Negative pole piece and preparation method thereof, lithium ion battery and power utilization device

Abstract

The embodiment of the invention provides a negative pole piece and a preparation method thereof, a lithium ion battery and an electric device. The negative pole piece comprises a negative current collector; the negative electrode film layer is arranged on at least one side of the negative electrode current collector, and the negative electrode film layer comprises lithium fluoride particles. The negative pole piece is applied to the lithium ion battery, so that lithium precipitation can be effectively inhibited, and the cycle performance of the lithium ion battery can be improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and more specifically, to a negative electrode plate and a preparation method thereof, a lithium-ion battery and an electrical device. Background Art

[0002] In recent years, lithium-ion batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields, and have thus achieved great development.

[0003] During the cycle of lithium-ion batteries, the negative electrode may be deposited with lithium due to the influence of process, use environment and other factors. In severe cases, it may lead to the growth of lithium dendrites, threatening the reversible capacity and cycle life of lithium-ion batteries. Therefore, how to improve the lithium deposition of lithium-ion batteries has become an urgent problem to be solved. Summary of the invention

[0004] The present application is made in view of the above technical problems, and its purpose is to provide a negative electrode plate. The negative electrode plate can be used in a lithium-ion battery to effectively inhibit lithium precipitation and help improve the cycle performance of the lithium-ion battery.

[0005] In order to achieve the above-mentioned objectives, the present application provides a negative electrode plate and a preparation method thereof, a lithium-ion battery and an electrical device.

[0006] In a first aspect, a negative electrode plate is provided, comprising a negative electrode current collector; a negative electrode film layer, wherein the negative electrode film layer is disposed on at least one side of the negative electrode current collector, and the negative electrode film layer comprises lithium fluoride particles.

[0007] In the embodiments of the present application, the negative electrode film layer of the negative electrode plate includes lithium fluoride particles. On the one hand, the lithium fluoride particles can make the lithium ion flow in the negative electrode plate evenly distributed, thereby inhibiting local lithium precipitation of the negative electrode plate; on the other hand, the lithium fluoride particles can adsorb fluorine-containing additives in the electrolyte, so that when the negative electrode plate is used in a lithium-ion battery, the lithium fluoride particles adsorb the fluorine-containing additives in the electrolyte to generate a lithium fluoride-rich solid electrolyte interface (SEI) film on the surface of the negative electrode plate, thereby improving the ionic conductivity of the SEI film and helping to improve the cycle performance of the lithium-ion battery.

[0008] In a possible implementation, the volume average particle size D of the lithium fluoride particles is V 50 satisfies: 50nm≤D V 50≤200nm, optionally, D V 50 satisfies: 50nm≤D V 50≤80nm.

[0009] The volume average particle size D of lithium fluoride particles V 50 is set within the above range, so that the lithium fluoride particles are easier to disperse in the negative electrode film layer, which is beneficial to the uniform distribution of the lithium fluoride particles in the negative electrode film layer, and can be more fully in contact with the electrolyte, thereby facilitating the uniform distribution of the lithium ion flow in the negative electrode sheet and improving the uniformity of the SEI film.

[0010] In a possible implementation, the specific surface area S of the lithium fluoride particles satisfies: 20 m 2 / g≤S≤200m 2 / g, optionally, S meets: 80m 2 / g≤S≤100m 2 / g.

[0011] The specific surface area S of the lithium fluoride particles is set within the above range, which is beneficial to the uniform distribution of lithium ion flow in the negative electrode sheet and improves the uniformity of the SEI film.

[0012] In a possible implementation, based on the total weight of the negative electrode film layer, the weight content of the lithium fluoride particles in the negative electrode film layer ranges from 1% to 10%, and optionally, ranges from 4% to 5%.

[0013] The weight content of lithium fluoride particles in the negative electrode film layer is set within the above range, which is beneficial to suppressing local lithium deposition of the negative electrode plate.

[0014] In a possible implementation, a ratio A of the diffraction intensity of the (111) crystal plane of the lithium fluoride particle to the diffraction intensity of the (200) crystal plane satisfies: 0.4≤A≤0.8. Optionally, A satisfies: 0.5≤A≤0.7.

[0015] The ratio of the diffraction intensity of the (111) crystal plane of the lithium fluoride particles to the diffraction intensity of the (200) crystal plane is set within the above range, which is conducive to the formation of a lithium fluoride-rich SEI film on the surface of the negative electrode plate, helping to improve the cycle performance of the lithium-ion battery.

[0016] In a possible implementation, the shape of the lithium fluoride particles includes at least one of a spherical shape and a cubic shape.

[0017] In a possible implementation, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes at least one of natural graphite, artificial graphite, expanded graphite, hard carbon, soft carbon, carbon microspheres, silicon, silicon oxide, silicon carbon, and lithium titanate.

[0018] In a second aspect, a negative electrode plate is provided, comprising: a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer comprising lithium fluoride particles; a SEI film, the SEI film is formed on the negative electrode film layer, and the SEI film comprises lithium fluoride.

[0019] In a possible implementation, the mass content of the lithium fluoride in the solid electrolyte interface film ranges from 10% to 80%, and optionally, ranges from 40% to 50%.

[0020] In a possible implementation, the volume average particle size D of the lithium fluoride particles is V 50 satisfies: 50nm≤D V 50≤200nm, optionally, D V 50 satisfies: 50nm≤D V 50≤80nm.

