Lithium battery positive electrode material interface boronizing method and solid-state lithium battery

Abstract

The invention belongs to the technical field of energy storage materials, and particularly relates to a lithium battery positive electrode material interface boronizing method and a solid-state lithium battery, and the method comprises the following steps: uniformly depositing metal boride on the surface of a positive electrode material through a magnetron sputtering process to construct a boron-rich interface layer. Atomic-scale thickness control is realized through magnetron sputtering, a compact and uniform interface layer is formed, side reaction between the positive electrode material and electrolyte under high charging voltage is inhibited, and accumulation of interface by-products and increase of impedance are reduced. And the boron-rich interface layer has high lithium ion conductivity, uniformly promotes lithium ion transmission, and relieves interface stress concentration caused by uneven diffusion, so that the cycling stability of the positive electrode material is ensured. According to the technology, the service life of the battery can be prolonged, the safety of the battery can be improved, the maintenance and replacement cost is remarkably reduced, popularization of energy storage equipment in the fields of new energy automobiles, renewable energy sources and the like is promoted, and remarkable economic and social benefits are brought.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage materials, and in particular relates to a method for boron-enriching the interface of a lithium battery positive electrode material and a solid-state lithium battery. Background Art

[0002] The development of new energy vehicles and the emerging energy storage industry has driven significant growth in lithium battery shipments. New energy storage devices, primarily lithium-ion batteries, have gradually established a significant position in consumer electronics, energy storage systems, and new energy vehicles, becoming one of the fastest-growing manufacturing sectors. Lithium-ion battery shipments have maintained rapid growth in recent years, and the future market holds significant potential. Within the battery system cost structure, the positive electrode accounts for approximately 45% of the total cost, the negative electrode for approximately 10%, the separator for approximately 10%, the electrolyte for approximately 10%, and other components for approximately 25%. The positive electrode material is a crucial factor in the electrochemical performance of lithium batteries, directly determining their energy density and safety, and thus their overall performance. Its cost also directly determines the overall cost of the battery. Therefore, positive electrode materials play a crucial role in lithium batteries and directly drive the development of the lithium battery industry.

[0003] The current cathode material system for lithium batteries is mainly divided into various technical routes such as lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate and ternary materials. For comparison, cost, energy density and safety are the core indicators. As the first generation of commercialized lithium battery cathode materials, lithium cobalt oxide has the advantages of high tap density, stable charge and discharge, and high operating voltage, and is widely used in small batteries. However, lithium cobalt oxide has high cost and poor cyclability and safety; lithium manganese oxide has low specific capacity and cyclability, especially high-temperature cyclability, which greatly limits its application; lithium iron phosphate is low in price, environmentally friendly, safe and has good high-temperature performance, but has low energy density and poor low-temperature performance; lithium nickel cobalt manganese oxide combines the advantages of lithium cobalt oxide, lithium nickel oxide and lithium manganese oxide, and has a significant ternary synergistic effect. It has higher energy density, but higher cost and higher safety requirements. However, layered materials are also prone to irreversible structural and performance degradation during the cycling process. It is currently widely believed that the problems and challenges faced by high-nickel materials can be summarized as: surface reconstruction, surface / interface degradation leading to the release of gases such as O2 and CO2; high charge cut-off voltage and microcracks between and within grains generated during long-term cycling; poor thermal stability, short circuit release of large amounts of heat, which can cause thermal runaway or even explosion and other safety issues.

[0004] In order to solve these problems, various methods have been proposed in the prior art to improve the electrochemical performance of layered cathode materials, such as element doping, surface coating, structural design, etc., to promote the commercialization of high energy density semi-solid lithium-ion batteries. Whether it is the phase transition from layered structure to rock salt structure, gas release or side reactions between electrodes and electrolytes, they all start from the surface or interface and gradually spread to the bulk phase. Therefore, surface structure design is the most direct and effective modification method for cathode materials. The simplest method is to introduce a passivation layer on the surface of the cathode to avoid direct contact with the electrolyte, thereby improving the stability of the interface. However, the uniformity of the chemical coating method is poor, and it is impossible to achieve mass production effects. Summary of the Invention

[0005] In order to solve the above technical problems, the present invention provides a method for boron-enriched interface of lithium battery positive electrode materials and a solid-state lithium battery, and proposes a technical innovation of preparing a boron-rich interface layer by magnetron sputtering to stabilize the interface of high-energy-density positive electrode materials. This method deposits metal boride on the surface of high-energy-density positive electrode materials. The interface layer has a uniform structure and controllable thickness, which is conducive to mass production. The designed metal boride interface layer can avoid the occurrence of side reactions between the positive electrode material and the electrolyte at high voltage, and alleviate the stress evolution process during its lithium insertion and delithiation process. Therefore, the stability of the interface composition of the positive electrode material and the structure of the material itself can be guaranteed, and the stable cycle of the high-energy-density positive electrode material can be achieved.

