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 plate, battery and electrical device This application claims priority to Chinese Patent Application No. 202410212235.0, filed on February 26, 2024, entitled "Negative Electrode, Battery and Electrical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0001] This application relates to the field of batteries, specifically to a negative electrode sheet, a battery, and an electrical device. Background Technology

[0002] The energy density of current lithium-ion batteries is insufficient and urgently needs to be improved. Silicon materials have a relatively high theoretical specific capacity (approximately 4200 mAh / g) and have broad application prospects in lithium-ion batteries. Adding silicon-based materials to the negative electrode can effectively improve energy density. However, during charge-discharge cycles, silicon materials undergo a volume change of 120% to 300% due to the insertion and extraction of lithium ions. This causes the silicon-based material to pulverize and detach 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, this application provides a negative electrode sheet, a battery, and an electrical device that can improve the energy density of the battery and improve the cycle performance of the battery.

[0004] In a first aspect, this application provides a negative electrode sheet, including a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative 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 expand and contract during cycling, which can cause ion channel breaks between the silicon-carbon composite materials, resulting in inconsistent lithium intercalation levels among different silicon-carbon composite materials and significantly degrading the electrochemical performance of the secondary battery. In the technical solution of this application, titanium-phosphorus compounds are distributed in the pores of the negative electrode active material layer and form a solid-solid contact with the silicon-carbon composite material. This compensates for the ion channel breaks caused by the expansion and contraction of the silicon-carbon composite material, thereby improving the overall lithium intercalation uniformity of the negative electrode active material layer, increasing the utilization rate of the ion channel network of the negative electrode active material layer, and ultimately 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, is a good conductor of lithium ions and can improve the ion transport capability of the anode;

[0008] At least a portion of the titanium-phosphorus compounds are distributed on the surface of the silicon-carbon composite material. The distribution of titanium-phosphorus compounds on the surface of the silicon-carbon composite material can improve ion transport and lithium intercalation uniformity of the anode.

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

[0010] In some embodiments, based on the mass of the negative electrode active material layer, wherein the mass percentage of titanium is C%, and 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, batteries can simultaneously achieve better cycle performance and energy density.

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

[0015] By controlling F, batteries can simultaneously achieve better cycle performance and energy density.

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

[0017] By controlling D, the battery can simultaneously achieve 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, a battery can simultaneously achieve better cycle performance and energy density; by controlling D / E, a battery can simultaneously achieve better cycle performance and energy density.

[0022] Secondly, this application provides a battery that includes the negative electrode sheet of the above embodiments.

[0023] In some embodiments, an electrolyte is also included, which satisfies at least one of the following conditions:

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

[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, 1.6≤A / H≤14.8.

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

[0027] Thirdly, this application provides an electrical device that includes the battery described in the above embodiments.

[0028] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0029] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0030] Figure 1 shows the distribution of elements at the same local location on the surface of the negative electrode sheet in Example 1;

[0031] Figure 2 is a SEM image of the cross-section of the negative electrode sheet in Example 1;

[0032] Figure 3 shows the EDS spectrum of the negative electrode sheet of Example 1. Detailed Implementation

[0033] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0035] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

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

[0037] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0038] In the description of the embodiments of this application, the technical terms "thickness", "upper", "lower", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0039] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms "installation," "connection," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the 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 improve energy density, but silicon materials will undergo large volume expansion during charge and discharge cycles. Therefore, the addition of silicon materials will deteriorate battery performance: the expansion rate increases and the cycle performance decreases.

[0041] Currently, the main strategies for improving the electrochemical performance of silicon materials include: silicon material nano-sizing, preparation of silicon-carbon composite materials, and silicon-oxygen composite materials. However, the expansion rate of such silicon anode batteries is still relatively large, and the cycle performance still needs to be improved.

