Secondary battery and preparation method therefor, and electric device

Abstract

A secondary battery and a preparation method therefor, and an electric device. In order to solve the problem of poor cycle life of battery cells, the secondary battery comprises a negative electrode sheet; the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer; the negative electrode film layer is located on at least one side of the negative electrode current collector; the negative electrode film layer comprises a negative electrode active material; a functional layer is provided on the side of the negative electrode film layer away from the negative electrode current collector, and / or a functional layer is provided on the surface of particles of the negative electrode active material and the functional layer comprises organic silicon.

Description

Secondary batteries, their preparation methods, and electrical devices

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese patent application No. 202510180355.1, filed on February 18, 2025, the entirety of which is incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to secondary batteries, their preparation methods, and electrical devices. Background Technology

[0004] The technological development of rechargeable batteries is moving towards higher energy density, faster charging speeds, longer cycle life, and lower costs. Taking lithium-ion batteries as an example, with their increasingly widespread applications, lithium-ion batteries are widely used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. Due to the significant advancements in lithium-ion battery technology, higher demands are being placed on their cycle life. Currently, there are some issues with the negative electrode of rechargeable batteries during cycling and storage, and the cycle life of the battery cells needs further improvement. Summary of the Invention

[0005] This application is made in view of the above-mentioned issues, and its purpose is to solve the problem of poor cycle life of battery cells, and to provide a secondary battery, a method for preparing the same, and an electrical device thereof.

[0006] The first aspect of this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet comprising: a negative electrode current collector; a negative electrode film layer, the negative electrode film layer being located on at least one side of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material; and satisfying at least one of the following (I) and (II):

[0007] (I) A functional layer is provided on the side of the negative electrode film layer away from the negative electrode current collector;

[0008] (II) The surface of the particles of the negative electrode active material is provided with a functional layer; the functional layer contains organosilicon.

[0009] The battery provided in this application coats the negative electrode film layer and / or the particle surface of the negative electrode active material with an organosilicon material. Compared with inorganic materials, the organosilicon material has a certain elasticity, which can provide a certain buffering effect on the volume change of the negative electrode active material. During the charging and discharging process, it helps to prevent the negative electrode active material from being exposed in the electrolyte due to the rupture of the surface SEI film. Thus, it reduces the chance of direct contact between the electrolyte and the negative electrode active material, reduces the consumption rate of active lithium, and improves the cycle life of the secondary battery.

[0010] In some implementations, the thickness d of the functional layer satisfies: 0 < d ≤ 100 nm. A functional layer thickness that meets this condition is beneficial for improving battery cycle performance, mitigating the increase in internal resistance, and enhancing battery performance.

[0011] In some implementations, the thickness d of the functional layer satisfies: 5nm < d ≤ 50nm. Meeting this condition helps improve the battery's cycle performance, mitigates the increase in internal resistance, and enhances overall battery performance.

[0012] In some implementations, based on X-ray photoelectron spectroscopy analysis of the functional layer, the silicon content is 20 wt% to 50 wt%. Meeting this silicon content condition is beneficial for improving the battery's cycle performance.

[0013] In some embodiments, the functional layer further includes doping elements; the doping elements include at least one selected from N, S, B, P, O, F, Cl, Br, and I. Doping with these elements helps to further improve the electrochemical performance of the battery.

[0014] In some implementations, the molar ratio of dopant elements to silicon is calculated based on X-ray photoelectron spectroscopy analysis of the functional layer, and the molar ratio of dopant elements to silicon is ≤10. Introducing dopant elements that meet this molar ratio into the functional layer helps to effectively leverage the improving effect of dopant elements on battery performance.

[0015] In some implementations, the dopant element is F. Based on the content of the dopant element and the content of silicon element obtained from the test of the functional layer by X-ray photoelectron spectroscopy analysis, the molar ratio of the dopant element to silicon element is ≤3. By introducing a dopant element that meets the above molar ratio into the functional layer, it is beneficial to effectively exert the effect of the dopant element on improving battery performance.

[0016] Alternatively, if the dopant element is S, then the molar ratio of the dopant element to silicon is calculated based on the content of the dopant element and the silicon content obtained from X-ray photoelectron spectroscopy analysis of the functional layer, and the molar ratio of the dopant element to silicon is ≤2. Introducing a dopant element that meets the above molar ratio into the functional layer is beneficial to effectively exert the effect of the dopant element on improving battery performance.

[0017] In some embodiments, the organosilicon includes at least one of the structural units shown in Formula I:

[0018] Wherein, R1, R2, and R3 are independently selected from at least one of substituted or unsubstituted alkyl groups, substituted or unsubstituted olefin groups, substituted or unsubstituted phenyl groups, ester groups, ether groups, sulfonyl groups, amide groups, and heteroelements from C1 to C20; and at least one of R1, R2, and R3 is selected from any one of substituted or unsubstituted alkyl groups or substituted or unsubstituted olefin groups from C1 to C20; the structural unit is a repeating unit. The main chain is formed by repeating the structural units shown in Formula I through covalent bonds. Since each repeating unit is connected to at least one organic hydrocarbon side chain (such as a substituted or unsubstituted alkyl group from C1 to C20), it is beneficial to improve the elasticity of organosilicon, enhance the buffering effect on the volume change of the negative electrode active material, and better improve the cycle performance of the battery.

[0019] In some implementations, the structural unit satisfies at least one of the following (a) to (c):

[0020] (a) In the substituted alkyl groups of C1-C20, the substituents include halogen elements, said halogen elements including at least one of F, Cl, Br, and I;

[0021] (b) In the C1-C20 substituted olefinic groups, the substituents include halogen elements, said halogen elements including at least one of F, Cl, Br, and I;

[0022] (c) In the substituted phenyl group, the substituent includes a halogen element, said halogen element including at least one of F, Cl, Br, and I.

[0023] In some embodiments, the molecular structure of organosilicon includes at least one of chain-like, cyclic, or combined chain-cyclic structures. In organosilicon, the structural unit represented by Formula I forms the main chain as a repeating unit, and the shape of the organosilicon molecular structure can be chain-like, cyclic, or a combined chain-cyclic structure.

[0024] In some embodiments, the film resistance of the negative electrode is 0.014 mΩ to 0.024 mΩ. This helps to limit the occurrence of side reactions that consume lithium in the electrolyte, thereby improving lifespan performance.

[0025] In some embodiments, the negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0026] The second aspect of this application discloses a method for preparing a secondary battery, including preparing a negative electrode sheet, wherein preparing the negative electrode sheet includes:

[0027] A negative electrode sheet is obtained by forming a negative electrode film layer on at least one side of a negative electrode current collector using a slurry containing a negative electrode active material; the method further includes at least one of the following:

[0028] (i) Prior to the step of forming a negative electrode film layer on at least one side of the negative electrode current collector with a slurry containing a negative electrode active material, a functional layer is formed on the surface of the particles of the negative electrode active material; the functional layer comprises organosilicon;

[0029] (ii) A functional layer is formed on the surface of the negative electrode film; the functional layer contains organosilicon.

[0030] This application forms a functional layer containing organosilicon on the surface of the negative electrode sheet and / or the particles of the negative electrode active material. The functional layer protects the negative electrode active material and prevents it from directly contacting the electrolyte. Compared with inorganic materials, organic materials have a certain degree of elasticity, which can provide a buffer for the volume changes of the negative electrode active material. During the charging and discharging process, this helps to prevent the negative electrode active material from being exposed in the electrolyte due to the rupture of the surface SEI film. Thus, it reduces the chance of direct contact between the electrolyte and the negative electrode active material, reduces the consumption rate of active lithium, and improves the lifespan performance.

[0031] In some embodiments, the method for forming the functional layer includes at least one of chemical vapor deposition and organic evaporation. This is advantageous for forming a functional layer with a relatively small thickness and high uniformity.

[0032] In some implementations, the chemical vapor deposition method is plasma-enhanced chemical vapor deposition. The reaction temperature is relatively mild, which helps to protect the negative electrode active material.

[0033] In some embodiments, the chemical vapor deposition process includes at least a first gas source, which comprises a siloxane. Using the siloxane as a raw material, a coating layer containing organosilicon is formed by plasma-enhanced chemical vapor deposition.

[0034] In some embodiments, the siloxane includes at least one of cyclic siloxanes, acyclic siloxanes, other hydrogen-containing silicone oils, and doped siloxanes. Negative electrode sheets with functional layers formed using these siloxanes exhibit good cycle life when used in batteries. Furthermore, siloxanes containing doped elements can be selected as raw materials, which participate in the reaction, allowing the doped elements to enter the organosilicon within the functional layer and exert their effect.

[0035] In some embodiments, the chemical vapor deposition method further includes a second gas source, which includes at least one of a halogen-containing gas source, a boron-containing gas source, a nitrogen-containing gas source, a phosphorus-containing gas source, a sulfur-containing gas source, and an oxygen-containing gas source; and satisfies at least one of the following (α) to (ζ):

[0036] (α) Halogenated gas sources include at least one of halogenated elements, haloalkanes, haloalkenes, and sulfur fluoride;

[0037] (β) Boron-containing gas sources include boron hydrides;

[0038] (γ) Nitrogen-containing gas sources include at least one of N2 and NH3;

[0039] (δ) Phosphorus-containing gas sources include phosphorus-containing compounds;

[0040] (ε) The sulfur-containing gas source includes at least one of SO2 and SO3;

[0041] (ζ) Oxygen sources include at least one of air, oxygen, ozone, carbon dioxide, and carbon monoxide.

[0042] The first gas source serves as the framework source for the functional layer, providing the basic unit structure of organosilicon and possessing side chains; under the action of plasma, the first gas source can initiate the film-forming reaction. The second gas source serves as the gas source for doping elements, providing doping elements such as F, Cl, Br, I, B, O, N, P, and S in the functional layer.