[0006] In addition, the insufficient charge transfer network in the solid-state positive electrode restricts its development. Unlike the integrated metal negative electrode, the solid-state positive electrode is composed of a composite of positive electrode active materials, electrolytes, electronically conductive carbon and adhesives, and contains complex multi-phase interfaces inside, which seriously affect the electron and ion transport in the electrochemical reaction. This is directly manifested in the huge impedance and chemical instability problems between the positive electrode and the solid electrolyte interface during the entire operating life cycle of the solid-state lithium battery, which has a bad effect. To this end, the present invention innovatively proposes an integrated design of a composite polymer solid electrolyte supported by the positive electrode, and coats the polymer solid electrolyte slurry on the porous positive electrode, which solves the poor interface contact caused by the point-like solid-solid contact between the positive electrode and the solid electrolyte, and reduces the interface impedance. The construction of the boron-rich interface layer and the integrated design of the positive electrode-solid electrolyte in the present invention are of great significance to improving the electrochemical performance of the solid-state composite positive electrode.

[0007] The present invention is specifically achieved through the following technical solutions.

[0008] The present invention provides a method for boron-enriching the interface of a lithium battery positive electrode material, comprising the following steps: A magnetron sputtering process deposits metal borides on the surface of lithium-ion battery cathode materials. After annealing, the surface is enriched with boron, resulting in a boron-rich interface layer. The magnetron sputtering process is equipped with a stirring and vibrating sample tray to ensure that the interface layer is evenly coated on the surface of the micron-sized cathode particles.

[0009] In a preferred embodiment of the present invention, the metal boride is any one or more of nanoborides of titanium, indium, aluminum, magnesium, calcium, barium, zirconium, vanadium, niobium, chromium, manganese, technetium, rhenium, zinc, germanium, antimony, bismuth, cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, tungsten, yttrium, tantalum, hafnium, rhodium, and molybdenum.

[0010] In a preferred embodiment of the present invention, the thickness of the boron-rich interface layer is 2 nm to 20 nm.

[0011] In a preferred embodiment of the present invention, during the magnetron sputtering process, the target distance is 10 cm to 50 cm, the sputtering temperature is 20°C to 30°C, and the background vacuum is 0.1×10 -4 Pa~9.9×10 -4 Pa, the working gas pressure is 0.30Pa~0.55 Pa, the substrate bias is -50V~-150V, and the sputtering time is 1min~10min.

[0012] In a preferred embodiment of the present invention, the metal boride target used in the magnetron sputtering process is prepared by a flash sintering method, with a sintering temperature of 1000°C to 3500°C, a heating rate of 15°C / s to 200°C / s, a holding time of 1 second to 100 seconds, and a purity of the sintered target of ≥99.99%.

[0013] In a preferred embodiment of the present invention, the lithium battery positive electrode material used in magnetron sputtering is lithium cobalt oxide (LCO), lithium nickel manganese cobalt oxide (NCM), lithium nickel aluminum cobalt oxide (NCA) or lithium rich manganese based (LRMO) material.

[0014] The present invention also provides a lithium battery positive electrode material containing a boron-rich interface layer prepared by the above method.

[0015] The present invention further provides the use of the above-mentioned lithium battery positive electrode material containing a boron-rich interface layer in a quasi-solid-state soft-pack lithium battery. The preparation method of the quasi-solid-state soft-pack lithium battery comprises the following steps: The lithium battery positive electrode material containing the boron-rich interface layer, a polymer binder and a conductive additive are dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry; the positive electrode slurry is scraped onto the surface of an aluminum foil and dried to prepare a porous positive electrode.

[0016] A polymer, oxide solid electrolyte nanoparticles and lithium salt are mixed and dispersed in N,N-dimethylformamide to prepare a polymer solid electrolyte slurry; the polymer solid electrolyte slurry is coated on the porous positive electrode and dried to obtain a composite structure of a positive electrode supporting a polymer solid electrolyte.

[0017] The composite structure of the positive electrode supporting the polymer solid electrolyte and the metal lithium negative electrode are assembled into an aluminum-plastic film bag punched in the shape of a battery, and the electrolyte is dripped into the bag to complete the assembly of the solid-state lithium battery.

[0018] In a preferred embodiment of the present invention, in the positive electrode slurry, the mass fraction of the lithium battery positive electrode material containing the boron-rich interface layer is 90% to 95%. Preferably, the mass ratio of the lithium battery positive electrode material containing the boron-rich interface layer to the polymer binder and the conductive additive is 90:5:5, and the viscosity of the positive electrode slurry is 1 Pa·s to 10 Pa·s; The polymer is one or more of polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polymethacrylic acid (PMMA), polyacrylonitrile (PAN), etc.

[0019] The thickness of the polymer solid electrolyte slurry coated on the porous positive electrode is 50 microns to 500 microns.

