Negative electrode sheet, battery, and electric device

Abstract

An electric device comprises a battery. The battery comprises a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector, and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector. The negative electrode active material layer comprises a silicon-carbon composite material and a titanium-phosphorus compound. The titanium-phosphorus compound comprises a titanium element and a phosphorus element. The energy density of the battery can be increased, thereby improving the cycle performance of the battery.

Description

Negative electrode, battery and electrical device This application claims priority to the Chinese patent application with application number 202410212235.0 and title “Negative electrode sheet, battery and electrical device” filed with the China Patent Office on February 26, 2024. All of the above contents are incorporated by reference into this application. Technical Field

[0001] The present application relates to the field of batteries, and in particular to a negative electrode plate, a battery, and an electrical device. Background Art

[0002] The energy density of current lithium-ion batteries is insufficient and urgently needs to be improved. Silicon materials have a relatively high theoretical gram capacity (approximately 4200mAh / g) and have broad application prospects in lithium-ion batteries. Adding silicon-based materials to the negative electrode can effectively increase the energy density. However, during the charge and discharge cycle, the silicon material undergoes a volume change of 120% to 300% as lithium ions are inserted and removed. This causes the silicon-based material to pulverize and separate from the current collector, resulting in poor conductivity of the negative electrode and reduced cycle performance of the lithium-ion battery. Summary of the Invention

[0003] In view of the above problems, the present application provides a negative electrode plate, a battery and an electrical device, which can increase the energy density of the battery and improve the cycle performance of the battery.

[0004] In a first aspect, the present application provides a negative electrode plate, comprising a negative electrode current collector and a negative electrode active material layer arranged on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a silicon-carbon composite material and a titanium-phosphorus compound, wherein the titanium-phosphorus compound comprises titanium and phosphorus.

[0005] Silicon-carbon composite materials will expand and contract during the cycle, which will cause the ion channel bridges between the silicon-carbon composite materials to break, resulting in inconsistent lithium insertion levels between different silicon-carbon composite materials, and thus greatly deteriorating the electrochemical performance of the secondary battery. In the technical solution of the embodiment of the present application, the titanium-phosphorus compound is distributed in the pores of the negative electrode active material layer and forms a solid-solid contact with the silicon-carbon composite material, compensating for the ion channel bridge breakage caused by the expansion and contraction of the silicon-carbon composite material, thereby improving the overall lithium insertion uniformity of the negative electrode active material layer, improving the utilization rate of the ion channel network of the negative electrode active material layer, and thus improving the energy density, cycle retention rate and expansion rate of the secondary battery.

[0006] In some embodiments, the titanium-phosphorus compound satisfies at least one of the following conditions:

[0007] The chemical formula of the titanium-phosphorus compound is Li 1+x Al x Ti 2-x(PO4)3, 0≤x≤0.5, as a good conductor of lithium ions, it can improve the ion transport capacity of the anode;

[0008] At least part of the titanium-phosphorus compound is distributed on the surface of the silicon-carbon composite material. The titanium-phosphorus compound is distributed on the surface of the silicon-carbon composite material, which can improve the ion transport and lithium insertion uniformity of the anode.

[0009] In some embodiments, based on the mass of the negative electrode active material layer, the mass percentage of silicon is A%, the mass percentage of carbon is B%, 20≤A≤40, 50≤B≤70, optionally, 25≤A≤32, 58≤B≤66.

[0010] In some embodiments, based on the mass of the negative electrode active material layer, the mass percentage of the titanium element is C%, where C satisfies at least one of the following relationships:

[0011] 0.01≤C≤2.1, optionally, 0.1≤C≤1;

[0012] 0.1×(A+B) <C<2.06×(A+B)。

[0013] By controlling C, the battery can have better cycle performance and energy density.

[0014] In some embodiments, based on the mass of the negative electrode active material layer, the mass percentage of the phosphorus element is F%, 0.04≤F≤2, optionally, 0.13≤F≤1.6.

[0015] By controlling F, the battery can have better cycle performance and energy density.

[0016] In some embodiments, the negative electrode active material layer includes a linear conductive agent, and the average diameter of the linear conductive agent is D nm, 0.5≤D≤20, optionally, 0.5≤D≤3.

[0017] By controlling D, the battery can have better cycle performance and energy density.

