A positive electrode active material and its preparation method and application

Abstract

The present invention provides a positive electrode active material, a preparation method thereof, and an application. The positive electrode active material of the present invention is composed of matrix particles and a boride coating layer covering at least part of the surface and / or pores of the matrix particles; wherein, the matrix particles have the structure shown in Formula 1; LiNi x Co y M 1‑x‑y O2 Formula 1, in Formula 1, 0.6 < x ≤ 0.96, 0 ≤ y < 0.2; M is at least one of Mn, Mg, Al, Ti, Nb, Zr, Y, Sb, Sr, Ta, Si, Mo, Sn or W; the boride coating layer includes zirconium boride and / or titanium boride. The special composition of this positive electrode active material helps to improve the cycle performance of the battery and reduce the DCR of the battery.

Description

Technical Field

[0001] The invention relates to a pole piece material, in particular to a positive electrode active material and a preparation method and application thereof, belonging to the technical field of secondary batteries. Background Art

[0002] In recent years, with the rapid development of new energy vehicles and the increase in cruising range, people have higher and higher requirements on the high-rate charge and discharge performance and service life of new energy vehicle power batteries. Among them, the direct current resistance DCR (Directive Current Resistance) is an important factor affecting the rate performance and service life of lithium-ion batteries.

[0003] At present, high nickel ternary cathode materials are considered to be the most promising and promising cathode materials for lithium-ion batteries due to their high reversible capacity and high operating voltage. However, since the surface of high nickel ternary cathode materials is relatively smooth and clean after washing and reducing alkali, they are easy to absorb moisture, carbon dioxide and other harmful impurities that react with the electrolyte during storage, thereby generating substances such as Li2CO3 or LiOH, which will then form an insulating layer on the surface of the high nickel ternary cathode materials, hindering the diffusion of lithium ions and electron transmission, causing an increase in DCR; at the same time, as the nickel content in the high nickel ternary cathode materials increases, their thermal decomposition temperature will decrease. During the charge and discharge process, they are accompanied by partial phase transition to spinel type and NiO type rock salt phase with poor conductivity and the formation of pores, causing irreversible destruction of the crystal phase structure. Therefore, during the reaction process with the electrolyte, the high nickel ternary cathode materials are easily continuously eroded by the electrolyte, which eventually leads to the deterioration of the cycle performance and DCR of the lithium-ion battery. Summary of the invention

[0004] The invention provides a positive electrode active material, the special composition of which is helpful to improve the cycle performance of a battery and reduce the DCR of the battery.

[0005] The present invention provides a method for preparing a positive electrode active material. The method can prepare the positive electrode active material mentioned above, and the preparation method is simple and suitable for wide application and promotion.

[0006] The present invention also provides a battery, which includes the positive electrode active material, so the battery has excellent performance in DCR and cycle performance.

[0007] The present invention provides a positive electrode active material, wherein the positive electrode active material is composed of a base particle and a boride coating layer covering at least a portion of the surface and / or pores of the base particle;

[0008] Wherein, the base particle has a structure shown in Formula 1;

[0009] LiNix Co y M 1-x-y O2 Formula 1

[0010] In formula 1, 0.6<x≤0.96, 0≤<y<0.2; M is at least one of Mn, Mg, Al, Ti, Nb, Zr, Y, Sb, Sr, Ta, Si, Mo, Sn or W;

[0011] The boride coating includes zirconium boride and / or titanium boride.

[0012] The positive electrode active material as described above, wherein the DCR growth rate of the positive electrode active material after 300 cycles is 10-40%.

[0013] The positive electrode active material as described above, wherein the boride coating layer further comprises boron nitride and / or boron oxide.

[0014] The positive electrode active material as described above, wherein the porosity of the base particles is 2-5%.

[0015] The positive electrode active material as described above, wherein the porosity between the primary particles of the positive electrode active material is less than or equal to the porosity of the base particles, and the porosity of the positive electrode active material is ≤3%.

