Secondary battery and preparation method therefor, and electric device

Abstract

A secondary battery and a preparation method therefor, and an electric device. The secondary battery comprises a negative electrode sheet, at least one side of the negative electrode sheet is provided with a functional layer, the material of the functional layer comprises a ceramic material, and the ceramic material comprises at least one of an oxide and a carbide. The thickness of the functional layer is greater than or equal to 5 nm and less than 30 nm.

Description

Secondary batteries and their preparation methods, and electrical equipment Technical Field

[0001] This application relates to the field of batteries, specifically to secondary batteries and their preparation methods and electrical devices. Background Technology

[0002] Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. Battery safety is a crucial aspect of its application and development, and among these, high-temperature thermal stability is one of the most important factors affecting battery safety.

[0003] Taking lithium-ion batteries as an example, lithium-ion batteries have the advantage of high energy density. However, due to this high energy density, lithium-ion batteries are prone to thermal runaway under improper use or extreme conditions (overcharging, over-discharging, short circuits, etc.), which limits their use in EVs ("Electric Vehicles") and HEVs ("Hybrid Electric Vehicles"). To adapt to the trend of larger lithium-ion batteries, the requirements for high-temperature thermal stability need to be further improved.

[0004] Application content

[0005] The first aspect of this application proposes a secondary battery, including a negative electrode sheet, at least one side of which is provided with a functional layer. The material of the functional layer includes a ceramic material, which includes at least one of oxides and carbides. The thickness of the functional layer is greater than or equal to 5 nm and less than 30 nm.

[0006] This application improves the high-temperature thermal stability of the battery by setting a functional layer of ceramic material on the negative electrode sheet, and helps to reduce the problem of battery internal resistance deterioration.

[0007] In some implementations, the thickness of the functional layer is 8nm to 28nm. This helps improve the high-temperature thermal stability of the battery and mitigate the deterioration of its internal resistance.

[0008] In some implementations, the thickness of the functional layer is 15nm to 25nm. This helps to improve the high-temperature thermal stability of the battery and reduce the problem of deterioration in battery internal resistance.

[0009] In some embodiments, the oxide contains at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, and Ta, and the non-metallic element includes one or more of Si and B. Oxide ceramic materials containing at least one of these metallic and non-metallic elements are beneficial for providing good thermal insulation and for isolating the negative electrode and the electrolyte.

[0010] In some embodiments, the carbide contains at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, and Ta, and the non-metallic element includes one or more of Si and B. Carbide ceramic materials containing at least one of these metallic and non-metallic elements are beneficial for providing good thermal insulation and for isolating the negative electrode and the electrolyte.

[0011] In some implementations, the secondary battery satisfies at least one of the following (I) and (II):

[0012] (I) Oxides include one or more of the following, whether stoichiometric or non-stoichiometric: aluminum oxide, zirconium oxide, magnesium oxide, chromium oxide, niobium pentoxide, tantalum oxide, silicon oxide, and boron oxide;

[0013] (II) Carbides include one or more of the following, whether stoichiometric or non-stoichiometric: aluminum carbide, zirconium carbide, magnesium carbide, chromium carbide, niobium carbide, tantalum carbide, silicon carbide, and boron carbide.

[0014] The aforementioned oxide ceramic materials or carbide ceramic materials are beneficial for providing better heat insulation and isolation between the negative electrode and the electrolyte. Furthermore, there is a certain difference in dielectric constant between stoichiometric metal oxides and non-stoichiometric metal oxides. This application can control the dielectric constant by adjusting the stoichiometric number of the non-stoichiometric metal oxides to obtain a relatively high dielectric constant, thereby reducing the energy barrier, improving lithium-ion transport efficiency, and thus helping to improve the problem of battery internal resistance degradation.

[0015] In some implementations, the secondary battery satisfies at least one of the following (A) and (B):

[0016] (A) Oxides include ZrO 2-x1 TiO 2-x2 ZnO 1-x3 CeO 2-x4 Nb2O 5-x5 Ta2O 5-x6 B2O 3-x7One or more of them; wherein, 0.05≤x1≤0.5, 0.05≤x2≤0.5, 0<x3<1, 0.1≤x4≤0.3, 0<x5<5, 0<x6<5, 0<x7<3;

[0017] (B) Carbides include TiC 1-x8 Where 0 < x8 < 1.

[0018] The aforementioned non-stoichiometric oxides or carbides help to better reduce the energy barrier and improve the lithium-ion transport efficiency, thereby helping to improve the problem of battery internal resistance deterioration.

[0019] In some embodiments, the standard deviation of the film resistance of the negative electrode is 0.2 mΩ to 1 mΩ. When the standard deviation of the film resistance of the negative electrode meets the above condition, the functional layer on the surface of the negative electrode has good uniformity, which is beneficial to improving the high-temperature thermal stability of the battery.

[0020] In some embodiments, the standard deviation of the film resistance of the functional layer is 0.3 mΩ to 0.8 mΩ. When the standard deviation of the film resistance of the negative electrode meets the above condition, the functional layer on the surface of the negative electrode has better uniformity, which is beneficial for improving the high-temperature thermal stability of the battery.

[0021] In some embodiments, the negative electrode includes a negative current collector and a negative electrode film layer, with a functional layer located on the side of the negative electrode film layer away from the negative current collector. The negative electrode film layer includes a negative electrode active material. The secondary battery also includes an electrolyte. The negative electrode active material layer is disposed on either or both of the two opposing surfaces of the negative current collector. The electrolyte acts as a conductor of ions between the positive and negative electrode sheets.

[0022] In some embodiments, the negative electrode active material includes one or more of the following: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and titanates. These negative electrode active materials may be used alone or in combination of two or more.

[0023] In some implementations, the dielectric constant of the ceramic material is lower than that of the electrolyte but higher than that of the negative electrode active material. This is beneficial for improving lithium-ion transport efficiency and mitigating the problem of increased battery internal resistance.

[0024] In some implementations, the dielectric constant of the ceramic material is between 15 and 90. This helps to improve the efficiency of lithium-ion transport at the interface and alleviate the problem of increased internal resistance in the battery.

[0025] In some implementations, the dielectric constant of the ceramic material is 20–70. This is beneficial for improving interfacial lithium-ion transport efficiency and mitigating the problem of increased battery internal resistance.

[0026] In some embodiments, the film resistance of the negative electrode is 9mΩ to 50mΩ. The relatively low film resistance of the provided negative electrode mitigates the problem of deterioration in the battery's internal resistance.

[0027] In some implementations, the mass of the ceramic material is 0.01% to 0.1% of the mass of the negative electrode sheet. This helps to balance improving the high-temperature thermal stability of the battery and mitigating the problem of battery internal resistance deterioration.

[0028] The second aspect of this application discloses a method for preparing a secondary battery, comprising:

[0029] A functional layer is formed on at least one side of the negative electrode; the material of the functional layer includes a ceramic material, which includes at least one of oxides and carbides, and the thickness of the functional layer is greater than or equal to 5 nm and less than 30 nm.

[0030] The negative electrode preparation steps provided in this application form a functional layer of ceramic material on the negative electrode, which can improve the high-temperature thermal stability of the battery and help reduce the problem of battery internal resistance deterioration.

[0031] In some embodiments, a functional layer is formed on at least one side of the negative electrode using thin-film deposition technology. The thin-film deposition technology includes one or more of physical vapor deposition (PVD) and chemical vapor deposition (CVD). PVD includes one or more of arc ion plating, magnetron sputtering, and electron beam evaporation. Using thin-film deposition technology to form a functional layer on at least one side of the negative electrode facilitates control over the thickness and uniformity of the functional layer.

[0032] In some embodiments, an arc ion plating method is used to form a functional layer on at least one side of the negative electrode, including the steps of:

[0033] In a vacuum environment, an arc power supply is turned on to generate an arc discharge on the target surface. The temperature of the negative electrode is controlled, a working gas is introduced, and a bias power supply is connected. The ions in the working gas bombard the target under the influence of the bias electric field. By adjusting the arc discharge power and the deposition time, a functional layer is deposited on the surface of the negative electrode, resulting in a negative electrode with a functional layer. By using arc ion plating to form a functional layer on the negative electrode surface, and by controlling various preparation parameters, it is possible to better control the thickness and uniformity of the functional layer.

[0034] In some embodiments, the working gas includes a carrier gas, and the target material includes one or more of oxides and carbides;

[0035] Alternatively, the working gas may include a carrier gas and a reactant gas, the reactant gas may include one or more of oxygen sources and carbon sources, and the target material may include one or more of elements, oxides, and carbides.

[0036] In this application, the working gas can be a carrier gas, or a combination of a carrier gas and a reactive gas; wherein, the reactive gas reacts with ions generated by sputtering the target material to form a ceramic material deposited on the surface of the negative electrode to form a functional layer.

[0037] In some implementations, arc ion plating satisfies one or more of the following (i) to (v):

[0038] (i) The oxygen source includes one or more of oxygen (O2) and ozone (O3);

[0039] (ii) The carbon source includes one or more of acetylene (C2H2), methane (CH4), propane (C3H8), carbon monoxide (CO), and carbon dioxide (CO2);

[0040] (iii) Elements include one or more of metallic elements and non-metallic elements; metallic elements include one or more of aluminum, zirconium, magnesium, chromium, niobium, and tantalum; non-metallic elements include one or more of silicon and boron.

[0041] (iv) The oxide contains one or more of the following elements: metal elements, non-metal elements, metal elements include one or more of Al, Zr, Mg, Cr, Nb, and Ta, and non-metal elements include one or more of Si and B.

[0042] (v) Carbides contain one or more of metallic and non-metallic elements; metallic elements include one or more of Al, Zr, Mg, Cr, Nb, and Ta, and non-metallic elements include one or more of Si and B.

[0043] In this application, a target material containing the aforementioned metallic or non-metallic elements can be selected, which can deposit to form a ceramic material containing oxides or carbides of these elements. This material has high high-temperature stability and chemical stability, and can play a good role in heat insulation, as well as in isolating the negative electrode and electrolyte.

[0044] In some embodiments, the arc ion plating satisfies at least one of the following (a) to (d):

[0045] (a) Control the temperature of the negative electrode to below 200°C;

[0046] (b) The vacuum level is 1×10 -2 Pa ~ 10 × 10 -2 Pa;

[0047] (c) The arc discharge power is 20kW~70kW;

[0048] (d) The deposition time is 50s to 1000s.

[0049] This application can meet the above conditions by controlling the temperature of the negative electrode, which is beneficial for regulating the formation of functional layers with the required thickness, uniformity and other characteristics.

[0050] This application can meet the above conditions by controlling the vacuum level, which is beneficial to obtaining ceramic materials with higher purity, improving the high-temperature thermal stability of the battery, and reducing the problem of battery internal resistance deterioration.