[0021] In a possible implementation, the specific surface area S of the lithium fluoride particles satisfies: 20 m 2 / g≤S≤200m 2 / g, optionally, S meets: 80m 2 / g≤S≤100m 2 / g.

[0022] In a third aspect, a method for preparing a negative electrode plate is provided, comprising: disposing a negative electrode film layer on at least one side of a negative electrode current collector to obtain the negative electrode plate; wherein the negative electrode film layer comprises lithium fluoride particles.

[0023] In a possible implementation, the negative electrode film layer is provided on at least one side of the negative electrode current collector to obtain the negative electrode plate, comprising: preparing a negative electrode slurry, wherein the negative electrode slurry comprises a negative electrode active material and the lithium fluoride particles; applying the negative electrode slurry on at least one side of the negative electrode current collector; drying the negative electrode slurry to form a negative electrode coating layer on the negative electrode current collector; and rolling the negative electrode current collector and the negative electrode coating layer to obtain the negative electrode plate.

[0024] In a fourth aspect, a lithium-ion battery is provided, comprising at least one of the negative electrode sheet in any possible implementation of the first aspect, the negative electrode sheet in any possible implementation of the second aspect, and the negative electrode sheet prepared by the preparation method in any possible implementation of the third aspect.

[0025] In a fifth aspect, an electrical device is provided, wherein the electrical device comprises the lithium-ion battery in the fourth aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0027] Figure 1 A schematic diagram of a negative electrode sheet disclosed in one embodiment of the present application;

[0028] Figure 2 A schematic diagram of a negative electrode sheet disclosed in one embodiment of the present application;

[0029] Figure 3 A schematic flow chart of a method for preparing a negative electrode sheet of the present application;

[0030] Figure 4 A schematic diagram of a battery cell disclosed in an embodiment of the present application;

[0031] Figure 5 A schematic diagram of the exploded structure of a battery cell disclosed in one embodiment of the present application;

[0032] Figure 6 A schematic diagram of the exploded structure of a battery disclosed in one embodiment of the present application;

[0033] Figure 7 A schematic diagram of an electrical device disclosed in an embodiment of the present application. DETAILED DESCRIPTION

[0034] Below, the embodiments of the negative electrode plate and its preparation method, lithium-ion battery and electric device of the present application are specifically disclosed in detail with appropriate reference to the drawings. However, there are cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0035] In the description of this application, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inner", "outer", etc., indicating directions or positional relationships, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting this application. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0036] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0038] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0039] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0040] Next, embodiments of the present application are introduced.

[0041] In recent years, secondary batteries have been widely used in power tools, electronic products, electric vehicles, aerospace and other fields due to their high energy density and long service life, and have achieved great development. Usually, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the charge and discharge process of the battery, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. Among them, the electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, which allows active ions to pass through while preventing the positive and negative electrodes from short-circuiting, so that the electrochemical reaction of the secondary battery proceeds normally.

[0042] Take lithium-ion batteries as an example. Lithium-ion batteries are a typical secondary battery. Because they rely on the chemical reaction of lithium ions intercalating and disintercalating between the positive and negative electrodes for charging and discharging, lithium-ion batteries are also called rocking-chair batteries. During the charging process of lithium-ion batteries, lithium ions are released from the positive electrode active material, move to the negative electrode through the conduction of the electrolyte and embed into the negative electrode active material; and during the discharge process, lithium ions are released from the negative electrode active material, move to the positive electrode through the conduction of the electrolyte and embed into the positive electrode active material.

[0043] It should be understood that the "lithium insertion" and "embedding" processes described in this application refer to the process in which lithium ions are embedded in the positive electrode active material or the negative electrode active material due to an electrochemical reaction, and the "extraction", "delithium" and "extraction" processes described in this application refer to the process in which lithium ions are extracted from the positive electrode active material or the negative electrode active material due to an electrochemical reaction.

[0044] During the cycle of lithium-ion batteries, the process of lithium ion embedding into the negative electrode active material is hindered by factors such as battery preparation technology and battery aging, and lithium deposition will occur on the surface of the negative electrode. For example, the large difference in ionic conductivity at the interface between the SEI film and the electrolyte, the low ionic conductivity inside the negative electrode, and the uneven distribution of lithium ion flow will all lead to lithium deposition problems, causing the reversible capacity of the battery to decay and the cycle life to decrease.

[0045] In view of this, the embodiment of the present application provides a negative electrode sheet and a preparation method thereof, a lithium ion battery and an electric device. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, and the negative electrode film layer includes lithium fluoride particles.

[0046] When the negative electrode plate is used in a lithium-ion battery, on the one hand, the lithium fluoride particles in the negative electrode film layer can make the lithium ion flow in the negative electrode plate evenly distributed, thereby inhibiting local lithium precipitation of the negative electrode plate; on the other hand, the lithium fluoride particles can adsorb fluorine-containing additives in the electrolyte to form a lithium fluoride-rich SEI film on the surface of the negative electrode plate, thereby improving the ionic conductivity of the SEI film and helping to improve the cycle performance of the lithium-ion battery.

[0047] Generally, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. Next, the lithium-ion battery provided in the present application and various parts of the lithium-ion battery are introduced.