[0016] The positive electrode active material as described above, wherein in the X-ray diffraction spectrum, the positive electrode active material has a 101 peak with a 2θ value of 36.61°-37.01° and a 012 peak with a 2θ value of 38.28°-38.68°, and the peak area of ​​the 101 peak is 101 And the peak area I of the 012 peak 012 Satisfy: (I 101 / I 012 ) 1 / 2 ≥1.7.

[0017] The positive electrode active material as described above, wherein Dn10 of the positive electrode active material satisfies, 0.6 μm<Dn10<12 μm; and / or,

[0018] The specific surface area A of the positive electrode active material satisfies: 0.3 m 2 / g<A<0.70m 2 / g; and / or,

[0019] The mass of the boride coating layer is 0.01-0.1% of the mass of the base particle.

[0020] The present invention also provides a method for preparing the positive electrode active material as described above, which comprises the following steps:

[0021] Heat treating the base particles of Formula 1 and the boride to obtain the positive electrode active material;

[0022] The boride includes zirconium boride and / or titanium boride.

[0023] In the method for preparing the positive electrode active material as described above, the temperature of the heat treatment is 200-500° C. and the time is 5-20 h.

[0024] The present invention also provides a battery, comprising the positive electrode active material as described above.

[0025] The positive electrode active material of the present invention has a special chemical composition. After being applied to a battery, the cycle performance of the battery is significantly improved and the DCR of the battery is significantly reduced.

[0026] The method for preparing the positive electrode active material of the present invention can prepare the positive electrode active material mentioned above, and the preparation method has simple production equipment, high production efficiency, low cost, and can realize large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a SEM image of the positive electrode active material of Example 1 of the present invention;

[0028] Figure 2 is the XRD diagram of Example 1 of the present invention;

[0029] Figure 3 DCR curves of batteries prepared with the positive electrode active materials of Example 1 and Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] A first aspect of the present invention provides a positive electrode active material, wherein the positive electrode active material is composed of a base particle and a boride coating layer covering at least a portion of the surface and / or pores of the base particle;

[0032] Wherein, the matrix particle has a structure shown in Formula 1;

[0033] LiNi x Co y M 1-x-y O2 Formula 1

[0034] In formula 1, 0.6<x≤0.96, 0≤y<0.2; M is at least one of Mn, Mg, Al, Ti, Nb, Zr, Y, Sb, Sr, Ta, Si, Mo, Sn or W;

[0035] The boride coating includes zirconium boride and / or titanium boride.

[0036] It can be understood that the boride coating layer may cover at least a portion of the surface of the base particle, may cover at least a portion of the pores of the base particle, or may cover at least a portion of the surface and at least a portion of the pores of the base particle simultaneously.

[0037] The base particles of the present invention have a structure of Formula 1, specifically, at least oxides of lithium, cobalt and sodium. Further, they may be doped with M, where M is at least one of Mn, Mg, Al, Ti, Nb, Zr, Y, Sb, Sr, Ta, Si, Mo, Sn or W.

[0038] According to the above scheme provided by the present invention, compared with other positive electrode active materials, after the positive electrode active material including the matrix material and the boride coating layer is applied to a lithium ion battery, the cycle performance of the lithium ion battery is significantly improved and the DCR of the lithium ion battery is significantly reduced.