[0020] The lithium salt in the electrolyte is one or more of lithium bis(trifluoromethylsulfonyl)amide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium hexafluorophosphate (LiPF6); the solvent is a mixture of equal volumes of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; the additive is fluoroethylene carbonate, and the lithium salt concentration of the electrolyte is 1 to 4 mol / L.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention discloses a method for uniformly coating the surface of positive electrode particles with a boron-rich interface layer using magnetron sputtering technology. During the magnetron sputtering process, the positive electrode material of the lithium battery is in a vibrating and stirring state, and the prepared boron-rich interface layer is uniform, thereby avoiding the interface passivation phenomenon caused by serious side reactions between the material and the electrolyte, and ensuring the structural stability of the positive electrode material during long-term circulation. Compared with the use of dry coating and wet coating processes, it is difficult to obtain a uniform and thin coating on the entire material, and the formed coating layer is rough and uneven. The coating obtained on the surface of the microparticles by the magnetron sputtering method is uniform and dense, and has good bonding strength with the positive electrode material particles. The sputtered boron-rich interface layer can inhibit the interface side reactions, maintain the stability of the interface structure, and is conducive to mass production.

[0022] (2) The present invention combines the above-prepared positive electrode material with a solid electrolyte, and coats the polymer solid electrolyte slurry on the porous positive electrode. The designed positive electrode-supported composite polymer solid electrolyte integrated structure improves the cycle life and Coulomb efficiency of the quasi-solid-state battery, while also preventing it from experiencing irreversible capacity decay. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Co prepared in Example 1 x SEM image of B-NCM811 positive electrode material.

[0024] Figure 2 Ni prepared in Example 2 x SEM image of B-NCM811 positive electrode material. DETAILED DESCRIPTION

[0025] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention is further described below with reference to specific examples and accompanying drawings. However, the examples are not intended to limit the present invention. The experimental methods and detection methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0026] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0027] The present invention discloses a technological innovation for stabilizing the interface of a high-energy-density cathode material by preparing a boron-rich interface layer by magnetron sputtering, as well as a structural design for a solid-state lithium battery using a composite polymer solid electrolyte supported by an interface-coated cathode. The designed boron-rich interface can avoid the occurrence of side reactions between the cathode material and the electrolyte at high voltage, as well as the accumulation of the generated by-products at the interface; on the other hand, the construction of the boron-rich interface layer can accelerate the cross-interface transport of lithium ions and alleviate the stress evolution process during the lithium insertion and delithiation process. Therefore, the construction of the boron-rich interface layer can ensure the stability of the interface components and the bulk structure of the cathode material, thereby achieving stable cycling of the high-energy-density cathode material.

[0028] Furthermore, the present invention innovatively proposes an integrated design of a cathode-supported composite polymer solid electrolyte, which addresses the poor interfacial contact caused by point-like solid-solid contact between the cathode and solid electrolyte, thereby reducing interfacial impedance. The construction of the boron-rich interfacial layer and the integrated cathode-solid electrolyte design are of great significance for improving the electrochemical performance of the solid composite cathode.

[0029] The present invention provides a method for boron-enriching the interface of a lithium battery positive electrode material, comprising the following steps: A magnetron sputtering process is used to deposit metal borides on the surface of a lithium battery positive electrode material. After annealing, boron enrichment is achieved on the surface of the lithium battery positive electrode material, and a lithium battery positive electrode material containing a boron-rich interface layer is obtained. During the magnetron sputtering process, the lithium battery positive electrode material is in a vibrating and stirring state.

[0030] The specific steps are: In step 1, a certain amount of metal boride powder and an excess of acetone solvent are placed in a ball mill at a ball-to-material ratio of 10:1. The ball mill and beads are made of zirconium oxide. The mixture is ball milled in a planetary ball mill at 400 rpm for 2 hours. After ball milling, the mixture is allowed to air dry to obtain a modified metal boride powder.

[0031] In step 2, the trimmed and dried metal boride powder from step 1 is placed in a mold and pressed into a size and properties that meet the target material requirements. The green metal boride target is then flash-sintered to produce the desired metal boride target. The sintering temperature is 1000-3500°C, the heating rate is 15-200°C / s, and the holding time is 1-100 seconds. The purity of the fired target is ≥99.99%.

[0032] In step 3, the cleaned and dried positive electrode particles are placed on a vibrating and stirring flat plate and covered with a baffle. The corresponding target material is selected according to the predetermined composition of the deposited layer. The metal boride target obtained in step 2 is assembled into an RF magnetron sputtering device and pre-sputtered for 5 minutes to remove oxides and other impurities on the target surface. The baffle of the sample tray is opened and the sample tray is rotated at 8 rpm. The metal boride target is opened and the metal boride nanolayer is sputtered. The process parameters of the RF magnetron sputtering are: target distance of 10 to 50 cm, sputtering temperature of 20 to 30°C, and background vacuum of (0.1 to 9.9) × 10 -4 Pa, the working gas pressure is 0.30-0.55 Pa, the substrate bias is -50--150 V, and the sputtering time is 1-10 minutes. Depending on the target material, the optimal sputtering time, sputtering power, and sputtering pressure must be selected. The resulting metal boride nanolayer-coated cathode particles are annealed at 500°C under argon to produce a lithium battery cathode material containing a boron-rich interface layer.