[0051] This application can meet the above conditions by controlling the arc discharge power, which is beneficial for regulating the formation of a functional layer with a smaller thickness and better uniformity.

[0052] This application can meet the above conditions by controlling the deposition time, which is conducive to obtaining a functional layer with a smaller thickness. This helps to improve the high-temperature thermal stability of the battery while reducing the problem of battery internal resistance deterioration.

[0053] In some embodiments, the arc ion plating satisfies at least one of the following (a) to (b):

[0054] (a) Control the temperature of the negative electrode plate to 50℃~170℃;

[0055] (b) The vacuum degree is 1.5 × 10⁻⁶ -2 Pa ~ 5 × 10 -2 Pa;

[0056] (c) Output power is 30kW~50kW;

[0057] (d) The deposition time is 100s to 500s.

[0058] This application can meet the above conditions by controlling the temperature of the negative electrode, which is conducive to better controlling the formation of functional layers with the required thickness, uniformity and other characteristics.

[0059] This application can meet the above conditions by controlling the vacuum level, which is conducive to obtaining ceramic materials with higher purity, and better improving the high-temperature thermal stability of the battery and reducing the problem of battery internal resistance deterioration.

[0060] This application can meet the above conditions by controlling the arc discharge power, which is beneficial for regulating the formation of functional layers with smaller thickness and better uniformity.

[0061] This application can meet the above conditions by controlling the deposition time, which is conducive to obtaining a functional layer with a smaller thickness. This helps to improve the high-temperature thermal stability of the battery while reducing the problem of battery internal resistance deterioration.

[0062] The third aspect of this application discloses an electrical device comprising the secondary battery described in the first aspect, or a secondary battery prepared by the method described in the second aspect. The electrical device provided by this application possesses the beneficial effects of the aforementioned secondary battery and exhibits better safety performance.

[0063] Additional aspects and advantages of this application 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 application. Attached Figure Description

[0064] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0065] Figure 1 is a schematic diagram of a battery according to one embodiment of this application.

[0066] Figure 2 is an exploded view of the battery according to one embodiment of this application shown in Figure 1.

[0067] Figure 3 is a schematic diagram of a battery module according to one embodiment of this application.

[0068] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0069] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0070] Figure 6 is a schematic diagram of an electrical device in which a battery is used as a power source according to an embodiment of this application.

[0071] The markings in Figures 1-6 are as follows: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Battery; 51 Housing; 52 Electrode assembly; 53 Cover plate.

[0072] Figure 7 is an XPS image of the negative electrode of the battery obtained in the embodiment of this application.

[0073] Figure 8 is a graph showing the DCR changes of the battery obtained in the embodiments of this application.

[0074] Figure 9 is a DSC test diagram of the zirconium-containing material of the negative electrode obtained in the embodiments and comparative examples of this application; wherein, line b represents the test result of comparative example 1; and line a represents the test result of example 5. Detailed Implementation

[0075] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0076] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0077] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0078] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0079] 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.

[0080] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing. Battery safety is a crucial aspect of its application and development, and among these, high-temperature thermal stability is one of the important factors affecting battery safety.

[0081] Taking lithium-ion batteries as an example, improper use or extreme conditions (overcharging, over-discharging, short circuits, etc.) can easily lead to thermal runaway, necessitating further improvements in high-temperature thermal stability. Specifically, polyolefin microporous separators used in lithium-ion batteries are prone to short circuits at high temperatures, causing safety accidents. To address this issue, researchers have proposed coated separators, which involve applying a high-temperature resistant coating to the separator surface to provide insulation and prevent thermal runaway. However, the high-temperature thermal stability needs further improvement, and this has ironically worsened the battery's internal resistance. This is because during charging, lithium ions escape from the positive electrode, move through the electrolyte to the negative electrode, and embed themselves in the negative electrode active material; during discharging, lithium ions escape from the negative electrode, move through the electrolyte to the positive electrode, and embed themselves in the positive electrode active material. Current technologies typically use a slurry containing insulating materials to form an insulating coating on the separator surface. This coating is quite thick, even reaching the micrometer level, which lengthens the lithium ion transport path, increasing the diffusion resistance and significantly worsening the battery's internal resistance.

[0082] Therefore, the first aspect of this application proposes a secondary battery, including a negative electrode sheet, at least one side of which is provided with a functional layer, the material of which includes a ceramic material, the ceramic material including at least one of oxides and carbides, and the thickness of the functional layer being greater than or equal to 5 nm and less than 30 nm.

[0083] The "thickness" of the functional layer has a well-known definition in the art and can be measured using well-known testing methods, such as transmission electron microscopy (TEM). As an example, using TEM specifically, FIB-TEM refers to a technique combining focused ion beam (FIB) technology with transmission electron microscopy (TEM). The procedure is as follows: First, the target area of ​​the negative electrode is finely milled using FIB to obtain a sufficiently thin sheet for subsequent TEM testing. The sample holder with the sheet is then loaded into the TEM microscope. The thickness of the functional layer is directly measured on the image using TEM software tools. To improve accuracy, measurements can be repeated at multiple locations, and the average value can be calculated as the thickness of the functional layer. FIB: Thermo Scientific-Scios 2HiVac; TEM: Thermo Scientific-Talos F200S G2.

[0084] As an example, the thickness of the functional layer can be 5nm~29nm, 5nm~28nm, 5nm~27nm, 5nm~26nm, etc. Specifically, the thickness of the functional layer is 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, etc., or a range of any two of the above values ​​or a value within the range.

[0085] By setting a functional layer containing ceramic materials on the negative electrode, the high-temperature thermal stability of the battery can be improved, and the problem of battery internal resistance deterioration can be mitigated.

[0086] In this embodiment, the functional layer containing ceramic material can improve the high-temperature thermal stability of the battery because: 1) Ceramic materials, such as oxide ceramic materials or carbide ceramic materials, have high melting points (for example, above 2000℃), poor thermal conductivity, and good chemical stability at high temperatures. The functional layer can act as a heat insulation layer, slowing down the heat transfer rate in the battery and reducing thermal conductivity, thereby improving the battery's high-temperature stability. 2) Side reactions occur when the negative electrode comes into contact with the electrolyte, especially at higher temperatures, which exacerbates the severity of these reactions and releases more heat. By providing a functional layer on the surface of the negative electrode, the contact between the electrolyte and the negative electrode can be isolated, reducing the occurrence and rate of side reactions, thus reducing the exothermic reaction and improving the battery's high-temperature thermal stability. 3) During battery charging and discharging, the negative electrode experiences volume changes and mechanical stress. The functional layer on the surface of the negative electrode provides some protection, reducing damage during cycling and thus improving high-temperature thermal stability.

[0087] In this embodiment, the functional layer of ceramic material also helps to mitigate the deterioration of battery internal resistance. The ceramic material functional layer formed on the surface of the negative electrode in this embodiment has a small thickness, at the nanometer level (below 30 nm). Therefore, the lithium-ion transport path is relatively short, resulting in less impact on lithium-ion transport efficiency. This effectively mitigates the deterioration of battery internal resistance and achieves better battery dynamic performance.

[0088] In some embodiments of this application, the thickness of the functional layer is 8 nm to 28 nm.

[0089] In this embodiment, the thickness of the functional layer meets the above conditions, which can improve the high-temperature thermal stability of the battery and help to further reduce the problem of battery internal resistance deterioration.

[0090] In some embodiments of this application, the thickness of the functional layer is 15nm to 25nm.

[0091] In this embodiment, the thickness of the functional layer meets the above conditions, which can improve the high-temperature thermal stability of the battery and reduce the change in the battery's internal resistance, thus effectively mitigating the problem of battery internal resistance deterioration. As an example, taking the battery internal resistance DCR of a negative electrode without a functional layer as a benchmark, the increase in the battery internal resistance DCR of a negative electrode with a functional layer is within 5%, which is beneficial to effectively mitigating the problem of battery internal resistance deterioration.

[0092] In some embodiments of this application, the oxide contains at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, and Ta, and the non-metallic element includes one or more of Si and B.

[0093] In the embodiments of this application, the oxide used as the ceramic material can be an oxide containing one or more metal elements, an oxide containing one or more non-metal elements, or an oxide containing both metal and non-metal elements.

[0094] As an example, the metal element can be one or more of Al, Zr, Mg, Cr, Nb, and Ta. Oxide ceramic materials containing these metal elements have high high-temperature stability and chemical stability, and can play a good role in heat insulation, as well as isolation of the negative electrode and electrolyte.

[0095] As an example, non-metallic elements can be, but are not limited to, one or more of Si and B. Oxide ceramic materials containing these non-metallic elements have high high-temperature stability and chemical stability, and can play a good role in heat insulation, as well as isolation of the negative electrode and electrolyte.

[0096] In some embodiments of this application, the carbide contains at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, and Ta, and the non-metallic element includes one or more of Si and B.

[0097] In the embodiments of this application, the carbide used as the ceramic material can be a carbide containing one or more metal elements, a carbide containing one or more non-metal elements, or a carbide containing both metal and non-metal elements.

[0098] As an example, the metal element can be one or more of Al, Zr, Mg, Cr, Nb, and Ta. Carbide ceramic materials containing these metal elements have high high-temperature stability and chemical stability, and can play a good role in heat insulation, as well as isolation of the negative electrode and electrolyte.

[0099] As an example, non-metallic elements can be, but are not limited to, one or more of Si and B. Carbide ceramic materials containing these non-metallic elements have high high-temperature stability and chemical stability, and can play a good role in heat insulation, as well as isolation of the negative electrode and electrolyte.

[0100] In some embodiments of this application, the ceramic material may be one or a combination of two of the above-mentioned oxides and carbides.

[0101] Under normal operating conditions, a solid electrolyte interphase (SEI) film forms on the surface of the negative electrode, protecting the active material. However, when the battery temperature is too high or subjected to thermal shock, unstable components in the SEI layer decompose, releasing heat. In this embodiment, a ceramic functional layer is formed on the surface of the negative electrode. The SEI is mainly adsorbed onto the surface of the functional layer through van der Waals forces. Furthermore, since the functional layer contains metal ions, they may form ionic bonds with the SEI film, thus anchoring the SEI to the surface of the functional layer through chemical bonding. In this way, the functional layer provides good fixation and protection for the SEI film, increases the decomposition temperature of the SEI film, reduces heat release, and improves the high-temperature thermal stability of the SEI, thereby enhancing the high-temperature thermal stability of the battery.

[0102] Furthermore, in the embodiments of this application, the material of the functional layer can be directly ceramic material, without binders, dispersants and other auxiliary materials, which is conducive to better improving the high-temperature thermal stability of the battery.