[0039] The inventors analyzed this phenomenon and believed that it may be: on the one hand, the present invention provides a boride coating layer including zirconium boride and / or titanium boride, so that the positive electrode active material is a core-shell structure including a base particle core and a boride coating layer covering the base particle core. The coating layer helps to reduce or inhibit the side reaction of lithium metal oxide and electrolyte. Even when the battery is working under high voltage, a stable interface can still be formed between the positive electrode active material and the electrolyte. By avoiding the transitional dissolution of metal ions in the positive electrode active ions and avoiding the lack of liquid, the cycle performance of the battery is improved. At the same time, the inhibition or reduction of side reactions can also reduce the gas production inside the battery, thereby ensuring the safety performance of the battery. On the other hand, the zirconium boride and / or titanium boride in the boride coating layer also has excellent mechanical properties. Covering the boride coating layer on the surface and / or between the pores of the base particles helps to suppress the stress strain of the base particles, improve the crystalline structure stability of the positive electrode active material, and thus help improve the cycle performance of the lithium-ion battery. At the same time, the zirconium boride and / or titanium boride in the boride coating layer has excellent antioxidant properties and thermal stability, which helps to reduce the side reactions between the positive electrode active material and the electrolyte and improve the cycle performance of the battery. It is worth mentioning that the excellent conductivity of the zirconium boride and / or titanium boride in the boride coating layer is conducive to reducing the transmission resistance and transmission distance of electrons, thereby reducing the DCR of the battery.

[0040] Preferably, when the boride coating layer includes titanium boride, the positive electrode active material can better improve the performance of the battery.

[0041] Furthermore, the DCR growth rate of the positive electrode active material of the present invention after 300 cycles is 10-40%, which helps to better improve the electrical performance of the battery.

[0042] In some embodiments of the present invention, the boride coating further comprises boron nitride and / or boron oxide.

[0043] In particular, when the boride coating layer also includes boron oxide, boron oxide can effectively inhibit the penetration and precipitation of oxygen, maintain the stability of the crystal structure of the positive electrode active material, and reduce the possibility of crystal structure damage of the positive electrode active material due to mechanical stress, thereby further reducing the side reactions between the positive electrode active material and the electrolyte and improving the cycle performance of the battery.

[0044] In some embodiments of the present invention, the porosity of the base particles is 2-5%.

[0045] It can be understood that the base particles of the present invention are secondary particles formed by agglomeration of primary particles, so the base particles have pores. Specifically, they can be secondary particles formed by a continuous method or an intermittent method. When the porosity of the base particles meets the above range, the boride coating layer can be more fully embedded in the pores while maintaining the mechanical strength of the base particles, thereby improving the structural stability and conductivity of the positive electrode active material, thereby improving the cycle performance and DCR performance of the battery.

[0046] It can be understood that the boride coating layer of the present invention will be embedded in the pores of the base particles to form a positive electrode active material. Since the pores of the base particles are partially filled with the boride coating layer, the porosity of the positive electrode active material will be less than or equal to the porosity of the base particles. Further, when the porosity of the positive electrode active material is ≤3%, the positive electrode active material has both better cycle performance and DCR performance.

[0047] In some embodiments of the present invention, in the X-ray diffraction spectrum, the positive electrode active material has a 101 peak with a 2θ value of 36.61°-37.01° and a 012 peak with a 2θ value of 38.28°-38.68°, and the peak area of ​​the 101 peak is 101 And the peak area I of the 012 peak 012 Satisfy: (I 101 / I 012 ) 1 / 2 ≥1.7.

[0048] The positive electrode active material of the present invention has oxygen defects, and the degree of oxygen defects in the positive electrode active material can be determined by the relationship between the peak intensities of the 101 peak and the 012 peak in the X-ray diffraction spectrum.101 And the peak area I of the 012 peak 012 When the above relationship is satisfied, it is proved that the oxygen defect of the positive electrode active material is small, and thus the positive electrode active material has excellent structural stability. The use of the positive electrode active material can further improve the cycle performance of the battery.

[0049] The inventors have also found that further limiting the particle size, specific surface area, and mass ratio of the positive electrode active material to the matrix particles is helpful to improve the performance of the positive electrode active material.

[0050] For example, the Dn10 of the positive electrode active material satisfies 0.60μm<Dn10<12μm. In the present invention, Dn10 refers to the particle size of the particle when the number of a certain particle accounts for 10% of the number of all particles, when all the particles of the positive electrode active material are arranged in order from small to large, and the serial number of each particle corresponds to the position where the particle is arranged. Dn10 can be measured by a laser particle size analyzer. In a specific embodiment, the Dn10 of the positive electrode active material is tested using a laser particle size analyzer Malvern 3000. When the Dn10 of the positive electrode active material satisfies the above relationship, it is beneficial to reduce the side reactions between the positive electrode active material and the electrolyte, and helps to improve the cycle performance of the battery.

