Nanocrystal positive electrode material and preparation method and application thereof

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to a nanocrystalline positive electrode material and a preparation method and application thereof. The nanocrystalline positive electrode material comprises a positive electrode material matrix, the first coating layer is coated on the surface of the positive electrode material substrate; the raw material of the first coating layer is boron nitride; the second coating layer is coated on one side, far away from the positive electrode material substrate, of the first coating layer; the raw materials of the second coating layer are a first metal oxide and a second metal oxide; the first metal oxide is aluminum oxide; the second metal oxide is at least one of yttrium oxide, lanthanum trioxide, cerium dioxide and bismuth trioxide. The nanocrystalline positive electrode material has good stability in a long-period cyclic process, and can effectively overcome the cyclic stress-strain effect in a cyclic charge-discharge process and slow down the damage of a coating layer.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and particularly relates to a nanocrystalline cathode material, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium-ion secondary batteries have the advantages of high energy density, long cycle life, stable battery voltage, no memory effect, and environmental friendliness. Today, with the increasingly serious energy problem, as a sustainable energy source, lithium-ion batteries have been widely used in fields such as electric vehicles and mobile devices. However, in fields such as electric vehicles that have certain requirements for battery endurance, higher requirements are put forward for the energy density of lithium-ion batteries.

[0003] High-nickel, ultra-high-nickel, medium-nickel cathode materials, high-voltage cathode materials, etc. have become the key development directions for high-energy-density batteries due to their higher specific capacity. However, as the nickel content or voltage increases, the problem of increased lithium ion extraction in the battery will follow, which poses a huge challenge to the structural stability of the material. In the prior art, methods of doping or coating the surface of the cathode material are mostly used to build a protective barrier on the surface of the cathode material to prevent the active substance from directly contacting the electrolyte and being eroded, and to inhibit the dissolution of transition metals, thereby improving the structural stability of the cathode material. However, in the presence of a coating layer, as the number of cycles increases, the cathode material will still gradually crack under the repeated action of stress and strain. The coating layer cannot effectively confine the cathode material and will be damaged together with the cracking of the cathode material. Eventually, the coating layer fails and the cathode material cracks, which will ultimately lead to a sharp decline in the cycle stability of the battery. Summary of the Invention

[0004] Therefore, the purpose of the present invention is to provide a nanocrystalline cathode material, a preparation method thereof, and an application thereof. The nanocrystalline cathode material can effectively overcome the repeated stress and strain during the charge and discharge cycles, slow down the damage of the coating layer, and thus improve the cycle stability.

[0005] For this purpose, the present invention provides the following technical solutions.

[0006] The present invention provides a nanocrystalline cathode material, including a cathode material matrix; a first coating layer wrapped on the surface of the cathode material matrix; the raw material of the first coating layer is boron nitride; a second coating layer wrapped on the side of the first coating layer away from the cathode material matrix; the raw materials of the second coating layer are a first metal oxide and a second metal oxide; the first metal oxide is aluminum oxide; the second metal oxide is at least one of yttrium oxide, lanthanum sesquioxide, cerium dioxide, and bismuth trioxide.

[0007] Optionally, in the raw materials of the second coating layer, the mass ratio of the second metal oxide to the first metal oxide is 1:0.5 to 1.5; optionally, the mass ratio of the second metal oxide to the first metal oxide is 1:0.8 to 1.3.

[0008] Optionally, the second metal oxide is yttrium oxide.

[0009] Optionally, the mass ratio of the cathode material matrix to boron nitride is 100:0.5 to 2.0; optionally, the mass ratio of the cathode material matrix to boron nitride is 100:1 to 1.5.

[0010] Optionally, the mass ratio of the sum of the mass of the cathode material matrix and the first coating layer to the sum of the mass of the first metal oxide and the second metal oxide is 100:0.5 to 2.0; optionally, the mass ratio of the sum of the mass of the cathode material matrix and the first coating layer to the sum of the mass of the first metal oxide and the second metal oxide is 100:0.7 to 1.2.

[0011] Optionally, the D50 particle size of the cathode material matrix is between 8 and 15 μm.

