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

[0001] This application is a divisional application of the invention application with the application number of 202310791513.8, the title of "Negative electrode active material, negative electrode sheet, lithium ion battery and electric device", and the filing date of June 30, 2023. TECHNICAL FIELD

[0002] The present application relates to the field of batteries, and more particularly, to a negative electrode active material, a negative electrode sheet, a lithium ion battery and an electric device. BACKGROUND

[0003] In recent years, lithium ion batteries have been widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc., thus obtaining great development.

[0004] Lithium dendrites are dendritic lithium metal formed by further deposition of lithium after lithium precipitation occurs on the negative electrode sheet during the cycle process of lithium ion batteries. The existence of lithium dendrites can easily lead to a decrease in reversible capacity, a decrease in coulombic efficiency, and a deterioration in cycle performance of lithium ion batteries, and in severe cases, can also pierce the separator to cause a short circuit between the positive and negative electrodes. Therefore, how to inhibit the growth of lithium dendrites is a technical problem to be solved. SUMMARY

[0005] The present application is made in view of the above technical problems, and aims to provide a negative electrode active material, a negative electrode sheet, a lithium ion battery and an electric device. When the negative electrode active material is applied to a negative electrode sheet, a lithium ion battery and an electric device, it can effectively inhibit lithium precipitation, and help to improve the capacity retention rate and cycle performance of the battery.

[0006] In a first aspect, a negative electrode active material is provided, which comprises a negative electrode active substance and a coating layer on the surface of the negative electrode active substance; the coating layer comprises a lithiumophilic metal and / or a compound of the lithiumophilic metal.

[0007] In an embodiment of the present application, by providing a coating layer containing a lithiumophilic metal and / or a compound of the lithiumophilic metal on the surface of the negative electrode active material, the SEI film on the surface of the negative electrode active material after formation reaction contains the lithiumophilic metal and / or the compound of the lithiumophilic metal. The lithiumophilic metal and / or the compound of the lithiumophilic metal can induce uniform deposition of lithium during the cycle process of the lithium ion battery, thereby inhibiting the growth of lithium dendrites. In addition, in the case of lithium precipitation occurring on the negative electrode sheet, the lithiumophilic metal can react with lithium to form lithium-metal alloy; the compound of the lithiumophilic metal can react with lithium to form lithium-metal alloy and inorganic lithium salt. Thus, the negative electrode active material can effectively inhibit lithium precipitation and the growth of lithium dendrites, and help to improve the capacity retention rate and cycle performance of the lithium ion battery.

[0008] In one possible implementation, the lithium-loving metal includes at least one of magnesium, tin, zinc, antimony, silver, and indium.

[0009] In one possible implementation, the lithium-ion metal compound includes at least one of the following: an oxide of the lithium-ion metal, a fluoride of the lithium-ion metal, and a carbonate of the lithium-ion metal.

[0010] In one 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.

[0011] In one possible implementation, the mass content 'a' of the coating layer, based on the weight of the negative electrode active material, satisfies: 0.1% ≤ a ≤ 2%; alternatively, 0.5% ≤ a ≤ 2%.

[0012] In one possible implementation, the thickness d of the coating layer satisfies: 1 nm ≤ d ≤ 100 nm; alternatively, 5 nm ≤ d ≤ 10 nm.

[0013] In the embodiments of this application, by controlling the mass content and thickness of the coating layer within a suitable range, it is helpful to suppress lithium plating while reducing the impact of the coating layer on the energy density of the lithium-ion battery.

[0014] In one possible implementation, the negative electrode active material comprises a carbon-based material.

[0015] In one possible implementation, the carbon-based material includes artificial graphite, natural graphite, soft carbon, hard carbon, graphene, and carbon nanotubes.

[0016] In a second aspect, a negative electrode sheet is provided, the negative electrode sheet comprising the negative electrode active material in any possible implementation of the first aspect.

[0017] Thirdly, a negative electrode sheet is provided, the negative electrode sheet comprising: a current collector and a negative electrode active material layer disposed on at least one side of the current collector; an SEI film disposed on the negative electrode active material layer, the SEI film comprising a lithium-philic metal and / or a compound of the lithium-philic metal.

[0018] In one possible implementation, the lithium-loving metal includes at least one of magnesium, tin, zinc, antimony, silver, and indium.

