Positive electrode material and preparation method thereof, lithium ion battery and electric device

Abstract

The invention relates to a positive electrode material and a preparation method thereof, a lithium ion battery and a power utilization device, the positive electrode material comprises an inner core and a carbon coating layer coating the surface of the inner core, and the inner core comprises LiyFeaMebPO4; the positive electrode material satisfies the following conditions: 0.50 lt; sigma < lt >; 0.90, 0.90; the carboxyl group content is 0.002 mmol / g to 0.02 mmol / g; wherein sigma is the geometric standard deviation of the sub-grain size sample of the positive electrode material, which is obtained by utilizing the cumulative probability characteristic of logarithmic normal distribution. The positive electrode material can well consider the compaction density, the specific capacity, the high-temperature cycle performance, the low-temperature performance and the safety performance, and meanwhile has good machinability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of lithium ion batteries, and particularly relates to a positive electrode material and a preparation method thereof, a lithium ion battery and an electric device. BACKGROUND

[0002] In today's development of battery technology, improving the energy density of the battery is a key research direction. As an important lithium ion battery positive electrode material, lithium iron phosphate has the advantages of high safety and long cycle life, and is widely used in electric vehicles, energy storage and other fields. However, the lithium iron phosphate synthesized by the high-temperature solid phase method has the problems of incompatible compaction density, specific capacity and cycle performance. Therefore, it has important practical significance to develop a positive electrode material with good comprehensive performance in terms of compaction density, cycle performance and capacity. SUMMARY

[0003] The present application aims to at least solve one of the technical problems in the related art. To this end, the present application provides a positive electrode material with good comprehensive performance, a preparation method thereof, a lithium ion battery and an electric device.

[0004] In a first aspect, the present application provides a positive electrode material. According to an embodiment of the present application, the positive electrode material comprises an inner core and a carbon coating layer coated on the surface of the inner core, and the inner core comprises a compound as follows: Li y Fe a Me b PO4 wherein 0.950≤a≤0.990, 0.001≤b≤0.1, 1.000≤y≤1.080; Me comprises at least one of Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, Gd; The positive electrode material satisfies: 0.50<σ<0.90; The carboxyl content is 0.002 mmol / g to 0.02 mmol / g; wherein σ is the geometric standard deviation of the subgrain size sample of the positive electrode material obtained by using the cumulative probability characteristics of the logarithmic normal distribution, σ = ln(C 90 / C 10 ) / (2×z 0.9 ), z 0.9 is the 90% quantile of the standard normal distribution, z 0.9 =1.282, C 10 , C 90These are the subgrain sizes corresponding to the cumulative volume percentage of the subgrain size of the cathode material reaching 10% and 90%, respectively.

[0005] According to embodiments of this application, the cathode material satisfies at least one of the following conditions: 0.55 < σ < 0.85; The carboxyl content is 0.002 mmol / g to 0.01 mmol / g.

[0006] According to embodiments of this application, the cathode material satisfies: 60nm≤C 10 ≤180nm; 140nm≤C 50 ≤300nm; 300nm≤C 90 ≤600nm; Among them, C 50 It is the subgrain size corresponding to when the cumulative volume percentage of the subgrain size of the cathode material reaches 50%.

[0007] According to embodiments of this application, the cathode material satisfies at least one of the following conditions: The primary particle size of the positive electrode material is 0.15 μm to 0.30 μm, preferably 0.17 μm to 0.23 μm; The proportion of primary particles with a primary particle size of no more than 0.3 μm in the cathode material is >50%, preferably >60%; The K of the positive electrode material 90 =(D 90 -D 10 ) / D 50 The value is 1.00~5.00, preferably 1.50~4.50; D 10 D 50 D 90 These are the particle sizes corresponding to the cumulative volume percentage of the positive electrode material reaching 10%, 50%, and 90%, respectively.

[0008] According to embodiments of this application, the cathode material satisfies at least one of the following conditions: The particle sphericity of the positive electrode material is 0.50~0.90, preferably 0.7~0.90; The aspect ratio of the positive electrode material particles is 0.1~2, preferably 0.5~1.7; The 3T compaction density of the cathode material is 2.47 g / cm³. 3 ~2.5 g / cm 3 ; The powder resistance of the positive electrode material is less than or equal to 20 Ω cm. The carbon content of the positive electrode material is 1.0wt%-5.0wt%.

[0009] In a second aspect, the application provides a method for preparing the positive electrode material described above. According to an embodiment of the application, the method comprises: mixing and grinding an iron source, a phosphorus source, an organic acid, a lithium source, a first carbon source, an additive containing an element Me, and a first solvent to obtain a first slurry; spray drying the first slurry to obtain a spray material; first sintering the spray material to obtain a precursor; mixing the spray material and a carboxylated carbon source, and second sintering to obtain the positive electrode material; the element Me includes at least one of Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, Gd. The method has the advantages of easy-to-obtain raw materials, simple process, low cost, etc., and is suitable for large-scale industrial production.

[0010] According to an embodiment of the application, the carboxylated carbon source is prepared by the following steps: adding a second carbon source to a strong acid with a mass concentration of 30%-70% and stirring for 2h-5h, and then washing and drying to obtain the carboxylated carbon source; Preferably, the strong acid comprises at least one of nitric acid, sulfuric acid, and hydrochloric acid.

[0011] According to an embodiment of the application, the method satisfies at least one of the following conditions: The grinding comprises sand grinding and ultra-fine grinding in sequence, wherein the D 50 of the product of the sand grinding is 1.0 µm-8.0 µm, preferably 1.0 µm-4.0 µm, and more preferably 1.5 µm-3.5 µm; and the D 50 of the first slurry is 0.2 µm-0.6 µm; The molar ratio Li / Me of the lithium element in the lithium source to the element Me in the additive is 1.01-1.08:1; The molar ratio P / Me of the phosphorus element in the phosphorus source to the element Me in the additive is 1.00-1.07:1, and preferably 1.02-1.05:1; The mass ratio of the organic acid to the phosphorus source is 0.001-0.1:1, and preferably 0.01-0.08:1.

[0012] According to an embodiment of the application, the method satisfies at least one of the following conditions: The temperature of the first sintering is 500°C-900°C; The first sintering time is 5h-15h, preferably 7h-10h.