[0103] In some embodiments of this application, the secondary battery satisfies at least one of the following (I) and (II):

[0104] (I) Oxides include one or more of the following, whether stoichiometric or non-stoichiometric: aluminum oxide, zirconium oxide, magnesium oxide, chromium oxide, niobium pentoxide, tantalum oxide, silicon oxide, and boron oxide;

[0105] (II) Carbides include one or more of the following, whether stoichiometric or non-stoichiometric: aluminum carbide, zirconium carbide, magnesium carbide, chromium carbide, niobium carbide, tantalum carbide, silicon carbide, and boron carbide.

[0106] The oxides include one or more of aluminum oxide (Al₂O₃), zirconium oxide (ZrO₂), magnesium oxide (MgO), chromium oxide (Cr₂O₃), niobium pentoxide (Nb₂O₅), and tantalum oxide (Ta₂O₅), or one or more non-stoichiometric oxides of these oxides. Among them, "non-stoichiometric oxides" include: ① anion-deficient type, in which the number of oxygen atoms is less than the theoretical value, leading to the formation of oxygen vacancies; ② cation-excess type, in which the number of metal atoms is more than the theoretical value, leading to the formation of interstitial defects.

[0107] Oxides also include one or more of silicon oxide (SiO2) and boron oxide (B2O3), or one or more of the non-stoichiometric oxides of these oxides. "Non-stoichiometric oxides" include: ① anion-deficient type, in which the number of oxygen atoms is less than the theoretical value, leading to the formation of oxygen vacancies; ② cation-excess type, in which the number of non-metallic atoms is more than the theoretical value, leading to the formation of non-metallic interstitial defects.

[0108] Furthermore, the oxide includes one or more of aluminum oxide (Al2O3), zirconium oxide (ZrO2), magnesium oxide (MgO), chromium oxide (Cr2O3), niobium pentoxide (Nb2O5), and tantalum oxide (Ta2O5).

[0109] Furthermore, the oxides also include one or more of silicon oxide (SiO2) and boron oxide (B2O3).

[0110] Carbides include one or more of aluminum carbide (Al4C3), zirconium carbide (ZrC), magnesium carbide (Mg2C3 or MgC2), chromium carbide (Cr3C2), niobium carbide (NbC), and tantalum carbide (TaC), or one or more non-stoichiometric carbides of these carbides. Among them, "non-stoichiometric carbides" include: ① anion-deficient type, in which the number of carbon atoms is less than the theoretical value, leading to the formation of carbon vacancies; ② cation-excess type, in which the number of metal atoms is more than the theoretical value, leading to the formation of intermetallic defects.

[0111] Oxides also include one or more of silicon carbide (SiC) and boron carbide (B4C), or one or more non-stoichiometric carbides of these carbides. "Non-stoichiometric carbides" include: ① anion-deficient types, in which the number of carbon atoms is less than the theoretical value, leading to the formation of carbon vacancies; ② cation-excess types, in which the number of non-metallic atoms is more than the theoretical value, leading to the formation of non-metallic interstitial defects.

[0112] Furthermore, the carbides include one or more of aluminum carbide (Al4C3), zirconium carbide (ZrC), magnesium carbide (Mg2C3 or MgC2), chromium carbide (Cr3C2), niobium carbide (NbC), and tantalum carbide (TaC).

[0113] Furthermore, the oxides also include one or more of silicon carbide (SiC) and boron carbide (B4C).

[0114] In some embodiments of this application, the secondary battery satisfies at least one of the following (A) and (B):

[0115] (A) Oxides include ZrO 2-x1 TiO 2-x2 ZnO 1-x3 CeO 2-x4 Nb2O 5-x5 Ta2O 5-x6 B2O 3-x7 One or more of them; wherein, 0.05≤x1≤0.5, 0.05≤x2≤0.5, 0<x3<1, 0.1≤x4≤0.3, 0<x5<5, 0<x6<5, 0<x7<3;

[0116] (B) Carbides include TiC 1-x8 Where 0 < x8 < 1.

[0117] There is a certain difference in dielectric constant between stoichiometric metal oxides and non-stoichiometric metal oxides. In this application, the dielectric constant is controlled by adjusting the stoichiometric coefficient of the non-stoichiometric metal oxide to obtain a relatively high dielectric constant, thereby reducing the energy barrier, improving the lithium-ion transport efficiency, and thus helping to improve the problem of battery internal resistance deterioration.

[0118] As an example, non-stoichiometric zirconium oxide (ZrO) 2-x1 With a dielectric constant of 0.05≤x1≤0.5, compared to the stoichiometric ZrO2, the dielectric constant is appropriately increased, which can effectively reduce the internal resistance of the battery and also achieve a good effect in preventing battery thermal runaway.

[0119] As an example, non-stoichiometric titanium dioxide (TiO2)2-x2 When x2 ≤ 0.5, the presence of oxygen vacancies introduces additional electronic states, altering the electron cloud distribution and polarization characteristics. This is especially true when x2 is in the range of 0.05–0.15 in TiO2. 2-x The dielectric constant of the stoichiometric TiO2 is significantly increased compared to that of the stoichiometric TiO2, which helps to reduce the internal resistance of the battery.

[0120] As an example, non-stoichiometric ZnO 1-x3 0 < x3 < 1. Ideally stoichiometric ZnO has a specific crystal structure and dielectric properties. The dielectric constant of non-stoichiometric ZnO can be increased from that of stoichiometry, and it is located between the dielectric constant of the electrolyte and the dielectric constant of the negative electrode active material, which is beneficial to reducing the internal resistance of the battery.

[0121] As an example, non-stoichiometric CeO 2-x4 If 0.1≤x4≤0.3, the dielectric constant may increase significantly, which is beneficial for reducing the internal resistance of the battery.

[0122] In some embodiments of this application, the standard deviation of the film resistance of the negative electrode is 0.2mΩ to 1mΩ.

[0123] The "standard deviation of the film resistance of the negative electrode" refers to the degree of deviation between the film resistance and the average film resistance. It is used to evaluate the uniformity of the functional layer, that is, the consistency of the thickness distribution of the functional layer on the surface of the negative electrode. The uniformity of the functional layer affects the uniformity of the film resistance. Uneven thickness of the functional layer will cause differences in film resistance at different locations, thus increasing the standard deviation of the film resistance. Therefore, the uniformity of the functional layer can be evaluated by the standard deviation of the film resistance. The larger the standard deviation, the more dispersed the distribution of film resistance and the lower the uniformity of the functional layer; the smaller the standard deviation, the more concentrated the distribution of film resistance and the higher the uniformity of the functional layer.

[0124] The standard deviation of the diaphragm resistance can be determined using testing methods known in the art. As an example, the diaphragm resistance can be measured multiple times at different locations on the negative electrode (e.g., selecting ≥9 points; nine or more points can be selected on the surface of the negative electrode in an array with equal spacing). The standard deviation of the diaphragm resistance can then be calculated based on the measured values. The testing method for diaphragm resistance is as follows:

[0125] Diaphragm resistor: Model BER1300, electrode diameter 14mm, applied pressure 25MPa, holding time 25s.

[0126] Test procedure: Cut the diaphragm into a rectangle of approximately 5cm × 10cm and place it between the two electrodes of the diaphragm resistance meter. Set the test pressure and holding time parameters on the MRMS software and start the test. The software will automatically read the diaphragm resistance value.

[0127] As an example, the standard deviation of the film resistance of the negative electrode is 0.2mΩ, 0.3mΩ, 0.4mΩ, 0.5mΩ, 0.6mΩ, 0.7mΩ, 0.8mΩ, 0.9mΩ, 1mΩ, etc., or a range of any two of the above values, or a value within the range.

[0128] In this embodiment, the standard deviation of the film resistance of the negative electrode is small, and the functional layer on the surface of the negative electrode has good uniformity, which is beneficial to improving the high-temperature thermal stability of the battery.

[0129] This is because poor uniformity of the functional layer on the surface of the negative electrode leads to inconsistent contact area and degree between the electrolyte and the negative electrode, easily triggering more local side reactions and causing excessive local heat release. Furthermore, the non-uniformity of the negative electrode surface (such as sharp protrusions or unevenness) may also cause a significant increase in electric field strength in these pointed areas. This enhanced electric field causes electrolyte salt cations (such as lithium ions) to more easily accumulate and deposit in these areas, leading to lithium plating and promoting lithium dendrite growth. Therefore, the exacerbation of local side reactions and the growth of lithium dendrites reduce the high-temperature thermal stability of the battery, which is detrimental to improving battery safety. The negative electrode provided in this application has a functional layer with high uniformity in thickness, which helps to mitigate the exacerbation of local side reactions, reduce lithium plating and even lithium dendrite growth, thereby improving the high-temperature thermal stability of the battery.

[0130] In addition, the thickness uniformity of the functional layer of the negative electrode provided in this application is good, which can promote the effective transport of lithium ions and help reduce the problem of increased local DCR due to local thickening of the functional layer.

[0131] In some embodiments of this application, the standard deviation of the film resistance of the functional layer is 0.3mΩ to 0.8mΩ.

[0132] In this embodiment, the standard deviation of the film resistance of the functional layer satisfies the above conditions, indicating that the functional layer on the surface of the negative electrode has good uniformity, which is beneficial to reduce the occurrence of local side reactions, slow down lithium plating and other problems, and also to reduce the problem of local DCR increase due to local thickening of the functional layer, thereby improving the high-temperature thermal stability of the battery.

[0133] In some embodiments of this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer, the functional layer is located on the side of the negative electrode film layer away from the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material; the secondary battery also includes an electrolyte.

[0134] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector, the negative electrode film layer including a negative electrode active material. As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0135] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0136] In some embodiments of this application, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and titanates.

[0137] As an example, when the battery is a lithium-ion battery, lithium titanate is used; when the battery is a sodium-ion battery, sodium titanate is used. However, the embodiments of this application are not limited to these materials, and other conventional materials that can be used as negative electrode active materials of batteries can also be used. These negative electrode active materials can be used alone or in combination of two or more.

[0138] In some embodiments of this application, the solvent includes one or more 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.

[0139] The solvent can be one of the solvents mentioned above, or a combination of two or more. Furthermore, from a mass percentage perspective, the solvent, as a major component of the electrolyte, affects the overall dielectric constant of the electrolyte.

[0140] As an example, a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) can be used as a solvent for the electrolyte.

[0141] EC has a high dielectric constant, effectively dissolving lithium salts, but its high viscosity can hinder lithium-ion movement to some extent. DMC has a lower viscosity, which facilitates rapid lithium-ion movement in the electrolyte, but its relatively low dielectric constant results in lower lithium salt dissolution and lithium-ion dissociation compared to EC. EMC has a dielectric constant similar to DMC. Using a mixture of EC, DMC, and EMC as a solvent in the electrolyte yields suitable dielectric constants and viscosities, which helps reduce lithium-ion transport resistance. The volume ratio of EC can be controlled between 10% and 40%, and the total volume ratio of DMC and EMC can be controlled between 60% and 90%.

