A high-nickel ternary cathode material and its preparation method

Abstract

The present invention discloses a high-nickel ternary cathode material and a preparation method thereof. The high-nickel ternary cathode material comprises a matrix, a first coating layer, and a second coating layer which are sequentially arranged from the inside to the outside. The first coating layer comprises a lactic acid oligomer and a conductive lithium salt, and the second coating layer comprises polylactic acid. In the preparation process, a high-nickel ternary precursor, a lithium source, and a dopant are mixed and sintered to obtain the matrix, and then the matrix, a lactic acid solution, and a conductive lithium salt are reacted at a temperature of 130°C to 160°C for 4 to 10 hours to obtain the first coating layer disposed on the outside of the matrix. Finally, under the action of a catalyst, the second coating layer is disposed on the outside of the first coating layer. The present invention realizes double modification of coating modification and secondary repair of microcracks for the high-nickel ternary cathode material on the premise of ensuring the capacity of the lithium battery, significantly reduces the residual alkali value of the material, and significantly enhances the cycle stability.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of high energy density, long life, environmental friendliness, etc., and are widely used in the fields of mobile communication, new energy vehicles, aerospace and military industries. Among them, as an essential component of lithium-ion batteries, the cathode material not only has an important impact on the cycle performance and rate performance of the battery, but also is the bottleneck affecting the energy density of the battery. In order to address issues such as energy crisis and environmental pollution, in recent years, the new energy industry mainly based on electric vehicles has received increasing attention. The key lies in the development of high-energy-density power batteries. To achieve the goal of a specific energy density of 300 Wh / kg for a single battery, high-nickel ternary cathode materials are an ideal choice. High-nickel ternary cathode materials generally refer to ternary layered cathode oxides with a nickel content ≥ 0.6 in the transition metal layer. Compared with traditional lithium iron phosphate and lithium cobalt oxide, they have the advantages of high reversible capacity, high working voltage, low cobalt, and low cost, and are therefore widely used in the power batteries of electric vehicles.

[0003] Increasing the nickel content in layered cathode materials can provide high capacity, but such materials also face some challenges in large-scale applications: one is poor structural stability. For example, during the charge and discharge process of high-nickel ternary cathode materials, there is a relatively large volume change in the c direction during the H2-H3 phase transition. The higher the nickel content, the greater the volume expansion ratio, which will lead to microcracks. The electrolyte will penetrate along the microcracks into the interior of the secondary particles, causing structural degradation on the surface of the primary particles. The cracks will cause the electrochemical performance of the cathode material to decline. The other is poor surface chemical stability. For example, the chemically unstable surface of nickel-rich cathode materials will react with moisture or air, forming residual Li 2 CO 3 and LiOH, which not only leads to an increase in the slurry viscosity, forming a gel state and affecting the electrochemical performance of the material, but also these residual lithium compounds react with the electrolyte during the battery cycle to generate gas, which will cause safety problems such as battery swelling, and there is a potential risk of fire and explosion. Therefore, preparing a high-nickel ternary cathode material with good structural stability and good surface chemical stability is crucial for improving the performance of lithium-ion batteries. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-nickel ternary cathode material and a preparation method thereof, aiming to solve the above problems. On the premise of ensuring the capacity of the lithium battery, the present invention realizes the dual modification of coating modification and secondary repair of microcracks for the high-nickel ternary cathode material, significantly reducing the residual alkali value of the material and significantly enhancing the cycle stability.

[0005] The present invention is mainly implemented through the following technical solutions:

[0006] A high-nickel ternary cathode material, comprising a matrix, a first coating layer and a second coating layer. The matrix is a high-nickel ternary active material. The first coating layer is disposed outside the matrix, and the second coating layer is disposed outside the first coating layer. The first coating layer includes a lactic acid oligomer and a conductive lithium salt, and the second coating layer includes polylactic acid.

[0007] To better implement the present invention, further, the matrix is obtained by sintering a high-nickel ternary precursor, a lithium source and a dopant, and the molar ratio of the lithium source, the high-nickel ternary precursor and the dopant is (1.00 - 1.06):(0.98 - 1):(0 - 0.02). The dopant is a compound containing a doping element M, and the doping element M is any one or more of W, Mo, Ta, Zr, A1, Ti, Mg, Nb, Ba, B. The second coating layer further includes a catalyst.

