High-nickel ternary positive electrode composite material and preparation method thereof

Abstract

The invention discloses a high-nickel ternary positive electrode composite material and a preparation method thereof. The high-nickel ternary positive electrode composite material is characterized by comprising a substrate, and a first coating layer and a second coating layer which are coated outside the substrate from inside to outside, the matrix is high-nickel ternary positive electrode material particles; the first coating layer is a Li2X coating layer, wherein X is one or two of S and Se; and the second coating layer is a carbon coating layer. According to the invention, the Li2X coating layer can effectively improve the ionic conductivity of the high-nickel ternary positive electrode material; the carbon coating layer can effectively improve the electronic conductivity of the high-nickel ternary positive electrode material. The prepared high-nickel ternary positive electrode material has double coating layers, and the capacity, the rate capability and the cycle performance of the material are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery material preparation, and particularly relates to a high-nickel ternary cathode composite material and a preparation method thereof. Background Art

[0002] Due to its relatively high theoretical reversible capacity (>200 mAh / g), the high-nickel ternary cathode material has still become the focus of the current research field of cathode materials. However, the high-nickel ternary cathode material itself also has some deficiencies: there is more residual alkali on the surface of the high-nickel ternary cathode material, which affects the processing of the electrode slurry and even causes gas swelling and bulging in the prepared battery cells during the cycling process; the high-nickel ternary cathode material is prone to side reactions with the electrolyte under a fully charged state, resulting in a decrease in the capacity of the battery cell, a deterioration in the cycling performance, and even potential safety hazards.

[0003] Coating is an important method for surface modification of the high-nickel ternary cathode material. In industrial production, the common coating method is to mechanically mix the cathode material and metal oxide and then perform high-temperature sintering. However, this coating method often reduces the ionic conductivity and electronic conductivity of the cathode material, leading to deterioration of the rate performance of the material, and the coating uniformity and firmness are poor, and there will be a situation of shedding during the battery cycling process, thus affecting the capacity and safety of the battery. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-nickel ternary cathode composite material and a preparation method thereof. This coating method can reduce the residual alkali on the surface of the high-nickel ternary cathode material while improving its capacity, rate performance, and cycling performance.

[0005] In the first aspect, the present invention provides a high-nickel ternary cathode composite material, including a matrix and a first coating layer and a second coating layer from inside to outside coated on the outside of the matrix; The matrix is high-nickel ternary cathode material particles; The first coating layer is a Li2X coating layer, where X is one or both of S and Se; The second coating layer is a carbon coating layer.

[0006] Based on the above technical solutions, the Li2X coating layer on the surface of the high-nickel ternary cathode material of the present invention can effectively improve the ionic conductivity of the high-nickel ternary cathode material, where X is one or both of S and Se; the carbon coating layer can effectively improve the electronic conductivity of the high-nickel ternary cathode material. This double-layer coating method can improve the ionic conductivity and electronic conductivity of the high-nickel ternary cathode material simultaneously while reducing the residual alkali on the surface of the high-nickel ternary cathode material, thereby further improving its capacity, rate performance, and cycling performance.

[0007] In the above-mentioned high-nickel ternary cathode composite material, further, the mass of the Li2X coating layer is 0.1% to 5% of the mass of the matrix, including but not limited to 2% to 4%, 2%, 3%, or 4%. Among them, if the mass percentage of the Li2X coating layer in the matrix is too high, the capacity of the cathode material will be reduced, and if it is too low, the improvement of the cathode material will not be obvious.

[0008] In the above-mentioned high-nickel ternary cathode composite material, further, the mass of the carbon coating layer is 0.1% to 3% of the mass of the matrix, including but not limited to 1%.

[0009] In the above-mentioned high-nickel ternary cathode composite material, further, the general formula of the high-nickel ternary cathode material is LiNi x Co y M (1-x-y) O2, where 0.65 ≤ x < 1, 0 < y ≤ 0.2, (x + y) < 1, and M is one or more of Al, Mn, and Mg. As an example, x = 0.90 and y = 0.05.

