Positive electrode material containing NANO aluminum oxide coating layer and preparation method for positive electrode material

Abstract

A positive electrode material containing a nano aluminum oxide coating layer and a preparation method for the positive electrode material. The method comprises the following steps: adding an aluminum source and a carbon source into a solvent to obtain a dispersion system; adding a positive electrode material into the dispersion system, stirring and carrying out a reaction to obtain a gel; drying the gel and sintering in an inert atmosphere to obtain a precursor; and carrying out heat treatment on the precursor in an oxidizing atmosphere to obtain a positive electrode material containing a nano aluminum oxide coating layer.

Description

A positive electrode material containing a nano-aluminum oxide coating layer and a preparation method thereof Technical Field

[0001] This article belongs to the field of lithium-ion battery positive electrode materials, and specifically relates to a positive electrode material containing a nano-aluminum oxide coating layer and a preparation method thereof. Background Art

[0002] Rechargeable lithium-ion battery technology, due to its high energy density, long cycle life, and excellent rate capability, is widely used in portable consumer electronics, distributed energy storage, electric vehicles, and other fields. Cathode materials have a crucial impact on the performance of lithium-ion batteries, making the development of higher-performing cathode materials crucial to their development.

[0003] The failure of positive electrode materials includes changes in bulk structure and surface structure. Changes in surface structure are accompanied by interfacial side reactions (metal dissolution, surface defect formation, etc.) and oxygen transfer, which lead to electrolyte oxidation, increased internal resistance, gas production, decreased thermal stability and safety performance, etc., resulting in a series of macroscopic battery failure behaviors. At present, the application of various coating chemicals to stabilize the interface of electrode-electrolyte solution can significantly improve the cycle life, high temperature stability and safety of positive electrode materials. For example, a common method is to form a coating layer on the surface of the positive electrode material in order to effectively avoid the corrosion of the electrode by trace hydrofluoric acid in the electrolyte, effectively inhibit surface side reactions, inhibit the release of surface lattice oxygen in the positive electrode material and the dissolution of transition metals. However, traditional coating methods such as wet chemical methods are difficult to avoid the phenomenon of island-shaped (discontinuous) rough coating layers formed by rapid nucleation during the growth of the coating layer, and the thickness of the coating layer is difficult to control, thereby affecting the coating effect, resulting in unsatisfactory performance of the positive electrode material battery containing the coating layer. Therefore, there is still a need to continue to develop a process that can form a continuous, uniform and stable coating layer of electrode material, so as to achieve the purpose of significantly improving the electrical performance and stability of lithium batteries.

[0004] Summary of the Invention

[0005] In order to solve the problems involved in the above-mentioned related technologies, such as the difficulty in preparing a continuous and uniform coating layer of a positive electrode material, this article will provide a positive electrode material containing a nano-alumina coating layer and a preparation method thereof. A positive electrode material coated with alumina@C (i.e., a carbon-coated alumina positive electrode material) is prepared by a sol-gel method and high-temperature sintering. The carbon matrix is ​​then sintered and heat-treated to oxidize the carbon matrix, thereby realizing a lithium-ion battery positive electrode material coated with a uniform and continuous nano-alumina layer, which can effectively solve the problem that the conventional coating layer is island-shaped (discontinuous), rough, and uneven in thickness.

[0006] To achieve the above objectives, the following technical solutions are specifically included:

[0007] A cathode material with a nano-aluminum oxide coating layer, which includes a cathode material and a coating layer coated on the surface of the cathode material. Its composition is represented by the general formula LiAO₂-M, where the letter A represents at least one of Li, Co, Ni, Mn, and Al, and the letter M represents at least one of Al₂O₃, LiAlO₂, LiAl x B 1-x O₂, and the value of x is 0 < x ≤ 1, and the letter B represents at least one of Li, Co, Ni, Mn, and Al.

