Secondary battery, method for preparing negative electrode sheet, battery module, battery pack, and electric device

Abstract

The application provides a secondary battery, a method for preparing a negative electrode sheet, a battery module, a battery pack and a power utilization device. The secondary battery comprises a negative electrode sheet, a standard deviation of a sheet resistance of the negative electrode sheet is less than 0.7 Ω; the negative electrode sheet comprises: a negative electrode current collector; a negative electrode active material layer located on at least one side of the negative electrode current collector; and a coating layer located on a side of the negative electrode active material layer away from the negative electrode current collector, the coating layer comprising an inorganic substance containing fluorine elements. Thus, the secondary battery has good storage life and cycle life.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a secondary battery, a method for preparing a negative electrode sheet, a battery module, a battery pack, and an electrical device. Background Technology

[0002] Secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. Taking lithium-ion batteries as an example, they have been widely adopted due to their advantages such as high energy density, long cycle life, low self-discharge, and no memory effect. However, with advancements in battery technology, consumers expect lithium-ion batteries to have even higher quality and performance, which places higher demands on their energy storage and cycle performance. Summary of the Invention

[0003] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery that aims to improve the battery's storage life and cycle life.

[0004] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a negative electrode sheet, wherein the standard deviation of the film resistance of the negative electrode sheet is less than 0.7Ω; the negative electrode sheet includes: a negative current collector; a negative active material layer, wherein the negative active material layer is located on at least one side of the negative current collector; and a coating layer, wherein the coating layer is located on the side of the negative active material layer away from the negative current collector, and the coating layer includes an inorganic material containing fluorine.

[0005] This application includes at least the following beneficial effects: the negative electrode of the secondary battery has a small standard deviation of film resistance, which indicates that the surface of the negative electrode active material layer has a dense and uniformly distributed coating. The coating can isolate the negative electrode and the electrolyte, reduce the rate of battery aging and degradation, and thus extend the battery's storage life and cycle life.

[0006] In some embodiments, the fluorine-containing inorganic material includes at least one selected from LiF, NaF, AgF, CaF2, MgF2, AlF3, TiF4, TaF5, and WF6. Therefore, selecting a suitable fluorine-containing inorganic material can further extend the battery's storage life and cycle life.

[0007] In some embodiments, the thickness of the coating is 0.5 nm to 100 nm. Thus, choosing an appropriate coating thickness aims to balance coating durability with battery storage life and cycle life.

[0008] In some embodiments, the thickness of the coating is 5nm-50nm. This can further improve the battery's storage life and cycle life.

[0009] In some embodiments, the negative electrode active material layer includes a first portion and a second portion stacked together; the first portion is located on the side closer to the negative electrode current collector, and the second portion is located on the side closer to the coating layer; the second portion includes the fluorine-containing inorganic material. Therefore, the fluorine-containing inorganic material can further prevent direct contact between the electrolyte and the active sites of the negative electrode active material layer, further reducing side reactions between the electrolyte and the main or auxiliary materials, thereby further extending the battery's storage life and cycle life.

[0010] In some embodiments, the thickness of the second portion is 2μm-5μm. Therefore, controlling the thickness of the second portion is beneficial for obtaining better battery dynamic performance, and can further extend the battery's storage life and cycle life.

[0011] In some embodiments, based on the total mass of the elements contained in the second portion, the second portion contains 0.0005 wt% to 0.0060 wt% of the inorganic matter containing the fluorine element. Therefore, by controlling the content of the inorganic matter containing the fluorine element in the negative electrode active material layer, it is beneficial to obtain better battery kinetic performance, and the battery's storage life and cycle life can be further extended.

[0012] In some embodiments, the adhesion strength between the coating and the negative electrode active material layer is 10 MPa-25 MPa. This allows the coating to adhere firmly to the surface of the negative electrode active material layer, reducing coating peeling.

[0013] In some embodiments, the thickness of the negative electrode active material layer is 50 μm-90 μm. This optimizes the performance of the secondary battery.

[0014] In some embodiments, the negative electrode further includes a solid electrolyte interface film located on the side of the negative electrode active material layer away from the negative electrode current collector; the solid electrolyte interface film comprises an organic compound containing fluorine. Therefore, the fluorine-containing organic compound can improve the stability of the solid electrolyte interface film, thereby extending the battery's storage life and cycle life.

[0015] In some embodiments, based on the total mass of elements contained in the solid electrolyte interface membrane, the solid electrolyte interface membrane contains 0.57 wt% to 0.6 wt% of fluorine-containing organic matter. Therefore, the increased content of fluorine-containing organic matter in the solid electrolyte interface membrane can improve the stability of the solid electrolyte interface membrane, thereby extending the battery's storage life and cycle life.

[0016] In some embodiments, the secondary battery includes a lithium-ion battery, which further includes a positive electrode. Therefore, the negative electrode of this application is suitable for lithium-ion battery systems.

[0017] In some embodiments, the positive electrode includes: a positive current collector; and a positive active material layer located on at least one side of the positive current collector; the positive active material layer includes a positive active material that satisfies the chemical formula LiM. (1-x) Fe x PO4, where element M includes at least one metallic element from Groups IIA, IIIA, IVA, VA, VIA, IIIB, VB, VIB, VIIB, and VIII, and x is 0-1. Therefore, selecting a suitable positive electrode active material can improve the overall performance of lithium-ion batteries.

[0018] In a second aspect, this application provides a method for preparing a negative electrode sheet for a secondary battery, comprising: forming a negative electrode sheet comprising a negative electrode active material layer on at least one side of a negative electrode current collector; forming a coating layer on the side of the negative electrode active material layer away from the negative electrode current collector, the coating layer comprising an inorganic material containing fluorine; the method for forming the coating layer comprising magnetron sputtering, the magnetron sputtering method satisfying at least one of the following conditions: the vacuum degree of the magnetron sputtering method is less than or equal to 1 × 10⁻⁶. -3 Pa; the sputtering power of the magnetron sputtering method is 1W-100W; the sputtering voltage of the magnetron sputtering method is 5KV-30KV; the sputtering time of the magnetron sputtering method is 10min-200min. By controlling the parameters of the magnetron sputtering method, the density and uniformity of the coating can be controlled, so that the standard deviation of the film resistance of the negative electrode sheet is less than 0.7Ω. Therefore, by controlling the vacuum degree, sputtering power, sputtering voltage, and sputtering time of the magnetron sputtering method to suitable conditions, the standard deviation of the film resistance of the negative electrode sheet can be controlled to be less than 0.7Ω. The secondary battery with the negative electrode sheet obtained by this method has excellent storage life and cycle life.