[0018] In some embodiments, the average particle size of the silicon-carbon composite material is E μm, where E satisfies at least one of the following relationships:

[0019] 6≤E≤13, optionally, 7≤E≤10;

[0020] 0.036≤D / E≤3.33, optionally, 0.056≤D / E≤2.23.

[0021] By controlling E, the battery can have better cycle performance and energy density at the same time; by controlling D / E, the battery can have better cycle performance and energy density at the same time.

[0022] In a second aspect, the present application provides a battery comprising the negative electrode sheet of the above embodiment.

[0023] In some embodiments, the electrolyte further comprises an electrolyte that satisfies at least one of the following conditions:

[0024] The electrolyte contains lithium difluorophosphate, and the content of the lithium difluorophosphate is G%, 0.01≤G≤1.5, and 18.7≤A / G≤2807 based on the mass of the electrolyte;

[0025] The electrolyte contains fluoroethylene carbonate, and based on the mass of the electrolyte, the content of the fluoroethylene carbonate is H%, 1.9≤H≤17.5, and 1.6≤A / H≤14.8.

[0026] By controlling G, the battery has both better cycle performance and energy density; by controlling A / G, the battery has both better cycle performance and energy density; by controlling H, the battery has both better cycle performance and energy density; by controlling A / H, the battery has both better cycle performance and energy density.

[0027] In a third aspect, the present application provides an electrical device comprising the battery of the above embodiment.

[0028] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present application. The same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0030] FIG1 is a diagram showing the distribution of various elements at the same local position on the surface of the negative electrode sheet of Example 1;

[0031] FIG2 is a SEM image of a cross section of the negative electrode sheet of Example 1;

[0032] FIG3 is an EDS spectrum of the negative electrode sheet of Example 1. DETAILED DESCRIPTION

[0033] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned figure descriptions are intended to cover non-exclusive inclusions.

[0035] In the description of the embodiments of this application, the technical terms "first," "second," etc. are used only to distinguish different objects and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0036] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0037] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0038] In the description of the embodiments of the present application, the orientation or positional relationship indicated by technical terms such as "thickness", "up", "down", "inside", and "outside" is based on the orientation or positional relationship shown in the accompanying drawings. It is only for the convenience of describing the embodiments of the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the embodiments of the present application.

[0039] In the description of the embodiments of this application, unless otherwise expressly specified or limited, technical terms such as "installation," "connection," and "fixation" should be understood in a broad sense. For example, they may refer to fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two components or interaction between two components. Those skilled in the art will understand the specific meanings of the above terms in the embodiments of this application based on specific circumstances.

[0040] The energy density of current lithium-ion batteries is insufficient and urgently needs to be improved. The addition of silicon materials can effectively increase the energy density, but silicon materials will undergo a large volume expansion during the charge and discharge cycle. Therefore, the addition of silicon materials will deteriorate battery performance: the expansion rate increases and the cycle performance decreases.

[0041] Currently, the main strategies to improve the electrochemical performance of silicon materials include: nano-sizing of silicon materials, preparation of silicon-carbon composite materials, and silicon-oxygen composite materials. However, the expansion rate of this type of silicon anode battery is still large, and the cycle performance still needs to be improved.

[0042] In order to effectively improve the problems of large expansion rate and poor cycle performance of silicon anode batteries, a negative electrode plate can be designed. The silicon anode is formed by combining silicon-carbon composite materials and titanium-phosphorus compounds. This can increase the energy density of the battery and effectively improve the ion transmission path of the silicon anode, thereby effectively improving the expansion rate and cycle performance of the battery.

[0043] According to some embodiments of the present application, the present application provides a negative electrode plate, including a negative electrode current collector and a negative electrode active material layer arranged on the surface of at least one side of the negative electrode current collector, the negative electrode active material layer contains a silicon-carbon composite material and a titanium-phosphorus compound, and the titanium-phosphorus compound includes titanium and phosphorus.

[0044] The negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is provided on either one or both of the two facing surfaces of the negative electrode current collector.

[0045] A silicon-carbon composite material is a composite material composed of silicon and carbon. It serves as the negative electrode active material. In the embodiments of this application, the negative electrode plate is a silicon anode containing silicon. The negative electrode active material layer is also called a composite layer. In some embodiments, the negative electrode plate is a pure silicon anode containing the silicon-carbon composite material and without graphite, enabling higher energy density.