[0042] To effectively address the issues of high expansion rate and poor cycle performance in silicon anode batteries, a negative electrode can be designed. This negative electrode is formed by combining silicon-carbon composite materials and titanium-phosphorus compounds to create a silicon anode. This approach can improve the battery's energy density and effectively enhance the ion transport pathway of the silicon anode, thereby improving the battery's expansion rate and cycle performance.

[0043] According to some embodiments of this application, this application provides a negative electrode sheet, including a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector. The negative active material layer comprises a silicon-carbon composite material and a titanium-phosphorus compound, wherein the titanium-phosphorus compound comprises titanium and phosphorus.

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

[0045] Silicon-carbon composite material is a composite material composed of silicon and carbon elements. As a negative electrode active material, the negative electrode sheet in this application embodiment is a silicon anode containing silicon, and the negative electrode active material layer is also called the composite layer. In some embodiments, the negative electrode sheet is a pure silicon anode containing silicon-carbon composite material but without graphite, which can achieve higher energy density.

[0046] Titanium-phosphorus compounds refer to compounds containing titanium and phosphorus. In some embodiments, titanium-phosphorus compounds are oxides of titanium, phosphorus, and other metallic elements, such as lithium and aluminum.

[0047] This application embodiment improves the ion transport capability and lithium intercalation uniformity of silicon-carbon composite materials by adding titanium-phosphorus compounds, thereby effectively improving the cycle performance and expansion rate of the battery and simultaneously increasing the energy density.

[0048] According to some embodiments of this application, the titanium-phosphorus compounds satisfy at least one of the following conditions:

[0049] The chemical formula of titanium phosphate compounds is Li 1+x Al x Ti 2-x (PO4)3, 0≤x≤0.5; for example, the chemical formula of titanium-phosphorus compounds 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 some of the titanium-phosphorus compounds are distributed on the surface of the silicon-carbon composite material.

[0051] According to some embodiments of this 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, and optionally, 25≤A≤32, 58≤B≤66. As an example, the value of A can be 20, 25, 30, 32, 35, 40, or any intermediate value between two values; the value of B can be 50, 55, 58, 60, 66, 70, or any intermediate value between two values.

[0052] The mass percentage of silicon refers to the total mass percentage of silicon in the negative electrode active material layer. In some embodiments, the silicon mainly comes from silicon-carbon composite materials.

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

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

[0055] 0.01≤C≤2.1, optionally, 0.1≤C≤1; for example, the value of C can be 0.01, 0.1, 0.5, 0.7, 1, 1.5, 2.1 or any intermediate value between 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 refers to the total mass proportion of titanium in the negative electrode active material layer. In some embodiments, the titanium is mainly derived from titanium-phosphorus compounds. The mass percentage of titanium in the negative electrode active material layer can be controlled by controlling the amount of titanium-phosphorus compounds added.

[0058] According to some embodiments of this 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. Exemplarily, 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 two values.

[0059] The mass percentage of phosphorus refers to the total mass percentage of phosphorus in the negative electrode active material layer. In some embodiments, the 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 amount of titanium-phosphorus compounds added.

[0060] According to some embodiments of this application, the negative electrode active material layer comprises a linear conductive agent with an average diameter of D nm, where 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 any intermediate value between two values.

[0061] Linear conductive agents refer to conductive materials with an aspect ratio greater than 1. In some embodiments, the linear conductive agent may be selected from at least one of carbon nanotubes, graphene tubes, and carbon fibers.

[0062] According to some embodiments of this application, the silicon-carbon composite material comprises silicon and carbon materials bonded together. The silicon-carbon composite material is granular 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 any intermediate value between 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 any intermediate value between two values.

