Positive electrode material, preparation method therefor, and use thereof

Abstract

The present invention belongs to the technical field of lithium-ion batteries, and specifically relates to a positive electrode material, a preparation method therefor, and the use thereof. The positive electrode material comprises positive electrode material matrix particles and additive particles. The surface of each positive electrode material matrix particle is provided with concave multi-faceted structures, and the additive particles are concentrated at the concave multi-faceted structures, the length of the longest axis of the positive electrode material matrix particles being 10-50 μm, and the length of the longest axis of the additive particles being 30 nm or less. Additive particles are concentrated at the concave multi-faceted structures of the provided positive electrode material, protecting the positive electrode material characteristics at the concave multi-faceted structures, avoiding battery failure caused by the presence of the concave multi-faceted structures, and improving cycling performance and stability performance.

Description

A positive electrode material and its preparation method and application Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and in particular relates to a positive electrode material and a preparation method and application thereof. Background Art

[0002] Compared to traditional batteries, lithium-ion batteries offer significant advantages in energy density, lifespan, and ease of use, making them the most competitive power source in areas such as portable mobile devices and new energy vehicles. Cathode materials are key components of lithium-ion batteries, determining their performance and constraining their energy density, power density, cycle life, and safety. Therefore, improving the performance of cathode materials is a hot topic for researchers in this field.

[0003] In the existing material system, coating is a common modification method for cathode materials. Coating cathode materials can improve cycle performance to a certain extent, but the improvement is relatively limited and can introduce problems such as reduced material capacity and increased impedance, all of which affect the quality of the cathode materials and the operating environment. Summary of the Invention

[0004] The first aspect of the present invention is to overcome the defects of the existing positive electrode materials in terms of poor cycle performance and stability, and to provide a new positive electrode material that can improve the cycle performance and stability of lithium-ion batteries.

[0005] Specifically, the positive electrode material provided by the present invention includes positive electrode material base particles and additive particles. The surface of the positive electrode material base particles has a concave polyhedral structure, and the additive particles are enriched in the concave polyhedral structure; the longest axis length of the positive electrode material base particles is 10~50μm; the longest axis length of the additive particles is less than 30nm.

[0006] In a preferred embodiment, the number of additive particles concentrated in the concave polyhedral structure is not less than 10 particles / (2 μm*2 μm).

[0007] In a preferred embodiment, the positive electrode material matrix particles are selected from at least one of lithium cobalt oxide positive electrode material matrix particles, lithium iron phosphate positive electrode material matrix particles, nickel cobalt manganese ternary positive electrode material matrix particles and nickel cobalt aluminum positive electrode material matrix particles.

[0008] In a preferred embodiment, the additive particles are compounds with different physical phases and / or different structures from the positive electrode material matrix particles.

[0009] In a preferred embodiment, the additive is a metal oxide and / or a metal lithium salt.

[0010] In a preferred embodiment, the metal oxide is selected from at least one of aluminum oxide, magnesium oxide, titanium oxide, zirconium oxide, manganese oxide, manganese oxide, lanthanum oxide, tungsten oxide and cerium oxide.

[0011] In a preferred embodiment, the metal lithium salt is selected from at least one of lithium titanate, lithium manganate, lithium aluminate and lithium zirconate.

[0012] In a preferred embodiment, the concentration of the additive particles is 0.1-0.5 wt % of the mass of the positive electrode material.

[0013] In a preferred embodiment, the positive electrode material further includes a coating layer, which is located on the outermost side of the positive electrode material, and the material of the coating layer is the same as that of the additive particles.

[0014] The second aspect of the present invention is to provide a method for preparing a positive electrode material.

[0015] Specifically, the method for preparing the positive electrode material provided by the present invention comprises the following steps:

[0016] S1. Mixing the positive electrode material base particles and the additive particles through a multi-stage mixing process and then discharging the mixture to obtain a mixture;

[0017] S2, calcining the mixture to obtain a positive electrode material;

[0018] The surface of the positive electrode material matrix particle has a concave polyhedral structure, and the longest axis length of the positive electrode material matrix particle is 10~50 μm; the longest axis length of the additive particle is less than 30 nm; the mixing speed of the multi-stage mixing process is set from slow to fast, and the multi-stage mixing process includes at least a first mixing stage and a second mixing stage performed in sequence, the linear speed of the first mixing stage is 5~10 m / s, and the linear speed of the second mixing stage is 20~30 m / s.

