Negative active material, negative pole piece, lithium ion battery and electric device

Abstract

The embodiment of the invention discloses a negative electrode active material, a negative electrode plate, a lithium ion battery and an electric device. The negative electrode active material comprises a negative electrode active substance and a coating layer on the surface of the negative electrode active substance, the cladding layer includes a lithium-loving metal and / or a compound of a lithium-loving metal. When the negative electrode active material is applied to a negative electrode plate, a lithium ion battery and an electric device, lithium precipitation can be effectively inhibited, and the capacity retention ratio and the cycle performance of the battery can be improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more specifically, to a negative electrode active material, a negative electrode plate, 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] Lithium dendrites are dendritic lithium metals formed by further deposition of lithium on the negative electrode during the cycle of lithium-ion batteries. The presence of lithium dendrites can easily lead to a decrease in the reversible capacity of lithium-ion batteries, a decrease in coulombic efficiency, and a deterioration in cycle performance. In severe cases, they can puncture the separator and cause a short circuit between the positive and negative electrodes. Therefore, how to inhibit the growth of lithium dendrites is a technical problem that needs to be solved urgently. 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 active material, a negative electrode plate, a lithium ion battery and an electric device. When the negative electrode active material is used in the negative electrode plate, the lithium ion battery and the electric device, it can effectively inhibit lithium precipitation and help improve the capacity retention rate and cycle performance of the battery.

[0005] In a first aspect, a negative electrode active material is provided, wherein the negative electrode active material comprises a negative electrode active substance and a coating layer on the surface of the negative electrode active substance; the coating layer comprises a lithium-philic metal and / or a compound of the lithium-philic metal.

[0006] In an embodiment of the present application, a coating layer containing a lithium-philic metal and / or a lithium-philic metal compound is provided on the surface of the negative electrode active material, so that after the negative electrode active material undergoes a formation reaction, the SEI film on its surface contains a lithium-philic metal and / or a lithium-philic metal compound. The lithium-philic metal and / or the lithium-philic metal compound can induce uniform lithium deposition during the cycle of the lithium-ion battery, thereby inhibiting the growth of lithium dendrites. In addition, in the case of lithium precipitation on the negative electrode plate, the lithium-philic metal can react with lithium to form a lithium-metal alloy; the lithium-philic metal compound can react with lithium to form a lithium-metal alloy and an inorganic lithium salt. As a result, the negative electrode active material can effectively inhibit lithium precipitation and the growth of lithium dendrites, helping to improve the capacity retention rate and cycle performance of the lithium-ion battery.

[0007] In a possible implementation, the lithium-philic metal includes at least one of magnesium, tin, zinc, antimony, silver, and indium.

[0008] In a possible implementation, the lithium-philic metal compound includes at least one of the lithium-philic metal oxide, the lithium-philic metal fluoride, and the lithium-philic metal carbonate.

[0009] In a possible implementation, the negative electrode active material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon microspheres, silicon, silicon oxide, silicon carbon, and lithium titanate.

[0010] In a possible implementation, based on the weight of the negative electrode active material, the mass content a of the coating layer satisfies: 0.1%≤a≤2%; optionally, 0.5%≤a≤2%.

[0011] In a possible implementation, the thickness d of the coating layer satisfies: 1 nm≤d≤100 nm; optionally, 5 nm≤d≤10 nm.

[0012] In the embodiments of the present application, by controlling the mass content of the coating layer and the thickness of the coating layer within a suitable range, it helps to suppress lithium deposition while reducing the effect of the coating layer on the energy density of the lithium-ion battery.

[0013] In a possible implementation, the negative electrode active material includes a carbon-based material.

[0014] In a possible implementation, the carbon-based material includes artificial graphite, natural graphite, soft carbon, hard carbon, graphene, and carbon nanotubes.

[0015] In a second aspect, a negative electrode plate is provided, wherein the negative electrode plate comprises the negative electrode active material in any possible implementation of the first aspect.

[0016] In a third aspect, a negative electrode plate is provided, the negative electrode plate comprising: a current collector and a negative electrode active material layer arranged on at least one side of the current collector; a SEI film, the SEI film is arranged on the negative electrode active material layer, and the SEI film comprises a lithium-philic metal and / or a compound of the lithium-philic metal.

[0017] In a possible implementation, the lithium-philic metal includes at least one of magnesium, tin, zinc, antimony, silver, and indium.

[0018] In a possible implementation, the lithium-philic metal compound includes at least one of the lithium-philic metal oxide, the lithium-philic metal fluoride, and the lithium-philic metal carbonate.