[0033] The present invention also provides a solid-state lithium battery prepared using the lithium battery positive electrode material containing the boron-rich interface layer, and the specific preparation method is as follows: Step 4: Disperse the lithium battery positive electrode material containing the boron-rich interface layer obtained in step 3 with a polymer binder (such as PVDF) and a conductive additive (such as Super-P) in a N A positive electrode slurry is formed by mixing methyl-2-pyrrolidone with a lithium battery positive electrode material containing a boron-rich interface layer at a mass fraction of 90% to 95%. Preferably, the mass ratio of the lithium battery positive electrode material containing a boron-rich interface layer to the polymer binder and the conductive additive is 90:5:5, and the viscosity is controlled to be 1 Pa·s to 10 Pa·s. The positive electrode slurry is then applied to the surface of a metal aluminum foil and vacuum dried at a temperature of 100°C for 2 hours to form a porous positive electrode.

[0034] Step 5: Mix and disperse one or more polymers with oxide solid electrolyte nanoparticles and one or more lithium salts in N , N- A polymer solid electrolyte slurry with a viscosity of 1 Pa·s to 10 Pa·s is formed in dimethylformamide. This slurry is then coated on the porous positive electrode obtained in step 4, with a coating thickness of 50 μm to 500 μm. The composite structure of the positive electrode-supported polymer solid electrolyte is then prepared by drying at 100°C for 2 hours and rolling to the desired density.

[0035] Step 6: Mix equal volumes of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate to prepare a mixed solvent, dissolve the same lithium salt used in step 5 in the mixed solvent to prepare a basic electrolyte with a concentration of 1 mol / L; add fluoroethylene carbonate as a metal lithium negative electrode film-forming agent, and its addition amount is 5% to 10% of the basic electrolyte.

[0036] In step 7, the composite structure of the positive electrode-supported polymer solid electrolyte prepared in step 5 and the lithium metal negative electrode are placed in a pre-formed aluminum-plastic film battery strip. A small amount of the electrolyte prepared in step 6 is injected. After packaging, the battery is subjected to a constant current charge and discharge process at a current density of 0.05C for the formation process. The gases produced during the formation process are then removed and the edges are vacuum sealed. The resulting full battery is then tested for charge and discharge performance at 30°C and a 0.2C rate, with a test voltage range of 3.0 V to 4.5 V.

[0037] Example 1 Preparation of Co x B interface layer and Co x B-NCM811 benchmark solid-state soft-pack battery, the specific steps are: (1) Co x Preparation of B interface layer Cobalt boride (Co2B) powder is ball-milled and shaped, then pressed into the target material with the required size and properties. The sputtering target is prepared by a flash sintering process with a sintering temperature of 2000°C, a heating rate of 50°C / s, and a holding time of 30 seconds. The purity of the fired target is ≥99.99%.

[0038] The Co2B target and NCM811 cathode material were placed in the magnetron sputtering equipment. The Co2B target was pre-sputtered for 5 minutes to remove surface impurities and oxide film. The sputtering parameters of the Co2B target were: at a background vacuum of 5.0×10 -4 When the working pressure is 0.30 Pa, the target distance is 40 cm, the sputtering power is 80 W, the sputtering bias is -80 V, the sputtering temperature is 25 ° C, the sputtering is 10 min, and the thickness of the interface layer is 10 nm. The sputtered NCM811 particles are annealed at 500 ° C in argon to obtain Co x B-NCM811 cathode material, such as Figure 1 shown.

[0039] (2) Co x Preparation of B-NCM811 benchmark solid-state soft-pack batteries Co x B-NCM811 cathode material, PVDF and Super-P are dispersed in a mass ratio of 90:5:5. N -methyl-2-pyrrolidone to form a positive electrode slurry, and its viscosity is controlled to be 5 Pa·s.

[0040] The positive electrode slurry was scraped onto the surface of the aluminum foil and then dried at 100° C. in a vacuum oven to form a porous positive electrode.

[0041] PEO, PAN, LATP and LiTFSI were mixed in a mass ratio of 60:20:10:10. N , N- The slurry was then coated on the porous cathode in dimethylformamide to a thickness of 200 μm. After drying at 100°C, the slurry was rolled to the desired density to obtain Co x Composite structure of B-NCM811 cathode supporting polymer solid electrolyte.

[0042] The Co prepared above x The B-NCM811 cathode-supported polymer solid electrolyte composite structure and the lithium metal anode were placed in a pre-formed aluminum-plastic film battery strip. A trace amount of electrolyte was injected, and after packaging, the battery was subjected to constant current charge and discharge at a current density of 0.05C for the formation process. The prepared full battery was then tested for charge and discharge performance at 30°C and a 0.2C rate over a voltage range of 3.0 V to 4.5 V.

