspect, the present application provides a positive electrode sheet comprising the positive electrode active material of the first aspect or the positive electrode active material prepared by the method for preparing the positive electrode active material of the second aspect. Because the positive electrode active material has high crystallinity and, therefore, high ionic and electronic conductivity, the application of a positive electrode sheet comprising the positive electrode active material in a lithium-ion battery can effectively improve the rate performance of the battery.

[0080] A fourth aspect of the present application provides a lithium-ion battery comprising the positive electrode active material of the first aspect, or the positive electrode active material prepared by the method for preparing the positive electrode active material of the second aspect, or the positive electrode sheet of the third aspect. Because the lithium-ion battery includes the positive electrode sheet of the third aspect, the lithium-ion battery has high rate performance.

[0081] Hereinafter, the positive electrode active material of the present application will be described in detail through specific examples.

[0082] Example 1

[0083] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed in a molar ratio of 0.50:0.59:0.4:0.6:0.01, respectively, and mixed to obtain a second raw material; then the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, 1.88 kg of the first raw material was weighed according to the first raw material accounting for 12% of the theoretical generated mass of the positive electrode active material, 1.757 kg of sucrose was weighed according to the sucrose accounting for 10% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material, the first raw material, sucrose and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes, in terms of mass percentage, 80 wt% of lithium manganese iron phosphate, 8 wt% of lithium iron phosphate, and 12 wt% of lithium manganese phosphate, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0084] (2) coarsely grinding the first mixed slurry at a grinding speed of 1700 r / min for 60 min, and then grinding at a grinding speed of 1800 r / min for 50 min to obtain a second mixed slurry with a median particle size of 330 nm;

[0085] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0086] (4) The third raw material was placed in a nitrogen atmosphere and heated from room temperature to a sintering temperature of 650°C at a heating rate of 5°C / min, and sintered for 6 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of the carbon element in the positive electrode active material is 1.93%.

[0087] Example 2

[0088] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed in a molar ratio of 0.50:0.59:0.4:0.6:0.01, respectively, and mixed to obtain a second raw material; then the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, 1.88 kg of the first raw material was weighed according to the first raw material accounting for 12% of the theoretical generated mass of the positive electrode active material, 1.406 kg of sucrose was weighed according to the sucrose accounting for 8% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material, the first raw material, sucrose and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes: 80 wt% of lithium manganese iron phosphate, 8 wt% of lithium iron phosphate, and 12 wt% of lithium manganese phosphate according to the mass percentage, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0089] (2) the first mixed slurry was coarsely ground at a grinding speed of 1700 r / min for 60 min, and then at a grinding speed of 1800 r / min for 50 min to obtain a second mixed slurry with a median particle size of 330 nm;

[0090] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0091] (4) The third raw material was placed in a nitrogen atmosphere and heated from room temperature to a sintering temperature of 670°C at a heating rate of 3°C / min, and sintered for 8 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01(PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of the carbon element in the positive electrode active material is 1.85%.

[0092] Example 3

[0093] (1) According to the molar ratio of 1:0.59:0.2:1:0.01, 2.39 kg of lithium hydroxide, 6.78 kg of manganese carbonate, 3.19 kg of ferric oxide, 11.50 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide are weighed and mixed to obtain a second raw material; then the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, and according to the first raw material accounting for 12% of the theoretical generated mass of the positive electrode active material, 1.88 kg of the first raw material is weighed, and according to the sucrose accounting for 12% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material, 2.108 kg of sucrose is weighed, the first raw material, sucrose and the second raw material are mixed, and deionized water is added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes, according to the mass percentage, 80 wt% of lithium iron manganese phosphate, 8 wt% of lithium iron phosphate, and 12 wt% of lithium manganese phosphate, and the chemical composition of the lithium iron manganese phosphate is LiFe 0.4 Mn 0.6 PO4;

[0094] (2) coarsely grinding the first mixed slurry at a grinding speed of 1700 r / min for 60 min, and then grinding at a grinding speed of 1800 r / min for 50 min to obtain a second mixed slurry with a median particle size of 330 nm;

[0095] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0096] (4) The third raw material was heated from room temperature to a sintering temperature of 650°C at a heating rate of 8°C / min under a nitrogen atmosphere, and sintered for 6 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of carbon element in the positive electrode active material is 1.96%.