[0008] Mix and sinter the high-nickel ternary precursor, the lithium source and the dopant to obtain a matrix, and then react the matrix, a lactic acid solution and a conductive lithium salt at a temperature of 130°C - 160°C for 3 - 7 h to obtain a first coating layer disposed outside the matrix, and the first coating layer includes a lactic acid oligomer and a conductive lithium salt. The excess lactic acid and part of the lactic acid oligomer are used to form a second coating layer outside the first coating layer under the action of a catalyst.

[0009] To better implement the present invention, further, the high-nickel ternary precursor is Ni x Co y Mn (1-x-y) (OH) 2 or Ni x Co y Al (1-x-y) (OH) 2 , where 0.6 ≤ x ≤ 1 and 0 ≤ y ≤ 0.2.

[0010] To better implement the present invention, further, the lithium source is any one or more of lithium hydroxide, lithium carbonate, lithium acetate, and lithium nitrate.

[0011] To better implement the present invention, further, the conductive lithium salt is any one or more of anhydrous lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide salt, lithium bis(oxalato)borate, and lithium hexafluorophosphate.

[0012] The present invention is mainly implemented through the following technical solutions:

[0013] A method for preparing a high-nickel ternary cathode material, comprising the following steps:

[0014] Step S1: Mix a high-nickel ternary precursor, a lithium source, and a dopant evenly to obtain a blend. Sinter the blend in an oxygen-containing atmosphere once, grind it, and sieve it to obtain Material A;

[0015] Step S2: Mix Material A, a lactic acid solution, and a conductive lithium salt evenly, heat them to 80°C - 110°C in an inert atmosphere, then reduce the pressure and gradually heat them to 130°C - 160°C, stop the reaction after 3 - 7 h, and obtain Mixture B;

[0016] Step S3: Add a catalyst to Mixture B, keep the pressure at atmospheric pressure, gradually raise the temperature to 160°C - 180°C, then keep the temperature and reduce the pressure, stop the reaction after 8 - 15 h, cool it to room temperature and dry it to prepare the high-nickel ternary cathode material.

[0017] In Step S2, during the process of raising the temperature to 80 - 110°C, the heating rate is relatively fast. The relatively fast heating rate can reduce the experimental time, and there is no holding time set in this process; subsequently, when slowly raising the temperature to 130 - 160°C, it should be very slow, so as to better coat and repair cracks. Preferably, in Step S1, the sintering temperature is 650°C - 900°C. Preferably, in Step S1, in the atmosphere of the first sintering, the volume percentage of oxygen content is 1% - 100%. Preferably, in Step S3, dry it in a vacuum drying oven at 60°C - 90°C for 3 - 8 h.

[0018] To better implement the present invention, further, in Step S2, the molar concentration of the conductive lithium salt dissolved in the lactic acid solution is 0.8 - 2 mol / L. Preferably, in Step S2, add a lactic acid solution with a mass fraction of 0.3 wt% - 1 wt%.

[0019] To better implement the present invention, further, in Step S2, the dosage of lactic acid is 0.3 wt% - 1 wt% of the dosage of Material A, and in Step S3, the dosage of the catalyst is 1 wt% - 10 wt% of the dosage of lactic acid. Preferably, the lactic acid is L-lactic acid or D-lactic acid.

[0020] To better implement the present invention, further, the catalyst is any one or more of stannous chloride, tin powder, stannous octoate, and dibutyltin.

[0021] To better implement the present invention, further, in Step S2, the inert atmosphere is any one of argon, helium, and neon.