[0048] [Negative electrode]

[0049] The present application first provides a negative electrode sheet, such as Figure 1 As shown, the negative electrode plate 1 includes a negative electrode current collector 11 and a negative electrode film layer 12 disposed on at least one side of the negative electrode current collector 11 , and the negative electrode film layer 12 includes lithium fluoride particles.

[0050] As an example, the negative electrode current collector 11 has two surfaces opposite to each other in its thickness direction, and the negative electrode film layer 12 is disposed on any one or both of the two opposite surfaces of the negative electrode current collector 11. Figure 1 As shown, negative electrode film layers 12 are provided on both surfaces of the negative electrode current collector 11 .

[0051] Figure 2 Schematic diagram of a negative electrode sheet of an embodiment of the present application. In some other embodiments, such as Figure 2 As shown, a negative electrode film layer 12 is provided on one of two surfaces of the negative electrode current collector 11 that are opposite to each other in the thickness direction.

[0052] The negative electrode current collector may be a metal foil or a composite current collector. For example, as the metal foil, a copper foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0053] In the embodiment of the present application, the negative electrode film layer of the negative electrode plate includes lithium fluoride particles. On the one hand, the lithium fluoride particles can make the lithium ion flow in the negative electrode plate evenly distributed, thereby inhibiting local lithium precipitation of the negative electrode plate; on the other hand, the lithium fluoride particles can adsorb fluorine-containing additives in the electrolyte, so that when the negative electrode plate is used in a lithium-ion battery, the lithium fluoride particles adsorb the fluorine-containing additives in the electrolyte to generate a lithium fluoride-rich SEI film on the surface of the negative electrode plate, and the ionic conductivity of the SEI film is improved, which helps to improve the cycle performance of the lithium-ion battery.

[0054] In some embodiments, the volume average particle size D of the lithium fluoride particles is V 50 satisfies: 50nm≤D V 50≤200nm, optionally, D V50 satisfies: 50nm≤D V 50≤80nm.

[0055] Specifically, the volume average particle size D of lithium fluoride particles is V 50 can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, or its value is within the range obtained by combining any two of the above values.

[0056] The volume average particle size D of lithium fluoride particles V 50 is set within the above range, so that the lithium fluoride particles are easier to disperse in the negative electrode film layer, which is beneficial to the uniform distribution of the lithium fluoride particles in the negative electrode film layer, and can be more fully in contact with the electrolyte, thereby facilitating the uniform distribution of the lithium ion flow in the negative electrode sheet and improving the uniformity of the SEI film.

[0057] In some embodiments, the specific surface area S of the lithium fluoride particles satisfies: 20 m 2 / g≤S≤200m 2 / g, optionally, S meets: 80m 2 / g≤S≤100m 2 / g.

[0058] Specifically, the specific surface area S of lithium fluoride particles can be 20 m 2 / g, 30m 2 / g, 40m 2 / g, 50m 2 / g, 60m 2 / g, 70m 2 / g, 80m 2 / g, 90m 2 / g、100m 2 / g, 110m 2 / g, 120m 2 / g, 130m 2 / g, 140m 2 / g, 150m 2 / g, 160m 2 / g, 170m 2 / g, 180m 2 / g, 190m 2 / g, 200m 2 / g, or its value is within the range obtained by combining any two of the above values.

[0059] The specific surface area S represents the total area per unit mass of a substance. Common methods for measuring the specific surface area S include gas adsorption method and solution adsorption method. In the embodiments of the present application, the test methods for the specific surface area S of lithium fluoride particles include but are not limited to the above two methods.

[0060] The specific surface area S of the lithium fluoride particles is set within the above range, which is beneficial to the uniform distribution of lithium ion flow in the negative electrode sheet and improves the uniformity of the SEI film.

[0061] In some embodiments, based on the total weight of the negative electrode film layer, the weight content of the lithium fluoride particles in the negative electrode film layer ranges from 1% to 10%, and optionally, ranges from 4% to 5%.

[0062] Specifically, the weight content of lithium fluoride particles in the negative electrode film layer can be 1%, 1.5%, 2%, 3%, 4%, 5%, 5.5%, 6%, 7%, 8%, 9%, 9.5%, 10%, or its value is within the range obtained by combining any two of the above values.

[0063] The weight content of lithium fluoride particles in the negative electrode film layer is set within the above range, which is beneficial to suppressing local lithium deposition of the negative electrode plate.

[0064] In some embodiments, a ratio A of the diffraction intensity of the (111) crystal plane of the lithium fluoride particle to the diffraction intensity of the (200) crystal plane satisfies: 0.4≤A≤0.8. Optionally, A satisfies: 0.5≤A≤0.7.

[0065] The diffraction intensity of the (111) crystal plane here represents the intensity of the diffraction peak when the X-ray diffracts onto the (111) crystal plane; similarly, the diffraction intensity of the (200) crystal plane represents the intensity of the diffraction peak when the X-ray diffracts onto the (200) crystal plane.

[0066] Specifically, the ratio A of the diffraction intensity of the (111) crystal plane of the lithium fluoride particles to the diffraction intensity of the (200) crystal plane can be 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, or a value within the range obtained by combining any two of the above values.