[0008] In one embodiment, the LiAO₂ is one of lithium cobalt oxide (LiCoO₂), ternary material, lithium-rich manganese-based, and nickel manganese spinel.

[0009] In one embodiment, the M is one of Al₂O₃, LiAlO, LiAl x B 1-x O₂, and the value of x is 0 < x ≤ 1, and the letter B represents at least one of Li, Co, Ni, Mn, and Al.

[0010] Al₂O₃ in the coating layer on the cathode material in this article can effectively remove trace hydrofluoric acid in the electrolyte, thus avoiding its erosion on the electrode, and the metal fluoride generated by the reaction with hydrofluoric acid serves as a protective layer to stabilize the electrode surface. At the same time, the alumina coating layer of the cathode material in this article is a highly continuous and uniform nano-layer, which can significantly improve the cycling and high-temperature stability. This is due to the fact that this continuous and uniform nano-alumina coating layer can more effectively inhibit the surface interface side reactions, inhibit the dissolution of transition metals and surface reconstruction, reduce the gas overflow on the material surface, thereby playing a role in improving the cycling and high-temperature stability. At the same time, after coating, it is easy to form LiAl y TM 1-y O₂ (the value of y can be selected from 0 - 1) solid solution or lithiated alumina Li x A₂O₃ / LiAlO₂ promotes the transport of lithium ions at the electrode interface and reduces the charge transfer impedance.

[0011] A preparation method of a cathode material with a nano-aluminum oxide coating layer includes the following steps:

[0012] Add an aluminum source and a carbon source to a solvent to obtain a dispersion system, and the solvent includes at least one of ethanol and water;

[0013] Add the cathode material to the dispersion system and react under stirring to obtain a gel;

[0014] Dry the gel and sinter it in an inert atmosphere to obtain a precursor;

[0015] The precursor is heat-treated in an oxidizing atmosphere to obtain the positive electrode material containing the nano-aluminum oxide coating layer.

[0016] Al from aluminum source 3+ It forms a metal chelate complex with the carbon source to form a uniform and stable dispersion system. In the dispersion system, the negatively charged hydroxyl and carboxyl oxygen of the carbon source will interact with the positively charged transition metal ions on the surface of the added positive electrode material, making Al 3+ The salt is evenly adsorbed on the surface of the positive electrode material, and the solution is stirred, dried, and aged, and the solvent evaporates, and sol-gelation is carried out, and finally a three-dimensional network structure gel is formed. This structure can effectively inhibit the Al 3+ The salt solution is redistributed and aggregated on the surface of the positive electrode material, and the carbon source also inhibits the agglomeration of metal particles. Subsequently, during the sintering process of the gel, the sol carbon source decomposes and gradually forms a carbon matrix on the surface of the positive electrode material to wrap the Al 3+ Salt precursor, and Al 3+ The salt precursors block each other and prevent agglomeration, ultimately forming a continuous and uniform nano-layered alumina@C-coated cathode material precursor. During heat treatment of the nano-layered alumina@C-coated cathode material precursor in an oxidizing atmosphere, the carbon matrix is ​​oxidized and decomposed to form CO. Gases such as CO2 are expelled, and the Al salt precursors do not agglomerate into discontinuous islands. Instead, a highly continuous and uniform thin alumina coating is formed on the cathode material surface, which is only approximately 2-20nm thick. This continuous and uniform nano-alumina-coated lithium-ion battery cathode material can improve the material's cycling stability and high-temperature stability for the following reasons: the highly continuous and uniform thin alumina coating effectively inhibits surface interfacial side reactions, inhibits transition metal dissolution and surface reconstruction, and the favorable covalent Al-O bonds promote oxygen reduction, reduce gas outflow from the material surface, and inhibit surface oxidation, thereby improving cycling and high-temperature stability.