[0010] In a second aspect, the present invention provides a method for preparing the high-nickel ternary cathode composite material described in any one of the above, including the following steps: S1. Uniformly mix the high-nickel ternary cathode material precursor with an excessive lithium source and then sinter to obtain the high-nickel ternary cathode material; S2. Perform a first annealing treatment on the high-nickel ternary cathode material obtained in step S1 in an H2X atmosphere, where X is one or both of S and Se, to form the first coating layer; S3. Perform a second annealing treatment on the product obtained in step S2 in an atmosphere of a mixed gas composed of an olefin gas and an inert protective gas to form the second coating layer, thereby obtaining the high-nickel ternary cathode composite material.

[0011] In the above-mentioned method for preparing the high-nickel ternary cathode composite material, further, in step S1, the chemical general formula of the high-nickel ternary cathode material precursor is Ni x Co y M (1-x-y) O2, where 0.65 ≤ x < 1, 0 < y ≤ 0.2, (x + y) < 1, and M is one or more of Al, Mn, and Mg; as an example, x = 0.90 and y = 0.05; The stoichiometric ratio of the high-nickel ternary cathode material precursor to the lithium source is 1:(1.01 to 1.2), including but not limited to 1:1.02, 1:1.04, or 1:1.06; The lithium source is at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium citrate; The sintering step includes: first heating to 500 - 600 °C for pre-sintering for 3 - 8 h, then continuing to heat to 700 - 950 °C for heat preservation for 10 - 20 h, and the heating rate is 1 - 10 °C / min. As an example, the sintering is first heating to 500 °C at a rate of 2 °C / min for pre-sintering for 5 h, and then continuing to heat to 750 °C at a rate of 2 °C / min for heat preservation for 12 h. It can be understood that the method further includes the following steps after the sintering: cooling the sintered product and then pulverizing and sieving it.

[0012] In the above preparation method of the high-nickel ternary cathode composite material, further, in step S2, the first annealing treatment step includes: pumping the air pressure in the annealing furnace cavity to below 100 Pa, heating to 300 - 500 °C, and introducing 5 - 50 kPa of the H2X gas, heat preservation for 0.5 - 5 h, and the heating rate is 1 - 10 °C / min. As an example, the annealing treatment step includes: pumping the air pressure in the annealing furnace cavity to below 100 Pa, heating to 350 °C at a rate of 2 °C / min, and introducing 10 kPa or 20 kPa of H2Se gas, heat preservation for 3 h.

[0013] In the above preparation method of the high-nickel ternary cathode composite material, further, in step S3, the olefin gas is one or more of ethylene, propylene, 1-butene, 2-butene, 1,3-butadiene; The inert protective gas is one or more of nitrogen, helium, neon, argon, krypton, xenon; The volume ratio of the olefin gas to the inert protective gas is 1:(7 - 10), including but not limited to 1:8.

[0014] In the above preparation method of the high-nickel ternary cathode composite material, further, in step S3, the second annealing treatment step includes: pumping the air pressure in the annealing furnace cavity to below 100 Pa, heating to 500 - 650 °C, and introducing 10 - 50 kPa of the mixed gas composed of the olefin gas and the inert protective gas, heat preservation for 0.5 - 4 h, and the heating rate is 1 - 10 °C / min. As an example, the second annealing treatment step includes: pumping the air pressure in the annealing furnace cavity to below 100 Pa, heating to 550 °C at a rate of 2 °C / min, and introducing 3 kPa of 1-butene and 24 kPa of argon, heat preservation for 1 h. It can be understood that the method further includes the following steps after the second annealing treatment: pumping the air pressure in the annealing furnace cavity to below 100 Pa and waiting for natural cooling.

[0015] In the present invention, in steps S2 and S3, the mass of the high-nickel ternary cathode material participating in the reaction can be derived according to the ideal gas equation PV = NRT. Where P is the internal pressure of the furnace chamber, V is the volume of the furnace chamber, N is the amount of substance of H2X or olefin, R is the gas constant, and T is the temperature inside the furnace chamber. After determining the pressure of the introduced gas, the volume of the furnace chamber, and the temperature inside the furnace chamber, the amount of substance of the coating material is calculated, and based on the coating ratio, the mass of the high-nickel ternary cathode material participating in the reaction can be derived.