[0013] According to the embodiments of the present application, the method meets at least one of the following conditions: The second sintering temperature is 150℃-350℃; The second sintering time is 2h-5h; The mass ratio of the precursor and the carboxylated carbon material is 1:0.0001-0.1, preferably 1:0.002-0.02.

[0014] According to the embodiments of the present application, the method meets at least one of the following conditions: The iron source includes at least one of anhydrous ferric phosphate, dihydrate ferric phosphate, iron powder, diiron trioxide, triiron tetroxide and ferric nitrate; The phosphorus source includes at least one of anhydrous ferric phosphate, dihydrate ferric phosphate, industrial-grade phosphoric acid, food-grade phosphoric acid, electrical-grade phosphoric acid or electronic-grade phosphoric acid; The organic acid includes at least one of formic acid, acetic acid, oxalic acid, citric acid, malic acid, tartaric acid and ascorbic acid; The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, lithium acetate, lithium oxalate and lithium nitrate; The first carbon source includes at least one of glucose, sucrose, starch, cellulose, organic carboxylic acid, polyethylene glycol, polyvinyl alcohol and polyethylene; The additive includes an oxide of Me element; The carboxylated carbon source includes at least one of carbon black with carboxyl group, graphite with carboxyl group, carbon nanotube with carboxyl group and carbon fiber with carboxyl group.

[0015] In a third aspect, the present application provides a lithium ion battery. According to the embodiments of the present application, the lithium ion battery includes the positive electrode material described above. The lithium ion battery has all the features and advantages of the positive electrode material described above, which will not be repeated here.

[0016] In a fourth aspect, the present application provides a power-using device. According to the embodiments of the present application, the power-using device includes the positive electrode material described above or the lithium ion battery described above. The power-using device has all the features and advantages of the positive electrode material described above or the lithium ion battery described above, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 FIG. 1 is an SEM photo of the positive electrode material of Example 1 of the present application.

[0018] Figure 2 FIG. 2 is a subgrain size distribution diagram of the positive electrode material of Example 1 of the present application.

[0019] Figure 3 These are the capacity-voltage curves of the lithium-ion batteries of Example 1 and Comparative Example 1 of this application. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] In a first aspect, this application provides a cathode material. According to an embodiment of this application, the cathode material includes a core and a carbon coating layer covering the surface of the core, wherein the core comprises the following compounds: Li y Fe a Me b PO4 Where, 0.950≤a≤0.990, 0.001≤b≤0.1, 1.000≤y≤1.080; Me includes at least one of Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, and Gd; The cathode material satisfies: 0.50 < σ < 0.90; The carboxyl content is 0.002 mmol / g to 0.02 mmol / g; Where σ is the geometric standard deviation of the subgrain size sample of the cathode material obtained using the cumulative probability characteristics of the log-normal distribution, σ=ln(C 90 / C 10 ) / (2×z 0.9 ), z 0.9 It is the 90th quantile of the standard normal distribution, z 0.9 =1.282; C 10 C 90 These are the subgrain sizes corresponding to the cumulative volume percentage of the subgrain size of the cathode material reaching 10% and 90%, respectively.

[0022] The cathode material of this application can achieve a good balance between compaction density, specific capacity, high-temperature cycling performance, low-temperature performance and safety performance, while also having good processability.

[0023] Specifically, when σ meets the above-mentioned range, the particle size distribution is uniform, there are fewer voids during stacking, and the compaction density of the cathode material is higher. Simultaneously, the reaction area of ​​the cathode material particles is uniform, the lithium-ion diffusion path is consistent, and battery polarization is smaller, thus improving cycle stability and rate performance. Furthermore, during coating and compaction processes, the cathode material has consistent flowability, making it less prone to problems such as uneven thickness and powder shedding, resulting in strong process controllability. If σ is too small or too large, there may be too much fine powder in the cathode material, increasing the specific surface area, making it prone to moisture absorption and agglomeration, leading to increased electrode impedance; or too much coarse powder in the cathode material results in large voids during stacking, low compaction density, and may puncture the separator, causing safety risks.

[0024] When the carboxyl group content in the cathode material is within the aforementioned range, the carbon material can be strongly bonded to the core surface. The high elastic modulus of the carbon coating provides mechanical support for the cathode material, buffers stress changes, reduces the probability of breakage, and increases the compaction density. Effective bonding between the carbon material and the core also isolates the electrolyte, reducing corrosion from acidic substances like HF. Simultaneously, the carbon material provides good ionic conductivity, improving lithium-ion transport performance and reducing impedance. If the carboxyl group content is too low, the bonding between the core and the carbon coating will be poor, causing the carbon coating to detach during transportation or processing, failing to achieve the desired effect. If the carboxyl group content is too high, the excess carboxyl groups can undergo side reactions with HF, accelerating electrolyte decomposition and transition metal dissolution, and exacerbating battery gas production.

[0025] The above-mentioned effects work together to enable the cathode material to better balance different properties, thereby achieving high compaction density, good high-temperature cycling performance, low-temperature performance, and safety performance.

[0026] In some embodiments, 0.50 < σ < 0.90, specifically, 0.55 < σ < 0.85. As a specific example, σ can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or any range between two of these. This can further improve the compaction density of the cathode material, enhance the cycle stability and rate performance of the battery, and further improve process controllability.

[0027] In some embodiments, the carboxyl content of the cathode material is 0.002 mmol / g to 0.02 mmol / g, specifically 0.002 mmol / g to 0.01 mmol / g. As an example, the carboxyl content of the cathode material can specifically be 0.002 mmol / g, 0.003 mmol / g, 0.004 mmol / g, 0.005 mmol / g, 0.006 mmol / g, 0.007 mmol / g, 0.008 mmol / g, 0.009 mmol / g, 0.01 mmol / g, 0.011 mmol / g, 0.012 mmol / g, 0.015 mmol / g, 0.018 mmol / g, 0.02 mmol / g, or any range between two of these. This can further improve the compaction density of the cathode material, reduce its impedance, enhance ion transport performance, and reduce side reactions, thereby improving the cycle stability and rate performance of the battery.

[0028] According to embodiments of this application, the cathode material satisfies: 60nm ≤ C 10 ≤180nm, specifically, C 10 It can be 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm or any two of them.