[0067] When the ratio of the diffraction intensity of the (111) crystal plane of the lithium fluoride particles to the diffraction intensity of the (200) crystal plane is set within the above range, the lithium fluoride particles are particles rich in (111) crystal planes. The (111) crystal planes of the lithium fluoride particles can adsorb more fluorine-containing additives in the electrolyte, which is beneficial to the formation of a lithium fluoride-rich SEI film on the surface of the negative electrode plate, helping to improve the cycle performance of lithium-ion batteries.

[0068] In some embodiments, the shape of the lithium fluoride particles includes at least one of a spherical shape and a cubic shape.

[0069] In some embodiments, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material can be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, expanded graphite, soft carbon, hard carbon, carbon microspheres, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0070] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0071] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0072] In some embodiments, the negative electrode film layer may optionally include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0073] In some embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0074] [Positive electrode]

[0075] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector.

[0076] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two facing surfaces of the positive electrode current collector.

[0077] In one embodiment, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0078] In one embodiment, the positive electrode active material may adopt a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO 2 ), lithium nickel oxide (such as LiNiO 2 ), lithium manganese oxide (such as LiMnO 2 、LiMn 2 O 4 ), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O 2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O 2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O 2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05 O 2) and its modified compounds, etc. Examples of lithium phosphates containing olivine structures may include, but are not limited to, lithium iron phosphate (such as LiFePO 4 (also referred to as LFP), composite materials of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO 4 ), at least one of a composite material of lithium manganese phosphate and carbon, a composite material of lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.

[0079] The battery will be accompanied by Li deintercalation and consumption during the charging and discharging process. The molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the list of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system. After the charge and discharge cycle, the molar content of Li will change. In the list of positive electrode active materials in this application, the molar content of O is only an ideal state value. Lattice oxygen release will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0080] In one embodiment, the positive electrode active material layer further includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0081] In one embodiment, the positive electrode active material layer further includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0082] In one embodiment, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet are respectively formed into positive electrode slurries. For example, the first positive electrode active material and / or the second positive electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry. Then, the positive electrode slurry is coated on the positive electrode current collector, and after drying, rolling and other processes, the positive electrode sheet can be obtained.

[0083] [Electrolyte]

[0084] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. The present application has no specific restrictions on the type of electrolyte, which can be selected according to needs. The electrolyte may include an electrolyte salt and a solvent.

[0085] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0086] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane sulfone, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0087] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0088] [Isolator]

[0089] In some embodiments, the lithium-ion battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous structure separator with good chemical stability and mechanical stability can be selected.

[0090] In some embodiments, the material of the isolation membrane can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane can be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0091] The above embodiments introduce negative electrode sheets that can effectively inhibit lithium deposition. Next, the negative electrode sheet obtained after the lithium-ion battery formed by assembling the above negative electrode sheet with the positive electrode sheet, electrolyte and separator is introduced.

[0092] The present application provides a negative electrode plate, which includes: a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, the negative electrode film layer includes lithium fluoride particles; an SEI film, the SEI film is formed on the negative electrode film layer, and the SEI film includes lithium fluoride.

[0093] Generally speaking, after the lithium-ion battery is formed, a SEI film will be formed on the surface of the negative electrode film layer. The SEI film is a passivation layer covering the surface of the negative electrode film layer formed by the reaction between the electrode material and the electrolyte at the solid-liquid interface during the formation process of the lithium-ion battery. Therefore, the lithium fluoride particles in the negative electrode film layer in this embodiment can participate in the formation of the SEI film, so that after the lithium-ion battery is formed, a lithium fluoride-rich SEI film is formed.

[0094] In one embodiment, the mass content of lithium fluoride in the SEI film ranges from 10% to 80%, and optionally, ranges from 40% to 50%.

[0095] Specifically, the mass content of lithium fluoride in the SEI film can be 10%, 15%, 20%, 25%, 30%, 40%, 50%, 60%, 70%, 75%, 80%, or a value within the range obtained by combining any two of the above values.

[0096] The mass content of lithium fluoride in the SEI film is within the above range, so that the ionic conductivity of the SEI film is improved, the difference in ionic conductivity at the interface between the SEI film and the electrolyte is reduced, and lithium precipitation can be effectively inhibited.

[0097] In one embodiment, the volume average particle size D of the lithium fluoride particles is V 50 satisfies: 50nm≤D V 50≤200nm, optionally, D V 50 satisfies: 50nm≤D V 50≤80nm.

[0098] Specifically, the volume average particle size D of lithium fluoride particles is V 50 can be 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, or its value is within the range obtained by combining any two of the above values.

[0099] The volume average particle size D of lithium fluoride particles V 50 is set within the above range, which is beneficial to the uniform distribution of lithium fluoride particles in the negative electrode film layer, thereby facilitating the uniform distribution of lithium ion flow in the negative electrode plate and improving the uniformity of the SEI film.

[0100] In some embodiments, the specific surface area S of the lithium fluoride particles satisfies: 20 m 2 / g≤S≤200m 2 / g, optionally, S meets: 80m 2 / g≤S≤100m 2 / g.

[0101] Specifically, the specific surface area S of lithium fluoride particles can be 20 m 2 / g, 30m 2 / g, 40m 2 / g, 50m 2 / g, 60m 2 / g, 70m 2 / g, 80m 2 / g, 90m 2 / g、100m 2 / g, 110m 2 / g, 120m 2 / g, 130m 2 / g, 140m 2 / g, 150m 2 / g, 160m 2 / g, 170m 2 / g, 180m 2 / g, 190m 2 / g, 200m 2 / g, or its value is within the range obtained by combining any two of the above values.