[0016] In a third aspect, the present invention provides a lithium-ion battery, including a positive electrode and a negative electrode. The positive electrode includes the high-nickel ternary cathode composite material described in any one of the above or the high-nickel ternary cathode composite material obtained by the preparation method described in any one of the above. As a test example, the battery is a half-cell. The positive electrode includes a carbon-coated aluminum foil and the high-nickel ternary cathode composite material, carbon black SuperP, and polyvinylidene fluoride (Solvey5130) with a mass ratio of 90:5:5 provided on the carbon-coated aluminum foil. The negative electrode uses a lithium sheet as the negative electrode plate, uses a solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) of 1 mol / L lithium hexafluorophosphate (the mass ratio of EC to DMC is 1:1) as the electrolyte, and uses cell gard2300 as the separator.

[0017] The present invention has the following beneficial effects: (1) In the present invention, H2X gas is used to coat Li2X on the high-nickel ternary cathode material particles, where X is one or both of S and Se, which can effectively improve the ionic conductivity of the high-nickel ternary cathode material particles and improve their rate performance.

[0018] (2) In the present invention, carbon materials are used for secondary coating, which can effectively improve the electronic conductivity of the material, improve the power performance of the material, and also play a role in protecting the material from being eroded by the electrolyte.

[0019] (3) The composite material obtained by the present invention has excellent performance. The entire preparation process has a simple process, low cost, is easy to scale up, and has very good commercial value. Description of the Drawings

[0020] Figure 1 XRD pattern of the high-nickel ternary cathode material prepared in Example 2 of the present invention and the material prepared in Comparative Example 1; Figure 2 Cross-sectional morphology characterization diagram of the high-nickel ternary cathode material prepared in Example 2 of the present invention; Figure 3 EDS diagram of the high-nickel ternary cathode material prepared in Example 2 of the present invention. Detailed Embodiments

[0021] The present invention will be further described in detail below in conjunction with specific embodiments. The provided embodiments are only for clarifying the present invention and not for limiting the scope of the present invention. The following provided embodiments can be used as a guide for those of ordinary skill in the art to make further improvements, and do not constitute any limitation to the present invention in any way.

[0022] The methods used in the following embodiments are all conventional methods unless otherwise specified, and are carried out according to the techniques or conditions described in the literature in this field or according to the product instructions. The materials, reagents, etc. used in the following embodiments can be obtained from commercial channels unless otherwise specified.

[0023] Example 1 This example provides a method for preparing a high-nickel ternary cathode material, which includes the following steps: S1. Take a certain amount of the high-nickel ternary cathode material precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2, and uniformly mix it with LiOH according to a stoichiometric ratio of 1:1.02. First, heat it to 500°C at a rate of 2°C / min for pre-sintering for 5 h, then continue to heat it to 750°C at a rate of 2°C / min for heat preservation for 12 h, cool it and then crush and screen it to obtain high-nickel ternary cathode material particles; S2. Take 100 g of the high-nickel ternary cathode material lithium particles obtained in step S1 and place them in an annealing furnace (with a volume of 18 L). Pump the air pressure in the annealing furnace cavity to below 100 Pa, raise the temperature of the annealing furnace to 350°C at a rate of 2°C / min, and introduce 10 kPa of H2Se gas. Keep the temperature of the annealing furnace at 350°C for a duration of 3 h.

[0024] S3. Pump the air pressure in the annealing furnace (with a volume of 18 L) cavity to below 100 Pa, raise the temperature of the annealing furnace to 550°C at a rate of 2°C / min, introduce 3 kPa of 1-butene and 24 kPa of argon, keep the temperature of the annealing furnace at 550°C, after a duration of 1 h, pump the air pressure in the annealing furnace cavity to below 100 Pa, and wait for natural cooling to obtain the high-nickel ternary cathode composite material.

