Cathode Material and Battery

Abstract

The present application provides a cathode material and a battery. The cathode material includes a core and a carbon material located on at least part of the surface of the core; the cathode material includes first particles with a particle size of ≤ 3 μm and second particles with a particle size of ≥ 8 μm; the cathode material is tested by Raman, and according to the Tuinstra-Koenig equation, the crystallite size of the graphite crystal along the a-axis direction on the surface of the cathode material is La, where λ is the excitation wavelength of light in the Raman test; among them, the crystallite size of the graphite microcrystal on the surface of the first particles is La1 nm, and the crystallite size of the graphite microcrystal on the surface of the second particles is La2 nm, and the cathode material satisfies: 1.3 ≤ La2 / La1 ≤ 1.91. The cathode material of the present application can have high ionic conductivity and electronic conductivity, and improve the rate performance of the cathode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of cathode materials, and particularly relates to cathode materials and batteries. Background Art

[0002] With the transformation of global energy, new clean energies such as wind energy, solar energy, and tidal energy have received extensive attention. However, these energies have problems of intermittency and uncertainty, and a energy storage device is needed to convert them into stably storable energy. As an excellent energy storage device, lithium-ion batteries can convert these new energies into electrical energy for long-term storage and stably output these power sources when needed. Lithium-ion batteries have been widely used in portable electronic products such as mobile phones, laptop computers, and cameras, and their applications in the field of electric vehicles are also becoming more and more extensive. As the cathode material of high-performance lithium-ion batteries, olivine lithium manganese iron phosphate LiMn x Fe 1-x PO4 (LMFP), lithium iron phosphate LiFePO4 (LFP), and their low conductivity limits their further applications.

[0003] Therefore, how to improve the conductivity of cathode materials is one of the problems that need to be solved urgently at present. Summary of the Invention

[0004] The present application provides a cathode material and a battery. The cathode material of the present application has both high ionic conductivity and electronic conductivity, and improves the rate performance while ensuring the capacity of the cathode material.

[0005] In a first aspect, the present application provides a cathode material, the cathode material includes a core and a carbon material located on at least a part of the surface of the core; the cathode material includes first particles with a particle size ≤ 3 μm and second particles with a particle size ≥ 8 μm;

[0006] The cathode material is tested by Raman, and the microcrystalline size of the graphite crystal along the a-axis direction on the surface of the cathode material is calculated as La according to the Tuinstra-Koenig equation, , where λ is the excitation wavelength of light in Raman testing;

[0007] wherein, the microcrystalline size of the graphite on the surface of the first particles is La1 nm, the microcrystalline size of the graphite on the surface of the second particles is La2 nm, and the cathode material satisfies: 1.3 ≤ La2 / La1 ≤ 1.91.

[0008] In some embodiments, the ratio of I D / I G on the surface of the first particles is A, and the ratio of I D / I G on the surface of the second particles is B, and 1.25 ≤ A / B ≤ 1.7.

[0009] In some embodiments, 2.6 ≤ A ≤ 3.2.

[0010] In some embodiments, 1.8 ≤ B ≤ 2.4.

[0011] In some embodiments, 5.0 ≤ La1 ≤ 6.8.

[0012] In some embodiments, 7.5 ≤ La2 ≤ 10.2.

[0013] In some embodiments, the particle size number distribution curve of the positive electrode material has a peak conforming to the Voigt function distribution, and the particle size distribution width of the particles in the range of 1.5 μm to 11 μm is Span(b), satisfying 1.7 < Span(b) < 2.4.

[0014] In some embodiments, the chemical general formula of the positive electrode material is Li n Mn x Fe y M 1-x-y PO4, where 0.9 ≤ n ≤ 1.2, 0 ≤ x < 0.8, 0.2 < y < 1, and M includes at least one of Ti, Nb, Ta, Ba, Sr, Mg, Zn, V, Mo, Y, and W.

[0015] In some embodiments, the positive electrode material includes secondary particles formed by aggregation of primary particles, wherein the particle size of the primary particles is 50 nm to 250 nm.

[0016] In some embodiments, the sphericity of the secondary particles is 0.85 to 0.90.

[0017] In some embodiments, the tap density of the positive electrode material is 1.4 g / cm 3 ~1.85 g / cm 3 .

[0018] In some embodiments, the specific surface area of the positive electrode material is 7 m 2 / g ~ 15 m 2 / g.

[0019] In some embodiments, the compaction density of the positive electrode material is 2.05 g / cm 3 ~2.35 g / cm 3 .

[0020] In some embodiments, the pH value of the positive electrode material is 9.5 to 10.5.

[0021] In some embodiments, the oil absorption value of the positive electrode material is 20 mL / 100g to 40 mL / 100g.

[0022] In some embodiments, the powder resistivity of the positive electrode material is 10 to 100 Ω·m.

[0023] In some embodiments, the mass content of carbon element in the positive electrode material is 1.4wt% to 1.7wt%.

[0024] In some embodiments, the mass content of magnetic substances in the positive electrode material is 0.1 to 0.75 mg / kg.

[0025] In a second aspect, the present application provides a battery, and the battery includes a positive electrode material.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] For the positive electrode material provided by the present application, at least part of the surface of the core of the positive electrode material is coated with a carbon material, and the graphite crystallite size La1 in the carbon material on the surface of the first particles with small particle size and the graphite crystallite size La2 in the carbon material on the surface of the second particles with large particle size. Since the electron transport path of the second particles with large particle size is long and the electron transport path of the first particles with small particle size is short, the inventor found in the research process that by controlling the graphite crystallite sizes on the surfaces of the first particles and the second particles to satisfy: 1.3 ≤ La2 / La1 ≤ 1.91, graphite crystallites with larger sizes in the a-axis direction are formed on the surface of the second particles with large particle size. The large-sized graphite crystallites in the a-axis direction can transport electrons faster. Due to ion-coupled electron transfer, the transport efficiency of lithium ions on the surface of the second particles can also be greatly improved, which is beneficial to improving the intercalation and deintercalation efficiency of lithium ions. Graphite crystallites with smaller sizes in the a-axis direction are formed on the surface of the first particles with small particle size. Since the first particles themselves have small particle sizes, the first particles can have high ion and electron transport efficiencies, and the smaller-sized graphite crystallites have little influence on the electron and ion transport of the first particles, so that the first particles and the second particles in the positive electrode material can show a high degree of lithium ion conduction consistency as a whole; in addition, the formation of smaller graphite crystallite sizes on the surface of the first particles can inhibit the growth of primary particles in the first particles and reduce the capacity attenuation caused by the excessive growth of primary particles in the first particles. Therefore, the positive electrode material of the present application has good conductivity, capacity and rate performance. Description of the Drawings

[0028] To more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0029] Figure 1 It is a schematic diagram of the discharge state of the battery provided by the embodiment of the present application.

[0030] Figure 2 It is the SEM image of the positive electrode material prepared in Example 1 of the present application;

[0031] Figure 3 It is the Raman spectrum of the positive electrode material prepared in Example 1 of the present application;

[0032] Figure 4 It is a schematic diagram of 30 test points selected for the Raman test of the positive electrode material prepared in Example 1 of the present application;

[0033] Figure 5 It is the EDS spectrum of the carbon element on the surface of the positive electrode material prepared in Comparative Example 1 of the present application. Detailed implementation manners

[0034] To better understand the technical solutions of the present application, the embodiments of the present application will be described in detail below with reference to the drawings.

[0035] It should be clear that the described embodiments are only some embodiments of the present application, rather than all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application.

[0036] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features.

[0037] For easy understanding of the present invention, specific terms are properly defined in the present application. Unless otherwise defined herein, the scientific and technical terms used in the present invention have the meanings commonly understood by those skilled in the art to which the present invention pertains.

[0038] The present application provides a positive electrode material, which includes a core and a carbon material located on at least part of the surface of the core; the positive electrode material includes first particles with a particle size ≤ 3 μm and second particles with a particle size ≥ 8 μm;

[0039] The positive electrode material is tested by Raman, and the microcrystalline size of the graphite crystal on the surface of the positive electrode material along the a-axis direction is calculated to be La according to the Tuinstra-Koenig equation, , where λ is the excitation wavelength of light in the Raman test;

[0040] Among them, the microcrystalline size of the graphite on the surface of the first particle is La1 nm, the microcrystalline size of the graphite on the surface of the second particle is La2 nm, and the positive electrode material satisfies: 1.3 ≤ La2 / La1 ≤ 1.91.