[0102] The specific surface area S of the lithium fluoride particles is set within the above range, which is beneficial to the uniform distribution of lithium ion flow in the negative electrode sheet and improves the uniformity of the SEI film.

[0103] [Method for preparing negative electrode sheet]

[0104] The embodiment of the present application also provides a method for preparing a negative electrode plate. Figure 3 FIG. 1 is a schematic flow chart of a method for preparing a negative electrode sheet. Figure 3 As shown, the preparation method 300 includes the following steps.

[0105] Step 310 , disposing a negative electrode film layer on at least one side of the negative electrode current collector to obtain a negative electrode plate.

[0106] Wherein, the negative electrode film layer includes lithium fluoride particles.

[0107] Specifically, the preparation method 300 includes:

[0108] (a) preparing a negative electrode slurry, the negative electrode slurry comprising a negative electrode active material and lithium fluoride particles.

[0109] (b) applying the negative electrode slurry to at least one side of the negative electrode current collector.

[0110] (c) drying the negative electrode slurry to form a negative electrode coating layer on the negative electrode current collector.

[0111] (d) rolling the negative electrode current collector and the negative electrode coating layer to obtain a negative electrode sheet.

[0112] Thus, in the negative electrode sheet prepared through the above steps (a) to (d), the negative electrode film layer contains lithium fluoride particles.

[0113] The present application also provides a lithium-ion battery, which includes the negative electrode plate in any of the aforementioned embodiments, and / or the negative electrode plate prepared by the preparation method in any of the aforementioned embodiments.

[0114] In one embodiment, the negative electrode sheet, the positive electrode sheet and the separator may be formed into an electrode assembly by a winding process or a lamination process.

[0115] In one embodiment, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0116] In one embodiment, the outer packaging of the battery cell may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0117] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square or any other shape. Figure 4 The battery cell 40 is a square structure as an example.

[0118] It should be understood that the battery cell 40 may include the lithium-ion battery in the aforementioned embodiment.

[0119] In some embodiments, reference Figure 5 , the outer packaging may include a shell 41 and a cover plate 43. Among them, the shell 41 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 41 has an opening connected to the receiving cavity, and the cover plate 43 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 42 through a winding process or a lamination process. The electrode assembly 42 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 22. The number of electrode assemblies 42 contained in the battery cell 40 can be one or more, and those skilled in the art can choose according to specific actual needs.

[0120] In some embodiments, the battery 50 may include a plurality of battery cells 40. For example, Figure 6, which is a schematic diagram of the structure of a battery 50 according to an embodiment of the present application, wherein the battery 50 may include a plurality of battery cells 40. The battery 50 may also include a box 51, wherein the box 51 is a hollow structure, and the plurality of battery cells 40 are accommodated in the box 51. For example, the plurality of battery cells 40 are connected in parallel, in series, or in a mixed combination and then placed in the box 51.

[0121] Optionally, the battery 50 may also include other structures, which are not described one by one here. For example, the battery 50 may also include a busbar component, which is used to realize electrical connection between multiple battery cells 40, such as parallel connection, series connection or mixed connection. Specifically, the busbar component can realize electrical connection between battery cells 40 by connecting the electrode terminals of the battery cells 40. Further, the busbar component can be fixed to the electrode terminals of the battery cells 40 by welding. The electrical energy of multiple battery cells 40 can be further led out through the box 51 through a conductive mechanism. Optionally, the conductive mechanism may also belong to the busbar component.

[0122] According to different power requirements, the number of battery cells 40 can be set to any value. Multiple battery cells 40 can be connected in series, parallel or hybrid to achieve a larger capacity or power. Since the number of battery cells 40 included in each battery 50 may be large, for ease of installation, the battery cells 40 can be grouped, and each group of battery cells 40 constitutes a battery module. The number of battery cells 40 included in the battery module is not limited and can be set according to demand. The battery can include multiple battery modules, which can be connected in series, parallel or hybrid.

[0123] In addition, the present application also provides an electric device, which includes at least one of the battery cells, battery modules or batteries provided in the present application. The battery cells, battery modules or batteries can be used as the power source of the electric device, and can also be used as the energy storage unit of the electric device. The electric device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0124] As the electrical device, a battery cell, a battery module or a battery can be selected according to its usage requirements.

[0125] Figure 7 The power consumption device is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for battery cells, batteries or battery modules can be used.

[0126] As another example, the device may be a mobile phone, a tablet computer, a notebook computer, etc. The device is usually required to be light and thin, and a battery cell may be used as a power source.

[0127] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0128] 1. Preparation of negative electrode sheet

[0129] Negative electrode sheet 1: Active material artificial graphite, lithium fluoride nanocubes, conductive agent carbon black, binder styrene butadiene rubber (SBR), and thickener sodium hydroxymethyl cellulose (CMC) are dissolved in solvent deionized water according to a weight ratio of 93.2:4:0.8:0.8:1.2, and mixed evenly to prepare a negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil, and the negative electrode sheet 1 is obtained after drying, cold pressing, and cutting, wherein the ratio of the (111) crystal plane strength to the (200) crystal plane strength in the lithium fluoride nanocube is 0.65, and the volume average particle size D of the lithium fluoride nanocube is V 50 means 50nm.