[0029] According to embodiments of this application, the cathode material satisfies: 140nm ≤ C 50 ≤300nm, specifically, C 50 It can be a range of 140nm, 150nm, 180nm, 200nm, 220nm, 250nm, 280nm, 300nm, or any two of them. Where C... 50 It is the subgrain size corresponding to when the cumulative volume percentage of the subgrain size of the cathode material reaches 50%.

[0030] According to embodiments of this application, the cathode material satisfies: 300nm ≤ C 90 ≤600nm, specifically, C 90 It can be 300nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm or any two of them.

[0031] In this article, C 10 C 50 C 90The powder X-ray diffraction pattern of the cathode material can be determined by CuKα-ray powder X-ray diffraction, and then the subgrain size can be obtained by the FundamentalParameter fitting algorithm.

[0032] The cathode material satisfies the above C 10 C 50 C 90 This indicates that the subgrain size distribution of the cathode material is uniform, resulting in fewer voids during stacking and a higher compaction density. At the same time, the subgrain reaction area of ​​the cathode material is uniform, the lithium-ion diffusion path is consistent, and the battery polarization is smaller, thereby improving cycle stability and rate performance. Furthermore, the cathode material has consistent fluidity during coating, compaction, and other processes, making it less prone to problems such as uneven thickness and powder shedding, resulting in strong process controllability.

[0033] According to embodiments of this application, the primary particle size of the cathode material is 0.15 μm to 0.30 μm, specifically 0.17 μm to 0.23 μm, and more specifically, it can be within the range of 0.15 μm, 0.18 μm, 0.2 μm, 0.22 μm, 0.23 μm, or any two of these ranges. Therefore, the cathode material can achieve multi-scale morphology control from nanoscale primary structures to micrometer-scale secondary structures, possessing a suitable primary particle distribution, which can improve compaction density and reduce the problems of large particle gaps and uneven filling of small particles, thereby achieving a balance between high electrochemical performance and processability.

[0034] In this paper, the primary particle size refers to the average of the length and width of the minimum bounding rectangle of the primary particle (i.e., primary particle size = (length of minimum bounding rectangle + width of minimum bounding rectangle) / 2). It can be obtained by taking three 10K images at 10KV using a Thermo Fisher scanning electron microscope, model Apreo 2, and using intelligent image analysis software to identify and detect the primary particle.

[0035] According to embodiments of this application, the proportion of primary particles with a primary particle size of no more than 0.3 μm in the cathode material is >50%, specifically >60%, and more specifically, it can be within the range of 51%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, or any two of these ranges. Within the above range, the diffusion path length of lithium ions is shorter, which can significantly accelerate the lithium ion diffusion rate and thus improve the electrochemical performance of the cathode material.

[0036] According to an embodiment of this application, the K of the positive electrode material 90 =(D 90 -D 10 ) / D 50The range is 1.00 to 5.00, specifically 1.50 to 4.50, and more specifically, it can be a range of 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, or any two of them. In the above K... 90 Within this range, the particle size distribution in the cathode material is relatively uniform, which can improve the compaction density to a certain extent and also improve the electrochemical performance and high-temperature cycling performance of the cathode material.

[0037] In this article, D 10 For a positive electrode material, the particle size with a volumetric cumulative distribution of 10% is D. 50 For the positive electrode material, where the volumetric cumulative distribution of the particle size is 50%, D 90 The particle size at which the volumetric cumulative distribution of the positive electrode material is 90% can be measured using a Marvern Mastersizer 3000 laser particle size analyzer.

[0038] According to embodiments of this application, the particle sphericity of the cathode material is 0.50~0.90, specifically 0.7~0.90, and more specifically, it can be within the range of 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, or any two of these ranges. This achieves multi-scale morphology control of the cathode material particles, from nanoscale primary structures to micrometer-scale secondary structures, thereby balancing high electrochemical performance and processability.

[0039] In this paper, the particle sphericity of the cathode material is calculated as 4πA / P. 2 (A is the projected area of ​​the cathode material particle, P is the perimeter of the cathode material particle, Π≈3.14). The sphericity of the cathode material particles is a parameter that measures how close the particle shape is to an ideal circle. When the particle is an ideal circle, the sphericity = 1; the more irregular the particle shape (such as needle-like, plate-like, or angular), the closer the sphericity is to 0. It can be obtained by taking three 10K images at 10KV using a Thermo Fisher scanning electron microscope, model Apreo 2, and using intelligent image analysis software to identify and detect the cathode material particles.

[0040] According to embodiments of this application, the aspect ratio of the cathode material particles is 0.1 to 2, specifically 0.5 to 1.7, and more specifically 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, 0.2, 0.5, 1, 1.2, 1.5, 1.7, or any two of these ranges. Therefore, by controlling the multi-scale morphology of the cathode material, compaction density, lithium-ion transport performance, capacity, and cycle performance are well balanced, resulting in better overall performance.

[0041] In this paper, the aspect ratio of the cathode material particles refers to the ratio of the longest axis length to the shortest axis length of the particles. It can be obtained by taking three 10K images at 10KV using a Thermo Fisher scanning electron microscope, model Apreo 2, and using intelligent image analysis software to identify and detect the cathode material particles.

[0042] According to an embodiment of this application, the 3T compaction density of the cathode material is 2.47 g / cm³. 3 ~2.5 g / cm 3 Specifically, such as 2.47 g / cm³ 3 2.48 g / cm 3 2.49 g / cm 3 2.5g / cm 3 Or a range between or any two of them. This allows for higher energy density while maintaining other performance characteristics.

[0043] In this paper, the 3T compaction density of the cathode material was measured using a Sansi Zongheng (UTM7305) compaction density meter, and a sample of 1±0.01g was weighed.

[0044] According to an embodiment of this application, the powder resistance of the positive electrode material is ≤20 Ω. cm, specifically 20 Ω cm, 18Ω cm, 15Ω cm, 12Ω cm, 10Ω The range is cm or any two of these. Therefore, it exhibits good conductivity and low impedance, which in turn facilitates better cycling and rate performance.

[0045] In this paper, the powder resistivity of the cathode material can be measured using an ST2742B automated powder resistivity tester, by weighing 0.45±0.005g of sample.

