Secondary battery, method for manufacturing the same, and electric device

Abstract

The application provides a secondary battery, a preparation method thereof and an electric device. The secondary battery comprises a negative electrode sheet, the negative electrode sheet comprising: a negative electrode current collector; a negative electrode active material layer located on at least one side of the negative electrode current collector; and a diamond-like film located on a side of the negative electrode active material layer away from the negative electrode current collector; the diamond-like film comprising an organic compound containing a heteroatom, the heteroatom comprising one or more of a fluorine atom, a nitrogen atom, a sulfur atom, a boron atom, a silicon atom, a phosphorus atom, a chlorine atom, a bromine atom and an iodine atom. Thus, the cycle life of the secondary battery is further improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery, its preparation method, and an electrical device thereof. Background Technology

[0002] Rechargeable batteries are widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. As the application range of batteries expands, the performance requirements for rechargeable batteries are becoming increasingly stringent. Summary of the Invention

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

[0004] To achieve the above objectives, a 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 active material layer, the negative electrode active material layer being located on at least one side of the negative electrode current collector; and a diamond-like carbon film, the diamond-like carbon film being located on the side of the negative electrode active material layer away from the negative electrode current collector; the diamond-like carbon film comprising an organic compound containing heteroatoms, the heteroatoms being one or more selected from fluorine atoms, nitrogen atoms, sulfur atoms, boron atoms, silicon atoms, phosphorus atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0005] This application includes at least the following beneficial effects: organic compounds have a certain degree of elasticity, and the interaction between carbon atoms and heteroatoms in the diamond-like carbon film can reduce the brittleness of the diamond-like carbon film containing heteroatoms, thereby reducing the possibility of cracks in the diamond-like carbon film under stress due to volume changes of the negative electrode active material. This can enhance the stability and durability of the diamond-like carbon film, thereby effectively slowing down the rate of battery capacity decay and further improving the cycle life of the battery.

[0006] In some embodiments, the mass fraction of the organic compound is 10%-40% based on the total mass of the diamond-like carbon film. Therefore, by controlling the content of organic compounds in the diamond-like carbon film, it is beneficial to obtain better battery kinetic performance and further extend the battery's cycle life.

[0007] In some embodiments, the organic compound includes one or more of organic fluorine, organic nitrogen, and organic sulfur. Therefore, when the organic compound is organic fluorine, the diamond-like carbon (DLC) film exhibits good stability and durability, thereby further improving the cycle life of the battery; when the organic compound is organic nitrogen, the interlayer spacing between DLC film molecules increases, thereby improving the transport efficiency of electrons and active ions, and further improving the fast-charging performance of the battery; when the organic compound is organic sulfur, the DLC film can maintain structural integrity during multiple charge-discharge cycles, reducing stress-induced cracks or defects, thereby further improving the battery's storage life.

[0008] In some embodiments, the organic fluorine content is 15%-35% by mass based on the total mass of the diamond-like carbon film; and / or, the organic nitrogen content is 5%-30% by mass based on the total mass of the diamond-like carbon film; and / or, the organic sulfur content is 10%-25% by mass based on the total mass of the diamond-like carbon film. Therefore, by controlling the organic fluorine content in the diamond-like carbon film, the cycle life of the battery can be further improved; by controlling the organic nitrogen content in the diamond-like carbon film, the fast-charging performance of the battery can be further improved; and by controlling the organic sulfur content in the diamond-like carbon film, the storage life of the battery can be further improved.

[0009] In some embodiments, the thickness of the diamond-like carbon film is 5 nm to 100 nm. Therefore, selecting an appropriate diamond-like carbon film thickness aims to balance the durability of the diamond-like carbon film with the cycle life of the battery.

[0010] In other embodiments, the thickness of the diamond-like carbon film is 10 nm to 50 nm. This allows for a further balance between the durability of the diamond-like carbon film and the cycle life of the battery.

[0011] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0012] In some embodiments, the thickness of the negative electrode active material layer is 50 μm-90 μm. This optimizes the performance of the secondary battery.

[0013] In a second aspect of this application, a method for preparing a secondary battery is provided, comprising preparing a negative electrode sheet, the preparation of the negative electrode sheet comprising: forming a negative electrode sheet comprising a negative electrode active material layer on at least one side of a negative electrode current collector; and forming a diamond-like carbon film on the side of the negative electrode active material layer away from the negative electrode current collector, the diamond-like carbon film comprising an organic compound containing heteroatoms, the heteroatoms comprising one or more of fluorine atoms, nitrogen atoms, sulfur atoms, boron atoms, silicon atoms, phosphorus atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0014] In some embodiments, the method for forming the diamond-like carbon film includes one or more of plasma chemical vapor deposition, plasma-enhanced chemical vapor deposition, and microwave plasma chemical vapor deposition. Thus, selecting a suitable chemical vapor deposition method allows the diamond-like carbon film to adhere to the surface of the negative electrode active material layer.