[0019] In a fourth aspect, a negative electrode plate is provided, the negative electrode plate comprising: a current collector and a negative electrode active material layer arranged on at least one side of the current collector; a SEI film, the SEI film is arranged on the negative electrode active material layer, and the SEI film comprises a lithium-metal alloy.

[0020] In a possible implementation, the lithium-metal alloy includes an alloy formed by a lithium-philic metal and lithium; and / or an alloy formed by a compound of a lithium-philic metal and lithium.

[0021] In a possible implementation, the SEI film further includes an inorganic lithium salt, and the inorganic lithium salt includes at least one of lithium oxide, lithium fluoride, and lithium carbonate.

[0022] In a possible implementation, the negative electrode plate includes a lithium deposition area and a non-lithium deposition area; per unit area, the mass content of the inorganic lithium salt in the lithium deposition area is greater than the mass content of the inorganic lithium salt in the non-lithium deposition area.

[0023] In a fifth aspect, a method for preparing a negative electrode plate is provided, the method comprising: preparing a coating layer on the surface of a negative electrode active material; the coating layer comprises a lithium-philic metal and / or a compound of the lithium-philic metal.

[0024] In a sixth aspect, a lithium-ion battery is provided, wherein the lithium-ion battery comprises at least one of the negative electrode plates in any possible implementation of the second aspect, the third aspect, and the fourth aspect.

[0025] In a seventh aspect, an electrical device is provided, wherein the electrical device comprises the lithium-ion battery in the sixth 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 This is a schematic diagram of a negative electrode sheet according to an embodiment of the present application.

[0028] Figure 2 A schematic flow chart of a method for preparing a negative electrode sheet according to the present application.

[0029] Figure 3 A schematic diagram of a battery cell.

[0030] Figure 4 A schematic diagram of a battery module.

[0031] Figure 5 A schematic diagram of a battery.

[0032] Figure 6 Another schematic diagram of a battery. DETAILED DESCRIPTION

[0033] Hereinafter, the embodiments of the negative electrode active material, negative electrode sheet, lithium-ion battery and electric device of the present application are specifically disclosed with appropriate reference to the drawings in detail. However, there may be 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 structures 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.

[0034] Hereinafter, the lithium-ion battery of the present application, its preparation method, and the implementation mode of the electric device thereof will be specifically disclosed with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be 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 description 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] "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.

[0036] 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.

[0037] If not otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A and / or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0038] 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.

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

[0040] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their generally accepted meanings in the art.

[0041] As mentioned, "lithiophilic metal" refers to a metal element that can form a lithium-metal alloy with lithium, such as magnesium, zinc, aluminum, etc.

[0042] As mentioned above, "lithiophilic metal compound" refers to a metal compound that can form a lithium-metal alloy with lithium, such as fluoride, carbonate.

[0043] Where mentioned, “lithium dendrites” refer to the dendritic lithium metal that forms when lithium ions are reduced during the cycling process of lithium-ion batteries.

[0044] If mentioned, "SEI membrane" refers to the solid electrolyte interface (SEI) membrane. The SEI membrane is a passivation layer covering the surface of the active material formed when the active material reacts with the electrolyte at the solid-liquid interface during the charging process of the lithium-ion battery.

[0045] Next, embodiments of the present application are introduced.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] During the charge and discharge process of lithium-ion batteries, factors such as the change in the internal resistance of lithium-ion batteries, the balance between the speed of electrochemical reactions at the positive and negative electrodes and the speed of electron movement, and the diffusion rate of lithium ions involved in the electrochemical reaction will lead to the polarization of the battery, causing lithium ions to precipitate from the surface of the negative electrode active material layer, i.e., lithium deposition. With the further deposition of lithium ions, the formation and growth of lithium dendrites may occur. The formation and growth of lithium dendrites will continuously consume lithium ions, resulting in the attenuation of the battery's capacity and cycle life; in severe cases, lithium dendrites may also pierce the separator, causing a short circuit between the positive and negative electrodes, causing battery safety problems.

[0050] In view of this, the embodiments of the present application provide a negative electrode active material, a negative electrode pole piece and a preparation method thereof, a lithium ion battery and an electrical device. The negative electrode active material includes a coating layer containing a lithium-philic metal and / or a lithium-philic metal compound. The lithium-philic metal and / or the lithium-philic metal compound can induce lithium ions to be uniformly deposited on the negative electrode pole piece during the cycle of the lithium ion battery, thereby inhibiting the growth of lithium dendrites. Moreover, once lithium deposition occurs on the negative electrode pole piece, the lithium-philic metal and / or the lithium-philic metal compound can react with the deposited lithium to form an alloy, thereby inhibiting lithium deposition or the growth of lithium dendrites. Therefore, when the negative electrode active material is applied to a lithium ion battery, it can effectively inhibit lithium deposition and lithium dendrite growth, and help improve the capacity retention rate and cycle performance of the lithium ion battery.