[0043] In some implementations, the second gas source satisfies at least one of the following (①) to (⑤):

[0044] (①) Halogen elements include at least one of F2, Cl2, Br2, and I2;

[0045] (②) The haloalkane includes CF 4、 At least one of C2F6, CCl4, C2Cl6, CBr4, C2Br6, CIr4, and C2I6;

[0046] (③) The haloalkene includes at least one of C2F4, C2Cl4, C2Br4, and C2I4;

[0047] (④) The borohydride compounds include BH3, B2H6, and B4H 10 At least one of them;

[0048] (⑤) The phosphorus compounds contained include at least one of phosphine, phosphorus trichloride, trimethylphosphine, triethylphosphine, phosphorus pentoxide, methyl phosphate, dimethyl phosphate, trimethyl phosphate, polyoxyethylene ether phosphate, siloxane phosphate, and polyphosphate.

[0049] The third aspect of this application proposes an electrical device, including a secondary battery according to the first aspect of this application, or a secondary battery obtained by the preparation method according to the second aspect of this application.

[0050] The electrical device provided in this application includes the aforementioned secondary battery and has the beneficial effects of the aforementioned secondary battery, which will not be elaborated here.

[0051] 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

[0052] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0053] Figure 1 is a schematic diagram of the negative electrode sheet according to one embodiment of this application.

[0054] Figure 2 is a schematic diagram of the negative electrode sheet according to one embodiment of this application.

[0055] Figure 3 is a schematic diagram of the particles of the negative electrode active material according to an embodiment of this application.

[0056] Figure 4 is a schematic diagram of the negative electrode sheet according to one embodiment of this application.

[0057] Explanation of the markings in Figures 1-4: 1 Negative electrode sheet; 2 Negative electrode film layer; 3 Negative electrode active material; 4 Functional layer on the surface of the negative electrode film layer; 5 Functional layer on the surface of the particles of the negative electrode active material; d1 Thickness of the functional layer on the surface of the negative electrode film layer; d2 Thickness of the functional layer on the surface of the particles of the negative electrode active material.

[0058] Figure 5 is a schematic diagram of a secondary battery according to an embodiment of this application.

[0059] Figure 6 is an exploded view of a secondary battery according to an embodiment of this application, as shown in Figure 5.

[0060] Figure 7 is a schematic diagram of a battery module according to one embodiment of this application.

[0061] Figure 8 is a schematic diagram of a battery pack according to one embodiment of this application.

[0062] Figure 9 is an exploded view of a battery pack according to an embodiment of this application, as shown in Figure 8.

[0063] Figure 10 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0064] Explanation of the markings in Figures 5-10: 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0065] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0066] In this application, the reference to "embodiment" means that a specific 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 mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments.

[0067] The "range" disclosed in this application is defined in the form of a lower limit and / or an upper limit. A given range is defined by selecting a lower limit and / or an upper limit, which defines the boundary of the particular range. Ranges defined in this way may or may not include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form an undefined range, and any lower limit can be combined with other lower limits to form an undefined range. Similarly, any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, each individually disclosed point or single value can itself serve as a lower limit or upper limit, combined with any other point or single value, or combined with other lower limits or upper limits to form an undefined range.

[0068] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0069] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0070] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps S1 and S2, indicating that the method may include steps S1 and S2 performed sequentially, or it may include steps S2 and S1 performed sequentially. For example, the method may also include step S3, indicating that step S3 may be added to the method in any order. For example, the method may include steps S1, S2, and S3, or it may include steps S1, S3, and S2, or it may include steps S3, S1, and S2, etc.

[0071] Unless otherwise specified, in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0072] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0073] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; the terms "comprising" and "having," and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion. Unless otherwise stated, the terms used in this application have their commonly understood meanings as understood by one of ordinary skill in the art. Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0074] Taking lithium-ion batteries as an example, during the cycling and storage process, the volume of the negative electrode material may expand and contract as lithium ions insert into and extract from the negative electrode active material. This repeated volume change may cause the SEI film (short for "Solid Electrolyte Interphase") to expand. The SEI film is constantly damaged and repaired due to expansion and cracking, resulting in the consumption of active lithium and electrolyte, leading to poor cell cycle life.

[0075] Based on this, this application proposes a secondary battery, including a negative electrode sheet, the negative electrode sheet comprising: a negative current collector; a negative electrode film layer, the negative electrode film layer being located on at least one side of the negative current collector, the negative electrode film layer comprising a negative electrode active material; and satisfying at least one of the following (I) and (II):

[0076] (I) A functional layer is provided on the side of the negative electrode film layer away from the negative electrode current collector;

[0077] (II) The surface of the particles of the negative electrode active material is provided with a functional layer; the functional layer contains organosilicon.

[0078] The secondary battery provided by this solution protects the negative electrode active material by covering the surface of the negative electrode film and / or the particles of the negative electrode active material with an organosilicon material, preventing direct contact between the negative electrode active material and the electrolyte. Compared with inorganic materials, organosilicon materials have a certain degree of elasticity, which can provide a buffer for the volume changes of the negative electrode active material. During the charging and discharging process, it helps to prevent the negative electrode active material from being exposed in the electrolyte due to the rupture of the surface SEI film. Thus, it reduces the chance of direct contact between the electrolyte and the negative electrode active material, reduces the rate of active lithium consumption, and improves cycle life.

[0079] This application proposes that secondary batteries can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices can include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0080] The first aspect of this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet comprising:

[0081] Negative electrode current collector;

[0082] A negative electrode film layer is located on at least one side of the negative electrode current collector, and the negative electrode film layer includes a negative electrode active material;

[0083] A functional layer is provided on the side of the negative electrode film away from the negative electrode current collector, and / or, a functional layer is provided on the surface of the particles of the negative electrode active material; the functional layer contains organosilicon.

[0084] "A functional layer is provided on the side of the negative electrode film away from the negative electrode current collector" means that a functional layer is provided on the surface of the negative electrode film away from the negative electrode current collector. Since the surface of the negative electrode film is not a flat surface, but is composed of a large number of particles, it more specifically means that a functional layer is provided on the outer surface of the particles on the surface of the negative electrode film.

[0085] In this embodiment, the functional layer can be located on the side of the negative electrode film layer away from the negative electrode current collector, thereby improving the cycle life of the secondary battery; the functional layer can also be located on the surface of the particles of the negative electrode active material, that is, a coating layer is formed on the surface of the particles of the negative electrode active material, and then the negative electrode film layer is made through the negative electrode active material with the coating layer, thereby improving the cycle life of the secondary battery; in addition, the functional layer can be located on both the surface of the particles of the negative electrode active material and the side of the negative electrode film layer away from the negative electrode current collector, that is, a functional layer is formed on the surface of the particles of the negative electrode active material, and then the negative electrode film layer is made through the negative electrode active material with the functional layer, and then a functional layer is formed on the surface of the negative electrode film layer, thereby improving the cycle life of the secondary battery.

[0086] This application embodiment protects the negative electrode active material by coating its surface with an organosilicon material, preventing direct contact between the negative electrode active material and the electrolyte. This reduces the rate of active lithium consumption and improves cycle life. Compared to inorganic materials, organosilicon materials have a certain degree of elasticity, providing a buffer against volume changes in the negative electrode active material. During charge and discharge, this helps prevent the surface SEI film from rupturing and exposing the negative electrode active material to the electrolyte. Therefore, it reduces the chance of direct contact between the electrolyte and the negative electrode active material, lowers the rate of active lithium consumption, and improves cycle life.

[0087] In some implementations, the thickness d of the functional layer satisfies: 0 < d ≤ 100 nm. Specifically, the thicknesses of the functional layers are 0 < d ≤ 100 nm, 0 < d ≤ 99 nm, 0 < d ≤ 98 nm, 0 < d ≤ 97 nm, 0 < d ≤ 96 nm, 0 < d ≤ 95 nm, 0 < d ≤ 94 nm, 0 < d ≤ 93 nm, 0 < d ≤ 92 nm, 0 < d ≤ 91 nm, 0 < d ≤ 90 nm, 0 < d ≤ 89 nm, 0 < d ≤ 88 nm, 0 < d ≤ 87 nm, 0 < d ≤ 86 nm, 0 < d ≤ 85 nm, 0 < d ≤ 84 nm, 0 < d ≤ 83 nm, 0 < d ≤ 82 nm, 0 < d ≤ 81 nm, 0 < d ≤ 80 nm, 0 < d ≤ 79 nm, 0 < d ≤ 78 nm, 0 < d ≤ 7 7nm, 0<d≤76nm, 0<d≤75nm, 0<d≤74nm, 0<d≤73nm, 0<d≤72nm, 0<d≤71n m, 0<d≤70nm, 0<d≤69nm, 0<d≤68nm, 0<d≤67nm, 0<d≤66nm, 0<d≤65nm, 0 <d≤64nm, 0<d≤63nm, 0<d≤62nm, 0<d≤61nm, 0<d≤60nm, 0<d≤99nm, 0<d≤ 58nm, 0<d≤57nm, 0<d≤56nm, 0<d≤55nm, 0<d≤54nm, 0<d≤53nm, 0<d≤52n m, 0<d≤51nm, 0<d≤50nm, 0<d≤49nm, 0<d≤48nm, 0<d≤47nm, 0<d≤46nm, 0<d≤45nm, 0<d≤44nm, 0<d≤43nm, 0<d≤42nm, 0<d≤41nm, 0<d≤40nm, 0<d ≤39nm, 0<d≤38nm, 0<d≤37nm, 0<d≤36nm, 0<d≤35nm, 0<d≤34nm, 0<d≤3 3nm, 0<d≤32nm, 0<d≤31nm, 0<d≤30nm, 0<d≤29nm, 0<d≤28nm, 0<d≤27nm 0 < d ≤ 26 nm, 0 < d ≤ 25 nm, 0 < d ≤ 24 nm, 0 < d ≤ 23 nm, 0 < d ≤ 22 nm, 0 < d ≤ 21 nm, 0 < d ≤ 20 nm, 0 < d ≤ 19 nm, 0 < d ≤ 18 nm, 0 < d ≤ 17 nm, 0 < d ≤ 16 nm, 0 < d ≤ 15 nm, 0 < d ≤ 14 nm, 0 < d ≤ 13 nm, 0 < d ≤ 12 nm, 0 < d ≤ 11 nm, 0 < d ≤ 10 nm, 0 < d ≤ 9 nm, 0 < d ≤ 8 nm, 0 < d ≤ 7 nm, 0 < d ≤ 6 nm, 0 < d ≤ 5 nm, 0 < d ≤ 4 nm, 0 < d ≤ 3 nm, 0 < d ≤ 2 nm, 0 < d ≤ 1 nm, etc.