[0046] According to embodiments of this application, the carbon content of the cathode material is 1.0 wt% to 5.0 wt%, specifically 1.0 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, or any range between two of these. Therefore, the high elastic modulus of the carbon material can provide mechanical support for the cathode material, buffer stress changes, reduce the probability of breakage, and increase the compaction density. The carbon material can also isolate the electrolyte, reducing corrosion from acidic substances such as HF. Simultaneously, the carbon material provides good ionic conductivity, improving lithium-ion transport performance and reducing impedance.

[0047] In this paper, the carbon content of the cathode material can be measured using a Beijing Wanlianda CS-901B high-frequency infrared carbon-sulfur analyzer. A sample of 0.2 ± 0.05 g was weighed for testing.

[0048] In a second aspect, this application provides a method for preparing the aforementioned cathode material. According to embodiments of this application, the method includes: mixing and grinding an iron source, a phosphorus source, an organic acid, a lithium source, a first carbon source, an additive containing element Me, and a first solvent to obtain a first slurry; spray-drying the first slurry to obtain a spray material; performing a first sintering on the spray material to obtain a precursor; mixing the spray material with a carboxylated carbon source and performing a second sintering to obtain the cathode material; wherein the element Me includes at least one selected from Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, and Gd.

[0049] In the preparation method of this application, the chelating effect of the organic acid enables it to react with Fe. 3+ Li + The formation of stable complexes between metal ions restricts their free migration, preventing rapid aggregation and growth of cathode material particles and effectively controlling grain size. On the other hand, the carboxylated carbon source binds strongly to the core, while the high elastic modulus of carbon provides mechanical support, buffering stress changes, reducing breakage probability, and increasing compaction density. The effective bonding between carbon and the core also isolates the electrolyte, reducing corrosion from acidic substances like HF. Simultaneously, carbon provides good ionic conductivity, improving lithium-ion transport performance and reducing impedance. These synergistic effects result in excellent high-temperature cycling performance, low-temperature performance, and safety performance of the cathode material, while achieving high compaction density and high specific capacity. High compaction density increases the cathode material content per unit volume, while high specific capacity ensures that a unit mass of cathode material can release more electricity; together, they significantly improve the battery's energy density.

[0050] According to embodiments of this application, the iron source includes at least one selected from anhydrous ferric phosphate, ferric phosphate dihydrate, iron powder, ferric oxide, ferric oxide, and ferric nitrate. Therefore, the material is widely available and the cost is low. In some embodiments, the chemical formula of ferric phosphate is Fe. x P y O4, where x:y = 0.95~0.99:1, ferric phosphate D 50 The thickness ranges from 1μm to 5μm, while SSA is 5μm. 2 / g~3m 2 / g. This allows for a more complete reaction and improves the performance of the resulting cathode material.

[0051] According to embodiments of this application, the phosphorus source includes at least one of anhydrous ferric phosphate, ferric phosphate dihydrate, industrial-grade phosphoric acid, food-grade phosphoric acid, electrical-grade phosphoric acid, or electronic-grade phosphoric acid. Therefore, the material is widely available, has low cost, and is beneficial for improving the electrochemical performance and compaction density of the cathode material.

[0052] According to embodiments of this application, the organic acid includes at least one selected from formic acid, acetic acid, oxalic acid, citric acid, malic acid, tartaric acid, and ascorbic acid. Therefore, the material is widely available and has a low cost. Furthermore, the aforementioned organic acids can better control the grain size, obtaining cathode feed with suitable grain size, thereby improving the compaction density and electrochemical performance of the cathode material.

[0053] According to embodiments of this application, the mass ratio of the organic acid to the phosphorus source is 0.001 to 0.1:1, specifically 0.01 to 0.08:1, and more specifically 0.001:1, 0.01:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, or any range between two of these. Within the above range, the organic acid can better control the grain size, obtain a cathode feed with suitable grain size, and thus improve the compaction density and electrochemical performance of the cathode material.

[0054] According to embodiments of this application, the lithium source includes at least one selected from lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, lithium acetate, lithium oxalate, and lithium nitrate. This results in high reactivity, which is beneficial for obtaining a stable cathode material structure and better electrochemical performance, while also reducing manufacturing costs.

[0055] According to embodiments of this application, the first carbon source includes at least one of glucose, sucrose, starch, cellulose, organic carboxylic acids, polyethylene glycol, polyvinyl alcohol, and polyethylene. Therefore, the first carbon source can not only participate in the carbothermic reduction reaction as a reducing agent, but also improve the quality of the carbon coating layer, thereby improving the conductivity, rate performance, and cycle life of the cathode material.

[0056] According to embodiments of this application, the additive includes oxides of the element Me, specifically oxides of at least one element selected from Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, and Gd. This improves the structural stability of the cathode material, thereby enhancing its overall performance.

[0057] According to embodiments of this application, the molar ratio of lithium in the lithium source to Me in the additive, Li / Me, is 1.01 to 1.08:1, specifically within the ranges of 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, 1.08:1, or any two of these ranges. Therefore, the above ratio range can compensate for sintering lithium loss and suppress cation mixing, while an appropriate excess of lithium can stabilize the crystal structure, reduce the lithium-ion diffusion barrier, and improve rate performance.

[0058] According to embodiments of this application, the molar ratio of phosphorus in the phosphorus source to me in the additive, P / Me, is 1.00~1.07:1, specifically 1.02~1.05:1, and more specifically, 1:1, 1.01:1, 1.02:1, 1.03:1, 1.04:1, 1.05:1, 1.06:1, 1.07:1, or any range between two of these. This improves the surface stability of the cathode material, suppresses transition metal dissolution, and regulates lattice parameters, thereby enhancing electronic / ionic conductivity.

[0059] According to embodiments of this application, the specific type of the first solvent is not particularly limited, as long as it can effectively disperse the aforementioned raw materials. In some embodiments, the first solvent can be water, such as deionized water, pure water, etc.

[0060] According to an embodiment of this application, the grinding includes sequential sand milling and ultrafine milling, wherein the D of the product of the sand milling is... 50 The diameter is 1.0µm to 8.0µm, specifically 1.0µm to 4.0µm, and more specifically 1.5µm to 3.5µm; the D of the first slurry 50 The thickness is 0.2µm to 0.6µm. This allows for more uniform mixing of the raw materials, which is beneficial for a complete reaction.