[0017] This article provides a positive electrode material with a highly continuous and uniform thin alumina coating layer prepared by the sol-gel method, high-temperature sintering and heat treatment process. The carbon source raw materials of this synthesis method are cheap and easy to purchase, the process is simple, the conditions are mild, the coating process is simple and scalable, and the formed alumina coating layer is continuous and uniform, has high mechanical properties, strong bonding with the substrate, and is thin and controllable in thickness. It can remain stable after charge / discharge cycles and has high industrial value.

[0018] In one embodiment, the aluminum source includes at least one of aluminum chloride, aluminum sulfate, and aluminum isopropoxide.

[0019] In one embodiment, the carbon source includes at least one of citric acid, polyvinyl pyrrolidone (PVP), soluble starch, β-cyclodextrin, Tianqing powder, chitosan, urea, guar gum, xanthan gum, and glucose.

[0020] In one embodiment, the molar ratio of the aluminum source to the carbon source is 1:(0.3-3).

[0021] In one embodiment, the solvent includes ethanol.

[0022] In one embodiment, in the dispersed system, the concentration of the aluminum source is 0.01-5 mol / L.

[0023] In one embodiment, the positive electrode material includes at least one of a lithium cobalt oxide positive electrode material, a ternary material positive electrode material, a lithium-rich manganese-based positive electrode material, and a nickel-manganese spinel positive electrode material.

[0024] In one embodiment, the aluminum source is calculated based on the mass of aluminum oxide, and the mass ratio of aluminum oxide to the positive electrode material is (0.001-0.03):1.

[0025] In one embodiment, the reaction temperature is 60-120° C., and the reaction time is 4-72 hours.

[0026] In one embodiment, the drying temperature is 80-150° C., and the drying time is 24-120 hours.

[0027] In one embodiment, the sintering temperature is 350-550° C., and the sintering time is 2-6 hours.

[0028] In one embodiment, during the sintering, the heating rate is 2-10° C. / min.

[0029] Under the above sintering conditions, the battery cycle performance showed better.

[0030] In one embodiment, the heat treatment temperature is 300-550° C., and the heat treatment time is 2-12 hours.

[0031] In one embodiment, during the heat treatment, the heating rate is 2-10° C. / min.

[0032] Under the above heat treatment conditions, the battery cycle performance showed better.

[0033] In one embodiment, the inert atmosphere includes at least one of a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere.

[0034] In one embodiment, the oxidizing atmosphere includes at least one of oxygen and CO2.

[0035] Compared with the related art, this article has the following beneficial effects: This article discloses a positive electrode material with a highly continuous and uniform thin alumina coating layer prepared by the sol-gel method, high-temperature sintering, and heat treatment processes. The carbon source raw materials of this synthesis method are cheap and easy to purchase, the process is simple, the conditions are mild, the coating process is simple and scalable, and the formed alumina coating layer is continuous and uniform, has high mechanical properties, strong bonding with the substrate, is thin and controllable in thickness, and can remain stable after charge / discharge cycles, and has high industrial value. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG1 is a schematic diagram of the synthesis path of the positive electrode material containing a nano-alumina coating layer in the embodiment.

[0037] FIG2 is a TEM image of the positive electrode material containing a nano-alumina coating layer in Example 1.

[0038] FIG3 is a TEM image of the positive electrode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2, wherein the left, middle, and right images correspond to the TEM images of the positive electrode materials prepared in Example 1, Comparative Example 1, and Comparative Example 2, respectively.

[0039] Figure 4 is a graph showing the effect of different aluminum coating amounts on the first-efficiency performance of LCO, where 0Al@LCO, 1.0Al@LCO, 1.5Al@LCO, 2.0Al@LCO, and 3.0Al@LCO correspond to the first-efficiency performance curves of pure commercial positive electrode lithium cobalt oxide and the positive electrode materials in Examples 2-4, respectively.