[0019] In one possible implementation, the lithium-ion metal compound includes at least one of the following: an oxide of the lithium-ion metal, a fluoride of the lithium-ion metal, and a carbonate of the lithium-ion metal.

[0020] Fourthly, a negative electrode sheet is provided, the negative electrode sheet comprising: a current collector and a negative electrode active material layer disposed on at least one side of the current collector; and an SEI film disposed on the negative electrode active material layer, the SEI film comprising a lithium-metal alloy.

[0021] In one possible implementation, the lithium-metal alloy comprises an alloy formed of a lithium-loving metal and lithium; and / or an alloy formed of a compound of a lithium-loving metal and lithium.

[0022] In one possible implementation, the SEI membrane further includes an inorganic lithium salt, which includes at least one of lithium oxide, lithium fluoride, and lithium carbonate.

[0023] In one possible implementation, the negative electrode includes a lithium-plated region and a non-lithium-plated region; per unit area, the mass content of the inorganic lithium salt in the lithium-plated region is greater than the mass content of the inorganic lithium salt in the non-lithium-plated region.

[0024] Fifthly, a method for preparing a negative electrode sheet is provided, the method comprising: preparing a coating layer on the surface of a negative electrode active material; the coating layer comprising a lithium-philic metal and / or a compound of the lithium-philic metal.

[0025] In a sixth aspect, a lithium-ion battery is provided, the lithium-ion battery comprising at least one negative electrode sheet in any possible implementation of the second, third, and fourth aspects.

[0026] In a seventh aspect, an electrical device is provided, the electrical device comprising the lithium-ion battery of the sixth aspect. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of a negative electrode sheet according to an embodiment of this application.

[0029] Figure 2 This is a schematic flowchart illustrating a method for preparing a negative electrode sheet according to this application.

[0030] Figure 3 This is a schematic diagram of a single battery cell.

[0031] Figure 4 This is a schematic diagram of a battery module.

[0032] Figure 5 This is a schematic diagram of a type of battery.

[0033] Figure 6 This is another schematic diagram of a battery. Detailed Implementation

[0034] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the negative electrode active material, negative electrode sheet, lithium-ion battery, and power application device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0035] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the lithium-ion battery, its preparation method, and the power-using device thereof. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0036] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0037] In the description of this application, it should be noted that, unless otherwise stated, "a plurality of" means two or more; the terms "upper," "lower," "left," "right," "inner," "outer," etc., indicating orientation 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 orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, the terms "first," "second," "third," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0038] Unless otherwise specified, in this application, the phrase "A and / or B" means "A, B, or both A and B". More specifically, the condition "A and / or B" is satisfied by any of the following conditions: 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).

[0039] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0040] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0041] Unless otherwise specified, the following terms have the following meanings. Any undefined terms have their technically accepted meanings.

[0042] If mentioned, "lithophile metals" refers to elemental metals that can form lithium-metal alloys with lithium, such as magnesium, zinc, and aluminum.

[0043] If mentioned, "lithophile metal compounds" refers to compounds of metallic elements that can form lithium-metal alloys with lithium. Examples include fluorides and carbonates.

[0044] If mentioned, "lithium dendrites" refers to the dendritic metallic lithium formed when lithium ions are reduced during the cycling process of a lithium-ion battery.

[0045] If mentioned, "SEI film" refers to the solid electrolyte interface (SEI) film. The SEI film is a passivation layer formed on the surface of the active material by the reaction between the active material and the electrolyte at the solid-liquid interface during the charging process of a lithium-ion battery.

[0046] The embodiments of this application will be described next.

[0047] In recent years, rechargeable batteries have seen significant development due to their high energy density and long lifespan, finding widespread application in power tools, electronic products, electric vehicles, aerospace, and other fields. Typically, a rechargeable battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of these active ions between the electrodes. The separator, positioned between the positive and negative electrodes, prevents short circuits while allowing active ions to pass through, ensuring the normal electrochemical reaction of the rechargeable battery.