[0142] In some embodiments of this application, the dielectric constant of the ceramic material is less than that of the electrolyte and greater than that of the negative electrode active material.

[0143] The dielectric constant, as it is known in the art, is a physical quantity describing a material's ability to store charge in an electric field. It is the ratio of the material's permittivity to the permittivity of vacuum; in the International System of Units (SI), the dielectric constant is a dimensionless ratio. Test methods known in the art can be used. For example, the dielectric constants of electrolytes, ceramic materials, and negative electrode active materials can be tested using the following methods:

[0144] Testing instruments and equipment: Wheatstone bridge, vernier calipers, high and low temperature chamber, muffle furnace, tablet press.

[0145] Required materials: sample, conductive silver paste, glue.

[0146] For the electrolyte: Place the sample in the sample bath and then into a high-low temperature chamber. Set the temperature range, and gradually increase the temperature of the chamber from low to high. During the heating process, measure the capacitance C of the sample using a bridge at specific temperature points. ε is then calculated using the formula... r =ε / ε0=Cd / ε0S, where: ε is the absolute dielectric constant, ε0 is the vacuum dielectric constant, S is the area of ​​the capacitor plates facing each other, d is the distance between the capacitor plates, and C is the capacitance of the sample being tested. Typically, three or more discs are prepared for each sample, and outliers are removed during testing before taking the average value.

[0147] For ceramic materials and negative electrode active materials: The sample powder is granulated with binder, and the granulated powder is pressed into tablets (round discs) using a tablet press. The discs are then placed in a muffle furnace for slow heating and holding to remove the binder. The debinded discs are removed, and silver is applied to the front side. They are then placed back into the muffle furnace for silver firing. After removal, the back side is silver-coated and fired. After silver firing, the discs are placed in a special fixture, and the fixture is placed in a high-low temperature chamber. A temperature range is set, and the chamber is heated from low to high. During the heating process, the capacitance C of the disc is measured using a bridge at specific temperature points. The capacitance is then calculated using the formula ε. r=ε / ε0=Cd / ε0S, where: ε is the absolute dielectric constant, ε0 is the vacuum dielectric constant, S is the area of ​​the capacitor plates facing each other, d is the distance between the capacitor plates, and C is the capacitance of the sample being tested. Typically, three or more discs are made for each powder sample, and outliers are removed during testing before taking the average value.

[0148] Taking a lithium-ion battery with an electrolyte as an example, the electrolyte acts as a transport medium for lithium ions, allowing them to move freely between the positive and negative electrodes. During charging, lithium ions are released from the positive electrode, move through the electrolyte to the negative electrode, and embed themselves in the negative electrode active material; during discharging, lithium ions are released from the negative electrode, move through the electrolyte to the positive electrode, and embed themselves in the positive electrode active material.

[0149] When lithium ions are inserted and extracted from the electrode surface, they need to be desolvated, that is, freed from the binding of solvent molecules. Since the dielectric constant of the negative electrode active material is relatively small (for example, the dielectric constant of graphite is 15), while the dielectric constant of the electrolyte is relatively large (for example, the dielectric constant of ethylene carbonate is 90), the interfacial interaction between the negative electrode active material and the electrolyte will affect the transport of lithium ions. By setting a functional layer with a dielectric constant higher than that of the negative electrode active material on the surface of the negative electrode, since the dielectric constant of the ceramic material is between that of the negative electrode active material and the electrolyte, it helps to reduce the interfacial energy between lithium ions and the negative electrode material, thereby reducing the energy barrier. In addition, since the dielectric constant of the ceramic material is greater than that of the negative electrode active material, it is also conducive to the desolvation of lithium ions, thereby reducing the energy barrier, improving the transport efficiency of lithium ions, and thus helping to improve the problem of battery internal resistance deterioration.

[0150] In some embodiments of this application, the dielectric constant of the ceramic material is 15 to 90.

[0151] As an example, the dielectric constants of the ceramic materials are 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54. 55, 55, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, etc., or a range consisting of any two of the above values, or values ​​within a range.

[0152] In this embodiment, the dielectric constant of the ceramic material of the functional layer satisfies the above conditions, which helps to reduce the energy barrier for lithium ion transport between the electrolyte and the negative electrode active material, facilitates interfacial lithium ion transport, and better improves the problem of increased battery internal resistance.

[0153] In some embodiments of this application, the dielectric constant of the ceramic material is 20 to 70.

[0154] In this embodiment, the dielectric constant of the ceramic material of the functional layer satisfies the above conditions, which helps to reduce the energy barrier for lithium ion transport between the electrolyte and the negative electrode active material, facilitates interfacial lithium ion transport, and further reduces the internal resistance of the battery.

[0155] In some embodiments of this application, the film resistance of the negative electrode is 9mΩ to 50mΩ.

[0156] The film resistance of the negative electrode refers to the resistance encountered by electrons as they travel through the electrode material in the negative electrode of a battery, and has a meaning known in the art. Under the same conditions, a lower film resistance of the negative electrode indicates a lower internal resistance of the battery; conversely, a higher film resistance indicates a higher internal resistance of the battery. Film resistance can be tested using methods known in the art. For example, the film resistance test method is as follows: Film resistance meter: Model BER1300, electrode diameter 14mm, applied pressure 25MPa, holding time 25s. Test operation: Cut the film into a rectangle approximately 5cm × 10cm, place it between the two electrodes of the film resistance meter, set the test pressure and holding time parameters on the MRMS software, start the test, and the software automatically reads the film resistance value.

[0157] As an example, the film resistance of the negative electrode is 9mΩ, 10mΩ, 11mΩ, 12mΩ, 13mΩ, 14mΩ, 15mΩ, 16mΩ, 17mΩ, 18mΩ, 19mΩ, 20mΩ, 21mΩ, 22mΩ, 23mΩ, 24mΩ, 25mΩ, 26mΩ, 27mΩ, 28mΩ, 29mΩ, 30mΩ, 31mΩ, 32mΩ, 33mΩ, 34mΩ, 35mΩ, 36mΩ, 37mΩ, 38mΩ, 39mΩ, 40mΩ, 41mΩ, 142mΩ, 43mΩ, 44mΩ, 45mΩ, 46mΩ, 47mΩ, 48mΩ, 49mΩ, 50mΩ, etc., or a range of any two of the above values, or a value within a range.

[0158] In this embodiment, the film resistance of the provided negative electrode sheet is relatively small, thereby alleviating the problem of battery internal resistance deterioration. It can even achieve a change in battery internal resistance within ±5%, that is, based on the battery internal resistance of the negative electrode sheet without a functional layer, the film resistance of the negative electrode sheet with a functional layer increases by less than 5%, and may even achieve the effect of reducing internal resistance by 5%.

[0159] Furthermore, the film resistance of the negative electrode is 9mΩ to 20mΩ.

[0160] In some embodiments of this application, the mass of the ceramic material is 0.01% to 0.1% of the mass of the negative electrode sheet.

[0161] The mass of the ceramic material is a percentage of the mass of the negative electrode sheet, which refers to a negative electrode sheet with a functional layer. It can be determined using methods known in the art, such as ICP (Inductively Coupled Plasma) detection. For example, ICP-MS (Inductively Coupled Plasma Mass Spectrometry) is used. Specifically, the negative electrode current collector is removed from the negative electrode sheet before detection, meaning the negative electrode film layer (containing the negative electrode active material) and the functional layer on the surface of the current collector are retained for detection. The detection standard can refer to EPA 6010D-2018. For example, the mass of the ceramic material can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, etc., of the mass of the negative electrode sheet, or a range of any two of the above values, or a value within a range of such values.

[0162] In this embodiment, the higher the mass ratio of ceramic material to the negative electrode sheet, the thicker the functional layer containing ceramic material on the surface of the negative electrode sheet. Meeting these conditions helps improve the high-temperature stability of the battery and achieve better safety performance. At the same time, it helps to improve the problem of battery internal resistance deterioration and improve battery dynamic performance.

[0163] Furthermore, the mass of the ceramic material is 0.03% to 0.9% of the mass of the negative electrode sheet.

[0164] In this embodiment, the quality of the ceramic material meets the above conditions, which helps to better balance improving the high-temperature thermal stability of the battery and mitigating the problem of battery internal resistance deterioration.

[0165] The second aspect of this application discloses a method for preparing a secondary battery, comprising:

[0166] A functional layer is formed on at least one side of the negative electrode; the material of the functional layer includes a ceramic material, which includes at least one of oxides and carbides, and the thickness of the functional layer is greater than or equal to 5 nm and less than 30 nm.

[0167] The negative electrode preparation steps provided in this application form a functional layer of ceramic material on the negative electrode, which can improve the high-temperature thermal stability of the battery and help reduce the problem of battery internal resistance deterioration.

[0168] In this embodiment, the functional layer of ceramic material can improve the high-temperature thermal stability of the battery because: 1) Ceramic materials, such as oxide ceramic materials or carbide ceramic materials, have high melting points (for example, above 2000℃), poor thermal conductivity, and good chemical stability at high temperatures. The functional layer can act as a heat insulation layer, slowing down the heat transfer rate in the battery and reducing thermal conductivity, thereby improving the high-temperature stability of the battery. 2) Side reactions occur when the negative electrode comes into contact with the electrolyte, especially at higher temperatures, which exacerbates the severity of these reactions and releases more heat. By setting a functional layer on the surface of the negative electrode, the contact between the electrolyte and the negative electrode can be isolated, reducing the occurrence and rate of side reactions, thus reducing the heat released by side reactions and improving the high-temperature thermal stability of the battery. 3) During battery charging and discharging, the negative electrode experiences volume changes and mechanical stress. The functional layer on the surface of the negative electrode provides some protection, reducing damage during cycling and thus improving high-temperature thermal stability.

[0169] In this embodiment, the functional layer of ceramic material also helps to mitigate the deterioration of battery internal resistance. The ceramic material functional layer formed on the surface of the negative electrode in this embodiment has a small thickness, at the nanometer level (below 30 nm). Therefore, the lithium-ion transport path is relatively short, resulting in less impact on lithium-ion transport efficiency. This effectively mitigates the deterioration of battery internal resistance and achieves better battery dynamic performance.

[0170] In some embodiments of this application, a functional layer is formed on at least one side of the negative electrode using thin film deposition technology; the thin film deposition technology includes one or more of physical vapor deposition and chemical vapor deposition; physical vapor deposition includes one or more of arc ion plating, magnetron sputtering, and electron beam evaporation.

