Double-coated lithium-rich manganese-based positive electrode material, positive electrode sheet and solid-state battery

Abstract

This application provides a double-layer coated lithium-rich manganese-based cathode material, cathode sheet, and solid-state battery, comprising a lithium-rich manganese-based material, an oxide coating layer covering the lithium-rich manganese-based material, and a carbon material coating layer covering the oxide coating layer. The inner oxide coating layer stabilizes the cathode structure, inhibits manganese dissolution from the lithium-rich manganese-based material, reduces interfacial impedance, and simultaneously reduces direct contact between the cathode material and the solid electrolyte, suppressing the formation of a space charge layer and reducing charge transfer impedance. The outer carbon material coating layer improves the cathode's electronic conductivity and enhances the interfacial contact between the cathode and the solid electrolyte, thereby improving the battery's electrochemical performance and cycle performance.

Description

Technical Field

[0001] This application relates to solid-state battery technology, and more particularly to a double-layer coated lithium-rich manganese-based cathode material, cathode sheet, and solid-state battery. Background Technology

[0002] Lithium-rich manganese-based materials are a class of advanced cathode materials for lithium-ion batteries. When adapted to solid-state electrolytes, lithium-rich manganese-based materials can exhibit advantages such as higher energy density and safety, thus showing better application prospects in solid-state batteries.

[0003] Because the contact between the cathode material and the solid electrolyte is a solid-solid contact, there are problems such as poor interfacial contact, element diffusion, and space charge layer, resulting in large interfacial contact impedance and charge transfer impedance.

[0004] Therefore, there is an urgent need for a way to improve cathode stability, suppress the space charge layer to reduce interfacial impedance, and improve the electrochemical performance and cycle performance of solid-state batteries. Summary of the Invention

[0005] This application provides a double-layer coated lithium-rich manganese-based cathode material, cathode sheet, and solid-state battery to improve electrochemical performance and cycle performance.

[0006] In a first aspect, this application provides a double-layer coated lithium-rich manganese-based cathode material, comprising:

[0007] A lithium-rich manganese-based material, an oxide coating layer covering the lithium-rich manganese-based material, and a carbon material coating layer covering the oxide coating layer.

[0008] In some embodiments, the chemical formula of the lithium-rich manganese-based material is Li a Mn b Ni c Co d O x , where 1.2≥a≥1, 0.8≥b>0.4, 0.6≥c>0.2, 0.2≥d≥0, 3≥x>2.

[0009] In some embodiments, the oxide includes aluminum oxide or zirconium oxide.

[0010] In some embodiments, the oxide coating layer accounts for 1 wt% to 3 wt% of the lithium-rich manganese-based material;

[0011] And / or, the carbon material coating layer accounts for 1 wt% to 3 wt% of the lithium-rich manganese-based material.

[0012] In some embodiments, the thickness of the oxide coating layer is 1 nm to 3 nm;

[0013] And / or, the thickness of the carbon material coating layer is 2nm to 5nm.

[0014] Secondly, this application provides a method for preparing the double-layer coated lithium-rich manganese-based cathode material described in the first aspect, the method comprising:

[0015] The lithium-rich manganese-based material, metal salt, and sodium hydroxide solution are mixed evenly and then calcined at high temperature.

[0016] A carbon source is introduced during high-temperature calcination to obtain the double-layer coated lithium-rich manganese-based cathode material.

[0017] In some embodiments, the step of uniformly mixing the lithium-rich manganese-based material, the metal salt, and the sodium hydroxide solution followed by high-temperature calcination includes:

[0018] Lithium-rich manganese-based materials and metal salts are added to pure water and stirred for the first time to obtain a mixture;

[0019] Sodium hydroxide solution was added to the mixture, and after a second stirring, the mixture was filtered, washed, and dried to obtain a dried product.

[0020] The dried product is then calcined at high temperature.

[0021] In some embodiments, the metal salt includes at least one of nitrates, sulfates, and chlorides.

[0022] In some embodiments, the method satisfies any one of the following:

[0023] The mass ratio of the lithium-rich manganese-based material to the metal salt is 1:0.01 to 1:0.03;

[0024] The first stirring time is 2 to 4 hours;

[0025] The molar concentration of the sodium hydroxide solution is 0.5 mol / L to 2 mol / L;

[0026] The high-temperature calcination time is 2 to 4 hours;

[0027] The high-temperature calcination temperature is 500 degrees Celsius to 800 degrees Celsius.

[0028] In some embodiments, the process of introducing a carbon source during high-temperature calcination to obtain the double-layer coated lithium-rich manganese-based cathode material includes:

[0029] Organic gas is introduced during the high-temperature calcination process, and the temperature is lowered after the high-temperature calcination is completed to obtain the double-layer coated lithium-rich manganese-based cathode material.

[0030] In some embodiments, the organic gas includes at least one of methane, ethane, ethylene, and acetylene.

[0031] In some embodiments, the flow rate of the organic gas is 20 L / min to 40 L / min.

[0032] Thirdly, this application provides a positive electrode sheet comprising the lithium-rich manganese-based positive electrode material with double-layer coating as described in the first aspect.