[0048] Taking lithium-ion batteries as an example, lithium-ion batteries are a typical type of rechargeable battery. Because they rely on the chemical reaction of lithium ions intercalating and deintercalating between the positive and negative electrodes for charging and discharging, lithium-ion batteries are also known as rocking chair batteries. During the charging process of a lithium-ion battery, lithium ions are extracted from the positive electrode active material, move to the negative electrode through the conduction of the electrolyte, and intercalate into the negative electrode active material; while during the discharging process, lithium ions are extracted from the negative electrode active material, move to the positive electrode through the conduction of the electrolyte, and intercalate into the positive electrode active material.

[0049] It should be understood that the “lithium intercalation” or “intercalation” process described in this application refers to the process in which lithium ions are intercalated into the positive electrode active material or the negative electrode active material due to an electrochemical reaction, while the “de-lithium extraction”, “de-lithium extraction”, or “de-intercalation” process described in this application refers 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.

[0050] During the charging and discharging process of a lithium-ion battery, factors such as changes in the battery's internal resistance, the balance between the rates of electrochemical reactions at the positive and negative electrodes and the speed of electron movement, and the diffusion rate of lithium ions participating in the electrochemical reactions all contribute to battery polarization. This causes lithium ions to deposit from the surface of the negative electrode active material layer, a process known as lithium plating. Further lithium ion deposition can lead to the formation and growth of lithium dendrites. The formation and growth of lithium dendrites continuously consume lithium ions, resulting in a decrease in battery capacity and cycle life. In severe cases, lithium dendrites may even puncture the separator, causing a short circuit between the positive and negative electrodes and triggering battery safety issues.

[0051] In view of this, embodiments of this application provide a negative electrode active material, a negative electrode sheet, a method for preparing the same, a lithium-ion battery, and a power 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 uniform deposition of lithium ions on the negative electrode sheet during the cycling process of the lithium-ion battery, thereby inhibiting the growth of lithium dendrites. Furthermore, once lithium plating occurs on the negative electrode sheet, the lithium-philic metal and / or the lithium-philic metal compound can react with the deposited lithium to form an alloy, inhibiting lithium plating or the growth of lithium dendrites. Therefore, when this negative electrode active material is applied to a lithium-ion battery, it can effectively inhibit lithium plating and lithium dendrite growth, helping to improve the capacity retention and cycle performance of the lithium-ion battery.

[0052] 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 compound of a lithium-philic metal.

[0053] It should be understood that "the coating layer includes a lithium-philic metal and / or a lithium-philic metal compound" can mean that the coating layer includes only a lithium-philic metal, or that the coating layer includes only a lithium-philic metal compound, or that the coating layer includes both a lithium-philic metal and a lithium-philic metal compound. In the case where the coating layer includes both a lithium-philic metal and a lithium-philic metal compound, the metal element in the lithium-philic metal compound can be the same as or different from the element in the lithium-philic metal compound.

[0054] For example, the coating may consist of only zinc, only zinc carbonate, or both zinc and zinc carbonate.

[0055] For example, the coating layer may consist of only magnesium, only magnesium carbonate, or both magnesium and magnesium carbonate.

[0056] In one embodiment, the lithium-loving metal includes at least one selected from magnesium, tin, zinc, antimony, silver, and indium.

[0057] In one embodiment, the lithium-ion metal compound includes at least one of the following: lithium-ion metal oxide, lithium-ion metal fluoride, and lithium-ion metal carbonate.

[0058] Specifically, lithium-loving metals such as magnesium, tin, zinc, antimony, silver, and indium can react with lithium to form lithium-metal alloys. Compounds of these lithium-loving metals, such as oxides, fluorides, and carbonates, can also react with lithium to form lithium-metal alloys and inorganic lithium salts. Therefore, negative electrode active materials containing lithium-loving metals and / or compounds of lithium-loving metals can effectively suppress lithium plating.

[0059] 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.

[0060] In one embodiment, the mass content 'a' of the coating layer, based on the weight of the negative electrode active material, satisfies: 0.1% ≤ a ≤ 2%; optionally, 0.5% ≤ a ≤ 2%.

[0061] 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 can be within the range obtained by combining any two of the above values.

[0062] On the one hand, the coating layer contains lithium-loving metals and / or lithium-loving metals that can effectively suppress lithium plating. If the mass content of the coating layer is too low, the effect of the negative electrode active material in suppressing lithium plating is limited. On the other hand, the coating layer does not participate in the charge-discharge reaction of the lithium-ion battery and cannot contribute to the capacity of the lithium-ion battery. An excessively high coating layer content is detrimental to improving the energy density of the lithium-ion battery.