[0012] Optionally, the D50 particle size of the nanocrystalline cathode material is between 8 and 15 μm.

[0013] Optionally, the general formula of the cathode material matrix is Li a Ni x Co y Mn z M 1-x-y-z O2, where M is selected from at least one of W, B, Ti, Zr, In, Nb, Y, Sr, Si, Mo, Ba, Mg, Cu, La, Ce, Li, C, Ca, Bi; 0.95 ≤ a ≤ 1, 0.7 ≤ x < 1, y > 0, z > 0, 0.95 ≤ x + y + z ≤ 1.

[0014] The present invention provides a method for preparing the above-mentioned nanocrystalline cathode material, comprising the following steps: S1: mixing the cathode material matrix and boron nitride, and performing a first sintering to obtain a first-sintered material; S2: mixing the first-sintered material and an additive, and performing a second sintering to obtain a nanocrystalline cathode material; the additive is a mixture of a first metal oxide and a second metal oxide.

[0015] Optionally, the mass ratio of the second metal oxide to the first metal oxide is 1:0.5 to 1.5; optionally, the mass ratio of the second metal oxide to the first metal oxide is 1:0.8 to 1.3.

[0016] Optionally, the second metal oxide is yttrium oxide.

[0017] Optionally, in S1, the mass ratio of the positive electrode material matrix to boron nitride is 100:0.5 to 2.0; optionally, the mass ratio of the positive electrode material matrix to boron nitride is 100:1 to 1.5.

[0018] Optionally, in S2, the mass ratio of the first fired material to the additive is 100:0.5 to 2.0; optionally, the mass ratio of the first fired material to the additive is 100:0.7 to 1.2.

[0019] Optionally, in S1, the first sintering is carried out in an oxygen-containing atmosphere, the temperature is 500 - 600 °C, and the time is 4 - 10 h; optionally, the temperature is 530 - 570 °C, and the time is 5 - 7 h.

[0020] Optionally, in S2, the second sintering is carried out in an oxygen-containing atmosphere, the temperature is 700 - 800 °C, and the time is 6 - 12 h; optionally, the temperature is 720 - 770 °C, and the time is 7 - 10 h.

[0021] Typically and non-limitingly, the oxygen-containing atmosphere during sintering can be maintained by introducing oxygen into the furnace, and the oxygen introduction rate is 5 m 3 / h.

[0022] Optionally, the steps for preparing the positive electrode material matrix include mixing a lithium source and a precursor, and sintering to obtain the positive electrode material matrix.

[0023] Optionally, in the steps for preparing the positive electrode material matrix, the sintering is carried out in an oxygen-containing atmosphere, the temperature is 350 - 450 °C, and the time is 4 - 10 h; optionally, the temperature is 380 - 430 °C, and the time is 5 - 7 h.

[0024] Optionally, the lithium source and the precursor are taken according to the stoichiometric numbers in the general formula of the positive electrode material matrix; optionally, the lithium source includes lithium hydroxide.

[0025] The present invention also provides the application of the above-mentioned nanocrystalline positive electrode material, or the nanocrystalline positive electrode material prepared by the above-mentioned preparation method, in secondary batteries; optionally, the secondary battery includes a lithium-ion battery. Typically and non-limitingly, an assembly method for a lithium-ion coin half-cell can be: preparing a positive electrode sheet, using N-methylpyrrolidone as a dispersant, mixing the nanocrystalline positive electrode material: carbon black: PVDF (polyvinylidene fluoride) in a mass ratio of 90:3 - 7:3 - 7, preparing a positive electrode slurry, uniformly coating the positive electrode slurry on a carbon-coated aluminum foil, and the coating areal density is 12 - 13 cm 2 / mg, dried in an oven at 80 °C for 2 h to obtain the positive electrode sheet; in an argon atmosphere in a glove box, a Celgard 2500 type separator, a lithium metal sheet as the negative electrode sheet, and an LBC3021C011 type electrolyte were used; the battery was assembled in the order of the negative electrode sheet, the electrolyte, the separator, the electrolyte, and the positive electrode sheet.