[0046] The titanium-phosphorus compound refers to a compound containing titanium and phosphorus. In some embodiments, the titanium-phosphorus compound is an oxide of titanium, phosphorus, and other metal elements, such as lithium and aluminum.

[0047] The embodiment of the present application adds a titanium-phosphorus compound to the silicon-carbon composite material to enhance the ion transport capability and lithium insertion uniformity of the silicon-carbon composite material, thereby effectively improving the cycle performance and expansion rate of the battery, and at the same time enhancing the energy density.

[0048] According to some embodiments of the present application, the titanium-phosphorus compound satisfies at least one of the following conditions:

[0049] The chemical formula of titanium-phosphorus compound is Li 1+x Al x Ti 2-x (PO4)3, 0≤x≤0.5; For example, the chemical formula of the titanium-phosphorus compound is LiTi2(PO4)3, Li 1.3 Al 0.3 Ti 1.7 (PO4)3、Li 1.5 AlTi 1.5 (PO4)3.

[0050] At least part of the titanium-phosphorus compound is distributed on the surface of the silicon-carbon composite material.

[0051] According to some embodiments of the present application, based on the mass of the negative electrode active material layer, the mass percentage of silicon is A%, the mass percentage of carbon is B%, 20≤A≤40, 50≤B≤70, optionally, 25≤A≤32, 58≤B≤66. As an example, the value of A can be 20, 25, 30, 32, 35, 40, or an intermediate value between any two values; the value of B can be 50, 55, 58, 60, 66, 70, or an intermediate value between any two values.

[0052] The mass percentage of silicon refers to the mass proportion of all silicon elements in the negative electrode active material layer. In some embodiments, silicon elements mainly come from the silicon-carbon composite material.

[0053] The mass percentage of carbon element refers to the mass proportion of all carbon elements in the negative electrode active material layer. In some embodiments, the carbon element mainly comes from the silicon-carbon composite material, and may also come from carbon material added as a conductive agent.

[0054] According to some embodiments of the present application, based on the mass of the negative electrode active material layer, the mass percentage of the titanium element is C%, and C satisfies at least one of the following relationships:

[0055] 0.01≤C≤2.1, optionally, 0.1≤C≤1; illustratively, the value of C can be 0.01, 0.1, 0.5, 0.7, 1, 1.5, 2.1 or an intermediate value between any two values.

[0056] A, B and C satisfy the following relationship: 0.1×(A+B) <C<2.06×(A+B)。

[0057] The mass percentage of titanium element refers to the mass proportion of all titanium elements in the negative electrode active material layer. In some embodiments, the titanium element mainly comes from titanium-phosphorus compounds, and the mass percentage of titanium element in the negative electrode active material layer can be controlled by controlling the addition amount of titanium-phosphorus compounds.

[0058] According to some embodiments of the present application, based on the mass of the negative electrode active material layer, the mass percentage of phosphorus is F%, 0.04≤F≤2, and optionally, 0.13≤F≤1.6. For example, the value of F can be 0.04, 0.13, 0.3, 0.5, 0.7, 1.1, 1.6, 2, or any intermediate value between any two values.

[0059] The mass percentage of phosphorus refers to the mass proportion of all phosphorus elements in the negative electrode active material layer. In some embodiments, phosphorus mainly comes from titanium-phosphorus compounds. The mass percentage of phosphorus in the negative electrode active material layer can be controlled by controlling the addition amount of titanium-phosphorus compounds.

[0060] According to some embodiments of the present application, the negative electrode active material layer includes a linear conductive agent, and the average diameter of the linear conductive agent is D nm, 0.5≤D≤20, and optionally, 0.5≤D≤3. As an example, the value of D can be 0.5, 1, 2, 3, 8, 10, 15, 20, or an intermediate value between any two values.

[0061] The linear conductive agent refers to a conductive material with an aspect ratio greater than 1. In some embodiments, the linear conductive agent can be selected from at least one of carbon nanotubes, graphene tubes, and carbon fibers.