[0022] To better implement the present invention, further, in step S2, after the solution is heated to 80°C to 110°C, it is maintained in an inert atmosphere, and the solution is heated to temperature a at a heating rate of 5 to 40°C / h, and the air pressure is reduced from atmospheric pressure to pressure b at a rate of 220 to 720 mmHg / h; the reaction is maintained for 2 - 5 h, and then the solution is heated more slowly to temperature c at a heating rate of 5 to 20°C / h, and the air pressure is further reduced more slowly to pressure d at a rate of 5 to 20 mmHg / h. After the reaction for 1 - 2 h, it is stopped to obtain mixture B; wherein, temperature a is 120°C to 160°C, temperature c is 130°C to 160°C, and c > a; pressure b is 20 to 40 mmHg, pressure d is 10 to 30 mmHg, and b > d. In step S3, after adding a catalyst to mixture B, the solution is heated to 160°C to 180°C at a heating rate of 2 to 10°C / h, and then the temperature is maintained and the air pressure is reduced from atmospheric pressure to 1 to 10 mmHg at a rate of 60 to 150 mmHg / h.

[0023] In step S2, when heating to 130°C to 160°C and reducing the pressure to 10 to 30 mmHg, it is carried out in two stages. Among them, the heating rate and the pressure reduction rate in the first stage are relatively fast, and those in the second stage are slower. Such a setting ensures the reliable progress of the reaction, improves the stability of the reaction, promotes the formation of the first coating layer, and better repairs the microcracks on the surface of the high-nickel ternary cathode material. During the reaction, the purpose of reducing the pressure is that under the action of reduced pressure, small-molecule water is easily removed from the system, making the reaction proceed in the direction of polycondensation and increasing the molecular weight of the prepolymer. However, at the same time, lactic acid and small-molecule oligomers will be distilled out, reducing the yield. Therefore, the pressure reduction speed should be as slow as possible to avoid the entrainment and distillation of lactic acid and its oligomers when small-molecule water is removed.

[0024] The present invention first uniformly mixes a high-nickel ternary precursor, a lithium source, and a dopant to obtain a blend, and sinters the blend in an oxygen-containing atmosphere. During the sintering process, the doping element can change the lattice constant or the valence state of certain elements of the high-nickel ternary cathode material, enhance the stability of the material structure, and at the same time can also reduce the cation mixing of the high-nickel ternary cathode material, improving the electronic conductivity and ionic conductivity of the high-nickel ternary cathode material. However, there are microcracks on the surface of the obtained first-fired material. The first-fired material, a conductive lithium salt, and an aqueous lactic acid solution are added to a four-necked flask, and the reaction between the first-fired material and lactic acid effectively removes the residual alkali. After replacement with an inert atmosphere, through slow heating and pressure reduction, lactic acid dehydrates and prepolymerizes to obtain a mixture of the first-fired material, a conductive lithium salt, and lactic acid oligomers. Then, a catalyst is added, and heating and pressure reduction continue slowly. The lactic acid oligomers melt and polycondense to synthesize polylactic acid, that is, a mixture of the first-fired material, a conductive lithium salt, and polylactic acid is obtained.

[0025] The beneficial effects of the present invention are as follows:

[0026] (1) The present invention improves the structural stability of the matrix through dopants, and repairs the microcracks on the surface of the matrix through the lactic acid oligomers of the first coating layer. Utilizing the stable thermoplasticity and erosion resistance of polylactic acid, it penetrates into the microcracks of the first calcined material through diffusion, realizing the secondary repair of the microcracks of the first calcined material, reducing the specific surface area of the material while enhancing the structural stability of the material. At the same time, the conductive lithium salt constructs an ion pathway inside the cathode material, providing a lithium ion source for its ion transport; through the reaction of lactic acid, part of the lactic acid oligomers with the catalyst, a polylactic acid coating layer is obtained, forming a second coating layer, further realizing the inhibition of the growth of primary particles, reducing stress, increasing the wettability of the electrolyte and reducing the interfacial charge transfer resistance, reducing side reactions, thereby enhancing the surface chemical stability of the material.