[0041] For the positive electrode material provided in this application, at least part of the surface of the core of the positive electrode material is coated with a carbon material. The microcrystalline size La1 of the graphite along the a-axis direction in the carbon material on the surface of the first particle with a small particle size and the microcrystalline size La2 of the graphite along the a-axis direction in the carbon material on the surface of the second particle with a large particle size. Since the electron transport path of the second particle with a large particle size is long and the electron transport path of the first particle with a small particle size is short, the inventor found in the research process that by controlling the microcrystalline size of the graphite on the surfaces of the first particle and the second particle to satisfy: 1.3 ≤ La2 / La1 ≤ 1.91, graphite microcrystals with a larger size along the a-axis direction are formed on the surface of the second particle with a large particle size. The large-size graphite microcrystals along the a-axis direction can transport electrons faster. Due to ion-coupled electron transfer, the transport efficiency of lithium ions on the surface of the second particle can also be greatly improved, which is beneficial to improving the intercalation and deintercalation efficiency of lithium ions. Graphite microcrystals with a smaller size along the a-axis direction are formed on the surface of the first particle with a small particle size. Since the first particle itself has a small particle size, the first particle can have a high ion and electron transport efficiency. The graphite microcrystals with a smaller size along the a-axis direction have little influence on the electron and ion transport of the first particle, so that the first particle and the second particle in the positive electrode material can show a high degree of lithium ion conduction consistency as a whole; in addition, the formation of a smaller graphite microcrystalline size on the surface of the first particle can inhibit the growth of primary particles in the first particle and reduce the capacity attenuation caused by the overgrowth of primary particles in the first particle. Therefore, the positive electrode material of this application has good conductivity, capacity and rate performance.

[0042] In some embodiments, the I D / I G value on the surface of the first particle with a particle size ≤ 3 μm is A, and the I D / I G value on the surface of the second particle with a particle size ≥ 8 μm is B, and I D / I GThe value can characterize the graphitization degree of the carbon material. In this application, by controlling 1.25 ≤ A / B ≤ 1.7, the graphitization degrees on the surfaces of the first particles and the second particles can both be controlled within a suitable range, such that the carbon material on the surface of the second particles with a large particle size has a higher graphitization degree. Electrons can rapidly transfer in the carbon material with a higher graphitization degree, which can improve the electronic conductivity and ion transport efficiency of the second particles with a large particle size. At the same time, the carbon material on the surface of the first particles with a small particle size has a relatively low graphitization degree, and the small graphite microcrystals are not sufficient to affect the excellent electronic and ion transport properties of the first particles, thereby enabling the overall cathode material to exhibit a high degree of lithium-ion conduction consistency.

[0043] Specifically, A / B can specifically be 1.25, 1.26, 1.28, 1.3, 1.35, 1.4, 1.45, 1.5, 1.56, 1.62, 1.69, 1.7 or any value therebetween, which is not limited herein. When the ratio of A / B is too large, generally, the I D / I G value on the surface of the first particles with a small particle size increases, that is, the proportion of amorphous carbon (sp3 carbon) is more, which is likely to form a poor conductive region, resulting in a decrease in the electronic conductivity of the first particles with a small particle size. At the same time, the graphite microcrystal size in the a-axis direction decreases, and the electronic conductivity of the cathode material decreases. When the ratio of A / B is too small, generally, the I D / I G value on the surface of the first particles with a small particle size decreases, that is, the carbon material on the surface of the first particles decreases, and the primary particles inside the first particles are prone to overgrowth and become large-particle-size single-crystal particles (i.e., overburning phenomenon). The large single-crystal particles have low lithium-ion transport efficiency, resulting in a decrease in the capacity of the cathode material.

[0044] In this application, by performing Raman testing on the cathode material, the cathode material has a D characteristic peak at and a G characteristic peak at , which respectively correspond to sp3 defective carbon and sp2 ordered carbon of C. By performing peak shape fitting on the Raman data, the areas of these two peaks can be obtained, that is, the I D / I G value is the ratio of the peak areas of the D characteristic peak and the G characteristic peak.

[0045] In some embodiments, the I D / I G ratio on the surface of the first particles is A, 2.6 ≤ A ≤ 3.2. The value of A can specifically be 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2 or any value therebetween, which is not limited herein.

[0046] In some embodiments, the I D / IG The ratio is B, where 1.8 ≤ B ≤ 2.4. The value of B can specifically be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, or any value between them, which is not limited herein.

[0047] In some embodiments, the size of the graphite crystallite along the a-axis direction on the surface of the first particle is La1 nm, and the size of the graphite crystallite along the a-axis direction on the surface of the second particle is La2 nm, where 1.3 ≤ La2 / La1 ≤ 1.91. La2 / La1 can specifically be 1.3, 1.35, 1.4, 1.45, 1.5, 1.55, 1.6, 1.65, 1.7, 1.75, 1.8, 1.85, 1.91, or any value between them, which is not limited herein. When La2 / La1 is too large, the difference in the size of the graphite crystallites on the surface of the second particles with large particle size and the size of the graphite crystallites on the surface of the second particles with small particle size is too large. The size of the graphite crystallites on the surface of the second particles with large particle size is too large, and the carbon coating layer on the surface of the second particles is too thick, which inhibits the lithium ion insertion / extraction performance on the surface of the second particles. At the same time, the small graphite crystallites on the surface of the first particle are not sufficient to affect the excellent electron and ion transport performance of the first particle, resulting in an increase in the difference in lithium ion insertion / extraction performance between particles of different particle sizes in the cathode material, and low lithium ion conduction consistency of the overall cathode material. When La2 / La1 is too small, the difference in the size of the graphite crystallites on the surface of the second particles with large particle size and the size of the graphite crystallites on the surface of the first particles with small particle size is small, and it is difficult to significantly improve the lithium ion insertion / extraction performance on the surface of the second particles and slightly increase the lithium ion insertion / extraction performance on the surface of the first particles at the same time, resulting in an increase in the difference in lithium ion insertion / extraction performance between particles of different particle sizes in the cathode material, and low lithium ion conduction consistency of the overall cathode material.

[0048] In some embodiments, the size of the graphite crystallite on the surface of the first particle is La1 nm, where 5.0 ≤ La1 ≤ 6.8. The value of La1 can specifically be 5.0 nm, 5.1 nm, 5.2 nm, 5.3 nm, 5.5 nm, 5.8 nm, 6.0 nm, 6.2 nm, 6.4 nm, 6.8 nm, or any value between them, which is not limited herein.

[0049] In some embodiments, the size of the graphite crystallite on the surface of the second particle is La2 nm, where 7.5 ≤ La2 ≤ 10.2. The size of the graphite crystallite can specifically be 7.5 nm, 7.8 nm, 8.0 nm, 8.5 nm, 9.0 nm, 9.5 nm, 9.8 nm, 10.0 nm, 10.2 nm, or any value between them, which is not limited herein.

[0050] In some embodiments, the chemical general formula of the cathode material is Li n Mnx Fe y M 1-x-y PO4, where 0.9 ≤ n ≤ 1.2, 0 ≤ x < 0.8, 0.2 < y < 1, and M includes at least one of Ti, Nb, Ta, Ba, Sr, Mg, Zn, V, Mo, Y, and W.

[0051] Specifically, the value of n can specifically be 0.90, 0.92, 0.95, 0.96, 0.98, 0.99, 1.0, 1.05, 1.08, 1.1, or 1.2, etc.; the value of x can specifically be 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, or 0.79, etc.; the value range of y can be 0.21, 0.28, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.85, 0.9, 0.95, or 0.99, etc. Of course, it can also be other values within the above ranges, which are not limited herein.

[0052] It should be noted that the content of each element in the positive electrode material can be measured by well-known instruments for qualitative analysis and / or quantitative analysis of each element, such as ICP and ICP-MS.

[0053] In some embodiments, the positive electrode material includes secondary particles formed by agglomeration of primary particles. Specifically, the secondary particles are spherical in structure, and the primary particles in the secondary particles are tightly combined to form secondary particles, which is beneficial to improving the tap density of the positive electrode material.

[0054] In some embodiments, the secondary particles are spherical particles. It can be understood that the surface curvature of the spherical secondary particles tends to be consistent, and the uniformity of the carbon material coating on its surface is improved, which can increase the conductivity of the particles.