[0063] Therefore, by controlling the mass content 'a' of the coating layer within a suitable range, this embodiment can effectively suppress lithium plating while reducing the impact of the coating layer on the energy density of the lithium-ion battery.

[0064] In one embodiment, the thickness d of the coating layer satisfies: 1 nm ≤ d ≤ 100 nm; optionally, 5 nm ≤ d ≤ 10 nm.

[0065] Specifically, d can be 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 76 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, or a value within the range obtained by any combination of the above two values.

[0066] On the one hand, all other things being equal, the thicker the coating layer, the higher the content of lithium-philic metals and / or lithium-philic metal compounds in the negative electrode active material, and the better the inhibition effect on lithium plating. On the other hand, the thicker the coating layer, the greater its mass proportion in the negative electrode active material, and the greater its impact on the energy density of the negative electrode active material.

[0067] Therefore, in this embodiment, by controlling the thickness d of the coating layer within a suitable range, it is possible to effectively suppress lithium plating while reducing the impact of the coating layer on the energy density of the lithium-ion battery.

[0068] Typically, a lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The following sections will describe each component of the lithium-ion battery provided in this application.

[0069] [Negative electrode plate] A negative electrode typically includes a current collector and a layer of negative electrode active material disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material. It should be understood that the current collector in the negative electrode is also referred to as the negative electrode current collector.

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

[0071] In one embodiment, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric 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 polymeric material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0072] The foregoing embodiments have listed some possible negative electrode active materials. In another embodiment, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may also include at least one of the following materials: silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional 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 foregoing embodiments, some possible lithiophilic metals have been listed. In another embodiment, the negative electrode active material layer comprises a lithiophilic metal and / or a compound of a lithiophilic metal. The lithiophilic metal may also be other metals known in the art capable of forming alloys with lithium. As an example, the lithiophilic metal may include at least one of the following metals: Al, Sr, Ba, Sc, Y, Rh, Ir, Pd, Pt, Au, Cd, Ga, Ge, Pb, and 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. The conductive agent includes at least one selected from 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 also includes other additives, such as thickeners (e.g., sodium carboxymethyl cellulose, CMC-Na).

[0077] In one embodiment, the negative electrode sheet can be prepared by forming a negative electrode slurry using the components described above. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent to form the negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, and after processes such as drying and rolling, the negative electrode sheet is obtained.

[0078] The above embodiments illustrate negative electrode sheets that can effectively suppress lithium plating and lithium dendrite growth. Next, the negative electrode sheets obtained after formation of a lithium-ion battery composed of the above negative electrode sheets will be described.

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

[0080] Typically, after formation, a SEI film forms on the surface of the negative electrode active material layer in a lithium-ion battery. The SEI film is a passivation layer covering the surface of the negative electrode active material layer, formed during the formation process when the negative electrode active material and the electrolyte react at the solid-liquid interface. Therefore, in this embodiment, the coating layer of the negative electrode active material can participate in the formation of the SEI film, resulting in the formed SEI film containing a lithium-philic metal and / or a lithium-philic metal compound.

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

[0082] In one embodiment, the lithium-ion metal compound includes at least one of lithium-ion metal oxides, lithium-ion metal fluorides, and lithium-ion metal carbonates.

[0083] Next, the negative electrode sheet obtained after cycling the lithium-ion battery composed of the negative electrode sheet in the aforementioned embodiments will be described.

[0084] It should be understood that, in the embodiments of this application, the cycled lithium-ion battery can be considered as a lithium-ion battery that has undergone lithium plating, i.e., a lithium-ion battery after lithium plating. As mentioned in the foregoing embodiments, the negative electrode active material, or the SEI film on the surface of the negative electrode active material layer, contains a lithium-philic metal and / or a lithium-philic metal compound. Therefore, in the cycled lithium-ion battery, once lithium plating occurs at the negative electrode, the deposited lithium will be consumed by the lithium-philic metal and / or a lithium-philic metal compound, resulting in the negative electrode of the cycled lithium-ion battery comprising a lithium-metal alloy.