[0065] In some embodiments, the negative electrode current collector can be any material suitable for use as a negative electrode current collector in lithium-ion batteries, specifically a metal foil or a composite current collector. Optionally, 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 includes a binder, which includes at least one of polyacrylate, polyimide, polyamide, polyamide-imide, 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, silicon-carbon composite materials can be prepared by chemical vapor deposition. One method involves placing a carbon precursor into a reactor, introducing a silane / argon mixture of a certain volume fraction, and depositing it at a certain temperature for a period of time to obtain the silicon-carbon composite material. The carbon precursor includes, but is not limited to, biomass carbon, resin carbon, and petroleum coke. The silicon and carbon content in 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, which can be controlled by crushing and then classifying it.

[0068] In some embodiments, the negative electrode sheet can be prepared by dispersing silicon-carbon composite material, titanium-phosphorus compound, binder, conductive agent and any other components in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then drying, cold pressing and other processes to obtain the negative electrode sheet (silicon anode).

[0069] According to some embodiments of this application, this application provides a battery that includes a negative electrode sheet of any of the above schemes.

[0070] According to some embodiments of this application, an electrolyte is also included, which satisfies at least one of the following conditions:

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

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

[0073] According to some embodiments of this application, the electrolyte contains an organic solvent, including at least one selected from 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 one or more combinations of 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(oxalateborate)borate LiB(C2O4)2 (LiBOB), and lithium difluorooxalateborate LiBF2(C2O4) (LiDFOB).

[0075] In some embodiments, the electrolyte may also contain other additives, exemplarily including at least one of succinic acid, glutaronitrile, 1,3-propanesulfonate lactone, and adiponitrile.

[0076] To better understand the technical solution of this application, the embodiments of this 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 this application includes an electrode assembly and an electrolyte according to any of the above schemes. The electrode assembly includes a positive electrode, a negative electrode according to any of the above schemes, and a separator.

[0078] [Positive electrode plate]

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

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

[0081] In some embodiments, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel manganese cobalt oxide, 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-type lithium manganese oxide, spinel-type lithium nickel manganese oxide, and lithium titanate.

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

[0083] In some embodiments, the conductive agent includes carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fiber; metal-based materials, such as metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0084] [Isolation membrane]

[0085] This application does not impose any particular restrictions on the material and shape of the separator, which can be any technology disclosed in the prior art.

[0086] In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application. For example, the separator may include a substrate layer and a surface treatment layer.

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

[0088] A surface treatment layer is disposed 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 mixture of polymer and inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, 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 polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0089] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

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

[0091] In some embodiments, the battery's outer packaging can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The battery's outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0092] According to some embodiments of this application, this application provides an electrical device that includes a battery of any of the above-described schemes, and the battery is used to provide electrical energy to the electrical device.

[0093] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0094] Example 1

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

[0096] A carbon precursor (biochar) with an average particle size of 8.5 μm was placed in a furnace. A silane / argon mixture with a silane volume concentration of 40% was introduced, and deposition was carried out at 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 a titanium-phosphorus compound (Li) were then added. 1.3 Al 0.3 Ti 1.7The raw materials (PO4)3), binder (polyacrylic acid), and linear conductive agent (carbon nanotubes) are dispersed in deionized water at a mass ratio of 83:2:14:1. The proportion of titanium-phosphorus compounds added in the raw materials is 1%, and the average diameter of the linear conductive agent is 1 nm, forming a negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector (copper foil, 10 μm thick), and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0097] (2) Preparation of positive electrode sheet: 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 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 positive electrode sheet.

[0098] (3) Preparation of electrolyte: Under a dry argon atmosphere, methyl ethyl carbonate and propylene carbonate were mixed at a mass ratio of 1:1 to obtain a first mixture. Fluoroethylene carbonate was added to the first mixture to obtain a second mixture. Then, fully dried lithium salts, lithium difluorophosphate (LiPO2F2) and lithium hexafluorophosphate (LiPF6), were dissolved in the aforementioned second mixture and mixed thoroughly to obtain the 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 mixture.

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

[0100] The positive and negative electrodes prepared as described above are connected to the tabs respectively. Using a 9.5μm thick PE porous polymer film as a separator, the positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to provide isolation. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer packaging, injected with the prepared electrolyte, and then sealed. After formation, capacity testing, degassing, and edge trimming processes, a complete cell is obtained.

