Negative electrode sheet and its preparation method, lithium battery

Abstract

This invention provides a negative electrode sheet and its preparation method, as well as a lithium battery, belonging to the field of lithium battery technology. It can at least partially solve the problems of high internal resistance and poor cycle capacity in existing lithium batteries. The negative electrode sheet of this invention is used in a lithium battery. The negative electrode sheet includes: a negative electrode substrate; and a negative electrode coating with a thickness of 1μm to 3μm disposed on the negative electrode substrate. The negative electrode coating includes a non-graphite carbon-based conductive material and a dopant element, wherein the dopant element is a non-metallic element capable of forming compounds with unsaturated bonds.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a negative electrode sheet and its preparation method, and a lithium battery. Background Technology

[0002] Some lithium batteries using related technologies suffer from problems such as high internal resistance and poor cycle capacity. Summary of the Invention

[0003] This invention at least partially solves the problems of high internal resistance and poor cycle capacity in existing lithium batteries, and provides a negative electrode sheet with low internal resistance, good cycle performance and no other performance degradation, as well as its preparation method and lithium battery.

[0004] In a first aspect, embodiments of the present invention provide a negative electrode sheet for use in a lithium battery, the negative electrode sheet comprising:

[0005] Negative electrode substrate;

[0006] A negative electrode coating with a thickness of 1 μm to 3 μm is disposed on the negative electrode substrate. The negative electrode coating comprises a non-graphite carbon-based conductive material and a dopant element, wherein the dopant element is a non-metallic element capable of forming a compound with unsaturated bonds.

[0007] Optionally, the doping element includes at least one of the following:

[0008] Nitrogen, phosphorus, sulfur, oxygen, and fluorine.

[0009] Optionally, the concentration of the dopant element in the negative electrode coating is between 1000 ppm and 10000 ppm.

[0010] Optionally, the non-graphite carbon-based conductive material includes at least one of the following:

[0011] Single-walled carbon nanotubes, multi-walled carbon nanotubes, single-layer graphene, multi-layer graphene, single-layer graphene oxide, multi-layer graphene oxide, amorphous carbon, carbon fiber, carbon aerogel, carbon nanofoam, biomass carbon.

[0012] Optionally, the material of the negative electrode substrate includes graphite or lithium metal.

[0013] Optionally, the thickness of the negative electrode substrate is between 50 μm and 200 μm.

[0014] In a second aspect, embodiments of the present invention provide a lithium battery, comprising:

[0015] Any one of the negative electrode sheets in the embodiments of the present invention.

[0016] Thirdly, embodiments of the present invention provide a method for preparing a negative electrode sheet, wherein the negative electrode sheet is any type of negative electrode sheet according to embodiments of the present invention, and the method includes:

[0017] A layer of negative electrode slurry is formed on the negative electrode substrate; the negative electrode slurry includes a solvent, the non-graphite carbon-based conductive material, and the doping element;

[0018] The layer of the cured negative electrode slurry forms the negative electrode coating.

[0019] Optionally, before forming the layer of negative electrode slurry on the negative electrode substrate, the method further includes:

[0020] A doped conductive material is formed; the doped conductive material includes the non-graphite carbon-based conductive material and the doping element;

[0021] The negative electrode slurry is prepared using the doped conductive material.

[0022] Optionally, the formation of the doped conductive material includes:

[0023] The non-graphite carbon-based conductive material is heat-treated in an atmosphere containing the dopant element.

[0024] or,

[0025] The mixture of the doping element and the non-graphite carbon-based conductive material is subjected to heat treatment.

[0026] Optionally, the solvent includes at least one of the following:

[0027] N-methylpyrrolidone, N,N-dimethylformamide, diethyl carbonate, water.

[0028] Optionally, the slurry further includes at least one of the following components:

[0029] Dispersants, film-forming agents, defoamers, and leveling agents.

[0030] Optionally, in the negative electrode slurry:

[0031] The total mass percentage of the non-graphite carbon-based conductive material and the doped elements is 30% to 40%.

[0032] The solvent has a mass percentage content of 28% to 50%;

[0033] The mass percentage of the dispersant is 5% to 10%;

[0034] The film-forming agent has a mass percentage content of 14% to 20%;

[0035] The defoamer has a mass percentage content of 0.5% to 1%.

[0036] The leveling agent has a mass percentage content of 0.5% to 1%.

[0037] The lithium battery of this invention has a negative electrode coating on the surface of the negative electrode substrate. The negative electrode coating is a non-graphite carbon-based conductive material containing doped elements and is very thin, that is, the negative electrode coating is an "ultra-thin, highly active non-graphite carbon-based conductive material layer" with high chemical activity and specific surface area. Due to the thin thickness of the negative electrode coating, it has high wettability to the electrolyte and low electron transfer impedance at the lithium-ion interface, which can improve rate performance. Since the doped elements in the negative electrode coating have high chemical activity and low chemical reaction energy barrier, they can form a large number of reaction sites. Thus, when solvated lithium ions pass through the negative electrode coating, the solvent molecules and salt anions they carry can react rapidly to form a dense, stable, and compositionally controllable SEI (solid electrolyte interphase), which reduces the volume expansion effect, avoids side reactions in the first charge of the lithium battery, reduces the consumption of active lithium and electrolyte, and improves the coulombic efficiency and early cycle capacity in the first charge. As the cycle time increases, the SEI remains stable and will not be repeatedly damaged / formed. Therefore, the internal resistance of the lithium battery is stable and the cycle capacity is good. Attached Figure Description

[0038] Figure 1 This is a cross-sectional view of a negative electrode sheet according to an embodiment of the present invention;

[0039] Figure 2 This is a schematic flowchart of a method for preparing a negative electrode sheet according to an embodiment of the present invention.