[0055] In some embodiments, the sphericity of the secondary particles is 0.85 - 0.90. For irregular positive electrode material particles, local accumulation of carbon materials is likely to occur, resulting in poor conductivity in some areas, and the electron conduction between particles is easily affected. By controlling the sphericity of the secondary particles in the present application within the above range, the uniformity of the carbon material coating on the particle surface can be improved, and at the same time, the graphitization degree on the surface of particles with different particle sizes can be controlled. Under the synergistic effect of the particle sphericity and graphitization degree, the electronic conductivity of the positive electrode material can be further improved.

[0056] In some embodiments, the particle size of the primary particles is 50 nm - 250 nm, specifically it can be 50 nm, 80 nm, 100 nm, 120 nm, 140 nm, 160 nm, 200 nm, 210 nm, 230 nm, 250 nm, or any value between them, which is not limited herein.

[0057] In some embodiments, at least a part of the surface of the core has a carbon material, and the carbon material forms a coating layer. Through transmission electron microscope testing, the thickness of the carbon layer is measured to be about 2 nm to 5 nm. Forming a carbon layer on the surface of the cathode material particles is beneficial to improving the electronic conductivity.

[0058] In some embodiments, the carbon material includes amorphous carbon and graphitized carbon. That is to say, the carbon material is a metastable amorphous carbon material with sp1, sp2, and sp3 hybridizations simultaneously. Among them, sp2-ordered carbon has π bonds, and electrons can move freely within the conjugated system. Sp2-ordered carbon has better electrical conductivity than sp3-defective carbon.

[0059] In some embodiments, the core can be lithium iron phosphate or lithium manganese iron phosphate. Preferably, the core can be lithium manganese iron phosphate.

[0060] In some embodiments, the particle size number distribution curve of the cathode material has a peak conforming to the Voigt function distribution, and the particle size distribution width of the particles in the range of 1.5 μm to 11 μm is , satisfying 1.7 < < 2.4.

[0061] Specifically, it can be 1.71, 1.72, 1.80, 1.83, 1.9, 1.95, 2.0, 2.15, 2.2, 2.34, or 2.39, etc., which are not limited herein. Preferably, satisfying 1.9 < < 2.1.

[0062] The peak in the particle size range of 1.5 μm to 11 μm in the number distribution pattern conforms to the Voigt function distribution. At the same time, the sharper the peak and the narrower the full width at half maximum, the better the dispersion of the cathode material particles. The particles of different sizes fill each other, which can improve the tap density of the cathode material and the energy density of the cathode material.

[0063] In some embodiments, the specific surface area of the cathode material is 7 m² / g to 15 m² / g; specifically, it can be 7 m 2 / g, 8 m 2 / g, 9 m 2 / g, 10 m 2 / g, 11 m 2 / g, 12 m 2 / g, 13 m 2 / g, 14 m 2 / g, 15 m 2 / g or any value therebetween, which is not limited herein. Controlling the specific surface area of the cathode material within the above range, the cathode material can exhibit high capacity, first Coulombic efficiency, cycle stability and low gas generation.

[0064] In some embodiments, the tapped density of the cathode material is 1.4 g / cm 3 ~1.85 g / cm 3 , specifically, it can be 1.4 g / cm 3 , 1.45 g / cm 3 , 1.5 g / cm 3 , 1.55 g / cm 3 , 1.6 g / cm 3 , 1.65 g / cm 3 , 1.7 g / cm 3 , 1.75 g / cm 3 , 1.80 g / cm 3 , 1.85 g / cm 3 or any value therebetween, which is not limited herein. Controlling the tapped density of the cathode material within the above range is beneficial to improving the processing performance of the material and increasing the energy density of the battery.

[0065] In some embodiments, the compression density of the cathode material is 2.05 g / cm 3 ~2.35 g / cm 3 , specifically, it can be 2.05 g / cm 3 , 2.06 g / cm 3 , 2.09 g / cm 3 , 2.1 g / cm 3 , 2.12 g / cm 3 , 2.15 g / cm 3 , 2.18 g / cm 3 , 2.2 g / cm 3 , 2.22 g / cm 3 , 2.25 g / cm 3 , 2.35 g / cm 3 or any value therebetween, which is not limited herein. Controlling the compression density of the cathode material within the above range is beneficial to increasing the energy density of the battery.

[0066] In some embodiments, the pH value of the cathode material is 9.5~10.5, specifically, it can be 9.5, 9.7, 9.8, 9.9, 10.0, 10.1, 10.2, 10.4, 10.5 or any value therebetween, which is not limited herein. Controlling the pH of the cathode material within the above range is beneficial to improving the processing performance of the cathode material.

[0067] In some embodiments, the oil absorption value of the positive electrode material is 20 mL / 100g to 40 mL / 100g, and specifically may be 20 mL / 100g, 22 mL / 100g, 25 mL / 100g, 28 mL / 100g, 29 mL / 100g, 30 mL / 100g, 32 mL / 100g, 34 mL / 100g, 35 mL / 100g, 38 mL / 100g, 40 mL / 100g or any value therebetween, which is not limited herein. The oil absorption value of the positive electrode material is related to the pore ratio of the positive electrode material. During the preparation of the positive electrode paste, if the oil absorption value of the positive electrode material is too high, the amount of dispersant and binder consumed for preparing the paste will increase, that is, the mass ratio of the positive electrode material in the positive electrode paste will decrease, reducing the battery energy density and increasing the processing cost; when the oil absorption value of the positive electrode material is too low, the dispersibility of the positive electrode material in the positive electrode paste will decrease. In the present application, on the basis of not affecting the processing performance and processing cost of the positive electrode material, the oil absorption value of the positive electrode material is controlled within the above range, which is beneficial to improving the compatibility between the positive electrode material and the electrolyte, and the adsorption and wetting properties of the positive electrode material to the electrolyte are better, which can effectively reduce the interfacial resistance between the positive electrode material and the electrolyte, is beneficial to improving the transmission of lithium ions and electrons, and makes the electrochemical performance of the positive electrode material better.

[0068] In some embodiments, the powder resistivity of the positive electrode material is 10 Ω·m to 100 Ω·m, and specifically may be 10 Ω·m, 20 Ω·m, 30 Ω·m, 40 Ω·m, 50 Ω·m, 80 Ω·m, 100 Ω·m or any value therebetween, which is not limited herein.

[0069] In some embodiments, the mass content of carbon element in the positive electrode material is 1.4 wt% to 1.7 wt%; specifically may be 1.4 wt%, 1.45 wt%, 1.5 wt%, 1.55 wt%, 1.6 wt%, 1.65 wt%, 1.7 wt% or any value therebetween, which is not limited herein. If the carbon element content of the positive electrode material is too high, the capacity of the positive electrode material will decrease. If the carbon element content of the positive electrode material is too low, the integrity of the carbon layer coating on the surface of the positive electrode material will decrease, the side reaction between the positive electrode material and the electrolyte will intensify, and the electronic conductivity of the positive electrode material will decrease significantly. Controlling the mass content of carbon element in the positive electrode material within the above range in the present application is beneficial to obtaining a positive electrode material with high capacity and high electronic conductivity.

[0070] In some embodiments, the mass content of the magnetic substance in the positive electrode material is 0.1 mg / kg to 0.75 mg / kg. Specifically, it can be 0.1 mg / kg, 0.2 mg / kg, 0.3 mg / kg, 0.4 mg / kg, 0.5 mg / kg, 0.6 mg / kg, 0.7 mg / kg, 0.75 mg / kg, or any value therebetween, which is not limited herein. The magnetic substance poses a risk of triggering a short circuit. If there are excessive magnetic foreign substances in the battery positive electrode material, such as iron, chromium, nickel, etc., these foreign substances may move inside the battery and pierce the separator, resulting in a battery short circuit. In this application, the magnetic substance is controlled within the above range, which is beneficial to improving the safety of the battery prepared from the positive electrode material.

[0071] In a second aspect, the present application provides a method for preparing a positive electrode material, comprising the following steps:

[0072] S10. Pre-mix the mixed solution containing a carbon source, a dispersant, and water, then add a lithium source, a phosphorus source, an iron source, and a dopant, and stir evenly to obtain a feed solution;

[0073] S20. Grind the feed solution, add an embedding agent to obtain a slurry, and spray-dry the slurry to obtain a precursor;

[0074] S30. Sinter the precursor to obtain a positive electrode material. The sintering treatment includes a first stage, a second stage, and a third stage carried out in sequence. The sintering temperature in the first stage is 200°C to 600°C, the sintering temperature in the second stage is 650°C to 700°C, and the sintering temperature in the third stage is 750°C to 800°C.

