Lithium-ion battery and preparation method therefor, and electric device

Abstract

A lithium-ion battery and a preparation method therefor, and an electric device. The lithium-ion battery comprises: a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode active material and a solid electrolyte interface layer, the solid electrolyte interface layer comprises a first film layer and a second film layer, the first film layer covers at least part of the surface of the negative electrode active material, and the second film layer covers at least part of the surface of the side of the first film layer away from the negative electrode active material; and the oxygen content of the second film layer is greater than the oxygen content of the first film layer. The solid electrolyte interface layer in the lithium-ion battery has a double-layer structure and strong stability, and can reduce active lithium loss and lithium ion transmission impedance during cycling, thereby improving the cycle stability of the battery.

Description

Lithium-ion batteries, their preparation methods, and electrical equipment

[0001] Priority information

[0002] This disclosure claims priority to Chinese Patent Application No. 202411228220.X, filed with the China National Intellectual Property Administration on September 2, 2024, entitled "Lithium-ion Battery and Method for Preparation Thereof and Electrical Equipment Thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery technology, specifically to negative electrode sheets, lithium-ion batteries, their preparation methods, and electrical equipment. Background Technology

[0004] In recent years, lithium-ion batteries have been widely used in the field of portable power sources, but with social development, people have increasingly higher requirements for the performance of lithium-ion batteries. Summary of the Invention

[0005] This disclosure aims to at least partially address one of the technical problems in the related art. To this end, one objective of this disclosure is to provide a negative electrode sheet, a lithium-ion battery, a method for preparing the same, and an electrical device thereof. The lithium-ion battery of this disclosure has a double-layer structure in its solid electrolyte interface layer, exhibiting strong stability and reducing active lithium loss and lithium-ion transport impedance during battery cycling, thereby improving battery cycle stability.

[0006] In a first aspect, this disclosure provides a lithium-ion battery. According to an embodiment of this disclosure, the lithium-ion battery includes:

[0007] The negative electrode sheet includes a negative electrode active material;

[0008] A solid electrolyte interface layer, comprising a first film layer and a second film layer, wherein the first film layer covers at least a portion of the surface of the negative electrode active material, and the second film layer covers at least a portion of the surface of the first film layer on the side away from the negative electrode active material;

[0009] The oxygen content of the second membrane layer is greater than that of the first membrane layer.

[0010] According to the lithium-ion battery disclosed herein, the solid electrolyte interface layer comprises two film layers with different compositions, wherein the oxygen content of the second film layer is greater than that of the first film layer. This improves the stability of the solid electrolyte interface layer, reduces the likelihood of cracking due to decreased resistance to negative electrode volume changes during battery cycling, thereby reducing active lithium loss during cycling and achieving higher capacity retention. Simultaneously, it effectively buffers the volume expansion of the negative electrode during lithium insertion / extraction, prevents direct contact between the electrolyte and the negative electrode active material, enhances battery cycle stability, and increases battery life. Furthermore, the higher oxygen content in the second film layer reduces lithium-ion transport impedance, improving battery charge / discharge efficiency and cycle stability.

[0011] According to embodiments of this disclosure, the lithium-ion battery may also have at least one of the following additional technical features:

[0012] According to an embodiment of this disclosure, the oxygen content of the first membrane layer is W1, where W1 is in mass %, and the oxygen content of the second membrane layer is W2, where W2 is in mass %, satisfying W2-W1≥0.5 mass %.

[0013] And / or, the oxygen content of the first membrane layer is 3% to 15% by mass;

[0014] And / or, the oxygen content of the second membrane layer is 5% to 17% by mass.

[0015] According to embodiments of this disclosure, the oxygen content of the solid electrolyte interface layer is 3% to 16% by mass.

[0016] According to an embodiment of this disclosure, the thickness ratio of the first film layer to the second film layer is (0.3~2):1;

[0017] And / or, the thickness of the first film layer and the second film layer are each independently 5 nm to 10 nm.

[0018] According to embodiments of this disclosure, the first film layer includes an organic component, which includes one or more of the following: lithium alkoxy, lithium alkenoxy, lithium alkoxy carbonate, lithium alkoxy carbonate, dilithium alkoxy carbonate, polyvinyl carbonate, and polyvinyl carbonate.

[0019] And / or, the second film layer includes an inorganic component, said inorganic component including at least one of lithium oxide, lithium carbonate, lithium fluoride, lithium phosphate, lithium sulfate, lithium borate and lithium silicate.

[0020] According to embodiments of this disclosure, the negative electrode active material includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials, and tin-based materials.

[0021] According to embodiments of this disclosure, the lithium-ion battery further includes: a positive electrode and an electrolyte;

[0022] The electrolyte includes lithium salt and electrolyte additives, wherein the electrolyte additives include at least one of carbonate compounds, phosphate compounds, siloxane compounds and ether compounds.

[0023] In a second aspect of this disclosure, a method for preparing the lithium-ion battery described in the second aspect is provided. According to embodiments of this disclosure, the method includes:

[0024] After the electrolyte is injected into the battery cell, a first charging process is performed to form the first film layer.

[0025] The battery cell after the first charging treatment is subjected to a second charging treatment to form the second film layer, thereby obtaining the lithium-ion battery. The voltage of the first charging treatment is lower than the voltage of the second charging treatment.

[0026] According to embodiments of this disclosure, the battery cell and / or the electrolyte contains a lithium replenishing agent, the voltage of the first charging process is lower than the decomposition voltage of the lithium replenishing agent, and the voltage of the second charging process is not lower than the decomposition voltage of the lithium replenishing agent.

[0027] According to embodiments of this disclosure, the lithium supplement includes at least one of lithium ferrite, lithium nickelate, lithium carbonate, and lithium oxalate.

[0028] According to an embodiment of this disclosure, when the first charging process reaches a SOC value of 5% to 15% for the battery cell, charging is stopped, and then a first aging process is performed to form the first film layer.

[0029] And / or, the current of the first charging process is 0.02C to 0.1C.