[0085] Based on this, embodiments of this application also provide a negative electrode sheet, the negative electrode sheet comprising: a current collector and a negative electrode active material layer disposed on at least one side of the current collector; an SEI film disposed on the negative electrode active material layer, wherein the SEI film comprises a lithium-metal alloy.

[0086] Specifically, when lithium plating first occurs on the surface of the negative electrode active material layer, the deposited lithium can react with the lithium-philic metal in the negative electrode active material layer to form a lithium-metal alloy. Therefore, the SEI (Sediment Interphase) of a cycled lithium-ion battery includes a lithium-metal alloy.

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

[0088] For example, when 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 lithium-bearing metal compound and lithium. In other words, when the negative electrode active material coating layer includes only a lithium-bearing metal compound, or includes both lithium-bearing metals and lithium-bearing metal compounds, the lithium-metal alloy in the SEI film is formed by the reaction of the lithium-bearing metal compound with deposited lithium; or by the reaction of both lithium-bearing metals and lithium-bearing metal compounds with deposited lithium.

[0090] For example, when 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] For example, when 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] For example, when 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 membrane further includes an inorganic lithium salt, which 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 deposited lithium, in addition to generating a lithium-metal alloy, an inorganic lithium salt is also generated. Thus, the SEI film of the negative electrode after cycling also includes the inorganic lithium salt generated by the reaction of the lithium-philic metal compound and lithium.

[0095] For example, when the coating layer of the negative electrode active material includes sodium carbonate, the sodium carbonate reacts with the deposited lithium to generate a lithium-sodium alloy and lithium carbonate.

[0096] Figure 1 This is a schematic diagram of a cycled negative electrode sheet provided in an embodiment of this application.

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

[0098] Specifically, the SEI film forms after lithium-ion formation, and its components generally include inorganic lithium salts and organic matter. Therefore, on the negative electrode 1, the SEI films in both the lithium-plated region s1 and the non-lithium-plated region s2 contain inorganic lithium salts. When lithium plating occurs in the battery, the lithiophilic metal in the lithium-plated region s1 reacts with the deposited lithium to form a lithium-metal alloy. This lithium-metal alloy further induces the electrolyte to reduce and decompose, generating inorganic lithium salts. The compounds of the lithiophilic metal react with the deposited lithium to form both lithium-metal alloys and inorganic lithium salts, and the lithium-metal alloy further induces the electrolyte to reduce and decompose, generating inorganic lithium salts. Therefore, after cycling, the mass content of inorganic lithium salts in the lithium-plated region s1 is greater than that in the non-lithium-plated region s2.

[0099] [Positive electrode plate] 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 referred to as the positive electrode current collector.

[0100] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0101] In one embodiment, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. 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 substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0102] In one embodiment, the positive electrode active material may be a known positive electrode active material for batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional 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 include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium-containing phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. During the charging and discharging process, Li undergoes insertion / extraction and consumption, resulting in different molar contents of Li in the positive electrode active material when the battery is discharged to different states. In the examples of positive electrode active materials in this application, the molar content of Li refers to the initial state of the material, i.e., the state before feeding. After charge-discharge cycles, the molar content of Li changes when the positive electrode active material is applied to the battery system. In the examples of positive electrode active materials in this application, the molar content of O is only an ideal value; lattice oxygen release causes changes in the molar content of O, and the actual molar content of O will fluctuate.

[0103] 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), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0104] 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 selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0105] In one embodiment, the positive electrode sheet can be prepared by forming a positive electrode slurry from the components described above. For example, a first positive electrode active material and / or a second positive electrode active material, a conductive agent, a binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and after processes such as drying and rolling, the positive electrode sheet is obtained.

[0106] Electrolyte The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements. Electrolytes include electrolyte salts and solvents.

[0107] In one embodiment, the electrolyte salt includes 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 difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0108] In one embodiment, the solvent includes at least one selected from ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0109] In one embodiment, the electrolyte may also include additives, which may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0110] [Isolation Component] In one embodiment, the battery also includes a separator. This application does not impose any particular limitation on the type of separator; for example, any known porous membrane with good chemical and mechanical stability can be selected.

[0111] In one embodiment, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0112] [Preparation Method] This application also provides a method for preparing a negative electrode sheet. Figure 2 This is a schematic flowchart illustrating the preparation method of the negative electrode sheet.