[0040] In this embodiment of the invention, the reference numerals in the drawings have the following meanings: 11, negative electrode substrate; 12, negative electrode coating. Detailed Implementation

[0041] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0042] It is understood that the specific embodiments and accompanying drawings described herein are merely for explaining the invention and are not intended to limit the invention.

[0043] It is understood that, without conflict, the various embodiments of the present invention and the features thereof can be combined with each other.

[0044] It is understood that, for ease of description, the accompanying drawings of this invention only show the parts related to the embodiments of this invention, while the parts unrelated to the embodiments of this invention are not shown in the drawings.

[0045] It is understood that, without conflict, the functions and steps marked in the flowcharts and block diagrams of the embodiments of the present invention may occur in a different order than that marked in the accompanying drawings.

[0046] Lithium batteries (lithium secondary batteries) have advantages such as high energy density, high operating voltage, long cycle life, low self-discharge, and no memory effect, so they have been widely used in power generation and energy storage (such as photovoltaic power generation and storage), new energy vehicles and other fields.

[0047] During lithium battery charging, due to the electrical double layer (EDL) effect, a large number of charged particles are distributed on the negative electrode surface of materials such as graphite, thereby promoting the reaction between the negative electrode material and solvent molecules and salt anions in the electrolyte to form a solid electrolyte interface (SEI).

[0048] If the SEI (Sediment Intake) continuously and dynamically forms and expands and breaks down during the use of lithium batteries, it will lead to the generation of a passivation layer with complex composition, disordered structure, and uncontrollable thickness. This will cause a large loss of electrolyte and active lithium, resulting in a decrease in electrolyte ionic conductivity and capacity, which in turn increases the internal resistance of the lithium battery and reduces its cycle capacity.

[0049] Therefore, it is desirable to rapidly form a stable and dense SEI during the formation stage of lithium batteries.

[0050] In some related technologies, SEI formation can be promoted in certain ways, but these methods all have some negative effects, such as:

[0051] (1) Adding additives to the electrolyte will lead to a complex composition of the electrolyte, and different components will easily interfere with each other, resulting in a decrease in electrolyte performance.

[0052] (2) Increase the formation temperature of lithium batteries, but the SEI formed in this way is a porous and loose structure, which is not dense and cannot provide sufficient protection and consumes a lot of energy.

[0053] (3) Change the formation cutoff voltage of lithium battery, but this will make the formation process (the process of forming SEI) time-consuming and costly;

[0054] (4) Change the formation charge and discharge rate of lithium battery. However, if a small current is used, although the SEI density is high, it takes a long time and costs a lot. If a large current is used, the SEI will be porous and loose, resulting in poor performance.

[0055] In summary, lithium batteries using related technologies cannot quickly form a dense and stable SEI without causing other performance degradation, resulting in high internal resistance and poor cycle capacity.

[0056] In a first aspect, embodiments of the present invention provide a negative electrode sheet for use in lithium batteries.

[0057] This invention provides an electrode sheet (negative electrode sheet) used as a negative electrode structure in a lithium battery.

[0058] Among them, lithium batteries are secondary batteries that use lithium ions as the main conductive ions. They can be lithium-ion batteries (LIB, Lithium Ion Battery) that use graphite or other materials as the negative electrode, or lithium metal batteries (LMB, Lithium Metal Battery) that directly use metallic lithium as the negative electrode.

[0059] Reference Figure 1 The negative electrode sheet in this embodiment of the invention includes:

[0060] Negative electrode substrate 11;

[0061] A negative electrode coating 12 with a thickness of 1 μm to 3 μm is disposed on the negative electrode substrate 11. The negative electrode coating 12 includes a non-graphite carbon-based conductive material and a dopant element, wherein the dopant element is a non-metallic element that can form a compound with unsaturated bonds.

[0062] The negative electrode sheet of the present invention includes a negative electrode substrate 11 (such as a sheet-like negative electrode substrate 11) that serves as the negative electrode body and conductive structure, and the negative electrode substrate 11 has a negative electrode coating 12 formed on at least the side for contact with the electrolyte.

[0063] It should be understood that it is also feasible to form a negative electrode coating 12 in all directions of the negative electrode substrate 11.

[0064] The thickness of the negative electrode coating 12 is between 1 μm and 3 μm, and further between 1 μm and 1.5 μm, falling into the "ultra-thin" range. The main material of the negative electrode coating 12 is a "non-graphite carbon-based conductive material," that is, a carbon-based conductive material (excluding diamond) other than graphite. Simultaneously, the non-graphite carbon-based conductive material also contains dopant elements. These dopant elements are non-metallic elements that can react with other components in the electrolyte to form compounds. These compounds contain unsaturated bonds, thus readily reacting with lithium ions to form inorganic substances (compounds of non-metallic elements and lithium).