[0097] Example 4

[0098] (1) 5.10 kg of lithium oxalate, 6.78 kg of manganese carbonate, 5.75 kg of ferrous oxalate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed in a molar ratio of 0.50:0.59:0.4:0.6:0.01, and mixed to obtain a second raw material; then the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, 1.88 kg of the first raw material was weighed according to the first raw material accounting for 12% of the theoretical generated mass of the positive electrode active material, and 1.757 kg of sucrose was weighed according to the sucrose accounting for 10% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material, the first raw material, sucrose and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes: 80 wt% of lithium manganese iron phosphate, 8 wt% of lithium iron phosphate, and 12 wt% of lithium manganese phosphate according to the mass percentage, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0099] (2) coarsely grinding the first mixed slurry at a grinding speed of 1700 r / min for 70 min, and then grinding at a grinding speed of 2000 r / min for 70 min to obtain a second mixed slurry with a median particle size of 200 nm;

[0100] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0101] (4) The third raw material was heated from room temperature to a sintering temperature of 650°C at a heating rate of 8°C / min under a nitrogen atmosphere, and sintered for 6 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of carbon element in the positive electrode active material is 1.92%.

[0102] Example 5

[0103] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed in a molar ratio of 0.50:0.59:0.4:0.6:0.01, respectively, and mixed to obtain a second raw material; the theoretical generated mass of the positive electrode active material is 15.69 kg, 1.88 kg of the first raw material was weighed according to the first raw material accounting for 12% of the theoretical generated mass of the positive electrode active material, 1.757 kg of sucrose was weighed according to the sucrose accounting for 10% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material, the first raw material, sucrose and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes, in terms of mass percentage, 80 wt% of lithium manganese iron phosphate, 8 wt% of lithium iron phosphate, and 12 wt% of lithium manganese phosphate, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0104] (2) the first mixed slurry was coarsely ground at a grinding speed of 1400 r / min for 50 min, and then at a grinding speed of 1600 r / min for 50 min to obtain a second mixed slurry with a median particle size of 400 nm;

[0105] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0106] (4) The third raw material was placed in a nitrogen atmosphere and heated from room temperature to a sintering temperature of 670°C at a heating rate of 3°C / min, and sintered for 8 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of the carbon element in the positive electrode active material is 1.90%.

[0107] Example 6

[0108] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed in a molar ratio of 0.50:0.59:0.4:0.6:0.01, respectively, and mixed to obtain a second raw material; then the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, 1.88 kg of the first raw material was weighed according to the first raw material accounting for 12% of the theoretical generated mass of the positive electrode active material, and 1.757 kg of sucrose was weighed according to the sucrose accounting for 10% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material, the first raw material, sucrose and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes, in terms of mass percentage, 75 wt% of lithium manganese iron phosphate, 10 wt% of lithium iron phosphate, and 15 wt% of lithium manganese phosphate, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0109] (2) the first mixed slurry was coarsely ground at a grinding speed of 1400 r / min for 50 min, and then at a grinding speed of 1600 r / min for 50 min to obtain a second mixed slurry with a median particle size of 400 nm;

[0110] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0111] (4) The third raw material was heated from room temperature to a sintering temperature of 650°C at a heating rate of 3°C / min under a nitrogen atmosphere, and sintered at this temperature for 6 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of the carbon element in the positive electrode active material is 1.93%.

[0112] Example 7

[0113] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed in a molar ratio of 0.50:0.59:0.4:0.6:0.01, respectively, and mixed to obtain a second raw material; then the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, 1.88 kg of the first raw material was weighed according to the first raw material accounting for 12% of the theoretical generated mass of the positive electrode active material, 1.757 kg of sucrose was weighed according to the sucrose accounting for 10% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material, the first raw material, sucrose and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes, in terms of mass percentage, 84 wt% of lithium manganese iron phosphate, 7 wt% of lithium iron phosphate, and 9 wt% of lithium manganese phosphate, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0114] (2) coarsely grinding the first mixed slurry at a grinding speed of 1700 r / min for 70 min, and then grinding at a grinding speed of 2000 r / min for 70 min to obtain a second mixed slurry with a median particle size of 200 nm;

[0115] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0116] (4) The third raw material was heated from room temperature to a sintering temperature of 670°C at a heating rate of 8°C / min under a nitrogen atmosphere, and sintered for 8 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of the carbon element in the positive electrode active material is 1.90%.

