Positive electrode material and preparation method and application thereof

Abstract

The invention relates to a positive electrode material and a preparation method and application thereof, and the preparation method of the positive electrode material provided by the invention comprises the following steps: taking a positive electrode material matrix, and reducing surface residual alkali to obtain a pretreated positive electrode material matrix; the method for reducing the residual alkali on the surface comprises the following steps: mixing with a solvent to perform solvothermal reaction, sequentially depositing aluminum, fluorine and lithium on the surface of the pretreated positive electrode material substrate through an aluminum source, a fluorine source and a lithium source, and repeating the deposition steps to obtain the fluorine-aluminum-lithium layer with a target thickness. The surface of the obtained positive electrode material is coated with a fluorine-aluminum-lithium thin film, and fluorine-aluminum-lithium nano-particles protrude on the fluorine-aluminum-lithium thin film. According to the positive electrode material, the interface problem existing between the high-nickel nickel-cobalt-manganese ternary positive electrode material and the sulfide solid electrolyte can be weakened, and the capacity and the cycle performance of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, specifically to a cathode material, its preparation method, and its application. Background Technology

[0002] With the gradual development of electric vehicles, the market and users have placed higher demands on their driving range and safety. Improving the energy density and safety of secondary batteries while controlling costs is a major development direction. All-solid-state lithium batteries (ASSLBs) have become the focus of industry attention due to their non-flammability and high energy density. The high-nickel NCM ternary cathode material used in all-solid-state lithium batteries has excellent characteristics such as high capacity, high voltage platform and low cost. However, there are interfacial problems between the high-nickel NCM ternary cathode material and sulfide solid electrolytes (SSEs), such as interfacial reactions, chemical-mechanical failure, and space charge layer. The NCM ternary cathode material itself also has certain structural stability issues, which seriously restrict the performance of all-solid-state lithium batteries.

[0003] Existing technologies include coating the surface of the positive electrode active material substrate with materials such as fluorine-containing fast ion conductors, transition metal oxides, and halogen-partially substituted metal oxides to improve the stability of the positive electrode material. However, the preparation methods are relatively cumbersome, and the performance of the obtained positive electrode material still has room for improvement. Another existing technology involves alternately depositing aluminum fluoride and lithium fluoride layers on the surface of the positive electrode active material substrate to improve battery specific capacity and high-temperature cycle life. However, the interlayer interface between the aluminum fluoride and lithium fluoride layers may provide additional resistance to lithium ion migration, reducing the material's conductivity and mechanical flexibility. This approach is only suitable for liquid battery systems and has limited performance in solid-state battery systems. Summary of the Invention

[0004] One objective of this invention is to provide a cathode material and its preparation method to solve the problem of interface issues between high-nickel NCM ternary cathode materials and sulfide solid electrolytes (SSEs) in the prior art, which affect battery performance; the second objective is to provide a secondary battery.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] This invention provides a method for preparing a cathode material, comprising the following steps:

[0007] S1: Take the cathode material matrix, reduce the surface residual alkali, and obtain the pretreated cathode material matrix;

[0008] The step of reducing surface residual alkali includes mixing the positive electrode material matrix with a solvent and carrying out a solvothermal reaction;

[0009] S2: Aluminum is deposited onto the surface of the pretreated cathode material substrate using an aluminum source;

[0010] S3: Deposit fluorine onto the surface of the cathode material substrate obtained in S2 using a fluorine source;

[0011] S4: Deposit lithium onto the surface of the cathode material substrate obtained in S3 using a lithium source;

[0012] Repeat steps S2 to S4 to obtain a lithium aluminum fluoride layer of the target thickness.

[0013] The method for preparing the cathode material provided by this invention, in the step of reducing surface residual alkali, further includes a step of solid-liquid separation and drying of the obtained mixture after the solvothermal reaction. Typically, but not limited to, the drying temperature is 60–100°C, and the time is 6–12 h; the solid-liquid separation method includes at least one of filtration and centrifugation; when using centrifugation for solid-liquid separation, the centrifugation speed is 2000–4000 rpm, and the time is 5–10 min.