[0171] This application employs thin-film deposition technology to form a functional layer on at least one side of the negative electrode sheet, which facilitates better control over the thickness and uniformity of the functional layer. Compared to existing methods that use slurry spin coating to prepare thermal insulation functional layers, the functional layer obtained in this application has a thickness at the nanometer level and does not require a binder, thus improving the purity of the functional layer. This is beneficial for improving the high-temperature thermal stability of the battery and mitigating the problem of battery internal resistance deterioration.

[0172] In addition, as an example, a functional layer is formed on at least one side of the negative electrode using one of the following methods: arc ion plating, magnetron sputtering, or electron beam evaporation.

[0173] For example, arc ion plating utilizes the principle of electric arc discharge. The arc discharge generates high-energy electrons, which can ionize part of the working gas to form plasma. These high-energy electrons and plasma bombard the target material, melting and ionizing it. The resulting metal ions are deposited on the substrate (i.e., the surface of the negative electrode) under a negative bias. This method typically uses high-temperature materials such as tungsten electrodes as electrodes and is suitable for preparing coating materials with high hardness and high wear resistance, with relatively high film formation efficiency.

[0174] For example, magnetron sputtering uses a magnetic field to accelerate ions and bombard the surface of a target material, causing the target atoms or molecules to detach and deposit onto a substrate. Magnetron sputtering typically uses inert gases such as argon as the ion source and is suitable for preparing high-quality, high-performance thin film materials, resulting in denser films.

[0175] For example, electron beam evaporation uses accelerated electrons to bombard the coating material, converting the kinetic energy of the electrons into heat energy to heat and evaporate the coating material.

[0176] In some embodiments of this application, an arc ion plating method is used to form a functional layer on at least one side of the negative electrode sheet, including the following steps:

[0177] In a vacuum environment, the arc power supply is turned on to generate an arc discharge on the surface of the target material. The temperature of the negative electrode is controlled, a working gas is introduced, and a bias power supply is turned on. The ions of the working gas bombard the target material under the action of the bias electric field. The arc discharge power of the bombardment and the coating deposition time are adjusted to deposit a functional layer on the surface of the negative electrode, thus obtaining a negative electrode with a functional layer.

[0178] In this embodiment, an electric arc ion plating is used to form a functional layer on the surface of the negative electrode. By applying high voltage and high current, an electric arc is ignited between the evaporation source (i.e., the target material) and the substrate (i.e., the negative electrode sheet); the high temperature of the electric arc causes the target material to evaporate and ionize rapidly, forming plasma; the ionized plating particles are accelerated towards the surface of the substrate under the action of the electric field and deposited on the surface of the substrate, gradually forming a thin film.

[0179] The functional layer is deposited on the surface of the negative electrode by arc ion plating. The material of the functional layer can be controlled by selecting the target material and the type of working gas. The performance of the functional layer (such as thickness, uniformity, standard deviation of film resistance, film resistance, etc.) can be controlled by adjusting the preparation parameters, such as heating temperature, vacuum degree, arc discharge power, and deposition time.

[0180] In some embodiments of this application,

[0181] The working gas includes a carrier gas, and the target material includes one or more of oxides and carbides.

[0182] Alternatively, the working gas may include a carrier gas and a reactant gas, the reactant gas may include one or more of oxygen sources and carbon sources, and the target material may include one or more of elements, oxides, and carbides.

[0183] In the embodiments of this application, the working gas can be a carrier gas, such as argon. As an example, if an oxide is used as the target material, the plasma formed after the target material is bombarded by high-energy electrons and plasma is deposited on the surface of the negative electrode to form a functional layer of oxide-based ceramic material; if a carbide is used as the target material, the plasma formed after the target material is bombarded by high-energy electrons and plasma is deposited on the surface of the negative electrode to form a functional layer of carbide-based ceramic material.

[0184] In this embodiment, the working gas can also be a carrier gas and a reactant gas. For example, if the reactant gas is an oxygen source, such as oxygen, and the target material is an element, then the plasma formed after the target material is bombarded by high-energy electrons and plasma reacts with the plasma of the reactant gas and deposits on the surface of the negative electrode to form a functional layer of oxide-based ceramic material. Alternatively, if the reactant gas is a carbon source, such as acetylene, and the target material is an element, then the plasma formed after the target material is bombarded by high-energy electrons and plasma reacts with the plasma of the reactant gas and deposits on the surface of the negative electrode to form a functional layer of carbide-based ceramic material.

[0185] In some embodiments of this application, arc ion plating satisfies one or more of the following (i) to (v):

[0186] (i) The oxygen source includes one or more of oxygen (O2) and ozone (O3);

[0187] (ii) The carbon source includes one or more of acetylene (C2H2), methane (CH4), propane (C3H8), carbon monoxide (CO), and carbon dioxide (CO2);

[0188] (iii) Elements include one or more of metallic elements and non-metallic elements; metallic elements include one or more of aluminum, zirconium, magnesium, chromium, niobium, and tantalum; non-metallic elements include one or more of silicon and boron.

[0189] (iv) The oxide contains one or more of the following elements: metal elements, non-metal elements, metal elements include one or more of Al, Zr, Mg, Cr, Nb, and Ta, and non-metal elements include one or more of Si and B.

[0190] (v) Carbides contain one or more of metallic and non-metallic elements; metallic elements include one or more of Al, Zr, Mg, Cr, Nb, and Ta, and non-metallic elements include one or more of Si and B.

[0191] In this embodiment, a target material containing the aforementioned metallic or non-metallic elements can be selected, which can deposit to form a ceramic material containing oxides or carbides of these elements. This material has high high-temperature stability and chemical stability, and can play a good role in heat insulation, as well as in isolating the negative electrode and electrolyte.

[0192] In some embodiments of this application, the arc ion plating satisfies at least one of the following (a) to (d):

[0193] (a) Control the temperature of the negative electrode to below 200°C;

[0194] (b) The vacuum level is 1×10 -2 Pa ~ 10 × 10 -2 Pa;

[0195] (c) The arc discharge power is 20kW~70kW;

[0196] (d) The deposition time is 50s to 1000s.

[0197] In this embodiment, controlling the temperature of the negative electrode affects the thickness, uniformity, and other properties of the functional layer. Controlling the temperature of the negative electrode to meet the above conditions facilitates the formation of the functional layer with the required thickness and uniformity, and also helps prevent the negative electrode from being damaged by heat.

[0198] Controlling the temperature of the negative electrode affects the crystal growth process of oxides or nitrides on its surface. Taking zirconium as the target material, argon as the carrier gas, and oxygen as the reactant gas as an example: as the temperature decreases, the atomic diffusion rate slows down, making it difficult for Zr and O atoms to diffuse sufficiently and arrange themselves according to the stoichiometric ratio, which may lead to an incomplete ZrO2 crystal structure and deviations in the stoichiometric coefficients. As the temperature increases, ZrO2 crystals may overgrow, resulting in lattice distortion, which will also indirectly affect the stoichiometric coefficients.

[0199] As an example, the temperature of the negative electrode is controlled to be 200℃, 195℃, 195℃, 190℃, 185℃, 180℃, 175℃, 170℃, 165℃, 160℃, 155℃, 150℃, 145℃, 140℃, 135℃, 130℃, 125℃, 120℃, 115℃, 110℃, 105℃, 100℃, 95℃, 90℃, 85℃, 80℃, 75℃, 70℃, 65℃, 60℃, 55℃, 50℃, 45℃, 40℃, etc., or a range of any two of the above values, or a value within a range of the above values.

[0200] In this embodiment, the vacuum level affects the purity and stoichiometry of the ceramic material in the functional layer. A lower vacuum level results in fewer impurities in the reaction environment. A vacuum level that meets these conditions facilitates the acquisition of high-purity ceramic materials, better improving the high-temperature thermal stability of the battery and mitigating the problem of internal resistance deterioration. Furthermore, the vacuum level may also affect the stoichiometry of oxides or nitrides. Taking zirconium as the target material, argon as the carrier gas, and oxygen as the reactant gas as an example: as the vacuum level increases, the presence of other gases in the system dilutes the partial pressure of oxygen, making it difficult to precisely control the number of oxygen ions participating in the reaction to generate ZrO2, causing the ZrO2 stoichiometry to deviate from the expected value. Conversely, as the vacuum level decreases, the gas molecule density increases, making it easier for metal ions and oxygen ions to scatter and collide with other gas molecules during transport. This alters the ion trajectory and energy, reducing the probability of effective collisions and combinations between metal ions and oxygen ions to generate ZrO2, thus affecting the stoichiometry.

[0201] As an example, the vacuum level is 1×10⁻⁶. -2 Pa, 2×10 -2 Pa, 3×10 -2 Pa, 4×10 -2 Pa, 5×10 -2 Pa, 6×10 -2 Pa, 7×10 -2 Pa, 8×10 -2 Pa, 9×10 -2 Pa, 10×10 -2 Pa, etc., is either a range consisting of any two of the above values ​​or a value within the range.

[0202] In this embodiment, the arc discharge power affects the thickness, uniformity, and other characteristics of the functional layer. When the arc discharge power meets the above conditions, it is beneficial to control the formation of a functional layer with a smaller thickness and better uniformity.

[0203] As the arc discharge power decreases, the ionization rate becomes low, resulting in fewer and lower-energy metal or non-metal ions (such as Zr ions), making it difficult for them to uniformly reach and deposit on the negative electrode surface, leading to a decrease in the uniformity of the functional layer thickness. As the arc discharge power increases, the arc becomes unstable, and there may be violent jumping or sputtering phenomena in the arc spot, causing a decrease in the uniformity of the distribution of metal or non-metal ions (such as Zr ions), which may result in problems such as excessive deposition in some areas and insufficient deposition in others on the negative electrode surface.

[0204] As an example, the arc discharge power is 20kW, 22kW, 24kW, 26kW, 28kW, 30kW, 32kW, 34kW, 36kW, 38kW, 40kW, 42kW, 44kW, 46kW, 48kW, 50kW, 52kW, 54kW, 56kW, 58kW, 60kW, 62kW, 64kW, 66kW, 68kW, 70kW, etc., or a range of any two of the above values, or a value within a range.

[0205] In this embodiment, the deposition time affects the thickness of the functional layer. A deposition time that meets the above conditions facilitates the acquisition of a thinner functional layer, enabling improvements in the battery's high-temperature thermal stability while mitigating the problem of deteriorating internal resistance.

[0206] As an example, the deposition time is 50s, 60s, 70s, 80s, 90s, 100s, 150s, 200s, 250s, 300s, 350s, 400s, 450s, 500s, 550s, 600s, 650s, 700s, 750s, 800s, 850s, 900s, 950s, 1000s, etc., or a range of any two of the above values, or a value within a range of the above values.