[0088] In this embodiment, the thickness of the functional layer is as follows:

[0089] If the functional layer is located on the side of the negative electrode film layer away from the negative electrode current collector, the thickness of the functional layer refers to the thickness of the functional layer covering the surface of the negative electrode film layer. As shown in Figure 1, a negative electrode film layer 2 is formed on the negative electrode current collector 1. The negative electrode film layer 2 contains a negative electrode active material 3. A functional layer, namely the functional layer 4 on the surface of the negative electrode film layer 2, is formed on the surface of the negative electrode film layer. Therefore, the thickness of the functional layer is the thickness d1 of the functional layer on the surface of the negative electrode film layer, where d = d1.

[0090] If the functional layer is located on the surface of the particles of the negative electrode active material, that is, when a functional layer exists on the surface of the particles of the negative electrode active material, the thickness of the functional layer refers to the thickness of the functional layer on the surface of the particles of the negative electrode active material. As shown in Figure 2, a negative electrode film layer 2 is formed on the negative electrode current collector 1, and the negative electrode film layer 2 contains the negative electrode active material 3; as shown in Figure 3, a functional layer is formed on the surface of the particles of the negative electrode active material 3, that is, the functional layer 5 on the surface of the particles of the negative electrode active material. Therefore, the thickness of the functional layer is the thickness d2 of the functional layer on the surface of the particles of the negative electrode active material, where d = d2.

[0091] If the functional layer is located on both the particle surface of the negative electrode active material and the side of the negative electrode film layer away from the negative electrode current collector, the thickness of the functional layer refers to the sum of the thickness of the functional layer on the particle surface of the negative electrode active material and the thickness of the functional layer on the surface of the negative electrode film layer. As shown in Figure 4, a negative electrode film layer 2 is formed on the negative electrode current collector 1, and the negative electrode film layer 2 contains the negative electrode active material 3; a functional layer, namely the functional layer 4 on the surface of the negative electrode film layer 2, is formed; a functional layer, namely the functional layer 5 on the particle surface of the negative electrode active material 3, is formed. Therefore, the thickness of the functional layer is the sum of the thickness d1 of the functional layer on the particle surface of the negative electrode active material and the thickness d2 of the functional layer on the surface of the negative electrode film layer, where d = d1 + d2.

[0092] The thickness of the functional layer can be measured using a transmission electron microscope (TEM) or an ellipsometry (ELLIPS or Ellips).

[0093] In this embodiment, a functional layer is formed on the surface of the negative electrode active material particles or the negative electrode film layer. The thickness of the functional layer meets the above conditions, thus acting as a barrier between the negative electrode active material and the electrolyte, protecting the negative electrode active material, and reducing the consumption of active lithium. Simultaneously, it helps to reduce the impact on internal resistance. This is because increasing the thickness of the functional layer increases the lithium-ion transport distance, affecting ionic conductivity, increasing DC resistance (DCR), and causing a decrease in the battery's charge / discharge capacity.

[0094] In some implementations, the thickness d of the functional layer satisfies: 5nm < d ≤ 50nm.

[0095] In this embodiment, a functional layer is formed on the surface of the negative electrode active material particles or the negative electrode film layer. The thickness of the functional layer meets the above conditions, thus acting as a barrier between the negative electrode active material and the electrolyte, protecting the negative electrode active material, and reducing the consumption of active lithium. Simultaneously, it helps to further reduce the impact on internal resistance. Further, the thickness d of the functional layer satisfies: 10nm ≤ d ≤ 40nm. In specific examples, the thickness d of the functional layer is: 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm, 21nm, 22nm, 23nm, 24nm, 25nm, 26nm, 27nm, 28nm, 29nm, 30nm, 31nm, 32nm, 33nm, 34nm, 35nm, 36nm, 37nm, 38nm, 39nm, 40nm, etc.

[0096] In some embodiments, based on the test results of the functional layer by X-ray photoelectron spectroscopy analysis, the silicon content is 20wt% to 50wt%. Specific examples show that the silicon content is 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%, etc., or can be a range of any of the above values.

[0097] X-ray photoelectron spectroscopy (XPS) analysis is a well-known detection method in the field, and the oxygen content is obtained based on the well-known detection method of XPS.

[0098] XPS is a surface analysis technique that obtains qualitative and quantitative information about the elements on a material surface by measuring the energy distribution of photoelectrons emitted from the surface, including the type and content of the elements. The detection depth of XPS is 0 to 10 nm.

[0099] In XPS analysis, the relative baseline for elemental content is determined by the characteristic peak areas of all detected elements on the sample surface; it is a relative content. In an XPS spectrum, the characteristic peak area of ​​each element is proportional to the element's content in the sample. To calculate elemental content, peak area measurement, background correction, and normalization are required. The elemental content is then calculated based on the processed peak areas. The elemental content is calculated using the following formula:

[0100] Element content (%) = (element peak area / total peak area) × 100%;

[0101] The total peak area refers to the sum of the peak areas of all elements detected in the sample.

[0102] Within the bulk particles of the negative electrode active material or the bulk of the negative electrode film, the silicon content can be 0 or close to 0. At the interface between the functional layer and the particles of the negative electrode active material, or between the functional layer and the negative electrode film, there may be mutual doping and interactions, resulting in a relatively low silicon content. The closer the functional layer is to the surface, the closer its silicon content is to that of organosilicon compounds. By measuring the surface silicon content and chemical valence state using XPS, the formation of the target organosilicon material in the functional layer can be determined. A silicon content that meets these conditions is beneficial for improving the cycle performance of the battery.

[0103] In some embodiments, the functional layer further includes a doping element; the doping element includes at least one of N, S, B, P, O, F, Cl, Br, and I.

[0104] In this embodiment, elements can be doped into the functional layer to further improve the performance of the electrode and the battery. The content of doped elements in the functional layer can be characterized by XPS or CP-EDS technology.

[0105] In this embodiment, the high-temperature storage performance of the battery can be improved by doping with fluorine (F). The fluorine (F) in the functional layer can play a positive role in the formation and stability of the SEI film. F has high electronegativity, which helps to form a LiF-rich SEI film during the first charge of the battery. Because LiF has high chemical stability and low ionic conductivity, it is less prone to secondary reactions that could lead to other side reactions. This helps to reduce electrolyte decomposition and enhance film stability.

[0106] In this embodiment, the high-temperature storage performance of the battery can be improved by doping with sulfur (S). S in the functional layer has a positive impact on the formation and stability of the SEI film. S can participate in the formation of the SEI film, contributing to the generation of a Li₂S-rich SEI film. Li₂S is a material with good chemical stability and ionic conductivity, which can enhance the stability and ion transport characteristics of the SEI film. This helps reduce electrolyte decomposition and enhance film stability.

[0107] In this embodiment, the fast-charging performance of the battery can be improved by doping with at least one of N (nitrogen) and O (oxygen). Experimental studies have shown that, under the same conditions, doping the functional layer with N is more beneficial to improving the fast-charging performance of the battery compared to not doping with N.

[0108] In this embodiment, the high-temperature storage performance of the battery can be improved by doping with boron (B). Boron may participate in the formation of the SEI film, contributing to the generation of an SEI film rich in boron compounds such as Li3BO3. These compounds possess high chemical and mechanical stability, which helps reduce electrolyte decomposition and enhance film stability.

[0109] In addition, doping with at least one of the elements such as P, Cl, Br, and I can improve the high-temperature storage performance of the battery.

[0110] In some implementations, the doping element includes at least one of F, N, and S.

[0111] Experimental studies have shown that doping the functional layer with at least one of F, N, and S can effectively improve battery performance.

[0112] In some embodiments, the molar ratio of the dopant element to the silicon element is calculated based on the content of the dopant element and the silicon element obtained from the X-ray photoelectron spectroscopy analysis of the functional layer, wherein the molar ratio of the dopant element to the silicon element is ≤10.

[0113] X-ray photoelectron spectroscopy (XPS) analysis is a well-known detection method in the field, and the oxygen content is obtained based on the well-known detection method of XPS.

[0114] XPS is a surface analysis technique that obtains qualitative and quantitative information about the elements on a material surface by measuring the energy distribution of photoelectrons emitted from the surface, including the type and content of the elements. The detection depth of XPS is 0 to 10 nm.

[0115] In XPS analysis, the relative baseline for elemental content is determined by the characteristic peak areas of all detected elements on the sample surface; it is a relative content. In an XPS spectrum, the characteristic peak area of ​​each element is proportional to the element's content in the sample. To calculate elemental content, peak area measurement, background correction, and normalization are required. The elemental content is then calculated based on the processed peak areas. The elemental content is calculated using the following formula:

[0116] Element content (%) = (element peak area / total peak area) × 100%;

[0117] The total peak area refers to the sum of the peak areas of all elements detected in the sample.