[0027] (2) On the one hand, during the heating process, due to the diffusion effect, the lactic acid polymer with good thermoplasticity will spontaneously enter the microcracks of the first calcined material in the molten state, realizing the secondary repair of the microcracks of the first calcined material, reducing the specific surface area of the material while enhancing the structural stability of the material. At the same time, the excessive polylactic acid and the residual tin element in the catalyst will cover the surface of the first calcined material to in-situ generate a polylactic acid coating layer, inhibiting the growth of primary particles, reducing stress, increasing the wettability of the electrolyte and reducing the interfacial charge transfer resistance, reducing side reactions, thereby enhancing the surface chemical stability of the material. The excessive lactic acid and lactic acid oligomers will cover the surface of the first calcined material to in-situ generate a polylactic acid coating layer. In addition to improving the reaction rate of synthesizing polylactic acid, the quality and chemical properties of the catalyst itself do not change before and after the reaction. Therefore, this polylactic acid coating layer also contains the residual catalyst, and the tin element in the catalyst will further enhance the conductivity of the material.

[0028] (3) The catalyst in the polylactic acid coating layer is evenly dispersed therein, and the catalyst particles also act as aggregates. When the polylactic acid adheres to the material surface, the presence of the catalyst can improve the dispersion effect of the polylactic acid on the material surface, enabling the polylactic acid to coat the material surface more uniformly, and well avoiding the situation of local coating deficiency, with a better coating effect.

[0029] (4) The strongly oxidizing Ni formed after the high-nickel ternary cathode material is delithiated 4+ is prone to side reactions with the electrolyte, being reduced to NiO, undergoing a phase transformation from the layered phase to the NiO phase, releasing oxygen, and having poor thermal stability. The high-nickel ternary cathode material undergoes side reactions with air and water, and is prone to generating LiOH and Li 2 CO 3, which results in a high surface residual alkali, causing poor electrochemical performance and an increase in battery processing costs. Therefore, the polylactic acid coating layer can provide a physical barrier on the material surface, reduce stress, reduce the direct contact between the material and the electrolyte, air, and water, reduce the side reactions between the cathode material and the electrolyte, air, and water, effectively inhibit the phase transition from the layered phase to the NiO phase during charge and discharge, and reduce the surface residual alkali value, thereby enhancing the surface chemical stability of the material and improving the long-cycle performance of the material.

[0030] (5) During this process, the conductive lithium salt will construct an ion pathway at the surface and interface of the cathode material, provide a lithium ion source for its ion transport, and enhance the lithium ion migration ability and stability at the surface and interface of the material. Therefore, this polylactic acid coating layer not only achieves a three-dimensional coating on the material, but also integrates / superimposes the conductivity of tin and the multiple functional properties of an ion conductor, thus effectively optimizing the high-nickel ternary cathode material. Moreover, lactic acid is widely sourced and inexpensive, eliminating the need for conventional water washing and two-burn operations, with a simple preparation process and cost savings.

[0031] (6) The lithium ions in the conductive lithium salt complex with lactic acid to form a complex with a cyclic structure containing lithium ions, which can stably deposit in the microcracks of the first-burn material, thereby achieving the purpose of stably repairing the microcracks on the particle surface. Increasing the temperature is beneficial to improving the reaction activity and accelerating the complexation and repair rates. During the dehydration polycondensation of lactic acid in the molten state, the viscosity of the slurry increases, which can slow down the mechanical collision strength between secondary particles and prevent further cracking. The repaired cathode material has no microcracks, a complete surface structure, good wear resistance, and is not prone to secondary cracking during subsequent grinding and sieving, which is beneficial to stably improving the consistency of the battery. Brief Description of the Drawings

[0032] Figure 1 is the SEM image of the cathode material prepared in Example 1 of the present invention;

[0033] Figure 2 is the SEM image of the cathode material prepared in Comparative Example 1 of the present invention. Detailed Description of the Embodiments

[0034] Example 1:

[0035] A preparation method of a high-nickel ternary cathode material, wherein the high-nickel ternary precursor is Ni 0.9 Co 0.06 Mn 0.04 (OH) 2 , including the following steps:

[0036] 1) Mix lithium hydroxide, high-nickel ternary precursor, Ta 2 O 5Mix uniformly at a molar ratio of 1.03:0.99:0.01, and raise the temperature to 400 °C at a heating rate of 5 °C / min in an oxygen-containing atmosphere, hold for 6 h, then raise the temperature to 700 °C at a heating rate of 2 °C / min, hold for 10 h, and then cool naturally. After sintering, a first-fired material is obtained, which is ground and sieved through a 400-mesh sieve to obtain Material A;