[0026] The beneficial effects of the present invention are as follows:

[0027] The nanocrystalline positive electrode material provided by the present invention includes a positive electrode material matrix; a first coating layer, which is wrapped on the surface of the positive electrode material matrix; the raw material of the first coating layer is boron nitride; a second coating layer, which is wrapped on the side of the first coating layer away from the positive electrode material matrix; the raw materials of the second coating layer are a first metal oxide and a second metal oxide; the first metal oxide is aluminum oxide; the second metal oxide is at least one of yttrium oxide, lanthanum sesquioxide, cerium dioxide, and bismuth trioxide. This nanocrystalline positive electrode material has good stability during long-term cycling, can effectively overcome the cyclic stress-strain effect during charge-discharge cycling, and slow down the damage of the coating layer. Using boron nitride as the first coating material to coat the positive electrode material matrix, boron nitride will form a coating layer at the grain boundaries to limit the growth of primary grains. Using a mixture of a second metal oxide and aluminum oxide to coat the first-fired material, the mixture of the second metal oxide and aluminum oxide will form a glass phase at the grain boundaries, which slows down ion diffusion, controls the grain growth kinetics, and further limits the growth of primary grains. The nanocrystalline positive electrode material prepared by the above two-stage coating has primary grains in the nanoscale. During the Li ion extraction-insertion process during charge-discharge, the anisotropy of the nanoscale primary grains is greatly weakened, thereby reducing the damage of stress-strain to the positive electrode material, greatly improving the matrix stability of the positive electrode material, and extending the cycle stability of the material. Description of the Drawings

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

[0029] Figure 1 It is the SEM image of the nanocrystalline positive electrode material obtained in Example 1 of the present invention. Detailed Embodiments

[0030] The following embodiments are provided to better understand the present invention further. It is not limited to the described optimal implementation mode, and does not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with those of other prior arts falls within the protection scope of the present invention.

[0031] For those not specifying specific experimental steps or conditions in the embodiments, operations or conditions of conventional experimental steps described in the literature in this field can be followed. For reagents or instruments without indicating the manufacturer, they are all conventional reagent products that can be obtained through commercial purchase.

[0032] Example 1

[0033] This example provides a nanocrystalline cathode material and its preparation method, including the following steps:

[0034] (1) Take Ni 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate in a molar ratio of 1:1, mix them in a high-speed mixer, send them into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 400 °C for 6 h to obtain the cathode material matrix, and control and screen to make the D50 of the cathode material matrix between 8 and 15 μm.

[0035] (2) Take 500 g of the cathode material matrix obtained in (1), add 5 g of boron nitride, mix evenly in a high-speed mixer, send it into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 500 °C for 6 h to obtain a first-fired material.

[0036] (3) Take 500 g of the first-fired material obtained in (2), add 5 g of an additive (mass ratio of yttrium oxide and alumina is 1:1), mix evenly in a high-speed mixer, send it into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 750 °C for 6 h to obtain the nanocrystalline cathode material.

[0037] Example 2

[0038] This example provides a nanocrystalline cathode material and its preparation method, including the following steps:

[0039] (1) Take Ni 0.7 Co 0.15 Mn 0.15 (OH)2 ternary precursor and lithium hydroxide monohydrate in a molar ratio of 1:1, mix them in a high-speed mixer, send them into the furnace, and introduce oxygen into the furnace at a rate of 5 m3 Oxygen is introduced at a rate of 5 m / h to maintain an oxygen-containing atmosphere, and sintering is carried out at 450 °C for 6 h to obtain the matrix of the cathode material. Control and screening are carried out to make the D50 of the matrix of the cathode material between 8 and 15 μm.

[0040] (2) Take 500 g of the matrix of the cathode material obtained in (1), add 5 g of boron nitride, mix evenly in a high-speed mixer, feed it into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 550 °C for 6 h to obtain the first sintered material.

[0041] (3) Take 500 g of the first sintered material obtained in (2), add 5 g of an additive (the mass ratio of cerium dioxide to alumina is 1:1), mix evenly in a high-speed mixer, feed it into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 700 °C for 6 h to obtain the nanocrystalline cathode material.