[0065] The lithium battery of this invention has a negative electrode coating on the surface of the negative electrode substrate. The negative electrode coating is a non-graphite carbon-based conductive material containing doped elements and is very thin, that is, the negative electrode coating is an "ultra-thin, highly active non-graphite carbon-based conductive material layer" with high chemical activity and specific surface area. Due to the thin thickness of the negative electrode coating, it has high wettability to the electrolyte and low electron transfer impedance at the lithium-ion interface, which can improve rate performance. Since the doped elements in the negative electrode coating have high chemical activity and low chemical reaction energy barrier, they can form a large number of reaction sites. Thus, when solvated lithium ions pass through the negative electrode coating, the solvent molecules and salt anions they carry can react rapidly to form a dense, stable, and compositionally controllable SEI (solid electrolyte interphase), which reduces the volume expansion effect, avoids side reactions in the first charge of the lithium battery, reduces the consumption of active lithium and electrolyte, and improves the coulombic efficiency and early cycle capacity in the first charge. As the cycle time increases, the SEI remains stable and will not be repeatedly damaged / formed. Therefore, the internal resistance of the lithium battery is stable and the cycle capacity is good.

[0066] Optionally, the doping element includes at least one of the following:

[0067] Nitrogen, phosphorus, sulfur, oxygen, and fluorine.

[0068] As one embodiment of the present invention, the doping elements in the negative electrode coating can be selected from N, P, S, O, F, etc. These elements have a strong binding ability with lithium ions, so they can quickly form inorganic SEI such as Li3N, Li2S, LiF, etc. After the solvent molecules undergo a reduction reaction, a flexible organic layer (such as a polymer) can be formed on the outside. The combination of inorganic and organic materials can reduce the volume expansion effect and further ensure the rapid formation of a stable and dense SEI.

[0069] Optionally, the concentration of dopant elements in the negative electrode coating is between 1000 ppm and 10000 ppm.

[0070] As one embodiment of the present invention, the content of doping elements in the negative electrode coating can be 1000ppm to 10000ppm, and further can be 2000ppm to 3500ppm, so as to ensure that enough reaction sites are provided without affecting the conductivity of the negative electrode coating itself.

[0071] Optionally, non-graphite carbon-based conductive materials include at least one of the following:

[0072] Single-walled carbon nanotubes, multi-walled carbon nanotubes, single-layer graphene, multi-layer graphene, single-layer graphene oxide, multi-layer graphene oxide, amorphous carbon, carbon fiber, carbon aerogel, carbon nanofoam, biomass carbon.

[0073] As one embodiment of the present invention, the non-graphite carbon-based conductive material used as the main body of the negative electrode coating can be selected from carbon nanotubes (single-walled or multi-walled), graphene (single-layer or multi-layer), graphene oxide (single-layer or multi-layer), amorphous carbon, carbon fiber, carbon aerogel, carbon nanofoam, biomass carbon, etc.

[0074] Alternatively, the negative electrode substrate material may include graphite or lithium metal.

[0075] As one embodiment of the present invention, the negative electrode substrate, which serves as the main body of the negative electrode sheet, can be made of graphite material, that is, the negative electrode sheet can be the negative electrode in a lithium-ion battery (LIB); or, the negative electrode substrate can also be made directly of metallic lithium material (such as a metallic lithium sheet), that is, the negative electrode sheet can be the negative electrode in a lithium metal battery (LMB).

[0076] Optionally, the thickness of the negative electrode substrate is between 50 μm and 200 μm.

[0077] As one embodiment of the present invention, the thickness of the negative electrode substrate, which serves as the main body of the negative electrode sheet, can be 50μm to 200μm, further 60μm to 180μm, and even further 75μm to 150μm.

[0078] In a second aspect, embodiments of the present invention provide a lithium battery, comprising:

[0079] Any one of the negative electrode sheets in the embodiments of the present invention.

[0080] The lithium battery of this invention includes the above-mentioned negative electrode sheet.

[0081] Depending on the material of the negative electrode substrate, lithium batteries can be in the form of lithium-ion batteries (LIB), lithium metal batteries (LMB), etc.

[0082] It should be understood that the lithium battery in the embodiments of the present invention may also include other structures, such as positive electrode, separator (isolation membrane), electrolyte, casing, etc.

[0083] The positive electrode sheet may include a current collector and a positive electrode active material located on the current collector; the current collector may be copper foil, etc., and the positive electrode active material may include positive electrode active material, conductive agent, binder, etc.; the positive electrode active material may be selected from artificial graphite, natural graphite, composite graphite, etc., and its mass percentage in the positive electrode active material is 90% to 97%; the conductive agent may be selected from conductive carbon black, acetylene black, Ketjen black, carbon fiber tube, multi-walled carbon nanotube, single-walled carbon nanotube, graphene, etc., and its mass percentage in the positive electrode active material is 1% to 5%; the binder may be selected from fluorinated resin, polypropylene resin, polyacrylic acid binder, modified polyacrylic acid binder, polyaniline binder, polyimide binder, rubber binder, etc., and its mass percentage in the positive electrode active material is 2% to 5%.