[0030] According to the embodiments of this disclosure, the temperature of the first aging treatment is 30°C to 60°C, and the time is not less than 24 hours.

[0031] According to an embodiment of this disclosure, when the second charging process reaches a voltage of not less than 3.5V, charging is stopped, and then a second aging process is performed to form the second film layer;

[0032] And / or, the current of the second charging process is 0.05C to 0.3C.

[0033] According to an embodiment of this disclosure, when the second charging process reaches 3.8V to 4.4V, charging is stopped, and then a second aging process is performed to form the second film layer.

[0034] According to the embodiments of this disclosure, the temperature of the second aging treatment is 30°C to 60°C, and the time is not less than 24 hours.

[0035] According to an embodiment of this disclosure, the battery cell includes a positive electrode sheet, the positive electrode sheet includes a positive active material and a lithium replenishing agent, and the mass ratio of the lithium replenishing agent to the positive active material is (0.5-5):100.

[0036] According to an embodiment of this disclosure, the battery cell includes a negative electrode sheet, the negative electrode sheet includes a negative electrode active material, and before the first charging treatment, the oxygen content on the surface of the negative electrode active material is 1% to 10% by mass.

[0037] In a third aspect, this disclosure provides an electrical device. According to embodiments of this disclosure, the electrical device includes a lithium-ion battery as described in the first aspect or a lithium-ion battery prepared by the method for preparing a lithium-ion battery as described in the second aspect.

[0038] Additional aspects and advantages of this disclosure will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this disclosure. Attached Figure Description

[0039] The above and / or additional aspects and advantages of this disclosure will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0040] Figure 1 shows a schematic diagram of the interface layer structure of the negative electrode active material and the solid electrolyte according to one embodiment of the present disclosure;

[0041] Figure 2 shows a schematic flowchart of a method for preparing a lithium-ion battery according to one embodiment of the present disclosure.

[0042] Reference numerals: 100: negative electrode active material; 200: solid electrolyte interface layer; 210: first film layer; 220: second film layer. Detailed Implementation

[0043] The embodiments of this disclosure are described in detail below. The embodiments described below are exemplary and are only used to explain this disclosure, and should not be construed as limiting this disclosure.

[0044] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. Furthermore, in the description of this disclosure, unless otherwise stated, "a plurality of" means two or more.

[0045] The endpoints and any values ​​of the ranges disclosed in this disclosure are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be regarded as specifically disclosed in this disclosure.

[0046] In this disclosure, the terms “comprising” or “including” are open-ended expressions, meaning that they include the contents specified in this disclosure but do not exclude other contents.

[0047] Currently, lithium replenishing agents are often added to the positive electrode active material layer of lithium-ion batteries. The main function of these agents is to provide additional lithium ions to compensate for the active lithium ions consumed during the first charge (formation) process due to the formation of the solid electrolyte interphase (SEI). This process helps improve the battery's initial coulombic efficiency (ICE), thereby increasing the battery's actual output energy density and cycle life. However, lithium replenishing agents generate oxygen, oxygen free radicals, and carbon dioxide during battery manufacturing. These substances modify the negative electrode SEI film, significantly increasing its inorganic components and making the SEI film brittle. This, in turn, reduces its resistance to negative electrode volume changes during battery cycling, making it prone to cracking. Consequently, the active lithium is lost more rapidly during battery cycling, leading to a faster decline in battery cycle performance. Therefore, although lithium replenishing agents have the potential to improve battery performance, due to gas generation issues, their actual effect on improving battery cycle life may not be as expected.

[0048] Existing technologies for modifying the SEI film typically involve adding additives to the electrolyte to form the desired SEI components. However, the introduction of new electrolyte additives increases manufacturing costs and may also affect other battery performance aspects, such as increased active lithium loss, increased electrolyte impedance, and increased gas production. Furthermore, this approach generally results in a single-layer SEI film, which is often insufficient to withstand the complex operating conditions during battery use, leading to a higher probability of SEI film damage and faster battery cycle capacity decay.

[0049] In view of this, this disclosure designs the solid electrolyte interface layer of a lithium-ion battery as comprising two film layers with different compositions. The oxygen content of the first film layer, which contacts the negative electrode active material, is lower than that of the second film layer, which contacts the electrolyte. Since the oxygen content in the film layer is positively correlated with the inorganic component content, the first film layer has a higher organic component content, while the second film layer has a higher inorganic component content. Because the first film layer is rich in organic components, it can form a dense film structure, thereby resisting the insertion of oxygen atoms into the first film layer during the formation of the second film layer. This reduces the inorganic component content in the first film layer to a certain extent, resulting in a lower overall inorganic component content in the solid electrolyte interface layer. This improves the stability of the solid electrolyte interface layer, reduces the phenomenon of decreased resistance to negative electrode volume changes and easy breakage during battery cycling, thereby reducing active lithium loss during cycling and achieving higher capacity retention. Furthermore, the first film layer has good plasticity, which can effectively buffer the volume expansion of the negative electrode during lithium insertion / extraction, prevent direct contact between the electrolyte and the negative electrode active material, improve battery cycle stability, and increase battery life. In addition, since the second film layer contains more inorganic components, it can reduce lithium-ion transport impedance and improve battery charging and discharging efficiency.

[0050] Therefore, the first aspect of this disclosure provides a negative electrode sheet, referring to Figure 1, the negative electrode sheet comprising: a negative electrode sheet including a negative electrode active material 100; a solid electrolyte interface layer 200 including a first film layer 210 and a second film layer 220, the first film layer 210 covering at least a portion of the surface of the negative electrode active material 100, and the second film layer 220 covering at least a portion of the surface of the first film layer 210 away from the negative electrode active material 100; the oxygen content of the second film layer 220 is greater than the oxygen content of the first film layer 210.

[0051] Figure 1 shows a schematic diagram of the interface layer between the negative electrode active material and the double-layer solid electrolyte. The advantages of the lithium-ion battery structural design disclosed in this invention will be explained in detail below with reference to Figure 1:

[0052] In this disclosure, the terms "first membrane layer" and "inner SEI membrane" are used interchangeably, and the terms "second membrane layer" and "outer SEI membrane" are used interchangeably.