[0075] The preparation method of the cathode material provided by the present application forms a feed liquid by wet mixing of each component, adds a dispersant to fully disperse the carbon source, and adds an embedding agent after grinding. The embedding agent can be evenly distributed on the surface of the spray material during the spraying process, which is beneficial to subsequent carbonization. A secondary particle precursor with high sphericity is prepared by spray drying, and finally sintering treatment is carried out. During the sintering process, the carbon source on the surface of the secondary particles first melts. When the temperature rises above 200 °C, the carbon source dehydrates to form coke-like compounds. After the sintering temperature is further increased, further dehydrogenation and deoxygenation occur to produce disordered hexagonal carbon planes, that is, graphite microcrystals are generated. Most of the carbon source is converted into sp3 carbon (amorphous carbon) with a disordered structure. As the sintering temperature continues to rise, some graphite microcrystal lamellae that are roughly in the same plane gradually combine into a new planar body, that is, short-range ordered sp2 carbon (graphitized carbon). In the preparation method of the present application, the embedding agent and the carbon source can cooperate with each other so that the carbon material on the surface of the sintered cathode material can have an appropriate degree of graphitization. The sintering treatment is beneficial to the transformation of more sp3 carbon to sp2 carbon. At the same time, the segmented high-temperature sintering is used to prevent the matrix material from growing excessively and causing overburning. And due to the difference in the size of the secondary particles, carbon layers with different sp3 carbon / sp2 carbon ratio components are formed on the surfaces of secondary particles with different particle sizes. Different particle sizes are suitable for appropriate degrees of graphitization, so that the first particles and the second particles in the cathode material satisfy 1.3 ≤ La2 / La1 ≤ 1.91 and 1.25 ≤ A / B ≤ 1.7, making the electronic conductivity of different particles tend to be close, so that the cathode material has both high ionic conductivity and electronic conductivity, while ensuring the capacity of the cathode material, improving the rate performance.

[0076] The preparation method of the present application is specifically introduced below in conjunction with embodiments:

[0077] S10, premix the mixed liquid containing a carbon source, a dispersant and water, then add a lithium source, a phosphorus source, an iron source and a dopant, and stir evenly to obtain a feed liquid.

[0078] In some embodiments, the carbon source includes at least one of monosaccharides, polysaccharides and soluble sugar sources.

[0079] In some embodiments, the carbon source includes at least two of polyvinyl alcohol monohydrate, ascorbic acid, galactose, maltose, arabinose, fructose, glucose and sucrose. The applicant found through testing that when using monosaccharides or soluble sugar sources alone, wall sticking may occur during the spray drying process, affecting the morphology of the particles and also the distribution of the carbon material on the particle surface. Preferably, the carbon source is a mixture of glucose monohydrate and maltose.

[0080] In some embodiments, the mass content of the carbon source in the feed liquid is 2% - 4%, specifically it can be 2%, 2.3%, 2.5%, 3%, 3.5%, 3.8%, 4% or any value therebetween, which is not limited herein. If the addition amount of the carbon source is too much, it will affect the graphitization degree of the carbon coating layer on the surface of the cathode material during the sintering process. Under the same heat, it is difficult to drive most of the sp3 carbon materials to transform into sp2 carbon materials, resulting in an increase in the proportion of sp3 carbon materials in the finally prepared cathode material, which affects the electrical conductivity and compaction performance of the cathode material. If the addition amount of the carbon source is too low, there will not be enough carbon source to effectively coat lithium iron phosphate manganese, and some lithium iron phosphate manganese materials will undergo redox reactions during the sintering process, affecting the capacity of the cathode material.

[0081] In some embodiments, the dispersant includes at least one of an anionic wetting dispersant and a polymeric hyperdispersant. Exemplarily, the anionic wetting dispersant can be sulfosuccinates, dodecyl sulfonates, citric acid, etc., and the polymeric hyperdispersant can be polyvinylpyrrolidone PVP, polyethylene glycol PEG, etc. In the technical solution of the present application, due to the addition of an appropriate amount of dispersant to the feed liquid, the presence of the dispersant can enable each component in the feed liquid to utilize the steric hindrance effect or the electrostatic stabilization mechanism to keep each component in the feed liquid relatively stable.

[0082] In some embodiments, the dispersant includes dodecyl sulfonate. The dispersant adsorbs on the surface of solid particles (such as lithium source, manganese source, etc.), reduces the surface tension between the solid and the liquid, makes the surface of the aggregated solid particles easy to be wetted. The dispersant enables the solid particles to be fully dispersed through the electrostatic force, van der Waals force or hydrogen bond acting on the particle agglomerates, and can effectively reduce the re-aggregation phenomenon of the solid particles. The dodecyl sulfonate forms a bilayer structure on the surface of the solid particles. The polar end of the outer layer dispersant has a strong affinity with water, increasing the degree of wetting of the solid particles by water. During the subsequent spray drying process, the carbon source particles are not likely to agglomerate locally, and the carbon source particles are evenly distributed around the solid particles, improving the evenness of the carbon source distribution, which is beneficial to improving the electrical conductivity of the cathode material.

[0083] In some embodiments, the molecular weight of the polymeric hyperdispersant is 800 - 2500, which is not limited herein.

[0084] In some embodiments, the lithium salt can be selected from lithium carbonate, lithium hydroxide, etc. The phosphorus source can be selected from phosphoric acid, iron phosphate, manganese phosphate, lithium iron phosphate manganese, etc. The iron source can be selected from ferrous oxalate, iron phosphate, lithium iron phosphate manganese, iron powder, etc.

[0085] In some embodiments, an appropriate amount of manganese source is further added to the feed liquid, and the manganese source can be selected from manganese tetroxide, manganese dioxide, lithium iron phosphate manganese.

[0086] In some embodiments, the addition amount of the lithium salt is 1.02 to 1.05 times the theoretical addition amount to ensure that there are sufficient lithium ions that can be deintercalated and intercalated.

[0087] In some specific embodiments, S10 specifically includes:

[0088] Adding an organic carbon source and a dispersant to a part of pure water, and stirring and mixing uniformly for the first time to obtain a first mixture;

[0089] Adding the remaining pure water and a lithium-containing phosphate or its raw material salt to the first mixture, and stirring and mixing uniformly for the second time to obtain a feed liquid.

[0090] In some embodiments, the conductivity of the pure water is ≤0.165 μs / cm.

[0091] In some embodiments, the time for the first stirring is 10 min to 20 min, and the time for the second stirring is 1 h to 2 h.

[0092] S20: After grinding the feed liquid, adding an embedding agent to obtain a slurry, and spray-drying the slurry to obtain a precursor.

[0093] In some embodiments, the grinding includes coarse grinding and fine grinding.

[0094] In some embodiments, the average particle size of the particles in the feed liquid after coarse grinding is ≤1.2 μm.

[0095] In some embodiments, the average particle size of the particles in the feed liquid after fine grinding is 0.2 μm to 0.4 μm.

[0096] It can be understood that through the coarse grinding and fine grinding treatments, the particle size in the slurry can be controlled within a suitable range, which is beneficial to improving the capacity of the cathode material and the lithium ion transmission efficiency. When the average particle size of the particles in the feed liquid after grinding is too small, these small particles are prone to overburning during the sintering process, affecting the capacity of the cathode material. When the average particle size of the particles in the feed liquid after grinding is too large, the lithium ion transmission path in the cathode material becomes longer, and the lithium ion transmission efficiency decreases. By controlling the particle size in the slurry within the above range in this application, the tap density of the particles can be increased, the compaction density of the cathode material can be improved, and the capacity and conductivity of the cathode material can also be ensured.