[0084] The diaphragm can be a porous sheet or layered membrane made of materials such as polyethylene, polypropylene, or non-woven fabric; the surface of the diaphragm can be coated with a coating made of materials such as ceramics, boehmite, silica, barium sulfate, polyvinylidene fluoride, polymethyl methacrylate, polyacrylonitrile, or aramid.

[0085] The electrolyte may include a solvent and a lithium salt; the solvent may be a non-aqueous organic solvent, which may be selected from carbonate solvents, carboxylic acid ester solvents, ether solvents, ketone solvents, etc., while the lithium salt may be selected from LiPF6 (lithium hexafluorophosphate), LiFSI (lithium bisfluorosulfonylimide), LiTFSI (lithium bistrifluoromethanesulfonylimide), LiBOB (lithium dioxolaneborate), LiBF4 (lithium tetrafluoroborate), LiCF3SO3 (lithium trifluoromethanesulfonate), LiCF3CO2 (lithium trifluoroacetate), LiAsF6 (lithium hexafluoroarsenate), LiSbF6 (lithium hexafluoroantimonylate), LiAlCl4 (lithium tetrachloroaluminate), LiPO2F2 (lithium difluorophosphate), Li2PO3F (lithium monofluorophosphate), etc.

[0086] The lithium battery of this invention has a negative electrode coating on the surface of the negative electrode substrate. The negative electrode coating is a non-graphite carbon-based conductive material containing doped elements and is very thin, that is, the negative electrode coating is an "ultra-thin, highly active non-graphite carbon-based conductive material layer" with high chemical activity and specific surface area. Due to the thin thickness of the negative electrode coating, it has high wettability to the electrolyte and low electron transfer impedance at the lithium-ion interface, which can improve rate performance. Since the doped elements in the negative electrode coating have high chemical activity and low chemical reaction energy barrier, they can form a large number of reaction sites. Thus, when solvated lithium ions pass through the negative electrode coating, the solvent molecules and salt anions they carry can react rapidly to form a dense, stable, and compositionally controllable SEI (solid electrolyte interphase), which reduces the volume expansion effect, avoids side reactions in the first charge of the lithium battery, reduces the consumption of active lithium and electrolyte, and improves the coulombic efficiency and early cycle capacity in the first charge. As the cycle time increases, the SEI remains stable and will not be repeatedly damaged / formed. Therefore, the internal resistance of the lithium battery is stable and the cycle capacity is good.

[0087] Thirdly, embodiments of the present invention provide a method for preparing a negative electrode sheet, wherein the negative electrode sheet is any type of negative electrode sheet according to embodiments of the present invention.

[0088] This invention provides a method for preparing the above-mentioned negative electrode sheet.

[0089] Reference Figure 2 The method for preparing the negative electrode sheet according to an embodiment of the present invention includes:

[0090] S301, A layer of negative electrode slurry is formed on the negative electrode substrate.

[0091] The negative electrode slurry includes a solvent, a non-graphite carbon-based conductive material, and doping elements.

[0092] S302, The layer of cured negative electrode slurry forms a negative electrode coating.

[0093] In this embodiment of the invention, a negative electrode substrate (such as a lithium metal sheet, a graphite sheet, etc.) can be provided first, and the non-graphite carbon-based conductive material, doping elements and solvent contained in the negative electrode coating can be configured as a negative electrode slurry; then the negative electrode slurry is coated on the negative electrode substrate, and then the negative electrode slurry layer is cured to form the above negative electrode coating, that is, the above negative electrode sheet is obtained.

[0094] Among them, the methods for coating the negative electrode slurry onto the negative electrode substrate can include self-coating, electrostatic spraying, high-pressure airless spraying, etc.

[0095] One method for solidifying the negative electrode slurry layer is by heating and drying, such as drying at a temperature of 50℃~70℃ for 24h~72h in a vacuum environment.

[0096] The lithium battery of this invention has a negative electrode coating on the surface of the negative electrode substrate. The negative electrode coating is a non-graphite carbon-based conductive material containing doped elements and is very thin, that is, the negative electrode coating is an "ultra-thin, highly active non-graphite carbon-based conductive material layer" with high chemical activity and specific surface area. Due to the thin thickness of the negative electrode coating, it has high wettability to the electrolyte and low electron transfer impedance at the lithium-ion interface, which can improve rate performance. Since the doped elements in the negative electrode coating have high chemical activity and low chemical reaction energy barrier, they can form a large number of reaction sites. Thus, when solvated lithium ions pass through the negative electrode coating, the solvent molecules and salt anions they carry can react rapidly to form a dense, stable, and compositionally controllable SEI (solid electrolyte interphase), which reduces the volume expansion effect, avoids side reactions in the first charge of the lithium battery, reduces the consumption of active lithium and electrolyte, and improves the coulombic efficiency and early cycle capacity in the first charge. As the cycle time increases, the SEI remains stable and will not be repeatedly damaged / formed. Therefore, the internal resistance of the lithium battery is stable and the cycle capacity is good.

[0097] Optional, refer to Figure 2 Before forming the negative electrode slurry layer (S301) on the negative electrode substrate, the method further includes:

[0098] S3001, forming a doped conductive material.