[0019] In a preferred embodiment, the method for preparing the positive electrode material further comprises adding a liquid before mixing in the first mixing stage and / or during mixing in the first mixing stage.

[0020] In a preferred embodiment, the liquid is water.

[0021] In a preferred embodiment, the amount of the liquid added is 1-10 wt % of the additive mass.

[0022] In a preferred embodiment, the method for preparing the positive electrode material further comprises controlling the discharge temperature to be between 60°C and 90°C.

[0023] In a preferred embodiment, the mixing time of the first mixing stage is 1 to 5 minutes.

[0024] In a preferred embodiment, the mixing time of the second mixing stage is 15 to 30 minutes.

[0025] In a preferred embodiment, the calcination temperature is 750-1000°C.

[0026] In a preferred embodiment, the calcination treatment time is 6 to 8 hours.

[0027] In a preferred embodiment, the oxygen concentration during the calcination treatment is 18-22%.

[0028] The third aspect of the present invention is to provide a positive electrode material prepared by the above method.

[0029] A fourth aspect of the present invention is to provide application of the above-mentioned positive electrode material in lithium-ion batteries.

[0030] After extensive and in-depth research, the inventors of the present invention found that the location where the surface defects of the positive electrode material are produced is the key area for failure such as subsequent cycle life safety. The presence of these defects will affect the cycle performance and stability of the lithium-ion battery. Therefore, it is crucial to identify and protect these key areas where surface defects exist. In addition, there are two structural features, convex polyhedron and concave polyhedron, on the surface of the positive electrode material particles. According to the surface energy formula and related principles, it can be known that the energy of the convex polyhedron is relatively low, while the energy of the concave polyhedron is relatively high. Therefore, the concave polyhedron is also the location where surface defects are prone to occur. Although the existing coating method is beneficial to improving the cycle performance and stability of the positive electrode material, the coating material cannot be effectively enriched in these concave polyhedrons. Therefore, the surface defects caused by the concave polyhedrons still exist.

[0031] The key to the present invention lies in selecting additives with specific particle sizes (maximum axis length of 30 nm or less) and employing a multi-stage mixing process consisting of at least two stages. The linear speed of the first mixing stage is controlled between 5 and 10 m / s, and the linear speed of the second mixing stage is controlled between 20 and 30 m / s. Initially, at a linear speed of 5 to 10 m / s, most additive particles are broken up and uniformly mixed with the positive electrode material base particles. The remaining unbroken additive particles are selectively adsorbed to highly active sites (i.e., concave surfaces) due to surface energy. Subsequently, the linear speed is increased to 20 to 30 m / s to firmly bind the remaining additive to the raw material. This results in a concentration of additive particles in the concave polyhedral structures of the resulting positive electrode material base particles, which protects the positive electrode material properties at these concave polyhedral structures, preventing battery failure due to the presence of these concave polyhedral structures and improving cycling performance and stability.

[0032] In addition, in a preferred embodiment, the method for preparing the positive electrode material further includes adding a liquid before mixing in the first mixing stage and / or during mixing in the first mixing stage and controlling the discharge temperature. At this time, the agglomeration effect of the liquid can be used to achieve better enrichment of the additive in key areas, thereby improving the structural stability of the positive electrode material and reducing the risk of cracking of the positive electrode material during the cycle, thereby more effectively improving the cycle stability performance and discharge capacity of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG1 is a scanning electron microscope image (SEM) of the lithium cobalt oxide positive electrode material of Example 1.

[0034] FIG2 is a scanning electron microscope image (SEM) of the lithium cobalt oxide positive electrode material of Example 1.

[0035] FIG3 is a scanning electron microscope image (SEM) of the nickel-cobalt-manganese ternary positive electrode material of Example 6. DETAILED DESCRIPTION

[0036] The positive electrode material provided by the present invention includes positive electrode material base particles and additive particles. The surface of the positive electrode material base particles has a concave polyhedral structure, and the additive particles are enriched in the concave polyhedral structure. The number of additive particles enriched in the concave polyhedral structure is preferably not less than 10 particles / (2 μm*2 μm), such as 10, 15, 20, 25, 30, 35, 40, 45, 50 particles / (2 μm*2 μm), or any value therebetween.