[0053] During the initial charging (formation) of the battery, the lithium replenishing agent and the solvent and lithium salt in the electrolyte undergo a reduction reaction on the surface of the negative electrode material, decomposing to form inorganic components. These decomposition reactions are usually accompanied by the participation of oxygen atoms; compared to organic components, inorganic components typically contain more oxygen atoms. Therefore, the oxygen content in the SEI film is positively correlated with the inorganic component content; a higher oxygen content in the SEI film indicates a higher inorganic component content, and vice versa.

[0054] According to the lithium-ion battery disclosed herein, the solid-phase electrolyte interface layer comprises two film layers with different compositions: an inner SEI film and an outer SEI film. The inner SEI film is close to the negative electrode active material, while the outer SEI film is in contact with the electrolyte. Since the oxygen content of the outer SEI film is greater than that of the inner SEI film, and the oxygen content in the film layer is positively correlated with the inorganic component content, the inner SEI film has a higher organic component content, while the outer SEI film has a higher inorganic component content. Because the inner SEI film is rich in organic components, it can form a dense film structure, thereby resisting the insertion of oxygen atoms into the inner SEI film during the formation of the outer SEI film. This reduces the inorganic component content of the inner SEI film to a certain extent, resulting in a lower overall inorganic component content in the solid-phase electrolyte interface layer. This improves the stability of the solid-phase electrolyte interface layer, reduces the phenomenon of decreased resistance to negative electrode volume changes and easy breakage during battery cycling, and thus reduces active lithium loss during cycling, resulting in higher capacity retention. Furthermore, the inner SEI film, rich in organic components, possesses good plasticity. This plasticity allows the film to adapt to the volume changes that occur during lithium-ion insertion (charging) and extraction (discharging) of the negative electrode material, thereby reducing mechanical stress and film rupture. It also prevents direct contact between the electrolyte and the negative electrode active material, minimizing unnecessary side reactions, electrolyte decomposition, and loss, thus improving battery cycle stability and extending battery life. Additionally, the outer SEI film, rich in inorganic components such as LiF, Li₂O, and Li₂CO₃, provides effective lithium-ion transport channels, reducing polarization during battery charging and discharging, increasing lithium-ion migration rate, lowering lithium-ion transport impedance, and improving battery charge / discharge efficiency and cycle stability.

[0055] It should be noted that the oxygen content of the first film layer, the second film layer, and the solid electrolyte interface layer can be detected using conventional instruments and detection methods in this field. For example, the method for detecting oxygen content includes:

[0056] Oxygen content can be characterized using XPS etching or cryo-electron microscopy (cryo-EM) electron energy loss spectroscopy to obtain oxygen content distribution information from the outside to the inside. The sum of the products of the thickness percentage of each film layer and the corresponding oxygen content is the overall oxygen content of the solid electrolyte interface layer. When at least 80% of the test results from different locations of the same film layer meet the oxygen content conditions given in this disclosure for that film layer, the entire test sample is considered to have met the given conditions, that is, the film layer has met the given conditions.

[0057] According to embodiments of this disclosure, the oxygen content of the first film layer is W1, where W1 is in mass %; the oxygen content of the second film layer is W2, where W2 is in mass %; and the oxygen content satisfies W2-W1≥0.5 mass %, for example, W2-W1 can be 0.5 mass %, 1 mass %, 1.5 mass %, 2 mass %, 2.5 mass %, 3 mass %, etc. Compared to the oxygen content of the second film layer, reducing the oxygen content of the first film layer is beneficial for forming a dense structure. Reducing the oxygen content in the first film layer further reduces the inorganic component content of the solid electrolyte interface layer as a whole, thereby improving its stability and reducing the phenomenon of decreased resistance to negative electrode volume change and easy breakage during battery cycling, thus reducing active lithium loss during cycling and achieving higher capacity retention. Furthermore, reducing the oxygen content of the first film layer can improve its plasticity, allowing the film layer to adapt to the volume changes of the negative electrode material during lithium-ion insertion (charging) and extraction (discharging). This reduces mechanical stress and film layer rupture, prevents direct contact between the electrolyte and the negative electrode active material, reduces unnecessary side reactions, minimizes electrolyte decomposition and loss, improves battery cycle stability, and increases battery life. Compared to the oxygen content of the first film layer, increasing the oxygen content of the second film layer helps improve the stability of the entire solid electrolyte interface layer, which is more conducive to lithium-ion transport, increases the migration rate of lithium-ions, reduces lithium-ion transport impedance, and improves battery charge and discharge efficiency. Using the first and second film layer contents that meet the above conditions is beneficial to improving the overall stability of the solid electrolyte interface layer, better reducing active lithium loss and lithium-ion transport impedance during cycling, and improving battery cycle stability.

[0058] According to embodiments of this disclosure, the oxygen content of the first film layer is 3% to 15% by mass, for example, it can be 3% by mass, 4% by mass, 5% by mass, 6% by mass, 8% by mass, 10% by mass, 12% by mass, 14% by mass, 15% by mass, etc. The oxygen content of the first film layer meets the given conditions, and the first film layer is rich in a suitable amount of organic components, which can form a suitable and dense structure, reducing the embedding of oxygen atoms in the first film layer, thereby reducing the oxygen content and inorganic components of the first film layer. Simultaneously, it can further improve the plasticity of the first film layer, enabling the film layer to adapt to the volume changes that occur in the negative electrode material during lithium-ion insertion (charging) and extraction (discharging), thereby reducing mechanical stress and film layer rupture, preventing direct contact between the electrolyte and the negative electrode active material, reducing unnecessary side reactions, reducing electrolyte decomposition and loss, improving battery cycle stability, and increasing battery life.