[0099] Among them, doped conductive materials include non-graphite carbon-based conductive materials and doping elements.

[0100] S3002, Use doped conductive materials to prepare negative electrode paste.

[0101] As one embodiment of the present invention, dopant elements can be first infiltrated into a non-graphite carbon-based conductive material to obtain a highly active non-graphite carbon-based conductive material (doped conductive material). Then, a negative electrode slurry can be prepared using the doped conductive material and solvents to introduce the dopant elements into the negative electrode coating.

[0102] Optionally, forming the doped conductive material (S3001) includes:

[0103] S30011. Heat-treat non-graphite carbon-based conductive materials in an atmosphere containing doped elements.

[0104] As one embodiment of the present invention, a non-graphite carbon-based conductive material may be placed in an atmosphere containing doped elements and heated to allow the doped elements to diffuse into the non-graphite carbon-based conductive material, thereby obtaining a doped conductive material.

[0105] The processing atmosphere may also include inert gases such as argon (Ar) as a carrier gas; and the dopant element may be added to the processing atmosphere in gaseous form (such as ammonia), or the inert gas may be flowed through a volatile solid material containing the dopant element (such as urea, sodium dihydrogen phosphate, etc.) to form the processing atmosphere.

[0106] The temperature of the above heat treatment can be between 400℃ and 700℃, and the treatment time can be between 1 hour and 8 hours.

[0107] Optionally, forming the doped conductive material (S3001) also includes:

[0108] S30012, Heat treatment of a mixture of doped elements and non-graphite carbon-based conductive materials.

[0109] Alternatively, as another embodiment of the present invention, a solid material containing both doped elements and non-graphite carbon-based conductive materials can be heated to allow the doped elements to diffuse into the non-graphite carbon-based conductive material to form a doped conductive material.

[0110] Specifically, solid materials can be in the form of nitrided amorphous carbon, etc.

[0111] The temperature of the above heat treatment can be between 500℃ and 700℃, and the treatment time can be between 1 hour and 3 hours.

[0112] The non-graphite carbon-based conductive materials used above can also undergo pretreatment such as ultrasonic dispersion (e.g., in deionized water) and freeze-drying, which will not be described in detail here.

[0113] It should be understood that the preparation of the negative electrode sheet in the embodiments of the present invention is not limited to the methods described above.

[0114] For example, a layer of non-graphite carbon-based conductive material can be formed on the negative electrode substrate first, and then dopant elements can be introduced into it through heat treatment or other means.

[0115] Optionally, the solvent includes at least one of the following:

[0116] N-methylpyrrolidone, N,N-dimethylformamide, diethyl carbonate, water.

[0117] As one embodiment of the present invention, the solvent in the negative electrode slurry can be selected from NMP, DMF, DEC, water, etc.

[0118] Optionally, the slurry may also include at least one of the following components:

[0119] Dispersants, film-forming agents, defoamers, and leveling agents.

[0120] As one embodiment of the present invention, in order to improve the performance of the obtained negative electrode coating, the negative electrode slurry may further contain other additives such as dispersants, film-forming agents, defoamers, and leveling agents.

[0121] The dispersant, film-forming agent, defoamer, and leveling agent can be selected from conventional additives.

[0122] For example, the dispersant can be a surfactant, such as selected from polyoxyethylene derivatives, polycarboxylic acids, sodium methylene dinaphthalene sulfonate, polystyrene maleic anhydride copolyammonium salt, ethoxynonylphenol, Solperse 27000, etc.

[0123] For example, film-forming agents can be selected from ethylene glycol monopropyl ether, propylene glycol monomethyl ether acetate, acrylic acid, polyurethane, epoxy resin, alkyd resin, etc.

[0124] For example, defoamers can be selected from silicone, polyacrylic acid, alcohol, amide, phosphate ester, polyether, etc.

[0125] For example, leveling agents can be selected from polyether siloxane, polyether ethyl nonylphenol, fluorocarbon polymers, acrylic acid, etc.

[0126] Optionally, in the negative electrode slurry:

[0127] The total mass percentage of non-graphite carbon-based conductive materials and doping elements is between 30% and 40%.

[0128] The solvent's mass percentage is between 28% and 50%.

[0129] The mass percentage of the dispersant is 5% to 10%;

[0130] The film-forming agent has a mass percentage content of 14% to 20%;

[0131] The defoamer has a mass percentage content of 0.5% to 1%.

[0132] The leveling agent has a mass percentage content of 0.5% to 1%.

[0133] In one embodiment of the present invention, the mass percentage of conductive material (non-graphite carbon-based conductive material and doping element) in the negative electrode slurry can be 30%–40%, more preferably 32%–38%; the mass percentage of dispersant can be 5%–10%, more preferably 6%–8%; the mass percentage of film-forming agent can be 14%–20%, more preferably 16%–18%; the mass percentage of defoamer can be 0.5%–1%, more preferably 0.6%–0.8%; and the mass percentage of leveling agent can be 0.5%–1%, more preferably 0.6%–0.8%.

[0134] Example 1:

[0135] This embodiment 1 provides a lithium battery and its preparation method.