[0130] Negative electrode sheet 2: The preparation of negative electrode sheet 2 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 2, the volume average particle size D of lithium fluoride nanocubes is V 50 is 80nm.

[0131] Negative electrode sheet 3: The preparation of negative electrode sheet 3 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 3, the volume average particle size D of lithium fluoride nanocubes is V 50 is 100nm.

[0132] Negative electrode sheet 4: The preparation of negative electrode sheet 4 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 4, the volume average particle size D of lithium fluoride nanocubes is V 50 is 200nm.

[0133] Negative electrode sheet 5: The preparation of negative electrode sheet 5 is similar to that of negative electrode sheet 1, except that, in negative electrode sheet 5, the weight ratio of active material artificial graphite, lithium fluoride nanocubes, conductive agent carbon black, binder SBR, and thickener CMC is 96.2:1:0.8:0.8:1.2.

[0134] Negative electrode sheet 6: The preparation of negative electrode sheet 6 is similar to that of negative electrode sheet 1, except that, in negative electrode sheet 6, the weight ratio of active material artificial graphite, lithium fluoride nanocubes, conductive agent carbon black, binder SBR, and thickener CMC is 95.2:2:0.8:0.8:1.2.

[0135] Negative electrode sheet 7: The preparation of negative electrode sheet 7 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 7, the mass ratio of active material artificial graphite, lithium fluoride nanocubes, conductive agent carbon black, binder SBR, and thickener CMC is 94.2:3:0.8:0.8:1.2.

[0136] Negative electrode sheet 8: The preparation of negative electrode sheet 8 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 8, the mass ratio of active material artificial graphite, lithium fluoride nanocubes, conductive agent carbon black, binder SBR, and thickener CMC is 92.2:5:0.8:0.8:1.2.

[0137] Negative electrode sheet 9: The preparation of negative electrode sheet 9 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 9, the mass ratio of active material artificial graphite, lithium fluoride nanocubes, conductive agent carbon black, binder SBR, and thickener CMC is 91.2:6:0.8:0.8:1.2.

[0138] Negative electrode sheet 10: The preparation of negative electrode sheet 10 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 10, the mass ratio of active material artificial graphite, lithium fluoride nanocubes, conductive agent carbon black, binder SBR, and thickener CMC is 87.2:10:0.8:0.8:1.2.

[0139] Negative electrode sheet 11: The preparation of negative electrode sheet 11 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 11, the ratio of the (111) crystal plane strength to the (200) crystal plane strength of the lithium fluoride nanocube is 0.4.

[0140] Negative electrode sheet 12: The preparation of negative electrode sheet 12 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 12, the ratio of the (111) crystal plane strength to the (200) crystal plane strength of lithium fluoride nanocubes is 0.5.

[0141] Negative electrode sheet 13: The preparation of negative electrode sheet 13 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 13, the ratio of the (111) crystal plane strength to the (200) crystal plane strength of the lithium fluoride nanocube is 0.6.

[0142] Negative electrode sheet 14: The preparation of negative electrode sheet 14 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 14, the ratio of the (111) crystal plane strength to the (200) crystal plane strength of the lithium fluoride nanocube is 0.7.

[0143] Negative electrode sheet 15: The preparation of negative electrode sheet 15 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 15, the ratio of the (111) crystal plane strength to the (200) crystal plane strength of the lithium fluoride nanocube is 0.8.

[0144] Negative electrode sheet 16: The preparation of negative electrode sheet 16 is similar to that of negative electrode sheet 1, except that in negative electrode sheet 16, the volume average particle size D of lithium fluoride particles is V 50 is 1000nm.

[0145] Negative electrode sheet 17: The preparation of negative electrode sheet 17 is similar to that of negative electrode sheet 1, except that, during the preparation of negative electrode sheet 17, the negative electrode slurry includes active material artificial graphite, conductive agent carbon black, binder SBR and thickener CMC, but does not include lithium fluoride particles.

[0146] 2. Preparation of lithium-ion batteries

[0147] [Example 1]

[0148] (1) Preparation of positive electrode sheet

[0149] The positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 0.5 Co 0.2 Mn 0.3 O 2 ), conductive carbon black, binder polyvinylidene fluoride, and solvent N-methylpyrrolidone are mixed and stirred in a weight ratio of 91:3:6:40 to obtain a positive electrode slurry, which is coated on a positive electrode current collector aluminum foil and vacuum dried to obtain a positive electrode sheet.

[0150] (2) Negative electrode

[0151] The negative electrode sheet adopts the negative electrode sheet 1 prepared as above.

[0152] (3) Preparation of isolation membrane

[0153] Polypropylene film is used as the isolation film.

[0154] (4) Preparation of electrolyte

[0155] In an argon atmosphere glove box (H 2 O<0.1ppm, O 2 <0.1ppm), the organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly in a volume ratio of 3:7, and 1 mol / L lithium hexafluorophosphate (LiPF 6 ) The electrolyte salt is evenly dispersed, and then 2% of fluoroethylene carbonate is dissolved in the above organic solvent, and stirred evenly to obtain an electrolyte solution.