[0059] According to embodiments of this disclosure, the oxygen content of the second membrane layer is 5% to 17% by mass, for example, 5% by mass, 8% by mass, 10% by mass, 12% by mass, 15% by mass, 17% by mass, etc. Thus, the second membrane layer is rich in an appropriate amount of inorganic components, which helps to form a stable solid electrolyte interface layer, reduces further decomposition of the electrolyte, and thereby improves the chemical stability of the battery. Furthermore, it helps to better provide appropriate lithium-ion channels, optimize lithium-ion transport, and reduce battery internal resistance. In addition, the outer SEI membrane containing the above-mentioned oxygen content can reduce the inorganic component content of the entire double-layer SEI membrane, further improving the stability of the solid electrolyte interface layer, reducing the phenomenon of decreased resistance to negative electrode volume changes and easy breakage during battery cycling, thereby reducing active lithium loss during cycling and achieving higher capacity retention.

[0060] According to embodiments of this disclosure, the oxygen content of the solid electrolyte interface layer is 3% to 16% by mass. This helps to further promote the formation of a stable solid electrolyte interface layer, effectively reducing electrolyte decomposition and thus significantly extending the battery's cycle life. This solid electrolyte interface layer not only better resists further chemical reactions between the electrolyte and electrode materials, protecting the electrodes from corrosion, but also further maintains its internal lithium-ion channels, optimizing lithium-ion mobility, thereby improving the battery's charge / discharge efficiency and overall performance.

[0061] According to the embodiments of this disclosure, the thickness ratio of the first film layer to the second film layer is (0.3 to 2):1, for example, it can be 0.3:1, 0.5:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, etc. This results in a better overall oxygen content, inorganic component content, and organic component content in the double-layer SEI film, further improving the stability of the solid electrolyte interface layer and reducing the phenomenon of easy breakage due to decreased resistance to negative electrode volume changes during battery cycling, thereby reducing active lithium loss during cycling and achieving higher capacity retention. Furthermore, it can further reduce mechanical stress and film layer rupture, prevent direct contact between the electrolyte and the negative electrode active material, reduce unnecessary side reactions, reduce electrolyte decomposition and loss, improve battery cycle stability, and increase battery life. Moreover, it can further improve the lithium-ion migration rate, reduce lithium-ion transport impedance, and improve battery charge and discharge efficiency.

[0062] According to embodiments of this disclosure, the thicknesses of the first and second films are each independently 5 nm to 10 nm, for example, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, etc. The thickness of the first film, meeting the given conditions, is beneficial for providing better electronic insulation, reducing direct reactions between electrons and the electrolyte, reducing the lithium-ion transport path, and lowering the battery's internal resistance. Furthermore, it facilitates the formation of a dense structure, reducing the oxygen content in the inner SEI film, further reducing the overall inorganic component content of the solid electrolyte interface layer, thereby improving its stability and reducing the phenomenon of decreased resistance to negative electrode volume changes and easy breakage during battery cycling, thus reducing active lithium loss during cycling and achieving higher capacity retention. The thickness of the second film, meeting the given conditions, can effectively improve lithium-ion transport performance, reduce battery charge / discharge impedance, improve the thermal stability and mechanical strength of the SEI film, reduce the phenomenon of decreased resistance to negative electrode volume changes and easy breakage during battery cycling, protect battery performance under high temperature or other harsh conditions, and achieve excellent charge / discharge efficiency.

[0063] According to embodiments of this disclosure, a first film layer covers at least a portion of the surface of a negative electrode active material, the negative electrode active material including at least one of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials, and tin-based materials.

[0064] According to embodiments of the present disclosure, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0065] According to embodiments of this disclosure, 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 polymer material substrate 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, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0066] According to embodiments of this disclosure, the negative electrode active material layer may also optionally include a binder, a conductive agent, and other optional additives.

[0067] 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.

[0068] As an example, the adhesive may include at least one of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA), and polyvinyl butyral (PVB).

[0069] As an example, other optional additives may include thickeners and dispersants (such as sodium carboxymethyl cellulose CMC-Na) and PTC thermistor materials.

[0070] According to embodiments of this disclosure, the first film layer includes an organic component, which includes one or more of the following: lithium alkoxy, lithium alkenoxy, lithium alkoxy carbonate, lithium alkoxy carbonate, dilithium alkoxy carbonate, polyvinyl carbonate, and polyvinyl carbonate.

[0071] And / or, the second membrane layer includes an inorganic component, which includes at least one of lithium oxide, lithium carbonate, lithium fluoride, lithium phosphate, lithium sulfate, lithium borate, and lithium silicate.

[0072] According to embodiments of this disclosure, the lithium-ion battery further includes: a positive electrode and an electrolyte; the electrolyte includes a lithium salt and an electrolyte additive, the electrolyte additive including at least one of carbonate compounds, phosphate compounds, siloxane compounds, and ether compounds. During battery charging and discharging, active lithium ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of ions between the positive and negative electrode. During the initial charging of the battery to form the SEI film, the lithium salt and electrolyte additive in the electrolyte undergo a decomposition reaction on the surface of the negative electrode. The lithium salt can react with the lithium replenishing agent and oxygen in the negative electrode active material to generate inorganic components; the electrolyte additive is mainly organic and can react with oxygen to generate organic components. The inner SEI film is rich in organic components, while the outer SEI film is rich in inorganic components, which helps to improve the overall performance of the SEI film.

[0073] According to embodiments of the present disclosure, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, the positive active material layer including a positive active material.

[0074] Exemplarily, the positive electrode active material may be a known positive electrode active material for lithium-ion 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 disclosure is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials 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 NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.8 Co 0.15 Al 0.05 At least one of O2) or its modified compounds. Examples of lithium phosphates with an olivine structure may include, but are not limited to, at least one of 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, or lithium manganese iron phosphate and carbon composites.

[0075] According to embodiments of this disclosure, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. For example, the composite negative electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0076] According to embodiments of this disclosure, the positive electrode active material layer may optionally include 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.