[0037] In the present invention, the longest axis length of the positive electrode material base particles is 10 to 50 μm, such as 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, or any value therebetween. In the present invention, the term "longest axis" refers to the maximum distance between any two points on the particle. The longest axis can be measured using a characterization method capable of observing particle morphology, such as SEM or TEM. The measurement result can be obtained by software measurement or manual measurement on an image.

[0038] The surface features of the positive electrode material matrix particles include two structural features, convex polyhedrons and concave polyhedrons, and the convex polyhedrons and concave polyhedrons are obtained based on the mathematical definitions of convex polyhedrons and concave polyhedrons. The purpose of distinguishing the surface features of the positive electrode material matrix particles is to facilitate the determination of the enrichment position of subsequent additives. According to the principle of the surface energy formula, it can be known that the energy of convex polyhedrons is relatively low, while the energy of concave polyhedrons is relatively high, so concave polyhedrons are also the locations where surface defects are prone to occur. Surface defects include at least one of cracks, fissures and structural discontinuities. Among them, cracks and cracks refer to defects that occur when the fusion between particles is not good or the growth is incomplete. Structural discontinuity refers to the structural discontinuity phenomenon that occurs after two or more particles are bonded together.

[0039] In the present invention, the positive electrode material matrix particles are preferably selected from at least one of lithium cobalt oxide positive electrode material matrix particles, lithium iron phosphate positive electrode material matrix particles, nickel cobalt manganese ternary positive electrode material matrix particles, and nickel cobalt aluminum positive electrode material matrix particles. The positive electrode material matrix particles can be purchased or prepared using various existing methods. In a specific embodiment, the lithium cobalt oxide positive electrode material matrix particles can be prepared by the following method: weighing the corresponding mass of cobalt oxide and lithium carbonate, mixing them thoroughly in an inclined mixer, and then feeding them into a muffle furnace for calcination. After being removed from the furnace, the particles are pulverized by air flow to obtain lithium cobalt oxide positive electrode material matrix particles with a chemical formula of Li1-xCoxO2. The molar ratio of cobalt in the cobalt oxide to lithium in the lithium carbonate is preferably 1:(1-1.1), such as 1:1, 1:1.02, 1:1.05, 1:1.08, 1:1.1, or any value therebetween. The oxygen concentration during the calcination treatment is preferably 18% to 22%, such as 18%, 19%, 20%, 22%, or any value therebetween. The calcination treatment temperature is preferably 900 to 1100°C, such as 900°C, 950°C, 1000°C, 1050°C, 1100°C, or any value therebetween. The calcination treatment time is preferably 10 to 14 hours, such as 10 hours, 10.5 hours, 11 hours, 11.5 hours, 12 hours, 12.5 hours, 13 hours, 13.5 hours, 14 hours, or any value therebetween.

[0040] In a specific embodiment, the nickel-cobalt-manganese ternary positive electrode material matrix particles can be prepared by the following method: weigh the corresponding mass of nickel-cobalt-manganese hydroxide and lithium hydroxide, mix them thoroughly in an inclined mixer, enter a muffle furnace for calcination, and after being taken out of the furnace, obtain ternary positive electrode material matrix particles with a chemical formula of LiNixCoyMn1-x-yO2 by air flow crushing. Wherein, the molar ratio of the transition metal element in the nickel-cobalt-manganese hydroxide to the lithium in the lithium hydroxide is preferably 1: (1~1.1), such as 1: 1, 1: 1.02, 1: 1.05, 1: 1.08, 1: 1.1 or any value therebetween. The oxygen concentration of the calcination treatment is preferably 88%~92%, such as 88%, 89%, 90%, 91%, 92% or any value therebetween. The calcination temperature is preferably 900-1000° C., such as 900° C., 920° C., 950° C., 980° C., 1000° C., or any value therebetween. The calcination time is preferably 10-14 h, such as 10 h, 10.5 h, 11 h, 11.5 h, 12 h, 12.5 h, 13 h, 13.5 h, 14 h, or any value therebetween.