[0019] In some embodiments, the magnetron sputtering method satisfies at least one of the following conditions: the vacuum degree of the magnetron sputtering method is 5 × 10⁻⁶. -4 Pa-1×10 -3Pa; the sputtering power of the magnetron sputtering method is 1W-20W; the sputtering voltage of the magnetron sputtering method is 5KV-10KV; the sputtering time of the magnetron sputtering method is 50min-120min. Therefore, by controlling the vacuum degree, sputtering power, sputtering voltage, and sputtering time of the magnetron sputtering method to suitable conditions, it is possible to further control the coating thickness to a suitable level, control the standard deviation of the film resistance of the negative electrode sheet to be less than 0.7Ω, and control the depth of the fluorine-containing inorganic material penetrating into the negative electrode active material layer, i.e., the thickness of the second part.

[0020] In some embodiments, before forming the coating on the side of the negative electrode active material layer away from the negative electrode current collector, the method further includes: pre-treating the negative electrode active material layer to obtain a pre-treated negative electrode active material layer. This removes surface impurities from the negative electrode active material layer and improves its roughness.

[0021] In some embodiments, the pretreatment includes plasma treatment. This can further improve the roughness of the negative electrode active material layer.

[0022] In some embodiments, the plasma treatment satisfies at least one of the following conditions: the plasma treatment further includes introducing a carrier gas, the carrier gas including at least one of O2, N2, CO2, and NH3; the vacuum degree of the plasma treatment is less than or equal to 1 × 10⁻⁶. -3 Pa; the discharge power of the plasma treatment is 100W-1200W; the gas flow rate of the plasma treatment is 100mL / min-1000mL / min; the treatment time of the plasma treatment is 1min-20min. Therefore, by controlling the vacuum degree, discharge power, gas flow rate, and treatment time of the plasma treatment to suitable conditions, the roughness of the negative electrode active material layer can be controlled to a suitable size.

[0023] Optionally, the plasma treatment satisfies at least one of the following conditions: the vacuum degree of the plasma treatment is 5 × 10⁻⁶. -4 Pa-1×10 -3 Pa; the discharge power of the plasma treatment is 100W-1000W; the gas flow rate of the plasma treatment is 100mL / min-800mL / min; the treatment time of the plasma treatment is 2min-10min. This allows for further control of the roughness of the negative electrode active material layer.

[0024] In some embodiments, the pretreated negative electrode active material layer satisfies at least one of the following conditions: the roughness of the pretreated negative electrode active material layer is 50 nm-200 nm; the surface of the pretreated negative electrode active material layer has active groups. This increases the adhesion between the negative electrode active material layer and the coating.

[0025] In some embodiments, the active group includes at least one of -OH, -NH2, -COOH, -C=O, and -SO3H. Thus, plasma treatment of the carrier gas can transfer the corresponding active group to the surface of the negative electrode active material layer.

[0026] In a third aspect, this application provides a battery module, including the secondary battery of the first aspect of this application, or a secondary battery having a negative electrode sheet obtained by the preparation method of the second aspect of this application. Thus, the battery possesses all the features and advantages of the aforementioned negative electrode sheet, which will not be repeated here.

[0027] In a fourth aspect, this application provides a battery pack that includes the battery module of the third aspect of this application.

[0028] In a fifth aspect, this application provides an electrical device comprising at least one selected from the following: a secondary battery according to the first aspect of this application, a secondary battery having a negative electrode sheet obtained using the preparation method of the second aspect of this application, a battery module according to the third aspect of this application, and a battery pack according to the fourth aspect of this application. Thus, the battery possesses all the features and advantages of the aforementioned negative electrode sheet, which will not be elaborated further here. Attached Figure Description

[0029] Figure 1 This is a test graph of the standard deviation of diaphragm resistance according to one embodiment of this application.

[0030] Figure 2 This is a CP element surface scan analysis diagram according to an embodiment of this application, wherein, Figure 2 Figure (a) in the image is a scanning electron microscope (SEM) image of the negative electrode plate. Figure 2 Figure (b) in the figure is the distribution of F element at the corresponding position in Figure (a).

[0031] Figure 3 This is an elemental variation curve diagram of an embodiment of this application, wherein, Figure 3 Figure (a) in the diagram is a graph showing the changes in element C. Figure 3 Figure (b) in the diagram is a graph showing the variation of element F.

[0032] Figure 4 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0033] Figure 5 yes Figure 4An exploded view of a secondary battery according to one embodiment of this application is shown.

[0034] Figure 6 This is a schematic diagram of a battery module according to one embodiment of this application.

[0035] Figure 7 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0036] Figure 8 yes Figure 7 An exploded view of a battery pack according to one embodiment of this application is shown.

[0037] Figure 9 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0038] Explanation of reference numerals in the attached figures:

[0039] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0040] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the secondary battery, method for preparing the negative electrode sheet, battery module, battery pack, and power-consuming 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 to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0041] 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.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0044] 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.

[0045] Storage life and cycle life are crucial indicators of long-term battery reliability. However, during prolonged use, lithium-ion batteries experience irreversible lithium loss due to reactions with moisture, material defects, and oxygen-containing functional groups, impacting battery life. To extend battery life, electrolyte additives can be added to form a stable and dense passivation film on the positive electrode surface, inhibiting oxidation and reducing electrolyte decomposition during cycling or storage. However, these additives may thicken the solid electrolyte interphase (SEI) film, affecting lithium-ion transport performance. Artificial SEI films, such as carbon-coated or polymer-coated films, can be fabricated on the powder-level surface of the negative electrode active material. These artificial SEI films exhibit good cycle stability and can reduce irreversible capacity loss in lithium-ion batteries. However, modifying the powder-level of the negative electrode active material typically involves adjusting slurry formulations and optimizing process parameters, increasing the complexity of mass production. Therefore, effectively extending the storage life and cycle life of lithium-ion batteries remains a pressing issue.

[0046] Based on this, this application proposes a secondary battery, including a negative electrode sheet, wherein the standard deviation of the film resistance of the negative electrode sheet is less than 0.7Ω; the negative electrode sheet includes: a negative current collector; a negative active material layer, wherein the negative active material layer is located on at least one side of the negative current collector; and a coating layer, wherein the coating layer is located on the side of the negative active material layer away from the negative current collector, and the coating layer includes an inorganic material containing fluorine.

[0047] The negative electrode has a small standard deviation of film resistance, indicating that the surface of the negative electrode active material layer has a dense and uniformly distributed coating. This dense and uniform coating better isolates the negative electrode from the electrolyte, thereby reducing electrolyte decomposition and consumption of active lithium and / or active sodium caused by direct contact between the two. This, in turn, slows down battery aging and degradation, and extends battery storage and cycle life.