[0077] According to embodiments of this disclosure, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0078] According to embodiments of this disclosure, a positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet (e.g., positive electrode active material, conductive agent, binder) in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive electrode current collector, and obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0079] According to embodiments of this disclosure, the lithium-ion battery further includes a separator. The separator is disposed between the positive electrode and the negative electrode, primarily serving to prevent short circuits between the positive and negative electrodes, while simultaneously allowing ions to pass through.

[0080] This disclosure does not impose any particular limitation on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected. In some embodiments of this disclosure, the material of the separator membrane may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride.

[0081] The lithium-ion batteries disclosed herein may be in the form of individual battery cells, battery modules, and battery packs. In some embodiments, individual battery cells may be assembled into battery modules, and the number of individual battery cells contained in a battery module may be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into battery packs, and the number of battery modules contained in a battery pack may be one or more, the specific number of which can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0082] The second aspect of this disclosure provides a method for preparing a lithium-ion battery according to the first aspect, as shown in Figure 2. The method includes: S100 forming a first film layer and S200 forming a second film layer. Each part will be described in detail below.

[0083] S100 forms the first film layer

[0084] In this step, after the electrolyte is injected into the battery cell, a first charging process is performed to form the first film layer.

[0085] According to embodiments of this disclosure, the battery cell and / or electrolyte contains a lithium replenishing agent, and the voltage of the first charging process is lower than the decomposition voltage of the lithium replenishing agent.

[0086] The primary function of the lithium replenisher is to provide additional lithium ions to compensate for the active lithium ions consumed during the first charge (formation) of the battery due to the formation of the solid electrolyte interphase (SEI). This process helps improve the battery's initial coulombic efficiency (ICE), thereby increasing the battery's actual output energy density and cycle life. During the formation of the SEI film during the first charge (formation), when the decomposition voltage of the lithium replenisher is reached, it decomposes to release oxygen atoms. These oxygen atoms participate in inorganic and organic reactions on the negative electrode surface. To increase the organic component in the first film layer, the voltage of the first charge treatment is set lower than the decomposition voltage of the lithium replenisher. This avoids the decomposition of the lithium replenisher, reduces the generation of oxygen atoms, and promotes the formation of a dense structure in the first film layer. This helps resist the embedding of oxygen atoms into the inner SEI film during the formation of the outer SEI film, thus reducing the inorganic component content in the inner SEI film to some extent. This reduces the overall inorganic component content of the solid electrolyte interphase layer, improving its stability and reducing the likelihood of cracking due to decreased resistance to negative electrode volume changes during battery cycling. Consequently, it reduces active lithium loss during cycling and results in higher capacity retention. In addition, the inner SEI film is rich in organic components, which gives it good plasticity. This plasticity allows the film to adapt to the volume changes that occur in the negative electrode material during lithium ion insertion (charging) and extraction (discharging), thereby reducing mechanical stress and film rupture, preventing direct contact between the electrolyte and the negative electrode active material, reducing unnecessary side reactions, reducing electrolyte decomposition and loss, improving battery cycle stability, and increasing battery life.

[0087] According to embodiments of this disclosure, the lithium replenishing agent includes at least one of lithium ferrite, lithium nickelate, lithium carbonate, and lithium oxalate. When more than one lithium replenishing agent is used, the voltage of the first charging process is lower than the decomposition voltage of any one lithium replenishing agent, and the voltage of the second charging process is not lower than the decomposition voltage of any one lithium replenishing agent.

[0088] According to embodiments of this disclosure, the battery cell includes a positive electrode, a negative electrode, and a separator. At least one of the positive electrode, negative electrode, and separator contains a lithium replenishing agent. That is, the lithium replenishing agent can be contained in the positive electrode, negative electrode, separator, or electrolyte of the battery cell, or in any two, three, or all four of the above four components. In some embodiments, the battery cell includes a positive electrode, which comprises a positive electrode active material and a lithium replenishing agent. The mass ratio of the lithium replenishing agent to the positive electrode active material is (0.5–5):100, for example, 0.5:100, 1:100, 2:100, 3:100, 4:100, or 5:100. When the ratio of the lithium replenishing agent to the positive electrode active material satisfies the above conditions, the prepared lithium-ion battery has a high initial discharge capacity. Furthermore, by adjusting the mass ratio of the lithium replenisher to the positive electrode active material, the oxygen content of the outer SEI film can be controlled. When the ratio of the lithium replenisher to the positive electrode active material meets the above conditions, the outer SEI film is rich in an appropriate amount of inorganic components, which helps to form a stable SEI film, reduces further decomposition of the electrolyte, and thus improves the chemical stability of the battery. It also helps to better provide appropriate lithium-ion channels, optimize lithium-ion transport, reduce battery internal resistance, and improve cycle performance.

[0089] According to an embodiment of the present invention, the battery cell includes a negative electrode sheet, which includes negative electrode active material particles. Before the first charging treatment, the oxygen content on the surface of the negative electrode active material particles is 1% to 10% by mass. During the formation of the SEI film during the first charging of the battery, oxygen atoms on the surface of the negative electrode active material particles also participate in the reaction, reacting with lithium ions in the electrolyte or lithium replenishment agent to form a stable SEI film, such as inorganic compounds like Li2CO3, LiF, or Li2O. Since different negative electrode active material particles can have different oxygen contents on their surfaces, the oxygen content of the inner SEI film can be controlled by selecting negative electrode active material particles with different surface oxygen contents. Meeting the above-mentioned conditions regarding the oxygen content on the surface of the negative electrode active material particles is beneficial for obtaining an inner SEI film with the oxygen content that meets the aforementioned conditions, ensuring an appropriate inorganic component content throughout the SEI film, thereby improving its stability and reducing the occurrence of cracking due to decreased resistance to negative electrode volume changes during battery cycling. This reduces active lithium loss during cycling and results in higher capacity retention. At the same time, it can further improve the lithium-ion transport performance, charge and discharge efficiency and cycle stability of lithium-ion batteries.