[0118] The content of dopant elements and silicon can be obtained through XPS. Then, the mass ratio of dopant elements to silicon can be obtained by the ratio of the content of dopant elements to the content of silicon. Finally, by combining the atomic weights of dopant elements and silicon, the molar ratio of dopant elements to silicon can be calculated.

[0119] As an example, in a region within 10 nm of depth from the surface of the functional layer, the molar ratio of dopant to silicon is 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.5, 0.1, 0.05, 0.01, etc.

[0120] Since organosilicon contains Si-O basic structural units and some side chains, dopants can be introduced into organosilicon through substitution, such as by placing substitution sites on the side chains. The amount of dopant incorporated is related to the number of substitution sites in the organosilicon; the more substitution sites there are, the greater the amount of dopant incorporated. Therefore, for organosilicon molecules, the amount of dopant incorporated will be greater than the amount of Si in the organosilicon.

[0121] In this embodiment, by controlling the molar ratio of dopant elements to silicon elements to meet the above conditions, and considering the amount of dopant elements that can be introduced into organosilicon, more dopant elements are introduced into the functional layer, which is beneficial to effectively exert the effect of dopant elements on improving battery performance.

[0122] Furthermore, when the dopant element is a halogen, the molar ratio of the dopant element F to silicon is ≤5.

[0123] In some implementations, the dopant element is F. The molar ratio of the dopant element to the silicon element is calculated based on the content of the dopant element obtained from the test of the functional layer by X-ray photoelectron spectroscopy analysis and the content of the silicon element. The molar ratio of the dopant element to the silicon element is ≤3.

[0124] Alternatively, if the dopant element is S, the molar ratio of the dopant element to the silicon element is calculated based on the content of the dopant element and the silicon element obtained from the X-ray photoelectron spectroscopy analysis of the functional layer, and the molar ratio of the dopant element to the silicon element is ≤2.

[0125] By controlling the molar ratio of dopant element S to silicon to meet the above conditions, it is beneficial to better leverage the effect of dopant element S on improving the high-temperature storage performance of batteries.

[0126] By controlling the molar ratio of dopant element F to silicon to meet the above conditions, it is beneficial to better leverage the effect of dopant element S on improving the high-temperature storage performance of batteries.

[0127] In some embodiments, the organosilicon includes at least one of the structural units shown in Formula I:

[0128] Wherein, R1, R2, and R3 are independently selected from at least one of substituted or unsubstituted alkyl groups, substituted or unsubstituted olefin groups, substituted or unsubstituted phenyl groups, ester groups, ether groups, sulfonyl groups, amide groups, and heteroelements from C1 to C20; and at least one of R1, R2, and R3 is selected from any one of substituted or unsubstituted alkyl groups and substituted or unsubstituted olefin groups from C1 to C20.

[0129] The structural unit is a repeating unit.

[0130] In this embodiment of the application, XPS, or X-ray photoelectron spectroscopy, is a surface analysis technique that obtains information about the composition, chemical state, and electronic state of the elements on the sample surface by measuring the energy distribution of photoelectrons emitted when X-rays excite the sample surface.

[0131] The organosilicon in the functional layer provided in this application embodiment includes structural units with the structure shown in Formula I. These structural units form organosilicon as repeating units, and the number of repeating units can be determined based on actual needs or actual synthesis conditions. The main chain is formed by repeating the structural units shown in Formula I through covalent bonds. Since each repeating unit is connected to at least one organic hydrocarbon side chain (such as substituted or unsubstituted alkyl groups of C1-C20), it is beneficial to improve the elasticity of organosilicon, enhance the buffering effect on the volume change of the negative electrode active material, and better improve the cycle performance of the battery.

[0132] In this embodiment, the main chain or side chain of organosilicon may contain elements such as O, S, and N with lone pairs of electrons, which can provide high ionic conductivity and improve kinetics, such as reducing DCR (direct current resistance) and shortening fast charging time. In addition, S element has high temperature chemical stability, and F in the side chain has high temperature chemical stability, which is beneficial to improving the high-temperature storage of the battery; the growth of the side chain is beneficial to adjusting the elasticity of the functional layer and improving the cycle stability of the battery.

[0133] Furthermore, dopant elements can be introduced into the organosilicon molecular structure by substituting side-chain elements. These hetero-elements can be elements inherent to the organosilicon itself or can be dopant elements; furthermore, the hetero-elements include at least one of O, C, S, N, Si, P, B, F, Cl, Br, and I.

[0134] In some implementations, the structural unit satisfies at least one of the following (a) to (c):

[0135] (a) Among the substituted alkyl groups of C1-C20, the substituents include halogen elements, and the halogen elements include at least one of F, Cl, Br, and I;

[0136] (b) In the C1-C20 substituted olefinic groups, the substituents include halogens, and the halogens include at least one of F, Cl, Br, and I;

[0137] (c) In the substituted phenyl group, the substituent includes a halogen element, which includes at least one of F, Cl, Br, and I.

[0138] At least one of R1, R2, and R3 is a substituted or unsubstituted alkyl group selected from C1-C20. This facilitates the preparation of organosilicon with better elasticity, improving the coating and buffering effect on the negative electrode active material. Further, at least one of R1, R2, and R3 is a substituted or unsubstituted alkyl group selected from C1-C10. Examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentane, isopentane, n-hexane, isohexane, n-heptane, isoheptane, n-octane, and isooctane.

[0139] In some embodiments, the molecular structure of organosilicon includes at least one of chain-like, cyclic, or combined chain-like and cyclic structures.

[0140] In the embodiments of this application, in organosilicon, the structural unit shown in Formula I forms the main chain as a repeating unit. The shape of the organosilicon molecular structure can be chain-like, cyclic, or a combination of chain-like and cyclic structures.

[0141] In some embodiments, the film resistance of the negative electrode is 0.014 mΩ to 0.024 mΩ.

[0142] The film resistance of the negative electrode refers to the resistance of the coating on the surface of the negative electrode current collector. When the functional layer is located on the particle surface of the negative electrode active material, the film resistance is the resistance of the negative electrode film layer; when the functional layer is at least located on the surface of the negative electrode film layer, the film resistance is the resistance of the negative electrode film layer with the functional layer. It can be measured using a film resistance meter.

[0143] In this embodiment, the functional layer contains organosilicon, which has a certain degree of insulation and low electronic conductivity. Therefore, the film resistance of the obtained negative electrode is relatively high, which satisfies the above conditions, helps to block electrons, reduces electronic conductivity, and further helps to limit the occurrence of side reactions that consume lithium in the electrolyte, thereby improving lifespan performance.

[0144] This is because the solvent in the electrolyte undergoes a reduction reaction with the active lithium at the negative electrode, and the active lithium at the negative electrode undergoes side reactions with the solvent and additives in the electrolyte, continuously consuming lithium and hindering the improvement of battery cycle life. By coating the surface of the negative electrode sheet and / or the particles of the negative electrode active material with organosilicon material, the negative electrode active material is protected, preventing direct contact between the negative electrode active material and the electrolyte. Simultaneously, this side reaction also consumes electrons from the negative electrode. The organosilicon-containing functional layer provided in this application embodiment has a certain degree of insulation and low electronic conductivity, which helps to block electrons, reduce electronic conductivity, and further limit the occurrence of side reactions that consume lithium in the electrolyte, thereby improving cycle life.

[0145] In this embodiment, the functional layer contains organosilicon. The organosilicon has lone pairs of electrons on its siloxanes, which can play a role in transporting lithium ions. Therefore, it exhibits a certain lithium conduction effect, which helps to reduce the DC resistance of the electrode and improve battery performance.

[0146] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries.

[0147] In some embodiments, the negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0148] The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials in batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0149] 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.).

[0150] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0151] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0152] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0153] In some implementations, the battery may include individual battery cells, battery modules, and battery packs.

[0154] Typically, a secondary 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 between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0155] [Positive electrode plate]

[0156] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0157] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0158] 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.).

[0159] 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.

[0160] In some embodiments, when the secondary 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.

[0161] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of positive electrode active materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before material addition. After charge-discharge cycles, the molar Li content changes when the positive electrode active material is applied to the battery system.

[0162] In the examples of positive electrode active materials for lithium-ion batteries in this application, the molar content of O is only a theoretical state value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0163] In some embodiments, when the battery is a sodium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for sodium-ion batteries.

[0164] As an example, the positive electrode active material may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue sodium compounds, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. The modified compounds of the above materials may be for doping modification and / or surface coating modification of the materials.

[0165] In some embodiments, the transition metal in the sodium transition metal oxide can be at least one selected from Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu. The chemical formula of the sodium transition metal oxide can satisfy Na x MO2, wherein M includes at least one of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, and 0 < x ≤ 1.

[0166] In some embodiments, the polyanionic compound may be a sodium ion, a transition metal ion, or a tetrahedral (YO4) compound. n- A class of compounds with anionic units. The transition metal may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include at least one of P, S, and Si; n represents (YO4). n- The price state.

[0167] In some embodiments, the polyanionic compound may also have sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds containing anionic units and halide anions. Transition metals may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include at least one of P, S, and Si, where n represents (YO4). n-The valence state of halogens can include at least one of F, Cl, and Br.

[0168] In some embodiments, the polyanionic compound may also be a tetrahedral compound containing sodium ions (YO4). n- Anionic unit, polyhedral unit ( ZO y ) m+ And a class of compounds with optional halide anions. M may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce, Y may include at least one of P, S and Si, and n represents (YO4). n- The valence state, Z represents transition metal, m represents (ZO) y ) m+ The valence state of halogens can include at least one of F, Cl, and Br.