[0051] Specifically, in one embodiment, the negative electrode active material includes a negative electrode active substance and a coating layer on the surface of the negative electrode active substance; the coating layer includes a lithium-philic metal and / or a lithium-philic metal compound.

[0052] It should be understood that “the coating layer includes a lithium-philic metal and / or a compound of a lithium-philic metal” may mean that the coating layer includes only a lithium-philic metal, or only a compound of a lithium-philic metal, or the coating layer includes a lithium-philic metal and a compound of a lithium-philic metal. In the case where the coating layer includes a lithium-philic metal and a compound of a lithium-philic metal, the metal element in the compound of the lithium-philic metal may be the same as or different from the element of the lithium-philic metal.

[0053] For example, the coating layer may include only zinc, only zinc carbonate, or both zinc and zinc carbonate.

[0054] Illustratively, the coating layer may include only magnesium, only magnesium carbonate, or both magnesium and magnesium carbonate.

[0055] In one embodiment, the lithium-philic metal includes at least one of magnesium, tin, zinc, antimony, silver, and indium.

[0056] In one embodiment, the lithium-philic metal compound includes at least one of the lithium-philic metal oxide, the lithium-philic metal fluoride, and the lithium-philic metal carbonate.

[0057] Specifically, lithium-philic metals such as magnesium, tin, zinc, antimony, silver, and indium can react with lithium to form lithium-metal alloys. Compounds such as oxides, fluorides, and carbonates of the aforementioned lithium-philic metals can also react with lithium to form lithium-metal alloys and inorganic lithium salts. Thus, the negative electrode active material containing lithium-philic metals and / or compounds of lithium-philic metals can effectively inhibit lithium precipitation.

[0058] In one embodiment, the negative electrode active material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon microspheres, silicon, silicon oxide, silicon carbon, and lithium titanate.

[0059] In one embodiment, based on the weight of the negative electrode active material, the mass content a of the coating layer satisfies: 0.1%≤a≤2%; alternatively, 0.5%≤a≤2%.

[0060] Specifically, a can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, or its value is within the range obtained by combining any two of the above values.

[0061] On the one hand, the coating layer contains lithium-philic metals and / or lithium-philic metals that can effectively inhibit lithium precipitation. If the mass content of the coating layer is too low, the negative electrode active material has limited effect in inhibiting lithium precipitation. On the other hand, the coating layer does not participate in the charge and discharge reaction of the lithium-ion battery and cannot contribute to the capacity of the lithium-ion battery. Too high a content of the coating layer is not conducive to improving the energy density of the lithium-ion battery.

[0062] Therefore, this embodiment can reduce the influence of the coating layer on the energy density of the lithium-ion battery while effectively suppressing lithium deposition by controlling the mass content a of the coating layer within a suitable range.

[0063] In one embodiment, the thickness d of the coating layer satisfies: 1 nm≤d≤100 nm; optionally, 5 nm≤d≤10 nm.

[0064] Specifically, d can be 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 76nm, 80nm, 85nm, 90nm, 95nm, 100nm or its value is within the range obtained by combining any two of the above values.

[0065] On the one hand, under the same other conditions, the thicker the coating layer, the higher the content of the lithium-philic metal and / or lithium-philic metal compound in the negative electrode active material, and the better the inhibition effect on lithium precipitation. On the other hand, the thicker the coating layer, the greater its mass proportion in the negative electrode active material, and the greater the impact on the energy density of the negative electrode active material.

[0066] Therefore, in this embodiment, by controlling the thickness d of the coating layer within a suitable range, it is also possible to effectively suppress lithium deposition while reducing the effect of the coating layer on the energy density of the lithium-ion battery.

[0067] Generally, a lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. Next, each part of the lithium-ion battery provided in the present application is introduced respectively.

[0068] [Negative electrode]

[0069] The negative electrode sheet generally includes a current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material. It should be understood that the current collector in the negative electrode sheet is also called a negative electrode current collector.

[0070] As an example, the negative electrode current collector has two surfaces facing each other in its thickness direction, and the negative electrode active material layer is disposed on any one or both of the two facing surfaces of the negative electrode current collector.

[0071] In one embodiment, 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.).

[0072] Some possible negative electrode active materials have been listed in the above embodiments. In another embodiment, the negative electrode active material may be a negative electrode active material for a battery known in the art. As an example, the negative electrode active material may also include at least one of the following materials: silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include 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.