[0097] In some embodiments, the embedding agent includes at least one of maltodextrin and polystyrene resin. Preferably, the embedding agent is maltodextrin MD10, that is, maltodextrin with a DE value of 10, where the DE value measures the number of dehydrated α-D glucose units, i.e., the number of reducing ends. The properties of maltodextrin are directly related to the DE value. When the DE value of maltodextrin is between 4 and 6, its sugar composition consists entirely of larger molecules with four sugars or more. When the DE value is between 9 and 12, the proportion of low-molecular-weight sugars in its sugar composition is relatively small, while the proportion of high-molecular-weight sugars is relatively large. Therefore, maltodextrin is not easily affected by moisture and is difficult to brown. When the DE value is too high, it will affect the wrapping effect of maltodextrin on the active material during grinding. Therefore, maltodextrin with a DE value of 10 is selected. Maltodextrin can play a role in wrapping the active material in the slurry after fine grinding, enabling the embedding agent to be evenly distributed on the surface of the spray material during the spraying process. The embedding agent and the carbon source can work together to make the carbon material on the surface of the sintered cathode material have an appropriate degree of graphitization.

[0098] In some embodiments, the inlet air temperature of the spray drying is 210°C to 250°C, and the outlet air temperature is 95°C to 110°C. Specifically, the inlet air temperature can be 210°C, 220°C, 230°C, 240°C, 250°C or any value between them, which is not limited herein. Specifically, the outlet air temperature can be 95°C, 100°C, 105°C, 110°C or any value between them, which is not limited herein.

[0099] In some embodiments, the frequency of the induced draft fan for spray drying is 35Hz to 42Hz. Specifically, it can be 35Hz, 37Hz, 38Hz, 39Hz, 40Hz, 42Hz or any value between them, which is not limited herein.

[0100] In some embodiments, during the spray drying process, the pressure of the compressed air is 0.4 Mpa to 1Mpa. Specifically, it can be 0.4 Mpa, 0.6Mpa, 0.8Mpa, 0.9Mpa, 1Mpa or any value between them, which is not limited herein.

[0101] In some embodiments, the time for spray drying is 4h to 8h. Specifically, it can be 4h, 5h, 6h, 7h, 8h or any value between them, which is not limited herein.

[0102] In the present application, by controlling process parameters such as the inlet air temperature, time, and pressure of the compressed air for spray drying, small particles agglomerate to form secondary particles during the spray drying process, and the embedding agent and the carbon source can be evenly distributed on the surface of the secondary particles; and under the action of the dispersant, the carbon source can be more evenly dispersed in the solution and is not prone to agglomeration during spray drying, which is beneficial to the formation of a precursor with a high degree of sphericity.

[0103] S30. Sinter the precursor to obtain the cathode material. The sintering process includes a first stage, a second stage, and a third stage that are carried out in sequence. The sintering temperature in the first stage is 200°C to 600°C, the sintering temperature in the second stage is 650°C to 700°C, and the sintering temperature in the third stage is 750°C to 800°C.

[0104] In some embodiments, the sintering process is carried out in an oxygen-containing atmosphere, and the oxygen concentration in the oxygen-containing atmosphere is ≥95%.

[0105] In some embodiments, the sintering process includes a first stage, a second stage, and a third stage that are carried out in sequence. The sintering temperature in the first stage is 500°C to 600°C, the sintering temperature in the second stage is 650°C to 700°C, and the sintering temperature in the third stage is 750°C to 800°C.

[0106] In some embodiments, the temperature in the first stage is 200°C to 600°C, specifically it can be 200°C, 300°C, 400°C, 500°C, 570°C, 580°C, 600°C or any value between them, which is not limited herein.

[0107] In some embodiments, the time in the first stage is 4h to 6h, specifically it can be 4h, 5h, 5.5h, 6h or any value between them, which is not limited herein.

[0108] In some embodiments, the temperature in the second stage is 650°C to 700°C, specifically it can be 650°C, 670°C, 680°C, 700°C or any value between them, which is not limited herein.

[0109] In some embodiments, the time in the second stage is 4h to 6h, specifically it can be 4h, 5h, 5.5h, 6h or any value between them, which is not limited herein.

[0110] In some embodiments, the temperature in the third stage is 750°C to 800°C, specifically it can be 750°C, 760°C, 780°C, 790°C, 800°C or any value between them, which is not limited herein.

[0111] In some embodiments, the time in the third stage is 3h to 8h, specifically it can be 3h, 4h, 5h, 6h, 7h, 8h or any value between them, which is not limited herein.

[0112] In some embodiments, the heating rate of the sintering process is controlled at 3°C / min to 5°C / min, which can enable the carbon source material to be fully transformed into inorganic carbon and partially achieve graphitization transformation. Controlling the heating rate can also prevent the particles from growing too large, causing insufficient phenomena, etc., and ensure the capacity and conductivity of the cathode material.

[0113] During the sintering process, the carbon source on the surface of the secondary particles first melts. When the temperature rises above 200°C, the carbon source dehydrates to form coke-like compounds. After the sintering temperature is further increased, further dehydrogenation and deoxygenation occur, producing disordered hexagonal carbon planes, that is, graphite microcrystals are generated. At this time, most of the carbon source is transformed into disordered carbon, that is, sp3 carbon (amorphous carbon) with a disordered structure. As the sintering temperature continues to rise, some graphite microcrystal lamellae roughly in the same plane gradually combine into a new planar body, that is, short-range ordered sp2 carbon (graphitized carbon). In the present application, by controlling the sintering temperature and time, it is beneficial for more sp3 carbon to transform into sp2 carbon. At the same time, the use of segmented high-temperature sintering can prevent the matrix material from growing excessively, causing overburning and loss of the capacity of the cathode material. And due to the difference in the size of the secondary particles, carbon layers with different sp3 carbon / sp2 carbon ratio compositions are formed on the surfaces of secondary particles with different particle sizes.

[0114] In a third aspect, the present application provides a battery, which includes the cathode material of the first aspect above or the cathode material prepared according to the preparation method of the above cathode material.

[0115] The battery provided by the present application can be a secondary battery (such as a lithium-ion battery, a sodium-ion battery, etc.), including a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located inside the housing. The housing can be a packaging bag encapsulated with a packaging film (such as an aluminum-plastic film). For example, if the secondary battery is a soft-pack battery.

[0116] In some other embodiments, the secondary battery can also be a steel-shell battery, an aluminum-shell battery, etc.

[0117] Figure 1 It is a schematic diagram of the discharge state of the battery provided by the embodiment of the present application. As Figure 1 shown, the battery includes a housing and an electrode assembly. The electrode assembly includes a positive electrode sheet 1, a negative electrode sheet 2, and a separator 3. The separator 3 is disposed between the positive electrode sheet 1 and the negative electrode sheet 2. The electrode assembly can be a stacked structure, which is formed by alternately stacking the positive electrode sheet 1, the separator 3, and the negative electrode sheet 2 in sequence.

[0118] In some other embodiments, the electrode assembly can also be a wound structure, which is formed by winding the positive electrode sheet, the separator, and the negative electrode sheet in sequence after stacking.

[0119] In some embodiments, the positive electrode sheet 1 includes a positive electrode current collector 101 and a positive electrode active material layer 102 provided on at least one surface of the positive electrode current collector 101.

[0120] In some embodiments, the positive electrode current collector 101 can be made of aluminum foil, nickel foil, etc., or can be a composite current collector disclosed in any prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil (aluminum foil, nickel foil, etc.) and a polymer substrate. The positive electrode active material layer 102 contains a positive electrode active material, a conductive agent, and a binder. Among them, the positive electrode active material is the positive electrode material of the above first aspect or the positive electrode material prepared according to the preparation method of the above positive electrode material.

[0121] In some embodiments, the negative electrode sheet 2 includes a negative electrode current collector 201 and a negative electrode active material layer 202 provided on at least one surface of the negative electrode current collector.

[0122] In some embodiments, the negative electrode current collector 201 can be made of at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector, etc., or can be a composite current collector disclosed in any prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate.

[0123] In some embodiments, the negative electrode active material layer 202 includes a negative electrode material, and the negative electrode material includes but is not limited to artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material can be selected from at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material can be selected from at least one of elemental tin, tin oxides, and tin alloys. However, the present application is not limited to these materials, and other conventional materials that can be used as the negative electrode active material of the battery can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0124] The battery provided by the embodiment of the present application has the advantages of high capacity, high first efficiency, long cycle life, excellent rate performance, and low expansion. The battery can be a lithium-ion battery, a sodium-ion battery, a solid electrolyte battery, etc., which is not limited herein.

[0125] The embodiments of the present invention will be further described in multiple embodiments below. Among them, the embodiments of the present invention are not limited to the following specific embodiments.