[0117] Example 8

[0118] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed and mixed according to a molar ratio of 0.50:0.59:0.4:0.6:0.01 to obtain a second raw material; the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, and 1.88 kg of the first raw material was weighed according to the fact that the first raw material accounts for 12% of the theoretical generated mass of the positive electrode active material, the first raw material and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes, according to the mass percentage, 80 wt% of lithium manganese iron phosphate, 8 wt% of lithium iron phosphate, and 12 wt% of lithium manganese phosphate, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0119] (2) coarsely grinding the first mixed slurry at a grinding speed of 1700 r / min for 60 min, and then grinding at a grinding speed of 1800 r / min for 50 min to obtain a second mixed slurry with a median particle size of 330 nm;

[0120] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0121] (4) The third raw material was placed in a nitrogen atmosphere and heated from room temperature to a sintering temperature of 650°C at a heating rate of 5°C / min, and sintered for 6 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4).

[0122] Example 9

[0123] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed in a molar ratio of 0.50:0.59:0.4:0.6:0.01, respectively, and mixed to obtain a second raw material; then the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, 1.88 kg of the first raw material was weighed according to the first raw material accounting for 12% of the theoretical generated mass of the positive electrode active material, 2.460 kg of sucrose was weighed according to the sucrose accounting for 14% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material, the first raw material, sucrose and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes, in terms of mass percentage, 80 wt% of lithium manganese iron phosphate, 8 wt% of lithium iron phosphate, and 12 wt% of lithium manganese phosphate, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0124] (2) coarsely grinding the first mixed slurry at a grinding speed of 1700 r / min for 60 min, and then grinding at a grinding speed of 1800 r / min for 50 min to obtain a second mixed slurry with a median particle size of 330 nm;

[0125] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0126] (4) The third raw material was placed in a nitrogen atmosphere and heated from room temperature to a sintering temperature of 650°C at a heating rate of 5°C / min, and sintered for 6 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of carbon element in the positive electrode active material is 2.11%.

[0127] Example 10

[0128] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed in a molar ratio of 0.50:0.59:0.4:0.6:0.01, respectively, and mixed to obtain a second raw material; then the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, 1.88 kg of the first raw material was weighed according to the first raw material accounting for 12% of the theoretical generated mass of the positive electrode active material, 1.054 kg of sucrose was weighed according to the sucrose accounting for 6% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material, the first raw material, sucrose and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes, in terms of mass percentage, 80 wt% of lithium manganese iron phosphate, 8 wt% of lithium iron phosphate, and 12 wt% of lithium manganese phosphate, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0129] (2) coarsely grinding the first mixed slurry at a grinding speed of 1700 r / min for 60 min, and then grinding at a grinding speed of 1800 r / min for 50 min to obtain a second mixed slurry with a median particle size of 330 nm;

[0130] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0131] (4) The third raw material was placed in a nitrogen atmosphere and heated from room temperature to a sintering temperature of 650°C at a heating rate of 5°C / min, and sintered for 6 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of carbon element in the positive electrode active material is 1.81%.

[0132] Example 11

[0133] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed in a molar ratio of 0.50:0.59:0.4:0.6:0.01, respectively, and mixed to obtain a second raw material; then the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, 1.88 kg of the first raw material was weighed according to the first raw material accounting for 12% of the theoretical generated mass of the positive electrode active material, 0.703 kg of sucrose was weighed according to the sucrose accounting for 4% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material, the first raw material, sucrose and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes, in terms of mass percentage, 80 wt% of lithium manganese iron phosphate, 8 wt% of lithium iron phosphate, and 12 wt% of lithium manganese phosphate, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0134] (2) coarsely grinding the first mixed slurry at a grinding speed of 1700 r / min for 60 min, and then grinding at a grinding speed of 1800 r / min for 50 min to obtain a second mixed slurry with a median particle size of 330 nm;

[0135] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0136] (4) The third raw material was placed in a nitrogen atmosphere and heated from room temperature to a sintering temperature of 650°C at a heating rate of 5°C / min, and sintered for 6 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of carbon element in the positive electrode active material is 1.52%.