[0073] In the above embodiments, some possible lithium-philic metals have been listed. In another embodiment, the negative electrode active material layer includes a lithium-philic metal and / or a compound of a lithium-philic metal. The lithium-philic metal can also be other metals known in the art that can form alloys with lithium. As an example, the lithium-philic metal can include at least one of the following metals: Al, Sr, Ba, Sc, Y, Rh, Ir, Pd, Pt, Au, Cd, Ga, Ge, Pb, Bi.

[0074] In one embodiment, the negative electrode active material layer further includes a binder. The binder may include 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).

[0075] In one embodiment, the negative electrode active material layer further includes a conductive agent, which includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0076] In one embodiment, the negative electrode active material layer further includes other additives, such as a thickener (eg, sodium carboxymethyl cellulose CMC-Na).

[0077] In one embodiment, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet are formed into a negative electrode slurry. For example, the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent to form a negative electrode slurry. Then, the negative electrode slurry is coated on the negative electrode current collector, and after drying, rolling and other processes, the negative electrode sheet can be obtained.

[0078] The above embodiments introduce a negative electrode sheet that can effectively inhibit lithium deposition and lithium dendrite growth. Next, the negative electrode sheet obtained after the lithium-ion battery composed of the above negative electrode sheet is formed is introduced.

[0079] The present application provides a negative electrode plate, which includes: a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector; an SEI film, which is arranged on the negative electrode active material layer, and the SEI film includes a lithium-philic metal and / or a lithium-philic metal compound.

[0080] Generally speaking, after the lithium-ion battery is formed, a SEI film will be formed on the surface of the negative electrode active material layer. The SEI film is a passivation layer covering the surface of the negative electrode active material layer formed by the reaction between the negative electrode active material and the electrolyte at the solid-liquid interface during the formation process of the lithium-ion battery. Therefore, the coating layer of the negative electrode active material in this embodiment can participate in the formation of the SEI film, so that the SEI film after formation includes lithium-philic metals and / or lithium-philic metal compounds.

[0081] In one embodiment, the lithium-philic metal includes at least one of magnesium, tin, zinc, antimony, silver, and indium.

[0082] In one embodiment, the lithium-philic metal compound includes at least one of a lithium-philic metal oxide, a lithium-philic metal fluoride, and a lithium-philic metal carbonate.

[0083] Next, the negative electrode sheet obtained after the lithium-ion battery composed of the negative electrode sheet in the above-mentioned embodiment is cycled is introduced.

[0084] It should be understood that in the embodiments of the present application, the lithium-ion battery after cycling can be considered as a lithium-ion battery in which lithium deposition has occurred, that is, a lithium-ion battery after lithium deposition. It has been mentioned in the aforementioned embodiments that the negative electrode active material or the SEI film on the surface of the negative electrode active material layer contains lithium-philic metals and / or lithium-philic metal compounds. Therefore, in the lithium-ion battery after cycling, once lithium deposition occurs at the negative electrode, the precipitated lithium will be consumed by the lithium-philic metals and / or lithium-philic metal compounds, so that the negative electrode plate of the lithium-ion battery after cycling includes a lithium-metal alloy.

[0085] Based on this, an embodiment of the present application also provides a negative electrode plate, which includes: a current collector and a negative electrode active material layer arranged on at least one side of the current collector; a SEI film, which is arranged on the negative electrode active material layer, wherein the SEI film includes a lithium-metal alloy.

[0086] Specifically, when lithium precipitation occurs on the surface of the negative electrode active material layer, the precipitated lithium can react with the lithium-philic metal in the negative electrode active material layer to form a lithium-metal alloy. Therefore, the SEI of the lithium-ion battery after cycling includes the lithium-metal alloy.

[0087] In one embodiment, the lithium-metal alloy includes an alloy formed by a lithium-philic metal and lithium. In other words, when the coating layer of the negative electrode active material only includes a lithium-philic metal, the lithium-metal alloy in the SEI film is formed by the reaction of the lithium-philic metal and the precipitated lithium.

[0088] Illustratively, in the case where the coating layer of the negative electrode active material includes sodium, the lithium-metal alloy in the SEI film includes a lithium-sodium alloy.

[0089] In another embodiment, the lithium-metal alloy is an alloy formed by a compound of a lithium-loving metal and lithium. In other words, when the negative electrode active material coating layer includes only a compound of a lithium-loving metal, or includes a lithium-loving metal and a compound of a lithium-loving metal, the lithium-metal alloy in the SEI film is formed by the reaction of the compound of the lithium-loving metal and the precipitated lithium; or by the reaction of the lithium-loving metal and the compound of the lithium-loving metal with the precipitated lithium.

[0090] Illustratively, in the case where the coating layer of the negative electrode active material includes sodium carbonate, the lithium-metal alloy in the SEI film includes a lithium-sodium alloy.