[0207] In some embodiments of this application, the arc ion plating satisfies at least one of the following (a) to (b):

[0208] (a) Control the temperature of the negative electrode plate to 50℃~170℃;

[0209] (b) The vacuum degree is 1.5 × 10⁻⁶ -2 Pa ~ 5 × 10 -2 Pa;

[0210] (c) Output power is 30kW~50kW;

[0211] (d) The deposition time is 100s to 500s.

[0212] In this embodiment, controlling the temperature of the negative electrode sheet to meet the above conditions is beneficial for regulating the formation of a functional layer with the required thickness, uniformity, and other characteristics, and also helps to prevent the negative electrode sheet from being damaged by heat.

[0213] In this embodiment, the vacuum degree meets the above conditions, which is beneficial to obtain ceramic materials with higher purity, better improve the high-temperature thermal stability of the battery, and reduce the problem of battery internal resistance deterioration.

[0214] In this embodiment, the arc discharge power meets the above conditions, which is beneficial for controlling the formation of a functional layer with a smaller thickness and better uniformity.

[0215] In this embodiment, the deposition time meets the above conditions, which is conducive to obtaining a functional layer with a smaller thickness. This can improve the high-temperature thermal stability of the battery while reducing the problem of battery internal resistance deterioration.

[0216] In one embodiment of this application, a battery is provided.

[0217] Typically, a battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor for ions between the positive and negative electrodes. The separator, located between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0218] [Positive electrode tablets]

[0219] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including the positive active material of the first aspect of this application.

[0220] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0221] 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.).

[0222] In some embodiments, when the battery is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art 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 application 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 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0223] In some implementations, such as when the battery is a sodium-ion battery, the positive electrode active material may, as an example, include, but is not limited to, at least one of layered transition metal oxides, polyanionic compounds, and Prussian blue analogues.

[0224] Examples of the aforementioned layered transition metal oxides include:

[0225] Na 1-x Cu h Fe k Mn l M 1 m O 2-y M 1 It is one or more of Li, Be, B, Mg, Al, K, Ca, Ti, Co, Ni, Zn, Ga, Sr, Y, Nb, Mo, In, Sn, and Ba, 0 <x≤0.33,0<h≤0.24,0≤k≤0.32,0<l≤0.68,0≤m<0.1,h+k+l+m=1,0≤y<0.2;

[0226] Na0.67 Mn 0.7 Ni z M 2 0.3-z O2, where M 2 It is one or more of Li, Mg, Al, Ca, Ti, Fe, Cu, Zn and Ba, 0 <z≤0.1;

[0227] Na a Li b Ni c Mn d Fe e O2, of which 0.67 <a≤1,0<b<0.2,0<c<0.3,0.67<d+e<0.8,b+c+d+e=1。

[0228] Examples of the aforementioned polyanionic compounds include:

[0229] A 1 f M 3 g (PO4) i O j X 1 3-j A 1 It is one or more of H, Li, Na, K and NH4, M 3 It is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu and Zn, X 1 It is one or more of F, Cl and Br, 0 <f≤4,0<g≤2,1≤i≤3,0≤j≤2;

[0230] Na n M 4 PO4X 2 M 4 It is one or more of Mn, Fe, Co, Ni, Cu and Zn, X 2 It is one or more of F, Cl and Br, 0 <n≤2;

[0231] Na p M 5 q (SO4)3, where M 5 It is one or more of Mn, Fe, Co, Ni, Cu and Zn, 0 <p≤2,0<q≤2;

[0232] Na s Mn t Fe 3-t(PO4)2(P2O7), where 0 < s ≤ 4, 0 ≤ t ≤ 3. For example, t is 0, 1, 1.5, 2, or 3.

[0233] Examples of the above-mentioned Prussian blue analogs include, for example:

[0234] A u M 6 v [M 7 (CN)6] w ·xH2O, where A is H + 、NH4 + 、one or more of alkali metal cations and alkaline earth metal cations, M 6 and M 7 are each independently one or more of transition metal cations, 0 < u ≤ 2, 0 < v ≤ 1, 0 < w ≤ 1, 0 < x < 6. For example, A is H + 、Li + 、Na + 、K + 、NH4 + 、Rb + 、Cs + 、Fr + 、Be 2+ 、Mg 2+ 、Ca 2+ 、Sr 2+ 、Ba 2+ and Ra 2+ one or more of them, M 6 and M 7 are each independently cations of one or more transition metal elements selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sn, and W.

[0235] The modified compounds of the above materials can be doping modification and / or surface coating modification of the materials.

[0236] In some embodiments, the positive electrode active material layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0237] In some embodiments, the positive electrode active material layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0238] 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 electrode 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.

[0239] [Negative electrode plate]

[0240] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer (i.e., a negative electrode film layer) disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0241] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0242] 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.).

[0243] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and titanates. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. When the battery is a lithium-ion battery, lithium titanate is used; when the battery is a sodium-ion battery, sodium titanate is used. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0244] In some embodiments, the negative electrode active material 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).

[0245] In some embodiments, the negative electrode active material layer 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.

[0246] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0247] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0248] [Electrolytes]

[0249] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0250] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0251] In some embodiments, the electrolyte salt may include 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.

[0252] In some embodiments of this application, when the battery is a sodium-ion battery, the electrolyte sodium salt may include at least one of sodium hexafluorophosphate, sodium difluorooxalate borate, sodium tetrafluoroborate, sodium dioxalate borate, sodium perchlorate, sodium hexafluoroarsenate, sodium bis(fluorosulfonyl)imide, sodium trifluoromethanesulfonate, or sodium bis(trifluoromethanesulfonyl)imide.

[0253] 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.

[0254] 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.

[0255] [Isolation membrane]

[0256] In some embodiments, the battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0257] 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.

[0258] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0259] In some embodiments, the battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0260] In some implementations, the battery's outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The battery's outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0261] This application does not impose any particular limitation on the shape of the battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery 5 as an example.

[0262] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 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 plate 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 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.

[0263] In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0264] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple batteries 5 can be fixed in place using fasteners.

[0265] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of batteries 5 are received.

[0266] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0267] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, 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 box 2 and a lower box 3, with the upper box 2 covering the lower box 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.

[0268] The third aspect of this application proposes an electrical device comprising the secondary battery described in the first aspect above, or a secondary battery prepared by the method described in the second aspect above.

[0269] In this embodiment, the electrical device includes the battery described in the first or second aspect above, possessing the performance characteristics of the battery and thus improving battery safety. The battery can be used in electrical devices that use it as a power source or in various energy storage systems that use it as an energy storage element. The electrical device may include, but is not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys may include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0270] Electrical equipment includes at least one of the batteries, battery modules, or battery packs provided in this application. The battery, battery module, or battery pack can be used as a power source for the electrical equipment or as an energy storage unit for the electrical equipment. Electrical equipment may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0271] As electrical equipment, batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0272] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used.

[0273] Another example device could be a mobile phone, tablet, laptop, etc. These devices typically require a slim and lightweight design and can use a battery as their power source.

[0274] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0275] [Battery Manufacturing]

[0276] Example 1

[0277] (1) Preparation of the positive electrode:

[0278] Lithium iron phosphate, conductive carbon black (Super P), and binder (PVDF) 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 homogeneous positive electrode slurry with a solid content of 45%. The positive electrode slurry was coated onto the surface of the positive electrode current collector aluminum foil, and then 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 .

[0279] (2) Preparation of negative electrode:

[0280] 1) The negative electrode active material, artificial graphite, conductive agent (Super P), thickener sodium carboxymethyl cellulose (CMC), and binder (SBR) were mixed in a mass ratio of 96.82:0.53:0.7:1.95. Deionized water was added as a solvent, and the mixture was stirred under vacuum until a homogeneous negative electrode slurry with a solid content of 50% was formed. The negative electrode slurry was uniformly coated on both surfaces of a 6 μm thick copper foil current collector and dried at 110 °C for 20 min. After drying, the electrode was cold-pressed to obtain a coating weight of 10.71 mg / cm². 2 The compacted density is 1.4 g / cm³. 3 The negative electrode has a thickness of 159μm.

[0281] 2) An arc ion plating method is used to deposit a functional layer on the surface of the negative electrode obtained in step 1). The specific operation is as follows:

[0282] The negative electrode and target material were assembled onto the experimental electrode. The vacuum pump was started to pre-evacuate the coating chamber, removing the air inside to a vacuum level of 2.6*10⁻⁶. -2 The arc power supply is turned on to generate an arc discharge on the target surface. The substrate temperature is controlled at 150℃ while Ar gas is simultaneously introduced. The bias power supply is then connected. At this time, Ar gas ions bombard the target under the action of the bias electric field. The arc discharge power of the bombardment is adjusted to 30kW and the film deposition time is 50s. Functional layers are deposited on both surfaces of the negative electrode, resulting in a negative electrode with functional layers.

[0283] (3) Preparation of the diaphragm:

[0284] A 12μm thick polyethylene film was selected as the separator.

[0285] (4) Preparation of electrolyte:

[0286] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Fully dried lithium salt LiPF6 was dissolved in the organic solvent at a concentration of 1 mol / L. The mixture was then thoroughly mixed to obtain an electrolyte.

[0287] (5) Battery assembly:

[0288] The positive electrode, negative electrode, and separator are stacked in a specific pattern to form a battery chip. Then, the battery chip is packaged in a suitable container, electrolyte is added, and a sealed cap is installed to fix the cell assembly, giving it a certain finished cell shape.

[0289] Examples 2-43

[0290] The lithium-ion secondary batteries provided in Examples 2-43 are prepared using the same method as those in Example 1. The specific differences are shown in Tables 1-1, 1-2, and 1-3.

[0291] Comparative Example 1

[0292] (1) Preparation of the positive electrode:

[0293] Lithium iron phosphate, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) 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 homogeneous positive electrode slurry with a solid content of 45%. The positive electrode slurry was coated onto the surface of the positive electrode current collector aluminum foil, and then 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 .

[0294] (2) Preparation of negative electrode:

[0295] Artificial graphite (anode active material), conductive agent (Super P), thickener sodium carboxymethyl cellulose (CMC), and binder (SBR) were mixed in a mass ratio of 96.82:0.53:0.7:1.95. Deionized water was added as a solvent, and the mixture was stirred under vacuum until a homogeneous anode slurry with a solid content of 50% was formed. The anode slurry was uniformly coated onto both surfaces of a 6 μm thick copper foil anode current collector and dried at 110 °C for 20 min. After drying, the electrode was cold-pressed to obtain a coating weight of 10.71 mg / cm². 2 The compacted density is 1.4 g / cm³. 3 The negative electrode has a thickness of 159μm.

[0296] (3) Preparation of the diaphragm:

[0297] A 12μm thick polyethylene film was selected as the separator.