[0040] FIG5 is an XRD spectrum of the positive electrode material containing the nano-alumina coating layer of Examples 5-9, wherein the XRD spectra from top to bottom in the figure correspond to the XRD spectra of the positive electrode material containing the nano-alumina coating layer of Examples 5-9 respectively.

[0041] Figure 6 is a battery cycle performance curve diagram of the pure ternary material NCM92 positive electrode material and the positive electrode material containing a nano-alumina coating layer in Example 10. The left figure is a battery cycle performance curve diagram of the positive electrode material containing a nano-alumina coating layer in Example 10, and the right figure is a battery cycle performance curve diagram of the pure ternary material NCM92 positive electrode material.

[0042] Figure 7 is a battery cycle performance curve diagram of pure commercial positive electrode lithium cobalt oxide, Example 1, and the positive electrode materials prepared in Comparative Examples 3-4, where Bare-LCO, O2-LCO, N2-O2-LCO, and N2-LCO correspond to the battery cycle performance curve diagrams of pure commercial positive electrode lithium cobalt oxide, Example 1, and the positive electrode materials prepared in Comparative Examples 3-4, respectively. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of this article will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of this article, rather than all the embodiments.

[0044] The performance testing methods involved in the following examples and comparative examples are:

[0045] Coin cell assembly: The positive electrode material is mixed with Super P and PVDF in a mass ratio of 95:2:3. The mixture is coated by a coating method to prepare an active material with an area density of about 7.4 mg / cm 2 The positive electrode sheet was cut into discs with a diameter of 14 mm, then vacuum-dried at 105 ° C for 4 h, and assembled into a 2430 model button battery in a glove box.

[0046] (1) Initial performance test of positive electrode material: at 50mAg -1 At a current density of 3.0-4.5V, the LCO button half-cell was tested using a Blue Electric test cabinet.

[0047] (2) Battery cycle performance curve: at 125mAg -1 At a current density of 1.5 V, a blue electric test cabinet was used to perform constant current cycle tests on LCO button half-cells between 3.0-4.5 V, and a constant current cycle test on high-nickel ternary button half-cells between 3.0-4.35 V was performed to evaluate their electrochemical performance.

[0048] Example 1

[0049] (1) 1 g of aluminum nitrate was ultrasonically dispersed in 1000 mL of ethanol solution, and stirring was started. 0.9020 g of citric acid was added at a molar ratio of aluminum source to citric acid of 1:1 and stirred and dispersed for 2 h to form a dispersion system. 47.8694 g of commercial positive electrode lithium cobalt oxide (LiCoO2) was weighed and added to the dispersion system at a stoichiometric ratio of 1.0 wt% Al2O3. The system was heated to 80°C and stirred for 48 h to obtain a gel.

[0050] (2) The gel was placed in a vacuum drying oven at 110°C for drying and aging for 60 h. The dried gel was then ground, sieved, and placed in a 200 mL crucible. The crucible was heated to 450°C at a rate of 5°C / min in a tube furnace with N2 atmosphere for sintering, and kept at this temperature for 4 h to prepare a nano-layered alumina@C-coated positive electrode material, lithium cobalt oxide.

[0051] (3) The temperature of the tube furnace was lowered to 400°C, the N2 atmosphere was switched to O2 atmosphere, and the carbon matrix was heat-treated and oxidized for 4 hours to obtain a lithium cobalt oxide positive electrode material containing a nano-alumina coating layer, which was recorded as N2-O2-LCO or 1.0Al@LCO.

[0052] Example 2

[0053] The only difference between this embodiment and embodiment 1 is that commercial positive electrode lithium cobalt oxide is added at a stoichiometric ratio of 1.5 wt % Al 2 O 3 .

[0054] Example 3

[0055] The only difference between this embodiment and embodiment 1 is that commercial positive electrode lithium cobalt oxide is added at a stoichiometric ratio of 2.0 wt % Al 2 O 3 .