[0091] Illustratively, in the case where the coating layer of the negative electrode active material includes sodium and sodium carbonate, the lithium-metal alloy in the SEI film includes a lithium-sodium alloy.

[0092] Illustratively, in the case where the coating layer of the negative electrode active material includes sodium and magnesium carbonate, the lithium-metal alloy in the SEI film includes a lithium-sodium alloy and a lithium-magnesium alloy.

[0093] In one embodiment, the SEI film further includes an inorganic lithium salt, and the inorganic lithium salt includes at least one of lithium oxide, lithium fluoride, and lithium carbonate.

[0094] Specifically, when the coating layer of the negative electrode active material includes a lithium-philic metal compound, after the lithium-philic metal compound reacts with the precipitated lithium, in addition to generating a lithium-metal alloy, an inorganic lithium salt is also generated. Therefore, the SEI film of the negative electrode plate after cycling also includes an inorganic lithium salt generated by the reaction of the lithium-philic metal compound and lithium.

[0095] Illustratively, in the case where the coating layer of the negative electrode active material includes sodium carbonate, the sodium carbonate reacts with the precipitated lithium to generate a lithium-sodium alloy and lithium carbonate.

[0096] Figure 1 A schematic diagram of a negative electrode plate after cycling provided in an embodiment of the present application.

[0097] like Figure 1 As shown, in one embodiment, per unit area, the mass content of the inorganic lithium salt in the lithium deposition region s1 is greater than the mass content of the inorganic lithium salt in the non-lithium deposition region s2.

[0098] Specifically, the SEI film is formed after lithium ionization, and its components generally include inorganic lithium salts and organic matter. Therefore, on the negative electrode plate 1, the SEI film itself in the lithium deposition area s1 and the non-lithium deposition area s2 includes inorganic lithium salts. In the case of lithium deposition in the battery, the lithium-philic metal in the lithium deposition area s1 will react with the deposited lithium to form a lithium-metal alloy, and the lithium-metal alloy will further induce the electrolyte to reduce and decompose to form inorganic lithium salts; the lithium-philic metal compound will react with the deposited lithium to form a lithium-metal alloy and an inorganic lithium salt, and the lithium-metal alloy will further induce the electrolyte to reduce and decompose to form an inorganic lithium salt. Therefore, in the negative electrode plate 1 after the cycle, it can be measured that the mass content of the inorganic lithium salt in the lithium deposition area s1 is greater than that in the non-lithium deposition area s2.

[0099] [Positive electrode]

[0100] The positive electrode sheet includes a current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material. It should be understood that the current collector in the positive electrode sheet is also called a positive electrode current collector.

[0101] 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.

[0102] 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.).

[0103] In one embodiment, the positive electrode active material may adopt a positive electrode active material for a battery that is well 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. Among them, examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), 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 O2 (also referred to as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi 0.85 Co 0.15 Al 0.05O2) and at least one of its modified compounds. Examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and at least one of a composite material of lithium iron manganese phosphate and carbon. The battery is accompanied by the deintercalation and consumption of Li during the charging and discharging process, and the molar content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration 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, and the molar content of Li will change after charge and discharge cycles. In the enumeration of positive electrode active materials in this application, the molar content of O is only an ideal state value. The release of lattice oxygen will cause the molar content of O to change, and the actual molar content of O will fluctuate.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] [Electrolyte]

[0108] 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 includes electrolyte salt and solvent.

[0109] In one embodiment, the electrolyte salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

[0110] In one embodiment, the solvent includes 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.

[0111] In one embodiment, the electrolyte may further include additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain performance of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, etc.

[0112] [Isolator]

[0113] In one embodiment, the battery further includes a separator. The present application has no particular limitation on the type of separator, for example, any known porous structure separator with good chemical stability and mechanical stability can be selected.

[0114] In one embodiment, 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.

[0115] [Preparation method]

[0116] The embodiment of the present application also provides a method for preparing a negative electrode plate. Figure 2 The schematic flow chart of the preparation method of the negative electrode sheet is shown in FIG.

[0117] like Figure 2 As shown, the method 200 includes:

[0118] S201, preparing a coating layer on the surface of the negative electrode active material.

[0119] Wherein, the coating layer comprises a lithium-philic metal and / or a compound of the lithium-philic metal.

[0120] In one embodiment, the coating layer can be prepared on the surface of the negative electrode active material by a method for preparing a coating layer known in the art. For example, the coating layer can be prepared on the surface of the negative electrode active material by hydrothermal, chemical vapor deposition, atomic layer deposition, pre-coating followed by thermal reduction, etc. Different methods can be selected depending on the negative electrode active material.