[0113] like Figure 2 As shown, method 200 includes: S201, a coating layer is prepared on the surface of the negative electrode active material.

[0114] The coating layer includes a lithium-loving metal and / or a compound of the lithium-loving metal.

[0115] In one embodiment, a coating layer can be prepared on the surface of the negative electrode active material using methods known in the art. For example, the aforementioned coating layer can be prepared on the surface of the negative electrode active material using methods such as hydrothermal deposition, chemical vapor deposition, atomic layer deposition, or thermal reduction after pre-coating. Different methods can be selected depending on the negative electrode active material.

[0116] Based on a similar principle, the negative electrode sheet in the aforementioned embodiments can be prepared by method 200. It has a compound including a lithium-loving metal and / or a lithium-loving metal, which can achieve the corresponding technical effects, which will not be elaborated here.

[0117] This application also provides a lithium-ion battery, which includes the negative electrode sheet of any of the foregoing embodiments, and / or the negative electrode sheet prepared by the method of any of the foregoing embodiments.

[0118] In one embodiment, the negative electrode, the positive electrode, and the separator can be fabricated into an electrode assembly using a winding process or a stacking process.

[0119] In one embodiment, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0120] In one embodiment, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0121] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured battery cell, 300.

[0122] It should be understood that the battery cell 300 may include the lithium-ion battery in the foregoing embodiments.

[0123] Figure 4 This is a sample battery module 400. (See reference...) Figure 4 In the battery module 400, multiple battery cells 300 can be arranged sequentially along the length of the battery module 400. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 300 can be fixed in place using fasteners. The multiple battery cells 300 can be battery cells 300 with the same chemical system or battery cells 300 with different chemical systems.

[0124] Alternatively, in one embodiment, the battery module 400 may further include a housing with a receiving space in which a plurality of battery cells 300 are received.

[0125] Optionally, in one embodiment, the battery module 400 can also be assembled into a battery. The number of battery modules 400 contained in the battery can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery.

[0126] Figure 5and Figure 6 This is a battery 500 used as an example. (See reference...) Figure 5 and Figure 6 The battery 500 may include a battery box and multiple battery modules 400 disposed within the battery box. The battery box includes an upper box 501 and a lower box 502, with the upper box 501 covering the lower box 502 to form a closed space for accommodating the battery modules 400. The multiple battery modules 400 may be arranged in any manner within the battery box.

[0127] It should be understood that in some embodiments, the battery 500 described above is also referred to as a battery pack. The individual battery cells 300 can be first assembled into a battery module 400, and the battery 500 is composed of the battery module 400. Alternatively, the battery 500 can be directly assembled from the individual battery cells 300, omitting the intermediate form of the battery module 400.

[0128] In addition, this application also provides an electrical device that includes the lithium-ion battery described in the foregoing embodiments.

[0129] In another embodiment, the electrical device includes at least one of the battery cell 300, battery module 400, or battery 500 provided in this application. The battery cell 300, battery module 400, or battery 500 can be the power source of the electrical device or the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., 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.

[0130] As an electrical device, you can choose a single battery cell (300), a battery module (400), or a battery (500) depending on your usage requirements.

[0131] This is an example of an electrical device. The device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0132] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0133] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0134] [Examples 1-10 and Comparative Examples 1-2] Example 1 (1) Preparation of negative electrode sheet Weigh 1 kg of magnesium oxide-coated artificial graphite (negative electrode active material), 10 g of acetylene black (conductive agent), 30 g of styrene-butadiene rubber (binder), and 20 g of sodium carboxymethyl cellulose, and add them to 1 kg of deionized water. After mixing evenly, a negative electrode slurry is obtained. The negative electrode slurry is then uniformly coated onto the negative electrode current collector copper foil. After rolling and slitting, the negative electrode sheet is obtained.

[0135] (2) Preparation of positive electrode sheet 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 a positive electrode slurry. The positive electrode slurry was then uniformly coated onto a positive electrode current collector aluminum foil. Finally, the positive electrode sheet was obtained through rolling and slitting.

[0136] (3) Preparation of lithium-ion batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The stacked components are then wound into a housing, dried, and injected with 1 mol / L LiPF6 electrolyte. After encapsulation, a lithium-ion battery is obtained.