[0048] The test method for the standard deviation of the film resistance of the negative electrode is as follows: Take n test sites evenly distributed on the surface of the negative electrode, and refer to... Figure 1 , Figure 1 The circles in the diagram indicate test sites; the diaphragm resistor is connected to a regulated power supply and an electrical measuring instrument. The sample to be tested is placed in the electrode clamp, the power is turned on to apply current to the sample, and the resistance X of the i-th (1≤i≤n) test site is recorded and calculated. i Through formula The standard deviation of the film resistance of the negative electrode in this application can be calculated. Where n represents the total number of test sites. This represents the average resistance of n test sites.

[0049] As an example, the standard deviation of the film resistance of the negative electrode can be 0.1Ω, 0.2Ω, 0.3Ω, 0.4Ω, 0.5Ω, or 0.6Ω.

[0050] In some embodiments, the fluorine-containing inorganic material includes at least one of LiF, NaF, AgF, CaF2, MgF2, AlF3, TiF4, TaF5, and WF6. Therefore, selecting a suitable fluorine-containing inorganic material can further extend the battery's storage life and cycle life.

[0051] In some embodiments, the coating thickness is 0.5 nm to 100 nm. If the coating thickness exceeds 100 nm, the transport path of lithium ions and / or sodium ions becomes longer, leading to increased battery internal resistance; when the coating thickness is less than 0.5 nm, the coating is prone to damage during charging and discharging. A coating thickness between 0.5 nm and 100 nm is beneficial for obtaining better battery kinetic performance, thereby improving the battery's storage and cycle performance. Therefore, selecting an appropriate coating thickness aims to balance coating durability with battery storage life and cycle life. As an example, the coating thickness can be 0.5 nm, 1 nm, 5 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, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, or 100 nm. In other embodiments of this application, the coating thickness is 5 nm to 50 nm.

[0052] In this application, the thickness of the coating can be obtained by focusing ion beam transmission electron microscopy (FIB-TEM). Specifically, before battery formation, a dual-beam electron microscope (FIB, model: Thermo Fisher-Scios2HiVac) is used to thin the surface and sides of the negative electrode sheet. Then, a TEM (Thermo Scientific-Talos F200SG2) is used to observe the surface film of the thinned sample. n test sites are selected, and the average thickness of the n test sites is measured and calculated to obtain the thickness of the coating.

[0053] In some embodiments, the negative electrode active material layer includes a first portion and a second portion stacked together; the first portion is located on the side closer to the negative electrode current collector, and the second portion is located on the side closer to the coating layer, the second portion comprising an inorganic material containing fluorine.

[0054] The negative electrode active material on the surface of the negative electrode sheet is damaged by the cold pressing process. Simultaneously, the negative electrode sheet surface comes into contact with more air, resulting in numerous defects or active sites. In the initial stage of solid electrolyte interphase (SEI) film formation, the SEI film is not dense, causing some electrolyte to contact the active sites of the negative electrode active material layer. Fluorine-containing inorganic materials can further prevent direct contact between the electrolyte and the active sites of the negative electrode active material layer, further reducing side reactions between the electrolyte and the main or auxiliary materials, thereby further extending the battery's storage life and cycle life.

[0055] In some embodiments, the thickness of the second portion is 2μm-5μm. Therefore, controlling the thickness of the second portion is beneficial for obtaining better battery dynamic performance, and can further extend the battery's storage life and cycle life.

[0056] As an example, the thickness of the second part can be 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm or 5μm.

[0057] In this application, before battery formation, the electrode surface is analyzed using argon ion polishing technology-scanning electron microscopy (CP elemental surface scan analysis). Specifically, the depth of fluorine content in the negative electrode is determined by CP elemental surface scan analysis, and the thickness of the coating obtained above is subtracted to obtain the thickness of the second part.

[0058] In some embodiments, based on the total mass of the elements contained in the second part, the second part contains 0.0005 wt% to 0.0060 wt% of fluorine-containing inorganic matter. If the content of fluorine-containing inorganic matter in the negative electrode active material layer is too high, it will lead to an increase in the interfacial impedance of the cell, affecting the battery's kinetic performance. Therefore, by controlling the content of fluorine-containing inorganic matter in the negative electrode active material layer, it is beneficial to obtain better battery kinetic performance, which can further extend the battery's storage life and cycle life. In this application, the content of fluorine-containing inorganic matter can be obtained by X-ray photoelectron spectroscopy (XPS).

[0059] As an example, based on the total mass of the elements contained in the second part, the second part may contain 0.0005 wt%, 0.0010 wt%, 0.0015 wt%, 0.0020 wt%, 0.0025 wt%, 0.0030 wt%, 0.0035 wt%, 0.0040 wt%, 0.0045 wt%, 0.0050 wt%, 0.0055 wt%, or 0.0060 wt% of inorganic compounds containing fluorine.

[0060] In some embodiments, the adhesion strength between the coating and the negative electrode active material layer is 10 MPa-25 MPa.

[0061] In this application, the bonding strength between the coating and the negative electrode active material layer refers to the bonding ability between the coating and the negative electrode active material layer. During the charging and discharging process of the battery, this bonding ability can make the coating firmly adhere to the surface of the negative electrode active material layer, thereby reducing the peeling of the coating.

[0062] In this application, the bonding strength can be tested using a nanoindentation test method. Specifically, a certain pressure is applied to the surface of the film layer using an indenter of a specific shape and size, causing deformation of the film layer and the graphite electrode sheet. By measuring parameters such as the size and shape of the indentation and the residual deformation after unloading, and combining them with the corresponding mechanical model, the mechanical properties of the film layer, such as hardness and elastic modulus, are calculated, thereby evaluating the bonding ability between the coating and the negative electrode active material layer.

[0063] As an example, the bonding strength between the coating and the negative electrode active material layer can be 10MPa, 11MPa, 12MPa, 13MPa, 14MPa, 15MPa, 16MPa, 17MPa, 18MPa, 19MPa, 20MPa, 21MPa, 22MPa, 23MPa, 24MPa or 25MPa.

[0064] In some embodiments, the thickness of the negative electrode active material layer is 50 μm-90 μm. This optimizes the performance of the secondary battery. In this application, the method for testing the thickness of the negative electrode active material layer includes determining the thickness using a micrometer. As an example, the thickness of the negative electrode active material layer can be 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, or 90 μm.

[0065] In some embodiments, the area of ​​the coating is greater than or equal to the area of ​​the negative electrode active material layer. Thus, the coating can isolate the negative electrode sheet from the electrolyte.

[0066] In some embodiments, the negative electrode sheet further includes a solid electrolyte interface membrane located on the side of the negative electrode active material layer away from the negative electrode current collector; the solid electrolyte interface membrane includes an organic material containing fluorine.