[0062] According to some embodiments of the present application, the silicon-carbon composite material includes a silicon material and a carbon material composited together. The silicon-carbon composite material is in a granular form with an average particle size of E μm, where E satisfies at least one of the following relationships:

[0063] 6≤E≤13, optionally, 7≤E≤10; as an example, the value of E can be 6, 7, 8, 10, 13 or an intermediate value between any two values.

[0064] D and E satisfy the following relationship: 0.036≤D / E≤3.33, optionally, 0.056≤D / E≤2.23. As an example, the value of D / E can be 0.036, 0.056, 0.1, 0.3, 0.5, 1, 1.5, 2.23, 3.33, or an intermediate value between any two values.

[0065] In some embodiments, the negative electrode current collector may be any material suitable for use as a negative electrode current collector for lithium-ion batteries, specifically a metal foil or a composite current collector. Alternatively, the negative electrode current collector includes copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0066] In some embodiments, the negative electrode active material layer further comprises a binder, and the binder comprises at least one of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, styrene-butadiene rubber (SBR), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, and potassium hydroxymethyl cellulose.

[0067] In some embodiments, a silicon-carbon composite material can be prepared by chemical vapor deposition. As an implementation method, the preparation process includes: placing a carbon precursor into a reactor, introducing a silane / argon mixture with a certain volume fraction, and depositing the mixture at a certain temperature for a period of time to obtain the silicon-carbon composite material. Carbon precursors include, but are not limited to, biomass carbon, resin carbon, and petroleum coke. The silicon and carbon content of the silicon-carbon composite material can be controlled by controlling the silane deposition time. The average particle size of the silicon-carbon composite material can be controlled by the carbon precursor, and the particle size of the carbon precursor can be controlled by crushing and then classifying.

[0068] In some embodiments, the negative electrode sheet can be prepared by the following method: dispersing the silicon-carbon composite material, titanium-phosphorus compound, binder, conductive agent and any other components in a solvent (such as deionized water) to form a negative electrode slurry; coating the negative electrode slurry on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet (silicon anode) can be obtained.

[0069] According to some embodiments of the present application, the present application provides a battery comprising the negative electrode plate of any of the above schemes.

[0070] According to some embodiments of the present application, an electrolyte is further included, and the electrolyte satisfies at least one of the following conditions:

[0071] The electrolyte contains lithium difluorophosphate (LiPO2F2) as a lithium salt, and the content of lithium difluorophosphate is G%, 0.01≤G≤1.5, 18.7≤A / G≤2807 based on the mass of the electrolyte; illustratively, the value of G can be 0.01, 0.1, 0.4, 0.8, 1.1, 1.5 or an intermediate value between any two values, and the value of A / G can be 18.7, 100, 500, 1000, 1500, 2000, 2807 or an intermediate value between any two values.

[0072] The electrolyte contains fluoroethylene carbonate, and the content of fluoroethylene carbonate is H%, based on the mass of the electrolyte, 1.9≤H≤17.5, 1.6≤A / H≤14.8; illustratively, the value of H can be 1.9, 3, 5, 10, 13, 15, 17.5 or an intermediate value between any two values, and the value of A / H can be 1.6, 3, 6, 10, 12, 14.8 or an intermediate value between any two values.

[0073] According to some embodiments of the present application, the electrolyte includes an organic solvent, wherein the organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, and ethyl propionate. The lithium salt includes a combination of one or more organic lithium salts or inorganic lithium salts.

[0074] In some embodiments, the electrolyte further comprises other lithium salts, including at least one of organic lithium salts and inorganic lithium salts. Optionally, the other lithium salts include at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB), and lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB).

[0075] In some embodiments, the electrolyte further comprises other additives. For example, the other additives include at least one of succinonitrile, glutaronitrile, 1,3-propane sultone, and adiponitrile.

[0076] In order to enable a clearer understanding of the technical solution of the present application, the embodiments of the present application are mainly described using lithium-ion batteries. Other types of batteries can be appropriately adjusted according to the battery type and will not be described in detail.

[0077] The lithium-ion battery provided in the present application includes an electrode assembly and an electrolyte according to any of the above solutions. The electrode assembly includes a positive electrode sheet, a negative electrode sheet according to any of the above solutions, and a separator.

[0078] [Positive electrode]

[0079] According to some embodiments of the present application, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode active material, a binder and a conductive agent.