[0043] Example 2 Preparation of Ni x B interface layer and Ni x B-NCM811 benchmark solid-state soft-pack battery, the specific steps are: (1) Ni x Preparation of B interface layer Nickel boride (Ni2B) powder is ball-milled and shaped, then pressed into the target material with the required size and properties. The sputtering target is prepared by a flash sintering process with a sintering temperature of 1500°C, a heating rate of 50°C / s, and a holding time of 25 seconds. The purity of the fired target is ≥99.99%.

[0044] The Ni2B target and NCM811 cathode material were placed in the magnetron sputtering equipment. The Ni2B target was pre-sputtered for 5 minutes to remove surface impurities and oxide film. The sputtering parameters of the Ni2B target were: at a background vacuum of 5.0×10 -4 Pa, 99.99% pure argon was introduced to the working pressure of 0.30 Pa, the target distance was 40 cm, the sputtering power was 80 W, the sputtering bias was -70 V, the sputtering temperature was 25 ° C, the sputtering was 10 min, and the thickness of the interface layer was 12 nm. The sputtered NCM811 particles were annealed at 500 ° C in argon to obtain Ni x B-NCM811 cathode material, such as Figure 2 shown.

[0045] (2) Ni x Preparation of B-NCM811 benchmark solid-state soft-pack batteries Ni x B-NCM811 cathode material, PVDF and Super-P are dispersed in a mass ratio of 90:5:5. N -methyl-2-pyrrolidone to form a positive electrode slurry, and its viscosity is controlled to be 5 Pa·s.

[0046] The positive electrode slurry was scraped onto the surface of the aluminum foil and then dried at 100° C. in a vacuum oven to form a porous positive electrode.

[0047] PEO, PAN, LATP and LiTFSI were mixed in a mass ratio of 60:20:10:10. N , N- The slurry formed in dimethylformamide was continuously coated on the porous positive electrode to control the coating thickness to be 200 microns. After drying at 100°C, the slurry was rolled to the required density to obtain Ni x Composite structure of B-NCM811 cathode supporting polymer solid electrolyte.

[0048] The Ni prepared above xThe B-NCM811 cathode-supported polymer solid electrolyte composite structure and the lithium metal anode were placed in a pre-formed aluminum-plastic film battery strip. A trace amount of electrolyte was injected, and after packaging, the battery was subjected to constant current charge and discharge at a current density of 0.05C for the formation process. The prepared full battery was then tested for charge and discharge performance at 30°C and a 0.2C rate over a voltage range of 3.0 V to 4.5 V.

[0049] Example 3 Preparation of LaB x Interface layer and LaB x -NCM811 benchmark solid-state soft-pack battery, the specific steps are: (1) LaB x Preparation of interface layer Lanthanum boride (LaB6) powder is ball-milled and shaped, then pressed into the target material with the required size and properties. The sputtering target is prepared by a flash sintering process with a sintering temperature of 2500°C, a heating rate of 100°C / s, and a holding time of 50 seconds. The purity of the fired target is ≥99.99%.

[0050] The LaB6 target and NCM811 cathode material were placed in the magnetron sputtering equipment. The LaB6 target was pre-sputtered for 5 minutes to remove surface impurities and oxide film. The sputtering parameters of the LaB6 target were: at a background vacuum of 5.0×10 -4 Pa, 99.99% pure argon was introduced to the working pressure of 0.30 Pa, the target distance was 40 cm, the sputtering power was 80 W, the sputtering bias was -70 V, the sputtering temperature was 25 ° C, the sputtering was 10 min, and the thickness of the interface layer was 15 nm. The sputtered NCM811 particles were annealed at 500 ° C in argon to obtain LaB x -NCM811 cathode material.

[0051] (2) LaB x -Preparation of NCM811 benchmark solid-state soft-pack batteries LaB x -NCM811 cathode material, PVDF and Super-P are dispersed in a mass ratio of 90:5:5 N -methyl-2-pyrrolidone to form a positive electrode slurry, and its viscosity is controlled to be 5 Pa·s.

[0052] The positive electrode slurry was scraped onto the surface of the aluminum foil and then dried at 100° C. in a vacuum oven to form a porous positive electrode.

[0053] PEO, PAN, LATP and LiTFSI were mixed in a mass ratio of 60:20:10:10. N , N-The slurry formed in dimethylformamide was continuously coated on the porous positive electrode to control the coating thickness to 200 microns. After drying at 100°C, it was rolled to the required density to obtain LaB x -Composite structure of NCM811 cathode supporting polymer solid electrolyte.

[0054] The LaB prepared above x The NCM811 cathode-supported polymer solid electrolyte composite structure and the lithium metal anode were placed in a pre-formed aluminum-plastic film battery strip. A trace amount of electrolyte was injected, and after packaging, the battery was subjected to constant current charge and discharge at a current density of 0.05C for the formation process. The prepared full battery was then tested for charge and discharge performance at 30°C and a 0.2C rate over a voltage range of 3.0 V to 4.5 V.