[0067] In this application, during the cell formation process, fluorine-containing inorganic materials can form a fluorine-rich SEI film on the surface of the negative electrode. This fluorine-rich SEI film is stable and can also isolate the negative electrode from the electrolyte, reducing the rate of battery aging and degradation, thereby extending the battery's storage life and cycle life. Therefore, fluorine-containing organic materials can improve the stability of the solid electrolyte interfacial film, thus extending the battery's storage life and cycle life.

[0068] In some embodiments, based on the total mass of elements contained in the solid electrolyte interface membrane, the solid electrolyte interface membrane contains 0.57wt%-0.6wt% of fluorine-containing organic matter.

[0069] In this application, X-ray photoelectron spectroscopy (XPS) testing was performed on the negative electrode of the formed battery cell. XPS testing is a surface analysis technique that obtains the elemental composition of the sample surface and determines the relative concentration of elements by measuring the energy distribution of photoelectrons emitted when X-rays excite the sample surface. Taking LiF coating as an example, the content of inorganic lithium carbonate decreases, the content of lithium fluoride is similar, and the content of organic fluorine increases significantly. This is because after the formation of LiF coating, electrons are blocked, allowing the electrolyte and lithium salt to gain a small number of electrons, making it easier to reduce to organic products rather than inorganic products. As a result, the content of fluorine-containing organic matter in the SEI film increases, which can improve the stability of the SEI film and thus extend the battery's storage life and cycle life.

[0070] As an example, based on the total mass of elements contained in the solid electrolyte interface membrane, the solid electrolyte interface membrane may contain 0.57wt%, 0.58wt%, 0.59wt%, or 0.6wt% of fluorine-containing organic matter.

[0071] In some embodiments, 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, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0072] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries.

[0073] In some embodiments, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. As an example, the silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0074] Furthermore, the negative electrode active material includes artificial graphite and / or natural graphite.

[0075] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0076] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0077] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0078] In some embodiments, the secondary battery proposed in this application further includes a positive electrode, an electrolyte, and a separator. During the charging and discharging process, active 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. The separator, disposed between the positive and negative electrode, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0079] [Positive electrode plate]

[0080] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0081] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0082] In some embodiments, 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.).

[0083] In some implementations, when the secondary battery is a lithium-ion battery, the positive electrode active material satisfies the chemical formula LiM (1-x) Fex PO4, wherein element M includes at least one metallic element from Group IIA, IIIA, IVA, VA, VIA, IIIB, VA, VIB, VIIB, and VIII, and x is 0-1.

[0084] As an example, the positive electrode active material may include at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt iron phosphate, lithium nickel iron phosphate, lithium magnesium iron phosphate, lithium titanium iron phosphate, and lithium zinc iron phosphate.

[0085] In some embodiments, the positive electrode active material may further include lithium transition metal oxides. 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 and its modified compounds.

[0086] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before material addition. After charge-discharge cycles, the molar Li content changes when the positive electrode active material is applied to the battery system.

[0087] In the examples of positive electrode active materials for lithium-ion batteries in this application, the molar content of O is only a theoretical state value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0088] In some embodiments, when the battery is a sodium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for sodium-ion batteries.

[0089] As an example, the positive electrode active material may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue sodium compounds, 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. The modified compounds of the above materials may be for doping modification and / or surface coating modification of the materials.

[0090] In some embodiments, the transition metal in the sodium transition metal oxide can be at least one selected from Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu. The chemical formula of the sodium transition metal oxide can satisfy Na x MO2, wherein M includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, and 0 < x ≤ 1.

[0091] In some embodiments, the polyanionic compound may be a sodium ion, a transition metal ion, or a tetrahedral (YO4) compound. n- A class of compounds with anionic units. The transition metal may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include at least one of P, S, and Si; n represents (YO4). n- The price state.

[0092] In some embodiments, the polyanionic compound may also have sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds containing anionic units and halide anions. Transition metals may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include at least one of P, S, and Si, where n represents (YO4). n- The valence state of halogens can include at least one of F, Cl, and Br.

[0093] In some embodiments, the polyanionic compound may also be a tetrahedral compound containing sodium ions (YO4). n- Anionic unit, polyhedral unit (ZO) y ) m+And a class of compounds with optional halide anions. M may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, Y may include at least one of P, S and Si, and n represents (YO4). n- The valence state, Z represents transition metal, m represents (ZO) y ) m+ The valence state of halogens can include at least one of F, Cl, and Br.

[0094] As an example, polyanionic compounds can satisfy the chemical formulas NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' includes at least one of V, Fe, Mn and Ni), and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0095] In some embodiments, Prussian blue compounds may contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. Transition metals may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce.

[0096] As an example, Prussian blue compounds can satisfy the chemical formula Na a Me b Me' c (CN)6, wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0097] During the charging and discharging process of a battery, sodium (Na) undergoes insertion / extraction and consumption, resulting in varying molar Na content at different discharge states. In the examples of positive electrode active materials in this application, the molar Na content refers to the initial state of the material, i.e., the state before material addition. After charge-discharge cycles, the molar Na content changes when the positive electrode active material is applied to the battery system.

[0098] In the enumeration of positive electrode active materials for sodium-ion batteries in this application, the molar content of O is only a theoretical state value. The release of oxygen from the crystal lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0099] In some embodiments, the positive electrode film layer may optionally include 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.

[0100] In some embodiments, the positive electrode film 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.

[0101] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0102] [Electrolytes]

[0103] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0104] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0105] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0106] In some embodiments, the solvent may be selected from at least one of 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.

[0107] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include 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.

[0108] [Isolation membrane]

[0109] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0110] In some embodiments, 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.

[0111] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0112] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0113] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0114] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 4 This is an example of a square-structured secondary battery 5.

[0115] In some implementations, refer to Figure 5 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0116] In a second aspect, this application provides a method for preparing a negative electrode sheet for a secondary battery, comprising:

[0117] S100, A negative electrode sheet containing a negative electrode active material layer is formed on at least one side of the negative electrode current collector.

[0118] In some embodiments, the negative electrode active material, conductive agent, binder and any other components are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry; the negative electrode slurry is coated onto a negative electrode current collector, and after drying, cold pressing and other processes, a negative electrode active material layer is formed on the surface of the negative electrode current collector, thus obtaining the initial electrode sheet.

[0119] In some embodiments, the negative electrode active material layer is pretreated to obtain a pretreated negative electrode active material layer. This removes surface impurities from the negative electrode active material layer and improves its surface roughness.