[0025] Example 2 This example provides a method for preparing a high-nickel ternary cathode material, which includes the following steps: S1. Take a certain amount of the high-nickel ternary cathode material precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2, and uniformly mix it with LiOH according to a stoichiometric ratio of 1:1.04. First, heat it to 500°C at a rate of 2°C / min for pre-sintering for 5 h, then continue to heat it to 750°C at a rate of 2°C / min for heat preservation for 12 h, cool it and then crush and screen it to obtain high-nickel ternary cathode material particles; S2. Take 100 g of the high-nickel ternary cathode material lithium particles obtained in step S1 and place them in an annealing furnace (with a volume of 18 L). Pump the air pressure in the annealing furnace cavity to below 100 Pa. Raise the temperature of the annealing furnace to 350 °C at a rate of 2 °C / min, and introduce 10 kPa of H2Se gas. Keep the temperature of the annealing furnace at 350 °C for 3 h.

[0026] S3. Pump the air pressure in the annealing furnace (with a volume of 18 L) to below 100 Pa. Raise the temperature of the annealing furnace to 550 °C at a rate of 2 °C / min, introduce 3 kPa of 1-butene and 24 kPa of argon. Keep the temperature of the annealing furnace at 550 °C for 1 h, then pump the air pressure in the annealing furnace cavity to below 100 Pa and wait for natural cooling to obtain the high-nickel ternary cathode composite material.

[0027] Example 3 A preparation method of a high-nickel ternary cathode material proposed in this example includes the following steps: S1. Take a certain amount of the high-nickel ternary cathode material precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and uniformly mix it with LiOH at a stoichiometric ratio of 1:1.06. First, raise the temperature to 500 °C at a rate of 2 °C / min for pre-sintering for 5 h, then continue to raise the temperature to 750 °C for heat preservation for 12 h. After cooling, pulverize and screen to obtain high-nickel ternary cathode material particles; S2. Take 100 g of the high-nickel ternary cathode material lithium particles obtained in step S1 and place them in an annealing furnace (with a volume of 18 L). Pump the air pressure in the annealing furnace (with a volume of 18 L) cavity to below 100 Pa. Raise the temperature of the annealing furnace to 350 °C at a rate of 2 °C / min, and introduce 10 kPa of H2Se gas. Keep the temperature of the annealing furnace at 350 °C for 3 h.

[0028] S3. Pump the air pressure in the annealing furnace cavity to below 100 Pa. Raise the temperature of the annealing furnace to 550 °C at a rate of 2 °C / min, introduce 3 kPa of 1-butene and 24 kPa of argon. Keep the temperature of the annealing furnace at 550 °C for 1 h, then pump the air pressure in the annealing furnace cavity to below 100 Pa and wait for natural cooling to obtain the high-nickel ternary cathode composite material.

[0029] Example 4 A preparation method of a high-nickel ternary cathode material proposed in this example includes the following steps: S1. Take a certain amount of the high-nickel ternary cathode material precursor Ni 0.90 Co 0.05 Mn 0.05(OH)2 is uniformly mixed with LiOH in a stoichiometric ratio of 1:1.02. First, it is heated to 500 °C at a rate of 2 °C / min for pre-sintering for 5 h, then continuously heated to 750 °C at a rate of 2 °C / min and held for 12 h. After cooling, it is pulverized and sieved to obtain high-nickel ternary cathode material particles; S2. Take 100 g of the high-nickel ternary cathode material lithium particles obtained in step S1 and place them in an annealing furnace (with a volume of 18 L). The air pressure in the furnace cavity of the annealing furnace (with a volume of 18 L) is pumped to below 100 Pa. The temperature of the annealing furnace is raised to 350 °C at a rate of 2 °C / min, and 20 kPa of H2Se gas is introduced. The temperature of the annealing furnace is maintained at 350 °C for a duration of 3 h.

[0030] S3. The air pressure in the furnace cavity of the annealing furnace is pumped to below 100 Pa. The temperature of the annealing furnace is raised to 550 °C at a rate of 2 °C / min, 3 kPa of 1-butene and 24 kPa of argon are introduced. The temperature of the annealing furnace is maintained at 550 °C. After 1 h, the air pressure in the furnace cavity of the annealing furnace is pumped to below 100 Pa, and wait for natural cooling to obtain the high-nickel ternary cathode composite material.