[0033] Fourthly, this application provides a solid-state battery, including the positive electrode sheet described in the third aspect.

[0034] In some embodiments, the system further includes a solid electrolyte, which includes a lithium lanthanum zirconium oxide solid electrolyte or a lithium titanium aluminum phosphate solid electrolyte.

[0035] Fifthly, this application provides a battery pack including the solid-state battery described in the fourth aspect.

[0036] Sixthly, this application provides an electrical device including the solid-state battery described in the fourth aspect, or the battery pack described in the fifth aspect.

[0037] This application provides a double-layer coated lithium-rich manganese-based cathode material, cathode sheet, and solid-state battery, comprising a lithium-rich manganese-based material, an oxide coating layer covering the lithium-rich manganese-based material, and a carbon material coating layer covering the oxide coating layer. The inner oxide coating layer stabilizes the cathode structure, inhibits manganese dissolution from the lithium-rich manganese-based material, reduces interfacial impedance, and simultaneously reduces direct contact between the cathode material and the solid electrolyte, suppressing the formation of a space charge layer and reducing charge transfer impedance. The outer carbon material coating layer improves the cathode's electronic conductivity and enhances the interfacial contact between the cathode and the solid electrolyte, thereby improving the battery's electrochemical performance and cycle performance. Attached Figure Description

[0038] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0039] Figure 1 A schematic diagram of the structure of the double-layer coated lithium-rich manganese-based cathode material provided in the embodiments of this application;

[0040] Figure 2 The XRD pattern of the cathode material provided in the embodiments of this application.

[0041] The accompanying drawings have illustrated specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to specific embodiments. Detailed Implementation

[0042] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0043] Lithium-rich manganese-based materials are more suitable for solid-state battery systems due to their advantages of high voltage and high energy density, and have better application prospects as cathode materials for solid-state batteries.

[0044] In related technologies, lithium-rich manganese-based materials are mainly modified through doping or single carbon coating to improve their chemical properties. For example, doping can increase the lithium-ion transport rate of lithium-rich manganese-based materials, while uniform and high-quality carbon coating can improve their conductivity.

[0045] However, since the contact between the cathode material and the solid electrolyte is a solid-solid contact, the contact between solid materials is usually rough and irregular, leading to poor interfacial contact and increased interfacial contact impedance. Furthermore, during high-temperature or long-term use, some elements in the cathode material may diffuse into the solid electrolyte, or vice versa. This diffusion may cause changes in the chemical composition at the interface, forming an interfacial layer or a new phase, affecting ionic conductivity and interfacial stability, and increasing interfacial impedance. In addition, due to the difference in ionic and electronic conductivity between the solid electrolyte and the cathode material, a space charge layer may form at the interface. This space charge layer leads to uneven charge distribution at the interface, creating a potential gradient, thereby increasing charge transfer impedance.

[0046] Therefore, it is urgent to improve the stability of the cathode and reduce the interfacial impedance by suppressing the space charge layer through targeted interface modification, thereby enhancing the electrochemical performance and cycle performance of solid-state batteries.

[0047] This application provides a double-layer coated lithium-rich manganese-based cathode material, including a lithium-rich manganese-based material, an oxide coating layer covering the lithium-rich manganese-based material, and a carbon material coating layer covering the oxide coating layer, such as... Figure 1 As shown.

[0048] According to the inventors' research, the inner oxide coating layer can provide a chemically stable interface, acting as a physical barrier to stabilize the cathode structure, inhibit manganese dissolution from lithium-rich manganese-based materials, and reduce interfacial impedance. Simultaneously, it can reduce direct contact between the cathode material and the solid electrolyte, suppressing the formation of a space charge layer and reducing charge transfer impedance. Furthermore, the outer carbon coating layer can improve the electron conductivity of the cathode and enhance the interfacial contact between the cathode and the solid electrolyte, thereby improving the battery's electrochemical performance and cycle performance.

[0049] In some embodiments, the chemical formula of the lithium-rich manganese-based material can be Li a Mn b Ni c Co d O x Among these, 1.2≥a≥1, 0.8≥b>0.4, 0.6≥c>0.2, 0.2≥d≥0, and 3≥x>2 are used to provide higher energy density. Furthermore, by adjusting the ratio of Ni, Mn, and Co, better cycle life and material performance can be achieved. For example, increasing the nickel content can increase the material's capacity, increasing the manganese content can improve its stability and safety, and increasing the cobalt content can improve its conductivity and electrical stability.

[0050] For example, a can be a range consisting of 1, 1.02, 1.04, 1.06, 1.08, 1.0, 1.02, 1.04, 1.06, 1.08, 1.1, 1.12, 1.14, 1.16, 1.18, 1.2, or any two of them.

[0051] For example, b can be a range consisting of 0.4, 0.43, 0.46, 0.49, 0.51, 0.54, 0.57, 0.6, 0.63, 0.66, 0.69, 0.72, 0.75, 0.78, 0.8, or any two of them.