[0042] Example 3

[0043] This example provides a nanocrystalline cathode material and a preparation method thereof, including the following steps:

[0044] (1) Take Ni 0.8 Co 0.1 Mn 0.1 (OH)2 ternary precursor and lithium hydroxide monohydrate in a molar ratio of 1:1, mix them in a high-speed mixer, feed them into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 350 °C for 6 h to obtain the matrix of the cathode material. Control and screening are carried out to make the D50 of the matrix of the cathode material between 8 and 15 μm.

[0045] (2) Take 500 g of the matrix of the cathode material obtained in (1), add 5 g of boron nitride, mix evenly in a high-speed mixer, feed it into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 600 °C for 6 h to obtain the first sintered material.

[0046] (3) Take 500 g of the first sintered material obtained in (2), add 5 g of an additive (the mass ratio of cerium dioxide, bismuth trioxide to alumina is 0.5:1:1), mix evenly in a high-speed mixer, feed it into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 700 °C for 6 h to obtain the nanocrystalline cathode material.

[0047] Example 4

[0048] This example provides a nanocrystalline cathode material and a preparation method thereof, including the following steps:

[0049] (1) Take Ni in a molar ratio of 1:0.97 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate, mix them in a high-speed mixer, feed them into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 430 °C for 5 h to obtain the matrix of the positive electrode material, and control and screen to make the D50 of the matrix of the positive electrode material between 8 and 15 μm.

[0050] (2) Take 500 g of the matrix of the positive electrode material obtained in (1), add 7.5 g of boron nitride, mix evenly in a high-speed mixer, feed it into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 530 °C for 7 h to obtain the first-fired material.

[0051] (3) Take 500 g of the first-fired material obtained in (2), add 3.5 g of an additive (mass ratio of yttrium oxide to alumina is 1:1.3), mix evenly in a high-speed mixer, feed it into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 770 °C for 7 h to obtain the nanocrystalline positive electrode material.

[0052] Example 5

[0053] This example provides a nanocrystalline positive electrode material and a preparation method thereof, including the following steps:

[0054] (1) Take Ni in a molar ratio of 1:0.98 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate, mix them in a high-speed mixer, feed them into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 380 °C for 7 h to obtain the matrix of the positive electrode material, and control and screen to make the D50 of the matrix of the positive electrode material between 8 and 15 μm.

[0055] (2) Take 500 g of the matrix of the positive electrode material obtained in (1), add 5 g of boron nitride, mix evenly in a high-speed mixer, feed it into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 570 °C for 5 h to obtain the first-fired material.

[0056] (3) Take 500 g of the first-fired material obtained in (2), add 6 g of an additive (mass ratio of yttrium oxide to alumina is 1:0.8), mix evenly in a high-speed mixer, feed it into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3Oxygen is introduced at a rate of / h to maintain an oxygen-containing atmosphere, and sintering is carried out at 720 °C for 10 h to obtain the nanocrystalline cathode material.

[0057] Example 6

[0058] This example provides a nanocrystalline cathode material and a preparation method thereof, including the following steps:

[0059] (1) Take Ni 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate, mix them in a high-speed mixer, send them into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 350 °C for 10 h to obtain the cathode material matrix, and control and screen to make the D50 of the cathode material matrix between 8 and 15 μm.

[0060] (2) Take 500 g of the cathode material matrix obtained in (1), add 2.5 g of boron nitride, mix evenly in a high-speed mixer, send it into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 600 °C for 4 h to obtain a first-fired material.

[0061] (3) Take 500 g of the first-fired material obtained in (2), add 10 g of an additive (mass ratio of lanthanum trioxide to alumina is 1:0.5), mix evenly in a high-speed mixer, send it into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 700 °C for 12 h to obtain the nanocrystalline cathode material.

[0062] Example 7

[0063] This example provides a nanocrystalline cathode material and a preparation method thereof, including the following steps:

[0064] (1) Take Ni 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate, mix them in a high-speed mixer, send them into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 450 °C for 4 h to obtain the cathode material matrix, and control and screen to make the D50 of the cathode material matrix between 8 and 15 μm.