[0121] Based on similar principles, the negative electrode plate in the aforementioned embodiment that can be prepared by method 200 has a lithium-philic metal and / or a lithium-philic metal compound and can achieve corresponding technical effects, which will not be elaborated here.

[0122] The present application also provides a lithium-ion battery, which includes the negative electrode sheet in any of the foregoing embodiments, and / or the negative electrode sheet prepared by the method in any of the foregoing embodiments.

[0123] 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.

[0124] In one embodiment, the battery cell may include an outer packaging, which may be used to encapsulate the electrode assembly and the electrolyte.

[0125] 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.

[0126] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 3 The battery cell 300 is a square structure as an example.

[0127] It should be understood that the battery cell 300 may include the lithium-ion battery in the aforementioned embodiment.

[0128] Figure 4 4 is a battery module 400 as an example. Figure 4 In the battery module 400, the plurality of battery cells 300 may be arranged in sequence along the length direction of the battery module 400. Of course, they may also be arranged in any other manner. The plurality of battery cells 300 may be further fixed by fasteners. The plurality of battery cells 300 may be battery cells 300 of the same chemical system or battery cells 300 of different chemical systems.

[0129] Optionally, in one embodiment, the battery module 400 may further include a housing having an accommodation space, and the plurality of battery cells 300 are accommodated in the accommodation space.

[0130] Optionally, in one embodiment, the battery modules 400 may also be assembled into a battery. The number of battery modules 400 contained in the battery may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery.

[0131] Figure 5and Figure 6 500 is an example of a battery. Figure 5 and Figure 6 The battery 500 may include a battery box and a plurality of battery modules 400 disposed in the battery box. The battery box includes an upper box body 501 and a lower box body 502. The upper box body 501 can cover the lower box body 502 and form a closed space for accommodating the battery modules 400. The plurality of battery modules 400 may be arranged in the battery box in any manner.

[0132] It should be understood that in other embodiments, the battery 500 is also referred to as a battery pack. The battery cells 300 may first form a battery module 400, and the battery 500 may be formed by the battery module 400. Alternatively, the battery 500 may be directly formed by the battery cells 300, omitting the intermediate form of the battery module 400.

[0133] In addition, the present application also provides an electrical device, which includes the lithium-ion battery in the aforementioned embodiment.

[0134] In another embodiment, the electrical device includes at least one of the battery cell 300, battery module 400, or battery 500 provided in the present application. The battery cell 300, battery module 400, or battery 500 can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical 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.

[0135] As an electric device, a battery cell 300, a battery module 400, or a battery 500 may be selected according to its usage requirements.

[0136] As an example of an electric device, the electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the electric device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module may be used.

[0137] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be thin and light, and a secondary battery may be used as a power source.

[0138] 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.

[0139] [Examples 1-10 and Comparative Examples 1-2]

[0140] Example 1

[0141] (1) Preparation of negative electrode sheet

[0142] Weigh 1kg of artificial graphite coated with magnesium oxide (negative electrode active material), 10g of acetylene black (conductive agent), 30g of styrene-butadiene rubber (binder), and 20g of sodium carboxymethyl cellulose, add them to 1kg of deionized water, mix them evenly to obtain negative electrode slurry, and then evenly coat the negative electrode slurry on the negative electrode current collector copper foil. Then roll and cut to obtain negative electrode sheets.

[0143] (2) Preparation of positive electrode sheet

[0144] 1 kg of LiNi5Co2Mn3O2 (positive electrode active material), 20 g of carbon nanotubes (conductive agent), and 20 g of polyvinylidene fluoride (binder) were added to 1 kg of N-methylpyrrolidone and mixed evenly to obtain positive electrode slurry. The positive electrode slurry was then evenly coated on the positive electrode current collector aluminum foil. After rolling and cutting, the positive electrode sheet was obtained.

[0145] (3) Preparation of lithium-ion batteries

[0146] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet and can separate the positive electrode sheet from the negative electrode sheet; then the stacked components are wound up and placed in a shell, and after drying, 1 mol / L LiPF6 electrolyte is injected, and a lithium-ion battery is obtained after packaging.

[0147] (4) Lithium-ion battery formation

[0148] The packaged lithium-ion battery was formed according to the following process: standing for 1 minute, charging at a constant current of 8 mA to 4.2 V, then charging at a constant voltage of 4.2 V with a cut-off current of 2 mA, standing for 10 minutes, discharging at a constant current of 8 mA with a cut-off voltage of 2.5 V, and standing for 50 hours.