[0126] Testing method:

[0127] (1) Raman test of the positive electrode material

[0128] At 140 μm Randomly select 3 - 5 particles within the range of 100 μm, with particle size ≤ 3 μm, and then take another 3 - 5 particles with particle size ≥ 8 μm; conduct Raman point scanning at the center of the particles, with the test conditions being an excitation wavelength of 532 nm, an exposure time of 60 s, a microscope objective of 50X Lwd, a detection range of 800 - 2000 cm-1, to obtain the Raman test results. The graphitization degree is obtained by calculating the area ratio of the peaks at 1340.5 cm-1 and 1599.7 cm-1 as I D / I G value.

[0129] According to the Tuinstra-Koenig equation, the crystallite size of the graphite crystal along the a-axis direction on the surface of the particles of the positive electrode material is calculated as La, , where λ is the excitation wavelength of light in the Raman test.

[0130] (2) Use Mastersizers 3000 to characterize the particle size number distribution and volume distribution of the positive electrode material. The specific method is as follows:

[0131] The particle size test method refers to GB / T 19077 - 2016. The volume-based cumulative particle size distribution can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 3000 type laser particle size analyzer from Malvern Instruments Limited in the UK.

[0132] D10 represents the particle size corresponding to when the cumulative particle size distribution percentage of the powder reaches 10%, D50 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 50%, and D90 represents the particle size corresponding to when the cumulative particle size distribution percentage reaches 90%.

[0133] Particle size distribution width is:

[0134]

[0135] The proportion parameters of particle sizes of particles with D90, D10, and D50 in the range of 1.5 μm - 11 μm.

[0136] (3) Test method for the specific surface area of the positive electrode material:

[0137] Use a specific surface area and pore size analyzer of model Tristar3020 from Micromeritics in the United States to test the specific surface area of the positive electrode material. Weigh a certain mass of powder, conduct complete degassing under vacuum heating to remove surface adsorbates, and then use the nitrogen adsorption method to calculate the specific surface area of the particles through the amount of adsorbed nitrogen, with the unit of m 2 / g.

[0138] (4) Tap density test of the positive electrode material:

[0139] Use the tap density meter (model: DAT-4-220) of Contakmer Instrument Trading (Shanghai) Co., Ltd., USA. The steps are as follows:

[0140] 1. Clean the graduated cylinder, and then weigh the mass of the graduated cylinder as m1;

[0141] 2. Add about 50 g of the sample into the graduated cylinder, try to make the surface of the sample horizontal, and wipe the surroundings with a paper towel;

[0142] 3. Weigh the total mass of the sample and the graduated cylinder as m2;

[0143] 4. Place the graduated cylinder on the vibration platform and fix it with three symmetric fixing feet;

[0144] 5. Turn on the instrument, set the number of vibrations to 5000 times; turn on the vibration switch, and the instrument will stop automatically after vibrating to the specified number of times;

[0145] 6. Take out the graduated cylinder and read the volume of the sample. If the surface of the sample is horizontal after tapping, directly read the volume; if it is in an inclined state, take the average value V of the readings at the highest point and the lowest point; Tap density = (m2 - m1) / V, unit: g / cm 3 .

[0146] (5)Testing method for tap density of cathode material:

[0147] The tap density of the cathode material is tested by using a tap density tester of model 4350 from Carver Company, USA. The steps are as follows: Weigh 1 g of the sample and put it into the mold, press it with a pressure of 3 T for 30 s, and measure the height after pressing to calculate the tap density, unit: g / cm 3 .

[0148] (6)IPC testing method for cathode material:

[0149] Take 0.3 g of the sample to be tested, dissolve it with aqua regia, cool and make the volume constant to 100 ml to prepare a determination mother liquor; Take 1 mL of the determination mother liquor, dilute it 100 times, and then test the contents of the main elements Li, Ni, Co, Mn and other elements such as doping elements by ICP. The determination is carried out by using an Agilent 5110 ICP-OES detection device.

[0150] (7)Testing method for oil absorption value of cathode material:

[0151] The oil absorption value is tested by using an oil absorption value tester of model ASAHI S-500 from ASAHI Metal Industry Co., Ltd., Japan. The oil absorption value is the amount of linseed oil added when the torque generated by the viscosity change reaches 70% of the maximum torque, unit: mL / 100 g.

[0152] (8) Test method for powder resistivity of the positive electrode material:

[0153] The powder resistivity of the positive electrode material is measured by a resistivity tester (Suzhou Jingge Electronics ST-2255A).

[0154] (9) Mass content of carbon element in the positive electrode material:

[0155] The sample is burned in a high-temperature oxygen stream by combustion-infrared absorption method, and carbon is converted into carbon dioxide ( ), and the concentration of is detected by infrared absorption spectroscopy, so as to calculate the carbon content. The specific operations include: the solid positive electrode material sample needs to be ground into uniform powder, placed in a high-temperature furnace (2000 °C), and oxygen is introduced to assist combustion. Carbon is completely oxidized to generate : the gas after combustion is passed through a purification device (such as a dust removal tube, desulfurizing agent) to remove interfering substances (such as , ). The gas enters the infrared detection cell, and infrared light of a specific wavelength is absorbed by . According to Lambert-Beer's law, the concentration of is calculated through absorbance, and then converted into the mass content of carbon element.

[0156] (10) pH value test of the positive electrode material:

[0157] Take about 5 g of the positive electrode material sample, add 45 mL of water, ultrasonicate for 5 min, then take it out and let it stand for 10 min. After calibrating the pH meter, insert the combined electrode into the upper clear liquid to be measured. According to the potential difference between the measuring electrode and the reference electrode, calculate the pH value of the solution.

[0158] (11) Test for the mass content of magnetic substances in the positive electrode material:

[0159] Weigh 200 ± 5 g of the sample into a 500 ml plastic wide-mouth bottle, add a cleaned magnetic bar and 300 ml of anhydrous ethanol to the wide-mouth bottle, cover the bottle cap, stir on a stirrer for 30 min, and use the magnetic bar to adsorb magnetic metal elements such as iron, nickel, chromium, and zinc in the material. Open the bottle cap, align the mouth of a cleaned conical flask with the mouth of the wide-mouth bottle, and use another magnetic bar outside the wide-mouth bottle to transfer the magnetic bar in the wide-mouth bottle to the conical flask, clean the non-magnetic materials remaining on the magnetic bar in the conical flask, add 6 mL of hydrochloric acid and 2 mL of nitric acid, heat on a hot plate for about 30 minutes, and after filtration and volume fixation, detect the content of magnetic substances by an inductively coupled plasma optical emission spectrometer (ICP-OES).

[0160] (12) Sphericity test:

[0161] According to the properties of the sample, the wet circulation module LIXELL is selected for dispersion to break the sample into individual particles, ensuring that the particles do not block or overlap each other within the test area, thus obtaining clear particle images. The stroboscopic light emitted from the stroboscopic light source becomes parallel light after passing through the beam expander and irradiates the well-dispersed individual particles in the test area. Through a proprietary optical imaging system, the images of the particles are projected onto the CMOS of the high-speed imaging system and captured at a rate of up to 500 frames per second to obtain clear images of each particle. The collected particle images are processed and analyzed using analysis software. The software automatically calculates the sphericity of each particle according to a preset algorithm. The sphericity is determined by comparing the actual surface area of the particle with the surface area of a perfect sphere of the same volume, and its calculation formula is: Sphericity = (square of the perimeter) / (4π×area). The closer the value of the sphericity is to 1, the closer the particle is to a perfect sphere.

[0162] (13)Electrochemical performance test:

[0163] The cathode material is mixed with conductive carbon black and binder PVDF (polyvinylidene fluoride) at a mass ratio of 80:10:10, then NMP (N-methylpyrrolidone) is added to make a uniform slurry. The slurry is evenly coated on aluminum foil and dried in an oven at 100°C for 12 h. After drying, it is rolled under a pressure of 10 Mpa and cut into circular electrodes with a diameter of 14 mm. The anode uses a Li metal sheet with a diameter of 14 mm. A lithium-ion battery is assembled according to the industrial CR2025 type button battery. The separator is a Cellgard separator, and the electrolyte uses an equal mixture of ethylene carbonate (EC), polycarbonate (PC), and diethyl carbonate (DEC) with 1 mol / L LiPF6 as the electrolyte. The positive electrode, separator, negative electrode, and electrolyte are assembled into a button battery in an Ar gas glove box with a water content and oxygen content both less than 0.5 ppm.