[0014] Optionally, the target thickness is 1–10 nm. The cathode material prepared by the method of the present invention includes a cathode material substrate and a lithium aluminum fluoride layer coating at least a portion of the surface of the cathode material substrate; the lithium aluminum fluoride layer includes a lithium aluminum fluoride film and lithium aluminum fluoride nanoparticles protruding from the lithium aluminum fluoride film. Here, the target thickness refers to the thickness of the lithium aluminum fluoride film. Further optionally, the size of the lithium aluminum fluoride nanoparticles ranges from 50 to 300 nm.

[0015] Optionally, the specific surface area of ​​the positive electrode material is 0.7–0.9 m². 2 / g.

[0016] Optionally, in S1, the surface residual alkali is reduced to a LiOH mass ratio of 500-1500 ppm and a Li2CO3 mass ratio of ≤1500 ppm.

[0017] Optionally, the solvent used in the step of reducing surface residual alkali includes at least one of water, isopropanol, and oxalic acid.

[0018] Optionally, between S2 and S1, a step of preheating the pretreated cathode material matrix may be included.

[0019] Optionally, in the step of reducing surface residual alkali, the liquid-solid mass ratio of the positive electrode material matrix to the solvent is 25-35:1.

[0020] Optionally, the temperature of the solvothermal reaction is 60–90°C, and the time is 2–6 hours.

[0021] Optionally, the solvent used in the step of reducing surface residual alkali includes an aqueous solution of isopropanol with a concentration of 80 vol% to 95 vol%.

[0022] Optionally, the solvent used in the step of reducing surface residual alkali includes an aqueous solution of oxalic acid with a concentration of 0.01 to 0.5 mol / L.

[0023] Optionally, in the step of preheating the pretreated cathode material matrix, the preheating temperature is 100-180°C and the time is 300-500 min.

[0024] Optionally, in S2, the deposition time is 5 to 30 seconds, the deposition pressure is 0.1 to 50 torr, and the carrier gas flow rate used for deposition is 10 to 80 sccm.

[0025] Optionally, in S3, the deposition time is 5 to 30 seconds, the deposition pressure is 0.1 to 50 torr, and the carrier gas flow rate used for deposition is 10 to 80 sccm.

[0026] Optionally, in S4, the deposition time is 5 to 30 seconds, the deposition pressure is 0.1 to 50 torr, and the carrier gas flow rate used for deposition is 10 to 80 sccm.

[0027] Optionally, the aluminum source includes at least one of trialkylaluminum, dialkylaluminum halide, alkylaminoaluminum and its derivatives, and alkoxyaluminum and its derivatives.

[0028] Optionally, the fluorine source includes at least one of hydrogen fluoride and fluorinated hydrocarbon compounds.

[0029] Optionally, the lithium source includes inorganic lithium compounds and / or organic lithium compounds.

[0030] Optionally, the carrier gas includes at least one of nitrogen and rare gases.

[0031] Optionally, the chemical formula of the cathode material matrix is ​​LiNi. x Co y Mn 1-x-y O2, where 0.9≤x<0.95, 0.01<y<0.1, 1-xy>0.

[0032] Optionally, the trialkylaluminum includes at least one of trimethylaluminum and triethylaluminum.

[0033] Optionally, the fluorinated hydrocarbon compound includes fluoroethane.

[0034] Optionally, the lithium source includes at least one of alkyl lithium and amino lithium.

[0035] Optionally, after steps S3, S4, and S5, an inert gas and / or nitrogen gas may be introduced to purge the deposition vessel. Typically, and not specifically, the inert gas and / or nitrogen gas is introduced for 60–120 s at a flow rate of 10–100 sccm.

[0036] In the preparation method provided by this invention, the inert gas includes a rare gas; the rare gas includes at least one selected from helium, neon, argon, krypton, xenon, and radon, with argon being preferred. In the step of purging the deposition vessel, the inert gas and / or nitrogen used can be the same as the carrier gas from the deposition step, or other gases can be used.