[0065] (2) Take 500 g of the cathode material matrix obtained in (1), add 10 g of boron nitride, mix evenly in a high-speed mixer, send it into the furnace, and introduce oxygen into the furnace at a rate of 5 m 3Oxygen is introduced at a rate of / h to maintain an oxygen-containing atmosphere, and sintering is carried out at 500 °C for 10 h to obtain a first-fired material.

[0066] (3) Take 500 g of the first-fired material obtained in (2), add 2.5 g of an additive (the mass ratio of bismuth trioxide to alumina is 1:1.5), mix evenly in a high-speed mixer, feed it into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 800 °C for 6 h to obtain a nanocrystalline cathode material.

[0067] Comparative Example 1

[0068] This comparative example provides a cathode material and its preparation method, including the following steps:

[0069] Take Ni 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate, mix them in a high-speed mixer, feed them into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 450 °C for 4 h to obtain a cathode material, and control and screen to make its D50 between 8 and 15 μm.

[0070] Comparative Example 2

[0071] This comparative example provides a cathode material and its preparation method, including the following steps:

[0072] (1) Take Ni 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate, mix them in a high-speed mixer, feed them into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 450 °C for 4 h to obtain a cathode material matrix, and control and screen to make the D50 of the cathode material matrix between 8 and 15 μm.

[0073] (2) Take 500 g of the cathode material matrix obtained in (1), add 10 g of boron nitride, mix evenly in a high-speed mixer, feed it into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 500 °C for 10 h to obtain a cathode material.

[0074] Comparative Example 3

[0075] This comparative example provides a cathode material and its preparation method, including the following steps:

[0076] (1) Take Ni in a molar ratio of 1:0.95 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate, mix them in a high-speed mixer, feed them into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 450 °C for 4 h to obtain the positive electrode material matrix, and control and screen to make the D50 of the positive electrode material matrix between 8 and 15 μm.

[0077] (2) Take 500 g of the positive electrode material matrix obtained in (1), add 10 g of boron nitride, mix them evenly in a high-speed mixer, feed them into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 500 °C for 10 h to obtain a first-fired material.

[0078] (3) Take 500 g of the first-fired material obtained in (2), add 2.5 g of acetylene black, mix them evenly in a high-speed mixer, feed them into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 800 °C for 6 h to obtain the positive electrode material.

[0079] Comparative Example 4

[0080] This comparative example provides a positive electrode material and its preparation method, including the following steps:

[0081] (1) Take Ni in a molar ratio of 1:0.95 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate, mix them in a high-speed mixer, feed them into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 450 °C for 4 h to obtain the positive electrode material matrix, and control and screen to make the D50 of the positive electrode material matrix between 8 and 15 μm.

[0082] (2) Take 500 g of the positive electrode material matrix obtained in (1), add 2.5 g of an additive (mass ratio of bismuth trioxide to alumina is 1:1.5), mix them evenly in a high-speed mixer, feed them into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 800 °C for 6 h to obtain the positive electrode material.

[0083] Comparative Example 5

[0084] This comparative example provides a positive electrode material and its preparation method, including the following steps:

[0085] (1) Take Ni in a molar ratio of 1:0.950.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate are mixed in a high-speed mixer and then fed into a furnace. Oxygen is introduced into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sintered at 450 °C for 4 h to obtain the matrix of the positive electrode material. Control and screening are carried out to make the D50 of the matrix of the positive electrode material between 8 and 15 μm.

[0086] (2) Take 500 g of the matrix of the positive electrode material obtained in (1), add 10 g of acetylene black, mix evenly in a high-speed mixer, and then feed it into a furnace. Oxygen is introduced into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sintered at 500 °C for 10 h to obtain the first-sintered material.

[0087] (3) Take 500 g of the first-sintered material obtained in (2), add 2.5 g of an additive (the mass ratio of bismuth trioxide to alumina is 1:1.5), mix evenly in a high-speed mixer, and then feed it into a furnace. Oxygen is introduced into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sintered at 800 °C for 6 h to obtain the positive electrode material.