[0136] The manufacturing process of this lithium battery includes:

[0137] (1) Preparation of negative electrode

[0138] A 100μm thick lithium metal sheet is provided as the negative electrode substrate for the negative electrode sheet.

[0139] 200g of carbon nanotubes and 100g of graphene oxide were dispersed in 1000ml of deionized water, ultrasonically dispersed twice, filtered under reduced pressure, and freeze-dried for 24h to obtain a non-graphite carbon-based conductive material.

[0140] Non-graphite carbon-based conductive materials were placed in a tube furnace and heated to 500°C at a rate of 10°C / min under a mixed atmosphere of 10 vol% NH3 / Ar (N being the dopant element), and held for 5 h to obtain highly active non-graphite carbon-based conductive materials (doped conductive materials).

[0141] Add 500g of N-methylpyrrolidone (solvent), 5g of sodium methylene dinaphthalene sulfonate (dispersant), 14g of alkyd resin (film-forming agent), 0.5g of polyether siloxane (leveling agent), and 0.5g of organosiloxane (defoamer) to a highly active non-graphite carbon-based conductive material, and stir until homogeneous to obtain a negative electrode slurry.

[0142] The negative electrode slurry was applied to the negative electrode substrate by electrostatic spraying within 90 seconds, and then dried in a vacuum oven at 60°C for 48 hours to obtain the negative electrode sheet.

[0143] (2) Preparation of positive electrode

[0144] Artificial graphite, SP (conductive carbon black), CMC (carboxymethyl cellulose), and SBR (styrene-butadiene rubber) are uniformly dispersed in deionized water at a mass ratio of 96:1.2:1:1.8 to form a positive electrode slurry.

[0145] After the positive electrode slurry is dried, it is die-cut to obtain the positive electrode sheet.

[0146] (3) Separator preparation

[0147] A diaphragm was obtained by coating a 9μm thick porous polyethylene membrane as a substrate with a 3μm thick ceramic layer and a 2μm thick PVDF (polyvinylidene fluoride) adhesive layer on its surface.

[0148] (4) Electrolyte preparation

[0149] An electrolyte with a concentration of 1 mol / L was prepared using EC (ethylene carbonate) / DMC (dimethyl carbonate) as the solvent and LiPF6 as the lithium salt.

[0150] (5) Lithium battery manufacturing

[0151] The above-mentioned negative electrode, positive electrode, separator, and electrolyte are installed into the casing of the 2032 type battery to form a lithium battery.

[0152] (6) Lithium battery testing

[0153] The thickness of the negative electrode coating on the negative electrode sheet was measured, and the first-cycle coulombic efficiency, cycle performance, and impedance spectrum of the lithium battery were tested within a test voltage window of 2.0V to 3.6V. The impedance (Rct), specific capacity, and energy retention rate of the lithium battery were calculated, and the results are shown in Table 1 below.

[0154] Example 2:

[0155] This embodiment 2 provides a lithium battery and its preparation method.

[0156] The preparation of this lithium battery is similar to that of Example 1, except that the preparation process of its (1) negative electrode sheet is different, including:

[0157] 200g of amorphous carbon and 100g of fibrous carbon were dispersed in 800ml of deionized water, ultrasonically dispersed twice, filtered under reduced pressure, and freeze-dried for 24h to obtain a non-graphite carbon-based conductive material.

[0158] A non-graphite carbon-based conductive material was placed in a tube furnace. 50g of urea (N is the dopant element) was placed on each side of the tube furnace and high-purity Ar was introduced. The temperature was raised to 600℃ at a rate of 15℃ / min and held for 4h to obtain a highly active non-graphite carbon-based conductive material (doped conductive material).

[0159] Add 500ml of deionized water (solvent), 5g of ethoxynonylphenol (dispersant), 14g of polyurethane (film-forming agent), 0.5g of polyether siloxane (leveling agent), and 0.5g of organosilicon (defoamer) to a highly active non-graphite carbon-based conductive material, and stir until homogeneous to obtain a negative electrode slurry.

[0160] The negative electrode slurry was applied to the negative electrode substrate by electrostatic spraying within 60 seconds, and then dried in a vacuum oven at 60°C for 36 hours to obtain the negative electrode sheet.

[0161] Example 3:

[0162] This embodiment 3 provides a lithium battery and its preparation method.

[0163] The preparation of this lithium battery is similar to that of Example 1, except that the preparation process of its (1) negative electrode sheet is different, including:

[0164] 200g of nitrided amorphous carbon (N being the dopant element) and 100g of carbon aerogel were dispersed in 1000ml of deionized water, ultrasonically dispersed twice, filtered under reduced pressure, and freeze-dried for 24h to obtain a mixture of non-graphite carbon-based conductive material and dopant element.

[0165] A mixture of non-graphite carbon-based conductive material and dopant elements was heat-treated in a muffle furnace under a high-purity Ar atmosphere. The conditions were: heating to 600°C at a rate of 15°C / min and holding for 2 hours to obtain a highly active non-graphite carbon-based conductive material (doped conductive material).

[0166] Add 500 ml of N,N-dimethylformamide (solvent), 5 g of ethoxynonylphenol (dispersant), 14 g of epoxy resin (film-forming agent), 0.5 g of polyether siloxane (leveling agent), and 0.5 g of organosilicon (defoamer) to a highly active non-graphite carbon-based conductive material, and stir until homogeneous to obtain a negative electrode slurry.