[0156] (5) Assembly of lithium-ion batteries

[0157] The positive electrode sheet, the isolation film, and the negative electrode sheet 1 are stacked in order, so that the isolation film is placed between the positive electrode sheet and the negative electrode sheet 1 to play an isolating role, and then wound to obtain an electrode assembly; the electrode assembly is placed in a battery casing, and after drying, the electrolyte is injected, and then the lithium-ion secondary battery 1 is obtained through processes such as formation and standing, which is Example 1.

[0158] [Examples 2-16, Comparative Example 1]

[0159] The preparation methods of the lithium-ion batteries of Examples 2-16 and Comparative Example 1 are similar to those of the lithium-ion battery of Example 1, except that different negative electrode sheets are used (among which, Examples 1-16 use negative electrode sheets 1-16, respectively, and Comparative Example 1 uses negative electrode sheet 17), as shown in Table 1 for details.

[0160] The lithium-ion battery obtained after packaging is formed according to the following process, and the specific formation process is:

[0161] After standing for 1 minute, the battery was charged at a constant current of 8mA to 4.2V. Then, it was charged at a constant voltage of 4.2V with a cut-off current of 2mA. After standing for 10 minutes, it was discharged at a constant current of 8mA with a cut-off voltage of 2.5V. It was then left to stand for 50 hours.

[0162] Table 1: Product parameters and performance data of Examples 1-16 and Comparative Example 1

[0163]

[0164] In Table 1, “D V 50” represents the volume average particle size of lithium fluoride particles; “C 1 " represents the weight content of lithium fluoride particles in the negative electrode film layer; "A" represents the ratio of the diffraction intensity of the (111) crystal plane of the lithium fluoride particles to the diffraction intensity of the (200) crystal plane; "C 2 " indicates the mass content of lithium fluoride in the SEI film formed after the lithium-ion battery is formed; "Whether lithium is deposited" indicates whether lithium is deposited on the negative electrode plate after the lithium-ion battery is cycled; "0.1C capacity retention rate" indicates the capacity retention rate of the lithium-ion battery after 5 cycles of charging and discharging at a 0.1C rate; "0.5C capacity retention rate" indicates the capacity retention rate of the lithium-ion battery after 5 cycles of charging and discharging at a 0.5C rate; "1C capacity retention rate" indicates the capacity retention rate of the lithium-ion battery after 5 cycles of charging and discharging at a 1C rate; "2C capacity retention rate" indicates the capacity retention rate of the lithium-ion battery after 5 cycles of charging and discharging at a 2C rate; "3C capacity retention rate" indicates the capacity retention rate of the lithium-ion battery after 5 cycles of charging and discharging at a 3C rate; "4C capacity retention rate" indicates the capacity retention rate of the lithium-ion battery after 5 cycles of charging and discharging at a 4C rate.

[0165] It should be understood that the SEI film after formation also includes components such as organic matter that are not reflected in Table 1.

[0166] In the embodiment of the present application, the cycled lithium-ion battery can be disassembled to observe whether lithium deposition occurs on the surface of the negative electrode.

[0167] By comparing the results of Examples 1-16 in Table 1 with Comparative Example 1, it can be seen that when the negative electrode sheet containing lithium fluoride particles in the negative electrode film layer is applied to a lithium-ion battery, the lithium plating problem of the negative electrode sheet is solved during the cycle of the lithium-ion battery, the capacity retention rate of the lithium-ion battery is improved, and the cycle performance is effectively improved.

[0168] By comparing the results of Examples 1-4 and 16, it can be seen that the volume average particle size D of the lithium fluoride particles is V 50 is set within an appropriate range, the effect of improving the cycle performance of the lithium-ion battery is more significant. In the embodiment of the present application, under the same other conditions, the volume average particle size D of the lithium fluoride particles is V 50In the range of 50nm to 80nm, the cycle performance of lithium-ion batteries is better.

[0169] By comparing the results of Examples 1, 5-10, it can be seen that when the weight content of lithium fluoride particles in the negative electrode film layer is controlled within an appropriate range, the effect of improving the cycle performance of the lithium ion battery is more significant. In the embodiments of the present application, under the same other conditions, the weight content of lithium fluoride particles in the negative electrode film layer is in the range of 4% to 5%, and the cycle performance of the lithium ion battery is better.

[0170] By comparing the results of Examples 1 and 11-15, it can be seen that the ratio of the diffraction intensity of the (111) crystal plane of the lithium fluoride particles to the diffraction intensity of the (200) crystal plane is controlled within an appropriate range, and the effect of improving the cycle performance of the lithium ion battery is more significant. In the embodiments of the present application, under the same other conditions, the ratio of the diffraction intensity of the (111) crystal plane of the lithium fluoride particles to the diffraction intensity of the (200) crystal plane is in the range of 0.5 to 0.7, and the cycle performance of the lithium ion battery is good.

[0171] The following is a brief introduction to the test methods of the physical and chemical parameters and performance parameters involved in the embodiments of the present application. It should be understood that the following test methods are only examples, and other test methods known in the art may also be used for testing.

[0172] 1. Test method for the mass content of lithium fluoride in SEI film

[0173] The lithium-ion battery after cycle was disassembled, the surface of the negative electrode was cleaned with DMC, and then an X-ray photoelectron spectroscopy test was performed. The content of organic components and inorganic lithium salt components in the SEI film on the surface of the negative electrode was calculated based on the energy spectrum intensity of lithium, oxygen, carbon, and fluorine elements.