[0169] As an example, polyanionic compounds can satisfy the chemical formulas NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' includes at least one of V, Fe, Mn and Ni), and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0170] In some embodiments, Prussian blue compounds may contain sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. Transition metals may include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce.

[0171] As an example, Prussian blue compounds can satisfy the chemical formula Na a Me b Me' c (CN)6, wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0172] During the charging and discharging process of a battery, sodium (Na) undergoes insertion / extraction and consumption, resulting in varying molar Na content at different discharge states. In the examples of positive electrode active materials in this application, the molar Na content refers to the initial state of the material, i.e., the state before material addition. After charge-discharge cycles, the molar Na content changes when the positive electrode active material is applied to the battery system.

[0173] In the enumeration of positive electrode active materials for sodium-ion batteries in this application, the molar content of O is only a theoretical state value. The release of oxygen from the crystal lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0174] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0175] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0176] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0177] [Electrolytes]

[0178] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0179] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0180] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0181] 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.

[0182] 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.

[0183] [Isolation membrane]

[0184] In some embodiments, the secondary 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.

[0185] 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.

[0186] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0187] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0188] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0189] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 5 shows a square secondary battery 5 as an example.

[0190] In some embodiments, referring to FIG6, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom 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. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0191] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the 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.

[0192] Figure 7 shows a battery module 4 as an example. Referring to Figure 7, in the battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, the multiple secondary batteries 5 can be fixed in place by fasteners.

[0193] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0194] 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.

[0195] Figures 8 and 9 illustrate a battery pack 1 as an example. Referring to Figures 8 and 9, the battery pack 1 may include a battery compartment and multiple battery modules 4 disposed within the battery compartment. The battery compartment includes an upper compartment 2 and a lower compartment 3, with the upper compartment 2 covering the lower compartment 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 compartment.

[0196] The second aspect of this application provides a method for preparing a secondary battery, including preparing a negative electrode sheet, wherein preparing the negative electrode sheet includes:

[0197] A negative electrode sheet is obtained by forming a negative electrode film layer on at least one side of a negative electrode current collector using a slurry containing a negative electrode active material; the method further includes at least one of the following:

[0198] (i) Prior to the step of forming a negative electrode film layer on at least one side of the negative electrode current collector with a slurry containing a negative electrode active material, a functional layer is formed on the surface of the particles of the negative electrode active material; the functional layer comprises organosilicon;

[0199] (ii) A functional layer is formed on the surface of the negative electrode film; the functional layer contains organosilicon.

[0200] This application embodiment forms a functional layer containing organosilicon on the surface of the negative electrode sheet and / or the particles of the negative electrode active material. The functional layer protects the negative electrode active material and prevents it from directly contacting the electrolyte. Compared with inorganic materials, organic materials have a certain degree of elasticity, which can provide a certain buffering effect on the volume change of the negative electrode active material. During the charging and discharging process, it helps to prevent the negative electrode active material from being exposed in the electrolyte due to the rupture of the surface SEI film. Thus, it reduces the chance of direct contact between the electrolyte and the negative electrode active material, reduces the consumption rate of active lithium, and improves the life performance.

[0201] In some embodiments, the preparation of the negative electrode sheet includes:

[0202] S1000: A functional layer is formed on the surface of the particles of the negative electrode active material to obtain the negative electrode active material (including the functional layer).

[0203] S2000: The negative electrode active material (including the functional layer), conductive agent, binder and any other components are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0204] In some embodiments, the preparation of the negative electrode sheet includes:

[0205] S1000: The negative electrode active material, conductive agent, binder and any other components are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0206] S2000: A functional layer is formed on the surface of the obtained negative electrode sheet.

[0207] In some embodiments, the preparation of the negative electrode sheet includes:

[0208] S1000: First, a functional layer is formed on the surface of the particles of the negative electrode active material to obtain the negative electrode active material (including the functional layer);

[0209] S2000: The negative electrode active material (including the functional layer), conductive agent, binder and any other components are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0210] S3000: A functional layer is formed on the surface of the negative electrode sheet.

[0211] In some embodiments, the method for forming the functional layer includes at least one of chemical vapor deposition and organic vapor deposition.

[0212] Chemical vapor deposition (CVD) is a technique that uses gaseous substances to undergo chemical reactions on a solid surface to generate solid deposits.

[0213] Organic vapor deposition (OVD) is a technique for preparing organic thin films. It involves heating and evaporating organic materials, then using an inert gas to transport the vapor to a low-temperature substrate surface, where organic molecules condense into a thin film.

[0214] In the embodiments of this application, a functional layer containing organosilicon can be formed on the particle surface of the negative electrode active material by chemical vapor deposition or organic evaporation, or a functional layer containing organosilicon can be formed on the surface of the negative electrode film layer.

[0215] Furthermore, when forming a functional layer on the particle surface of the negative electrode active material, chemical vapor deposition can be used for preparation. As an example, the negative electrode active material can be mixed with an organosilicon source (such as siloxane), heated to the decomposition temperature of the organosilicon source, and then stirred and kept warm. At this time, the various gaseous substances formed by the decomposition of the organosilicon source react to form organosilicon deposited on the particle surface of the negative electrode active material, thus obtaining a negative electrode active material with functional layer modification.

[0216] In some embodiments, the chemical vapor deposition method is plasma-enhanced chemical vapor deposition.

[0217] Plasma-enhanced chemical vapor deposition (PECVD) is a thin film deposition technique that uses plasma to promote chemical reactions. In this technique, the plasma provides the energy needed to activate the chemical reaction, allowing deposition to take place at lower temperatures. This helps reduce thermal damage to the substrate material (i.e., the film to be coated and / or the negative electrode active material) and enables the deposition of thin films with good uniformity and consistency.

[0218] In this embodiment, plasma-enhanced chemical vapor deposition can be used to deposit a functional layer on the particle surface of the negative electrode active material or the surface of the negative electrode film. The reaction temperature is relatively mild, which is beneficial to protecting the negative electrode active material.

[0219] In some embodiments, the chemical vapor deposition process includes at least a first gas source, which includes siloxanes.

[0220] Siloxanes are a class of compounds composed of silicon (Si) and oxygen (O), with the basic structural unit being the Si-O bond. Siloxanes can be linear, cyclic, or cross-linked polymers.

[0221] In this embodiment, siloxane is used as a raw material to form an organosilicon-containing coating layer through plasma-enhanced chemical vapor deposition. The gaseous siloxane raw material (or, if the raw material is liquid, it can be vaporized by heating, vacuum assistance, etc.) is excited by plasma to form a highly chemically reactive plasma. This plasma is then introduced onto the surface of the negative electrode sheet or the surface of particles of the negative electrode active material, causing a film-forming reaction to form a functional layer.

[0222] In some embodiments, the siloxane includes at least one of cyclic siloxanes, acyclic siloxanes, other hydrogen-containing silicone oils, and doped siloxanes.

[0223] Furthermore, cyclic siloxanes include at least one of tetramethylcyclotetrasiloxane, hexamethylcyclotrisiloxane, hexaphenylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, and dodecylcyclohexasiloxane.

[0224] Furthermore, the acyclic siloxane includes at least one of vinyltrimethoxysilane (VTMOS), ethyltriacetoxysilane, methylvinyldimethoxysilane (MVDMOS), vinyltriethoxysilane (VTES), xylenesiloxane (DMC), and dimethylcyclopentadienylsilane (DCP).

[0225] Furthermore, other hydrogen-containing silicone oils include at least one of vinyl hydrogen-containing silicone oil, methyl hydrogen-containing silicone oil, phenyl hydrogen-containing silicone oil, ethyl hydrogen-containing silicone oil, propyl hydrogen-containing silicone oil, butyl hydrogen-containing silicone oil, and allyltriethoxysilane.

[0226] Further, the doped siloxanes include bis(dimethylamino)dimethylsilane, triethoxy[5,5,6,6,7,7,7-heptafluoro-4,4-bis(trifluoromethyl)heptyl]silane, triethoxy(pentafluorophenyl)silane, triethoxy(3-epoxypropyloxypropyl)silane, trimethoxy[3-(phenylamino)propyl]silane, trimethoxy(pentafluorophenyl)silane, trimethoxy(p-tolyl)silane, trimethoxy(3,3,3-trifluoropropyl)silane, trimethylsilyl 2,2-difluoro-2-(fluorosulfonyl)acetate, triisopropyltrifluoromethanesulfonate, ureapropyltriethoxysilane, methylvinyldiethoxysilane, methyltrimethoxysilane, diethoxymethylphenylsilane, dimethoxymethylvinylsilane, dimethoxy(methyl)(3,3,3-trifluoro)silane, and dimethoxy(methyl)(3,3,3-trifluoro)silane. The following are at least one of the following: propyl silane, benzyltriethoxysilane, N-methyl-N-trimethylsilane trifluoroacetamide, N-methyl-N-(trimethylsilyl)acetamide, N,O-bis(trimethylsilyl)acetamide, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, 1,2-bis(trichlorosilyl)ethane, (chloromethyl)trimethoxysilane, (3-mercaptopropyl)triethoxysilane, decamethylcyclopentasiloxane, tri[3-(trimethoxysilyl)propyl] isocyanurate, 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane, 4,5-dimethoxy-2-(trimethylsilyl)phenyltrifluoromethanesulfonate, 1,2-bistrimethoxysilyl ethane, and N,O-bis(trimethylsilyl)trifluoroacetamide.

[0227] Through experiments, this application's embodiments have shown that negative electrode sheets using these siloxane-formed functional layers exhibit good cycle life when used in batteries.

[0228] In addition, siloxanes containing doped elements can be selected as raw materials. These raw materials participate in the reaction, and the doped elements enter the organosilicon in the functional layer to play a role.