[0037] 2) Take 10 g of Material A, 10 g of an aqueous solution of L-lactic acid with a mass fraction of 0.3% (the amount of lactic acid is 0.3 wt% of A), and 2.13 g of LiClO 4 powder (the molar concentration after dissolving in the lactic acid aqueous solution is 2 mol / L), add them to a four-necked flask, displace with helium, stir continuously, raise the oil temperature of the reflux column to 105 °C, slowly heat to 150 °C (heating rate 12 °C / h), then keep the temperature and gradually reduce the pressure from atmospheric pressure to 25 mmHg (pressure reduction rate 500 mmHg / h), keep the reaction for 4 h, then raise the temperature to 160 °C (heating rate 10 °C / h), then keep the temperature and reduce the pressure to 15 mmHg (pressure reduction rate 10 mmHg / h), keep the reaction for 2 h, to obtain a mixture B of Material A, LiClO 4 and L-lactic acid oligomers;

[0038] 3) Add 0.0015 g of stannous chloride catalyst (the amount of catalyst is 5 wt% of the lactic acid mass fraction) to B, keep the pressure at atmospheric pressure, slowly raise the temperature to 170 °C under stirring, then gradually reduce the pressure to 5 mmHg, stop after keeping the reaction for 11 h, cool to room temperature and transfer to a 70 °C vacuum drying oven to dry for 5 h, thus obtaining the cathode material C (NCM900604) under the dual modification system of coating modification and secondary repair of microcracks.

[0039] Example 2:

[0040] A preparation method of a high-nickel ternary cathode material, wherein the high-nickel ternary precursor is Ni 0.8 Co 0.1 Mn 0.1 (OH) 2 , including the following steps:

[0041] 1) Mix lithium acetate, high-nickel ternary precursor, WO 3 uniformly at a molar ratio of 1.05:0.98:0.02, and raise the temperature to 600 °C at a heating rate of 10 °C / min in an oxygen-containing atmosphere, hold for 2 h, then raise the temperature to 800 °C at a heating rate of 5 °C / min, hold for 12 h, and then cool naturally. After sintering, a first-fired material is obtained, which is ground and sieved through a 400-mesh sieve to obtain Material A;

[0042] 2) Take 10 g of A, 8 g of an aqueous solution of L-lactic acid with a mass fraction of 1% (the amount of lactic acid is 0.8 wt% of A), and 2.16 g of LiFSI powder (the molar concentration after dissolving in the aqueous lactic acid solution is 1.5 mol / L), add them to a four-necked flask, displace with helium, stir continuously, raise the oil temperature of the reflux column to 107 °C, slowly heat to 160 °C (heating rate 40 °C / h), then keep the temperature and gradually reduce the pressure from atmospheric pressure to 30 mmHg (pressure reduction rate 720 mmHg / h), keep the reaction for 4 h, then raise the temperature to 160 °C (heating rate 20 °C / h), then keep the temperature and reduce the pressure to 20 mmHg (pressure reduction rate 20 mmHg / h), keep the reaction for 2 h to obtain a mixture B of A, LiFSI and L-lactic acid oligomers;

[0043] 3) Add 0.0008 g of stannous octoate catalyst (the amount of catalyst is 1% of the lactic acid mass fraction) to B, keep the pressure at atmospheric pressure, slowly raise the temperature to 180 °C under stirring, then gradually reduce the pressure to 2 mmHg, stop after keeping the reaction for 10 h, cool to room temperature and transfer to an 80 °C vacuum drying oven for drying for 3 h to obtain the cathode material C (NCM811) under the dual modification system of coating modification and microcrack secondary repair.