[0031] Example 5 A preparation method of a high-nickel ternary cathode material proposed in this example includes the following steps: S1. Take a certain amount of the high-nickel ternary cathode material precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 is uniformly mixed with LiOH in a stoichiometric ratio of 1:1.04. First, it is heated to 500 °C at a rate of 2 °C / min for pre-sintering for 5 h, then continuously heated to 750 °C at a rate of 2 °C / min and held for 12 h. After cooling, it is pulverized and sieved to obtain high-nickel ternary cathode material particles; S2. Take 100 g of the high-nickel ternary cathode material lithium particles obtained in step S1 and place them in an annealing furnace (with a volume of 18 L). The air pressure in the furnace cavity of the annealing furnace (with a volume of 18 L) is pumped to below 100 Pa. The temperature of the annealing furnace is raised to 350 °C at a rate of 2 °C / min, and 20 kPa of H2Se gas is introduced. The temperature of the annealing furnace is maintained at 350 °C for a duration of 3 h.

[0032] S3. The air pressure in the furnace cavity of the annealing furnace is pumped to below 100 Pa. The temperature of the annealing furnace is raised to 550 °C at a rate of 2 °C / min, 3 kPa of 1-butene and 24 kPa of argon are introduced. The temperature of the annealing furnace is maintained at 550 °C. After 1 h, the air pressure in the furnace cavity of the annealing furnace is pumped to below 100 Pa, and wait for natural cooling to obtain the high-nickel ternary cathode composite material.

[0033] Example 6 A preparation method of a high-nickel ternary cathode material proposed in this example includes the following steps: S1. Take a certain amount of the high-nickel ternary cathode material precursor Ni0.90 Co 0.05 Mn 0.05 (OH)2 is uniformly mixed with LiOH at a stoichiometric ratio of 1:1.06. First, it is heated to 500 °C at a rate of 2 °C / min for pre-sintering for 5 h, then continuously heated to 750 °C at a rate of 2 °C / min and held for 12 h. After cooling, it is crushed and sieved to obtain high-nickel ternary cathode material particles; S2. Take 100 g of the high-nickel ternary cathode material lithium particles obtained in step S1 and place them in an annealing furnace (with a volume of 18 L). The air pressure in the annealing furnace cavity is pumped to below 100 Pa. The temperature of the annealing furnace is raised to 350 °C at a rate of 2 °C / min, and 20 kPa of H2Se gas is introduced. The temperature of the annealing furnace is maintained at 350 °C for a duration of 3 h.

[0034] S3. The air pressure in the annealing furnace (with a volume of 18 L) cavity is pumped to below 100 Pa. The temperature of the annealing furnace is raised to 550 °C at a rate of 2 °C / min, 3 kPa of 1-butene and 24 kPa of argon are introduced. The temperature of the annealing furnace is maintained at 550 °C. After 1 h, the air pressure in the annealing furnace cavity is pumped to below 100 Pa, and it is left to cool naturally to obtain the high-nickel ternary cathode composite material.

[0035] Example 7 A preparation method of a high-nickel ternary cathode material proposed in this example includes the following steps: S1. Take a certain amount of the high-nickel ternary cathode material precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 is uniformly mixed with LiOH at a stoichiometric ratio of 1:1.04. First, it is heated to 500 °C at a rate of 2 °C / min for pre-sintering for 5 h, then continuously heated to 750 °C at a rate of 2 °C / min and held for 12 h. After cooling, it is crushed and sieved to obtain high-nickel ternary cathode material particles; S2. Take 100 g of the high-nickel ternary cathode material lithium particles obtained in step S1 and place them in an annealing furnace (with a volume of 18 L). The air pressure in the annealing furnace cavity is pumped to below 100 Pa. The temperature of the annealing furnace is raised to 350 °C at a rate of 2 °C / min, and 10 kPa of H2Se gas is introduced. The temperature of the annealing furnace is maintained at 350 °C for a duration of 3 h.