[0080] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0081] In some embodiments, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel manganese cobaltate, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel lithium manganese oxide, spinel lithium nickel manganese oxide, and lithium titanate.

[0082] In some embodiments, the binder comprises an adhesive polymer, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, the polyolefin binder comprises at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0083] In some embodiments, the conductive agent includes a carbon-based material, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black or carbon fiber; a metal-based material, such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; a conductive polymer, such as a polyphenylene derivative; or a mixture thereof.

[0084] [Isolation film]

[0085] The present application has no particular limitation on the material and shape of the isolation membrane, which may be any material disclosed in the prior art.

[0086] In some embodiments, the isolation film includes a polymer or inorganic material formed of a material that is stable to the electrolyte of the present application. For example, the isolation film may include a substrate layer and a surface treatment layer.

[0087] The substrate layer is a non-woven fabric, film, or composite film having a porous structure. The material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film can be used.

[0088] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer includes a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0089] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0090] In some embodiments, the battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0091] In some embodiments, the outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery can also be a soft shell, such as a bag-type soft shell. The material of the soft shell can be plastic. Examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0092] According to some embodiments of the present application, the present application provides an electrical device, which includes a battery according to any of the above solutions, and the battery is used to provide electrical energy to the electrical device.

[0093] Next, one or more embodiments will be described in more detail with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0094] Example 1

[0095] (1) Preparation of negative electrode sheet:

[0096] The carbon precursor (biochar) was placed in a furnace, the average particle size of the silicon-carbon precursor was 8.5 μm, and a silane / argon mixed gas with a silane volume concentration of 40% was introduced, and the mixture was deposited at a temperature of 500 ° C for 8 hours to obtain a silicon-carbon composite material with an average particle size of 9 μm; the silicon-carbon composite material and the titanium-phosphorus compound (Li 1.3 Al 0.3 Ti 1.7(PO4)3), binder (polyacrylic acid), linear conductive agent (carbon nanotube) and other raw materials are dispersed in deionized water in a mass ratio of 83:2:14:1, the addition ratio of titanium-phosphorus compound in the raw materials is 1%, and the average diameter of the linear conductive agent is 1nm to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector (copper foil, thickness 10μm), and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0097] (2) Preparation of positive electrode sheet: The positive electrode active material lithium cobalt oxide (LCO), conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 90:7:3; an appropriate amount of solvent N-methylpyrrolidone (NMP) is added and stirred evenly to obtain a positive electrode slurry; the positive electrode slurry is coated on aluminum foil and dried in a vacuum oven at 100°C for 12 hours to obtain a positive electrode sheet.

[0098] (3) Preparation of electrolyte: Under a dry argon atmosphere, ethyl methyl carbonate and propylene carbonate were mixed in a mass ratio of 1:1 to obtain a first mixed solution. Fluoroethylene carbonate was added to the first mixture to obtain a second mixed solution. Thoroughly dried lithium salts: lithium difluorophosphate (LiPO2F2) and lithium hexafluorophosphate (LiPF6) were dissolved in the second mixture and mixed uniformly to obtain an electrolyte. Based on the total mass of the electrolyte, the mass percentage of lithium hexafluorophosphate was 12%, the mass percentage of lithium difluorophosphate was 0.8%, the mass percentage of fluoroethylene carbonate was 10%, and the remainder was the first mixed solution.

[0099] (4) Preparation of lithium-ion batteries:

[0100] The positive and negative electrodes, fabricated as described above, are each connected to the tabs. Using a 9.5μm thick PE porous polymer film as a separator, the positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative electrodes to provide isolation. The sheets are then wound to form a bare cell. The bare cell is then placed in outer packaging, injected with the prepared electrolyte, and packaged. The cell undergoes a series of processes, including formation, capacity measurement, degassing, and trimming, to create a fully charged cell.

[0101] Other Examples and Comparative Examples

[0102] The negative electrode sheets and batteries of Examples 2 to 24 and Comparative Example 1 were prepared by the same method as in Example 1. The parameters of the negative electrode sheets and the electrolyte components during the preparation process are shown in Table 1.

[0103] Table 1 Process parameters and electrolytes for preparing negative electrode sheets in various embodiments and comparative examples

[0104] Test section

[0105] 1. Negative electrode test

[0106] (1) Test of the mass percentage of silicon (A%), carbon (B%), titanium (C%), and phosphorus (F%) in the negative electrode active material layer:

[0107] The negative electrode cross-section samples were prepared by argon ion polishing technology for scanning electron microscopy testing.