[0167] The negative electrode slurry was applied to the negative electrode substrate by electrostatic spraying within 60 seconds, and then dried in a vacuum oven at 60°C for 24 hours to obtain the negative electrode sheet.

[0168] Example 4:

[0169] This embodiment 4 provides a lithium battery and its preparation method.

[0170] The preparation of this lithium battery is similar to that of Example 1, except that the preparation process of its (1) negative electrode sheet is different, including:

[0171] 200g of biomass carbon and 100g of carbon nanofoam were dispersed in 800ml of deionized water, ultrasonically dispersed twice, filtered under reduced pressure, and freeze-dried for 18h to obtain a non-graphite carbon-based conductive material.

[0172] Non-graphite carbon-based conductive material was placed in a tube furnace, and 50g of sodium dihydrogen phosphate (P is the dopant element) was placed at the gas inlet of the tube furnace and high-purity Ar was introduced. The temperature was raised to 550℃ at a rate of 10℃ / min and held for 2h to obtain a highly active non-graphite carbon-based conductive material (doped conductive material).

[0173] Add 500ml of diethyl carbonate (solvent), 5g of sodium methylene dinaphthalene sulfonate (dispersant), 14g of propylene glycol monomethyl ether acetate (film-forming agent), 0.5g of polyether ethyl nonylphenol (leveling agent), and 0.5g of organosilicon (defoamer) to a highly active non-graphite carbon-based conductive material, and stir until homogeneous to obtain a negative electrode slurry.

[0174] The negative electrode slurry was applied to the negative electrode substrate by electrostatic spraying within 45 seconds, and then dried in a vacuum oven at 60°C for 24 hours to obtain the negative electrode sheet.

[0175] Comparative Example 1:

[0176] This comparative example provides a lithium battery and its preparation method.

[0177] The preparation of this lithium battery is similar to that of Example 1, except that it directly uses a 100μm thick metallic lithium sheet as the negative electrode sheet and does not form a negative electrode coating.

[0178] Table 1. Lithium Battery Performance of Some Embodiments of the Invention and Related Technologies

[0179]

[0180] As can be seen from Table 1, the charge transfer impedance (Rct) of the lithium battery (lithium metal battery) in the embodiments of the present invention is significantly lower than that of the comparative example, especially the Rct of Example 2 is reduced to less than half of that of Comparative Example 1 (1.4Ω); moreover, the energy retention rate of each embodiment at 3C rate is also significantly improved, indicating that the negative electrode coating of the embodiments of the present invention can ensure the rapid formation of a stable and controllable SEI, which significantly improves the cycle performance of the lithium battery, increases the specific capacity (specific capacity) (by about 3.8%), and significantly increases the overall energy of the lithium battery.

[0181] Furthermore, in Example 3 above, the mAh*g at a 0.5C rate... -1 The specific capacity of / C still retains 88.4% of the energy after 1000 cycles, indicating that the improvement in specific capacity and energy retention is most significant when N (nitrogen) is used as the dopant element.

[0182] Example 5:

[0183] This embodiment 5 provides a lithium battery and its preparation method.

[0184] The manufacturing process of this lithium battery includes:

[0185] (1) Preparation of negative electrode

[0186] Artificial graphite, SP, CMC and SBR are uniformly dispersed in deionized water at a mass ratio of 96:1.2:1:1.8 to form a negative electrode slurry.

[0187] The negative electrode slurry is dried to obtain the negative electrode substrate.

[0188] The negative electrode slurry was prepared according to Example 1 and coated onto the negative electrode substrate. It was then dried in a vacuum oven at 60°C for 48 hours and die-cut to obtain the negative electrode sheet.

[0189] (2) Preparation of positive electrode

[0190] Lithium iron phosphate, SP, and PVDF are uniformly dispersed in deionized water at a mass ratio of 96:1.2:1.8 to form a positive electrode slurry.

[0191] After the positive electrode slurry is dried, it is die-cut to obtain the positive electrode sheet.

[0192] (3) Separator preparation

[0193] A diaphragm was obtained by coating a 9μm thick porous polyethylene membrane as a substrate with a 3μm thick ceramic layer and a 2μm thick PVDF (polyvinylidene fluoride) adhesive layer on its surface.

[0194] (4) Electrolyte preparation

[0195] An electrolyte with a concentration of 1 mol / L was prepared using EC (ethylene carbonate) / DMC (dimethyl carbonate) as the solvent and LiPF6 as the lithium salt.

[0196] (5) Lithium battery manufacturing

[0197] The above-mentioned negative electrode, positive electrode, separator, and electrolyte are installed into the casing of the 2032 type battery to form a lithium battery.

[0198] (6) Lithium battery testing

[0199] The thickness of the negative electrode coating on the negative electrode sheet was measured, and the first-cycle coulombic efficiency, cycle performance, and impedance spectrum of the lithium battery were tested in a constant temperature chamber at 45℃ within a test voltage window of 2.0V to 3.6V. The impedance (Rct), specific capacity, and energy retention rate of the lithium battery were calculated, and the results are shown in Table 2 below.