[0036] S3. The air pressure in the annealing furnace (with a volume of 18 L) cavity is pumped to below 100 Pa. The temperature of the annealing furnace is raised to 550 °C at a rate of 2 °C / min, 1 kPa of 1-butene and 29 kPa of argon are introduced. The temperature of the annealing furnace is maintained at 550 °C. After 1 h, the air pressure in the annealing furnace cavity is pumped to below 100 Pa, and it is left to cool naturally to obtain the high-nickel ternary cathode composite material.

[0037] Example 8 A preparation method of a high-nickel ternary cathode material proposed in this embodiment includes the following steps: S1. Take a certain amount of high-nickel ternary cathode material precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2, and uniformly mix it with LiOH according to a stoichiometric ratio of 1:1.04. First, heat it to 500°C at a rate of 2°C / min for pre-sintering for 5 h, then continue to heat it to 750°C at a rate of 2°C / min and hold for 12 h. After cooling, pulverize and screen it to obtain high-nickel ternary cathode material particles; S2. Take 100 g of the high-nickel ternary cathode material lithium particles obtained in step S1 and place them in an annealing furnace (with a volume of 18 L). Pump the air pressure in the annealing furnace cavity to below 100 Pa, heat the annealing furnace temperature to 350°C at a rate of 2°C / min, and introduce 10 kPa of H2Se gas. Keep the annealing furnace temperature at 350°C for 3 h.

[0038] S3. Pump the air pressure in the annealing furnace (with a volume of 18 L) cavity to below 100 Pa, heat the annealing furnace temperature to 550°C at a rate of 2°C / min, introduce 5 kPa of 1-butene and 25 kPa of argon. Keep the annealing furnace temperature at 550°C. After 1 h, pump the air pressure in the annealing furnace cavity to below 100 Pa and wait for natural cooling to obtain the high-nickel ternary cathode composite material.

[0039] Comparative Example 1 Take a certain amount of high-nickel ternary cathode material precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2, and uniformly mix it with LiOH according to a stoichiometric ratio of 1:1.04. First, heat it to 500°C at a rate of 2°C / min for pre-sintering for 5 h, then continue to heat it to 750°C at a rate of 2°C / min and hold for 12 h. After cooling, pulverize and screen it to obtain high-nickel ternary cathode material particles.

[0040] Comparative Example 2 S1. Take a certain amount of high-nickel ternary cathode material precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2, and uniformly mix it with LiOH according to a stoichiometric ratio of 1:1.04. First, heat it to 500°C at a rate of 2°C / min for pre-sintering for 5 h, then continue to heat it to 750°C at a rate of 2°C / min and hold for 12 h. After cooling, pulverize and screen it to obtain high-nickel ternary cathode material particles; S2. Take 100 g of the high-nickel ternary cathode material lithium particles obtained in step S1 and place them in an annealing furnace (with a volume of 18 L). Pump the air pressure in the cavity of the annealing furnace (with a volume of 18 L) to below 100 Pa. Raise the temperature of the annealing furnace to 350 °C at a rate of 2 °C / min, and introduce 10 kPa of H2Se gas. Keep the temperature of the annealing furnace at 350 °C. After 3 h, pump the air pressure in the cavity of the annealing furnace to below 100 Pa and wait for natural cooling to obtain the high-nickel ternary cathode composite material coated with Li2Se.

[0041] Comparative Example 3 S1. Take a certain amount of the high-nickel ternary cathode material precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and uniformly mix it with LiOH at a stoichiometric ratio of 1:1.04. First, raise the temperature to 500 °C at a rate of 2 °C / min and pre-sinter for 5 h, then continue to raise the temperature to 750 °C and hold for 12 h. After cooling, crush and screen to obtain high-nickel ternary cathode material particles; S2. Take 100 g of the high-nickel ternary cathode material lithium particles obtained in step S1 and place them in an annealing furnace. Pump the air pressure in the cavity of the annealing furnace (with a volume of 18 L) to below 100 Pa. Raise the temperature of the annealing furnace to 550 °C at a rate of 2 °C / min, introduce 3 kPa of 1-butene and 24 kPa of argon. Keep the temperature of the annealing furnace at 550 °C. After 1 h, pump the air pressure in the cavity of the annealing furnace to below 100 Pa and wait for natural cooling to obtain the high-nickel ternary cathode composite material coated with carbon.