[0037] The present invention provides a cathode material, which is prepared by the above-described preparation method.

[0038] The present invention also provides a secondary battery comprising the above-mentioned positive electrode material; optionally, the secondary battery comprises an all-solid-state lithium battery. Typically, but not limited to, the preparation method of the all-solid-state lithium battery comprises: grinding and mixing the above-mentioned positive electrode material or the positive electrode material prepared by the above method, a sulfide electrolyte, and a conductive agent in a ratio of 70-85:13-28:2 for 20-60 minutes to obtain a uniformly ground positive electrode mixture for later use; weighing the same type of sulfide electrolyte and pressing it into a sheet using a mold battery at 2-3 tons of pressure for 3-6 minutes; then weighing the uniformly ground positive electrode mixture and pressing it into a sheet using a mold battery at 2-3 tons of pressure for 3-6 minutes; then pressing the Li-In alloy negative electrode under 0.5-1 tons of pressure for 5-10 minutes using a mold battery, and tightening the screws of the mold battery, thus completing the battery assembly.

[0039] The beneficial effects of this invention are:

[0040] (1) The method for preparing the cathode material provided by the present invention includes the following steps: S1: Take a cathode material substrate, reduce the surface residual alkali, and obtain a pretreated cathode material substrate; the step of reducing the surface residual alkali includes mixing the cathode material substrate with a solvent and performing a solvothermal reaction; the solvent includes at least one of isopropanol and oxalic acid; S2: Deposit aluminum onto the surface of the pretreated cathode material substrate using an aluminum source; S3: Deposit fluorine onto the surface of the cathode material substrate obtained in S2 using a fluorine source; S4: Deposit lithium onto the surface of the cathode material substrate obtained in S3 using a lithium source; repeat S2 to S4 to obtain a fluorine-aluminum lithium layer of the target thickness. In the preparation process, a layer of aluminum atoms, a layer of fluorine atoms, and a layer of lithium atoms are deposited in a cycle, and the highly staggered deposition method forms a single "fluorine-aluminum lithium" phase, that is, the obtained fluorine-aluminum lithium layer is an amorphous ternary compound. In this amorphous lithium aluminum fluoride ternary compound, the lithium-ion migration barrier in the disordered network is low, resulting in high lithium-ion conductivity. Simultaneously, it also exhibits good mechanical flexibility and density. Furthermore, the lithium aluminum fluoride layer forms a continuous and uniform physical barrier on the surface of the cathode material substrate, which can suppress interfacial side reactions between the cathode material and the electrolyte, thereby reducing interfacial impedance. This makes it suitable for both all-solid-state systems (such as sulfide electrolyte systems, polyoxyethylene systems, etc.) and liquid systems. The lithium aluminum fluoride layer includes a lithium aluminum fluoride film and protruding lithium aluminum fluoride nanoparticles on the film. The protruding lithium aluminum fluoride nanoparticles act as an "island" structure, while the lithium aluminum fluoride film acts as a "bridge" structure. The "island" structure can promote the Li-ion exchange rate. + Transmission, reduce interface Li + Migration resistance: The "bridge" structure ensures that the coating layer maintains good stability during cycling, thereby improving the battery's specific capacity, rate capability, and cycle stability. The combination of the "island-bridge" structure alleviates the expansion of the cathode lattice and the mixing and loss of lithium and nickel during cycling through mechanical constraint, thus maintaining the structural integrity of the material.

[0041] The formation of protruding lithium aluminum fluoride nanoparticles is due to the use of specific solvents and solvothermal reactions during the process of reducing surface residual alkali. This method controls the retention of hydroxyl groups on the surface of the cathode material matrix while reducing the surface residual alkali content. The reduction of residual alkali content avoids material agglomeration and clumping during subsequent deposition, while the hydroxyl groups provide more reactive sites for subsequent deposition. Lithium aluminum fluoride nanoparticles can be deposited and formed at relatively dense reactive sites.