[0044] Example 3:

[0045] A preparation method of a high-nickel ternary cathode material, wherein the high-nickel ternary precursor is Ni 0.6 Co 0.2 Mn 0.2 (OH) 2 , including the following steps:

[0046] 1) Mix lithium carbonate, high-nickel ternary precursor, Al 2 O 3 uniformly at a molar ratio of 1.06:0.998:0.002, raise the temperature to 500 °C at a heating rate of 5 °C / min in an oxygen-containing atmosphere and keep it for 4 h, then raise the temperature to 900 °C at a heating rate of 3 °C / min and keep it for 15 h, and then cool naturally. After sintering, obtain a first-fired material, grind it and pass through a 400-mesh sieve to obtain material A;

[0047] 2) Take 10 g of A, 10 g of an aqueous solution of D-lactic acid with a mass fraction of 0.5% (the amount of lactic acid is 0.5 wt% of A), and 2.30 g of LiTFSI powder (the molar concentration after dissolving in the lactic acid aqueous solution is 0.8 mol / L), add them to a four-necked flask, displace with neon, stir continuously, raise the oil temperature of the reflux column to 80 °C, slowly heat to 120 °C (heating rate 5 °C / h), then keep the temperature and gradually reduce the pressure from atmospheric pressure to 40 mmHg (pressure reduction rate 220 mmHg / h), keep the reaction for 2 h, then raise the temperature to 130 °C (heating rate 5 °C / h), then keep the temperature and reduce the pressure to 30 mmHg (pressure reduction rate 5 mmHg / h), keep the reaction for 1 h to obtain a mixture B of A, LiTFSI and D-lactic acid oligomer;

[0048] 3) Add 0.0025 g of tin powder catalyst (the amount of catalyst is 5% of the mass fraction of lactic acid) to B, keep the pressure at atmospheric pressure, slowly raise the temperature to 160 °C with stirring, then gradually reduce the pressure to 10 mmHg, stop after keeping the reaction for 8 h, cool to room temperature and transfer to a 60 °C vacuum drying oven for drying for 8 h to obtain the cathode material C (NCM622) under the dual modification system of coating modification and microcrack secondary repair.

[0049] Example 4:

[0050] A preparation method of a high-nickel ternary cathode material, wherein the high-nickel ternary precursor is Ni(OH) 2 , including the following steps:

[0051] 1) Mix lithium nitrate, high-nickel ternary precursor, and ZrO 2 uniformly at a molar ratio of 1.00:0.995:0.005. Then take 30 g of the mixture and raise the temperature to 500 °C at a heating rate of 3 °C / min in an oxygen-containing atmosphere in a tubular furnace, hold for 4 h, then raise the temperature to 650 °C at a heating rate of 1 °C / min and hold for 8 h. After sintering, obtain a first-fired material, then cool naturally, grind, and pass through a 400-mesh sieve to obtain material A;

[0052] 2) Take 10 g of A, 12.5 g of an aqueous solution of D-lactic acid with a mass fraction of 0.8% (the amount of lactic acid is 1 wt% of A), and 2.42 g of LiBOB powder (the molar concentration after dissolving in the lactic acid aqueous solution is 1 mol / L), add them to a four-necked flask, displace with argon, stir continuously, raise the oil temperature of the reflux column to 110 °C, slowly heat to 130 °C, then keep the temperature and gradually reduce the pressure from atmospheric pressure to 20 mmHg, keep for 5 h, then raise the temperature to 150 °C, then keep the temperature and reduce the pressure to 10 mmHg, keep for 2 h to obtain a mixture B of A, LiBOB and D-lactic acid oligomer;

[0053] 3) Add 0.01 g of dibutyltin catalyst to B (the catalyst dosage is 10 wt% of the mass fraction of lactic acid), keep the pressure at atmospheric pressure, slowly heat up to 160 °C with stirring, then gradually reduce the pressure to 1 mmHg, stop the reaction after 15 h, cool to room temperature and transfer to a vacuum drying oven at 90 °C for drying for 5 h, thus obtaining the cathode material C (LNO) under the double modification system of coating modification and secondary repair of microcracks.

[0054] Comparative Example 1: Among them, the high-nickel ternary precursor is Ni 0.9 Co 0.06 Mn 0.04 (OH) 2 , mix lithium hydroxide monohydrate, high-nickel ternary precursor, Ta 2 O 5 uniformly at a molar ratio of 1.03:0.99:0.01, heat up to 400 °C at a heating rate of 5 °C / min in an oxygen-containing atmosphere and hold for 6 h, then heat up to 700 °C at a heating rate of 2 °C / min and hold for 10 h, and then cool naturally. After sintering, a first-fired material is obtained, ground and sieved through a 400-mesh sieve, thus obtaining a cathode material C (Bare-NCM900604) without coating modification and secondary repair of microcracks.