[0055] Example 4 Preparation of MoB x Interface layer and MoB x -NCM811 benchmark solid-state soft-pack battery, the specific steps are: (1) MoB x Preparation of interface layer Molybdenum boride (MoB2) powder is ball-milled and shaped, then pressed into the target material with the required size and properties. The sputtering target is prepared by a flash sintering process with a sintering temperature of 2500°C, a heating rate of 100°C / s, and a holding time of 50 seconds. The purity of the fired target is ≥99.99%.

[0056] The MoB2 target and NCM811 cathode material were placed in the magnetron sputtering equipment. The MoB2 target was pre-sputtered for 5 minutes to remove surface impurities and oxide film. The MoB2 target sputtering parameters were: at a background vacuum of 5.0×10 -4 Pa, 99.99% pure argon was introduced to the working pressure of 0.30 Pa, the target distance was 40 cm, the sputtering power was 80 W, the sputtering bias was -70 V, the sputtering temperature was 25 ° C, the sputtering was 10 min, and the thickness of the interface layer was 12 nm. The sputtered NCM811 particles were annealed at 500 ° C in argon to obtain MoB x -NCM811 cathode material.

[0057] (2) MoB x -Preparation of NCM811 benchmark solid-state soft-pack batteries MoB x -NCM811 cathode material, PVDF and Super-P are dispersed in a mass ratio of 90:5:5 N -methyl-2-pyrrolidone to form a positive electrode slurry, and its viscosity is controlled to be 5 Pa·s.

[0058] The positive electrode slurry was scraped onto the surface of the aluminum foil and then dried at 100° C. in a vacuum oven to form a porous positive electrode.

[0059] PEO, PAN, LATP and LiTFSI were mixed in a mass ratio of 60:20:10:10. N , N- The slurry formed in dimethylformamide was continuously coated on the porous positive electrode to control the coating thickness to 200 microns. After drying at 100°C, it was rolled to the required density to obtain MoB x -Composite structure of NCM811 cathode supporting polymer solid electrolyte.

[0060] The MoB prepared above x The NCM811 cathode-supported polymer solid electrolyte composite structure and the lithium metal anode were placed in a pre-formed aluminum-plastic film battery strip. A trace amount of electrolyte was injected, and after packaging, the battery was subjected to constant current charge and discharge at a current density of 0.05C for the formation process. The prepared full battery was then tested for charge and discharge performance at 30°C and a 0.2C rate over a voltage range of 3.0 V to 4.5 V.

[0061] Example 5 Preparation of NbB x Interface layer and NbB x -NCM811 benchmark solid-state soft-pack battery, the specific steps are: (1) NbB x Preparation of interface layer Niobium boride (NbB2) powder is ball-milled and shaped, then pressed into the target material with the required size and properties. The sputtering target is prepared by a flash sintering process with a sintering temperature of 3500°C, a heating rate of 200°C / s, and a holding time of 50 seconds. The purity of the fired target is ≥99.99%.

[0062] The NbB2 target and NCM811 cathode material were placed in the magnetron sputtering equipment. The NbB2 target was pre-sputtered for 5 minutes to remove surface impurities and oxide film. The sputtering parameters of the NbB2 target were: at a background vacuum of 5.0×10 -4 When the target distance is 40 cm, the sputtering power is 100 W, the sputtering bias is -60 V, the sputtering temperature is 25 ° C, the sputtering is 10 min, and the thickness of the interface layer is 15 nm. The sputtered NCM811 particles are annealed at 500 ° C in argon to obtain NbB x -NCM811 cathode material.

[0063] (2) NbB x -Preparation of NCM811 benchmark solid-state soft-pack batteries NbBx -NCM811 cathode material, PVDF and Super-P are dispersed in a mass ratio of 90:5:5 N -methyl-2-pyrrolidone to form a positive electrode slurry, and its viscosity is controlled to be 5 Pa·s.

[0064] The positive electrode slurry was scraped onto the surface of the aluminum foil and then dried at 100° C. in a vacuum oven to form a porous positive electrode.

[0065] PEO, PAN, LATP and LiTFSI were mixed in a mass ratio of 60:20:10:10. N , N- The slurry was then coated on the porous cathode in dimethylformamide to a thickness of 200 μm. After drying at 100°C, it was rolled to the desired density to obtain NbB x -Composite structure of NCM811 cathode supporting polymer solid electrolyte.

[0066] The NbB prepared above x The NCM811 cathode-supported polymer solid electrolyte composite structure and the lithium metal anode were placed in a pre-formed aluminum-plastic film battery strip. A trace amount of electrolyte was injected, and after packaging, the battery was subjected to constant current charge and discharge at a current density of 0.05C for the formation process. The prepared full battery was then tested for charge and discharge performance at 30°C and a 0.2C rate over a voltage range of 3.0 V to 4.5 V.

[0067] Example 6 Preparation of MgB x Interface layer and MgB x -NCM811 benchmark solid-state soft-pack battery, the specific steps are: (1) MgB x Preparation of interface layer Niobium boride (MgB2) powder is ball-milled and shaped, then pressed into the target material with the required size and properties. The sputtering target is prepared by a flash sintering process with a sintering temperature of 1000°C, a heating rate of 20°C / s, and a holding time of 50 seconds. The purity of the fired target is ≥99.99%.