[0088] Comparative Example 6

[0089] This comparative example provides a positive electrode material and its preparation method, including the following steps:

[0090] (1) Take Ni 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate in a molar ratio of 1:0.95, mix them in a high-speed mixer, and then feed them into a furnace. Oxygen is introduced into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sintered at 450 °C for 4 h to obtain the matrix of the positive electrode material. Control and screening are carried out to make the D50 of the matrix of the positive electrode material between 8 and 15 μm.

[0091] (2) Take 500 g of the matrix of the positive electrode material obtained in (1), add 2.5 g of an additive (the mass ratio of bismuth trioxide to alumina is 1:1.5), mix evenly in a high-speed mixer, and then feed it into a furnace. Oxygen is introduced into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sintered at 800 °C for 6 h to obtain the first-sintered material.

[0092] (3) Take 500 g of the first-sintered material obtained in (2), add 10 g of boron nitride, mix evenly in a high-speed mixer, and then feed it into a furnace. Oxygen is introduced into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sintered at 500 °C for 10 h to obtain the positive electrode material.

[0093] Comparative Example 7

[0094] This comparative example provides a cathode material and a preparation method thereof, including the following steps:

[0095] (1) Take Ni 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate, mix them in a high-speed mixer, send them into a furnace, and introduce oxygen into the furnace at a rate of 5m 3 / h to maintain an oxygen-containing atmosphere, sinter at 450 °C for 4 h to obtain a cathode material matrix, and control and screen to make the D50 of the cathode material matrix between 8 and 15 μm.

[0096] (2) Take 500 g of the cathode material matrix obtained in (1), add 10 g of boron nitride, mix evenly in a high-speed mixer, send it into a furnace, and introduce oxygen into the furnace at a rate of 5m 3 / h to maintain an oxygen-containing atmosphere, sinter at 500 °C for 10 h to obtain a first-fired material.

[0097] (3) Take 500 g of the first-fired material obtained in (2), add 2.5 g of an additive (mass ratio of yttrium oxide to cerium dioxide is 1:1.5), mix evenly in a high-speed mixer, send it into a furnace, and introduce oxygen into the furnace at a rate of 5m 3 / h to maintain an oxygen-containing atmosphere, sinter at 800 °C for 6 h to obtain the cathode material.

[0098] Comparative Example 8

[0099] This comparative example provides a cathode material and a preparation method thereof, including the following steps:

[0100] (1) Take Ni 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate, mix them in a high-speed mixer, send them into a furnace, and introduce oxygen into the furnace at a rate of 5m 3 / h to maintain an oxygen-containing atmosphere, sinter at 450 °C for 4 h to obtain a cathode material matrix, and control and screen to make the D50 of the cathode material matrix between 8 and 15 μm.

[0101] (2) Take 500 g of the cathode material matrix obtained in (1), add 10 g of boron nitride, mix evenly in a high-speed mixer, send it into a furnace, and introduce oxygen into the furnace at a rate of 5m 3 / h to maintain an oxygen-containing atmosphere, sinter at 500 °C for 10 h to obtain a first-fired material.

[0102] (3) Take 500 g of the first-fired material obtained in (2), add 2.5 g of an additive (zirconia and alumina in a mass ratio of 1:1.5), mix evenly in a high-speed mixer, feed it into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 800 °C for 6 h to obtain a cathode material.

[0103] Comparative Example 9

[0104] This comparative example provides a cathode material and a preparation method thereof, including the following steps:

[0105] (1) Take Ni 0.83 Co 0.05 Mn 0.12 (OH)2 ternary precursor and lithium hydroxide monohydrate in a molar ratio of 1:0.95, mix them in a high-speed mixer, feed them into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, sinter at 450 °C for 4 h to obtain a cathode material matrix, and control and screen to make the D50 of the cathode material matrix between 8 and 15 μm.

[0106] (2) Take 500 g of the cathode material matrix obtained in (1), add 10 g of boron nitride, mix evenly in a high-speed mixer, feed it into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 500 °C for 10 h to obtain a first-fired material.

[0107] (3) Take 500 g of the first-fired material obtained in (2), add 2.5 g of an additive (all alumina), mix evenly in a high-speed mixer, feed it into a furnace, and introduce oxygen into the furnace at a rate of 5 m 3 / h to maintain an oxygen-containing atmosphere, and sinter at 800 °C for 6 h to obtain a cathode material.