[0042] By depositing a lithium aluminum fluoride (LAF) layer onto the cathode material substrate, it is possible to precisely control the thickness of the LAF layer and achieve a more comprehensive coverage of the cathode material substrate, thereby enabling the regulation of surface reactivity.

[0043] (2) In the method for preparing the cathode material provided by the present invention, the target thickness is controlled to be 1-10 nm. This allows the cathode material to achieve further improvement in electrical performance without a significant increase in mass, which is beneficial for controlling the specific capacity.

[0044] (3) In the method for preparing the cathode material provided by the present invention, the specific surface area of ​​the cathode material is controlled to be 0.7–0.9 m². 2 / g. This indirectly controls the distribution of "island" structures on the surface of the cathode material, ensuring that the lithium aluminum fluoride layer maintains a complete "island-bridge" structure, rather than being entirely composed of "islands" or entirely of "bridges," thereby enabling further control over the electrical performance of the cathode material.

[0045] (4) In the preparation method of the cathode material provided by the present invention, in step S1, the surface residual alkali is reduced to a LiOH mass ratio of 500-1500 ppm and a Li2CO3 mass ratio of ≤1500 ppm. Controlling the LiOH mass ratio within a certain range can maintain the surface hydroxyl content of the cathode material matrix within a certain range, thus helping to control the formation of lithium aluminum fluoride nanoparticles.

[0046] (5) In the method for preparing the cathode material provided by the present invention, in the step of controlling the reduction of surface residual alkali, the liquid-solid mass ratio of the cathode material matrix to the solvent is 25-35:1; and the temperature of the solvothermal reaction is controlled at 60-90℃, and the time is 2-6h. This method can reduce surface residual alkali and retain hydroxyl groups on the surface of the cathode matrix material without using a large amount of solvent or consuming excessive energy, thus achieving effective cost control.

[0047] (6) In the method for preparing the cathode material provided by the present invention, between S2 and S1, a step of preheating the pretreated cathode material substrate is further included, and the preheating temperature is controlled at 100-180°C and the time is controlled at 300-500 min. Preheating the pretreated cathode material can facilitate subsequent deposition operations, and controlling the preheating temperature and time can ensure sufficient preheating and prevent damage to the cathode material substrate.

[0048] (7) In the method for preparing the cathode material provided by the present invention, in steps S2, S3, and S4, the deposition time is controlled to be 5–30 s, the deposition pressure to be 0.1–50 torr, and the carrier gas flow rate used for deposition to be 10–80 sccm. Controlling the deposition operation parameters can further ensure the quality of the obtained lithium aluminum fluoride layer, and thus improve the electrical performance of the final product.

[0049] (8) In the preparation method of the cathode material provided by the present invention, the chemical formula of the cathode material matrix is ​​LiNi. x Co y Mn 1-x-yO2, where 0.9 ≤ x < 0.95, 0.01 < y < 0.1, and 1 - xy > 0. The cathode material matrix used in this invention can be a high-nickel cathode material matrix, successfully achieving the modification of high-nickel cathode materials. Attached Figure Description

[0050] Figure 1 This is a SEM image of the cathode material prepared in Example 1 of the present invention;

[0051] Figure 2 The first charge-discharge test curves of the corresponding batteries with positive electrode materials obtained in the embodiments and comparative examples of the present invention are shown below.

[0052] Figure 3 The above are the rate cycle test curves of the corresponding batteries for the cathode materials obtained in the embodiments and comparative examples of the present invention. Detailed Implementation

[0053] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0054] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0055] Example 1

[0056] This embodiment provides a cathode material and its preparation method, using trimethylaluminum as the aluminum source, fluoroethane as the fluorine source, and ethyllithium as the lithium source, including the following steps:

[0057] (1) Using high-nickel cathode material LiNi 0.92 Co 0.6 Mn 0.2 The steps for pretreating O2(NCM) as the cathode material matrix to remove surface residual alkali include: dissolving the cathode material matrix in a solvent with a liquid-to-solid mass ratio of 30:1, the solvent composition being 85% isopropanol and 15% ultrapure water by volume, heating to 90°C for a solvothermal reaction for 4 hours, then centrifuging the resulting mixture at 4000 rpm for 5 minutes, taking the separated solid portion, and drying it at 80°C for 10 hours to obtain the pretreated cathode material matrix.