[0051] The specific surface area A of the positive electrode active material satisfies 0.3m 2 / g<A<0.70m 2 / g, the specific surface area within this range helps to reduce the side reactions between the positive electrode active material and the electrolyte and improve the cycle performance of the battery. In some embodiments, a dynamic chromatography specific surface area tester can be used to test the specific surface area (BET) of the positive electrode active material.

[0052] When the mass of the boride coating layer accounts for 0.01-0.1% of the mass of the base particles, the effects of the boride coating layer and the base particles can be fully exerted, the cycle performance of the battery is improved, and the DCR of the battery is reduced.

[0053] In some embodiments of the present invention, the compressive strength of the positive electrode active material is 80-200 MPa. In the present invention, compressive strength refers to the pressure value that the positive electrode active material can withstand per unit area. The compressive strength can be obtained using Shimadzu DUH-21 test. When the compressive strength of the positive electrode active material meets the above-mentioned limitations, the positive electrode active material has excellent mechanical properties, which helps to further improve the electrical and mechanical properties of the battery.

[0054] A second aspect of the present invention provides a method for preparing the above-mentioned positive electrode active material, which comprises the following steps:

[0055] Heat treating the base particles of Formula 1 and the boride to obtain a positive electrode active material;

[0056] The boride includes zirconium boride and / or titanium boride.

[0057] In the preparation method of the present invention, the base particles of the structure of Formula 1 and the boride are subjected to heat treatment. During the heat treatment, the boride is coated on the surface and / or in the pores of the base particles to form the positive electrode active material of the present invention.

[0058] In a specific embodiment, the base particles and the boride may be mixed, and during the mixing process, friction and collision occur between the boride and the base particles, so that the boride is evenly dispersed; then the base particles and the boride may be heat treated under the protection of oxygen and / or nitrogen to obtain a mixed system, and the mixed system may be quickly cooled to room temperature to obtain a positive electrode active material. The volume content of carbon dioxide in the oxygen and / or nitrogen is less than 15%.

[0059] The preparation method of the positive electrode active material of the present invention is dry coating, the used production equipment is simple, the production efficiency is high, the cost is low, and large-scale production can be realized.

[0060] In the present invention, the boride can be a primary particle of micron or submicron size; the matrix particles of the structure of formula 1 can be obtained by mixing the ternary precursor of the structure of formula 1a with a lithium source, and then sintering at high temperature, cooling, crushing and screening, washing and drying, and screening.

[0061] Ni x Co y M 1-x-y (OH)2 Formula 1a

[0062] Among them, 0.8<x<0.96, 0<y<0.2.

[0063] In some embodiments, the molar ratio of the ternary precursor of Formula 1a to the lithium source may be (1.025-1.078):1, and the lithium source may be lithium hydroxide and / or lithium carbonate.

[0064] In some embodiments of the present invention, the temperature and time of the heat treatment can be specifically selected so that the boride coating layer can fully cover the surface and / or pores of the substrate particles while saving energy consumption, thereby improving the comprehensive performance of the positive electrode active material. For example, the heat treatment temperature is 200-500°C, the time is 5-20h, and further, the heat treatment time is 10-15h.

[0065] A third aspect of the present invention provides a battery, comprising the above-mentioned positive electrode active material.

[0066] Since the battery of the present invention includes the above-mentioned positive electrode active material, it has excellent cycle performance and DCR.

[0067] The technical solution of the present invention will be further explained below in conjunction with specific embodiments.