[0090] It should be noted that "the surface of the negative electrode active material particles" refers to the region within 5 nm of the negative electrode surface. The oxygen content on the surface of the negative electrode active material particles can be detected using conventional instruments and detection methods in this field. For details, please refer to the aforementioned detection methods for the oxygen content of the first film layer, the second film layer, and the solid electrolyte interface layer.

[0091] According to embodiments of this disclosure, when the first charging process reaches a SOC value of 8% to 15% (e.g., 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc.), charging is stopped, and a first aging process is then performed to form a first film layer. The current of the first charging process is 0.02C to 0.1C, for example, 0.02C, 0.04C, 0.05C, 0.06C, 0.08C, or 0.1C. This facilitates the formation of an inner SEI film with suitable thickness and rich in organic components.

[0092] According to embodiments of this disclosure, the temperature of the first aging treatment is 30°C to 60°C; the duration of the first aging treatment is not less than 24 hours. Exemplarily, the temperature of the first aging treatment is 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, etc., and the duration of the first aging treatment is 24 hours, 32 hours, 36 hours, 38 hours, 42 hours, etc. This helps to further form a stable SEI film, improving the stability and reliability of the battery during subsequent charge and discharge processes.

[0093] S200 forms the second film layer.

[0094] In this step, the battery cell after the first charging treatment undergoes a second charging treatment to form a second film layer, thereby obtaining a lithium-ion battery.

[0095] According to embodiments of this disclosure, the voltage of the second charging process is not lower than the decomposition voltage of the lithium replenishing agent. Under this condition, the lithium replenishing agent decomposes to generate oxygen atoms, which participate in the formation of inorganic components in the second film layer, making the second film layer rich in stable inorganic components. Since the first film layer has a dense structure, it can resist the embedding of oxygen atoms into the inner SEI film during the formation of the outer SEI film, thereby reducing the inorganic component content in the inner SEI film to a certain extent. This reduces the overall inorganic component content of the solid electrolyte interface layer, thus improving the stability of the solid electrolyte interface layer. Furthermore, the outer SEI film rich in stable inorganic components helps to provide an effective lithium-ion transport channel, reduce polarization during battery charging and discharging, increase the lithium-ion migration rate, reduce lithium-ion transport impedance, and improve battery charging and discharging efficiency.

[0096] According to embodiments of this disclosure, when the second charging process reaches 3.8V to 4.4V (e.g., 3.8V, 3.9V, 4.0V, 4.1V, 4.2V, 4.3V, 4.4V, etc.), charging is stopped, and a second aging process is then performed to form a second film layer; the current of the second charging process is 0.05C to 0.3C, for example, 0.05C, 0.1C, 0.15C, 0.2C, 0.25C, 0.3C. This facilitates the formation of an outer SEI film of suitable thickness and rich in inorganic components.

[0097] In this disclosure, the term "SOC" refers to the current state of charge of the battery, i.e., the percentage of remaining charge in the battery. SOC is a value from 0% to 100%, where: "0% SOC" indicates that the battery is fully discharged with no remaining charge; "100% SOC" indicates that the battery is fully charged and has reached its maximum storage capacity. The SOC value can be determined using instruments and methods known in the art. For example, the test method includes: discharging the battery at 0.1C to the lower operating voltage of the battery in a battery charge-discharge test cabinet, recording the discharge capacity as C1, and then charging it at 0.1C to the upper operating voltage of the battery, recording the charging capacity as C2. C1 / C2 is the SOC state of the battery.

[0098] According to embodiments of this disclosure, the temperature of the second aging treatment is 30°C to 60°C; the duration of the second aging treatment is not less than 24 hours. Exemplarily, the aging treatment temperature is 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, etc., and the aging treatment time is 24 hours, 32 hours, 36 hours, 38 hours, 42 hours, etc. This helps to further form a stable SEI film, improving the stability and reliability of the battery during subsequent charge and discharge processes.

[0099] The fourth aspect of this disclosure provides an electrical device, which includes a lithium-ion battery prepared by the method of preparing a lithium-ion battery according to the second aspect of this disclosure or the third aspect.

[0100] Battery cells, battery modules, and battery packs can be used as power sources for electrical devices or as energy storage units for electrical devices. Electrical devices can include, but are not limited to, 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.

[0101] As electrical equipment, battery cells, battery modules, or battery packs can be selected according to their usage requirements.

[0102] One possible implementation method for the electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the battery for this electrical device, a battery pack or battery module can be used.

[0103] Another possible implementation is a mobile phone, tablet computer, laptop computer, etc. These devices are typically required to be thin and light, and can use individual battery cells as their power source.

[0104] It should be noted that the features and advantages described above for the negative electrode sheet of the first aspect of this disclosure are also applicable to the lithium-ion battery of the second aspect, the method for preparing a lithium-ion battery of the third aspect, and the electrical equipment of the fourth aspect, and will not be repeated here.

[0105] The present disclosure will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0106] Example 1

[0107] 1) Preparation of positive electrode sheet

[0108] The positive electrode active material (lithium iron phosphate LiFePO4), lithium supplementer (Li5FeO4), binder polyvinylidene fluoride, and conductive agent acetylene black were mixed in a mass ratio of 100:5:2.5:2.5 (the lithium supplementer content was 5% by mass of the positive electrode active material). 1.7 times the mass of the active material N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto a 12μm thick aluminum foil for the positive electrode current collector and dried. Then, it was transferred to a vacuum oven and dried at 120℃ for 24h. Finally, it was rolled and cut to obtain the positive electrode sheet.

[0109] 2) Preparation of negative electrode sheet

[0110] Artificial graphite (anode active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and carboxymethyl cellulose (CMC) (mass ratio 94:2:2:2) were mixed together with a certain amount of deionized water and stirred evenly under vacuum to obtain anode slurry. The anode slurry was then uniformly coated onto copper foil with a thickness of 8 μm and dried. It was then transferred to a vacuum oven and dried at 120°C for 24 hours. Finally, it was rolled and cut to obtain anode sheet.