[0164] Capacity test regime: The BlueTEC test system is used for electrical performance testing (charging and discharging voltages are 2.0 - 3.75 V, temperature condition is 25°C). The current magnitude in the first three cycles is 0.1C, and then the current is increased to 1C to measure the first-cycle capacity, discharge specific capacity, and first Coulombic efficiency.

[0165] The test results are shown in Table 2.

[0166] Example 1

[0167] (1) Add 10 kg of pure water into the ball milling tank, add fructose and maltose with a total mass of 3 wt% of the iron source and manganese source as carbon sources, where the mass ratio of fructose to maltose is 5:5. Then add polyethylene glycol PEG with a total mass of 1 wt% of the iron source and manganese source as a dispersant. After ball milling and stirring for 20 minutes, a first mixture is obtained. Add manganese tetraoxide, iron phosphate, and titanium dioxide into the first mixture according to the molar ratio of n(Mn):n(Fe):n(Ti) = 0.6:0.39:0.01. Then add phosphoric acid to supplement the lacking phosphorus source and 2 wt% excess lithium carbonate as the lithium source, and continue high-speed ball milling to control the D50 of the slurry after fine grinding to be 0.3μm ± 0.02μm.

[0168] (2) After fine grinding, based on the total mass of the iron source and manganese source being 100 wt%, add 1 wt.% of maltodextrin with a DE value of 10, and stir for another 10 minutes to obtain a spray slurry. Pump the slurry into a spray dryer through a peristaltic pump. Control the inlet air temperature at 230°C, the outlet air temperature at 100°C, the frequency of the induced draft fan at 42 Hz, the compressed air at 0.3 MPa, and the frequency of the atomizer at 350 Hz. Prepare spherical precursors with a D50 of 8 ± 2μm by spray drying with a two-fluid spray dryer.

[0169] (3) Place the spherical precursors in a nitrogen atmosphere for sintering. Control the heating rate at 3 °C / min, and keep them at 400°C, 700°C, and 750°C for 6 hours, 5 hours, and 5 hours respectively, and then cool to obtain the cathode material.

[0170] The cathode material prepared in Example 1 of this application includes lithium iron manganese phosphate and a carbon layer on the surface of lithium iron manganese phosphate. The chemical general formula of the cathode material is LiMn 0.6 Fe 0.39 Mg 0.01 PO4·C.

[0171] Figure 2 is the SEM image of the cathode material prepared in Example 1 of this application. As Figure 2 shown, the cathode material particles are spherical particles. Figure 3 is the Raman spectrum of the cathode material prepared in Example 1 of this application. As Figure 3 shown, 30 particles are selected for Raman testing. Figure 4 is the schematic diagram of 30 test points selected for Raman testing of the cathode material prepared in Example 1 of this application, and the particle size of the corresponding particles is obtained from the figure.

[0172] Example 2

[0173] The difference from Example 1 is:

[0174] (2) After fine grinding, based on the total mass of the iron source and the manganese source being 100 wt%, 0.5 wt.% of maltodextrin with a DE value of 10 was added, and after stirring for another 10 minutes, a spray slurry was obtained.

[0175] Example 3

[0176] Different from Example 1:

[0177] (2) After fine grinding, based on the total mass of the iron source and the manganese source being 100 wt%, 1.5 wt.% of maltodextrin with a DE value of 10 was added, and after stirring for another 10 minutes, a spray slurry was obtained.

[0178] Example 4

[0179] Different from Example 1:

[0180] (3) The lithium iron manganese phosphate precursor was sintered in a nitrogen atmosphere, the heating rate was controlled at 3 °C / min, and it was held at 400 °C, 700 °C, and 750 °C for 6 hours, 5 hours, and 3 hours respectively. Through gradient temperature setting, the organic carbon in the material was fully converted into inorganic carbon and graphitized, and the cathode material was obtained after cooling.

[0181] Example 5

[0182] Different from Example 1:

[0183] (3) The lithium iron manganese phosphate precursor was sintered in a nitrogen atmosphere, the heating rate was controlled at 3 °C / min, and it was held at 400 °C, 700 °C, and 750 °C for 6 hours, 5 hours, and 7 hours respectively. Through gradient temperature setting, the organic carbon in the material was fully converted into inorganic carbon and graphitized, and the cathode material was obtained after cooling.

[0184] Example 6

[0185] Different from Example 1:

[0186] (3) The lithium iron manganese phosphate precursor was sintered in a nitrogen atmosphere, the heating rate was controlled at 3 °C / min, and it was held at 400 °C, 700 °C, and 770 °C for 6 hours, 5 hours, and 5 hours respectively. Through gradient temperature setting, the organic carbon in the material was fully converted into inorganic carbon and graphitized, and the cathode material was obtained after cooling.

[0187] Example 7

[0188] Different from Example 1:

[0189] (3) Sinter the lithium iron manganese phosphate precursor in a nitrogen atmosphere, control the heating rate at 3 °C / min, hold for 6 hours at 400 °C, 5 hours at 700 °C, and 5 hours at 730 °C. Through gradient temperature setting, the organic carbon in the material is fully converted into inorganic carbon and graphitized, and then cooled to obtain the cathode material.

[0190] Example 8

[0191] Different from Example 1: (1) Add 10 kg of pure water into the ball mill tank, add fructose and maltose accounting for 4 wt% of the total mass of the iron source as carbon sources, where the mass ratio of fructose to maltose is 5:5, and then add polyethylene glycol PEG accounting for 1 wt% of the total mass of the iron source as a dispersant. After ball milling and stirring for 20 minutes, obtain the first mixture. Add manganese tetraoxide, iron phosphate, and titanium dioxide into the first mixture according to the molar ratio n(Mn):n(Fe):n(Ti) = 0.6:0.39:0.01, and then add phosphoric acid to supplement the lacking phosphorus source and 2 wt% excess lithium carbonate as the lithium source, and continue high-speed ball milling, controlling the D50 of the slurry after fine grinding to be 0.3 μm ± 0.02 μm.

[0192] Example 9

[0193] Different from Example 1:

[0194] (2) After fine grinding, taking the total mass of the iron source and manganese source as 100 wt%, add 1 wt. % of maltodextrin with a DE value of 10, and stir for another 10 minutes to obtain the spray slurry. Pump the slurry into the spray dryer through a peristaltic pump, control the inlet air temperature at 230 °C, the outlet air temperature at 100 °C, the frequency of the induced draft fan at 42 Hz, the compressed air at 0.7 MPa, and the frequency of the atomizer at 350 Hz. Prepare spherical precursors with D50 at 8 ± 2 μm by spray drying with a two-fluid spray dryer.

[0195] Example 10

[0196] Different from Example 1:

[0197] (1) Add 10 kg of pure water into the ball mill tank, add fructose and maltose accounting for 4 wt% of the total mass of the iron source as carbon sources, where the mass ratio of fructose to maltose is 5:5, and then add polyethylene glycol PEG accounting for 1 wt% of the total mass of the iron source as a dispersant. After ball milling and stirring for 20 minutes, obtain the first mixture. Add iron phosphate and titanium dioxide into the first mixture according to the molar ratio n(Fe):n(Ti) = 0.99:0.01, and then add phosphoric acid to supplement the lacking phosphorus source and 2 wt% excess lithium carbonate as the lithium source, and continue high-speed ball milling, controlling the D50 of the slurry after fine grinding to be 0.3 μm ± 0.02 μm.

[0198] (3) Place the spherical precursor in a nitrogen atmosphere for sintering. Control the heating rate at 3 °C / min, and hold for 6 hours at 400 °C, 5 hours at 720 °C, and 5 hours at 770 °C, then cool to obtain the cathode material.

[0199] Comparative Example 1

[0200] Different from Example 1:

[0201] (1) Add iron source and manganese source to the ball milling tank. Based on the total mass of the iron source and manganese source being 100 wt%, add an equal mass of pure water, and then add 3 wt% of fructose and maltose as carbon sources, where the mass ratio of fructose to maltose is 5:5. Stir for 10 minutes to evenly distribute the carbon sources in the slurry, thus obtaining the first mixture.