[0068] Example 1

[0069] The positive electrode active material of this embodiment is prepared according to the following method:

[0070] (1) The ternary precursor material Ni 0.93 Co 0.055 Mn 0.01 Al 0.005 (OH)2 and lithium hydroxide are mixed evenly by a high-speed mixer, and then sintered at high temperature in an oxygen atmosphere, and then cooled, crushed, sieved, washed and dried to obtain the matrix particles LiNi 0.93 Co 0.055 Mn 0.01 Al 0.005 O2;

[0071] The molar ratio of the total molar number of Ni, Co and Mn in the ternary precursor material to the Li element in lithium hydroxide is 1.05:1, the mass of the ternary precursor material is 7 kg, the high temperature sintering temperature is 740° C., and the high temperature sintering time is 16 hours.

[0072] (2) Weighing 7 kg of the matrix particles prepared above, adding 4.2 g of titanium boride, mixing in a high-speed mixer, then heat-treating under the protection of oxygen to obtain a mixed system, cooling the mixed system to room temperature, and sieving to obtain a positive electrode active material;

[0073] The heat treatment temperature is 320°C and the time is 12 hours.

[0074] The Dn10 of the positive electrode active material was 3.87 μm when tested by Malvern 3000 laser particle size analyzer. The specific surface area of ​​the positive electrode active material was 0.49 m 2 / g; The compressive strength of a single positive electrode active material tested using Shimadzu DUH-211S is 148MPa;

[0075] The surface morphology of the positive electrode active material of this example was observed using SEM. Figure 1 This is a surface morphology of the positive electrode active material of Example 1 of the present invention. Figure 1It can be seen that the positive electrode active material of the present invention is composed of a base particle and a boride coating layer coated on the surface and / or pores of the base particle. The outline of the positive electrode active material is automatically drawn on the SEM image by Metis.exe software, and the dark pores are extracted. The porosity of the positive electrode active material is 1.06% after fitting.

[0076] XRD was used to test the crystalline morphology of the positive electrode active material of this example. Figure 2 This is the XRD diagram of Example 1 of the present invention. Figure 2 It can be seen that the XRD graph of the positive electrode active material of this embodiment shows a clearly split and sharp diffraction peak, and no mixed peaks appear, indicating that the positive electrode active material obtained in this embodiment has a good crystal structure and high crystallinity. The 2θ of the 101 peak is 36.615°, the 2θ of the 012 peak is 38.282°, and the peak area of ​​the 101 peak is 1. 101 And the peak area I of the 012 peak 012 Satisfy: (I 101 / I 012 ) 1 / 2 =1.96.

[0077] Example 2

[0078] The preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that, in step (2), 7 g of zirconium boride is added;

[0079] The relevant parameters of the positive electrode active material were tested according to the method of Example 1. The Dn10 was 3.51 μm; the BET was 0.49 μm 2 / g; porosity is 1.19%; 2θ of 101 peak is 36.614°, 2θ of 012 peak is 38.281°, (I 101 / I 012 ) 1 / 2 =1.96; compressive strength is 139MPa.

[0080] Example 3

[0081] The preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that:

[0082] In step (2), 7 kg of the matrix particles prepared above were weighed, 4.2 g of titanium boride and 4 g of boron oxide were added, and mixed in a high-speed mixer, and then heat-treated under the protection of oxygen to obtain a mixed system, and the mixed system was cooled to room temperature and sieved to obtain a positive electrode active material;

[0083] The relevant parameters of the positive electrode active material were tested according to the method of Example 1. The Dn10 was 3.14 μm; the BET was 0.54 μm 2 / g; porosity is 1.24%; 2θ of 101 peak is 36.609°, 2θ of 012 peak is 38.265°, (I 101 / I 012 ) 1 / 2 =1.88; compressive strength is 131MPa.