[0229] In some embodiments, the chemical vapor deposition method further includes a second gas source, which includes at least one of a halogen-containing gas source, a boron-containing gas source, a nitrogen-containing gas source, a phosphorus-containing gas source, a sulfur-containing gas source, and an oxygen-containing gas source; and satisfies at least one of the following (α) to (ζ):

[0230] (α) Halogenated gas sources include at least one of halogenated elements, haloalkanes, haloalkenes, and sulfur fluoride;

[0231] (β) Boron-containing gas sources include boron hydrides;

[0232] (γ) Nitrogen-containing gas sources include at least one of N2 and NH3;

[0233] (δ) Phosphorus-containing gas sources include phosphorus-containing compounds;

[0234] (ε) The sulfur-containing gas source includes at least one of SO2 and SO3;

[0235] (ζ) Oxygen sources include at least one of air, oxygen, ozone, carbon dioxide, and carbon monoxide.

[0236] The "gas source" in the above "halogen gas source, boron-containing gas source, nitrogen-containing gas source, phosphorus-containing gas source, sulfur-containing gas source, and oxygen-containing gas source" refers to raw materials that can provide elements such as halogen, boron, nitrogen, phosphorus, sulfur, and oxygen as a second gas source. It can be gaseous, liquid, or solid. If it is liquid or solid, it can be used as a second gas source after being vaporized.

[0237] In this embodiment, the first gas source serves as the framework source for the functional layer, providing the basic unit structure of organosilicon and possessing side chains; under the action of plasma, the first gas source can initiate a film-forming reaction. The second gas source serves as the gas source for doping elements, providing doping of elements such as F, Cl, Br, I, B, O, N, P, and S in the functional layer.

[0238] In some implementations, the second gas source satisfies at least one of the following (①) to (⑤):

[0239] (①) Halogen elements include at least one of F2, Cl2, Br2, and I2;

[0240] (②) The haloalkane includes CF 4、 At least one of C2F6, CCl4, C2Cl6, CBr4, C2Br6, CIr4, and C2I6;

[0241] (③) The haloalkene includes at least one of C2F4, C2Cl4, C2Br4, and C2I4;

[0242] (④) The borohydride compounds include BH3, B2H6, and B4H 10 At least one of them;

[0243] (⑤) The phosphorus-containing compound includes at least one of phosphine, phosphorus trichloride, trimethylphosphine, triethylphosphine, phosphorus pentoxide, methyl phosphate, dimethyl phosphate, trimethyl phosphate, polyoxyethylene ether phosphate, siloxane phosphate, and polyphosphate.

[0244] In this embodiment of the application, a second gas source is introduced during the chemical vapor deposition process to introduce doping elements into the functional layer, thereby improving battery performance.

[0245] Gaseous siloxane raw materials (or vaporized by heating, vacuum assistance, etc. if the raw material is liquid) are excited by plasma to form plasma with high chemical reactivity. This plasma can be simultaneously modified by a second gas source containing specific elements (such as F, S, etc.). The modified plasma is then introduced into the surface of the electrode to form a film-forming reaction, resulting in a functional layer containing doped elements.

[0246] In this embodiment, when the second gas source is at least one of F2, CF4, C2F4, C2F6, and F2O2S, fluorine (F) can be doped to improve the high-temperature storage performance of the battery. The fluorine (F) in the functional layer can play a positive role in the formation and stability of the SEI film. F has high electronegativity, which helps to form a LiF-rich SEI film during the first charge of the battery. Because LiF has high chemical stability and low ionic conductivity, it is less prone to secondary reactions that could lead to other side reactions. This helps to reduce electrolyte decomposition and enhance film stability.

[0247] In this embodiment, when the second gas source is at least one of SO2, SO3, and F2O2S, sulfur (S) can be doped to improve the high-temperature storage performance of the battery. S in the functional layer has a positive impact on the formation and stability of the SEI film. S can participate in the formation of the SEI film, contributing to the generation of a Li2S-rich SEI film. Li2S is a material with good chemical stability and ionic conductivity, which can enhance the stability and ion transport characteristics of the SEI film, thus helping to reduce electrolyte decomposition and enhance film stability.

[0248] In this embodiment, when the second gas source is N2 and / or NH3, nitrogen (N) can be doped to improve the fast-charging performance of the battery. Experimental studies have shown that, under the same conditions, N doping in the functional layer is more beneficial to improving the fast-charging performance of the battery compared to the case without N doping.

[0249] In this embodiment, the second gas source is BH3, B2H6, or B4H. 10 When at least one of the elements is present, boron (B) can be doped to improve the high-temperature storage performance of the battery. B may participate in the formation of the SEI film, contributing to the generation of SEI films rich in boron compounds such as Li3BO3. These compounds possess high chemical and mechanical stability, which helps reduce electrolyte decomposition and enhance film stability.

[0250] In some embodiments, the second gas source contains at least one of CF4, N2, NH3 and SO2.

[0251] Experimental studies have shown that the second gas source, which contains the aforementioned gases, can dope at least one of F, N, and S into the functional layer, effectively improving battery performance.

[0252] In some embodiments, a functional layer containing organosilicon is formed on the particle surface of the negative electrode active material or on the surface of the negative electrode film layer using plasma-enhanced chemical vapor deposition. The control parameters include at least one of power, gas flow rate, and processing time.

[0253] Radio frequency (RF) or microwave (MW) can be used as energy sources to excite the gas, thereby generating plasma.

[0254] "Power" refers to the power applied during plasma generation. By controlling the power, the density of the plasma and the activity of chemical reactions can be affected, and even the quality of the functional layers can be influenced.

[0255] "Gas flow rate" refers to the flow rate of gas entering the reaction chamber. The gas flow rate affects the concentration of reactants and the chemical environment for film growth; different gas flow rates can alter the chemical composition and thickness of the functional layer.

[0256] "Processing time" typically refers to the duration of the deposition process, from the introduction of reactive gases into the reaction chamber to the end of the deposition process. The length of the processing time affects the thickness and uniformity of the functional layer.

[0257] In the embodiments of this application, one of the parameters can be controlled, or multiple parameters can be controlled in a coordinated manner, to obtain a functional layer containing organosilicon of a target thickness.

[0258] In some embodiments, a functional layer containing organosilicon is formed on the surface of the negative electrode film using plasma-enhanced chemical vapor deposition, including:

[0259] The first gas source (such as decamethylcyclopentasiloxane) is vaporized under vacuum and heating conditions, and after being excited by plasma into a reactive state, it is introduced into the environment of the negative electrode plate; the plasma reactants react on the surface of the electrode plate to form an organosilicon film, which is the functional layer.

[0260] Optionally, in the above-mentioned plasma-enhanced chemical vapor deposition process, multiple gas sources can be simultaneously introduced for plasma ionization. For example, the first gas source and the second gas source can be introduced simultaneously as multiple gases (such as decamethylcyclopentasiloxane vapor and CF4), or they can be plasma-ionized separately and then introduced.

[0261] A third aspect of this application provides an electrical device including the aforementioned secondary battery.

[0262] The electrical device provided in this application embodiment includes the aforementioned secondary battery and exhibits good cycle life.

[0263] Electrical devices include at least one of the secondary batteries, battery modules, or battery packs provided in this application. The secondary batteries, battery modules, or battery packs can be used as a power source for the electrical device or as an energy storage unit for the device. Electrical devices may include, but are 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.

[0264] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0265] Figure 10 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 the secondary battery for this device, a battery pack or battery module can be used.

[0266] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0267] Example

[0268] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0269] I. Lithium-ion batteries

[0270] (I) Preparation of Lithium-ion Batteries

[0271] Example 1

[0272] Preparation of the negative electrode sheet

[0273] Artificial graphite (negative electrode active material), Super P (conductive agent), sodium carboxymethyl cellulose (CMC-Na) (thickener), and styrene-butadiene rubber (SBR) (binder) were mixed, with the following mass percentages: negative electrode active material 96.8%, conductive agent 0.5%, binder 1%, and dispersant 1.7%. After thorough mixing, the mixture was dissolved in deionized water and stirred under vacuum until homogeneous, yielding a negative electrode slurry with a solid content of 66%. The negative electrode slurry was uniformly coated onto 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 the negative electrode sheet.

[0274] A functional layer was prepared on the surface of the obtained negative electrode sheet using plasma-enhanced chemical vapor deposition:

[0275] The first gas source (siloxane raw material: decamethylcyclopentasiloxane) is passed through a plasma excitation device with an inlet flow rate of 0.5 mmol / min and a discharge power of 500 W. During this process, the siloxane raw material, which serves as the first gas source, is excited into a plasma state. This plasma is introduced into the surface of the negative electrode sheet, where a film-forming reaction occurs, forming a functional layer on the surface of the negative electrode film.

[0276] Preparation of the positive electrode sheet

[0277] Lithium iron phosphate, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed thoroughly in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 97.2:1:1.8 to form a uniform positive electrode slurry. The positive electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and then dried, cold-pressed, slit, and cut to obtain the positive electrode sheet.

[0278] [Preparation of the diaphragm]

[0279] A 12μm thick polyethylene film was selected as the separator.

[0280] Preparation of Electrolyte

[0281] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), 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 above organic solvent at a concentration of 1 mol / L. The mixture was then thoroughly mixed to obtain an electrolyte.

[0282] [Battery Manufacturing]

[0283] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up to obtain an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0284] Examples 2-14

[0285] The preparation methods of Examples 2-14 are the same as those of Example 1, except that the parameters are different. The specific raw material composition and deposition conditions are shown in Table 1-1.