[0149] In Example 1, the negative electrode active material is artificial graphite, the coating layer includes a lithium-philic metal compound magnesium oxide, and the thickness of the coating layer is d=5nm. After the lithium-ion battery in Example 1 is formed, the mass content of the inorganic lithium salt c0 is 36.2% based on the mass of the SEI film. After the lithium-ion battery in Example 1 is cycled, the mass content of the metal lithium salt in the lithium precipitation area c1 is 40.8% based on the mass of the SEI film; the mass content of the metal lithium salt in the non-lithium precipitation area c2 is 37.1% based on the mass of the SEI film.

[0150] Example 2

[0151] Compared with Example 1, in Example 2, the coating layer includes magnesium fluoride.

[0152] Example 3

[0153] Compared with Example 1, in Example 3, the coating layer includes lithium-philic metal magnesium.

[0154] Example 4

[0155] Compared with Example 1, in Example 4, the coating layer includes lithium-philic metal zinc.

[0156] Example 5

[0157] Compared with Example 1, in Example 5, the coating layer includes lithium-philic metal magnesium and a lithium-philic metal compound magnesium oxide.

[0158] Example 6

[0159] Compared with Example 1, in Example 6, the coating layer includes lithium-philic metal zinc and a lithium-philic metal compound zinc oxide.

[0160] Example 7

[0161] Compared with Example 1, in Example 7, the negative electrode active material includes natural graphite.

[0162] Example 8

[0163] Compared with Example 1, in Example 8, d=1 nm.

[0164] Example 9

[0165] Compared with Example 1, in Example 9, d=10 nm.

[0166] Example 10

[0167] Compared with Example 1, in Example 10, d=100 nm.

[0168] Comparative Example 1

[0169] Compared with Example 1, Comparative Example 1 directly uses artificial graphite without a coating layer as the negative electrode active material.

[0170] Comparative Example 2

[0171] Compared with Example 1, the artificial graphite in Comparative Example 2 has a coating layer, but the coating layer does not contain lithium-philic metals or lithium-philic metal compounds.

[0172] The product parameters and performance data of Examples 1-10 and Comparative Examples 1-2 are detailed in Table 1.

[0173] Table 1: Product parameters and performance data of Examples 1-10 and Comparative Examples 1-2

[0174] In Table 1, "d" represents the thickness of the coating layer on the surface of the negative electrode active material layer; "SEI film after formation" represents the substances included in the SEI film generated after the formation reaction; "SEI film after cycle" represents the substances included in the SEI film after cyclic lithium precipitation; "c0" represents the percentage of inorganic lithium salts in the SEI film on the surface of the negative electrode of the lithium-ion battery after formation; "c1" represents the percentage of inorganic lithium salts in the SEI film in the area where lithium is not precipitated on the surface of the negative electrode after the lithium-ion battery is cycled (lithium precipitation); "c2" represents the percentage of inorganic lithium salts in the SEI film in the area where lithium is precipitated on the surface of the negative electrode after the lithium-ion battery is cycled (lithium precipitation); "capacity retention rate" represents the capacity retention rate of the lithium-ion battery after 200 cycles after formation; "inorganic lithium salts" include lithium oxide, lithium fluoride, and lithium carbonate.

[0175] It should be understood that the SEI film after formation and the SEI film after cycling also include components such as organic matter that are not reflected in Table 1.

[0176] The specific formation process, cycle process and performance test of the above-mentioned Examples 1-10 and Comparative Examples 1-2 will be described in detail later.

[0177] According to the comparative analysis of Examples 1-10 and Comparative Examples 1-2 in Table 1, it can be seen that by introducing lithium-philic metals and / or lithium-philic metal compounds into the coating layer of the negative electrode active material, it is helpful to induce uniform lithium deposition and inhibit lithium precipitation during the cycle of the lithium-ion battery, thereby effectively improving the capacity retention rate of the lithium-ion battery.

[0178] Through comparative analysis of Example 1 and Examples 8-10, it can be seen that by controlling the thickness of the coating layer within a suitable range, the amount of lithium-philic metal and / or lithium-philic metal compound in the coating layer can be indirectly controlled. It can be seen that the thicker the coating layer, the more lithium-philic metal and / or lithium-philic metal compound, the stronger the inhibitory effect on lithium precipitation, and the higher the capacity retention rate of the lithium-ion battery. In addition, since the coating layer does not contribute to capacity and affects the dynamics, the capacity retention rate of Example 10 is slightly lower than that of Example 9. Therefore, a coating layer that is too thick is not conducive to the energy density and dynamics of the lithium-ion battery. Therefore, by controlling the thickness of the coating layer within a suitable range, it helps to improve the capacity retention rate of the lithium-ion battery while reducing the impact on the energy density of the lithium-ion battery.

[0179] 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.