[0055] Table 1

[0056] Sample LiOH (ppm) <![CDATA[Li 2 CO 3 (ppm)]]> <![CDATA[Specific surface area (m 2 / g)]]> Example 1 2852 921 0.2093 Example 2 2064 1027 0.2075 Example 3 1857 886 0.1948 Example 4 2971 1192 0.2465 Comparative Example 1 6291 2709 0.2233

[0057] Table 2

[0058] Sample Initial discharge capacity at 0.1C / (mAh / g) 50-cycle performance (%) 200-cycle performance (%) Example 1 219.6 95.4 89.3 Example 2 208.5 96.5 90.3 Example 3 182.5 98.7 93.2 Example 4 232.5 92.3 84.7 Comparative Example 1 220.8 84.8 77.6

[0059] The test results of the surface residual alkali and specific surface area of the high-nickel ternary cathode materials obtained in Examples 1 to 4 and Comparative Example 1 are shown in Table 1.

[0060] Weigh the corresponding masses of the high-nickel ternary cathode material, conductive agent (Super P Li), and binder (5% PVDF dissolved in NMP) prepared according to Examples 1 to Comparative Example 1 in a mass ratio of 8:1:1 into a stirring box; place the stirring box in a homogenizer with a set program to mix the materials evenly, and then uniformly coat them on a 20-μm aluminum foil through a coater, with the coating thickness controlled at 250 μm. After drying, rolling, cutting, and weighing, a cathode plate with a diameter of 12 mm is obtained. The negative electrode uses metallic lithium, and a CR2032 coin cell is assembled using a KLD-1230C ternary electrolyte and a single-sided ceramic separator.

[0061] After the above-mentioned button cell is placed for 10 h, it is placed on a blue electrochemical workstation (CT2001C) for charge-discharge cycle performance testing. The test conditions are set as follows: 25 °C, 2.8-4.3 V. After activating the button half-cell by cycling 3 weeks at 0.1C / 0.1C, the specific capacity and cycle performance of the cathode material are investigated by cycling 200 weeks at 1C / 1C. The specific electrochemical performance is shown in Table 2.

[0062] As Figure 1 shown, spherical high-nickel ternary cathode materials without microcracks on the surface were successfully prepared in Example 1, while the high-nickel ternary cathode materials prepared in the comparative examples were spherical and had multiple obvious microcracks. By analyzing Table 1, it can be seen that the residual alkali value of the cathode material C (NCM622) prepared in Example 3 is relatively low, and the specific surface area is relatively small. Compared with the cathode material C (NCM900604) prepared in Comparative Example 1, the residual alkali value of the cathode material C (NCM900604) prepared in Example 1 is greatly reduced, and the specific surface area is significantly reduced. By analyzing Table 2, it can be seen that compared with the cathode material C (NCM900604) prepared in Comparative Example 1, the first discharge capacity at 0.1C of the cathode material C (NCM900604) prepared in Example 1 is not much different, but the cycle performance at 50 cycles and 200 cycles is significantly improved. In summary, the high-nickel ternary cathode material prepared by the present invention can effectively improve the long-cycle stability of the high-nickel ternary cathode material while ensuring the capacity.

[0063] The above are only the preferred embodiments of the present invention, and do not impose any form of limitation on the present invention. Any simple modification and equivalent change made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A high-nickel ternary cathode material, characterized in that, it comprises a matrix, a first coating layer and a second coating layer. The matrix is a high-nickel ternary active material. The first coating layer is disposed outside the matrix, and the second coating layer is disposed outside the first coating layer. The first coating layer includes a lactic acid oligomer and a conductive lithium salt, and the second coating layer includes polylactic acid; In the first coating layer, the lactic acid oligomer penetrates into the microcracks of the matrix through diffusion during the heating process to repair the microcracks on the surface of the matrix; the conductive lithium salt constructs an ion pathway inside the cathode material to provide a lithium ion source for its ion transport; The second coating layer includes polylactic acid and a catalyst. The tin element in the catalyst covers the surface of the matrix to in-situ generate a polylactic acid coating layer, realizing the inhibition of the growth of primary particles, reducing stress, increasing the wettability of the electrolyte and reducing the interfacial charge transfer resistance, and reducing side reactions.