[0056] Example 4

[0057] The only difference between this embodiment and embodiment 1 is that commercial positive electrode lithium cobalt oxide is added at a stoichiometric ratio of 3.0 wt % Al 2 O 3 .

[0058] Example 5

[0059] The only difference between this embodiment and embodiment 1 is that in this embodiment, the ternary material NCM811 positive electrode material is added at a stoichiometric ratio of 0.1 wt % Al 2 O 3 .

[0060] Example 6

[0061] The only difference between this embodiment and embodiment 1 is that in this embodiment, the ternary material NCM811 positive electrode material is added at a stoichiometric ratio of 0.5 wt % Al 2 O 3 .

[0062] Example 7

[0063] The only difference between this embodiment and embodiment 1 is that in this embodiment, the ternary material NCM811 positive electrode material is added at a stoichiometric ratio of 1.0 wt % Al 2 O 3 .

[0064] Example 8

[0065] The only difference between this embodiment and embodiment 1 is that in this embodiment, the ternary material NCM811 positive electrode material is added at a stoichiometric ratio of 2.0 wt % Al 2 O 3 .

[0066] Example 9

[0067] The only difference between this embodiment and embodiment 1 is that in this embodiment, the ternary material NCM811 positive electrode material is added at a stoichiometric ratio of 3.0 wt % Al 2 O 3 .

[0068] Example 10

[0069] The only difference between this embodiment and embodiment 1 is that in this embodiment, the ternary material NCM92 positive electrode material is added at a stoichiometric ratio of 1.0 wt % Al 2 O 3 .

[0070] Example 11

[0071] The only difference between this embodiment and embodiment 1 is that the molar ratio of the aluminum source to citric acid in this embodiment is 1:0.3.

[0072] Example 12

[0073] The only difference between this embodiment and embodiment 1 is that the molar ratio of the aluminum source to citric acid in this embodiment is 1:3.

[0074] Example 13

[0075] The only difference between this embodiment and embodiment 1 is that 0.047 mol of aluminum chloride aluminum source is added in this embodiment.

[0076] Example 14

[0077] The only difference between this embodiment and embodiment 1 is that 0.047 mol of aluminum sulfate as an aluminum source is added in this embodiment.

[0078] Example 15

[0079] The only difference between this embodiment and embodiment 1 is that 0.047 mol of aluminum isopropoxide aluminum source is added in this embodiment.

[0080] Example 16

[0081] The only difference between this embodiment and embodiment 1 is that, in this embodiment, 0.0282 mol of PVP carbon source is added based on the molar number of C.

[0082] Example 17

[0083] The only difference between this embodiment and embodiment 1 is that, in this embodiment, 0.0282 mol of soluble starch carbon source is added based on the molar number of C.

[0084] Example 18

[0085] The only difference between this embodiment and embodiment 1 is that, in this embodiment, 0.0282 mol of β-cyclodextrin carbon source is added based on the molar number of C.

[0086] Example 19

[0087] The only difference between this embodiment and embodiment 1 is that, in this embodiment, 0.0282 mol of Tianqing powder carbon source is added based on the molar number of C.

[0088] Example 20

[0089] The only difference between this embodiment and embodiment 1 is that, in this embodiment, 0.0282 mol of chitosan carbon source is added based on the molar number of C.

[0090] Example 21

[0091] The only difference between this embodiment and embodiment 1 is that, in this embodiment, 0.0282 mol of urea carbon source is added based on the molar number of C.

[0092] Example 22

[0093] The only difference between this embodiment and embodiment 1 is that, in this embodiment, 0.0282 mol of guar gum carbon source is added based on the molar number of C.

[0094] Example 23

[0095] The only difference between this embodiment and embodiment 1 is that in this embodiment, 0.0282 mol of xanthan gum carbon source is added based on the molar number of C.

[0096] Example 24

[0097] The only difference between this embodiment and embodiment 1 is that the sintering temperature in this embodiment is 350°C.