[0101] Other embodiments and comparative examples

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

[0103] Table 1. Process parameters and electrolytes used in the preparation of negative electrode sheets for each embodiment and comparative example.

[0104] Test section

[0105] I. Negative Electrode Test

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

[0107] A negative electrode cross-section sample was prepared by argon ion polishing technology for scanning electron microscopy testing.

[0108] The cross-sectional sample of the negative electrode was observed and scanned using a Philips XL-30 field emission scanning electron microscope. The microscope was used to perform the tests at 10 kV and 10 mA.

[0109] The values ​​of A, B, C, and F were obtained from the scanning electron microscope images at a magnification of 1k using X-ray energy dispersive spectroscopy (EDS).

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

[0111] A negative electrode cross-section sample was prepared by argon ion polishing technology for scanning electron microscopy testing.

[0112] The cross-sectional sample of the negative electrode was observed and scanned using a Philips XL-30 field emission scanning electron microscope. The microscope was used to perform the tests at 10 kV and 10 mA.

[0113] The D value can be obtained by statistically analyzing the diameter of 100 curves using the scale function of SEM and averaging the values; the E value can be obtained by statistically analyzing the particle size of 100 silicon-carbon composite particles using scanning electron microscopy and averaging the values.

[0114] Figure 1 shows the distribution of elements (Si, C, Ti, P) at the same local location on the surface of the negative electrode sheet in Example 1. By comparing the distribution of each element, it can be seen that the distribution positions of titanium and phosphorus are basically overlapping with those of silicon and carbon, indicating that titanium-phosphorus compounds are distributed on the surface of silicon-carbon composite material.

[0115] Figure 2 is an SEM image of the cross-section of the negative electrode sheet in Example 1. The cross-section refers to the cross-section perpendicular to the surface of the negative electrode sheet. As can be seen from Figure 2, the negative electrode active materials are connected together by linear materials (conductive agents).

[0116] Figure 3 shows the elemental spectra obtained by EDS surface scanning of the negative electrode sheet. From Figure 3, the content of each element (Si, C, Ti, P) present in the negative electrode sheet can be obtained.

[0117] II. Battery Performance Testing

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

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

[0120] (3) Expansion rate test: Use a micrometer to measure the thickness T0 of the lithium-ion battery when it is initially half-charged. After cycling 500 times according to the above 0.5C charging / 0.5C discharging cycle, the lithium-ion battery is in a fully charged state. Then use a 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 to obtain the expansion rate of the fully charged lithium-ion battery at this time (T1-T0) / T0×100%.

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

[0122] Table 2 Test Results

[0123] Note: In Table 2, the average diameter of the linear conductive agent in the negative electrode sheet of each embodiment (Examples 1-5) and Comparative Example 1 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), the content of fluoroethylene carbonate is the same (H=10), and correspondingly, D / E=0.11.

[0124] Table 3 Test Results

[0125] Note: In Table 3, the negative electrode sheets of the examples (Examples 6-10) have the same mass percentage of silicon (A=28.07), the same mass percentage of carbon (B=64.15), the same average diameter of the linear conductive agent (D=1), the same average particle size of the silicon-carbon composite material (E=9), the same content of lithium difluorophosphate in the electrolyte (G=0.8), and the same content of fluoroethylene carbonate (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: In Table 4, the negative electrode sheets of the various examples (Examples 11-14) have the same mass percentage content of silicon (A=28.07), carbon (B=64.15), titanium (C=0.12), and phosphorus (D=0.15), the same average particle size of the silicon-carbon composite material (E=9), the same content of lithium difluorophosphate in the electrolyte (G=0.8), and the same content of fluoroethylene carbonate (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: In Table 5, the negative electrode sheets of the various examples (Examples 15-19) have the same mass percentage content of silicon (A=28.07), carbon (B=64.15), titanium (C=0.12), and phosphorus (D=0.15), the same average diameter of the linear conductive agent (D=1), the same content of lithium difluorophosphate in the electrolyte (G=0.8), and the same content of fluoroethylene carbonate (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: In Table 6, the negative electrode sheets of the various examples (Examples 20-22) have the same mass percentage content of silicon (A=28.07), carbon (B=64.15), titanium (C=0.12), and phosphorus (D=0.15), the same average diameter of the linear conductive agent (D=1), the same average particle size of the silicon-carbon composite material (E=9), and the same content of fluoroethylene carbonate in the electrolyte (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: In the examples (Examples 23-24) in Table 7, the mass percentage of silicon in the negative electrode 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] Based on the results in Tables 2 to 7, we can conclude that:

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

[0136] According to Examples 1-5, based on the mass of the negative electrode active material layer, when the mass percentage of silicon is A% and the mass percentage of carbon is B%, 20≤A≤40, 50≤B≤70, and optionally 25≤A≤32, 58≤B≤66, it is possible to at least improve one of the following: energy density of the battery, improve the cycle performance of the battery, and reduce the expansion rate.

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

[0138] According to Examples 11-14, when the average diameter of the linear conductive agent is controlled to be D nm, 0.5 ≤ D ≤ 20, and optionally 0.5 ≤ D ≤ 3, it is possible to at least improve the energy density of the battery, improve the cycle performance of the battery, and reduce the expansion rate.

[0139] According to Examples 15-19, when the average particle size of the silicon-carbon composite material is controlled to be E μm, 6≤E≤13, and optionally 7≤E≤10, it is possible to at least improve the energy density of the battery, improve the cycle performance of the battery, and reduce the expansion rate.

[0140] According to Examples 20-22, 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, it is possible to at least increase the energy density of the battery, improve the cycle performance of the battery, and reduce the expansion rate.

[0141] According to Examples 23-24, 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, it is possible to at least increase the energy density of the battery, improve the cycle performance of the battery, and reduce the expansion rate.

[0142] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A negative electrode sheet, characterized by, It includes a negative electrode current collector and a negative electrode active material layer disposed 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, wherein the titanium-phosphorus compound comprises titanium and phosphorus.

2. The negative electrode sheet according to claim 1, characterized by 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 a portion of the titanium-phosphorus compounds are distributed on the surface of the silicon-carbon composite material.

3. The negative electrode sheet according to claim 1, characterized by Based on the mass of the negative electrode active material layer, wherein the mass percentage of silicon is A%, the mass percentage of carbon is B%, 20≤A≤40%, 50≤B≤70%, and optionally, 25≤A≤32%. 58≤B≤66。 4. The negative electrode sheet according to claim 3, characterized by Based on the mass of the negative electrode active material layer, wherein the mass percentage of titanium is C%, and 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, wherein Based on the mass of the negative electrode active material layer, wherein the mass percentage of phosphorus element is F%, 0.04≤F≤2, and optionally, 0.13≤F≤1.

6.

6. The negative electrode sheet according to any one of claims 1 to 4, wherein The negative electrode active material layer contains a linear conductive agent with an average diameter of D nm, where 0.5 ≤ D ≤ 20, and optionally, 0.5 ≤ D ≤ 3.

7. The negative electrode sheet according to claim 6, characterized by The average particle size of the silicon-carbon composite material is E μm, wherein 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 by It includes the negative electrode sheet according to any one of claims 1 to 7.

9. The battery of claim 8, wherein, It also includes an electrolyte that satisfies at least one of the following conditions: The electrolyte contains lithium difluorophosphate, and based on the mass of the electrolyte, the content of lithium difluorophosphate is G%, 0.01≤G≤1.5, 18.7≤A / G≤2807; 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, 1.6≤A / H≤14.

8.

10. An electrical device, characterized by It includes the battery as described in claim 8 or 9.

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