[0041] In the present invention, the longest axis length of the additive particles is 30 nm or less, such as 30 nm, 25 nm, 20 nm, 15 nm, 10 nm, 8 nm, 5 nm, 3 nm, 1 nm, 0.5 nm or any value therebetween.

[0042] In the present invention, the additive particles may be compounds of different phases and / or structures from the positive electrode material matrix particles, and the purpose of their addition is to improve the stability problem of the surface defect area. The additive particles may specifically be metal oxides and / or metal lithium salts. Among them, the metal oxide is preferably selected from at least one of aluminum oxide, magnesium oxide, titanium oxide, zirconium oxide, manganese oxide, manganese oxide, lanthanum oxide, tungsten oxide and cerium oxide. The metal lithium salt is preferably selected from at least one of lithium titanate, lithium manganate, lithium aluminum oxide and lithium zirconate. In addition, the content of the additive particles is preferably 0.1 to 0.5 wt% of the mass of the positive electrode material, such as 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt% or any value therebetween.

[0043] In the present invention, the positive electrode material further includes a coating layer, which is located on the outermost side of the positive electrode material. The material of the coating layer is the same as that of the additive particles. In this case, the corresponding lithium-ion battery has better cycle performance and stability.

[0044] The method for preparing the positive electrode material provided by the present invention comprises the following steps:

[0045] S1. Mixing the positive electrode material base particles and the additive particles through a multi-stage mixing process and then discharging the mixture to obtain a mixture;

[0046] S2. calcining the mixture to obtain a positive electrode material.

[0047] In the present invention, the mixing speed of the multi-stage mixing process is set from slow to fast. The multi-stage mixing process may include at least two mixing processes, that is, a first mixing stage and a second mixing stage performed sequentially. Wherein, the linear speed of the first mixing stage is 5~10 m / s, such as 5 m / s, 6 m / s, 7 m / s, 8 m / s, 9 m / s, 10 m / s or any value therebetween. The linear speed of the second mixing stage is 20~30 m / s, such as 20 m / s, 22 m / s, 25 m / s, 28 m / s, 30 m / s or any value therebetween. In addition, the mixing time of the first mixing stage is preferably 1~5 min, such as 1 min, 2 min, 3 min, 4 min, 5 min or any value therebetween; the mixing time of the second mixing stage is preferably 15~30 min, such as 15 min, 18 min, 20 min, 22 min, 25 min, 28 min, 30 min or any value therebetween. In addition, the number of stages in the mixing process can be increased as needed to ensure that the resulting mixture is uniform.

[0048] In the present invention, the method for preparing the positive electrode material provided by the present invention preferably further includes adding a liquid before and / or during the mixing process in the first mixing stage, the purpose of which is to utilize the agglomeration effect of the liquid to better aggregate the additive particles in the key area, thereby achieving effective encapsulation of the key area. The liquid is preferably water. The amount of the liquid added can be 1 to 10 wt% of the mass of the additive, more preferably 1 to 4 wt%, such as 1 wt%, 2 wt%, 3 wt%, 4 wt%, or any value therebetween.

[0049] In the present invention, the preparation method of the positive electrode material provided by the present invention further preferably includes controlling the discharge temperature at 60~90°C, such as 60°C, 62°C, 65°C, 68°C, 70°C, 72°C, 75°C, 78°C, 80°C, 82°C, 85°C, 88°C, 90°C or any value therebetween, in order to ensure that the liquid of the material evaporates in a short time of discharge and reduce the impact on the material properties. The discharge temperature is controlled within the above-mentioned preferred range mainly because if the temperature is too low, the added liquid such as water will remain too much, which is not conducive to the material properties, and if the temperature is too high, the agglomeration effect of the liquid cannot be exerted, resulting in the inability of the additive particles to be effectively filled and coated in the key area. The present invention does not particularly limit the temperature of the mixing process. For example, the initial mixing temperature can be at room temperature. Since the materials generate heat through friction during the mixing process, the system temperature will naturally rise, and the final discharge temperature can be controlled at 60-90°C. The temperature of the mixing process can also be controlled to be a constant temperature, such as 60-90°C.