[0058] The residual alkali content of the pretreated cathode material matrix was tested using a potentiometric titrator. The surface residual alkali LiOH mass percentage was 1380 ppm, and the Li2CO3 mass percentage was 1260 ppm.

[0059] (2) Place the pretreated cathode material substrate into the ALD (atomic layer deposition) reaction chamber and bake it at 100°C for 500 min.

[0060] (3) Introduce trimethylaluminum vapor into the reaction chamber for 10 seconds, with a reaction chamber pressure of 5 torr and a nitrogen flow rate of 30 sccm; then introduce argon into the reaction chamber for 60 seconds at a flow rate of 30 sccm to remove unreacted trimethylaluminum vapor.

[0061] (4) Fluoroethane vapor is introduced into the reaction chamber for 10s, the pressure of the reaction chamber is 5 torr, and the nitrogen flow rate is 30 sccm; argon gas is introduced into the reaction chamber for 60s, with a flow rate of 30 sccm, to remove the unreacted fluoroethane vapor.

[0062] (5) Introduce ethyl lithium vapor into the reaction chamber for 10s, with a reaction chamber pressure of 5 torr and a nitrogen flow rate of 30 sccm; introduce argon into the reaction chamber for 60s with a flow rate of 30 sccm to remove unreacted ethyl lithium vapor.

[0063] Steps (3) to (5) constitute a complete cycle. The above cycle is repeated 5 times to obtain a lithium aluminum fluoride film with a thickness of approximately 2 nm. The thickness of the lithium aluminum fluoride film is measured using a transmission electron microscope, and the same applies below.

[0064] The obtained cathode material has a specific surface area of ​​approximately 0.79 g / m². 2 .

[0065] The prepared cathode material was observed under SEM, see [image]. Figure 1 It can be seen that the formed lithium aluminum fluoride coating layer achieves a tight encapsulation of the NCM ternary material, and there are protruding lithium aluminum fluoride nanoparticles on the formed lithium aluminum fluoride film. Among them, the larger particles attached to the surface of the NCM ternary material particles are fine NCM ternary material particles generated by breakage, and the smaller particles are lithium aluminum fluoride nanoparticles protruding on the lithium aluminum fluoride film. The size range of the lithium aluminum fluoride nanoparticles is 50-300 nm.

[0066] Example 2

[0067] This embodiment provides a cathode material and its preparation method, using diethylaluminum bromide as the aluminum source, fluoroethane as the fluorine source, and butyllithium as the lithium source, including the following steps:

[0068] (1) A pretreated cathode material matrix was obtained using the same cathode material matrix and processing method as in Example 1.

[0069] (2) Place the pretreated cathode material substrate into the ALD reaction chamber and bake it at 120°C for 400 min.

[0070] (3) Introduce dialkylaluminum bromide vapor into the reaction chamber for 15s, with a reaction chamber pressure of 10 torr and a nitrogen flow rate of 25 sccm; then introduce argon into the reaction chamber for 60s with a flow rate of 25 sccm to remove the unreacted dialkylaluminum bromide vapor.

[0071] (4) Fluoroethane vapor is introduced into the reaction chamber for 15s, the pressure in the reaction chamber is 10 torr, and the nitrogen flow rate is 25 sccm; argon gas is introduced into the reaction chamber for 60s, with a flow rate of 25 sccm, to remove the unreacted fluoroethane vapor.

[0072] (5) Introduce butyllithium vapor into the reaction chamber for 15s, with a reaction chamber pressure of 10 torr and a nitrogen flow rate of 25 sccm; then introduce argon into the reaction chamber for 60s with a flow rate of 25 sccm to remove unreacted butyllithium vapor.