[0052] For example, c can be a range consisting of 0.2, 0.22, 0.25, 0.28, 0.3, 0.33, 0.36, 0.4, 0.42, 0.45, 0.48, 0.5, 0.54, 0.56, 0.6, or any two of them.

[0053] For example, d can be a range consisting of 0, 0.04, 0.07, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, or any two of them.

[0054] For example, x can be a range consisting of 2, 2.1, 2.2, 2.25, 2.3, 2.35, 2.4, 2.45, 2.5, 2.55, 2.6, 2.65, 2.7, 2.75, 2.8, 2.85, 2.9, 2.95, 3, or any two of them.

[0055] In some embodiments, the oxide may include aluminum oxide or zirconium oxide. The oxide layer of aluminum oxide or zirconium oxide is more dense. The dense oxide layer can better suppress the dissolution of manganese in lithium-rich manganese-based materials. Furthermore, the diffusion of aluminum in aluminum oxide or the diffusion of zirconium in zirconium oxide can stabilize the cubic phase structure in the solid electrolyte and improve the ionic conductivity.

[0056] In other embodiments, other oxides or compounds may also be used as the inner coating material.

[0057] In some embodiments, the inner oxide coating layer accounts for 1 wt% to 3 wt% of the lithium-rich manganese-based material, ensuring that the surface of the lithium-rich manganese-based material can be uniformly covered with oxide, effectively protecting the cathode material, avoiding unnecessary waste, and reducing production costs.

[0058] In some embodiments, the thickness of the inner oxide coating layer is 1 nm to 3 nm, which protects the lithium-rich manganese-based material while maintaining good conductivity and ion transport characteristics.

[0059] In some embodiments, the outer carbon material coating layer accounts for 1 wt% to 3 wt% of the lithium-rich manganese-based material, so as to provide sufficient coverage for the oxide coating layer, thereby further increasing the protective effect of the inner oxide coating layer on the lithium-rich manganese-based material while protecting it.

[0060] In some embodiments, the thickness of the outer carbon material coating layer is 2nm to 5nm to effectively isolate the electrolyte, reduce the occurrence of side reactions, protect the lithium-rich manganese-based material and the oxide coating layer, and provide a more stable interface to reduce the performance degradation of the battery during cycling.

[0061] A second aspect of this application provides a method for preparing a double-layer coated lithium-rich manganese-based cathode material, the method comprising the following steps:

[0062] The lithium-rich manganese-based material, metal salt, and sodium hydroxide solution are mixed evenly and then calcined at high temperature.

[0063] A carbon source was introduced during the high-temperature calcination process to obtain a double-layer coated lithium-rich manganese-based cathode material.

[0064] The above method involves uniformly mixing lithium-rich manganese-based materials, metal salts, and sodium hydroxide solution, followed by high-temperature calcination. This process coats the surface of the lithium-rich manganese-based materials with oxides, thereby inhibiting the dissolution of manganese from the materials, reducing interfacial impedance, suppressing the formation of a space charge layer, and reducing charge transfer impedance. Furthermore, the introduction of a carbon source during the high-temperature calcination process coats the oxide coating layer with a carbon material coating layer, improving the positive electrode's electronic conductivity and enhancing the interfacial contact between the positive electrode and the solid electrolyte. Ultimately, this double-layer coating improves electrochemical performance and cycle performance.

[0065] In some embodiments, lithium-rich manganese-based materials and metal salts can be added to pure water and stirred for the first time to obtain a mixture. Then, sodium hydroxide solution is added to the mixture, and after a second stirring, the mixture is filtered, washed, and dried to obtain a dried product. Subsequently, the dried product is calcined at high temperature to coat the surface of the lithium-rich manganese-based material with an oxide layer, thereby improving the interfacial stability of the lithium-rich manganese-based material, reducing interfacial impedance and charge transfer impedance, and improving electrochemical performance.

[0066] In some examples, the metal salt may include at least one of nitrates, sulfates, and chlorides, which have better solubility in water or other solvents, which helps to promote uniform chemical reactions or material deposition, thereby facilitating the formation of a uniform oxide coating on the surface of lithium-rich manganese-based materials.

[0067] In some examples, the mass ratio of lithium-rich manganese-based material to metal salt is 1:0.01 to 1:0.03. An appropriate mass ratio helps to form a uniform oxide coating on the surface of lithium-rich manganese-based material and improves the stability of the oxide coating.

[0068] For example, the quality ratio can be any value in a range of 1:0.01, 1:0.015, 1:0.02, 1:0.025, or 1:0.03, or any two of these.

[0069] In one specific embodiment, the ratio of lithium-rich manganese-based material to metal salt can be determined by the mass of the oxide generated on the surface of the lithium-rich manganese-based material. Taking alumina as an example, the amount of aluminum salt can be determined based on the desired mass of the alumina coating layer to be formed on the surface of the lithium-rich manganese-based material. Since the aluminum salt is converted to alumina during the reaction, the required amount of aluminum salt can be determined based on the mass of the desired alumina through stoichiometry. Accordingly, by setting the mass ratio of lithium-rich manganese-based material to aluminum salt, the thickness and uniformity of the alumina coating layer can be controlled, while avoiding excessive use of metal salt.