[0098] Example 25

[0099] The only difference between this embodiment and embodiment 1 is that the sintering temperature in this embodiment is 400°C.

[0100] Example 26

[0101] The only difference between this embodiment and embodiment 1 is that the sintering temperature in this embodiment is 500°C.

[0102] Example 27

[0103] The only difference between this embodiment and embodiment 1 is that the sintering temperature in this embodiment is 550°C.

[0104] Example 28

[0105] The only difference between this embodiment and embodiment 1 is that the heat treatment temperature in this embodiment is 300°C.

[0106] Example 29

[0107] The only difference between this embodiment and embodiment 1 is that the heat treatment temperature in this embodiment is 350°C.

[0108] Example 30

[0109] The only difference between this embodiment and embodiment 1 is that the heat treatment temperature in this embodiment is 450°C.

[0110] Example 31

[0111] The only difference between this embodiment and embodiment 1 is that the heat treatment temperature in this embodiment is 500°C.

[0112] Comparative Example 1

[0113] (1) 1 g of aluminum nitrate was ultrasonically dispersed in 1000 mL of ethanol solution, stirred, and dispersed for 2 h to form a dispersion system; 47.8694 g of commercial positive electrode lithium cobalt oxide was weighed according to a stoichiometric ratio of 1 wt% Al2O3 and added to the dispersion system, heated to 80°C and stirred for 48 h to obtain a mixture;

[0114] (2) The mixture was placed in a vacuum drying oven at 110°C and dried for 60 h. The dried solid was then ground, sieved, and placed in a 200 mL crucible. The crucible was heated to 450°C at a rate of 5°C / min in a N2 atmosphere in a tube furnace and kept at this temperature for 4 h.

[0115] (3) The temperature of the tube furnace was lowered to 400°C, the N2 atmosphere was switched to O2 atmosphere, and the heat treatment was carried out for 4 hours to obtain the prepared nano-layered alumina-coated positive electrode material lithium cobalt oxide.

[0116] Comparative Example 2

[0117] (1) 0.9020 g of citric acid was ultrasonically dispersed in 1000 mL of ethanol solution, and stirring was started. The mixture was stirred and dispersed for 2 h to form a dispersion system. 47.8694 g of commercial positive electrode lithium cobalt oxide was weighed and added to the dispersion system. The mixture was heated to 80° C. and stirred for 48 h to obtain a mixture.

[0118] (2) The mixture was placed in a vacuum drying oven at 110°C and dried for 60 h. The dried gel was then ground, sieved, and placed in a 200 mL crucible. The mixture was heated to 450°C at a rate of 5°C / min in a N2 atmosphere in a tube furnace and kept at this temperature for 4 h to prepare a carbon-coated positive electrode material, lithium cobalt oxide.

[0119] (3) The temperature of the tube furnace was lowered to 400°C, the N2 atmosphere was switched to O2 atmosphere, and the heat treatment was carried out for 4 hours to oxidize the carbon matrix and obtain the positive electrode material lithium cobalt oxide.

[0120] Comparative Example 3

[0121] (1) 1 g of aluminum nitrate was ultrasonically dispersed in 1000 mL of ethanol solution, and stirring was started. 0.9020 g of citric acid was added at a molar ratio of aluminum to citric acid of 1:1 and stirred and dispersed for 2 h to form a dispersion system. 47.8694 g of commercial positive electrode lithium cobalt oxide was weighed at a stoichiometric ratio of 1.0 wt% Al2O3 and added to the dispersion system. The system was heated to 80°C and stirred for 48 h to obtain a gel.

[0122] (2) The gel was placed in a vacuum drying oven at 110°C and dried for 60 hours. The dried gel was then ground, sieved, and placed in a 200 mL crucible. The crucible was heated to 450°C at a rate of 5°C / min in an O2 atmosphere in a tube furnace and kept at this temperature for 4 hours to prepare a nano-layered alumina@C-coated positive electrode material, lithium cobalt oxide.