[0073] Steps (3) to (5) constitute a complete cycle. Repeat the above cycle 10 times to obtain a lithium aluminum fluoride film with a thickness of about 5 nm.

[0074] The obtained cathode material has a specific surface area of ​​approximately 0.77 g / m². 2 .

[0075] Example 3

[0076] This embodiment provides a cathode material and its preparation method, using triethylaluminum as the aluminum source, hydrogen fluoride as the fluorine source, and ethyllithium as the lithium source, including the following steps:

[0077] (1) A pretreated cathode material matrix was obtained using the same cathode material matrix and processing method as in Example 1.

[0078] (2) Place the pretreated cathode material substrate into the ALD reaction chamber and bake it at 150°C for 300 min.

[0079] (3) Introduce triethylaluminum vapor into the reaction chamber for 20 seconds, with a reaction chamber pressure of 15 torr and a nitrogen flow rate of 20 sccm; then introduce argon into the reaction chamber for 60 seconds at a flow rate of 20 sccm to remove unreacted triethylaluminum vapor.

[0080] (4) Introduce hydrogen fluoride vapor into the reaction chamber for 20 seconds, with a reaction chamber pressure of 15 torr and a nitrogen flow rate of 20 sccm; introduce argon into the reaction chamber for 60 seconds with a flow rate of 20 sccm to remove unreacted hydrogen fluoride vapor.

[0081] (5) Introduce ethyl lithium vapor into the reaction chamber for 20 seconds, with a reaction chamber pressure of 15 torr and a nitrogen flow rate of 20 sccm; then introduce argon into the reaction chamber for 60 seconds at a flow rate of 20 sccm to remove unreacted ethyl lithium vapor.

[0082] Steps (3) to (5) constitute a complete cycle. Repeat the above cycle 15 times to obtain a lithium aluminum fluoride film with a thickness of about 8 nm.

[0083] The resulting cathode material has a specific surface area of ​​approximately 0.75 g / m². 2 .

[0084] Example 4

[0085] This embodiment provides a cathode material and its preparation method, using alkylaminoaluminum as the aluminum source, fluoroethane as the fluorine source, and amine lithium as the lithium source, including the following steps:

[0086] (1) Using high-nickel cathode material LiNi 0.92 Co 0.6 Mn 0.2 The steps for pretreating O2(NCM) as the cathode material matrix to remove surface residual alkali include: dissolving the cathode material matrix in a solvent with a liquid-to-solid mass ratio of 30:1, the solvent composition being 95% isopropanol and 5% ultrapure water by volume, heating to 60°C for a solvothermal reaction for 6 hours, then centrifuging the mixture obtained after the reaction at 2000 rpm for 10 minutes, taking the separated solid part, and drying it at 60°C for 12 hours to obtain the pretreated cathode material matrix.

[0087] The residual alkali content of the pretreated cathode material matrix was tested using a potentiometric titrator. The surface residual alkali LiOH mass percentage was 1360 ppm, and the Li2CO3 mass percentage was 1250 ppm.

[0088] (2) Place the pretreated cathode material substrate into the ALD reaction chamber and bake it at 180°C for 300 min.

[0089] (3) Introduce alkylaminoaluminum vapor into the reaction chamber for 5 seconds, with a reaction chamber pressure of 50 torr and a nitrogen flow rate of 80 sccm; introduce argon into the reaction chamber for 120 seconds with a flow rate of 10 sccm to remove unreacted alkylaminoaluminum vapor.

[0090] (4) Fluoroethane vapor is introduced into the reaction chamber for 5s, the pressure of the reaction chamber is 50 torr, and the nitrogen flow rate is 80 sccm; argon gas is introduced into the reaction chamber for 120s, with a flow rate of 10 sccm, to remove the unreacted fluoroethane vapor.

[0091] (5) Introduce lithium amino vapor into the reaction chamber for 5 seconds, with a reaction chamber pressure of 50 torr and a nitrogen flow rate of 80 sccm; introduce argon into the reaction chamber for 120 seconds at a flow rate of 10 sccm to remove unreacted lithium amino vapor.