[0068] The MgB2 target and NCM811 cathode material were placed in the magnetron sputtering equipment. The MgB2 target was pre-sputtered for 5 minutes to remove surface impurities and oxide film. The sputtering parameters of the MgB2 target were: at a background vacuum of 5.0×10 -4When the working pressure is 0.30 Pa, the target distance is 40 cm, the sputtering power is 100 W, the sputtering bias is -60 V, the sputtering temperature is 25 ° C, the sputtering is 10 min, and the thickness of the interface layer is 15 nm. The sputtered NCM811 particles are annealed at 500 ° C in argon to obtain MgB x -NCM811 cathode material.

[0069] (2) MgB x -Preparation of NCM811 benchmark solid-state soft-pack batteries MgB x -NCM811 cathode material, PVDF and Super-P are dispersed in a mass ratio of 90:5:5 N -methyl-2-pyrrolidone to form a positive electrode slurry, and its viscosity is controlled to be 5 Pa·s.

[0070] The positive electrode slurry was scraped onto the surface of the aluminum foil and then dried at 100° C. in a vacuum oven to form a porous positive electrode.

[0071] PEO, PAN, LATP and LiTFSI were mixed in a mass ratio of 60:20:10:10. N , N- The slurry was then coated on the porous cathode in dimethylformamide to a thickness of 200 μm. After drying at 100°C, it was rolled to the desired density to obtain MgB x -Composite structure of NCM811 cathode supporting polymer solid electrolyte.

[0072] The MgB prepared above x The NCM811 cathode-supported polymer solid electrolyte composite structure and the lithium metal anode were placed in a pre-formed aluminum-plastic film battery strip. A trace amount of electrolyte was injected, and after packaging, the battery was subjected to constant current charge and discharge at a current density of 0.05C for the formation process. The prepared full battery was then tested for charge and discharge performance at 30°C and a 0.2C rate over a voltage range of 3.0 V to 4.5 V.

[0073] Table 1 Performance comparison of magnetron sputtering interface boron-enriched NCM811 cathode materials in liquid batteries Table 2 Performance comparison of magnetron sputtering-processed NCM811 anode with boron-enriched interface in quasi-solid-state batteries Table 3 Co prepared by magnetron sputtering, dry ball milling and wet chemical method x Performance comparison of B-NCM811 cathode in liquid batteries Table 4 Magnetron sputtering, dry ball milling and wet chemical Ni x Performance comparison of B-NCM811 cathode in liquid batteries Table 5 Magnetron sputtering, dry ball milling and wet chemical LaB x -Performance comparison of NCM811 cathode in liquid batteries The dry ball milling method is a mechanical ball milling method, and the wet method is to dissolve the corresponding salt in the solution, then disperse the unmodified positive electrode into the solution, dry, and sinter. From the performance comparison between the examples and the comparative examples in Tables 1 to 5 above, it can be seen that the magnetron sputtering technology not only improves the stability and durability of the positive electrode in the construction of the boron-rich interface layer, but also significantly improves the performance of high-energy-density batteries under long-cycle conditions. The preparation of the boron-rich interface layer by magnetron sputtering has the following significant advantages in improving the positive electrode cycle performance: (1) Uniform deposition of the boron-rich interface: Magnetron sputtering technology can form a uniform boron-rich layer on the surface of the positive electrode material and accurately control the distribution of the boron element on the entire surface. The uniform boron distribution can effectively cover the surface of the positive electrode material, blocking direct contact with the electrolyte under high voltage, thereby inhibiting the occurrence of side reactions. This feature avoids the uneven thickness problem that may be caused by mechanical ball milling or wet chemical methods, thereby improving the consistency of the interface. (2) Improved interface conductivity and ion transport: After the boron-rich interface layer is uniformly deposited by magnetron sputtering technology, the lithium ion conductivity of the interface can be significantly improved. The uniform distribution of boron elements helps the smooth diffusion and transport of lithium ions, avoiding the degradation of electrochemical performance caused by excessive local transport resistance. In contrast, ball milling and wet processing may cause local uneven boron concentration, affecting the transmission efficiency of lithium ions. (3) Enhanced interface mechanical stability: The uniform boron-rich interface layer can better disperse the stress generated during the charge and discharge process, reduce the damage to the structure of the positive electrode material caused by local stress concentration, and ensure the mechanical stability of the positive electrode material during the cycle. The dense film formed by magnetron sputtering effectively alleviates the risk of local damage caused by uneven interface layer during ball milling or wet processing, ensuring the structural integrity of the interface under long cycles. (4) Avoiding interface thickness fluctuations: The boron-rich interface layer deposited by magnetron sputtering has high thickness accuracy and can be controlled at the nanometer level according to needs, avoiding the thickness fluctuation problem that is difficult to avoid in mechanical ball milling or wet chemical methods. This precise control ensures the stability of the interface, thereby improving the cycle stability and Coulombic efficiency of the cathode material. Therefore, combined with the application of magnetron sputtering in boron-rich interface treatment, it can significantly improve the stability and efficiency of the cathode material under high voltage and long cycle conditions, reduce side reactions and impedance increase, promote the uniform transmission of lithium ions, and fundamentally enhance the electrochemical performance of high-energy-density batteries.