[0061] As an example, coarse grinding can be performed first, with zirconium balls of 0.7mm~0.8mm size, for 0.5h~1h, to reduce the slurry particle size D. 50 The particle size is controlled within the range of 1.0µm to 4.0µm, specifically 1.5µm to 3.5µm; then ultrafine grinding is performed with zirconium balls of 0.3µm to 0.4mm in size, and the grinding time is 1h to 5h to obtain the first slurry, with the particle size D of the first slurry being... 50 The micrometer size should be controlled within the range of 0.2µm to 0.6µm.

[0062] According to embodiments of this application, the specific operation of spray drying can be selected according to actual needs. In some embodiments, the atomization frequency of spray drying is 20Hz~70Hz, the inlet temperature of heated air is 100℃~300℃, and the outlet temperature is 50℃~150℃.

[0063] According to an embodiment of this application, the first sintering temperature is 500℃~900℃, specifically 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, or any two of these ranges. Within the above temperature range, the raw materials can react more fully to obtain the lithium iron phosphate precursor.

[0064] According to the embodiments of this application, the first sintering time is 5h to 15h, specifically 7h to 10h, or more specifically 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, or any range between two of these. Within the above time range, the reaction can be ensured to proceed sufficiently without wasting time due to excessive duration.

[0065] According to embodiments of this application, the first sintering can be performed under a protective atmosphere. As an example, the protective atmosphere can be nitrogen, helium, etc.

[0066] According to an embodiment of this application, the carboxylated carbon source is prepared by the following steps: adding a second carbon source to a strong acid with a mass concentration of 30% to 70% and stirring for 2 to 5 hours, then washing and drying to obtain the carboxylated carbon source. Thus, suitable carboxyl groups can be introduced onto the second carbon source, thereby improving the overall performance of the cathode material.

[0067] In some embodiments, the second carbon source includes at least one of carbon black, graphite, carbon nanotubes, and carbon fibers. Correspondingly, the carboxylated carbon source includes at least one of carbon black having carboxyl groups, graphite having carboxyl groups, carbon nanotubes having carboxyl groups, and carbon fibers having carboxyl groups. Treating the second carbon source with a strong acid can oxidize its surface, generating a large number of carboxyl functional groups and providing more carboxyl groups to the second carbon source.

[0068] In some embodiments, the strong acid comprises one or more of nitric acid, sulfuric acid, and hydrochloric acid. In some embodiments, the mass concentration of the strong acid is 30% to 70%, specifically 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, or any range between two of these. Thus, the acid solution has moderate oxidizing power, capable of introducing carboxyl groups onto the surface of the second carbon source without excessively corroding it, maintaining its structural integrity. If the concentration is too high, the oxidizing power is too strong, potentially leading to over-oxidation of the second carbon source and damage to its structure; if the concentration is too low, the oxidizing power may be insufficient, resulting in fewer introduced carboxyl groups.

[0069] In some embodiments, the stirring reaction time is 2 to 5 hours, specifically 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, or any range between two of these. This ensures that a suitable number of carboxyl groups are uniformly introduced onto the surface of the second carbon source. If the processing time is too short, the number of carboxyl groups generated will be too small, resulting in a weakened adsorption effect of the carboxylated carbon source; if the processing time is too long, it may waste time and resources and reduce production efficiency.

[0070] According to embodiments of this application, the mass ratio of the precursor to the carboxylated carbon material is 1:0.0001~0.1, specifically 1:0.002~0.02, and more specifically, it can be 1:0.0001, 1:0.0005, 1:0.001, 1:0.002, 1:0.003, 1:0.004, 1:0.005, 1:0.006, 1:0.007, 1:0.008, 1:0.0001, 1:0.009, 1:0.01, 1:0.02, 1:0.05, 1:0.08, 1:0.02, or any two of these ranges. Therefore, carbon materials can bond with the core with strong binding force to form a uniform carbon coating layer. At the same time, the high elastic modulus of the carbon coating layer can provide mechanical support for the cathode material, buffer stress changes in the cathode material, reduce the probability of cathode material breakage, and increase the compaction density of the cathode material. The carbon coating layer can also isolate the electrolyte and reduce the corrosion of the cathode material by acidic substances such as HF. In addition, the carbon coating layer provides good ionic conductivity, improves lithium-ion transport performance, and reduces impedance.

[0071] According to an embodiment of this application, the second sintering temperature is 150°C to 350°C, specifically 150°C, 200°C, 250°C, 300°C, 350°C, or any two of these ranges. Within the above temperature range, the precursor can be fully coated with the carboxylated carbon source to obtain a cathode material with better overall performance.

[0072] According to an embodiment of this application, the second sintering time is 2 hours to 5 hours, specifically 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, or any two of these ranges. Within this time range, the reaction can be ensured to proceed sufficiently without wasting time due to excessive duration.

[0073] A third aspect of this application provides a lithium-ion battery. According to an embodiment of this application, the lithium-ion battery includes the aforementioned positive electrode material. This positive electrode material can balance compaction density, cycle performance, rate performance, and processing performance, exhibiting superior overall performance.

[0074] According to the embodiments of this application, it can be understood that there is no particular limitation on the specific type of lithium-ion battery, which can be a primary battery or a secondary battery; the shape of the lithium-ion battery can be a cylindrical battery, a square battery or other arbitrary shape battery, etc., and according to the outer packaging, the lithium-ion battery can be a hard-shell battery, a soft-pack battery, etc.

[0075] According to the embodiments of this application, the lithium-ion battery can be a single cell, a battery module, or a battery pack. The specific structure can be carried out with reference to conventional technology, and this application has no particular limitations.

[0076] Typically, a lithium-ion battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The positive electrode, negative electrode, and separator are manufactured into a cell using winding or stacking processes. The cell and electrolyte are then housed in an outer package. During charging and discharging, lithium ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing lithium ions to pass through.

[0077] The positive electrode in this lithium-ion battery may include a positive current collector and a positive active material layer, wherein the positive active material layer is disposed on at least one side of the positive current collector.