[0298] (4) Preparation of electrolyte:

[0299] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Fully dried lithium salt LiPF6 was dissolved in the organic solvent at a concentration of 1 mol / L. The mixture was then thoroughly mixed to obtain an electrolyte.

[0300] (5) Battery assembly:

[0301] The positive electrode, negative electrode, and separator are stacked in a specific pattern to form a battery chip. Then, the battery chip is packaged in a suitable container, electrolyte is added, and a sealed cap is installed to fix the cell assembly, giving it a certain finished cell shape.

[0302] Comparative Example 2

[0303] (1) Preparation of the positive electrode:

[0304] Lithium iron phosphate, conductive carbon black (Super P), and binder (PVDF) 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 homogeneous positive electrode slurry with a solid content of 45%. The positive electrode slurry was coated onto the surface of the positive electrode current collector aluminum foil, and then 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 .

[0305] (2) Preparation of negative electrode:

[0306] 1) The negative electrode active material, artificial graphite, conductive agent (Super P), thickener sodium carboxymethyl cellulose (CMC), and binder (SBR) were mixed in a mass ratio of 96.82:0.53:0.7:1.95. Deionized water was added as a solvent, and the mixture was stirred under vacuum until a homogeneous negative electrode slurry with a solid content of 50% was formed. The negative electrode slurry was uniformly coated on both surfaces of a 6 μm thick copper foil current collector and dried at 110 °C for 20 min. After drying, the electrode was cold-pressed to obtain a coating weight of 10.71 mg / cm². 2 The compacted density is 1.4 g / cm³. 3 The negative electrode has a thickness of 159μm.

[0307] 2) Nano-zirconia powder and PVDF were added to conductive NMP at a mass ratio of 70%, 15%, and 15%, respectively, and stirred to form a uniform slurry. An appropriate amount of the prepared slurry was dropped onto the surface of the negative electrode sheet, and a spin coater was started to coat the surface of the negative electrode sheet evenly. Then, the negative electrode sheet was placed in a vacuum drying oven and dried at 60°C for 10 hours to obtain a negative electrode sheet with a functional layer.

[0308] (3) Preparation of the diaphragm:

[0309] A 12μm thick polyethylene film was selected as the separator.

[0310] (4) Preparation of electrolyte:

[0311] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Fully dried lithium salt LiPF6 was dissolved in the organic solvent at a concentration of 1 mol / L. The mixture was then thoroughly mixed to obtain an electrolyte.

[0312] (5) Battery assembly:

[0313] The positive electrode, negative electrode, and separator are stacked in a specific pattern to form a battery chip. Then, the battery chip is packaged in a suitable container, electrolyte is added, and a sealed cap is installed to fix the cell assembly, giving it a certain finished cell shape.

[0314] Comparative Example 3

[0315] The battery provided in Comparative Example 3 uses the preparation method of Example 1, except that the step of forming a functional layer on the negative electrode sheet is different:

[0316] The negative electrode and target material were assembled onto the experimental electrode. The vacuum pump was started to pre-evacuate the coating chamber, removing the air inside to a vacuum level of 2.6*10⁻⁶. -2 The arc power supply is turned on to generate an arc discharge on the target surface. The substrate temperature is controlled at 150℃ while Ar gas is simultaneously introduced. The bias power supply is then connected, and Ar gas ions bombard the target under the influence of the bias electric field. The arc discharge power is adjusted to 30kW and the deposition time to 10s, depositing functional layers on both surfaces of the negative electrode to obtain a negative electrode with functional layers.

[0317] Comparative Example 4

[0318] The battery provided in Comparative Example 4 uses the preparation method of Example 1, except that the step of forming a functional layer on the negative electrode sheet is different:

[0319] The negative electrode and target material were assembled onto the experimental electrode. The vacuum pump was started to pre-evacuate the coating chamber, removing the air inside to a vacuum level of 2.6*10⁻⁶. -2 The arc power supply is turned on to generate an arc discharge on the target surface. The substrate temperature is controlled at 150℃ while Ar gas is simultaneously introduced. The bias power supply is then connected. At this time, Ar gas ions bombard the target under the action of the bias electric field. The arc discharge power of the bombardment is adjusted to 30kW and the film deposition time is 1300s. Functional layers are deposited on both surfaces of the negative electrode, resulting in a negative electrode with functional layers.

[0320] The parameters of Examples 1-43 and Comparative Examples 1-4 are shown in Tables 1-1, 1-2 and 1-3.

[0321] [Performance Testing]

[0322] I. Testing Methods

[0323] 1. Functional layer thickness test:

[0324] First, a sufficiently thin sheet is obtained by fine milling the target area of ​​the electrode using a FIB (Focused Ion Beam) microscope for subsequent TEM (Transmission Electron Microscopy) testing. The sample holder with the sheet is then loaded into the TEM microscope. The thickness of the film is directly measured on the image using TEM software. To improve accuracy, measurements can be repeated at multiple locations and the average value calculated.

[0325] FIB: Thermo Fisher Scientific-Scios 2HiVac; TEM: Thermo Scientific-Talos F200S G2.

[0326] 2. Standard deviation of diaphragm resistance:

[0327] Take n test sites evenly distributed on the surface of the negative electrode. Connect the diaphragm resistor to the regulated power supply and the electrical measuring instrument. Place the sample to be tested in the electrode fixture, turn on the power supply to apply current to the sample, record and calculate the resistance Xi of the i-th (1≤i≤n) test site using the formula:

[0328] The standard deviation of the film resistance of the negative electrode sheet of this application can be calculated. Here, n represents the total number of test sites, and represents the average resistance of the n test sites. In this embodiment, n = 9.

[0329] 3. Dielectric constant:

[0330] Testing instruments and equipment: Wheatstone bridge, vernier calipers, high and low temperature chamber, muffle furnace, tablet press.

[0331] Required materials: sample, conductive silver paste, special adhesive.

[0332] For the electrolyte: Place the sample in the sample bath and then into a high-low temperature chamber. Set the temperature range, and gradually increase the temperature of the chamber from low to high. During the heating process, measure the capacitance C of the sample using a bridge circuit at specific temperature points. The capacitance is calculated using the formula εr = ε / ε0 = Cd / ε0S, where ε is the absolute dielectric constant, ε0 is the vacuum dielectric constant, S is the area of ​​the capacitor plates facing each other, d is the distance between the capacitor plates, and C is the capacitance of the sample being tested. Typically, three or more discs are prepared for each sample, and outliers are removed during testing before taking the average value.

[0333] For ceramic materials and negative electrode active materials: The sample powder is granulated with binder, and the granulated powder is pressed into tablets (round discs) using a tablet press. The discs are then placed in a muffle furnace for slow heating and holding to remove the binder. The debinded discs are removed, and silver is applied to the front side. They are then placed back into the muffle furnace for silver firing. After removal, the back side is silver-coated and fired. After silver firing, the discs are placed in a special fixture, and the fixture is placed in a high-low temperature chamber. A temperature range is set, and the chamber is heated from low to high. During the heating process, the capacitance C of the disc is measured using a bridge at specific temperature points. The capacitance is calculated using the formula εr = ε / ε0 = C. d / ε0S, where: ε is the absolute dielectric constant, ε0 is the vacuum dielectric constant, S is the area of ​​the capacitor plates facing each other, d is the distance between the capacitor plates, and C is the capacitance of the sample being tested. Typically, three or more discs are made for each powder sample, and outliers are removed during testing before taking the average value.

[0334] 4. XPS (X-ray Photoelectron Spectroscopy): Testing instrument: Axis Supra / Supra+ X-ray photoelectron spectrometer, tested according to standard GB / T 33502-2017.

[0335] 5. Diaphragm resistance:

[0336] Diaphragm resistor: Model BER1300, electrode diameter 14mm, applied pressure 25MPa, holding time 25s.

[0337] Cut the diaphragm into a rectangle approximately 5cm x 10cm and place it between the two electrodes of the diaphragm resistance meter. Set the test pressure and holding time parameters on the MRMS software and start the test. The software will automatically read the diaphragm resistance value.

[0338] 6. DSC (Differential Scanning Calorimetry) test:

[0339] (1) Sample preparation: In the glove box, punch a small round piece with a diameter of 5mm from the middle of the electrode, put it into the HP crucible (High Pressure crucible), flatten it, and seal it.

[0340] (2) Parameter settings: nitrogen atmosphere, purge gas 60 mL / min, protective gas 20 mL / min.

[0341] (3) Temperature rise program: 10℃ / min, 35℃~460℃, to obtain the heat flow-temperature change graph.

[0342] Based on the heat flow-temperature change diagram, the differences in thermal stability of materials can be judged by comparing them and peak areas.

[0343] 7. DCR (Direct Current Resistance) Test:

[0344] (1) At 25℃, fully charge the battery at 0.33C and discharge it at 0.33C, and test the capacity C0. Then, at 25℃, discharge the battery at a rate of 0.33C to different SOCs (State of Charge), such as 90% SOC, 70% SOC, 50% SOC, 20% SOC, and 10% SOC. At each SOC, discharge and charge the battery for 60 seconds using a rate of 1C. Mark the voltage before discharge as U0, the voltage after discharge as U1, and the discharge rate of 1C as I. Then, the DC resistance DCR of the secondary battery at different SOCs is (U0-U1) / I.

[0345] (2) At 25℃, fully charge the battery at 0.33C and discharge it at 0.33C to test the capacity C0. Then, at 25℃, discharge the battery to 50% SOC at a rate of 0.33C. Use a rate of 1C to discharge and charge the battery for 60s. Mark the voltage before discharge as U0 and the voltage after discharge as U1. Mark the discharge rate of 1C as I. Then, the DC resistance DCR of the secondary battery at 50% SOC is (U0-U1) / I.

[0346] 8. Performance testing for preventing thermal runaway: Heat release (Mw / mg, representing the heat release per unit mass of negative electrode) is calculated by DSC heat release area test.

[0347] II. Test Results

[0348] 1. As shown in Figure 7, the negative electrode obtained in Example 5 was tested. The ceramic material of the functional layer of the negative electrode is zirconium oxide. By disassembling the electrode after formation, the corresponding metal element zirconium can be extracted.

[0349] 2. As shown in Figure 8, the negative electrode sheets obtained in Example 5 and Comparative Example 1 were tested. In Figure 8, "BD38" is the abbreviation for Base, which is the battery obtained in Comparative Example 1. It represents the DCR performance of the negative electrode sheet without functional layer tested at 25°C. Specifically, there are DCR at 90% SOC, DCR at 70% SOC, DCR at 50% SOC, DCR at 20% SOC, and DCR at 10% SOC.