[0137] Example 12

[0138] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed in a molar ratio of 0.50:0.59:0.4:0.6:0.01, respectively, and mixed to obtain a second raw material; then the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, 1.88 kg of the first raw material was weighed according to the first raw material accounting for 12% of the theoretical generated mass of the positive electrode active material, 1.757 kg of sucrose was weighed according to the sucrose accounting for 10% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material, the first raw material, sucrose and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes, in terms of mass percentage, 80 wt% of lithium manganese iron phosphate, 8 wt% of lithium iron phosphate, and 12 wt% of lithium manganese phosphate, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0139] (2) the first mixed slurry was coarsely ground at a grinding speed of 1400 r / min for 50 min, and then at a grinding speed of 1200 r / min for 50 min to obtain a second mixed slurry with a median particle size of 510 nm;

[0140] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.6 μm, wherein the inlet temperature of the spray dryer is 210° C. and the outlet temperature is 95° C.;

[0141] (4) The third raw material was placed in a nitrogen atmosphere and heated from room temperature to a sintering temperature of 650°C at a heating rate of 5°C / min, and sintered for 6 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of carbon element in the positive electrode active material is 1.92%.

[0142] Example 13

[0143] (1) 3.69 kg of lithium carbonate, 6.78 kg of manganese carbonate, 6.03 kg of iron phosphate, 6.90 kg of ammonium dihydrogen phosphate, and 0.04 kg of magnesium oxide were weighed according to the ratio of 0.50:0.59:0.4:0.6:0.01, and mixed to obtain a second raw material; then the theoretical generated mass of 100 mol of positive electrode active material is 15.69 kg, 1.88 kg of the first raw material was weighed according to the ratio of the first raw material to the theoretical generated mass of the positive electrode active material, and 1.757 kg of sucrose was weighed according to the ratio of sucrose to the theoretical generated mass of the positive electrode active material and the total mass of the first raw material; the first raw material, sucrose and the second raw material were mixed, and deionized water was added to obtain a first mixed slurry with a solid-liquid ratio of 1:4; wherein the first raw material includes: 80 wt% of lithium manganese iron phosphate, 8 wt% of lithium iron phosphate, and 12 wt% of lithium manganese phosphate according to the mass percentage, and the chemical composition of the lithium manganese iron phosphate is LiFe 0.4 Mn 0.6 PO4;

[0144] (2) coarsely grinding the first mixed slurry at a grinding speed of 1700 r / min for 60 min, and then grinding at a grinding speed of 1800 r / min for 50 min to obtain a second mixed slurry with a median particle size of 330 nm;

[0145] (3) granulating and reshaping the second mixed slurry through a spray dryer to obtain a third raw material with a median particle size of 3.9 μm, wherein the inlet temperature of the spray dryer is 190° C. and the outlet temperature is 85° C.;

[0146] (4) The third raw material was placed in a nitrogen atmosphere and heated from room temperature to a sintering temperature of 650°C at a heating rate of 5°C / min, and sintered for 6 hours to obtain the positive electrode active material of this embodiment. The chemical composition of the positive electrode active material is LiFe 0.4 Mn 0.59 Mg 0.01 (PO4), and the surface of the primary particles of the positive electrode active material is coated with a carbon coating layer. The carbon sulfur analyzer measures that the mass percentage of carbon element in the positive electrode active material is 1.94%.

[0147] Comparative Example 1

[0148] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that the first raw material is not added in this comparative example. At this time, sucrose accounts for 10% of the theoretical generated mass of the positive electrode active material, which is 1.569 kg.

[0149] Comparative Example 2

[0150] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that the first raw material is not added in step (1), the sintering temperature is 700° C., and the sintering time is 12 h.

[0151] Comparative Example 3

[0152] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that the dopant magnesium oxide is not added in step (1).

[0153] Comparative Example 4

[0154] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that in step (3), the sintering temperature is 620° C., the sintering time is 5 h, and the heating rate is 10° C. / min.