[0078] In some embodiments, the positive current collector can be a metal current collector or a composite current collector. For example, metal current collectors include, but are not limited to, aluminum foil current collectors; composite current collectors may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. Composite current collectors can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0079] In some embodiments, the positive electrode active material layer may include positive electrode active material, binder and conductive agent, and may also include additives with specific functions and effects, such as thickeners, sodium supplements, film-forming additives, flame retardants, high temperature / low temperature stabilizers, etc., as needed.

[0080] As an example, the positive electrode active material of a lithium-ion battery may include lithium nickel cobalt manganese oxide (including but not limited to NCM811, NCM613, NCM523, etc.), lithium cobalt oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials, or lithium-ion battery positive electrode active materials commonly used in the art.

[0081] As an example, the binder in the positive electrode active material layer may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0082] As an example, the conductive agent in the positive electrode active material layer may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0083] According to an embodiment of this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located at least on one side of the negative electrode sheet, wherein the negative electrode active material layer includes a positive electrode active material.

[0084] According to an embodiment of this application, the negative current collector includes copper foil.

[0085] According to embodiments of this application, the negative electrode active material layer may include a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder.

[0086] According to embodiments of this application, the negative electrode active material may include carbon-based materials (such as artificial graphite), silicon-based materials, tin-based materials, etc.

[0087] According to embodiments of this application, the negative electrode binder in the negative electrode active material layer includes at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0088] According to embodiments of this application, the negative electrode conductive agent in the negative electrode material layer includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] In some embodiments, the diaphragm is not particularly limited and can be any known porous diaphragm with electrochemical and chemical stability, such as at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The diaphragm can be single-layered or multi-layered.

[0090] In some embodiments, the electrolyte comprises an organic solvent and an electrolyte salt. The organic solvent serves as a medium for ion transport in the electrochemical reaction, and organic solvents known in the art for use in battery electrolytes may be employed.

[0091] For example, the organic solvent can be at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). In specific embodiments, two or more of the above-mentioned organic solvents can be selected.

[0092] Exemplarily, the electrolyte salt, as the ion source, can be an electrolyte salt known in the art for use in battery electrolytes. Exemplarily, the electrolyte salt can be at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium nitrate (LiNO3), and lithium fluoride (LiF).

[0093] A fourth aspect of this application provides an electrical device comprising the aforementioned positive electrode material or the aforementioned lithium-ion battery. This electrical device incorporates all the features and advantages of the aforementioned positive electrode material or the aforementioned lithium-ion battery, which will not be elaborated upon here.

[0094] It is understood that there are no particular restrictions on the specific type of electrical device; it can be any device that uses a lithium-ion battery as a power source or energy storage unit. For example, electrical devices include, but are not limited to, electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), mobile terminals (such as mobile phones, laptops, game consoles, wearable devices, etc.), drones, aerospace equipment, satellites, ships, energy storage systems, and so on.

[0095] It is understandable that, in addition to the lithium-ion battery mentioned above, the electrical device also includes necessary structures and components, all of which can be made with reference to conventional technologies. For example, an electric vehicle may include a body, chassis, tires, navigation system, radar system, steering system, braking system, lubrication system, cooling system, driving system, etc., which will not be described in detail here.

[0096] The embodiments of this application are described in detail below.

[0097] Example 1 Step 1: Add Fe 0.97 The phosphate precursor (Fe source and P source), lithium carbonate (Li source), and titanium dioxide of PO4 were mixed with pure water in a molar ratio of Li:Fe:Ti:P = 1.05:0.97:0.008:1. 5% glucose, 3% polyethylene glycol, and 7% citric acid were added by mass of phosphate to obtain a first slurry with a solid content of 40%.

[0098] Step 2: Coarsely grind the first slurry with zircon balls of 0.7~0.8mm for 0.5~1h. The slurry particle size D... 50 The particle size was controlled at 2.00±0.02µm; then ultrafine grinding was performed with zirconium balls of 0.3~0.4mm for 2~5 hours to obtain a second slurry. The particle size D of the second slurry was... 50 The value should be controlled within 0.40±0.02µm.

[0099] Step 3: Spray dry the second slurry to obtain the precursor. The atomization frequency is 20Hz, the inlet temperature of the heated air is 120℃, and the outlet temperature is 70℃.

[0100] Step 4: The precursor obtained in Step 3 is sintered under a nitrogen atmosphere. The sintering regime is as follows: heating to 800℃ at a rate of 3℃ / min and holding for 8 hours. After sintering, the material is crushed and sieved to obtain lithium iron phosphate material.

[0101] Step 5: Add carbon black to 50% HNO3 and stir for 3 hours, then rinse and dry.

[0102] Step 6: Mix the lithium iron phosphate obtained in Step 4 and the carboxylated carbon black obtained in Step 5 at a mass ratio of 1:0.01 using a high-speed mixer until homogeneous.

[0103] Step 7: The mixture is subjected to a second sintering under a nitrogen atmosphere, with the temperature increased to 250℃ at a rate of 3℃ / min and the sintering time being 2 hours. The material is then crushed and sieved to obtain the positive electrode material.

[0104] Example 2 Same as Example 1, except that the organic acid is replaced with oxalic acid.

[0105] Example 3 Same as Example 1, except that the amount of citric acid is adjusted to 10% of the mass of anhydrous ferric phosphate.

[0106] Example 4 Same as Example 1, except that the amount of citric acid is adjusted to 0.5% of the mass of anhydrous ferric phosphate.

[0107] Example 5 Same as Example 1, except that in step six, the lithium iron phosphate obtained in step four and the carboxylated carbon black obtained in step five are mixed evenly using a high-speed mixer at a mass ratio of 1:0.1.

[0108] Example 6 Same as Example 1, except that in step six, the lithium iron phosphate obtained in step four and the carboxylated carbon black obtained in step five are mixed evenly using a high-speed mixer at a mass ratio of 1:0.001.

[0109] Example 7 Same as Example 1, except that in step seven, the mixture is subjected to a second sintering under a nitrogen atmosphere, with the temperature increased to 350°C at a rate of 3°C / min, and the sintering time is 4 hours.

[0110] Example 8 Same as Example 1, except that the amount of citric acid is adjusted to 10% of the mass of anhydrous iron phosphate. In step six, the lithium iron phosphate obtained in step four and the carboxylated carbon black obtained in step five are mixed evenly using a high-speed mixer at a mass ratio of 1:0.1.