[0286] Example 15

[0287] The preparation method of Example 15 is the same as that of Example 1, except that: in the preparation step of the negative electrode sheet, a functional layer is prepared on the surface of the obtained negative electrode sheet by plasma-enhanced chemical vapor deposition.

[0288] A first gas source (siloxane raw material: decamethylcyclopentasiloxane) and a second gas source (raw material: CF4) are simultaneously passed through a plasma excitation device. The inlet flow rate of the first gas source is 0.5 mmol / min, the discharge power is 500 W, and the inlet time is 4 min; the inlet flow rate of the second gas source is 4 mmol / min, the inlet time is 4 min, and the discharge power is 400 W. During this process, both the siloxane raw material (first gas source) and the second gas source are excited into a plasma state and undergo modification. This plasma is introduced into the surface of the negative electrode sheet, causing a film-forming reaction and forming a functional layer on the surface of the negative electrode film.

[0289] Examples 16-24

[0290] The preparation methods of Examples 16 and 24 are as shown in Example 15, except that the parameters are different. The specific parameters such as the composition of each raw material and the deposition conditions are shown in Table 1-2.

[0291] Example 25

[0292] The preparation method of Example 25 is the same as that of Example 1, except that the preparation steps of the negative electrode sheet are different. Specifically, it is shown below:

[0293] A functional layer is formed on the particle surface of the negative electrode active material (artificial graphite) using chemical vapor deposition (CVD):

[0294] 1) Artificial graphite and decamethylcyclopentasiloxane are mixed and kept at 200°C in a rotary kiln under N2 atmosphere protection for 2 hours with stirring. The decamethylcyclopentasiloxane decomposes to produce organosilicon, which is deposited on the surface of the negative electrode active material particles to obtain organosilicon-coated negative electrode active material, that is, the surface of the negative electrode active material particles is coated with a functional layer.

[0295] 2) The above-mentioned silicone-coated negative electrode active material, conductive agent Super P, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) are mixed, wherein the mass percentage of the negative electrode active material is 96.8%, the mass percentage of the conductive agent is 0.5%, the mass percentage of the binder is 1%, and the mass percentage of the dispersant is 1.7%. After uniform mixing, it is dissolved in deionized water and stirred under vacuum until the system is homogeneous to obtain a negative electrode slurry with a solid content of 66%. The negative electrode slurry is uniformly coated on both surfaces of a 6μm thick negative electrode current collector copper foil and dried at 110℃ for 20 min. After drying, the electrode sheet is cold-pressed to obtain the negative electrode sheet.

[0296] Examples 26-27

[0297] The preparation methods of Examples 26 and 27 are the same as those of Example 25, except that the parameters are different. The specific parameters such as the composition of each raw material and deposition conditions are shown in Tables 1-3.

[0298] Example 28

[0299] The preparation method of Example 28 is the same as that of Example 1, except that the preparation steps of the negative electrode sheet are different. Specifically, it is shown below:

[0300] 1) A functional layer is formed on the particle surface of the negative electrode active material (artificial graphite) using chemical vapor deposition (CVD):

[0301] 1) Artificial graphite and trifluoropropylmethylcyclotrisiloxane are mixed and kept at 200°C in a rotary kiln under N2 atmosphere protection for 2 hours with stirring. The decamethylcyclopentasiloxane decomposes to produce organosilicon, which is deposited on the particle surface of the negative electrode active material to obtain organosilicon-coated negative electrode active material, that is, the particle surface of the negative electrode active material is coated with a functional layer.

[0302] 2) The above-mentioned artificial graphite with functional layers, conductive agent Super P, thickener sodium carboxymethyl cellulose (CMC-Na), and binder styrene-butadiene rubber (SBR) are mixed, wherein the mass percentage of the negative electrode active material is 96.8%, the mass percentage of the conductive agent is 0.5%, the mass percentage of the binder is 1%, and the mass percentage of the dispersant is 1.7%. After uniform mixing, it is dissolved in deionized water and stirred under vacuum until the system is homogeneous to obtain a negative electrode slurry with a solid content of 66%. The negative electrode slurry is uniformly coated on both surfaces of a 6μm thick negative electrode current collector copper foil and dried at 110℃ for 20 min. After drying, the electrode sheet is cold-pressed to obtain the negative electrode sheet.

[0303] Comparative Example 1

[0304] The method is the same as in Example 1, except that a functional layer is not prepared in the negative electrode preparation step. Specifically, as shown below:

[0305] Preparation of the negative electrode sheet

[0306] Artificial graphite (negative electrode active material), Super P (conductive agent), sodium carboxymethyl cellulose (CMC-Na) (thickener), and styrene-butadiene rubber (SBR) (binder) were mixed, with the following mass percentages: negative electrode active material 96.8%, conductive agent 0.5%, binder 1%, and dispersant 1.7%. After thorough mixing, the mixture was dissolved in deionized water and stirred under vacuum until homogeneous, yielding a negative electrode slurry with a solid content of 66%. The negative electrode slurry was uniformly coated onto 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 the negative electrode sheet.

[0307] Preparation of the positive electrode sheet

[0308] Lithium iron phosphate, conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed thoroughly in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 97.2:1:1.8 to form a uniform positive electrode slurry. The positive electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and then dried, cold-pressed, slit, and cut to obtain the positive electrode sheet.

[0309] [Preparation of the diaphragm]

[0310] A 12μm thick polyethylene film was selected as the separator.

[0311] Preparation of Electrolyte

[0312] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), 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 above organic solvent at a concentration of 1 mol / L. The mixture was then thoroughly mixed to obtain an electrolyte.

[0313] [Battery Manufacturing]

[0314] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up to obtain an electrode assembly. The electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0315] The relevant parameters of the batteries provided in Examples 1 to 28 above are shown in Tables 1-1, 1-2 and 1-3 below.

[0316] Performance testing

[0317] I. The negative electrode sheets obtained in Examples 1 to 28 and Comparative Example 1 were subjected to characterization tests. The test results are shown in Table 2 below.

[0318] 1. Testing method:

[0319] (1) Functional layer thickness detection:

[0320] The thickness of the functional layer on the surface of the negative electrode is measured by TEM (transmission electron microscopy).

[0321] (2) Element content detection: The surface chemical characterization test of the negative electrode sheet was performed using XPS. The testing instrument was an Axis Supra / Supra+ X-ray photoelectron spectrometer, referring to the standard GB / T 33502-2017, to obtain the X-ray photoelectron spectrum, with the horizontal axis representing the electron binding energy / eV.

[0322] (3) Diaphragm resistance: Diaphragm resistance meter: Model BER1300, electrode diameter 14mm, applied pressure 5MPa, holding time 25s.

[0323] Test method: Cut the diaphragm into a rectangle of about 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.

[0324] (4) High-temperature cycling test:

[0325] At 60℃, the lithium-ion secondary battery was first charged to 3.65V at a constant current of 0.5C, then further charged to 0.05C at a constant voltage of 3.65V, and finally discharged to 2.5V at a constant current of 0.5C. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The battery was subjected to 1000 charge-discharge cycles in the above manner to obtain the cycle capacity retention rate after 1000 cycles.

[0326] Cyclic capacity retention rate (%) = (Capacity at the 1000th cycle / Initial capacity) × 100%.

[0327] 2. Test Results:

[0328] The characterization test results of Examples 1-28 and Comparative Example 1 are shown in Table 2.

[0329] Table 2

[0330] As shown in Table 2, the test results indicate that the cycle capacity retention rate of the batteries provided in Examples 1-28 of this application is higher than that of Comparative Example 1. The embodiments of this application improve the cycle performance of the batteries by modifying the surface of the negative electrode sheet with organosilicon or by modifying the surface of the particles of the negative electrode active material with organosilicon. Furthermore, the film resistance of the negative electrode sheet in the embodiments of this application shows minimal change and no significant deterioration is observed.

[0331] II. Sodium-ion batteries

[0332] (I) Preparation of sodium-ion batteries

[0333] Example 29

[0334] Preparation of the positive electrode sheet

[0335] The positive electrode material Na4Fe3(PO4)2P2O7 was mixed with a conductive agent (SuperP), a binder (PVDF), and a solvent NMP in a mass ratio of 95:5:5:100 and stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto one surface of a positive electrode current collector (aluminum foil), and then dried, cold-pressed, and slit to obtain a positive electrode sheet.

[0336] Preparation of the negative electrode sheet

[0337] The negative electrode material hard carbon, conductive agent carbon black SuperP, binder CMC and solvent water are mixed and stirred evenly in a mass ratio of 8:1:1:10 to obtain a negative electrode slurry; the negative electrode slurry is then uniformly coated on one surface of the negative electrode current collector (copper foil); after drying, cold pressing and slitting, the negative electrode sheet is obtained.

[0338] A functional layer was prepared on the surface of the obtained negative electrode sheet using plasma-enhanced chemical vapor deposition:

[0339] The first gas source (siloxane raw material: decamethylcyclopentasiloxane) is passed through a plasma excitation device. The inlet flow rate of the first gas source is 0.5 mmol / min; the discharge power is 500 W; and the inlet time is 4 min. During this process, the siloxane raw material, which serves as the first gas source, is excited into a plasma state. This plasma is introduced into the surface of the negative electrode sheet, where a film-forming reaction occurs, forming a functional layer on the surface of the negative electrode film.

[0340] Preparation of Electrolyte

[0341] Sodium hexafluorophosphate (NaPF6) was dissolved in solvent EC / DEC (1:1, v / v) to obtain a NaPF6 electrolyte with a concentration of 1 mol / L.

[0342] [Battery Manufacturing]

[0343] The obtained positive electrode, separator (porous polyethylene membrane), and negative electrode are cut into round pieces and arranged in sequence, so that the separator is placed between the positive electrode and the negative electrode to play a role in isolation. The separator is impregnated with the electrolyte and then compacted to obtain a button sodium-ion battery.