[0050] In the present invention, the calcination temperature is preferably 750-1000°C, such as 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, or any value therebetween. The calcination time is preferably 6-8 hours, such as 6 hours, 6.5 hours, 7 hours, 7.5 hours, 8 hours, or any value therebetween. The oxygen concentration during the calcination is preferably 18-22%, such as 18%, 19%, 20%, 21%, 22%, or any value therebetween.

[0051] The present invention will be described in detail below through specific examples.

[0052] In the following examples and comparative examples, the morphology and longest axis length of the positive electrode material base particles and additive particles were measured by SEM. Example

[0053] S1. Cobaltous oxide and lithium carbonate were weighed separately at a cobalt:lithium molar ratio of 1:1.05, thoroughly mixed in an inclined mixer, and sintered in a muffle furnace at 1000°C for 12 hours at an oxygen concentration of 20%. After removal from the furnace, the mixture was subjected to airflow milling to produce lithium cobalt oxide positive electrode material matrix particles having a chemical formula of LiCoO2. The surface of the lithium cobalt oxide positive electrode material matrix particles had a concave polyhedral structure with a longest axis length of 40 to 45 μm.

[0054] S2. Add 0.2wt% alumina powder (with a maximum axis length of 10-15nm) by mass to 1000g of the lithium cobalt oxide positive electrode material matrix particles prepared above, and add 0.02wt% water by mass, mix them by a high-speed mixer, stir them at a linear speed of 5 m / s for 2 min, stir them at a linear speed of 20 m / s for 20 min, and control the discharge temperature at 78°C after stirring. Then, sinter the mixture in a muffle furnace with an oxygen concentration of 20%, the sintering temperature is 950°C, and the sintering time is 7 h to obtain a lithium cobalt oxide positive electrode material. From the SEM characterization, as shown in Figures 1 and 2, the concave polyhedral structure of the lithium cobalt oxide positive electrode material is enriched with additive particles. Figure 1 shows that there is obvious particle aggregation at the discontinuous structure where multiple particles are bonded. Figure 2 shows that there is obvious particle aggregation at the cracks of a single particle, and the number of additive particles enriched at each concave polyhedral structural defect is not less than 10 particles / (2 μm*2 μm). Example

[0055] A lithium cobalt oxide positive electrode material was prepared according to the method of Example 1, except that 2 g (0.2 wt %) of aluminum oxide powder was replaced with 1 g (0.1 wt %) of titanium dioxide powder (with the longest axis length of 5 to 10 nm). The other conditions were the same as those in Example 1 to obtain a lithium cobalt oxide positive electrode material. Example

[0056] A lithium cobalt oxide positive electrode material was prepared according to the method of Example 1, except that 2 g (0.2 wt %) of aluminum oxide powder was replaced with 5 g (0.5 wt %) of lithium titanate powder (with the longest axis length of 15-18 nm). The other conditions were the same as those in Example 1 to obtain a lithium cobalt oxide positive electrode material. Example

[0057] A lithium cobalt oxide positive electrode material was prepared according to the method of Example 1, except that water was replaced by an ethanol solution with the same mass fraction and a concentration of 0.02%. The other conditions were the same as in Example 1 to obtain a lithium cobalt oxide positive electrode material. Example

[0058] A lithium cobalt oxide positive electrode material was prepared according to the method of Example 1, except that no water was added in the mixing process. The other conditions were the same as in Example 1 to obtain a lithium cobalt oxide positive electrode material. Example

[0059] S1. Weigh nickel, cobalt, manganese hydroxide and lithium hydroxide at a molar ratio of (nickel, cobalt, manganese): lithium of 1:1.05, mix thoroughly in an inclined mixer, and sinter at 920°C for 12 hours in a muffle furnace with an oxygen concentration of 90% or greater. After being removed from the furnace, pulverize by airflow to obtain nickel, cobalt, manganese, and ternary positive electrode material matrix particles having a chemical formula of Li1Ni0.6Co0.2Mn0.2O2. The surface of the nickel, cobalt, and manganese ternary positive electrode material matrix particles has a concave multifaceted structure with a longest axis length of 10 to 18 μm.