[0070] In some examples, the initial stirring time is 2 to 4 hours to improve the dispersion of lithium-rich manganese-based materials and metal salts in pure water, ensure sufficient contact between lithium-rich manganese-based materials and metal salts, and thus form a uniformly coated oxide on the surface of lithium-rich manganese-based materials.

[0071] For example, the first stirring time can be any value within a range of 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or any two of these.

[0072] In some examples, the second stirring time is 1 to 4 hours. The second stirring is to mix the sodium hydroxide solution with the above mixture evenly. This time setting not only ensures that the sodium hydroxide solution and the above mixture are mixed evenly, but also further ensures that the lithium-rich manganese-based material and the metal salt are mixed evenly.

[0073] For example, the second stirring time can be any value within a range of 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or any two of these.

[0074] In the above embodiments, after the sodium hydroxide solution and mixture are subjected to a second stirring, filtration, washing, and drying are required to obtain a stable solid product. Filtration is performed to disperse the solid product and solvent from the mixture; washing is performed to remove soluble impurities or solvent adhering to the surface of the solid product; and drying is performed to remove residual solvent from the solid product.

[0075] In some examples, the molar concentration of sodium hydroxide solution is between 0.5 mol / L and 2 mol / L to control the reaction rate, which helps to form a uniform oxide coating on the surface of lithium-rich manganese-based materials. Higher concentrations generally accelerate the reaction rate, causing the coating to form too quickly, resulting in an uneven or incomplete coating. An appropriate molar concentration can control the reaction rate and ensure that the coating is uniform and dense.

[0076] For example, the molar concentration of a sodium hydroxide solution can be any value within a range of 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, or any combination thereof.

[0077] In some examples, the high-temperature calcination time can be 2 to 4 hours. An appropriate calcination time can ensure that the oxide is uniformly generated on the surface of the lithium-rich manganese-based material, which helps to improve the uniformity and integrity of the oxide coating layer, thereby improving the electrochemical performance of the cathode material.

[0078] For example, the high-temperature calcination time can be any value within a range of 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or any two of these.

[0079] In some examples, the high-temperature calcination temperature is between 500 degrees Celsius and 800 degrees Celsius. High-temperature calcination within this temperature range helps to improve the crystallinity and density of the oxide coating layer.

[0080] In some embodiments, an organic gas is introduced during the high-temperature calcination process, and the temperature is lowered after the high-temperature calcination is completed to form a carbon material coating layer on the surface of the oxide coating layer, thereby obtaining a double-coated lithium-rich manganese-based cathode material. The carbon material coating layer can improve the cathode electronic conductivity and improve the interfacial contact between the cathode and the solid electrolyte, thereby improving the electrochemical performance and cycle performance through double-coating.

[0081] In some examples, the organic gas includes at least one of methane, ethane, ethylene, and acetylene, thereby enabling the formation of a carbon material coating on the surface of the oxide coating.

[0082] In some examples, the flow rate of organic gas is 20 L / min to 40 L / min, which is beneficial for forming a dense and complete carbon material coating layer on the surface of the oxide coating layer, and can also avoid the adverse effects of adding too much carbon source on the battery energy density.

[0083] The third aspect of this application provides a positive electrode sheet, including the lithium-rich manganese-based positive electrode material with double-layer coating provided in the first aspect of this application.

[0084] The positive electrode of this application has high stability because it includes the above-mentioned double-layer coated lithium-rich manganese-based positive electrode material.

[0085] In some examples, the positive electrode sheet can be prepared by mixing a double-layer coated lithium-rich manganese-based positive electrode material, a binder and a conductive agent in a certain ratio, adding a certain amount of solvent and stirring to prepare a positive electrode slurry. The positive electrode slurry can then be coated on aluminum foil and dried to obtain the positive electrode sheet.

[0086] For example, conductive agents include, but are not limited to, one or more of conductive carbon black, Super-C, acetylene black, Ketjen black, and carbon nanofibers.

[0087] For example, the adhesive includes, but is not limited to, one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC-Na), polyvinylpyrrolidone, polytetrafluoroethylene, and styrene-butadiene rubber (SBR).

[0088] For example, the solvent may include N-methylpyrrolidone (NMP).

[0089] The fourth aspect of this application provides a solid-state battery, including the positive electrode provided in the third aspect.

[0090] The solid-state battery of this application has the above-mentioned positive electrode sheet, which includes the above-mentioned lithium-rich manganese-based positive electrode material, and therefore has superior electrochemical performance and cycle performance.

[0091] In some examples, solid-state batteries also include solid-state electrolytes, such as lithium lanthanum zirconium oxide (LLZO) or lithium titanium aluminum phosphate (LATP). The diffusion of metals (aluminum or zirconium) in the oxide coating layer of the bilayer lithium-rich manganese-based cathode material can stabilize the cubic phase structure of lithium lanthanum zirconium oxide and improve ionic conductivity. The carbon coating layer in the bilayer lithium-rich manganese-based cathode material can improve the cathode's electronic conductivity and enhance the interfacial contact between the cathode and the solid-state electrolyte.