[0084] Example 4

[0085] The preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that:

[0086] In step (1), the ternary precursor material Ni 0.83 Co 0.115 Mn 0.05 Al 0.005 (OH)2 and lithium hydroxide are mixed evenly by a high-speed mixer, and then sintered at high temperature in an oxygen atmosphere, and then cooled, crushed and sieved to obtain the matrix particles LiNi 0.83 Co 0.115 Mn 0.05 Al 0.005 O2;

[0087] Among them, the high temperature sintering temperature is 770°C, and the high temperature sintering time is 16h;

[0088] The relevant parameters of the positive electrode active material were tested according to the method of Example 1. The Dn10 was 2.27 μm; the BET was 0.56 m 2 / g; porosity is 1.64%; 2θ of 101 peak is 36.644°, 2θ of 012 peak is 38.310°, (I 101 / I 012 ) 1 / 2 =1.86; compressive strength is 122MPa.

[0089] Example 5

[0090] The preparation method of the positive electrode active material of this embodiment is basically the same as that of embodiment 1, except that:

[0091] In step (1), the high temperature sintering temperature is 735°C.

[0092] The relevant parameters of the positive electrode active material were tested according to the method of Example 1. The Dn10 was 0.36 μm; the BET was 0.75 μm 2 / g; porosity is 2.34%; 2θ of 101 peak is 36.613°, 2θ of 012 peak is 38.280°, (I 101 / I 012 ) 1 / 2 =1.82; compressive strength is 103MPa.

[0093] Comparative Example 1

[0094] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that in step (2), titanium boride is not added, and the base particles are directly heat treated;

[0095] The relevant parameters of the positive electrode active material were tested according to the method of Example 1. The Dn10 was 0.33 μm; the BET was 0.65 μm 2 / g; porosity is 3.01%; 2θ of 101 peak is 36.638°, 2θ of 012 peak is 38.309°, (I 101 / I 012 ) 1 / 2 =1.84; compressive strength is 78MPa.

[0096] Comparative Example 2

[0097] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that, in step (2), 4 g of boron oxide is added;

[0098] The relevant parameters of the positive electrode active material were tested according to the method of Example 1. The Dn10 was 0.42 μm; the BET was 0.58 μm 2 / g; porosity is 2.47%; 2θ of 101 peak is 36.645°, 2θ of 012 peak is 38.298°, (I 101 / I 012 ) 1 / 2 =1.86; compressive strength is 99MPa.

[0099] Comparative Example 3

[0100] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that, in step (2), 3.2 g of boron nitride is added;

[0101] The relevant parameters of the positive electrode active material were tested according to the method of Example 1. The Dn10 was 0.50 μm; the BET was 0.59 μm 2 / g; porosity is 2.73%; 2θ of 101 peak is 36.614°, 2θ of 012 peak is 38.281°, (I 101 / I 012 ) 1 / 2 =1.82; Particle compressive strength 87MPa.

[0102] Comparative Example 4

[0103] The preparation method of the positive electrode active material of this comparative example is basically the same as that of Example 1, except that, in step (2), 4.21 g of cobalt boride is added;

[0104] The relevant parameters of the positive electrode active material were tested according to the method of Example 1. The Dn10 was 1.15 μm; the BET was 0.62 m 2 / g; porosity is 1.89%; 2θ of 101 peak is 36.617°, 2θ of 012 peak is 38.284°, (I 101 / I 012 ) 1 / 2 =1.85; compressive strength is 113MPa.

[0105] Performance Testing

[0106] 1. Use a resistance tester to test the resistance of the positive electrode active materials of the embodiment and the comparative example. The test results are shown in Table 1:

[0107] Table 1

[0108] Resistance (Ohm-cm) Example 1 102 Example 2 117 Example 3 111 Example 4 127 Example 5 106 Comparative Example 1 156 Comparative Example 2 215 Comparative Example 3 129 Comparative Example 4 318

[0109] It can be seen from the examples and comparative examples that the boride coating layer including titanium boride and / or zirconium boride provided in the present invention can reduce the resistance of the positive electrode active material and help reduce the DCR of the battery;

[0110] Among them, compared with Example 1, the internal resistance of the positive electrode active material is significantly reduced in Example 1-2, indicating that the boride coating layer can significantly reduce the resistance of the positive electrode active material; compared with Example 2-3, it is shown that only by providing a boride coating layer including titanium boride and / or zirconium boride can the resistance of the positive electrode active material be better reduced.