[0180] 1. Test method for mass content of inorganic lithium salt

[0181] 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 negative electrode surface was calculated based on the energy spectrum intensity of lithium, oxygen, carbon, and fluorine elements.

[0182] 2. Thickness test method

[0183] By observing the surface of the negative electrode active material particles through a high-resolution transmission electron microscope, the thickness of the coating layer on the graphite surface can be observed, and the material of the coating layer can be determined by the lattice fringes and energy spectrum analysis of the coating layer.

[0184] 3. Test method for capacity retention of lithium-ion batteries

[0185] Use the Blue Electric test system to perform charge and discharge tests on the formed lithium-ion batteries.

[0186] First, the lithium-ion battery is charged and discharged for the first cycle. The first cycle discharge capacity W1 refers to the capacity W1 released by the battery when the battery is discharged at a constant current of 160mA to a voltage of 2.5V for the first time. After the first cycle of charge and discharge, the lithium-ion battery is cyclically charged and discharged. The cyclic charge and discharge process is: charging at a constant current of 160mA, with a cut-off voltage of 4.2V; constant voltage charging at 4.2V, with a cut-off current of 8mA; after standing for 10 minutes, discharge at a constant current of 1mA, with a cut-off voltage of 2.5V, and charge to 4.2V after 200 cycles before the test stops. The discharge capacity after 200 cycles is W2. The capacity retention rate of the lithium-ion battery after 200 cycles is W2 / W1×100%.

[0187] Although the present application has been described with reference to preferred embodiments, various modifications may be made thereto and parts thereof may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner as long as there are no structural conflicts. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A negative electrode active material, characterized in that: The negative electrode active material comprises: A negative electrode active material and a coating layer on the surface of the negative electrode active material; The coating layer includes a lithium-philic metal and / or a compound of the lithium-philic metal.

2. The negative electrode active material according to claim 1, characterized in that: The lithium-philic metal includes at least one of magnesium, tin, zinc, antimony, silver, and indium.

3. The negative electrode active material according to claim 1 or 2, characterized in that: The lithium-philic metal compound includes at least one of an oxide of the lithium-philic metal, a fluoride of the lithium-philic metal, and a carbonate of the lithium-philic metal.

4. The negative electrode active material according to any one of claims 1 to 3, characterized in that The negative electrode active material includes at least one of natural graphite, artificial graphite, hard carbon, soft carbon, carbon microspheres, silicon, silicon oxide, silicon carbon, and lithium titanate.

5. The negative electrode active material according to any one of claims 1 to 4, characterized in that The thickness d of the coating layer satisfies: 1nm≤d≤100nm; optionally, 5nm≤d≤10nm.

6. A negative electrode plate, characterized in that: The negative electrode sheet comprises the negative electrode active material according to any one of claims 1 to 5.

7. A negative electrode plate, characterized in that: The negative electrode plate comprises: A current collector and a negative electrode active material layer disposed on at least one side of the current collector; The SEI film is disposed on the negative electrode active material layer, and the SEI film includes a lithium-philic metal and / or a compound of the lithium-philic metal.

8. The negative electrode sheet according to claim 7, characterized in that: The lithium-philic metal includes at least one of magnesium, tin, zinc, antimony, silver, and indium.

9. The negative electrode sheet according to claim 7 or 8, characterized in that: The lithium-philic metal compound includes at least one of an oxide of the lithium-philic metal, a fluoride of the lithium-philic metal, and a carbonate of the lithium-philic metal.

10. A negative electrode plate, characterized in that: The negative electrode plate comprises: A current collector and a negative electrode active material layer disposed on at least one side of the current collector; The SEI film is disposed on the negative electrode active material layer, and the SEI film includes a lithium-metal alloy.

11. The negative electrode sheet according to claim 10, characterized in that: The lithium-metal alloy includes: an alloy formed by a lithium-philic metal and lithium; and / or an alloy formed by a lithium-philic metal compound and lithium.

12. The negative electrode sheet according to claim 10 or 11, characterized in that: The SEI film further comprises an inorganic lithium salt, and the inorganic lithium salt comprises: At least one of lithium oxide, lithium fluoride and lithium carbonate.

13. The negative electrode sheet according to claim 12, characterized in that: The negative electrode plate includes a lithium deposition area and a non-lithium deposition area; Per unit area, the mass content of the inorganic lithium salt in the lithium deposition area is greater than the mass content of the inorganic lithium salt in the non-lithium deposition area.

14. A lithium ion battery, characterized in that: The lithium-ion battery comprises at least one of the negative electrode sheet according to claim 6, the negative electrode sheet according to any one of claims 7 to 9, and the negative electrode sheet according to any one of claims 10 to 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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