[0092] The fifth aspect of this application provides a battery pack including the solid-state battery of the fourth aspect, which has advantages corresponding to the above-mentioned bilayer lithium-rich manganese-based cathode material, which will not be elaborated here.

[0093] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0094] The sixth aspect of this application also provides an electrical device, including the above-mentioned battery or battery pack, which has advantages corresponding to the above-mentioned double-layer coated lithium-rich manganese-based cathode material, which will not be elaborated further.

[0095] The electrical equipment used in the embodiments of this application can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no special limitations on this.

[0096] In this embodiment of the application, after obtaining the double-layer coated lithium-rich manganese-based cathode material, it can be analyzed by X-ray diffraction (XRD). Figure 2 As shown, due to the effect of double coating, the characteristic peaks of the double-coated lithium-rich manganese-based cathode material are weakened compared with those of the uncoated lithium-rich manganese-based cathode material.

[0097] The following will provide a detailed description of the solid-state battery, its preparation method, and its applications provided by the present invention through specific embodiments.

[0098] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0099] Example 1

[0100] This embodiment provides a solid-state battery, including a positive electrode sheet, which comprises a double-layer coated lithium-rich manganese-based positive electrode material, and its preparation method includes the following steps:

[0101] 1) Add 1 kg of lithium-rich manganese-based material and 26 g of aluminum chloride to 1 L of pure water and stir to disperse for 2 hours;

[0102] 2) Add the mixture obtained in step 1) to 200 ml of NaOH solution (molar concentration of 1 mol / L), stir rapidly for 4 hours, filter, wash, and then dry in an oven at 100℃.

[0103] 3) The dried product obtained in step 2) was placed in a crucible and calcined at 700℃ for 4 hours in a chemical vapor deposition (CVD) coating furnace, with a heating rate of 5℃ / min. Simultaneously, ethylene was introduced into the furnace as a carbon source for carbon coating, with the ethylene flow rate controlled at 20L / min. After high-temperature calcination, the material was cooled to obtain a double-layer coated lithium-rich manganese-based cathode material.

[0104] 4) The double-layer coated lithium-rich manganese-based cathode material obtained in step 3), polyvinylidene fluoride, and conductive carbon black are mixed in a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone is added and stirred to prepare a cathode slurry. The cathode slurry is coated on aluminum foil, dried in an 80°C oven for 12 hours, and then cut into round pieces with a diameter of 12 mm for later use.

[0105] 5) The disc obtained in step 4) is assembled into a solid-state battery in a glove box with a lithium lanthanum zirconium oxide solid electrolyte with a diameter of 16 mm and a lithium metal sheet with a diameter of 14 mm.

[0106] 6) Perform charge and discharge tests on the solid-state battery obtained in step 5) on a charge and discharge tester.

[0107] Example 2

[0108] This embodiment provides a solid-state battery, including a positive electrode sheet, which comprises a double-layer coated lithium-rich manganese-based positive electrode material, and its preparation method includes the following steps:

[0109] 1) Add 1 kg of lithium-rich manganese-based material and 26 g of aluminum chloride to 1 L of pure water and stir to disperse for 2 hours;

[0110] 2) Add the mixture obtained in step 1) to 200 ml of NaOH solution (molar concentration of 1 mol / L), stir rapidly for 4 hours, filter, wash, and then dry in an oven at 100℃.

[0111] 3) The dried product obtained in step 2) is placed in a crucible and calcined at 700℃ for 4 hours in a chemical vapor deposition coating furnace, with a heating rate of 5℃ / min. Simultaneously, ethylene is introduced into the coating furnace as a carbon source for carbon coating, with the ethylene flow rate controlled at 30L / min. After high-temperature calcination, the material is cooled to obtain a double-layer coated lithium-rich manganese-based cathode material.

[0112] 4) The double-layer coated lithium-rich manganese-based cathode material obtained in step 3), polyvinylidene fluoride, and conductive carbon black are mixed in a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone is added and stirred to prepare a cathode slurry. The cathode slurry is coated on aluminum foil, dried in an 80°C oven for 12 hours, and then cut into round pieces with a diameter of 12 mm for later use.

[0113] 5) The disc obtained in step 4) is assembled into a solid-state battery in a glove box with a lithium lanthanum zirconium oxide solid electrolyte with a diameter of 16 mm and a lithium metal sheet with a diameter of 14 mm.

[0114] 6) Perform charge and discharge tests on the solid-state battery obtained in step 5) on a charge and discharge tester.

[0115] Example 3

[0116] This embodiment provides a solid-state battery, including a positive electrode sheet, which comprises a double-layer coated lithium-rich manganese-based positive electrode material, and its preparation method includes the following steps:

[0117] 1) Add 1 kg of lithium-rich manganese-based material and 52 g of aluminum chloride to 1 L of pure water and stir to disperse for 2 hours;

[0118] 2) Add the mixture obtained in step 1) to 400 ml of NaOH solution (molar concentration of 1 mol / L), stir rapidly for 4 hours, filter, wash, and then dry in an oven at 100℃.