[0120] In some implementations, pretreatment includes plasma treatment. Plasma treatment is a dry processing technique in which the plasma medium contains ions, electrons, neutrons, photons, free radicals, metastable excited particles, and molecules. Under the action of an electromagnetic field, these particles diffuse into the material surface in a gradient manner, resulting in surface activation, grafting of chemical structures and functional groups, and material volatilization and removal. This alters the chemical structure and morphology of the material surface, thereby improving the surface properties of the material.

[0121] In some embodiments, the plasma treatment satisfies at least one of the following conditions: the plasma treatment further includes the introduction of a carrier gas, said carrier gas including at least one of O2, N2, CO2, and NH3; the vacuum degree of the plasma treatment is less than or equal to 1 × 10⁻⁶. -3 Pa; the discharge power of the plasma treatment is 100W-1200W; the gas flow rate of the plasma treatment is 100mL / min-1000mL / min; the treatment time of the plasma treatment is 1min-20min.

[0122] During plasma treatment, plasma impacts the surface of the negative electrode active material layer, increasing its surface roughness. Simultaneously, active groups are introduced onto the surface of the negative electrode active material layer via a carrier gas. These active groups can bind to fluorine-containing inorganic materials and the solid electrolyte interphase (SEI) film. The increased roughness and the introduced active groups result in a tighter adhesion of the coating to the negative electrode active material layer surface, improving the bonding strength between the two. This increased adhesion helps reduce coating peeling during battery use. However, excessive plasma treatment can lead to excessively high surface roughness of the negative electrode active material layer, resulting in an uneven surface and affecting the uniformity of the SEI film formation.

[0123] Therefore, it is necessary to control the carrier gas, vacuum degree, discharge power, gas flow rate, and processing time of plasma treatment to suitable conditions in order to control the roughness of the negative electrode active material layer to a suitable size, thereby improving the adhesion between the negative electrode active material layer and the coating while maintaining the uniformity of the SEI film.

[0124] In addition, plasma treatment can slightly increase the depth of fluorine-containing inorganic substances penetrating into the negative electrode active material, that is, it can increase the thickness of the second part, thereby further protecting the negative electrode active material layer.

[0125] As an example, the vacuum level for plasma processing can be 1×10⁻⁶. -5 Pa, 0.5×10 -4 Pa, 1×10 -4 Pa, 0.2×10 -3 Pa, 0.4×10 -3 Pa, 0.6×10 -3 Pa, 0.8×10 -3 Pa or 1×10 -3 Pa.

[0126] As an example, the discharge power of plasma treatment can be 100W, 300W, 500W, 700W, 900W, or 1200W.

[0127] As an example, the gas flow rate for plasma treatment can be 100 mL / min, 200 mL / min, 400 mL / min, 600 mL / min, 800 mL / min, or 1000 mL / min.

[0128] As an example, the plasma treatment time can be 1 min, 5 min, 10 min, 15 min, or 20 min.

[0129] In other embodiments of this application, the plasma treatment satisfies at least one of the following conditions: the vacuum degree of the plasma treatment is 5 × 10⁻⁶. -4 Pa-1×10 -3 Pa; the discharge power of plasma treatment is 100W-1000W; the gas flow rate of plasma treatment is 100mL / min-800mL / min; the treatment time of plasma treatment is 2min-10min.

[0130] In some embodiments, the roughness of the pretreated negative electrode active material layer is 50 nm to 200 nm. The roughness can be obtained by atomic force microscopy (AFM). This increases the adhesion between the negative electrode active material layer and the coating.

[0131] As an example, the roughness of the pretreated negative electrode active material layer can be 50nm, 70nm, 90nm, 110nm, 130nm, 150nm, 170nm, 190nm or 200nm.

[0132] In some embodiments, the surface of the pretreated negative electrode active material layer has active groups. Therefore, plasma treatment of the carrier gas can transfer the corresponding active groups to the surface of the negative electrode active material layer.

[0133] In some embodiments, the active groups include at least one of -OH, -NH2, -COOH, -C=O, and -SO3H. Therefore, by selecting different carrier gases, the surface of the pretreated negative electrode active material layer can have different active groups. Taking LiF as an example, introducing active groups, such as unsaturated bonds like -OH and NH2, onto the surface of the negative electrode active material layer allows them to tightly bind with LiF molecules, forming -O:LiF and / or -N:LiF interface layers. This makes the coating adhere more tightly to the negative electrode active material layer, thereby improving the adhesion between the two.

[0134] S200, A coating is formed on the side of the negative electrode active material layer away from the negative electrode current collector, the coating comprising an inorganic material containing fluorine.

[0135] In some embodiments, the method for forming the coating includes magnetron sputtering, wherein the magnetron sputtering method satisfies at least one of the following conditions: the vacuum level of the magnetron sputtering method is less than or equal to 1 × 10⁻⁶. -3 Pa; the sputtering power of magnetron sputtering is 1W-100W; the sputtering voltage of magnetron sputtering is 5KV-30KV; the sputtering time of magnetron sputtering is 10min-200min.

[0136] Magnetron sputtering is a physical vapor deposition (PVD) technique that increases the sputtering rate by introducing a magnetic field onto the target cathode surface and confining charged particles. The operation of magnetron sputtering involves placing the target material (in the case of LiF as the coating material, the target is a single crystal of lithium fluoride) in a vacuum chamber filled with an inert gas (argon is a suitable inert gas). A DC voltage is applied between the target and the substrate of the negative electrode active material layer, causing the inert gas to ionize and generate positive ions and new electrons. These new electrons are accelerated by the electric field and collide with the target, causing sputtering. The target material penetrates into the pores of the negative electrode active material layer and deposits on its surface to form a coating.

[0137] Therefore, by controlling the vacuum degree, sputtering power, sputtering voltage, and sputtering time of magnetron sputtering to suitable conditions, it is possible to control the coating to a suitable thickness, control the standard deviation of the film resistance of the negative electrode sheet to be less than 0.7Ω, and control the depth of the fluorine-containing inorganic material penetrating into the negative electrode active material layer, i.e., the thickness of the second part.

[0138] As an example, the vacuum level of magnetron sputtering can be 1×10⁻⁶. -5 Pa, 0.5×10 -4 Pa, 1×10-4 Pa, 0.2×10 -3 Pa, 0.4×10 -3 Pa, 0.6×10 -3 Pa, 0.8×10 -3 Pa or 1×10 -3 Pa.

[0139] As an example, the sputtering power of magnetron sputtering can be 1W, 10W, 20W, 30W, 40W, 50W, 60W, 70W, 80W, 90W or 100W.

[0140] As an example, the sputtering voltage for magnetron sputtering can be 5KV, 10KV, 15KV, 20KV, 25KV or 30KV.