[0174] 2. D V 50 test methods

[0175] Equipment model: Malvern 2000 (MasterSizer 2000) laser particle size analyzer, reference standard process: GB / T19077-2016 / ISO 13320:2009.

[0176] Specific test process: Take an appropriate amount of the sample to be tested (the sample concentration is sufficient to ensure 8-12% shading), add 20ml of deionized water, and simultaneously operate the device externally for 5min (53KHz / 120W) to ensure that the sample is completely dispersed, and then measure the sample according to GB / T19077-2016 / ISO13320:2009 standard.

[0177] 3. Test method for diffraction intensity of crystal surface

[0178] The product to be tested was scanned using a Bruker D8 Discover X-ray diffractometer within a scanning range of 0° to 80° at a scanning rate of 10° / min, and the area of ​​the diffraction peak of the corresponding crystal plane in the XRD spectrum of the product was calculated as its diffraction intensity.

[0179] 4. Test method for capacity retention rate of lithium-ion batteries

[0180] Use the Blue Electric test system to perform charge and discharge tests on the formed lithium-ion batteries.

[0181] First, at 25°C, the lithium-ion battery is discharged to 2.5V at a constant current of 0.1C, and then charged to 4.4V at 0.1C. The resulting capacity is recorded as the initial capacity C0; then constant current charge and discharge are performed at rates of 0.5C, 1C, 2C, 3C, and 4C, and the ratio of the resulting capacity to C0 is recorded as the capacity retention rate at the current rate. In the embodiment of the present application, the ratio of the capacity to C0 after 5 cycles of constant current charge and discharge at rates of 0.5C, 1C, 2C, 3C, and 4C is recorded as the capacity retention rate at the current rate.

[0182] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode plate, characterized in that: include: Anode current collector; A negative electrode film layer is disposed on at least one side of the negative electrode current collector, and the negative electrode film layer includes lithium fluoride particles.

2. The negative electrode sheet according to claim 1, characterized in that: The volume average particle size D of the lithium fluoride particles V 50 satisfies: 50nm≤D V 50≤200nm, optionally, D V 50 satisfies: 50nm≤D V 50≤80nm.

3. The negative electrode sheet according to claim 1 or 2, characterized in that: The specific surface area S of the lithium fluoride particles satisfies: 20m 2 / g≤S≤200m 2 / g, optionally, S meets: 80m 2 / g≤S≤100m 2 / g.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that: Based on the total weight of the negative electrode film layer, the weight content of the lithium fluoride particles in the negative electrode film layer ranges from 1% to 10%, and optionally, ranges from 4% to 5%.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that: The ratio A of the diffraction intensity of the (111) crystal plane of the lithium fluoride particle to the diffraction intensity of the (200) crystal plane satisfies: 0.4≤A≤0.

8. Optionally, A satisfies: 0.5≤A≤0.

7.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that: The shape of the lithium fluoride particles includes at least one of spherical and cubic shapes.

7. The negative electrode sheet according to any one of claims 1 to 6, characterized in that: The negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes at least one of natural graphite, artificial graphite, expanded graphite, hard carbon, soft carbon, carbon microspheres, silicon, silicon oxide, silicon carbon, and lithium titanate.

8. A negative electrode plate, characterized in that: include: A negative electrode current collector and a negative electrode film layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode film layer comprises lithium fluoride particles; A solid electrolyte interface film is formed on the negative electrode film layer, and the solid electrolyte interface film includes lithium fluoride.

9. The negative electrode sheet according to claim 8, characterized in that: The mass content of the lithium fluoride in the solid electrolyte interface film ranges from 10% to 80%, and optionally, ranges from 40% to 50%.

10. The negative electrode sheet according to claim 9, characterized in that: The volume average particle size D of the lithium fluoride particles V 50 satisfies: 50nm≤D V 50≤200nm, optionally, D V 50 satisfies: 50nm≤D V 50≤80nm.

11. The negative electrode sheet according to any one of claims 8 to 10, characterized in that: The specific surface area S of the lithium fluoride particles satisfies: 20m 2 / g≤S≤200m 2 / g, optionally, S meets: 80m 2 / g≤S≤100m 2 / g.

12. A method for preparing a negative electrode sheet, characterized in that: include: Disposing a negative electrode film layer on at least one side of the negative electrode current collector to obtain the negative electrode plate; Wherein, the negative electrode film layer includes lithium fluoride particles.

13. The preparation method according to claim 12, characterized in that: The negative electrode film layer is provided on at least one side of the negative electrode current collector to obtain the negative electrode plate, comprising: preparing a negative electrode slurry, wherein the negative electrode slurry comprises a negative electrode active material and the lithium fluoride particles; Applying the negative electrode slurry to at least one side of the negative electrode current collector; Drying the negative electrode slurry to form a negative electrode coating layer on the negative electrode current collector; The negative electrode current collector and the negative electrode coating layer are roll-pressed to obtain the negative electrode sheet.

14. A lithium ion battery, characterized in that: The lithium-ion battery comprises at least one of the negative electrode sheet according to any one of claims 1 to 7, the negative electrode sheet according to any one of claims 8 to 11, and the negative electrode sheet prepared by the preparation method according to claim 12 or 13.

15. An electrical device, characterized in that: The electric device comprises the lithium-ion battery as claimed in claim 14.

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