2. The high-nickel ternary cathode material according to claim 1, characterized in that, the matrix is obtained by sintering a high-nickel ternary precursor, a lithium source and a dopant, and the molar ratio of the lithium source, the high-nickel ternary precursor and the dopant is (1.00~1.06):(0.98~1):(0~0.02). The dopant is a compound containing a doping element M, and the doping element M is any one or more of W, Mo, Ta, Zr, A1, Ti, Mg, Nb, Ba, B.

3. The high-nickel ternary cathode material according to claim 2, characterized in that, the high-nickel ternary precursor is NixCoyMn(1-x-y)(OH)2 or NixCoyAl(1-x-y)(OH)2, wherein, 0.6≤x≤1, 0≤y≤0.

2.

4. The high-nickel ternary cathode material according to claim 2, characterized in that, the lithium source is any one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate.

5. The high-nickel ternary cathode material according to claim 1, characterized in that, the conductive lithium salt is any one or more of anhydrous lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide salt, lithium bis(oxalato)borate, lithium hexafluorophosphate.

6. A preparation method of a high-nickel ternary cathode material for preparing the high-nickel ternary cathode material according to any one of claims 1-5, characterized in that, it comprises the following steps: Step S1: Mix a high-nickel ternary precursor, a lithium source and a dopant evenly to obtain a blend, and perform a first sintering on the blend in an oxygen-containing atmosphere. After grinding and sieving, material A is obtained; Step S2: Mix material A, a lactic acid solution and a conductive lithium salt evenly, heat to 80°C~110°C in an inert atmosphere, then reduce the pressure and gradually heat to 130°C~160°C, stop after reacting for 3~7h to obtain mixture B; a lactic acid oligomer is generated during the reaction, and the lactic acid oligomer penetrates into the microcracks of material A through diffusion in the molten state to form a first coating layer; Step S3: Add a catalyst to mixture B, keep the pressure at atmospheric pressure, gradually heat up to 160°C - 180°C, then keep the temperature and reduce the pressure. Stop after reacting for 8 - 15 h, cool to room temperature and dry. React lactic acid, part of the lactic acid oligomers and the catalyst in step S2 to obtain a polylactic acid coating layer, form a second coating layer, and prepare the high-nickel ternary cathode material; In step S2, the molar concentration of the conductive lithium salt after being dissolved in the lactic acid solution is 0.8 - 2 mol / L; In step S2, the dosage of lactic acid is 0.3 wt% - 1 wt% of the dosage of material A. In step S3, the dosage of the catalyst is 1 wt% - 10 wt% of the dosage of lactic acid.

7. According to the preparation method of a high-nickel ternary cathode material described in claim 6, it is characterized in that the catalyst is any one or more of stannous chloride, tin powder, stannous octoate, and dibutyltin.

8. According to the preparation method of a high-nickel ternary cathode material described in claim 6, it is characterized in that in step S2, after the solution is heated to 80°C - 110°C, keep it in an inert atmosphere, heat the solution to temperature a at a heating rate of 5 - 40°C / h, and reduce the air pressure from atmospheric pressure to pressure b at a rate of 220 - 720 mmHg / h; keep reacting for 2 - 5 h, then more slowly heat the solution to temperature c at a heating rate of 5 - 20°C / h, and more slowly continue to reduce the air pressure to pressure d at a rate of 5 - 20 mmHg / h. Stop after reacting for 1 - 2 h to obtain mixture B; wherein, temperature a is 120°C - 160°C, temperature c is 130°C - 160°C, and c > a; pressure b is 20 - 40 mmHg, pressure d is 10 - 30 mmHg, and b > d; in step S3, after adding the catalyst to mixture B, heat the solution to 160°C - 180°C at a heating rate of 2 - 10°C / h, then keep the temperature and reduce the air pressure from atmospheric pressure to 1 - 10 mmHg at a rate of 60 - 150 mmHg / h.

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