[0108] The cross-section samples of the negative electrode pieces were observed and scanning electron microscope photos were taken using a Philips XL-30 field emission scanning electron microscope. The microscope was tested under the conditions of 10 kV and 10 mA.

[0109] The values ​​of A, B, C, and F were obtained by X-ray energy spectrum elemental imaging analysis technology under the condition of a scanning electron microscope photograph with a magnification of 1k.

[0110] (2) Test of the average diameter of the conductive agent in the negative electrode active material layer (D nm) and the average particle size of the silicon-carbon composite material particles (E μm):

[0111] The negative electrode cross-section samples were prepared by argon ion polishing technology for scanning electron microscopy testing.

[0112] The cross-section samples of the negative electrode pieces were observed and scanning electron microscope photos were taken using a Philips XL-30 field emission scanning electron microscope. The microscope was tested under the conditions of 10 kV and 10 mA.

[0113] The diameters of 100 curves are counted and averaged by the ruler function of the SEM to obtain the D value; the particle sizes of 100 silicon-carbon composite material particles are counted and averaged by the scanning electron microscope to obtain the E value.

[0114] Figure 1 is a distribution diagram of various elements (Si, C, Ti, P) at the same local position on the surface of the negative electrode plate of Example 1. By comparing the distribution diagrams of various elements, it is shown that the distribution positions of titanium and phosphorus elements and silicon and carbon elements basically overlap, indicating that titanium-phosphorus compounds are distributed on the surface of the silicon-carbon composite material.

[0115] FIG2 is an SEM image of a cross section of the negative electrode sheet of Example 1. The cross section is a cross section perpendicular to the surface of the negative electrode sheet. As can be seen from FIG2 , the negative electrode active materials are connected together by linear materials (conductive agents).

[0116] FIG3 is a spectrum of various elements obtained by performing EDS surface scanning on the negative electrode sheet. From FIG3 , the content of various elements (Si, C, Ti, P) present in the negative electrode sheet can be obtained.

[0117] 2. Battery performance test

[0118] (1) Energy density test: First measure the thickness H1, length L1 and width W1 of the full cell; then perform charge and discharge test. The test temperature is 25℃, charge to 4.45V at 0.2C constant current, charge to 0.025C constant voltage, let it stand for 5 minutes, then discharge to 3.0V at 0.2C. The discharge capacity obtained in this step is the initial capacity C capacity , the discharge platform is V capacity ; Then the energy density is: C capacity ×V capacity / H1 / L1 / W1.

[0119] (2) Cycling test: The test temperature is 25°C, and the battery is charged to 4.45V at a constant current of 0.5C, then charged to 0.025C at a constant voltage. After standing for 5 minutes, the battery is discharged to 3.0V at 0.5C. The discharge capacity obtained in this step is the initial capacity C0. The cycling test is carried out according to the above 0.5C charge / 0.5C discharge. The discharge capacity after 500 cycles is C1, and the capacity retention rate is C1 / C0×100%.

[0120] (3) Expansion rate test: Use a screw micrometer to measure the thickness T0 of the lithium-ion battery when it is initially half-charged. When the lithium-ion battery is cycled 500 times according to the above 0.5C charge / 0.5C discharge, the lithium-ion battery is in a fully charged state. Use a screw micrometer to measure the thickness T1 of the lithium-ion battery at this time. Compare it with the thickness T0 of the lithium-ion battery when it is initially half-charged. The expansion rate of the fully charged lithium-ion battery at this time can be obtained as (T1-T0) / T0×100%.

[0121] The test results are shown in Tables 2 to 7:

[0122] Table 2 Test results

[0123] Note: The average diameter of the linear conductive agent in the negative electrode sheets of each embodiment (Examples 1 to 5) and Comparative Example 1 in Table 2 is the same (D=1), the average particle size of the silicon-carbon composite material is the same (E=9), the content of lithium difluorophosphate in the electrolyte is the same (G=0.8), and the content of fluoroethylene carbonate is the same (H=10). Accordingly, D / E=0.11.