[0119] 3) The dried product obtained in step 2) is placed in a crucible and calcined at 700℃ for 4 hours in a chemical vapor deposition coating furnace, with a heating rate of 5℃ / min. Simultaneously, ethylene is introduced into the coating furnace as a carbon source for carbon coating, with the ethylene flow rate controlled at 30L / min. After high-temperature calcination, the material is cooled to obtain a double-layer coated lithium-rich manganese-based cathode material.

[0120] 4) The double-layer coated lithium-rich manganese-based cathode material obtained in step 3), polyvinylidene fluoride, and conductive carbon black are mixed in a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone is added and stirred to prepare a cathode slurry. The cathode slurry is coated on aluminum foil, dried in an 80°C oven for 12 hours, and then cut into round pieces with a diameter of 12 mm for later use.

[0121] 5) The disc obtained in step 4) is assembled into a solid-state battery in a glove box with a lithium lanthanum zirconium oxide solid electrolyte with a diameter of 16 mm and a lithium metal sheet with a diameter of 14 mm.

[0122] 6) Perform charge and discharge tests on the solid-state battery obtained in step 5) on a charge and discharge tester.

[0123] Example 4

[0124] This embodiment provides a solid-state battery, including a positive electrode sheet, which comprises a double-layer coated lithium-rich manganese-based positive electrode material, and its preparation method includes the following steps:

[0125] 1) Add 1 kg of lithium-rich manganese-based material and 35 g of zirconium sulfate to 1 L of pure water and stir to disperse for 2 hours;

[0126] 2) Add the mixture obtained in step 1) to 200 ml of NaOH solution (molar concentration of 1 mol / L), stir rapidly for 4 hours, filter, wash, and then dry in an oven at 100℃.

[0127] 3) The dried product obtained in step 2) is placed in a crucible and calcined at 700℃ for 4 hours in a chemical vapor deposition coating furnace, with a heating rate of 5℃ / min. Simultaneously, ethylene is introduced into the coating furnace as a carbon source for carbon coating, with the ethylene flow rate controlled at 20L / min. After high-temperature calcination, the material is cooled to obtain a double-layer coated lithium-rich manganese-based cathode material.

[0128] 4) The double-layer coated lithium-rich manganese-based cathode material obtained in step 3), polyvinylidene fluoride, and conductive carbon black are mixed in a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone is added and stirred to prepare a cathode slurry. The cathode slurry is coated on aluminum foil, dried in an 80°C oven for 12 hours, and then cut into round pieces with a diameter of 12 mm for later use.

[0129] 5) The disc obtained in step 4) is assembled into a solid-state battery in a glove box with a lithium lanthanum zirconium oxide solid electrolyte with a diameter of 16 mm and a lithium metal sheet with a diameter of 14 mm.

[0130] 6) Perform charge and discharge tests on the solid-state battery obtained in step 5) on a charge and discharge tester.

[0131] Comparative Example 1

[0132] This embodiment provides a solid-state battery, including a positive electrode sheet, which comprises an uncoated lithium-rich manganese-based positive electrode material, and its preparation method includes the following steps:

[0133] 1) Prepare a positive electrode slurry by mixing uncoated lithium-rich manganese-based positive electrode material, polyvinylidene fluoride, and conductive carbon black in a mass ratio of 8:1:1 and adding a certain amount of N-methylpyrrolidone. Coat the positive electrode slurry onto aluminum foil, dry it in an 80℃ oven for 12 hours, and then cut it into round pieces with a diameter of 12mm for later use.

[0134] 2) The discs obtained in step 1) are assembled into a solid-state battery in a glove box with a lithium lanthanum zirconium oxide solid electrolyte with a diameter of 16 mm and a lithium metal sheet with a diameter of 14 mm.

[0135] 3) Perform charge and discharge tests on the solid-state battery obtained in step 2) on a charge and discharge tester.

[0136] Comparative Example 2

[0137] This embodiment provides a solid-state battery, including a positive electrode sheet, which comprises a lithium-rich manganese-based positive electrode material coated with an alumina monolayer. The preparation method includes the following steps:

[0138] 1) Add 1 kg of lithium-rich manganese-based material and 26 g of aluminum chloride to 1 L of pure water and stir to disperse for 2 hours;

[0139] 2) Add the mixture obtained in step 1) to 200 ml of NaOH solution (molar concentration of 1 mol / L), stir rapidly for 4 hours, filter, wash, and dry in an oven at 100℃. After drying, lithium-rich manganese-based cathode material with a single layer of alumina coating is obtained.

[0140] 3) The lithium-rich manganese-based cathode material with alumina monolayer coating obtained in step 2), polyvinylidene fluoride, and conductive carbon black are mixed in a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone is added and stirred to prepare a cathode slurry. The cathode slurry is coated on aluminum foil, dried in an 80℃ oven for 12 hours, and then cut into round pieces with a diameter of 12mm for later use.