[0350] The downward-pointing bar chart represents the change in DCR of the battery relative to the battery with a non-functional negative electrode layer, that is, the difference between the DCR of the battery with a functional negative electrode layer made of zirconia ceramic material and the DCR of the battery with a non-functional negative electrode layer.

[0351] As can be seen from Figure 8, the internal resistance of the battery obtained in the embodiment of this application not only did not deteriorate, but also showed a decreasing trend, indicating that the battery impedance is reduced. Under the same charge and discharge rate, the cell generates less heat, and the safety is further improved.

[0352] 3. As shown in Figure 9, the negative electrode sheets obtained in Example 5 and Comparative Example 1 were tested.

[0353] Because the negative electrode sheet provided in Example 5 has a high-temperature resistant ceramic material on its surface, it provides better heat insulation than the base electrode sheet of Comparative Example 1. It releases less heat at high temperatures of ~130°C and ~180°C, respectively, which improves the high-temperature thermal stability of the lithium-ion battery and enhances its safety and reliability.

[0354] 4. The performance test results of the negative electrode and battery obtained in the examples and comparative examples are shown in Table 2.

[0355] Table 2

[0356] As shown in Table 2, for batteries with ceramic functional layer negative electrodes, a dielectric constant of the functional layer between 15 and 90 helps to improve the lithium-ion transport rate. Simultaneously, limiting the thickness of the functional layer to greater than or equal to 5 nm and less than 30 nm can improve the battery's high-temperature thermal stability and help mitigate the deterioration of the battery's internal resistance.

[0357] Specifically, as shown in Examples 1-7, the DSC heat dissipation shows a decreasing trend as the thickness of the functional layer increases, indicating an improving trend in the high-temperature stability of the battery. Furthermore, the average film resistance of the negative electrode shows a gradually increasing trend; while the DCR shows a trend of first decreasing and then increasing. This is because the DCR reflects the resistance of electrons and lithium ions in the electrochemical reaction. As the thickness of the functional layer increases, electrons are hindered, but the properties of the functional layer material (such as dielectric constant) increase the lithium ion transport rate. Therefore, there is a competitive relationship between electrons and lithium ions as the thickness increases. Before a certain thickness, lithium ion transport dominates, and the DCR shows a decreasing trend; after a certain thickness, electron resistance dominates, and the DCR shows an increasing trend.

[0358] As illustrated in Examples 8-14, with the increase of the standard deviation of the film resistance, the DCR shows a trend of first decreasing and then increasing, and the DSC heat dissipation also shows a trend of first decreasing and then increasing. This is because a larger standard deviation of the film resistance indicates a decreasing trend in the uniformity of the functional layer, leading to an increased trend in the transport paths of lithium ions and electrons, resulting in an increasing trend in DCR. Simultaneously, a decreasing trend in uniformity reduces the coating effect on the negative electrode surface, leading to an increasing trend in DSC heat dissipation. However, a smaller standard deviation of the film resistance indicates an increasing trend in the uniformity of the functional layer. Increased surface smoothness of the functional layer may generate greater stress. When the stress accumulates to a certain extent, it may cause cracks or even detachment of the functional layer, leading to an increasing trend in both DCR and DSC heat dissipation.

[0359] As illustrated in Examples 16-23, with the increase of the dielectric constant of the ceramic material in the functional layer, the DCR shows a decreasing trend, while the DSC heat release shows a relatively small fluctuation trend. This is because the electrolyte solvent has a high dielectric constant (in the examples, the electrolyte solvent is mainly EC, with a dielectric constant of 90). The closer the dielectric constant of the ceramic material in the functional layer is to 90, the better it can capture lithium ions from the EC solvent, meaning the lithium ion transport impedance at the interface is lower, and the DCR gradually decreases. Therefore, improving the dielectric constant of the ceramic material is beneficial for improving the problem of battery internal resistance deterioration.

[0360] As illustrated in Examples 40-43, the DCR generally shows an increasing trend as the mass ratio of ceramic material relative to the negative electrode increases. This is because as the ceramic material content increases, the corresponding functional layer thickness also tends to increase. Excessive thickness affects electron transport, thus causing the DCR to show an increasing trend. However, excessively low thickness means that the ceramic material content is low, contributing less to promoting lithium-ion transport. Therefore, when the mass ratio of ceramic material is low, a higher DCR will occur.

[0361] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A secondary battery, wherein, The device includes a negative electrode sheet, wherein at least one side of the negative electrode sheet is provided with a functional layer, the material of the functional layer includes a ceramic material, the ceramic material includes at least one of oxides and carbides, and the thickness of the functional layer is greater than or equal to 5 nm and less than 30 nm.

2. The secondary battery according to claim 1, wherein, The thickness of the functional layer is 8nm to 28nm.

3. The secondary battery according to claim 1 or 2, wherein, The thickness of the functional layer is 15nm to 25nm.

4. The secondary battery according to any one of claims 1 to 3, wherein, The oxide contains at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, and Ta, and the non-metallic element includes one or more of Si and B.

5. The secondary battery according to any one of claims 1 to 4, wherein, The carbide contains at least one of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, and Ta, and the non-metallic element includes one or more of Si and B.

6. The secondary battery according to any one of claims 1 to 5, wherein, Satisfy at least one of the following (I) and (II): (I) The oxides include one or more of the following, whether stoichiometric or non-stoichiometric: aluminum oxide, zirconium oxide, magnesium oxide, chromium oxide, niobium pentoxide, tantalum oxide, silicon oxide, and boron oxide; (II) The carbides include one or more of aluminum carbide, zirconium carbide, magnesium carbide, chromium carbide, niobium carbide, tantalum carbide, silicon carbide, and boron carbide, either stoichiometric or non-stoichiometric.

7. The secondary battery according to any one of claims 1 to 6, wherein, At least one of (A) and (B) below must be satisfied: (A) The oxide includes ZrO 2-x1 TiO 2-x2 ZnO 1-x3 CeO 2-x4 Nb2O 5-x5 Ta2O 5-x6 B2O 3-x7 One or more of them; wherein, 0.05≤x1≤0.5, 0.05≤x2≤0.5, 0<x3<1, 0.1≤x4≤0.3, 0<x5<5, 0<x6<5, 0<x7<3; (B) Carbides include TiC 1-x8 Where 0 < x8 < 1.

8. The secondary battery according to any one of claims 1 to 7, wherein, The standard deviation of the film resistance of the negative electrode is 0.2mΩ to 1mΩ.

9. The secondary battery according to any one of claims 1 to 8, wherein, The standard deviation of the film resistance of the functional layer is 0.3mΩ to 0.8mΩ.

10. The secondary battery according to any one of claims 1 to 9, wherein, The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer. The functional layer is located on the negative electrode film layer on the side away from the negative electrode current collector. The negative electrode film layer includes a negative electrode active material. The secondary battery also includes an electrolyte.

11. The secondary battery according to claim 10, wherein, The negative electrode active material includes one or more of the following: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and titanates.

12. The secondary battery according to claim 10 or 11, wherein, The dielectric constant of the ceramic material is less than that of the electrolyte and greater than that of the negative electrode active material.

13. The secondary battery according to any one of claims 10 to 12, wherein, The dielectric constant of the ceramic material is 15 to 90.

14. The secondary battery according to any one of claims 10 to 13, wherein, The dielectric constant of the ceramic material is 20 to 70.

15. The secondary battery according to any one of claims 1 to 14, wherein, The film resistance of the negative electrode is 9mΩ to 50mΩ.

16. The secondary battery according to any one of claims 1 to 15, wherein, The mass of the ceramic material is 0.01% to 0.1% of the mass of the negative electrode sheet.

17. A method for preparing a secondary battery, wherein, include: A functional layer is formed on at least one side of the negative electrode. The material of the functional layer includes ceramic materials, which include at least one of oxides and carbides, and the thickness of the functional layer is greater than or equal to 5 nm and less than 30 nm.

18. The method according to claim 17, wherein, The functional layer is formed on at least one side of the negative electrode using thin film deposition technology; the thin film deposition technology includes one or more of physical vapor deposition and chemical vapor deposition; the physical vapor deposition method includes one or more of arc ion plating, magnetron sputtering, and electron beam evaporation.

19. The method according to claim 18, wherein, The functional layer is formed on at least one side of the negative electrode using arc ion plating, comprising the steps of: In a vacuum environment, an arc power supply is turned on to generate an arc discharge on the surface of the target material. The temperature of the negative electrode is controlled, a working gas is introduced, and a bias power supply is turned on so that the ions of the working gas bombard the target material under the action of the bias electric field. The arc discharge power of the bombardment and the coating deposition time are adjusted to deposit the functional layer on the surface of the negative electrode, thus obtaining a negative electrode with the functional layer.

20. The method according to claim 19, wherein, The working gas includes a carrier gas, and the target material includes one or more of oxides and carbides. Alternatively, the working gas may include a carrier gas and a reactant gas, wherein the reactant gas may include one or more of an oxygen source and a carbon source, and the target material may include one or more of an element, an oxide, and a carbide.

21. The method according to claim 20, wherein, The arc ion plating satisfies one or more of the following (i) to (v): (i) The oxygen source includes one or more of oxygen and ozone; (ii) The carbon source includes one or more of acetylene, methane, propane, carbon monoxide, and carbon dioxide; (iii) The elemental substance includes one or more of metallic elements and non-metallic elements; the metallic elemental substance includes one or more of aluminum, zirconium, magnesium, chromium, niobium, and tantalum; and the non-metallic elemental substance includes one or more of silicon and boron. (iv) The oxide contains one or more of a metallic element and a non-metallic element; the metallic element includes one or more of Al, Zr, Mg, Cr, Nb, and Ta, and the non-metallic element includes one or more of Si and B; (v) The carbide contains one or more of metallic and non-metallic elements; the metallic elements include one or more of Al, Zr, Mg, Cr, Nb, and Ta, and the non-metallic elements include one or more of Si and B.

22. The method according to any one of claims 19 to 21, wherein, The arc ion plating satisfies at least one of the following (a) to (d): (a) Control the temperature of the negative electrode to below 200°C; (b) The vacuum level is 1×10 -2 Pa ~ 10 × 10 -2 Pa; (c) The arc discharge power is 20kW~70kW; (d) The deposition time is 50s to 1000s.

23. The method according to any one of claims 19 to 22, wherein, The arc ion plating satisfies at least one of the following (a) to (b): (a) Control the temperature of the negative electrode plate to 50℃~170℃; (b) The vacuum degree is 1.5 × 10⁻⁶ -2 Pa ~ 5 × 10 -2 Pa; (c) Output power is 30kW~50kW; (d) The deposition time is 100s to 500s.

24. An electrical appliance, wherein, The secondary battery includes any one of claims 1 to 16, or the secondary battery prepared by any one of claims 17 to 23.

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