[0123] (3) The temperature of the tube furnace was lowered to 400° C., and the heat treatment was continued for 4 h in an O 2 atmosphere to oxidize the carbon matrix, thereby obtaining a lithium cobalt oxide positive electrode material containing a nano-aluminum oxide coating layer.

[0124] Comparative Example 4

[0125] (1) 1 g of aluminum nitrate was ultrasonically dispersed in 1000 mL of ethanol solution, and stirring was started. 0.9020 g of citric acid was added at a molar ratio of aluminum to citric acid of 1:1 and stirred and dispersed for 2 h to form a dispersion system. 47.8694 g of commercial positive electrode lithium cobalt oxide was weighed at a stoichiometric ratio of 1.0 wt% Al2O3 and added to the dispersion system. The system was heated to 80°C and stirred for 48 h to obtain a gel.

[0126] (2) The gel was placed in a vacuum drying oven at 110°C for drying and aging for 60 h. The dried gel was then ground, sieved, and placed in a 200 mL crucible. The crucible was heated to 450°C at a rate of 5°C / min in a N2 atmosphere in a tube furnace and kept at this temperature for 4 h to prepare a nano-layered alumina@C-coated positive electrode material, lithium cobalt oxide.

[0127] (3) The temperature of the tube furnace was lowered to 400°C, and the heat treatment was continued for 4 hours under a N2 atmosphere to obtain a lithium cobalt oxide positive electrode material containing a nano-alumina coating layer @C.

[0128] Figure 1 shows the preparation process of the positive electrode material containing a nano-alumina coating layer. Figure 2 is a TEM image of the positive electrode material of Al2O3 coated LiCoO2 in Example 1. It can be seen from the figure that the alumina coating layer is a highly continuous and uniform nanolayer with a thickness of about 2-20nm.

[0129] FIG3 shows the lithium cobalt oxide positive electrode material containing a nano-alumina coating layer in Example 1, the positive electrode material without a carbon source in Comparative Example 1, and the positive electrode material without an aluminum source in Comparative Example 2. As shown in FIG3 , when no carbon source is added, heat treatment will cause alumina agglomeration; when no aluminum source is added, no protective layer similar to nano-alumina will be formed on the surface of the positive electrode material.

[0130] It can be seen from Examples 2-4 that changing the amount of positive electrode material added will change the amount of aluminum oxide coating (which can be referred to as aluminum coating). Figure 4 is a first-effect performance diagram of LCO of positive electrode materials coated with Al2O3 at different proportions. It can be seen from the figure that 1% Al2O3 coating has the highest discharge capacity, and too high a coating amount will inhibit the transport of lithium ions at the electrode interface.

[0131] Figure 5 is the XRD pattern of Al2O3 coated NCM811 with different proportions. It can be seen from the figure that the figure mainly shows the characteristic diffraction peaks of NCM811 without other impurities.

[0132] As can be seen from Figure 6, the alumina coating layer significantly improves the cycle and high temperature stability of NCM9244. This is due to the continuous and uniform nano-alumina coating layer effectively inhibiting the surface interface side reactions, inhibiting the dissolution of transition metals and surface reconstruction, and reducing the gas overflow on the material surface, thereby improving the cycle and high temperature stability. At the same time, after coating, LiAl is easily formed at the interface between the coating layer and the active material. y TM 1-y O2 solid solution or lithiated alumina Li x A2O3 / LiAlO2 promotes the transport of lithium ions at the electrode interface and reduces the charge transfer impedance.

[0133] FIG7 is a battery cycle performance curve diagram of the positive electrode materials obtained in Example 1 and Comparative Examples 3-4. It can be seen that the battery performance of the positive electrode material obtained by first sintering in an inert gas atmosphere and then heat-treating in an oxidizing atmosphere is better.