[0111] 2. Button batteries were prepared using the positive electrode active materials obtained in the examples and comparative examples, and the first charge and discharge specific capacity and the first coulomb efficiency of the button batteries were tested. The test results are shown in Table 2.

[0112] The button cell is prepared by a preparation method comprising the following steps:

[0113] Preparation of positive electrode sheet: The positive electrode active slurry was placed on the two functional surfaces of the aluminum foil, and then placed in a vacuum oven at 120°C for 2 hours for drying. After drying, a punching machine was used to cut it into a circular positive electrode sheet with a diameter of 10 mm including a positive electrode active layer. After recording its mass, it was placed in a vacuum oven at 120°C for 12 hours to remove moisture, and finally stored in a glove box under an ammonia atmosphere;

[0114] The positive electrode active layer includes positive electrode active material, conductive agent SP and binder PVDF. The mass ratio of positive electrode active material, conductive agent and binder is 96.5%:1.5%:2%. The surface loading of the positive electrode active layer is 15g / cm 2 ;

[0115] Preparation of negative electrode sheet: The negative electrode sheet is a lithium sheet;

[0116] Preparation of the battery: The positive electrode sheet, the separator and the negative electrode sheet are stacked to obtain an electrode assembly, the electrode assembly is placed in an aluminum-plastic film, 30 microliters of a ternary commercial electrolyte (LPF / EC-DEC-EMC, the volume ratio of EC, DEC and EMC is 1:1:1, and the concentration of LPF is 1M) is injected into the aluminum-plastic film, and a button battery is obtained by packaging with a sealing machine.

[0117] Test conditions: the battery's charge and discharge voltage window is 2.5-4.25V, the test is based on 0.2C charging, 0.2C discharging, and the temperature is 25°C.

[0118] Table 2

[0119]

[0120] It can be seen from Table 2 that the positive electrode active material obtained in the embodiment of the present invention is used in a battery, which can improve the initial efficiency of the battery.

[0121] 3. The positive electrode active materials obtained in the examples and comparative examples were used to prepare soft-pack full batteries, and the cycle performance and DCR of the soft-pack full batteries were tested at 45° C. and 2.8-4.5V. The test results are shown in Table 3.

[0122] The soft-pack full battery is prepared by a preparation method comprising the following steps:

[0123] Preparation of positive electrode sheet: placing positive electrode active slurry on two functional surfaces of aluminum foil, and drying to obtain a positive electrode sheet including a positive electrode active layer;

[0124] Among them, in the positive electrode active slurry, the total mass percentage of the positive electrode active material, the conductive agent and the binder is 94.5%, and the mass ratio of the positive electrode active material, the conductive agent SP and the binder PVDF is 94.5%:2.5%:3.0%; the surface area of ​​the positive electrode active layer is 160cm 2 , the coating density of the positive electrode active layer is 0.014g / cm2;

[0125] Preparation of negative electrode sheet: placing negative electrode active slurry on two functional surfaces of copper foil, and drying to obtain a negative electrode sheet including a negative electrode active layer;

[0126] The negative electrode active layer includes artificial graphite, conductive agent SP and binder PVDF, and the mass ratio of artificial graphite, conductive agent and binder is 95.5%:2.5%:2%;

[0127] Preparation of the battery: The positive electrode sheet, separator (PP / PE / PP) and negative electrode sheet are stacked to obtain an electrode assembly, the electrode assembly is placed in an aluminum-plastic film, 30 microliters of a ternary commercial electrolyte (LPF / EC-DEC-EMC, the volume ratio of EC, DEC and EMC is 1:1:1, and the concentration of LPF is 1M) is injected into the aluminum-plastic film, and a sealing machine is used to complete the packaging to obtain an 800mAh soft-pack battery.