[0137] (4) Formation of lithium-ion batteries The packaged lithium-ion battery is formed according to the following process: after resting for 1 minute, it is charged at a constant current of 8mA to 4.2V, then charged at a constant voltage of 4.2V with a cutoff current of 2mA. After resting for 10 minutes, it is discharged at a constant current of 8mA with a cutoff voltage of 2.5V and then rested for 50 hours.

[0138] In Example 1, the negative electrode active material is artificial graphite, and the coating layer includes magnesium oxide, a lithium-philic metal compound, with a coating layer thickness d = 5 nm. After formation of the lithium-ion battery in Example 1, the mass content of inorganic lithium salt, c0 = 36.2% based on the mass of the SEI film. After cycling, the mass content of metallic lithium salt in the lithium-plated region of the lithium-ion battery in Example 1, c1 = 40.8% based on the mass of the SEI film; and the mass content of metallic lithium salt in the non-lithium-plated region, c2 = 37.1% based on the mass of the SEI film.

[0139] Example 2 Compared to Example 1, in Example 2, the coating layer includes magnesium fluoride.

[0140] Example 3 Compared to Example 1, in Example 3, the coating layer includes the lithium-loving metal magnesium.

[0141] Example 4 Compared to Example 1, in Example 4, the coating layer includes lithium-loving zinc.

[0142] Example 5 Compared to Example 1, in Example 5, the coating layer includes lithium-loving metal magnesium and lithium-loving metal compound magnesium oxide.

[0143] Example 6 Compared to Example 1, in Example 6, the coating layer includes lithium-loving zinc and zinc oxide, a compound of lithium-loving metals.

[0144] Example 7 Compared to Example 1, in Example 7, the negative electrode active material includes natural graphite.

[0145] Example 8 Compared to Example 1, in Example 8, d = 1 nm.

[0146] Example 9 Compared to Example 1, in Example 9, d = 10 nm.

[0147] Example 10 Compared to Example 1, in Example 10, d = 100 nm.

[0148] Comparative Example 1 Compared to Example 1, Comparative Example 1 directly used uncoated artificial graphite as the negative electrode active material.

[0149] Comparative Example 2 Compared to Example 1, the artificial graphite in Comparative Example 2 has a coating layer, but the coating layer does not contain lithium-loving metals or lithium-loving metal compounds.

[0150] The product parameters and performance data of Examples 1-10 and Comparative Examples 1-2 are detailed in Table 1.

[0151] Table 1: Product parameters and performance data of Examples 1-10 and Comparative Examples 1-2

[0152] 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 cycling" represents the substances included in the SEI film after lithium plating cycling; "c0" represents the percentage content of inorganic lithium salts in the SEI film on the negative electrode surface after lithium-ion battery formation; "c1" represents the percentage content of inorganic lithium salts in the SEI film of the non-lithium-plated area on the negative electrode surface after lithium-ion battery cycling (lithium plating); "c2" represents the percentage content of inorganic lithium salts in the SEI film of the lithium-plated area on the negative electrode surface after lithium-ion battery cycling (lithium plating); "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.

[0153] It should be understood that the SEI membrane after formation and the SEI membrane after cycling also contain organic matter and other components not shown in Table 1.

[0154] The specific formation process, cycle process and performance test of Examples 1-10 and Comparative Examples 1-2 will be described in detail later.

[0155] According to the comparative analysis of Examples 1-10 and Comparative Examples 1-2 in Table 1, it can be seen that by introducing a lithium-loving metal and / or a lithium-loving metal compound into the coating layer of the negative electrode active material, it is helpful to induce uniform lithium deposition and suppress lithium plating during the cycling process of lithium-ion batteries, thereby effectively improving the capacity retention rate of lithium-ion batteries.

[0156] Comparative analysis of Examples 1 and 8-10 shows that by controlling the thickness of the coating layer within a suitable range, the amount of lithium-philic metal and / or lithium-philic metal compounds in the coating layer can be indirectly controlled. It can be seen that the thicker the coating layer, the greater the amount of lithium-philic metal and / or lithium-philic metal compounds, the stronger the inhibition of lithium plating, and the higher the capacity retention rate of the lithium-ion battery. Furthermore, since the coating layer does not contribute to capacity and affects kinetics, the capacity retention rate of Example 10 is slightly lower than that of Example 9. Therefore, an excessively thick coating layer is detrimental to the energy density and kinetics of the lithium-ion battery. Thus, controlling the thickness of the coating layer within a suitable range helps to improve the capacity retention rate of the lithium-ion battery while reducing its impact on the energy density.