[0111] Example 9 Same as Example 1, except that in step one, titanium dioxide is replaced with Nb2O5.

[0112] Example 10 Same as Example 1, except that in step one, titanium dioxide is replaced with V2O5.

[0113] Comparative Example 1 Same as Example 1, except that citric acid is not added in step one, and the product obtained in step four is used as the positive electrode material.

[0114] Comparative Example 2 Same as Example 1, except that the product obtained in step four is used as the positive electrode material.

[0115] Comparative Example 3 Same as Example 1, except that citric acid is not added in step one.

[0116] Comparative Example 4 Same as Example 1, except that the amount of citric acid is adjusted to 20% of the mass of anhydrous ferric phosphate.

[0117] Comparative Example 5 Same as Example 1, except that in step six, the lithium iron phosphate obtained in step four and the carboxylated carbon black obtained in step five are mixed evenly using a high-speed mixer at a mass ratio of 1:0.15.

[0118] Comparative Example 6 Same as Example 1, except that the sintering temperature in step seven is adjusted to 550°C.

[0119] Comparative Example 7 Same as Example 1, except that the sintering time in step seven is adjusted to 8 hours.

[0120] Table 1

[0121] Performance testing methods: 1. D 10 D 50 D90 The particle size distribution was obtained using a Marvern Mastersizer 3000 laser particle size analyzer.

[0122] 2. C 10 C 50 C 90 σ: Subgrain size of the cathode material was determined using CuKα-ray powder X-ray diffraction. The powder X-ray diffraction pattern was obtained by statistical analysis using the Fundamental Parameter method fitting algorithm. Wherein, C... 50 As a physical quantity representing the median of the quantity distribution, it can represent the size of the subgrain size; Using the cumulative probability property of the log-normal distribution, we derive: σ = ln(C 90 / C 10 ) / (2×z 0.9 ), where z 0.9 It is the 90th quantile of the standard normal distribution, with a fixed value z. 0.9 =1.282.

[0123] 3. Primary particle size / particle roundness / particle aspect ratio test method: Using a Thermo Fisher scanning electron microscope, model Apreo 2, three 10K images were taken at 10KV. The particles were identified using intelligent image analysis software, and the primary particle size / particle roundness / particle aspect ratio were calculated respectively.

[0124] 4. The content of carboxyl functional groups was determined by Boehm titration: 10g of cathode material powder was soaked in 50mL of 0.1M oxalic acid for 20min to remove surface Li2CO3 (to avoid interference). After filtration, the precipitate was collected and vacuum dried at 60℃ for 12h. 10g of the dried cathode material was added to 50mL of 0.05 mol / L NaHCO3 solution and shaken for 24h under nitrogen protection before filtration. 25mL of the filtrate was added to 3 drops of phenolphthalein indicator and titrated with 0.1mol / L HCl until the solution changed color. Substituting into the formula: Carboxyl content = m 样品 (V 空白 V 样品 )×C HCl / 10 V 空白 Volume of HCl consumed (mL) in titrating 50 mL of blank NaHCO3 solution. V 样品 Volume of HCl consumed in the titration of the sample (mL) C HCl HCl concentration (mol / L) Repeat the above operation 3 times and take the average value to obtain the content of carboxyl functional groups.

[0125] Table 2

[0126] Electrical performance testing methods: The battery preparation process is as follows: Positive electrode material, conductive agent carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are mixed with N-methylpyrrolidone (NMP) at a mass ratio of 96.5:1.5:2 to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated onto a current collector aluminum foil, then dried in a vacuum drying oven at 60°C for 20 hours. It is then pressed into a positive electrode sheet with a diameter of 11 mm and a thickness of 54 µm using a pressure of 100 MPa. The positive electrode sheet is then placed in a vacuum drying oven at 120°C and dried for 12 hours. A lithium metal sheet with a diameter of 15.6 mm and a thickness of 0.45 mm is used as the negative electrode; a porous polyethylene membrane with a surface coated with an alumina ceramic layer and a thickness of 25 µm is used as the separator; LiPF6 is dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) with a volume ratio of 1:1, and the molar concentration of LiPF6 is 1 mol / L; the positive electrode, separator, negative electrode and electrolyte are assembled into a 2025 type coin cell in an Ar gas glove box with a water content and oxygen content of less than 5 ppm.

[0127] 1. 0.1C initial charge / discharge specific capacity: The electrochemical performance of the R2025 coin cell was tested using the Shenzhen Xinwei Battery Testing System. The initial charge / discharge capacity test conditions were: 25℃, 0.1C charge / discharge, and voltage range of 2.5V~4.2V.

[0128] 2. 0.5C initial charge / discharge specific capacity: The electrochemical performance of the R2025 coin cell was tested using the Shenzhen Xinwei Battery Testing System. The initial charge / discharge capacity test conditions were: 25℃, 0.5C charge / discharge, and voltage range of 2.5V~4.2V.

[0129] 3. 0.1C initial charge / discharge specific capacity @ -10℃: The electrochemical performance of the R2025 coin cell was tested using the Shenzhen Xinwei Battery Testing System. The initial charge / discharge capacity test conditions were: -10℃, 0.1C charge / discharge, and voltage range of 2.5V~4.2V.

[0130] 4. High-temperature cycle retention rate: The electrochemical performance of the R2025 coin cell was tested using the Shenzhen Xinwei Battery Testing System. The charge and discharge conditions were: 45℃, 0.1C charge and discharge, voltage range of 2.5V~4.2V, 100 cycles, and the capacity retention rate was calculated.

[0131] Table 3

[0132] The data above shows that the addition of organic acid improved the particle size distribution and greatly increased the compaction density. At the same time, the use of carboxylated carbon source to form a carbon coating layer can uniformly cover the core surface, providing better ionic conductivity and improving low-temperature impedance.

[0133] Appropriate particle size allows for suitable lithium-ion transport paths, which is beneficial for increasing capacity. At the same time, it is less likely to form uncoated new interfaces and react with the electrolyte, resulting in better high-temperature cycle retention.

[0134] In addition, if the carboxyl content is too high, the high-temperature cycling performance of the cathode material will deteriorate to some extent; while if the carboxyl content is too low, the gradation effect will be poor, the carbon coating effect will be average, and the high-temperature cycling performance will be relatively poor.