[0344] Example 30

[0345] The preparation method of Example 31 is the same as that of Example 30, except that: in the preparation step of the negative electrode sheet, a functional layer is prepared on the surface of the obtained negative electrode sheet by plasma-enhanced chemical vapor deposition.

[0346] A first gas source (siloxane raw material: decamethylcyclopentasiloxane) and a second gas source (raw material: CF4) are simultaneously passed through a plasma excitation device. The inlet flow rate of the first gas source is 0.5 mmol / min, the discharge power is 500 W, and the inlet time is 4 min; the inlet flow rate of the second gas source is 1.25 mmol / min, the discharge power is 125 W, and the inlet time is 4 min. During this process, both the siloxane raw material of the first gas source and the second gas source are excited into a plasma state and undergo modification. This plasma is introduced into the surface of the negative electrode sheet, causing a film-forming reaction and forming a functional layer on the surface of the negative electrode film.

[0347] Comparative Example 2

[0348] The method is the same as in Example 30, except that no functional layer is prepared in the preparation step of the negative electrode sheet.

[0349] The parameters of Examples 29-30 and Comparative Example 2 are shown in Table 3.

[0350] (II) Performance Testing

[0351] 1. Detection Method

[0352] (1) Functional layer thickness detection:

[0353] The thickness of the functional layer on the surface of the negative electrode is measured by TEM (transmission electron microscopy).

[0354] (2) Element content detection: The surface chemical characterization test of the negative electrode sheet was performed using XPS. The testing instrument was an Axis Supra / Supra+ X-ray photoelectron spectrometer, referring to the standard GB / T 33502-2017, to obtain the X-ray photoelectron spectrum, with the horizontal axis representing the electron binding energy / eV.

[0355] (3) Diaphragm resistance: Diaphragm resistance meter: Model BER1300, electrode diameter 14mm, applied pressure 5MPa, holding time 25s.

[0356] Test method: Cut the diaphragm into a rectangle of about 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.

[0357] (4) High-temperature cycling test:

[0358] At 45°C, the lithium-ion secondary battery was first charged to 3.65V at a constant current of 0.5C, then further charged to 0.05C at a constant voltage of 3.65V, and finally discharged to 2.5V at a constant current of 0.5C. This constitutes one charge-discharge cycle, and the discharge capacity of this cycle is the discharge capacity of the first cycle. The battery was subjected to 1000 charge-discharge cycles in the above manner to obtain the cycle capacity retention rate after 1000 cycles.

[0359] Cyclic capacity retention rate (%) = (Capacity at the 1000th cycle / Initial capacity) × 100%.

[0360] 2. Test Results

[0361] The relevant parameters of the batteries in Examples 29-30 and Comparative Example 2 are shown in Table 4 below.

[0362] Table 4

[0363] As shown in Table 4, the cycle capacity retention rates of the batteries provided in Examples 29 and 30 of this application are higher than those in Comparative Example 2. The embodiments of this application improve the cycle performance of the battery by modifying the surface of the negative electrode sheet with organosilicon or by modifying the surface of the particles of the negative electrode active material with organosilicon. Furthermore, the film resistance of the negative electrode sheet in the embodiments of this application changes little, and no significant deterioration problem is observed.

[0364] 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, Includes a negative electrode sheet, wherein the negative electrode sheet comprises: Negative electrode current collector; A negative electrode film layer, the negative electrode film layer being located on at least one side of the negative electrode current collector, the negative electrode film layer comprising a negative electrode active material; and satisfying at least one of the following (I) and (II): (I) A functional layer is provided on the side of the negative electrode film layer away from the negative electrode current collector; (II) The surface of the particles of the negative electrode active material is provided with a functional layer; the functional layer contains organosilicon.

2. The secondary battery according to claim 1, wherein, The thickness d of the functional layer satisfies: 0 < d ≤ 100 nm.

3. The secondary battery according to claim 1 or 2, wherein, The thickness d of the functional layer satisfies: 5 nm < d ≤ 50 nm.

4. The secondary battery according to any one of claims 1 to 3, wherein, Based on the X-ray photoelectron spectroscopy analysis of the functional layer, the silicon content is 20 wt% to 50 wt%.

5. The secondary battery according to claim 4, wherein, The functional layer further comprises doping elements; the doping elements include at least one of N, S, B, P, O, F, Cl, Br, and I.

6. The secondary battery according to claim 5, wherein, Based on the content of the dopant element and the content of silicon obtained from the X-ray photoelectron spectroscopy analysis of the functional layer, the molar ratio of the dopant element to the silicon element is ≤10.

7. The secondary battery according to claim 5 or 6, wherein, If the dopant element is F, then the molar ratio of the dopant element to the silicon element is calculated based on the content of the dopant element and the content of the silicon element obtained from the X-ray photoelectron spectroscopy analysis of the functional layer. The molar ratio of the dopant element to the silicon element is ≤3. Alternatively, if the dopant element is S, then the molar ratio of the dopant element to the silicon element is calculated based on the content of the dopant element and the content of silicon element obtained from the X-ray photoelectron spectroscopy analysis of the functional layer, and the molar ratio of the dopant element to the silicon element is ≤2.

8. The secondary battery according to any one of claims 1 to 7, wherein, The organosilicon includes at least one of the structural units shown in Formula I: Wherein, R1, R2, and R3 are independently selected from at least one of substituted or unsubstituted alkyl groups, substituted or unsubstituted olefin groups, substituted or unsubstituted phenyl groups, ester groups, ether groups, sulfonyl groups, amide groups, and heteroelements from C1 to C20; and at least one of R1, R2, and R3 is selected from any one of substituted or unsubstituted alkyl groups and substituted or unsubstituted olefin groups from C1 to C20; the structural unit is a repeating unit.

9. The secondary battery according to claim 8, wherein, The structural unit satisfies at least one of the following (a) to (c): (a) In the C1-C20 substituted alkyl groups, the substituents include halogen elements, and the halogen elements include at least one of F, Cl, Br, and I; (b) In the C1-C20 substituted olefinic groups, the substituents include halogen elements, and the halogen elements include at least one of F, Cl, Br, and I; (c) In the substituted phenyl group, the substituent includes a halogen element, which includes at least one of F, Cl, Br, and I.

10. The secondary battery according to claim 8 or 9, wherein, The molecular structure of the organosilicon includes at least one of chain-like, cyclic, or combined chain-like and cyclic structures.

11. The secondary battery according to any one of claims 1 to 10, wherein, The film resistance of the negative electrode is 0.014 mΩ to 0.024 mΩ.

12. The secondary battery according to any one of claims 1 to 11, wherein, The negative electrode active material includes at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

13. A method for preparing a secondary battery, wherein, This includes preparing a negative electrode sheet, wherein preparing the negative electrode sheet includes: A negative electrode sheet is obtained by forming a negative electrode film layer on at least one side of a negative electrode current collector using a slurry containing a negative electrode active material; the negative electrode sheet further includes at least one of the following (i) to (ii): (i) Prior to the step of forming a negative electrode film layer on at least one side of the negative electrode current collector with a slurry containing a negative electrode active material, a functional layer is formed on the surface of the particles of the negative electrode active material; the functional layer comprises organosilicon. (ii) A functional layer is formed on the surface of the negative electrode film; the functional layer contains organosilicon.

14. The preparation method according to claim 13, wherein, The method for forming the functional layer includes at least one of chemical vapor deposition and organic vapor deposition.

15. The preparation method according to claim 14, wherein, The chemical vapor deposition method is plasma-enhanced chemical vapor deposition.

16. The preparation method according to claim 15, wherein, The chemical vapor deposition method includes at least a first gas source, which comprises siloxane.

17. The preparation method according to claim 16, wherein, The siloxane includes at least one of cyclic siloxanes, acyclic siloxanes, other hydrogen-containing silicone oils, and doped siloxanes.

18. The preparation method according to claim 16 or 17, wherein, The chemical vapor deposition method further includes a second gas source, which includes at least one of a halogen-containing gas source, a boron-containing gas source, a nitrogen-containing gas source, a phosphorus-containing gas source, a sulfur-containing gas source, and an oxygen-containing gas source; and satisfies at least one of the following (α) to (ζ): (α) The halogen-containing gas source includes at least one of the following: halogen elements, haloalkanes, haloolefins, and sulfur fluoride; (β) The boron-containing gas source includes boron hydride compounds; (γ) The nitrogen-containing gas source includes at least one of N2 and NH3; (δ) The phosphorus-containing gas source includes phosphorus-containing compounds; (ε) The sulfur-containing gas source includes at least one of SO2 and SO3; (ζ) The oxygen source includes at least one of air, oxygen, ozone, carbon dioxide, and carbon monoxide.

19. The preparation method according to claim 18, wherein, The second gas source satisfies at least one of the following (①) to (⑤): (①) Halogen elements include at least one of F2, Cl2, Br2, and I2; (②) The haloalkane includes CF 4、 At least one of C2F6, CCl4, C2Cl6, CBr4, C2Br6, CIr4, and C2I6; (③) The haloalkene includes at least one of C2F4, C2Cl4, C2Br4, and C2I4; (④) The borohydride compounds include BH3, B2H6, and B4H 10 At least one of them; (⑤) The phosphorus-containing compound includes at least one of phosphine, phosphorus trichloride, trimethylphosphine, triethylphosphine, phosphorus pentoxide, methyl phosphate, dimethyl phosphate, trimethyl phosphate, polyoxyethylene ether phosphate, siloxane phosphate, and polyphosphate.

20. An electrical appliance, wherein, The secondary battery includes any one of claims 1 to 12, or the secondary battery obtained by the preparation method according to any one of claims 13 to 19.

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