[0111] 3) Preparation of electrolyte

[0112] In a nitrogen-atmospheric glove box with a water content <1 ppm and an oxygen content <1 ppm, ethylene carbonate (EC), dimethyl carbonate (DMC), dimethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed as a mixed solvent in a mass ratio of EC:DMC:DEC:EMC = 1:1:1:1. Lithium salt LiPF6 was then slowly dissolved in the mixed organic solvent. Finally, the functional additive vinylene carbonate (VC) was added and mixed thoroughly to obtain the electrolyte. Based on the total mass of the electrolyte, the mass percentage of lithium salt LiPF6 was 16%, and the mass percentage of vinylene carbonate (VC) was 3%.

[0113] 4) Separating membrane

[0114] The diaphragm is a PE-coated ceramic diaphragm with a thickness of 12μm.

[0115] 5) Lithium-ion battery manufacturing

[0116] Stack the negative electrode, separator, positive electrode, and separator in sequence, repeat the above sequence, and fix them with high-temperature resistant tape. Then, weld the positive and negative electrode tabs and encapsulate them with aluminum-plastic film to obtain the battery cell. After vacuum drying the battery cell at 105°C for 72 hours, inject the corresponding electrolyte and encapsulate it.

[0117] 6) Formation

[0118] The assembled battery cells were aged at 45°C for 1 day, then charged with a constant current of 0.05C to a SOC value of 10%, charging was stopped, and the cells were aged at 45°C for 1 day to form an inner SEI film.

[0119] The cell with the inner SEI film was charged to 4.2V using a constant current of 0.1C, then charging was stopped, and the cell was aged at 45℃ for 1 day to form the outer SEI film, thus obtaining the solid-phase electrolyte interface layer. After degassing and capacity testing, a lithium iron phosphate battery was obtained.

[0120] Example 2-14

[0121] The differences between Examples 2-14 and Comparative Examples 1 and 2 and Example 1 are shown in Table 1.

[0122] The difference between Example 6 and Example 1 is that in step 6), the SOC value of 10% is replaced with 5%.

[0123] The difference between Example 7 and Example 1 is that in step 6), the SOC value of 10% is replaced with 15%.

[0124] The difference between Example 8 and Example 1 is that in step 6), the cell forming the inner SEI film is charged to 3.9V using a constant current of 0.1C.

[0125] The difference between Example 9 and Example 1 is that in step 6), the cell forming the inner SEI film is charged to 4.4V using a constant current of 0.1C.

[0126] Comparative Examples 1-2

[0127] The difference between Comparative Example 1 and Example 1 is that step 6) is as follows: the assembled battery cell is aged at 45°C for 1 day, and then charged with a constant current of 0.05C to a SOC value of 10%, and then charged with a constant current of 0.1C to 4.2V.

[0128] The difference between Comparative Example 2 and Comparative Example 1 is that in step 1, the mass ratio of the positive electrode active material (lithium iron phosphate LiFePO4), lithium supplementer (Li5FeO4), binder polyvinylidene fluoride, and conductive agent acetylene black is 100:3:2.5:2.5, that is, the content of lithium supplementer is 3% of the content of positive electrode active material, and the surface oxygen content of the negative electrode active material artificial graphite is 11%.

[0129] The oxygen content of the inner SEI film, outer SEI film, solid-phase electrolyte interface layer, and negative electrode active material particle surface was detected using the following methods:

[0130] The oxygen content of the SEI film was characterized using XPS etching. Etching was performed continuously from the outermost layer to the innermost layer to obtain information on the oxygen content distribution from the outside to the inside. The average value of the SEI measurement results for each layer was taken as the oxygen content of that layer. The sum of the products of the thickness percentage of each film layer and its corresponding oxygen content is the overall oxygen content of the solid electrolyte interface layer. The surface oxygen content of the region within a 5 nm depth of the negative electrode active material particles was directly characterized using XPS etching.

[0131] Table 1

[0132] Performance testing

[0133] The performance of the lithium-ion batteries prepared in Examples 1-14 and Comparative Examples 1 and 2 were tested, as follows:

[0134] After the battery undergoing its final aging process, it was cooled at 25°C for 6 hours, then discharged at 1 / 3C to 2V, and charged at 1 / 3C constant current and constant voltage to 3.8V, with a cutoff current of 0.05C. This charge-discharge cycle was repeated three times, and the discharge capacity of the third discharge was recorded as the initial discharge capacity. The lithium battery was then subjected to 500 charge-discharge cycles at 1 / 3C, within a voltage range of 2V-3.8V. The capacity after 500 cycles was recorded, and the percentage obtained by dividing this capacity by the initial discharge capacity was used as the capacity retention rate.

[0135] The results are shown in Table 2. Compared with Comparative Examples 1 and 2, the lithium-ion batteries prepared in Examples 1-14 exhibit superior performance. Comparative Example 1 uses a single-layer SEI film, and Comparative Example 2 shows that the oxygen content of the outer SEI film is lower than that of the inner SEI film. Compared with Comparative Examples 1 and 2, Example 1 uses a double-layer SEI film, with the oxygen content of the outer SEI film being higher than that of the inner SEI film. Correspondingly, the inner SEI film has a higher content of organic components, while the outer SEI film has a higher content of inorganic components. Because the inner SEI film is rich in organic components, it can form a dense film structure, thereby resisting the embedding of oxygen atoms into the inner SEI film during the formation of the outer SEI film. This reduces the inorganic component content in the inner SEI film to a certain extent, resulting in a lower overall inorganic component content in the solid electrolyte interface layer. This improves the stability of the solid electrolyte interface layer, reduces the phenomenon of decreased resistance to negative electrode volume changes and easy breakage during battery cycling, and thus reduces the loss of active lithium during battery cycling, resulting in higher capacity retention. In addition, the inner SEI film has good plasticity, which can effectively buffer the volume expansion of the graphite anode during lithium insertion / extraction, prevent direct contact between the electrolyte and the anode active material, improve battery cycle stability, and increase battery life. Furthermore, because the outer SEI film has a higher content of inorganic components, it can reduce lithium-ion transport impedance and improve battery charge / discharge efficiency.