[0141] As an example, the sputtering time for magnetron sputtering can be 10 min, 40 min, 70 min, 100 min, 130 min, 160 min or 200 min.

[0142] In other embodiments of this application, the magnetron sputtering method satisfies at least one of the following conditions: the vacuum degree of the magnetron sputtering method is 5 × 10⁻⁶. -4 Pa-1×10 -3 Pa; the sputtering power of magnetron sputtering is 1W-20W; the sputtering voltage of magnetron sputtering is 5KV-10KV; the sputtering time of magnetron sputtering is 50min-120min.

[0143] In a third aspect of this application, a battery module is provided, including the secondary battery of the first aspect of this application, or a secondary battery having a negative electrode sheet made using the method of the second aspect of this application.

[0144] In some implementations, the battery module may contain one or more secondary batteries, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0145] Figure 6 This is battery module 4, used as an example. (See reference...) Figure 6 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0146] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0147] In a fourth aspect, this application provides a battery pack that includes the battery module of the third aspect of this application.

[0148] In some implementations, the battery pack may contain one or more battery modules, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0149] Figure 7 and Figure 8 This is battery pack 1 as an example. (See reference...) Figure 7 and Figure 8 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0150] In a fifth aspect of this application, an electrical device is provided, comprising at least one selected from the following: a secondary battery of the first aspect of this application, a secondary battery having a negative electrode sheet manufactured using the method of the second aspect of this application, a battery module of the third aspect of this application, and a battery pack of the fourth aspect of this application.

[0151] Therefore, secondary batteries, battery modules, or 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.

[0152] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0153] Figure 9 This is an example of an electrical device. The device could be 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 secondary battery for this device, a battery pack or battery module can be used.

[0154] 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.

[0155] Example

[0156] 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.

[0157] Example 1

[0158] (1) Preparation of negative electrode sheet

[0159] S100: Artificial graphite (negative electrode active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (thickener) are thoroughly mixed in a deionized water solvent system at a weight ratio of 96.82:0.53:1.95:0.7. This mixture is then coated onto both surfaces of a 6 μm thick copper foil. After drying at 110°C for 20 min, it is cold-pressed to obtain an areal density of 10.71 mg / cm³. 2 The compacted density is 1.4 g / cm³. 3 The initial electrode sheet is a negative electrode current collector with a negative electrode active material layer and a thickness of 159 μm. The test results show that the porosity of the negative electrode active material layer in the initial electrode sheet is 40% and the roughness is 50 nm.

[0160] S200. Clean the LiF single crystal target with alcohol, install the cleaned target onto the sputtering target, and fix it in its target position within the sputtering chamber; cut the initial electrode sheet into 40cm×40cm pieces, clean the initial electrode sheet to remove surface impurities; place the initial electrode sheet on the substrate in the sputtering chamber, start the vacuum pump, and evacuate the sputtering chamber to a vacuum level of 0.75×10⁻⁶. -3 Pa; simultaneously set the sputtering power to 10W and the sputtering voltage to 7KV; introduce inert argon gas into the sputtering chamber; set a magnetic field on the back of the target to constrain electron movement and increase plasma density; apply a DC voltage between the target and the initial electrode to ionize the inert gas and generate plasma; charged particles (ions) bombard the target surface, causing target atoms or molecules to be sputtered out and deposited on the initial electrode to form a thin film, i.e., a coating; at the same time, LiF penetrates into the pores of the initial electrode to form the second part; after reaching the predetermined sputtering time of 85min, turn off the power; slowly release the gas in the sputtering chamber to gradually restore the chamber pressure to atmospheric pressure; remove the initial electrode with the coating completed, which is the negative electrode used in this embodiment.

[0161] (2) Preparation of positive electrode sheet

[0162] Lithium iron phosphate (LiFePO4), carbon black (Super P), and polyvinylidene fluoride (PVDF) binder were thoroughly mixed in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 97.2:0.7:2.1 to form a uniform positive electrode slurry. The positive electrode slurry was then coated onto the surface of an aluminum foil current collector, dried, cold-pressed, slit, and cut to obtain the positive electrode sheet. The compacted density of the positive electrode sheet was 2.45 g / cm³. 3 Its surface density is 21.68 mg / cm³. 2 .

[0163] (3) Separating membrane

[0164] A 12μm thick polyethylene film was selected as the separator.

[0165] (4) Preparation of electrolyte

[0166] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent; sodium hexafluorophosphate (NaPF6) was dissolved in the above mixed solvent and stirred until homogeneous, with a molar concentration of 1 mol / L, to form an electrolyte.

[0167] (5) Battery manufacturing

[0168] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. The bare cell is placed in an outer package, filled with the prepared electrolyte, and sealed to obtain a secondary battery.

[0169] The difference between Comparative Example 1 and Example 1 is that the negative electrode sheet is not subjected to magnetron sputtering treatment, denoted as G.

[0170] Material characterization

[0171] 1. CP element surface scan analysis

[0172] CP elemental surface scanning analysis refers to the process of analyzing the surface of an electrode using argon ion polishing (CP) combined with scanning electron microscopy (SEM). CP technology uses a high-energy argon ion beam to bombard the sample surface, removing a layer of material and exposing the internal structure, thus obtaining a smooth polished cross-section. Testing instrument: Zeiss Supra 55, reference standard GB / T 17359-2012.

[0173] CP elemental surface scan analysis was performed on the negative electrode sheet obtained in Example 1, with reference to... Figure 2 ,in, Figure 2Figure (a) in the image is a scanning electron microscope (SEM) image of the negative electrode. Energy-dispersive X-ray spectroscopy (EDS) surface scanning of the corresponding positions in Figure (a) yields the F element distribution map in Figure (b). Figure 2 As shown in Figure (b), the F element is enriched on the surface of the negative electrode sheet and dispersed inside the negative electrode sheet. Therefore, the surface of the negative electrode sheet in Example 1 has a coating containing fluorine element, and the pores of the negative electrode active material layer contain fluorine element.

[0174] 2. After formation, the negative electrode of the battery cell was disassembled and subjected to X-ray photoelectron spectroscopy (XPS) testing.

[0175] XPS testing is a surface analysis technique that uses X-ray photoelectron spectrometer (XPS) to measure the energy distribution of photoelectrons emitted when an X-ray excites the sample surface, thereby determining the elemental composition and relative concentration of elements. The instrument used is an Axis Supra / Supra+ X-ray photoelectron spectrometer, conforming to standard GB / T 33502-2017.

[0176] After the battery cells of Example 1 and Comparative Example 1 were formed, the formed cells were disassembled to separate the negative electrode plates, and X-ray photoelectron spectroscopy (XPS) was performed on the surface of the negative electrode plates. The elemental changes in the negative electrode plates after cell formation are shown in the reference [reference needed]. Figure 3 The graphs showing the changes in elements C and F are shown in Figure (a) and Figure (b), respectively. The green lines correspond to Example 1, and the black lines correspond to Example 1.