[0128] Test conditions: the battery's charge and discharge voltage window is 2.5-4.25V. The test is based on 0.2C charging and 0.2C discharging, the temperature is 45°C, the battery capacity is about 1Ah, and the cycle is 300 times.

[0129] Table 3

[0130]

[0131]

[0132] It can be seen from Table 3 that when the positive electrode active material in the embodiment of the present invention is used to prepare a battery, it helps to improve the cycle performance and DCR performance of the battery.

[0133] Figure 3 The DCR curves of the batteries prepared from the positive electrode active materials of Example 1 and Comparative Example 1 of the present invention are shown in FIG. Figure 3 It can be seen that compared with the battery prepared with the positive electrode active material of Comparative Example 1, the battery prepared with the positive electrode active material of Example 1 of the present invention has a slow increase in DCR after 300 cycles, indicating that the positive electrode active material of the embodiment of the present invention can improve the cycle performance and DCR performance of the battery.

[0134] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode active material, characterized in that: The positive electrode active material is composed of a base particle and a boride coating layer covering at least a portion of the surface and pores of the base particle, the base particle has pores, and the boride coating layer is embedded between the pores; Wherein, the base particle has a structure shown in Formula 1; ； In formula 1, 0.6<x≤0.96, 0≤y<0.2; M is at least one of Mn, Mg, Al, Ti, Nb, Zr, Y, Sb, Sr, Ta, Si, Mo, Sn or W; The boride coating comprises zirconium boride and / or titanium boride; The DCR growth rate of the positive electrode active material after 300 cycles is 10-40%; The porosity of the matrix particles is 2-5%; the porosity of the positive electrode active material is less than the porosity of the matrix particles, and the porosity of the positive electrode active material is ≤3%; In the X-ray diffraction spectrum, the positive electrode active material has a 101 peak with a 2θ value of 36.61°-37.01° and a 012 peak with a 2θ value of 38.28°-38.68°, and the peak area of ​​the 101 peak is 101 And the peak area I of the 012 peak 012 Satisfy: (I 101 / I 012 ) 1 / 2 ≥1.

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2. The positive electrode active material according to claim 1, characterized in that The boride coating layer further comprises boron nitride and / or boron oxide.

3. The positive electrode active material according to any one of claims 1 to 2, characterized in that: The positive electrode active material D n 10 meets, 0.6μm<D n 10<12μm; and / or, The specific surface area A of the positive electrode active material satisfies: 0.3 m 2 / g<A<0.70m 2 / g; and / or, The mass of the boride coating layer is 0.01-0.1% of the mass of the base particles.

4. A method for preparing a positive electrode active material according to any one of claims 1 to 3, characterized in that: The following steps are involved: The positive electrode active material is obtained by heat treating the base particles of Formula 1 and the boride, wherein the base particles have pores, and the boride coating layer is embedded between the pores; The boride comprises zirconium boride and / or titanium boride; The DCR growth rate of the positive electrode active material after 300 cycles is 10-40%; The porosity of the matrix particles is 2-5%; the porosity of the positive electrode active material is less than the porosity of the matrix particles, and the porosity of the positive electrode active material is ≤3%; In the X-ray diffraction spectrum, the positive electrode active material has a 101 peak with a 2θ value of 36.61°-37.01° and a 012 peak with a 2θ value of 38.28°-38.68°, and the peak area of ​​the 101 peak is 101 And the peak area I of the 012 peak 012 Satisfy: (I 101 / I 012 ) 1 / 2 ≥1.

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5. The method for preparing a positive electrode active material according to claim 4, characterized in that: The heat treatment temperature is 200-500°C and the time is .

6. A battery, characterized in that: The invention comprises the positive electrode active material according to any one of claims 1 to 3 or the positive electrode active material prepared by the preparation method according to any one of claims 4 to 5.

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