[0157] The following is a brief description of the testing methods for the physicochemical and performance parameters involved in the embodiments of this application. It should be understood that the following testing methods are only examples, and other testing methods known in the art can also be used for testing.

[0158] 1. Test method for the mass content of inorganic lithium salts After disassembling the cycled lithium-ion battery, the surface of the negative electrode was cleaned with DMC and then subjected to X-ray photoelectron spectroscopy. 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.

[0159] 2. Thickness testing methods High-resolution transmission electron microscopy (HRTEM) allows observation of the surface of negative electrode active material particles, revealing the thickness of the graphite coating layer. Furthermore, the material composition of the coating layer can be determined through lattice fringes and energy dispersive spectroscopy (EDS) analysis.

[0160] 3. Test methods for capacity retention of lithium-ion batteries The Blue Electric testing system was used to perform charge and discharge tests on the formed lithium-ion batteries.

[0161] First, the lithium-ion battery underwent its first charge-discharge cycle. The initial discharge capacity W1 refers to the capacity released when the battery was first discharged at a constant current of 160 mA to a voltage of 2.5 V. After the first charge-discharge cycle, the lithium-ion battery was subjected to cyclic charge-discharge, as follows: constant current charging at 160 mA with a cutoff voltage of 4.2 V; constant voltage charging at 4.2 V with a cutoff current of 8 mA; after resting for 10 minutes, constant current discharging at 1 mA with a cutoff voltage of 2.5 V; after 200 cycles, the battery was charged again to 4.2 V before the test stopped. The discharge capacity after 200 cycles is W2. The capacity retention rate of the lithium-ion battery after 200 cycles is W2 / W1×100%.

[0162] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This 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 includes: Negative electrode active material and the coating layer on the surface of the negative electrode active material; The coating layer comprises a lithium-loving metal and / or a compound of the lithium-loving metal.

2. The negative electrode active material according to claim 1, characterized in that, The lithiophilic 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-ion metal compound includes at least one of the following: lithium-ion metal oxide, lithium-ion metal fluoride, and lithium-ion metal carbonate.

4. The negative electrode active material according to any one of claims 1-3, 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 1-4, characterized in that, The thickness d of the coating layer satisfies: 1 nm ≤ d ≤ 100 nm; optionally, 5 nm ≤ d ≤ 10 nm.

6. A negative electrode sheet, characterized in that, The negative electrode sheet comprises the negative electrode active material as described in any one of claims 1-5.

7. A negative electrode sheet, characterized in that, The negative electrode sheet includes: A current collector and a negative electrode active material layer disposed on at least one side of the current collector; SEI film, wherein the SEI film is disposed on the negative electrode active material layer, the SEI film comprising 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 lithiophilic 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-ion metal compound includes at least one of the following: lithium-ion metal oxide, lithium-ion metal fluoride, and lithium-ion metal carbonate.

10. A negative electrode sheet, characterized in that, The negative electrode sheet includes: A current collector and a negative electrode active material layer disposed on at least one side of the current collector; SEI film, wherein the SEI film is disposed on the negative electrode active material layer, the SEI film comprising 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 lithiophilic metal and lithium; and / or an alloy formed by a compound of a lithiophilic metal and lithium.

12. The negative electrode sheet according to claim 10 or 11, characterized in that, The SEI membrane further includes an inorganic lithium salt, which 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 sheet includes a lithium-plated region and a non-lithium-plated region; Within a unit area, the mass content of the inorganic lithium salt in the lithium-plated region is greater than the mass content of the inorganic lithium salt in the non-lithium-plated region.

14. A lithium-ion battery, characterized in that, The lithium-ion battery includes at least one of the negative electrode sheet as described in claim 6, the negative electrode sheet as described in any one of claims 7-9, and the negative electrode sheet as described in any one of claims 10-13.

15. An electrical appliance, characterized in that, The electrical device includes the lithium-ion battery as described in claim 14.

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