[0124] Table 3 Test results

[0125] Note: The mass percentage of silicon element in the negative electrode sheets of each embodiment (Examples 6 to 10) in Table 3 is the same (A=28.07), the mass percentage of carbon element is the same (B=64.15), the average diameter of the linear conductive agent is the same (D=1), the average particle size of the silicon-carbon composite material is the same (E=9), the content of lithium difluorophosphate in the electrolyte is the same (G=0.8), and the content of fluoroethylene carbonate is the same (H=10). Accordingly, D / E=0.11, A / H=2.81, A / G=35.09, 0.1%×(A+B)=0.09, and 2.06%×(A+B)=1.9.

[0126] Table 4 Test results

[0127] Note: The mass percentage of silicon element in the negative electrode sheets of each embodiment (Examples 11 to 14) in Table 4 is the same (A=28.07), the mass percentage of carbon element is the same (B=64.15), the mass percentage of titanium element is the same (C=0.12), the mass percentage of phosphorus element is the same (D=0.15), the average particle size of the silicon-carbon composite material is the same (E=9), the content of lithium difluorophosphate in the electrolyte is the same (G=0.8), and the content of fluoroethylene carbonate is the same (H=10). Accordingly, A / H=2.81, A / G=35.09, 0.1%×(A+B)=0.09, and 2.06%×(A+B)=1.9.

[0128] Table 5 Test results

[0129] Note: The mass percentage of silicon in the negative electrode sheets of each embodiment (Examples 15 to 19) in Table 5 is the same (A=28.07), the mass percentage of carbon is the same (B=64.15), the mass percentage of titanium is the same (C=0.12), the mass percentage of phosphorus is the same (D=0.15), the average diameter of the linear conductive agent is the same (D=1), the content of lithium difluorophosphate in the electrolyte is the same (G=0.8), and the content of fluoroethylene carbonate is the same (H=10). Accordingly, A / H=2.81, A / G=35.09, 0.1%×(A+B)=0.09, and 2.06%×(A+B)=1.9.

[0130] Table 6 Test results

[0131] Note: The mass percentage of silicon in the negative electrode sheets of each embodiment (Examples 20 to 22) in Table 6 is the same (A=28.07), the mass percentage of carbon is the same (B=64.15), the mass percentage of titanium is the same (C=0.12), the mass percentage of phosphorus is the same (D=0.15), the average diameter of the linear conductive agent is the same (D=1), the average particle size of the silicon-carbon composite material is the same (E=9), and the content of fluoroethylene carbonate in the electrolyte is the same (H=10). Accordingly, D / E=0.11, A / H=2.81, 0.1%×(A+B)=0.09, and 2.06%×(A+B)=1.9.

[0132] Table 7 Test results

[0133] Note: The mass percentage of silicon in the negative electrode sheets of each embodiment (Examples 23 to 24) in Table 7 is the same (A=28.07), the mass percentage of carbon is the same (B=64.15), the mass percentage of titanium is the same (C=0.12), the mass percentage of phosphorus is the same (D=0.15), the average diameter of the linear conductive agent is the same (D=1), the average particle size of the silicon-carbon composite material is the same (E=9), and the content of lithium difluorophosphate in the electrolyte is the same (G=0.8). Accordingly, D / E=0.11, A / G=35.09, 0.1%×(A+B)=0.09, and 2.06%×(A+B)=1.9.

[0134] Combining the results in Tables 2 to 7, we can see that:

[0135] Compared with Comparative Example 1, Examples 1 to 24 simultaneously add silicon-carbon composite materials and titanium-phosphorus compounds to the negative electrode active material layer of the negative electrode sheet, which can at least increase the energy density of the battery, improve the cycle performance of the battery, and reduce the expansion rate.

[0136] According to Examples 1 to 5, based on the mass of the negative electrode active material layer, when the mass percentage of the silicon element is controlled to be A%, the mass percentage of the carbon element is controlled to be B%, 20≤A≤40, 50≤B≤70, optionally, 25≤A≤32, 58≤B≤66, at least one of the following conditions can be achieved: the energy density of the battery can be improved, the cycle performance of the battery can be improved, and the expansion rate can be reduced.