[0042] Effect verification 1. Structural characteristics It can be seen from Figure 1 that the material prepared in Example 2 shows the Li2Se characteristic peak. In addition, all characteristic peaks can be clearly attributed to the hexagonal layered α-NaFeO2 structure, accompanied by the R-3m space group. This indicates that Li2Se is generated during the annealing process and has no obvious effect on the crystal structure of the high-nickel ternary cathode material.

[0043] It can be seen from Figure 2 that there are two coating layers on the surface of the matrix material; the first coating layer is the Li2Se coating layer; the second coating layer is the carbon coating layer.

[0044] It can be seen from Figure 3 that the coating elements Se and C are evenly distributed, indicating that the coatings Li2Se and C can be relatively evenly coated on the surface of the material prepared in Example 2, thus improving the ionic conductivity and electronic conductivity of the material.

[0045] 2. Electrochemical performance The prepared high-nickel ternary cathode composite material, carbon black SuperP, and polyvinylidene fluoride (Solvey 5130) were mixed at a mass ratio of 90:5:5. Using N-methylpyrrolidone as the solvent, a slurry with a mass fraction of 5% was prepared and uniformly coated on the surface of the carbon-coated aluminum foil. It was dried at 100 °C for 5 h, and the positive electrode sheet was obtained after rolling. Using a lithium sheet as the negative electrode sheet, a solution of 1 mol / L lithium hexafluorophosphate in ethylene carbonate (EC) and dimethyl carbonate (DMC) (the mass ratio of EC to DMC is 1:1) as the electrolyte, and cellgard 2300 as the separator, it was assembled in a glove box to obtain a lithium-ion half-cell. And its electrochemical performance was tested.

[0046] When testing the high-nickel ternary cathode material, the charge cut-off voltage was 4.3 V (relative to the lithium sheet), and the discharge cut-off voltage was 2.8 V (relative to the lithium sheet).

[0047] The results are shown in Table 1.

[0048] Table 1. Test results of electrochemical performance

[0049] The discharge specific capacity of the electrode sheet made of the material obtained in Example 2 reached 217.3 mAh / g at 0.2C and 207.5 mAh / g at 1C. After 100 cycles at 1C, the capacity retention rate of the electrode sheet made of the material in Example 2 reached 97.2%.

[0050] The discharge specific capacity of the electrode sheet made of the material obtained in Comparative Example 1 reached 212.5 mAh / g at 0.2C and 198.3 mAh / g at 1C. After 100 cycles at 1C, the capacity retention rate of the electrode sheet made of the material in Comparative Example 1 reached 89.8%.

[0051] The discharge specific capacity of the electrode sheet made of the material obtained in Comparative Example 2 reached 215.1 mAh / g at 0.2C and 203.2 mAh / g at 1C. After 100 cycles at 1C, the capacity retention rate of the electrode sheet made of the material in Comparative Example 1 reached 93.3%.

[0052] The discharge specific capacity of the electrode sheet made of the material obtained in Comparative Example 3 reached 213.3 mAh / g at 0.2C and 200.5 mAh / g at 1C. After 100 cycles at 1C, the capacity retention rate of the electrode sheet made of the material in Comparative Example 1 reached 92.2%.

[0053] It can be seen from the comparison results of the above Example 2 and Comparative Examples 1-3 that the discharge specific capacity, rate performance, and cycle stability of the high-nickel ternary cathode material coated with Li2Se and C have been significantly improved. It can be seen from Examples 1-8 that the capacity, rate performance, and cycle performance of the high-nickel ternary cathode material of the present invention are excellent.

[0054] The present invention has been described in detail above. For those skilled in the art, within the scope of not departing from the purpose and spirit of the present invention, the present invention can be implemented within a relatively wide range under equivalent parameters, concentrations, and conditions. Although specific embodiments of the present invention are given, it should be understood that the present invention can be further improved. In short, according to the principle of the present invention, this application intends to cover any changes, uses, or improvements to the present invention, including those that depart from the scope disclosed in this application and are made using conventional techniques known in the art.