[0108] Test Example 1

[0109] Observe the image of the nanocrystalline cathode material prepared in Example 1, as shown in Figure 1 , it can be clearly seen that the primary grains undergoing agglomeration are at a tiny nanoscale. In the present invention, the size of the primary grains of the nanocrystalline cathode material is restricted by restricting the two-layer coating materials; the D50 of this nanocrystalline cathode material is measured to be 8.5 μm.

[0110] Test Example 2

[0111] Take the nanocrystalline cathode materials obtained in the examples and comparative examples. Using N-methylpyrrolidone as a dispersant, mix the nanocrystalline cathode material: carbon black: PVDF (polyvinylidene fluoride) in a mass ratio of 90:5:5 to prepare a cathode slurry. Uniformly coat the cathode slurry on the carbon-coated aluminum foil, and the coating areal density is 12 - 13 cm 2 / mg. Dry it in an oven at 80 °C for 2 h to obtain the cathode electrode sheet; in an argon atmosphere in a glove box, use a Celgard 2500 type separator, a lithium metal sheet as the anode electrode sheet, and an LBC3021C011 type electrolyte; assemble a CR2032 type button half-cell in the order of anode electrode sheet, electrolyte, separator, electrolyte, and cathode electrode sheet. Use a Siken test system to conduct electrical performance tests. In the charge-discharge cut-off voltage range of 2.5 - 4.25 V, test the first charge-discharge specific capacity at 0.1C, and the charge-discharge ratio is the first efficiency. At room temperature, test its 50-cycle capacity retention rate at 1C / 1C charge and discharge. All the obtained data are shown in Table 1.

[0112] Table 1

[0113]

[0114] Compared with Example 7, in Comparative Example 1, only the prepared cathode material matrix is used as the cathode material; in Comparative Example 2, only boron nitride is coated outside the cathode material matrix; in Comparative Example 3, boron nitride is coated outside the cathode material matrix first, and then carbon is coated; in Comparative Example 4, only bismuth trioxide and alumina additives are coated outside the cathode material matrix; in Comparative Example 5, carbon is coated outside the cathode material matrix first, and then bismuth trioxide and alumina additives are coated; in Comparative Example 6, bismuth trioxide and alumina additives are coated outside the cathode material matrix first, and then boron nitride is coated; in Comparative Example 7, the additives used are a mixture of yttrium oxide and cerium dioxide; in Comparative Example 8, the additives used are a mixture of alumina and zirconia; in Comparative Example 9, only alumina is used as the additive.

[0115] The nanocrystalline cathode materials in the comparative examples do not meet the requirements specified in the present invention. As can be seen from Table 1, their electrical properties are all worse than those of the nanocrystalline cathode materials in the examples of the present invention. Especially for the 50-cycle retention rate, the highest can only reach 96.1%, while the worst 50-cycle retention rate in the examples of the present invention is still 98%. This shows that the nanocrystalline cathode material provided in the present invention has a good cycle retention rate. And the highest first efficiency in the comparative examples only reaches 90%, while the first efficiency in the examples is all above 90.5%. The nanocrystalline cathode material provided in the present invention also has a good first efficiency.

[0116] Compared with other examples, in Examples 4 and 5 of the present invention, the dosage of each coating material, the sintering temperature, etc. are all within the preferred range. The 50-cycle retention rate of the obtained cathode material is as high as over 99%. Compared with other examples, the electrical properties of the cathode material are further improved.

[0117] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or alterations can be made based on the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. And the obvious changes or alterations derived therefrom still fall within the protection scope of the present invention.

Claims

1. A nanocrystalline positive electrode material, characterized in that: including a cathode material matrix; A first coating layer, wrapped on the surface of the positive electrode material substrate; the raw material of the first coating layer is boron nitride; A second coating layer, wrapped around the first coating layer on a side away from the positive electrode material substrate; The raw materials of the second coating layer are the first metal oxide and the second metal oxide; The first metal oxide is aluminum oxide; The second metal oxide is at least one of yttrium oxide, lanthanum trioxide, cerium dioxide, and bismuth trioxide.