[0092] Steps (3) to (5) constitute a complete cycle. Repeat the above cycle 5 times to obtain a lithium aluminum fluoride film with a thickness of about 1 nm.

[0093] The obtained cathode material has a specific surface area of ​​approximately 0.8 g / m². 2 .

[0094] Example 5

[0095] This embodiment provides a cathode material and its preparation method, using triethylaluminum as the aluminum source, hydrogen fluoride as the fluorine source, and ethyllithium as the lithium source, including the following steps:

[0096] (1) Using high-nickel cathode material LiNi 0.92 Co 0.6 Mn 0.2 The steps for pretreating O2(NCM) as the cathode material matrix to remove surface residual alkali include: dissolving the cathode material matrix in a solvent with a liquid-to-solid mass ratio of 30:1, the solvent composition being 90% isopropanol and 10% ultrapure water by volume, heating to 90°C for a solvothermal reaction for 2 hours, then centrifuging the mixture obtained after the reaction at 4000 rpm for 5 minutes, taking the separated solid part, and drying it at 100°C for 6 hours to obtain the pretreated cathode material matrix.

[0097] The residual alkali content of the pretreated cathode material matrix was tested using a potentiometric titrator. The surface residual alkali LiOH mass percentage was 1240 ppm, and the Li2CO3 mass percentage was 1150 ppm.

[0098] (2) Place the pretreated cathode material substrate into the ALD reaction chamber and bake it at 150°C for 300 min.

[0099] (3) Introduce triethylaluminum vapor into the reaction chamber for 30 seconds, with a reaction chamber pressure of 0.1 torr and a nitrogen flow rate of 10 sccm; then introduce argon into the reaction chamber for 60 seconds at a flow rate of 100 sccm to remove unreacted triethylaluminum vapor.

[0100] (4) Introduce hydrogen fluoride vapor into the reaction chamber for 30s, with a reaction chamber pressure of 0.1 torr and a nitrogen flow rate of 10 sccm; introduce argon into the reaction chamber for 60s at a flow rate of 100 sccm to remove unreacted hydrogen fluoride vapor.

[0101] (5) Introduce ethyl lithium vapor into the reaction chamber for 30s, with a reaction chamber pressure of 0.1 torr and a nitrogen flow rate of 10 sccm; introduce argon into the reaction chamber for 60s at a flow rate of 100 sccm to remove unreacted ethyl lithium vapor.

[0102] Steps (3) to (5) constitute a complete cycle. Repeat the above cycle 15 times to obtain a lithium aluminum fluoride film with a thickness of about 10 nm.

[0103] The obtained cathode material has a specific surface area of ​​approximately 0.73 g / m². 2 .

[0104] Comparative Example 1

[0105] This comparative example directly uses the pretreated cathode material matrix as the cathode material, without performing the subsequent deposition steps. The resulting cathode material has a specific surface area of ​​approximately 0.70 g / m². 2 .

[0106] Test Example 1

[0107] The positive electrode materials obtained in the comparative examples and Examples 1-3 were ground and mixed with sulfide electrolyte (LPSC) and conductive agent (VGCF) in a ratio of 70:28:2 for 30 minutes to obtain a uniformly ground positive electrode mixture for later use. Then, appropriate amounts of sulfide electrolyte and positive electrode mixture were weighed and pressed into a sheet using a mold battery with a pressure of 3t for 3 minutes. Then, the Li-In alloy negative electrode was pressed using a mold battery with a pressure of 1t for 5 minutes. After assembly, the screws of the mold battery were tightened and the sample was put on the rack for testing.

[0108] The first charge-discharge test image is shown below. Figure 2 The charge / discharge rate used in the first charge / discharge rate test was 0.1C / 0.1C; the rate cycle test images are shown below. Figure 3 The charge / discharge cutoff voltage range used in the rate cycle test is 1.9 to 3.65V.