[0074] The ultimate goal of the present invention is to improve the cyclic stability of high-energy-density positive electrode materials. To this end, magnetron sputtering technology is used to construct a boron-rich interface layer on the surface of positive electrode materials such as LCO, NCM, and LRMO, fundamentally avoiding the side reactions between the positive electrode materials and the electrolyte under high charging voltage conditions, reducing the accumulation of interface byproducts and the increase in interface impedance caused by this. At the same time, the boron-rich interface layer has a high lithium ion conductivity, which can evenly promote the transmission of lithium ions across the interface, alleviate the stress concentration phenomenon at the interface caused by uneven lithium ion diffusion, and ensure the structural stability of the positive electrode material during the cycle. The construction of the boron-rich interface layer can improve the cyclic stability and coulombic efficiency of high-energy-density positive electrode materials. The above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

[0075] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications of the present invention fall within the scope of the claims and their equivalents, such changes and modifications are intended to be included.

Claims

1. A method for boron enrichment of the interface of a lithium battery positive electrode material, characterized in that: The following steps are involved: The metal boride is deposited on the surface of the lithium battery positive electrode material by a magnetron sputtering process. After annealing, boron enrichment is achieved at the interface of the lithium battery positive electrode material, and a lithium battery positive electrode material containing a boron-rich interface layer is obtained. During the magnetron sputtering process, the lithium battery positive electrode material is in a vibrating and stirring state.

2. The method for boron enrichment of the interface of the lithium battery positive electrode material according to claim 1, characterized in that: The metal boride is any one or more of nanoborides of titanium, indium, aluminum, magnesium, calcium, barium, zirconium, vanadium, niobium, chromium, manganese, technetium, rhenium, zinc, germanium, antimony, bismuth, cerium, lanthanum, praseodymium, neodymium, promethium, samarium, europium, gadolinium, tungsten, yttrium, tantalum, hafnium, rhodium, molybdenum, nickel and cobalt.

3. The method for boron enrichment of the interface of the lithium battery positive electrode material according to claim 1, characterized in that: The thickness of the boron-rich interface layer is 2 nm to 20 nm.

4. The method for boron enrichment of the interface of the lithium battery positive electrode material according to claim 1, characterized in that: During magnetron sputtering, the target distance is 10 cm to 50 cm, the sputtering temperature is 20℃ to 30℃, and the background vacuum is 0.1×10 -4 Pa~9.9×10 -4 Pa, the working gas pressure is 0.30Pa~0.55 Pa, the substrate bias is -50V~-150V, and the sputtering time is 1min~10min.

5. The method for boron enrichment of the interface of the lithium battery positive electrode material according to claim 1, characterized in that: The metal boride target used in the magnetron sputtering process is prepared by a flash sintering method with a sintering temperature of 1000°C to 3500°C, a heating rate of 15°C / s to 200°C / s, a holding time of 1 second to 100 seconds, and a purity of 99.99% or higher.

6. The method for boron enrichment of the interface of the lithium battery positive electrode material according to claim 1, characterized in that: The positive electrode materials of lithium batteries used in magnetron sputtering are lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel aluminum cobalt oxide or lithium-rich manganese-based materials.

7. A lithium battery positive electrode material containing a boron-rich interface layer obtained according to the method according to any one of claims 1 to 6.

8. A method for preparing a solid-state lithium battery, characterized in that: The method is prepared by using the lithium battery positive electrode material containing a boron-rich interface layer according to claim 7, comprising the following steps: The lithium battery positive electrode material containing the boron-rich interface layer, a polymer binder, and a conductive additive are dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode slurry; the positive electrode slurry is scraped onto the surface of an aluminum foil and dried to prepare a porous positive electrode; Mixing and dispersing a polymer, oxide solid electrolyte nanoparticles, and lithium salt in N,N-dimethylformamide to prepare a polymer solid electrolyte slurry; coating the polymer solid electrolyte slurry on the porous positive electrode and drying the mixture to obtain a composite structure of a positive electrode supporting a polymer solid electrolyte; The composite structure of the positive electrode supporting the polymer solid electrolyte and the metal lithium negative electrode are assembled into an aluminum-plastic film bag punched in the shape of a battery, and the electrolyte is dripped into the bag to complete the assembly of the solid-state lithium battery.

9. The preparation method according to claim 8, characterized in that In the positive electrode slurry, the mass fraction of the lithium battery positive electrode material containing the boron-rich interface layer is 90% to 95%, and the viscosity of the positive electrode slurry is 1 Pa·s to 10 Pa·s; the thickness of the polymer solid electrolyte slurry coated on the porous positive electrode is 50 microns to 500 microns.

10. A solid-state lithium battery prepared according to the preparation method according to claim 8.

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