2. The nanocrystalline positive electrode material according to claim 1, characterized in that: In the raw material of the second coating layer, the mass ratio of the second metal oxide to the first metal oxide is 1:0.5-1.5; optionally, the mass ratio of the second metal oxide to the first metal oxide is 1:0.8-1.3; And / or, the second metal oxide is yttrium oxide; And / or, the mass ratio of the positive electrode material matrix to boron nitride is 100:0.5-2.0; optionally, the mass ratio of the positive electrode material matrix to boron nitride is 100:1-1.5; And / or, the mass ratio of the sum of the mass of the positive electrode material matrix and the first coating layer to the sum of the mass of the first metal oxide and the second metal oxide is 100:0.5-2.0; optionally, the mass ratio of the sum of the mass of the positive electrode material matrix and the first coating layer to the sum of the mass of the first metal oxide and the second metal oxide is 100:0.7-1.

2.

3. The nanocrystalline positive electrode material according to claim 1 or 2, characterized in that: The D50 particle size of the positive electrode material matrix is ​​between 8 and 15 μm; And / or, the D50 particle size of the nanocrystalline positive electrode material is between 8 and 15 μm; And / or, the general formula of the positive electrode material matrix is ​​Li a Ni x Co y Mn z M 1-x-y-z O2, wherein M is selected from at least one of W, B, Ti, Zr, In, Nb, Y, Sr, Si, Mo, Ba, Mg, Cu, La, Ce, Li, C, Ca, and Bi; 0.95≤a≤1, 0.7≤x<1, y>0, z>0, and 0.95≤x+y+z≤1.

4. A method for preparing a nanocrystalline positive electrode material according to any one of claims 1 to 3, characterized in that: The steps include: S1: mixing the positive electrode material matrix and boron nitride, and sintering for the first time to obtain a sintered material; S2: mixing the first sintered material and the additive, and sintering for a second time to obtain a nanocrystalline positive electrode material; The additive is a mixture of a first metal oxide and a second metal oxide.

5. The preparation method according to claim 4, characterized in that: In the additive, the mass ratio of the second metal oxide to the first metal oxide is 1:0.5-1.5; optionally, the mass ratio of the second metal oxide to the first metal oxide is 1:0.8-1.3; And / or, the second metal oxide is yttrium oxide.

6. The preparation method according to claim 4 or 5, characterized in that: In S1, the mass ratio of the positive electrode material matrix to boron nitride is 100:0.5-2.0; optionally, the mass ratio of the positive electrode material matrix to boron nitride is 100:1-1.5; And / or, in S2, the mass ratio of the burnt material to the additive is 100:0.5-2.0; optionally, the mass ratio of the burnt material to the additive is 100:0.7-1.

2.

7. The preparation method according to any one of claims 4 to 6, characterized in that: In S1, the first sintering is performed in an oxygen-containing atmosphere at a temperature of 500-600° C. for 4-10 hours; optionally, the temperature is 530-570° C. for 5-7 hours; And / or, in S2, the second sintering is carried out in an oxygen-containing atmosphere at a temperature of 700-800° C. for 6-12 hours; optionally, the temperature is 720-770° C. for 7-10 hours.

8. The preparation method according to any one of claims 4 to 7, characterized in that: The steps of preparing the positive electrode material matrix include mixing a lithium source and a precursor, and sintering to obtain the positive electrode material matrix.

9. The preparation method according to claim 8, characterized in that: In the step of preparing the positive electrode material matrix, sintering is performed in an oxygen-containing atmosphere at a temperature of 350 to 450° C. for 4 to 10 hours; optionally, the temperature is 380 to 430° C. for 5 to 7 hours; And / or, a lithium source and a precursor are taken according to the stoichiometric ratio in the general formula of the positive electrode material matrix; optionally, the lithium source includes lithium hydroxide.

10. Use of the nanocrystalline positive electrode material as claimed in any one of claims 1 to 3, or the nanocrystalline positive electrode material prepared by the preparation method as claimed in any one of claims 4 to 9 in a secondary battery; optionally, the secondary battery comprises a lithium-ion battery.

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