[0109] from Figure 2 As can be seen, the specific capacity of the cathode material obtained in the examples is higher than that of Comparative Example 1. Figure 3 As can be seen from the examples, the rate cycling performance of the material obtained in the examples is better than that of Comparative Example 1.

[0110] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that: Includes the following steps: S1: Take the cathode material matrix, reduce the surface residual alkali, and obtain the pretreated cathode material matrix; The step of reducing surface residual alkali includes mixing the positive electrode material matrix with a solvent and carrying out a solvothermal reaction; S2: Aluminum is deposited onto the surface of the pretreated cathode material substrate using an aluminum source; S3: Deposit fluorine onto the surface of the cathode material substrate obtained in S2 using a fluorine source; S4: Deposit lithium onto the surface of the cathode material substrate obtained in S3 using a lithium source; Repeat steps S2 to S4 to obtain a lithium aluminum fluoride layer of the target thickness.

2. The preparation method according to claim 1, characterized in that: The target thickness is 1–10 nm; And / or, the specific surface area of ​​the positive electrode material is 0.7–0.9 m². 2 / g.

3. The preparation method according to claim 1, characterized in that: In S1, the surface residual alkali is reduced to a LiOH mass ratio of 500-1500 ppm and a Li2CO3 mass ratio of ≤1500 ppm; And / or, the solvent used in the step of reducing surface residual alkali includes at least one of water, isopropanol, and oxalic acid; And / or, between S2 and S1, there is also a step of preheating the pretreated cathode material matrix.

4. The preparation method according to claim 3, characterized in that: In the step of reducing surface residual alkali, the liquid-solid mass ratio of the positive electrode material matrix to the solvent is 25-35:

1. And / or, the temperature of the solvothermal reaction is 60–90°C, and the time is 2–6 h; And / or, the solvent used in the step of reducing surface residual alkali includes an aqueous solution of isopropanol with a concentration of 80 vol% to 95 vol%. And / or, the solvent used in the step of reducing surface residual alkali includes an aqueous solution of oxalic acid with a concentration of 0.01 to 0.5 mol / L; And / or, in the step of preheating the pretreated cathode material matrix, the preheating temperature is 100-180°C and the time is 300-500 min.

5. The preparation method according to claim 1, characterized in that: In S2, the deposition time is 5–30 s, the deposition pressure is 0.1–50 torr, and the carrier gas flow rate used for deposition is 10–80 sccm; And / or, in S3, the deposition time is 5 to 30 s, the deposition pressure is 0.1 to 50 torr, and the carrier gas flow rate used for deposition is 10 to 80 sccm; And / or, in S4, the deposition time is 5 to 30 s, the deposition pressure is 0.1 to 50 torr, and the carrier gas flow rate used for deposition is 10 to 80 sccm.

6. The preparation method according to claim 5, characterized in that: The aluminum source includes at least one of trialkylaluminum, dialkylaluminum halide, alkylaminoaluminum and its derivatives, and alkoxyaluminum and its derivatives. And / or, the fluorine source includes at least one of hydrogen fluoride and fluorinated hydrocarbon compounds; And / or, the lithium source includes inorganic lithium compounds and / or organic lithium compounds; And / or, the carrier gas includes at least one of nitrogen and rare gases; And / or, the chemical formula of the cathode material matrix is ​​LiNi x Co y Mn 1-x-y O2, where 0.9≤x<0.95, 0.01<y<0.1, 1-xy>0.

7. The preparation method according to claim 6, characterized in that: The trialkylaluminum includes at least one of trimethylaluminum and triethylaluminum; And / or, the fluorinated hydrocarbons include fluoroethane; And / or, the lithium source includes at least one of alkyl lithium and amino lithium.

8. The preparation method according to claim 1, characterized in that: After steps S2, S3, and S4, the process includes introducing inert gas and / or nitrogen to purge the deposition container.

9. A positive electrode material, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. A secondary battery, characterized in that, The secondary battery includes the positive electrode material as described in claim 9; optionally, the secondary battery includes an all-solid-state lithium battery.

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