[0141] 4) The disc obtained in step 3) is assembled into a solid-state battery in a glove box with a lithium lanthanum zirconium oxide solid electrolyte with a diameter of 16 mm and a lithium metal sheet with a diameter of 14 mm.

[0142] 5) Perform charge and discharge tests on the solid-state battery obtained in step 4) on a charge and discharge tester.

[0143] Comparative Example 3

[0144] This embodiment provides a solid-state battery, including a positive electrode sheet, which comprises a lithium-rich manganese-based positive electrode material coated with an alumina monolayer. The preparation method includes the following steps:

[0145] 1) 1 kg of lithium-rich manganese-based material was placed in a crucible and calcined at 700℃ for 4 hours in a chemical vapor deposition coating furnace, with a heating rate of 5℃ / min. Simultaneously, ethylene was introduced into the furnace as a carbon source for carbon coating, with the ethylene flow rate controlled at 30 L / min. After high-temperature calcination, the material was cooled to obtain a double-layer coated lithium-rich manganese-based cathode material.

[0146] 2) The single-layer carbon-coated lithium-rich manganese-based cathode material obtained in step 1), polyvinylidene fluoride, and conductive carbon black are mixed in a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone is added and stirred to prepare a cathode slurry. The cathode slurry is coated on aluminum foil, dried in an 80℃ oven for 12 hours, and then cut into round pieces with a diameter of 12mm for later use.

[0147] 3) The disc obtained in step 2) is assembled into a solid-state battery in a glove box with a lithium lanthanum zirconium oxide solid electrolyte with a diameter of 16 mm and a lithium metal sheet with a diameter of 14 mm.

[0148] 4) Perform charge and discharge tests on the solid-state battery obtained in step 3) on a charge and discharge tester.

[0149] This embodiment provides a solid-state battery, including a positive electrode sheet, which comprises a single-layer carbon-coated lithium-rich manganese-based positive electrode material, and its preparation method includes the following steps:

[0150] 1) 1 kg of lithium-rich manganese-based material was placed in a crucible and calcined at 700 °C for 4 hours in a chemical vapor deposition coating furnace, with a heating rate of 5 °C / min. Simultaneously, ethylene was introduced into the furnace as a carbon source for carbon coating, with the ethylene flow rate controlled at 30 L / min. After high-temperature calcination, the material was cooled to obtain a single-layer carbon-coated lithium-rich manganese-based cathode material.

[0151] 2) The single-layer carbon-coated lithium-rich manganese-based cathode material obtained in step 1), polyvinylidene fluoride, and conductive carbon black are mixed in a mass ratio of 8:1:1, and a certain amount of N-methylpyrrolidone is added and stirred to prepare a cathode slurry. The cathode slurry is coated on aluminum foil, dried in an 80℃ oven for 12 hours, and then cut into round pieces with a diameter of 12mm for later use.

[0152] 3) The disc obtained in step 2) is assembled into a solid-state battery in a glove box with a lithium lanthanum zirconium oxide solid electrolyte with a diameter of 16 mm and a lithium metal sheet with a diameter of 14 mm.

[0153] 4) Perform charge and discharge tests on the solid-state battery obtained in step 3) on a charge and discharge tester.

[0154] The differences between the various embodiments and comparative examples can be found in Table 1. Then, the solid-state batteries from each embodiment and comparative example were subjected to the following performance tests, and the results are shown in Table 2.

[0155] 1. Ohmic impedance

[0156] 2. Charge transfer impedance

[0157] Ohmic impedance and charge transfer impedance were measured using electrochemical impedance spectroscopy (EIS). The solid-state battery described above was subjected to three cycles, and the state of charge (SOC) was adjusted to 25%. Subsequently, AC impedance testing was performed using an electrochemical workstation with a test voltage ranging from 2.5V to 4.4V, a frequency range of 0.1Hz to 1MHz, and a voltage increase of 10mV.

[0158] 3. Initial discharge specific capacity

[0159] 4. Coulomb efficiency

[0160] 5. Capacity retention rate over 100 laps

[0161] The initial discharge specific capacity, coulombic efficiency, and capacity retention after 100 cycles were tested using a cycle performance test. The battery was initially discharged at 0.33C to obtain the amount of electricity released during the initial discharge, thus determining the initial discharge specific capacity. After resting for 30 minutes, the battery was charged at a constant current of 2C to 3.8V, then charged at a constant voltage of 3.8V to 0.05C. After resting for 30 minutes, the battery was discharged at 0.33C to 2.0V, and this cycle was repeated 100 times. The ratio of discharge capacity to charge capacity in each charge-discharge cycle was calculated to obtain the coulombic efficiency. The ratio of discharge capacity to initial discharge capacity in each charge-discharge cycle was calculated to obtain the capacity retention.

[0162] Table 1

[0163]

[0164] Table 2

[0165]

[0166]

[0167] The following conclusions can be drawn from Table 2:

[0168] 1) By comparing Examples 1-4 with Comparative Examples 1-3, it can be seen that the double-layer coated lithium-rich manganese-based cathode material has lower ohmic impedance and charge transfer impedance, and higher first discharge specific capacity, coulombic efficiency and 100-cycle capacity retention. The double-layer coated lithium-rich manganese-based cathode material can improve the electrochemical performance and cycle performance of the battery.