[0177] Figure 3 As shown in Figure (a), the CC peak is at 284.8 eV (used as a reference for charge correction), the CO peak is at 286 eV, which is the CO peak of organic matter, and the metal carbonate peak is at 288 eV-290 eV, which is the inorganic peak. Figure 3 As shown in Figure (b), the peak at 688-689 eV represents organic fluorine, and the peak at 684-685.5 eV represents metal fluoride. In the LiF-coated negative electrode (Example 1), the surface SEI composition changed, with a decrease in the content of inorganic lithium carbonate, a similar content of lithium fluoride, and a significant increase in the content of organic fluorine. This is because the LiF coating blocks electrons, allowing the electrolyte and lithium salt to gain a small number of electrons, making it easier to reduce to organic products rather than inorganic products. Furthermore, based on the total mass of elements contained in the solid electrolyte interface film, the solid electrolyte interface film contains 0.59 wt% fluorine-containing organic matter.

[0178] The difference between Comparative Example 2 and Example 1 is that the initial electrode was subjected to vacuum evaporation treatment.

[0179] The preparation methods of the batteries in Examples 2-21 and Comparative Examples 3-9 are the same as those in Example 1, with the differences detailed in Table 1.

[0180] Table 1

[0181]

[0182]

[0183] Example 22

[0184] The difference between Example 22 and Example 1 is that, before forming the LiF coating, the negative electrode active material layer is pretreated to obtain a pretreated initial electrode.

[0185] The pretreatment method is plasma treatment, specifically involving the following steps: cleaning the initial electrode to remove surface impurities; placing the cleaned initial electrode on the sample stage of the plasma reaction chamber; and starting the vacuum pump to evacuate the reaction chamber to a vacuum level of 0.75 × 10⁻⁶. -3 Pa; set the discharge power of the reaction chamber to 550W; after the reaction chamber produces glow, introduce carrier gas O2 at a flow rate of 450mL / min; after 6 minutes of plasma treatment, when the reaction chamber returns to normal pressure and there is no sound of air intake, the pretreated initial electrode can be removed.

[0186] The preparation methods of the batteries in Examples 23-45 are the same as those in Example 22, and the differences are detailed in Table 2.

[0187] Table 2

[0188]

[0189] Performance testing

[0190] 1. Coating thickness

[0191] The thickness of the coating can be obtained by focusing ion beam transmission electron microscopy (FIB-TEM). Specifically, before battery formation, the surface and sides of the electrode sample are thinned using a dual-beam electron microscope (FIB, model: Thermo Fisher-Scios 2HiVac). Then, the surface film of the thinned sample is observed using a TEM microscope (model: Thermo Scientific-Talos F200S G2). n test sites are selected, and the average thickness of the n test sites is measured and calculated to obtain the coating thickness.

[0192] 2. Thickness of the second part

[0193] The electrode surface was analyzed using argon ion polishing technology combined with scanning electron microscopy (CP elemental surface scan analysis). Specifically, the depth of fluorine content in the negative electrode was determined by CP elemental surface scan analysis, and the thickness of the coating was subtracted to obtain the thickness of the second part.

[0194] 3. Standard deviation of diaphragm resistance

[0195] The method for testing the standard deviation of diaphragm resistance is as follows: Take n test sites evenly distributed on the surface of the negative electrode, and refer to... Figure 1 , Figure 1 The circles in the diagram indicate test sites; the diaphragm resistor is connected to a regulated power supply and an electrical measuring instrument. The sample to be tested is placed in the electrode clamp, the power is turned on to apply current to the sample, and the resistance X of the i-th (1≤i≤n) test site is recorded and calculated. i Through formula The standard deviation of the film resistance of the negative electrode in this application can be calculated. Where n represents the total number of test sites. This represents the average resistance of n test sites.

[0196] 4. Roughness

[0197] Roughness was obtained through atomic force microscopy (AFM). Specifically, the tip scans the sample surface, and the surface morphology is obtained by measuring the change in the interaction force between the tip and the sample surface. The surface morphology is then reconstructed in three dimensions using software, and the surface roughness is calculated.

[0198] 5. Bond strength

[0199] The bonding strength can be tested using the nanoindentation test method. Specifically, a certain pressure is applied to the surface of the film layer using an indenter of a specific shape and size, causing deformation of the film layer and the graphite electrode sheet. By measuring parameters such as the size and shape of the indentation and the residual deformation after unloading, and combining them with the corresponding mechanical model, the mechanical properties of the film layer, such as hardness and elastic modulus, can be calculated, thereby evaluating the bonding ability between the coating and the negative electrode active material layer.

[0200] 6. Battery storage performance testing methods

[0201] Let it stand at a constant temperature of 25℃ for 5 minutes; charge it to 3.65V at 0.33C0, then charge it to 0.05C0 at 3.65V constant voltage, let it stand for 5 minutes; discharge it to 2V at 0.33C, and record the capacity at this point as C. z (The capacity of the cell after storage is the reversible capacity, marked as C) t (t is the storage time); charge at 0.33C0 to 3.65V, then charge at 3.65V constant voltage to 0.05C0, at which point the cell is fully charged; place the fully charged secondary battery in a 60℃ constant temperature environment and store for 30 days. Remove the cell and test according to the first step. Repeat the above operation until t = 180 days, then calculate the reversible capacity retention rate F, F = C t ÷C z *100%.

[0202] 7. Battery Cycle Performance Test Method

[0203] At 60℃, the battery was charged at a constant current rate of 4C to a cutoff voltage of 4V, and then discharged at a rate of 1C to a cutoff voltage of 2.8V. The initial capacity was recorded as C0. After charging at a rate of 4C, the battery was discharged at a rate of 1C, and the discharge capacity C of each cycle was recorded. n Until the battery's capacity retention rate (capacity retention rate = C) is reached. n The percentage of (C0×100%) is 80%, and the number of cycles is recorded. The more cycles, the longer the cycle life of the secondary battery.

[0204] The test results of the negative electrode and battery in Examples 1-21 and Comparative Examples 1-9 are shown in Table 3.

[0205] Table 3

[0206]

[0207]

[0208] The test results of the negative electrode and battery in Examples 22-45 are shown in Table 4.