[0136] Compared with Example 1, Example 10 has a lower oxygen content in the inner SEI film, resulting in increased battery impedance, lithium plating probability, and active lithium loss, and a decrease in capacity retention after 500 cycles. Compared with Example 1, Example 11 has a higher oxygen content in the inner SEI film, which increases the brittleness of the SEI film, increases the probability of SEI film breakage, increases active lithium loss, and decreases capacity retention after 500 cycles.

[0137] Compared to Example 1, Example 12 has a higher oxygen content in the outer SEI film, which increases the brittleness of the SEI film, leading to a higher probability of SEI film breakage, increased active lithium loss, and a decrease in capacity retention after 500 cycles. Compared to Example 1, Example 13 has a lower oxygen content in the outer SEI film, resulting in increased battery impedance, higher lithium plating probability, and increased active lithium loss, while the capacity retention after 500 cycles is lower.

[0138] Compared with Example 1, Example 14 has a lower oxygen content difference between the outer and inner SEI films, resulting in increased battery impedance, lithium plating probability, and active lithium loss, and a decreased capacity retention rate after 500 cycles.

[0139] Table 2

[0140] Although embodiments of the present disclosure have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present disclosure.

Claims

1. A lithium-ion battery, wherein, include: A negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode active material (100); A solid electrolyte interface layer (200) includes a first film layer (210) and a second film layer (220). The first film layer (210) covers at least a portion of the surface of the negative electrode active material (100), and the second film layer (220) covers at least a portion of the surface of the first film layer (210) away from the negative electrode active material (100). The oxygen content of the second membrane layer (220) is greater than that of the first membrane layer (210).

2. The lithium-ion battery according to claim 1, wherein, The oxygen content of the first membrane layer (210) is W1, where W1 is in mass % and the oxygen content of the second membrane layer (220) is W2, where W2 is in mass % and satisfies W2-W1≥0.5 mass %. And / or, the oxygen content of the first film layer (210) is 3% to 15% by mass; And / or, the oxygen content of the second film layer (220) is 5% to 17% by mass.

3. The lithium-ion battery according to claim 1 or 2, wherein, The oxygen content of the solid electrolyte interface layer (200) is 3% to 16% by mass.

4. The lithium-ion battery according to any one of claims 1-3, wherein, The thickness ratio of the first film layer (210) to the second film layer (220) is (0.3~2):1; And / or, the thickness of the first film layer (210) and the second film layer (220) are each independently 5 nm to 10 nm.

5. The lithium-ion battery according to any one of claims 1 to 4, wherein, The first film layer (210) includes an organic component, which includes one or more of the following: lithium alkoxy, lithium alkenoxy, lithium alkoxy carbonate, lithium alkoxy carbonate, dilithium alkoxy carbonate, polyvinyl carbonate, and polyvinyl carbonate. And / or, the second film layer (220) includes an inorganic component, which includes at least one of lithium oxide, lithium carbonate, lithium fluoride, lithium phosphate, lithium sulfate, lithium borate and lithium silicate.

6. The lithium-ion battery according to any one of claims 1 to 5, wherein, The negative electrode active material (100) includes at least one of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials, and tin-based materials.

7. The lithium-ion battery according to any one of claims 1 to 6, wherein, Further includes: a positive electrode and an electrolyte; The electrolyte includes lithium salt and electrolyte additives, wherein the electrolyte additives include at least one of carbonate compounds, phosphate compounds, siloxane compounds and ether compounds.

8. A method for preparing the lithium-ion battery according to any one of claims 1 to 7, wherein, include: After the electrolyte is injected into the battery cell, a first charging process is performed to form the first film layer. The battery cell after the first charging treatment is subjected to a second charging treatment to form the second film layer, thereby obtaining the lithium-ion battery. The voltage of the first charging treatment is lower than the voltage of the second charging treatment.

9. The method according to claim 8, wherein, Also includes: The battery cell and / or the electrolyte contain a lithium replenishing agent, the voltage of the first charging process is lower than the decomposition voltage of the lithium replenishing agent, and the voltage of the second charging process is not lower than the decomposition voltage of the lithium replenishing agent.

10. The method according to claim 9, wherein, The lithium supplement includes at least one of lithium ferrite, lithium nickelate, lithium carbonate, and lithium oxalate.

11. The method according to any one of claims 8 to 10, wherein, When the first charging process reaches the SOC value of the cell at 5% to 15%, charging is stopped, and the first aging process is then performed to form the first film layer. And / or, the current of the first charging process is 0.02 C to 0.1 C.

12. The method according to claim 11, wherein, The temperature of the first aging treatment is 30℃~60℃, and the time is not less than 24 hours.

13. The method according to any one of claims 8 to 12, wherein, When the second charging process reaches a voltage of not less than 3.5V, charging is stopped, and then the second aging process is performed to form the second film layer. And / or, the current of the second charging process is 0.05C to 0.3C.

14. The method according to any one of claims 8 to 12, wherein, When the second charging process reaches 3.8V to 4.4V, charging is stopped, and the second aging process is then carried out to form the second film layer.

15. The method according to claim 13 or 14, wherein, The second aging treatment is performed at a temperature of 30℃ to 60℃ for a time of not less than 24 hours.

16. The method according to any one of claims 9 to 15, wherein, The battery cell includes a positive electrode sheet, which includes a positive active material and a lithium replenishing agent, wherein the mass ratio of the lithium replenishing agent to the positive active material is (0.5-5):

100.

17. The method according to any one of claims 8 to 16, wherein, The battery cell includes a negative electrode sheet, which includes a negative electrode active material. Before the first charging process, the oxygen content on the surface of the negative electrode active material is 1% to 10% by mass.

18. An electrical appliance, wherein, The lithium-ion battery includes the lithium-ion battery according to any one of claims 1 to 7 or the lithium-ion battery prepared by the method for preparing a lithium-ion battery according to any one of claims 8 to 17.

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