[0060] S2. Add 0.2wt% alumina powder (the longest axis length is 20~23nm) by mass to 1000g of the nickel-cobalt-manganese ternary positive electrode material matrix particles prepared above, and add 0.01wt% water by mass, mix them by a high-speed mixer, stir at a linear speed of 10 m / s for 1 min, stir at a linear speed of 28 m / s for 15 min, and control the discharge temperature at 78°C after stirring. Then, sinter the mixture in a muffle furnace with a temperature of 780°C and a sintering time of 7 h to obtain a nickel-cobalt-manganese ternary positive electrode material. As can be seen from the SEM characterization, as shown in Figure 3, the concave polyhedral structure of the nickel-cobalt-manganese ternary positive electrode material is enriched with additive particles, and the number of additive particles enriched at each concave polyhedral structure is not less than 10 particles / (2 μm*2 μm). Example

[0061] A ternary positive electrode material was prepared according to the method of Example 6, except that in step S2, the discharge temperature was controlled at 30°C. The remaining conditions were the same as in Example 6, resulting in a ternary positive electrode material. SEM characterization revealed that the concave polyhedral structures of the ternary positive electrode material were enriched with additive particles, and the number of additive particles enriched in each concave polyhedral structure was no less than 10 particles / (2 μm*2 μm). Example

[0062] A ternary positive electrode material was prepared according to the method of Example 6, except that in step S2, the discharge temperature was controlled at 118°C. The remaining conditions were the same as in Example 6, thereby obtaining a ternary positive electrode material. SEM characterization revealed that the concave polyhedral structures of the ternary positive electrode material were enriched with additive particles, and the number of additive particles enriched in each concave polyhedral structure was no less than 10 particles / (2 μm*2 μm).

[0063] Comparative Example 1

[0064] A lithium cobalt oxide positive electrode material was prepared according to the method of Example 1, except that the mixing using the high-speed mixer in step S2 included only one stage, with a linear speed of 20 m / s and a duration of 22 minutes. The remaining conditions were the same as in Example 1, yielding a lithium cobalt oxide positive electrode material. SEM characterization revealed that the additive particles coated the surface of the lithium cobalt oxide matrix particles, while the concave polyhedral structures of the lithium cobalt oxide matrix particles were not enriched with additive particles.

[0065] Comparative Example 2

[0066] A lithium cobalt oxide positive electrode material was prepared according to the method of Example 1, except that the longest axis length of the alumina powder was greater than 50 nm. The remaining conditions were the same as in Example 1, resulting in a lithium cobalt oxide positive electrode material. SEM characterization revealed that the additive particles were coated on the surface of the lithium cobalt oxide matrix particles, while the concave polyhedral structures of the lithium cobalt oxide matrix particles were not enriched with additive particles.

[0067] Comparative Example 3

[0068] A ternary positive electrode material was prepared according to the method of Example 6, except that the mixing using the high-speed mixer in step S2 included only one stage, with a linear speed of 28 m / s and a duration of 16 min. The remaining conditions were the same as in Example 6, to obtain a lithium cobalt oxide positive electrode material. SEM characterization revealed that the additive particles coated the surface of the lithium cobalt oxide matrix particles, while the concave polyhedral structures of the lithium cobalt oxide matrix particles were not enriched with additive particles.

[0069] Test Case

[0070] The positive electrode materials prepared in the above examples and comparative examples were respectively prepared into positive electrode sheets, and the positive electrode sheets and lithium sheets (negative electrodes) were combined to form button-type lithium-ion batteries. The electrical performance tests were performed respectively, and the results are shown in Table 1.

[0071] (1) Cyclic capacity retention rate (normal temperature) test: Place the battery in a 25°C environment, charge it from 3.0 V to 4.35 V or 4.55 V at a charging rate of 0.5 C, and then discharge it to 3.0 V at a discharge rate of 0.5 C. The discharge capacity at this time is determined as the first discharge capacity. Repeat the above charge and discharge cycle 50 times, and measure the discharge capacity of the 50th discharge. The cyclic capacity retention rate = 50th discharge capacity / first discharge capacity.

[0072] (2) Cycle capacity retention rate (high temperature) test: Place the battery in a 45°C environment, charge it from 3.0 V to 4.35 V (ternary positive electrode material) or 4.55 V (lithium cobalt oxide positive electrode material) at a charging rate of 0.5 C, and then discharge it to 3.0 V at a discharge rate of 0.5 C. The discharge capacity at this time is determined as the first discharge capacity. Repeat the above charge and discharge cycle 50 times, and measure the discharge capacity of the 50th discharge. The cycle capacity retention rate = 50th discharge capacity / first discharge capacity.