[0155] Comparative Example 5

[0156] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that, in step (2), the first mixed slurry is coarsely ground at a grinding speed of 1700 r / min for 70 min, and then at a grinding speed of 2200 r / min for 90 min to obtain a second mixed slurry with a median particle size of 165 nm.

[0157] Comparative Example 6

[0158] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that in step (3), the inlet temperature of the spray dryer is 230°C and the outlet temperature is 110°C, and a third raw material with a median particle size of 2.7 μm is obtained.

[0159] Test example

[0160] 1. The physical and chemical properties of the positive electrode active materials prepared in the above examples and comparative examples were characterized. The characterization results are shown in Table 1. The positive electrode active material prepared in the above Example 1 was characterized by SEM, as shown in FIG1 .

[0161] Figure 1 is a SEM image of the positive electrode active material of Example 1. As shown in Figure 1, the primary particles of the positive electrode active material have high uniformity and the secondary particles have good sphericity, which can shorten the distance between the particles of the positive electrode active material and improve the Li + The transmission rate is high and the surface is rough, which can effectively increase the contact area between the positive electrode active material and the electrolyte, increase the reaction rate of the battery, and make the battery have a higher rate performance.

[0162] 2. XRD characterization was performed on the first raw material in Example 1, the positive electrode active material in Example 1, and the positive electrode active material in Comparative Example 1, as shown in FIG2 and FIG3 .

[0163] FIG2 is an XRD diagram of the first raw material in Example 1, and FIG3 is an XRD diagram of the positive electrode active material in Example 1 and Comparative Example 1. As shown in FIG2 , the first raw material includes lithium manganese iron phosphate LiFe 0.4 Mn 0.6 PO4, lithium iron phosphate Li3Fe2(PO4)3 and lithium manganese phosphate LiMnPO4. This is because in the process of preparing the first raw material under an air environment, part of the lithium manganese iron phosphate will decompose to produce impurity phases (Li3Fe2(PO4)3 and LiMnPO4). Therefore, the above two impurity phases will inevitably exist in the first raw material. It can be seen from Figure 3 that the positive electrode active material prepared after adding the first raw material has a lower impurity phase content, while the positive electrode active material prepared without adding the first raw material has a higher impurity phase content. It can be seen that the positive electrode active material in Example 1 has a lower impurity phase content and a higher crystallinity.

[0164] 3. The positive electrode active materials prepared in the above examples and comparative examples are applied to lithium-ion batteries. The specific steps are as follows:

[0165] The positive electrode active material, conductive agent carbon black and binder polyvinylidene fluoride prepared above were mixed and dispersed in N-methylpyrrolidone in a mass ratio of 80:10:10 to prepare a positive electrode active material layer slurry, which was then coated on the surface of the positive electrode current collector aluminum foil. After drying, rolling, slitting and tab welding, the positive electrode sheet was obtained. The CR2032 button battery was prepared by combining it with a PE / PP composite separator, a lithium sheet and an electrolyte, wherein the electrolyte included 1 mol / L lithium hexafluorophosphate, ethylene carbonate and dimethyl carbonate in a volume ratio of 1:1.

[0166] The button cell prepared above was tested for rate performance and cycle performance:

[0167] (1) Rate performance test

[0168] The button battery prepared above was charged and discharged at a rate of 0.1C in the voltage range of 2.0-4.3V at 25°C. It was cycled for 3 cycles at 0.33C and 5 cycles at 1C to obtain the charge and discharge conditions of the battery at different rates. The results are shown in Table 2.

[0169] (2) Cyclic performance test

[0170] At 25°C, the button battery prepared above was charged and discharged for 500 cycles at 2.0-4.3V and 1C. The first discharge capacity was recorded as C0, and the discharge capacity after 500 cycles was recorded as C1. The 500-cycle capacity retention rate was calculated by formula 4:

[0171] 500-cycle capacity retention (%) = (C1 / C0) × 100% Formula 4

[0172] The test results are shown in Table 2.