Claims

1. A high-nickel ternary positive electrode composite material, characterized in that: It comprises a substrate and a first coating layer and a second coating layer which are coated outside the substrate from inside to outside; The matrix is ​​high-nickel ternary positive electrode material particles; The first coating layer is a Li2X coating layer, wherein X is one or two of S and Se; The second coating layer is a carbon coating layer.

2. The high-nickel ternary positive electrode composite material according to claim 1, characterized in that: The mass of the Li2X coating layer is 0.1% to 5% of the mass of the substrate.

3. The high-nickel ternary positive electrode composite material according to claim 1, characterized in that: The mass of the carbon coating layer is 0.1% to 3% of the mass of the substrate.

4. The high-nickel ternary positive electrode composite material according to claim 1, characterized in that: The general formula of the high nickel ternary positive electrode material is LiNi x Co y M (1-x-y) O2, wherein 0.65≤x<1, 0<y≤0.2, (x+y)<1, and M is one or more of Al, Mn, and Mg.

5. The method for preparing the high-nickel ternary positive electrode composite material according to any one of claims 1 to 4, characterized in that: The steps include: S1, uniformly mixing a high-nickel ternary positive electrode material precursor with an excess lithium source and sintering the mixture to obtain the high-nickel ternary positive electrode material; S2, performing a first annealing treatment on the high-nickel ternary positive electrode material obtained in step S1 under a H2X atmosphere, wherein X is one or both of S and Se, to form the first coating layer; S3. The product obtained in step S2 is subjected to a second annealing treatment in an atmosphere of a mixed gas consisting of an olefin gas and an inert protective gas to form the second coating layer, thereby obtaining the high-nickel ternary positive electrode composite material.

6. The method for preparing the high-nickel ternary positive electrode composite material according to claim 5, characterized in that: In step S1, the chemical formula of the high nickel ternary cathode material precursor is Ni x Co y M (1-x-y) O2, wherein 0.65≤x<1, 0<y≤0.2, (x+y)<1, M is one or more of Al, Mn, and Mg; The stoichiometric ratio of the high-nickel ternary positive electrode material precursor to the lithium source is 1:(1.01-1.2); The lithium source is at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium citrate; The sintering step includes: firstly heating to 500-600° C. for pre-sintering for 3-8 hours, then continuing to heat to 700-950° C. for keeping warm for 10-20 hours, with a heating rate of 1-10° C. / min.

7. The method for preparing the high-nickel ternary positive electrode composite material according to claim 5, characterized in that: In step S2, the first annealing treatment comprises: pumping the gas pressure in the annealing furnace chamber to below 100 Pa, heating to 300-500° C., introducing 5-50 kPa of H2X gas, keeping warm for 0.5-5 hours, and heating rate of 1-10° C. / min.

8. The method for preparing the high-nickel ternary positive electrode composite material according to claim 5, characterized in that: In step S3, the olefin gas is one or more of ethylene, propylene, 1-butene, 2-butene, and 1,3-dibutene; The inert protective gas is one or more of nitrogen, helium, neon, argon, krypton, and xenon; The volume ratio of the olefin gas to the inert protective gas is 1:(7-10).

9. The method for preparing the high-nickel ternary positive electrode composite material according to claim 5, characterized in that: In step S3, the second annealing treatment step includes: pumping the gas pressure in the annealing furnace chamber to below 100 Pa, heating it to 500-650° C., and introducing a mixed gas composed of olefin gas and inert protective gas at 10-50 kPa, keeping it warm for 0.5-4 hours, and the heating rate is 1-10° C. / min.

10. A lithium ion battery comprising a positive electrode and a negative electrode, characterized in that: The positive electrode comprises the high-nickel ternary positive electrode composite material according to any one of claims 1 to 4 or the high-nickel ternary positive electrode composite material obtained by the preparation method according to any one of claims 5 to 9.

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