[0073] (3) Discharge capacity test: The battery was charged from 3.0 V to 4.35 V or 4.55 V at a charge rate of 0.1 C at 25 °C, and then discharged to 3.0 V at a discharge rate of 0.1 C. The 0.1 C discharge capacity was measured.

[0074] Table 1

[0075]

[0076] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A positive electrode material, characterized in that: The positive electrode material includes positive electrode material matrix particles and additive particles. The surface of the positive electrode material matrix particles has a concave polyhedral structure, and the additive particles are enriched in the concave polyhedral structure; the longest axis length of the positive electrode material matrix particles is 10~50μm; the longest axis length of the additive particles is less than 30nm.

2. The positive electrode material according to claim 1, characterized in that The number of additive particles concentrated in the concave multi-faceted structure is not less than 10 particles / (2 μm*2 μm).

3. The positive electrode material according to claim 1, characterized in that The positive electrode material matrix particles are selected from at least one of lithium cobalt oxide positive electrode material matrix particles, lithium iron phosphate positive electrode material matrix particles, nickel-cobalt-manganese ternary positive electrode material matrix particles and nickel-cobalt-aluminum positive electrode material matrix particles.

4. The positive electrode material according to claim 1, characterized in that The additive particles are compounds with different physical phases and / or different structures from the positive electrode material matrix particles.

5. The positive electrode material according to claim 4, characterized in that The additive particles are metal oxides and / or metal lithium salts.

6. The positive electrode material according to claim 5, characterized in that The metal oxide is selected from at least one of aluminum oxide, magnesium oxide, titanium oxide, zirconium oxide, manganese oxide, manganese oxide, lanthanum oxide, tungsten oxide and cerium oxide.

7. The positive electrode material according to claim 5, characterized in that The metal lithium salt is selected from at least one of lithium titanate, lithium manganate, lithium aluminate and lithium zirconate.

8. The positive electrode material according to claim 4, characterized in that The content of the additive particles is 0.1-0.5wt% of the mass of the positive electrode material.

9. The positive electrode material according to claim 1, characterized in that The positive electrode material further includes a coating layer, which is located at the outermost side of the positive electrode material, and the material of the coating layer is the same as that of the additive particles.

10. A method for preparing a positive electrode material, characterized in that: The method comprises the following steps: S1, mixing the positive electrode material matrix particles and the additive particles through a multi-stage mixing process and then discharging the mixture to obtain a mixture; S2, calcining the mixture to obtain a positive electrode material; The surface of the positive electrode material matrix particle has a concave multi-faceted structure, and the longest axis length of the positive electrode material matrix particle is 10~50 μm; the longest axis length of the additive particle is less than 30nm; the mixing speed of the multi-stage mixing process is set from slow to fast, and the multi-stage mixing process at least includes a first mixing stage and a second mixing stage performed in sequence, the linear speed of the first mixing stage is 5~10 m / s, and the linear speed of the second mixing stage is 20~30 m / s.

11. The method for preparing the positive electrode material according to claim 10, characterized in that: The method further includes adding a liquid before mixing in the first mixing stage and / or during mixing in the first mixing stage.

12. The method for preparing the positive electrode material according to claim 11, characterized in that: The liquid is water.

13. The method for preparing the positive electrode material according to claim 11, characterized in that: The amount of the liquid added is 1-10 wt % of the additive mass.

14. The method for preparing the positive electrode material according to claim 10, characterized in that: The method also includes controlling the discharge temperature at 60-90°C.

15. The method for preparing the positive electrode material according to claim 10, characterized in that: The mixing time of the first mixing section is 1 to 5 min; the mixing time of the second mixing section is 15 to 30 min.

16. The method for preparing the positive electrode material according to claim 10, characterized in that: The calcination treatment conditions include a temperature of 750-1000°C, a time of 6-8 hours, and an oxygen concentration of 18-22%.

17. The positive electrode material prepared by the method according to claim 10.

18. Use of the positive electrode material according to claim 1 in a lithium ion battery.

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