[0169] 2) As can be seen from Examples 1 and 2, increasing the carbon source flow rate can reduce the ohmic impedance and improve the capacity retention rate after 100 cycles, but it will increase the charge transfer impedance and reduce the first discharge specific capacity and coulombic efficiency.

[0170] 3) As can be seen from Examples 2 and 3, by increasing the amount of metal salt, the charge transfer impedance can be reduced, and the first discharge specific capacity, coulombic efficiency and 100-cycle capacity retention rate can be improved, but the ohmic impedance will be increased.

[0171] 4) As can be seen from Examples 1 and 4, replacing the metal salt with zirconium sulfate can improve the capacity retention rate over 100 cycles, but it will increase the ohmic impedance and charge transfer impedance, and at the same time reduce the first discharge specific capacity and coulombic efficiency.

[0172] Other embodiments of this application will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this application are indicated by the following claims.

[0173] It should be understood that this application is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A double-layer coated lithium-rich manganese-based cathode material, characterized in that, include: A lithium-rich manganese-based material, an oxide coating layer covering the lithium-rich manganese-based material, and a carbon material coating layer covering the oxide coating layer.

2. The double-layer coated lithium-rich manganese-based cathode material according to claim 1, characterized in that, The chemical formula of the lithium-rich manganese-based material is Li a Mn b Ni c Co d O x , where 1.2≥a≥1, 0.8≥b>0.4, 0.6≥c>0.2, 0.2≥d≥0, 3≥x>2.

3. The double-layer coated lithium-rich manganese-based cathode material according to claim 1, characterized in that, The oxides include aluminum oxide or zirconium oxide.

4. The double-layer coated lithium-rich manganese-based cathode material according to any one of claims 1-3, characterized in that, The oxide coating layer accounts for 1 wt% to 3 wt% of the lithium-rich manganese-based material; And / or, the carbon material coating layer accounts for 1 wt% to 3 wt% of the lithium-rich manganese-based material.

5. The double-layer coated lithium-rich manganese-based cathode material according to any one of claims 1-3, characterized in that, The thickness of the oxide coating layer is 1 nm to 3 nm; And / or, the thickness of the carbon material coating layer is 2nm to 5nm.

6. A method for preparing a double-layer coated lithium-rich manganese-based cathode material according to any one of claims 1-5, characterized in that, The method includes: The lithium-rich manganese-based material, metal salt, and sodium hydroxide solution are mixed evenly and then calcined at high temperature. A carbon source is introduced during high-temperature calcination to obtain the double-layer coated lithium-rich manganese-based cathode material.

7. The preparation method according to claim 6, characterized in that, The process of uniformly mixing lithium-rich manganese-based materials, metal salts, and sodium hydroxide solution, followed by high-temperature calcination, includes: Lithium-rich manganese-based materials and metal salts are added to pure water and stirred for the first time to obtain a mixture; Sodium hydroxide solution was added to the mixture, and after a second stirring, the mixture was filtered, washed, and dried to obtain a dried product. The dried product is then subjected to high-temperature calcination.

8. The preparation method according to claim 6 or 7, characterized in that, The metal salt includes at least one of nitrates, sulfates, and chlorides.

9. The preparation method according to claim 7, characterized in that, The method satisfies any one of the following: The mass ratio of the lithium-rich manganese-based material to the metal salt is 1:0.01 to 1:0.03; The first stirring time is 2 to 4 hours; The molar concentration of the sodium hydroxide solution is 0.5 mol / L to 2 mol / L; The high-temperature calcination time is 2 to 4 hours; The high-temperature calcination temperature is 500 degrees Celsius to 800 degrees Celsius.

10. The preparation method according to claim 6 or 7, characterized in that, The process of introducing a carbon source during high-temperature calcination to obtain the double-layer coated lithium-rich manganese-based cathode material includes: Organic gas is introduced during the high-temperature calcination process, and the temperature is lowered after the high-temperature calcination is completed to obtain the double-layer coated lithium-rich manganese-based cathode material.

11. The preparation method according to claim 10, characterized in that, The organic gas includes at least one of methane, ethane, ethylene, and acetylene.

12. The preparation method according to claim 10, characterized in that, The flow rate of the organic gas is 20 L / min to 40 L / min.

13. A positive electrode plate, characterized in that, Including the lithium-rich manganese-based cathode material with double-layer coating as described in any one of claims 1-5.

14. A solid-state battery, characterized in that, Includes the positive electrode sheet as described in claim 13.

15. The solid-state battery according to claim 14, characterized in that, Also includes: Solid electrolyte, wherein the solid electrolyte includes lithium lanthanum zirconium oxide solid electrolyte or lithium titanium aluminum phosphate solid electrolyte.

16. A battery pack, characterized in that, Includes the solid-state battery as described in claim 14 or 15.

17. An electrical appliance, characterized in that, Includes the solid-state battery as described in claim 14 or 15, or the battery pack as described in claim 16.

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