[0202] Comparative Example 2

[0203] Different from Example 1:

[0204] (2) Pump the finely ground spray slurry into a spray dryer through a peristaltic pump. Control the inlet air temperature at 230 °C, the outlet air temperature at 100 °C, the frequency of the induced draft fan at 42 Hz, the compressed air at 0.3 MPa, and the frequency of the atomizer at 350 Hz. Prepare spherical lithium iron manganese phosphate precursor with D50 in the range of 8 ± 2 μm by spray drying with a two-fluid spray dryer.

[0205] Comparative Example 3

[0206] Different from Example 1:

[0207] (3) Place the lithium iron manganese phosphate precursor in a nitrogen atmosphere for sintering. Control the heating rate at 3 °C / min, hold at 680 °C for 10 hours, and then cool to obtain the cathode material.

[0208] Table 1 Comparison Table of Cathode Materials of Examples and Comparative Examples

[0209]

[0210] Electrochemical tests were carried out on the coin cells containing the cathode material, and the test results are shown in Table 2 below.

[0211] Table 2 Comparison Table of Physicochemical Properties of Cathode Materials of Examples and Comparative Examples and Performance of Batteries Prepared Therefrom

[0212]

[0213] According to the test data of Examples 1 to 10 (S1 to S10), it can be seen that in this application, by controlling the graphite crystallite sizes on the surfaces of the first particles and the second particles to satisfy 1.3 ≤ La2 / La1 ≤ 1.91, graphite crystallites with larger sizes along the a-axis direction are formed on the surface of the second particles with larger particle sizes. The large-sized graphite crystallites along the a-axis direction can transfer electrons faster. Due to ionic coupled electron transfer, the transport efficiency of lithium ions on the surface of the second particles can also be greatly improved, which is beneficial to improving the intercalation and deintercalation efficiency of lithium ions. Graphite crystallites with smaller sizes along the a-axis direction are formed on the surface of the first particles with smaller particle sizes. Since the first particles themselves have smaller particle sizes, the first particles can have higher ion and electron transport efficiencies. The smaller-sized graphite crystallites along the a-axis direction have less influence on the electron and ion transport of the first particles, so that the first particles and the second particles in the cathode material can show a high degree of lithium ion conduction consistency as a whole. In addition, forming smaller graphite crystallite sizes on the surface of the first particles can inhibit the growth of primary particles in the first particles and reduce the capacity attenuation caused by the excessive growth of primary particles in the first particles. The cathode material of this application has good conductivity, capacity and rate performance.

[0214] According to the test data of Example 9 and Example 1, it can be seen that during the spray drying process, the pressure of the compressed air is too high, resulting in too large fluctuations in the particle sizes of the spherical precursors. Finally, the span value of the prepared cathode material is too large, the tap density of the cathode material decreases, and the compaction density also decreases slightly; since the proportion of particles with smaller particle sizes increases, the specific surface area of the cathode material also increases, side reactions intensify, and the capacity decreases slightly compared with Example 1.

[0215] According to the test data of Comparative Example 1 (D1) and Example 1, it can be seen that in Comparative Example 1, no dispersant is added, and the materials are only fully mixed by mechanical stirring. Figure 5 is the EDS spectrum of carbon elements on the surface of the cathode material prepared in Comparative Example 1 of this application. As Figure 5 shown, there is obvious carbon element enrichment on the surface of the cathode material. It can be seen that the uniformity of carbon material coating decreases. Due to the aggregation of carbon materials, the accuracy of Raman testing decreases, so Raman testing is not carried out. The proportion of amorphous carbon (sp3 carbon) on the surface of the cathode material particles is more, which is easy to form a poor conductive area, the powder resistivity of the cathode material increases, and the capacity and initial efficiency of the cathode material both decrease.

[0216] From the test data of Comparative Example 2 (D2) and Example 1, it can be seen that without adding a carbon source after grinding, the retained carbon source on the surfaces of both large and small particles will decrease. During the subsequent sintering process, the carbon source on the particle surface will transform from amorphous carbon to graphitized carbon as much as possible, but it is difficult to significantly increase the graphite crystallite size. In particular, the graphite crystallite size on the surface of the second particles with large particle size decreases, and the La2 / La1 ratio is too small, resulting in a decrease in the electronic conductivity of the second particles with large particle size and also a decrease in the electronic conductivity of the cathode material.

[0217] From the test data of Comparative Example 3 (D3) and Example 1, it can be seen that without using a stepwise temperature increase during the sintering process and the sintering temperature not being gradually increased, the transformation of amorphous carbon to graphitized carbon on the particle surface decreases. The graphite crystallite size on the surface of the second particles with large particle size is too large, and the difference in the graphite crystallite size between the surface of the second particles with large particle size and the surface of the second particles with small particle size is too large. The La2 / La1 ratio is too large, resulting in an increase in the difference in lithium ion insertion / extraction performance between particles with different particle sizes in the cathode material, a decrease in the electronic conductivity of the cathode material, and a decrease in the capacity of the cathode material.

[0218] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A cathode material, characterized in that, The positive electrode material includes a core and a carbon material located on at least part of the surface of the core; the positive electrode material includes first particles with a particle size ≤ 3 μm and second particles with a particle size ≥ 8 μm; The positive electrode material is tested by Raman, and according to the Tuinstra-Koenig equation, the crystallite size of the graphite crystal along the a-axis direction on the surface of the particles of the positive electrode material is calculated as La, La = (2.4×10 -10 )λ 4 (I D / I G ) -1 , where λ is the excitation wavelength of light in the Raman test, and the value of I D / I G is the ratio of the peak areas of the D characteristic peak and the G characteristic peak in the Raman test; Among them, the graphite crystallite size on the surface of the first particles is La1 nm, the graphite crystallite size on the surface of the second particles is La2 nm, and the positive electrode material satisfies: 1.3 ≤ La2 / La1 ≤ 1.

91.

2. The cathode material according to claim 1, characterized in that, The I on the surface of the first particle D / I G ratio is A, and the I on the surface of the second particle D / I G ratio is B, and 1.25 ≤ A / B ≤ 1.

7.

3. The cathode material according to claim 2, wherein, The positive electrode material satisfies at least one of the following characteristics: （1）2.6≤A≤3.2； （2）1.8≤B≤2.4； (3) 5.0 ≤ La1 ≤ 6.8; (4) 7.5 ≤ La2 ≤ 10.

2.

4. The cathode material according to claim 1, wherein The particle size number distribution curve of the positive electrode material has a peak conforming to the Voigt function distribution, and the particle size distribution width of the particles in the range of 1.5 μm to 11 μm is Span(b), satisfying 1.7 < Span(b) < 2.

4.

5. The cathode material according to any one of claims 1 to 4, characterized in that, The chemical general formula of the positive electrode material is Li n Mn x Fe y M 1-x-y PO4, where 0.9 ≤ n ≤ 1.2, 0 ≤ x < 0.8, 0.2 < y < 1, and M includes at least one of Ti, Nb, Ta, Ba, Sr, Mg, Zn, V, Mo, Y, and W.

6. The cathode material according to any one of claims 1 to 4, characterized in that, The positive electrode material includes secondary particles formed by the agglomeration of primary particles; the positive electrode material satisfies at least one of the following characteristics: (1) The particle size of the primary particles is 50 nm to 250 nm; (2) The sphericity of the secondary particles is 0.85 to 0.

90.

7. The cathode material according to any one of claims 1 to 4, characterized in that, The positive electrode material satisfies at least one of the following characteristics: (1) The tap density of the positive electrode material is 1.4 g / cm 3 ~1.85 g / cm 3 ; (2) The specific surface area of the positive electrode material is 7 m 2 / g to 15 m 2 / g; (3) The tap density of the positive electrode material is 2.05 g / cm 3 ~2.35 g / cm 3 ; (4) The pH value of the positive electrode material is 9.5 to 10.

5.

8. The cathode material according to any one of claims 1 to 4, characterized in that, The positive electrode material satisfies at least one of the following characteristics: (1) The oil absorption value of the positive electrode material is 20 mL / 100g to 40 mL / 100g; (2) The powder resistivity of the positive electrode material is 10 to 100 Ω·m.

9. The cathode material according to any one of claims 1 to 4, characterized in that, The positive electrode material satisfies at least one of the following characteristics: (1) The mass content of carbon element in the positive electrode material is 1.4wt% to 1.7wt%; (2) The mass content of magnetic substances in the positive electrode material is 0.1 to 0.75 mg / kg.

10. A battery, characterized in that, The battery includes the positive electrode material according to any one of claims 1 to 9.

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