Claims

1. A method for preparing a positive electrode material containing a nano-alumina coating layer, characterized in that: The following steps are involved: Adding an aluminum source and a carbon source into a solvent to obtain a dispersed system, wherein the solvent comprises at least one of ethanol and water; Adding positive electrode material into the dispersed system, reacting under stirring to obtain a gel; The gel is dried and sintered under an inert atmosphere to obtain a precursor; The precursor is heat-treated in an oxidizing atmosphere to obtain the positive electrode material containing the nano-alumina coating layer.

2. The method for preparing a positive electrode material containing a nano-alumina coating layer according to claim 1, characterized in that: The molar ratio of the aluminum source to the carbon source is 1:(0.3-3).

3. The method for preparing a positive electrode material containing a nano-alumina coating layer according to claim 1, characterized in that: The aluminum source is calculated based on the mass of aluminum oxide, and the mass ratio of aluminum oxide to positive electrode material is (0.001-0.03):

1.

4. The method for preparing a positive electrode material containing a nano-alumina coating layer according to claim 1, characterized in that: The reaction temperature is 60-120° C., and the reaction time is 4-72 hours.

5. The method for preparing a positive electrode material containing a nano-alumina coating layer according to claim 1, characterized in that: The sintering temperature is 350-550°C.

6. The method for preparing a positive electrode material containing a nano-alumina coating layer according to claim 1, characterized in that: The sintering time is 2-6h.

7. The method for preparing a positive electrode material containing a nano-alumina coating layer according to claim 1, characterized in that: The temperature of the heat treatment is 300-550°C.

8. The method for preparing a positive electrode material containing a nano-alumina coating layer according to claim 1, characterized in that: The heat treatment time is 2-12h. 9 . The method for preparing a positive electrode material containing a nano-aluminum oxide coating layer according to claim 1 , wherein the aluminum source comprises at least one of aluminum chloride, aluminum sulfate, and aluminum isopropoxide.

10. The method for preparing a positive electrode material containing a nano-alumina coating layer according to claim 1, characterized in that: Include at least one of the following: The carbon source includes at least one of citric acid, polyvinyl pyrrolidone, soluble starch, β-cyclodextrin, field pine flour, chitosan, urea, guar gum, xanthan gum, and glucose; The drying temperature is 80-150°C; The drying time is 24-120h.

11. The method for preparing a positive electrode material containing a nano-alumina coating layer according to claim 1, characterized in that: In the dispersed system, the concentration of the aluminum source is 0.01-5 mol / L.

12. The method for preparing a positive electrode material containing a nano-alumina coating layer according to claim 1, characterized in that: The positive electrode material includes at least one of a lithium cobalt oxide positive electrode material, a ternary material type positive electrode material, a lithium-rich manganese-based positive electrode material, and a nickel-manganese spinel type positive electrode material.

13. The method for preparing a positive electrode material containing a nano-alumina coating layer according to claim 1, characterized in that: Include at least one of the following: When performing the heat treatment, the heating rate is 2 to 10°C / min; During the sintering, the heating rate is 2 to 10°C / min; The inert atmosphere includes at least one of a nitrogen atmosphere, an argon atmosphere, and a helium atmosphere; The oxidizing atmosphere includes at least one of oxygen and carbon dioxide.

14. A positive electrode material containing a nano-alumina coating layer, characterized in that: The preparation is obtained by the preparation method according to any one of claims 1 to 13.

15. The positive electrode material containing a nano-alumina coating layer according to claim 14, characterized in that: It includes a positive electrode material and a coating layer coated on the surface of the positive electrode material, and its composition is represented by the general formula LiAO2-M, where the letter A represents at least one of Li, Co, Ni, Mn, and Al, and the letter M represents at least one of Al2O3, LiAlO2, and LiAl x B 1-x O2, and the value of x is 0 < x ≤ 1, and the letter B represents at least one of Li, Co, Ni, Mn, and Al.

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