[0137] According to Examples 6 to 10, based on the mass of the negative electrode active material layer, when the mass percentage of the titanium element is controlled to be C%, 0.01≤C≤2.1, optionally, 0.1≤C≤1; the mass percentage of the phosphorus element is controlled to be F%, 0.04≤F≤2, optionally, 0.13≤F≤1.6, at least one of the energy density of the battery, the cycle performance of the battery, and the expansion rate can be improved.

[0138] According to Examples 11 to 14, when the average diameter of the linear conductive agent is controlled to be D nm, 0.5≤D≤20, optionally 0.5≤D≤3, at least one of the following can be improved: the energy density of the battery, the cycle performance of the battery, and the expansion rate.

[0139] According to Examples 15 to 19, when the average particle size of the silicon-carbon composite material is controlled to be Eμm, 6≤E≤13, optionally, 7≤E≤10, at least one of the following can be achieved: improving the energy density of the battery, improving the cycle performance of the battery, and reducing the expansion rate.

[0140] According to Examples 20 to 22, when the content of lithium difluorophosphate in the electrolyte is controlled to be G%, 0.01≤G≤1.5, and 18.7≤A / G≤2807, at least one of the following conditions can be achieved: the energy density of the battery can be increased, the cycle performance of the battery can be improved, and the expansion rate can be reduced.

[0141] According to Examples 23 to 24, when the content of fluoroethylene carbonate in the electrolyte is controlled to be H%, 1.9≤H≤17.5, and 1.6≤A / H≤14.8, at least one of the following can be achieved: improving the energy density of the battery, improving the cycle performance of the battery, and reducing the expansion rate.

[0142] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A negative electrode plate, characterized in that: The invention comprises a negative electrode current collector and a negative electrode active material layer provided on at least one side surface of the negative electrode current collector, wherein the negative electrode active material layer comprises a silicon-carbon composite material and a titanium-phosphorus compound, wherein the titanium-phosphorus compound comprises titanium and phosphorus.

2. The negative electrode sheet according to claim 1, characterized in that: The titanium-phosphorus compound satisfies at least one of the following conditions: The chemical formula of the titanium-phosphorus compound is Li 1+x Al x Ti 2-x (PO4)3, 0≤x≤0.5; Optionally, the chemical formula of the titanium-phosphorus compound is Li 1.3 Al 0.3 Ti 1.7 (PO4)3; At least part of the titanium-phosphorus compound is distributed on the surface of the silicon-carbon composite material.

3. The negative electrode sheet according to claim 1, characterized in that: Based on the mass of the negative electrode active material layer, the mass percentage of silicon is A%, the mass percentage of carbon is B%, 20≤A≤40, 50≤B≤70, optionally, 25≤A≤32, 58≤B≤66。 4. The negative electrode sheet according to claim 3, characterized in that: Based on the mass of the negative electrode active material layer, the mass percentage of the titanium element is C%, where C satisfies at least one of the following relationships: 0.01≤C≤2.1, optionally, 0.1≤C≤1; 0.1×(A+B) <C<2.06×(A+B)。 5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: Based on the mass of the negative electrode active material layer, the mass percentage of the phosphorus element is F%, 0.04≤F≤2, optionally, 0.13≤F≤1.

6.

6. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The negative electrode active material layer includes a linear conductive agent, and the average diameter of the linear conductive agent is D nm, 0.5≤D≤20, and optionally, 0.5≤D≤3.

7. The negative electrode sheet according to claim 6, characterized in that: The average particle size of the silicon-carbon composite material is E μm, and E satisfies at least one of the following relationships: 6≤E≤13, optionally, 7≤E≤10; 0.036≤D / E≤3.33, optionally, 0.056≤D / E≤2.

23.

8. A battery, characterized in that: It comprises the negative electrode sheet according to any one of claims 1 to 7.

9. The battery according to claim 8, characterized in that Also included is an electrolyte, the electrolyte meeting at least one of the following conditions: The electrolyte contains lithium difluorophosphate, and the content of the lithium difluorophosphate is G%, 0.01≤G≤1.5, and 18.7≤A / G≤2807 based on the mass of the electrolyte; The electrolyte contains fluoroethylene carbonate, and based on the mass of the electrolyte, the content of the fluoroethylene carbonate is H%, 1.9≤H≤17.5, and 1.6≤A / H≤14.

8.

10. An electrical device, characterized in that: It comprises the battery according to claim 8 or 9.

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