[0209] Table 4

[0210]

[0211]

[0212] As shown in Tables 3 and 4, the batteries obtained in Examples 1-45 all exhibit good storage life and cycle life. For example, in Examples 1-21, by controlling the parameters of the magnetron sputtering method, a uniform and dense coating is formed on the surface of the negative electrode sheet. This coating, along with the fluorine-rich SEI film, isolates the negative electrode sheet from the electrolyte, reducing the rate of battery aging and degradation, and extending the battery's storage life and cycle life. Furthermore, as in Examples 22-45, a plasma treatment method is used to treat the initial electrode sheet to improve the surface roughness of the negative electrode active material layer, which is more conducive to the formation of the coating.

[0213] In contrast, Comparative Example 1 did not undergo magnetron sputtering treatment, and Comparative Example 2 used vacuum evaporation. The storage life and cycle life of the battery were worse than those of Examples 1-45.

[0214] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, Includes a negative electrode, wherein the standard deviation of the film resistance of the negative electrode is less than 0.7Ω; the negative electrode comprises: Negative electrode current collector; A negative electrode active material layer, wherein the negative electrode active material layer is located on at least one side of the negative electrode current collector; A coating is located on the side of the negative electrode active material layer away from the negative electrode current collector, and the coating comprises an inorganic material containing fluorine.

2. The secondary battery according to claim 1, characterized in that, The inorganic compounds containing fluorine include at least one of LiF, NaF, AgF, CaF2, MgF2, AlF3, TiF4, TaF5, and WF6.

3. The secondary battery according to any one of claims 1-2, characterized in that, The thickness of the coating is 0.5 nm to 100 nm; Optionally, the thickness of the coating is 5nm-50nm.

4. The secondary battery according to any one of claims 2-3, characterized in that, The negative electrode active material layer includes a first part and a second part stacked together; the first part is located on the side closer to the negative electrode current collector, and the second part is located on the side closer to the coating layer, and the second part includes the inorganic material containing fluorine.

5. The secondary battery according to claim 4, characterized in that, The thickness of the second part is 2μm-5μm.

6. The secondary battery according to any one of claims 4-5, characterized in that, Based on the total mass of the elements contained in the second part, the second part contains 0.0005wt%-0.0060wt% of the inorganic compound containing the fluorine element.

7. The secondary battery according to any one of claims 1-6, characterized in that, The bonding strength between the coating and the negative electrode active material layer is 10MPa-25MPa.

8. The secondary battery according to any one of claims 1-6, characterized in that, The thickness of the negative electrode active material layer is 50μm-90μm.

9. The secondary battery according to any one of claims 1-8, characterized in that, The negative electrode sheet further includes a solid electrolyte interface membrane, which is located on the side of the negative electrode active material layer away from the negative electrode current collector; the solid electrolyte interface membrane includes an organic material containing fluorine.

10. The secondary battery according to claim 9, characterized in that, Based on the total mass of the elements contained in the solid electrolyte interface membrane, the solid electrolyte interface membrane contains 0.57wt%-0.6wt% of the fluorine-containing organic matter.

11. The secondary battery according to any one of claims 1-10, characterized in that, The secondary battery includes a lithium-ion battery, and the lithium-ion battery further includes a positive electrode.

12. The secondary battery according to claim 11, characterized in that, The positive electrode sheet includes; Positive current collector; A positive electrode active material layer, wherein the positive electrode active material layer is located on at least one side of the positive electrode current collector; The positive electrode active material layer includes a positive electrode active material, which satisfies the chemical formula LiM. (1-x) Fe x PO4, wherein element M includes at least one metallic element from Group IIA, IIIA, IVA, VA, VIA, IIIB, VA, VIB, VIIB, and VIII, and x is 0-1.

13. A method for preparing a negative electrode sheet for a secondary battery, characterized in that, include: A negative electrode sheet containing a negative electrode active material layer is formed on at least one side of the negative electrode current collector; A coating is formed on the side of the negative electrode active material layer away from the negative electrode current collector, the coating comprising an inorganic material containing fluorine. The method for forming the coating includes magnetron sputtering, wherein the magnetron sputtering satisfies at least one of the following conditions: The vacuum level of the magnetron sputtering method is less than or equal to 1×10⁻⁶. -3 Pa; The sputtering power of the magnetron sputtering method is 1W-100W; The sputtering voltage of the magnetron sputtering method is 5KV-30KV; The sputtering time for the magnetron sputtering method is 10 min to 200 min.

14. The method according to claim 13, characterized in that, The magnetron sputtering method satisfies at least one of the following conditions: The vacuum degree of the magnetron sputtering method is 5×10⁻⁶. -4 Pa-1×10 -3 Pa; The sputtering power of the magnetron sputtering method is 1W-20W; The sputtering voltage of the magnetron sputtering method is 5KV-10KV; The sputtering time for the magnetron sputtering method is 50-120 minutes.

15. The method according to any one of claims 13-14, characterized in that, Before forming a coating on the side of the negative electrode active material layer away from the negative electrode current collector, the method further includes: pre-treating the negative electrode active material layer to obtain a pre-treated negative electrode active material layer.

16. The method according to claim 15, characterized in that, The pretreatment includes plasma treatment.

17. The method according to claim 16, characterized in that, The plasma treatment satisfies at least one of the following conditions: The plasma treatment further includes introducing a carrier gas, the carrier gas including at least one of O2, N2, CO2, and NH3; The vacuum degree of the plasma treatment is less than or equal to 1 × 10⁻⁶. -3 Pa; The discharge power of the plasma treatment is 100W-1200W; The gas flow rate for plasma treatment is 100 mL / min - 1000 mL / min; The plasma treatment time is 1 min to 20 min.

18. The method according to claim 17, characterized in that, The plasma treatment satisfies at least one of the following conditions: The vacuum degree of the plasma treatment is 5 × 10⁻⁶. -4 Pa-1×10 -3 Pa; The discharge power of the plasma treatment is 100W-1000W; The gas flow rate for plasma treatment is 100 mL / min - 800 mL / min; The plasma treatment time is 2 min to 10 min.

19. The method according to any one of claims 15-18, characterized in that, The pretreated negative electrode active material layer satisfies at least one of the following conditions: The roughness of the pretreated negative electrode active material layer is 50nm-200nm; The surface of the pretreated negative electrode active material layer has active groups.

20. The method according to claim 19, characterized in that, The active group includes at least one of -OH, -NH2, -COOH, -C=O, and -SO3H.

21. A battery module, characterized in that, The secondary battery includes the secondary battery according to any one of claims 1-12, or the secondary battery including the negative electrode sheet prepared by the method according to any one of claims 13-20.

22. A battery pack, characterized in that, Includes the battery module as described in claim 21.

23. An electrical appliance, characterized in that, It includes at least one selected from the secondary battery according to any one of claims 1-12, the secondary battery having a negative electrode sheet prepared by the method according to any one of claims 13-20, the battery module according to claim 21, and the battery pack according to claim 22.

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