[0200] Example 6:

[0201] This embodiment 6 provides a lithium battery and its preparation method.

[0202] The preparation of this lithium battery is similar to that of Example 5, except that the negative electrode slurry is prepared and coated in the manner of Example 2.

[0203] Example 7:

[0204] This embodiment 7 provides a lithium battery and its preparation method.

[0205] The preparation of this lithium battery is similar to that of Example 5, except that the negative electrode slurry is prepared and coated in the manner of Example 3.

[0206] Example 8:

[0207] This embodiment 8 provides a lithium battery and its preparation method.

[0208] The preparation of this lithium battery is similar to that of Example 5, except that the negative electrode slurry is prepared and coated in the manner of Example 4.

[0209] Comparative Example 2:

[0210] This comparative example provides a lithium battery and its preparation method.

[0211] The preparation of this lithium battery is similar to that of Example 5, except that it directly uses the negative electrode substrate obtained above as the negative electrode sheet and does not form a negative electrode coating.

[0212] Table 2. Lithium Battery Performance Table of Some Embodiments of the Invention and Related Technologies

[0213]

[0214] As can be seen from Table 2, the charge transfer impedance (Rct) of the lithium battery (lithium-ion battery) of the present invention is significantly lower than that of Comparative Example 2, especially the Rct of Example 6, which is reduced to nearly half of that of Comparative Example 2 (8.2Ω). Moreover, after 1000 cycles at a rate of 1C at a high temperature of 45°C, the energy retention rate of each embodiment is also significantly improved. In particular, Example 6 exhibits an ultra-high energy retention rate of 88.9%, indicating that the negative electrode coating of the present invention can ensure the rapid formation of a stable and controllable SEI, which significantly improves the cycle performance (especially the high temperature performance) of the lithium battery, increases the specific capacity (specific capacity), and significantly increases the overall energy of the lithium battery.

[0215] In summary, the negative electrode sheet (negative electrode coating) of the present invention can significantly improve the performance of various types of lithium batteries, such as lithium metal batteries (LMB) that use lithium metal as the negative electrode and lithium-ion batteries (LIB) that use graphite materials as the negative electrode.

[0216] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A negative electrode sheet for use in a lithium battery, characterized in that, The negative electrode includes: The negative electrode substrate serves as both the negative electrode body and the conductive structure; wherein the thickness of the negative electrode substrate is between 50 μm and 200 μm. A negative electrode coating with a thickness of 1 μm to 1.5 μm is disposed on the negative electrode substrate. The negative electrode coating comprises a non-graphite carbon-based conductive material and doping elements. The doping elements are diffused into the non-graphite carbon-based conductive material by means of: The non-graphite carbon-based conductive material is heat-treated in an atmosphere containing the dopant element. Alternatively, the mixture of the dopant element and the non-graphite carbon-based conductive material may be subjected to heat treatment; Alternatively, a layer of the non-graphite carbon-based conductive material may first be formed on the negative electrode substrate, and then the dopant element may be diffused into it through heat treatment; The concentration of the dopant element in the negative electrode coating is between 1000 ppm and 10000 ppm; The doping element includes at least one of the following: nitrogen and phosphorus; The negative electrode substrate is made of graphite or lithium metal.

2. The negative electrode sheet according to claim 1, characterized in that, The non-graphite carbon-based conductive material includes at least one of the following: Single-walled carbon nanotubes, multi-walled carbon nanotubes, single-layer graphene, multi-layer graphene, single-layer graphene oxide, multi-layer graphene oxide, amorphous carbon, carbon fiber, carbon aerogel, carbon nanofoam, biomass carbon.

3. A lithium battery, characterized in that, include: The negative electrode sheet according to claim 1 or 2.

4. A method for preparing a negative electrode sheet, characterized in that, The negative electrode is the negative electrode as described in claim 1 or 2, and the method includes: A layer of negative electrode slurry is formed on the negative electrode substrate; the negative electrode slurry includes a solvent, the non-graphite carbon-based conductive material, and the doping element; The layer of the solidified negative electrode slurry forms the negative electrode coating; Prior to forming the layer of negative electrode slurry on the negative electrode substrate, the method further includes: The dopant element is incorporated into the non-graphite carbon-based conductive material to form a doped conductive material; the doped conductive material includes the non-graphite carbon-based conductive material and the dopant element. The negative electrode slurry is prepared using the doped conductive material.

5. The method according to claim 4, characterized in that, The solvent includes at least one of the following: N-methylpyrrolidone, N,N-dimethylformamide, diethyl carbonate, water.

6. The method according to claim 4, characterized in that, The slurry also includes at least one of the following components: Dispersants, film-forming agents, defoamers, and leveling agents.

7. The method according to claim 6, characterized in that, In the negative electrode slurry: The total mass percentage of the non-graphite carbon-based conductive material and the dopant elements is 30% to 40%. The solvent has a mass percentage content of 28% to 50%; The dispersant has a mass percentage content of 5% to 10%; The film-forming agent has a mass percentage content of 14% to 20%; The defoamer has a mass percentage content of 0.5% to 1%; The leveling agent has a mass percentage content of 0.5% to 1%.

Images