[0135] In the description of this invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0136] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0137] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A positive electrode material, characterized in that, It includes a core and a carbon coating layer covering the surface of the core, the core comprising the following compounds: Li y Fe a Me b PO4 Where, 0.950≤a≤0.990, 0.001≤b≤0.1, 1.000≤y≤1.080; Me includes at least one of Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, and Gd; The cathode material satisfies: 0.50 < σ < 0.90; The carboxyl content is 0.002 mmol / g to 0.02 mmol / g; Where σ is the geometric standard deviation of the subgrain size sample of the cathode material obtained using the cumulative probability characteristics of the log-normal distribution, σ=ln(C 90 / C 10 ) / (2×z 0.9 ), z 0.9 It is the 90th quantile of the standard normal distribution, z 0.9 =1.282, C 10 C 90 These are the subgrain sizes corresponding to the cumulative volume percentage of the subgrain size of the cathode material reaching 10% and 90%, respectively.

2. The cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: 0.55 < σ < 0.85; The carboxyl content is 0.002 mmol / g to 0.01 mmol / g.

3. The cathode material according to claim 1, characterized in that, satisfy: 60nm≤C 10 ≤180nm; 140nm≤C 50 ≤300nm; 300nm≤C 90 ≤600nm; Among them, C 50 It is the subgrain size corresponding to when the cumulative volume percentage of the subgrain size of the cathode material reaches 50%.

4. The cathode material according to claim 1, characterized in that, At least one of the following conditions must be met: The primary particle size of the positive electrode material is 0.15 μm to 0.30 μm, preferably 0.17 μm to 0.23 μm; The proportion of primary particles with a primary particle size of no more than 0.3 μm in the cathode material is >50%, preferably >60%; The K of the positive electrode material 90 =(D 90 -D 10 ) / D 50 The value is 1.00~5.00, preferably 1.50~4.50; D 10 D 50 D 90 These are the particle sizes corresponding to the cumulative volume percentage of the positive electrode material reaching 10%, 50%, and 90%, respectively.

5. The positive electrode material according to claim 1, characterized in that, At least one of the following conditions must be met: The particle sphericity of the positive electrode material is 0.50~0.90, preferably 0.7~0.90; The aspect ratio of the positive electrode material particles is 0.1~2, preferably 0.5~1.7; The 3T compaction density of the cathode material is 2.47 g / cm³. 3 ~2.5 g / cm 3 ; The powder resistivity of the positive electrode material is ≤20 Ω. cm; The carbon content of the cathode material is 1.0wt%~5.0wt%.

6. A method for preparing the cathode material according to any one of claims 1 to 5, characterized in that, include: The iron source, phosphorus source, organic acid, lithium source, first carbon source, Me-containing additive and first solvent are mixed and ground to obtain the first slurry; The first slurry is spray-dried to obtain a spray-dried material; The aerosol material is subjected to a first sintering to obtain a precursor; The aerosol material and carboxylated carbon source are mixed and subjected to a second sintering to obtain the cathode material; The Me element includes at least one selected from Ti, Na, K, Mg, V, W, Nb, La, Cr, Mo, Ca, Zn, Y, Zr, Sm, Co, Ni, B, Cu, and Gd.

7. The method according to claim 6, characterized in that, The carboxylated carbon source is prepared through the following steps: The second carbon source is added to a strong acid with a mass concentration of 30% to 70% and stirred for 2 to 5 hours. Then it is washed and dried to obtain the carboxylated carbon source. Preferably, the strong acid comprises at least one of nitric acid, sulfuric acid, and hydrochloric acid.

8. The method according to claim 6, characterized in that, At least one of the following conditions must be met: The grinding process includes sequential sand milling and ultrafine milling, wherein the product of the sand milling has a D... 50 The micrometer diameter (D) is 1.0µm to 8.0µm, preferably 1.0µm to 4.0µm, and more preferably 1.5µm to 3.5µm; the D of the first slurry 50 The range is 0.2µm to 0.6µm; The molar ratio of lithium in the lithium source to Me in the additive, Li / Me, is 1.01~1.08:1; The molar ratio of phosphorus in the phosphorus source to Me in the additive, P / Me, is 1.00~1.07:1, preferably 1.02~1.05:1; The mass ratio of the organic acid to the phosphorus source is 0.001 to 0.1:1, preferably 0.01 to 0.08:

1.

9. The method according to claim 6, characterized in that, At least one of the following conditions must be met: The temperature of the first sintering is 500℃~900℃; The first sintering time is 5h to 15h, preferably 7h to 10h.

10. The method according to claim 6, characterized in that, At least one of the following conditions must be met: The second sintering temperature is 150℃~350℃; The second sintering time is 2h~5h; The mass ratio of the precursor to the carboxylated carbon material is 1:0.0001~0.1, preferably 1:0.002~0.

02.

11. The method according to claim 6, characterized in that, At least one of the following conditions must be met: The iron source includes at least one of anhydrous ferric phosphate, ferric phosphate dihydrate, iron powder, ferric oxide, ferric oxide, and ferric nitrate. The phosphorus source includes at least one of anhydrous ferric phosphate, ferric phosphate dihydrate, industrial grade phosphoric acid, food grade phosphoric acid, electrical grade phosphoric acid, or electronic grade phosphoric acid. The organic acid includes at least one of formic acid, acetic acid, oxalic acid, citric acid, malic acid, tartaric acid, and ascorbic acid; The lithium source includes at least one of lithium carbonate, lithium hydroxide, lithium phosphate, lithium dihydrogen phosphate, lithium acetate, lithium oxalate, and lithium nitrate. The first carbon source includes at least one of glucose, sucrose, starch, cellulose, organic carboxylic acids, polyethylene glycol, polyvinyl alcohol, and polyethylene; The additives include oxides of the element Me; The carboxylated carbon source includes at least one of carbon black having a carboxyl group, graphite having a carboxyl group, carbon nanotubes having a carboxyl group, and carbon fibers having a carboxyl group.

12. A lithium-ion battery, characterized in that, The cathode material includes any one of claims 1 to 5.

13. An electrical appliance, characterized in that, The cathode material included in any one of claims 1 to 5 or the lithium-ion battery as described in claim 12.

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