[0173] Table 1

[0174] Table 2

[0175] From Table 1 and Table 2, we can see that:

[0176] The positive electrode active materials of Examples 1-13 have higher crystallinity, lower impurity content, higher ion diffusion coefficient and electronic conductivity than the positive electrode active materials of Comparative Examples 1-6. At the same time, the button batteries including the positive electrode active materials of Examples 1-13 have higher capacity retention and rate performance. The crystallinity of the positive electrode active materials of Examples 1-13 can reach up to 99.6%, the impurity content is as low as 0.2%, and the ion diffusion coefficient is as high as 7.9×10 -13 , the highest electronic conductivity is 2.62S / m, the corresponding capacity retention rate is up to 96.2%, and the rate performance is up to 98.6%. This shows that the positive electrode active material of this application has a higher crystallinity and can significantly improve the rate performance of lithium-ion batteries.

[0177] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some or all of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A positive electrode active material, wherein The secondary particles are composed of primary particles, wherein the primary particles have a chemical composition as shown in Formula 1, Li 1+a Fe 1-x-y Mn x A y (PO4) Formula 1 In formula 1, -0.1≤a≤0.4, 0.5≤x≤0.7, 0≤y≤0.01, A includes at least one of Al, Mg, Ni, Co, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn, and Y; The positive electrode active material has a crystallinity of not less than 98%.

2. The positive electrode active material according to claim 1, wherein The positive electrode active material further includes a carbon coating layer covering the surface of the primary particles; The mass percentage of carbon element in the positive electrode active material is 1.8-2.0wt%.

3. The positive electrode active material according to any one of claims 1 or 2, wherein The specific surface area of ​​the positive electrode active material is 17 to 22 m 2 / g, and / or, the powder compaction density of the positive electrode active material is 2.1-2.4 g / cm 3 .

4. The positive electrode active material according to any one of claims 1 to 3, wherein The median particle size of the primary particles is 0.25 to 0.4 μm, and / or the median particle size of the secondary particles is 5 to 6 μm.

5. A method for preparing a positive electrode active material according to any one of claims 1 to 4, wherein: The following steps are involved: (1) adding a first raw material and deionized water to a second raw material to obtain a first mixed slurry; the second raw material comprises a lithium source, an iron source, a manganese source, a phosphorus source, and a dopant, and the first raw material comprises lithium iron manganese phosphate having a chemical composition shown in Formula 2, Li 1+b Fe 1-c Mn c PO4 Formula 2 In formula 2, -0.1≤b≤0.4, 0.5≤c≤0.7; (2) grinding the first mixed slurry to obtain a second mixed slurry; The median particle size of the second mixed slurry is 200 to 400 nm; (3) granulating the second mixed slurry to obtain a third raw material having a median particle size of 3 to 4 μm; (4) Sintering the third raw material under a protective atmosphere at a sintering temperature of 650-670° C., a sintering time of 6-8 h, and a heating rate of 3-8° C. / min to obtain the positive electrode active material.

6. The method for preparing a positive electrode active material according to claim 5, wherein: In step (1), the first raw material also includes lithium iron phosphate Li3Fe2(PO4)3 and lithium manganese phosphate LiMnPO4; The first raw material comprises, by weight percentage, 75-84 wt % of lithium iron manganese phosphate, 7-10 wt % of lithium iron phosphate, and 9-15 wt % of lithium manganese phosphate; And / or, the first raw material accounts for 10-15% of the theoretical generated mass of the positive electrode active material.

7. The method for preparing a positive electrode active material according to claim 5 or 6, wherein: In step (1), the second raw material further includes a carbon source; the carbon source accounts for 8 to 12% of the total mass of the theoretical generated mass of the positive electrode active material and the first raw material.

8. The method for preparing a positive electrode active material according to any one of claims 5 to 7, wherein: In step (2), the grinding includes a first grinding and a second grinding; The first grinding has a grinding speed of 1400-1700 r / min and a grinding time of 50-70 min; The second grinding has a grinding speed of 1600-2000 r / min and a grinding time of 50-70 min.

9. A positive electrode sheet, wherein: The invention comprises the positive electrode active material according to any one of claims 1 to 4 or comprises the positive electrode active material prepared by the method for preparing the positive electrode active material according to any one of claims 5 to 8.

10. A lithium ion battery, wherein: The positive electrode active material comprises the positive electrode active material according to any one of claims 1 to 4, or the positive electrode active material prepared by the method for preparing the positive electrode active material according to any one of claims 5 to 8, or the positive electrode sheet according to claim 9.

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