[0015] In some embodiments, the method of forming a diamond-like carbon film includes introducing a first gas source and a second gas source; wherein the first gas source comprises substituted or unsubstituted C1-C. 13 Hydrocarbons; the second gas source includes one or more of the following: fluorine-containing gas source, nitrogen-containing gas source, and sulfur-containing gas source. Thus, a portion of the carbon plasma dissociated from the first gas source flows towards sp... 2 Hybridized carbon and sp 3 The carbon undergoes a hybridization transformation; another portion of the carbon plasma after dissociation from the first gas source combines with fluorine-containing, nitrogen-containing, or sulfur-containing free radicals after dissociation from the second gas source to form organic compounds containing heteroatoms. 2 Hybridized carbon, sp 3 Hybridized carbon and organic compounds containing heteroatoms are deposited together on the surface of the negative electrode active material layer to form a diamond-like film.

[0016] In some embodiments, the fluorine-containing gas source includes one or more of fluorinated hydrocarbons, fluorinated siloxanes, and fluorinated silanes; and / or, the nitrogen-containing gas source includes one or more of nitrogen, ammonia, nitrogen oxides, nitrogen-containing hydrocarbons, and nitrogen-containing siloxanes; and / or, the sulfur-containing gas source includes one or more of sulfur vapor, sulfur oxides, sulfur-containing hydrocarbons, and sulfur-containing siloxanes. Thus, these fluorine-containing, nitrogen-containing, or sulfur-containing gas sources can provide fluorine-containing free radicals, nitrogen-containing free radicals, or sulfur-containing free radicals.

[0017] In some embodiments, the flow rate ratio of the first gas source to the second gas source is (0.1-100):1. Therefore, by controlling the flow rate ratio of the first gas source and the second gas source, the content of organic compounds in the diamond-like carbon film can be controlled.

[0018] In a third aspect of this application, an electrical device is provided, including a secondary battery as described in the first aspect of this application, or a secondary battery prepared using the method described in the second aspect of this application. Attached Figure Description

[0019] Figure 1 This is a transmission electron microscope (TEM) image of the negative electrode sheet in Example 1.

[0020] Figure 2 This is the chemical state spectrum of carbon in the diamond-like carbon film of Example 1.

[0021] Figure 3 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0022] Figure 4 yes Figure 3 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0023] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application.

[0024] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0025] Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown.

[0026] Figure 8 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0027] Explanation of reference numerals in the attached figures:

[0028] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0029] The following detailed description, with appropriate reference to the accompanying drawings, discloses the secondary battery, its preparation method, and embodiments of the power-using device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0030] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0033] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0034] During the use of secondary batteries, the negative electrode active material undergoes volume expansion and contraction as active ions (such as lithium or sodium ions) are inserted and extracted. This volume change causes the solid electrolyte interphase (SEI) film on the surface of the negative electrode to rupture due to the stress caused by the volume change. The rupture of the SEI film exposes new negative electrode active material, which reacts with the electrolyte to form a new SEI film. This process leads to continuous electrolyte consumption and depletion of active materials, resulting in a shortened cell cycle life. Therefore, reducing unnecessary interfacial reactions on the surface of the negative electrode is crucial for improving its performance.

[0035] To improve the performance of the negative electrode, an effective method is to coat its surface with a diamond-like carbon (DLC) film. DLC films contain sp... 3 Hybridized carbon, these sp 3 Hybridized carbon gives DLC films high hardness and high elastic modulus, thus DLC films can improve the structural stability of the negative electrode and reduce the overall volume change of the negative electrode caused by the volume changes of the negative electrode active material during charging and discharging. However, these sp... 3 Hybridized carbon also makes DLC films more brittle. High brittleness means that DLC films are more prone to cracking when subjected to stress, which can lead to the rupture of the DLC film. This results in direct contact between the electrolyte and the negative electrode active material, causing continuous loss of electrolyte and active material, and shortening the cycle life of the battery cell.

[0036] Based on this, 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 active material layer, the negative electrode active material layer being located on at least one side of the negative electrode current collector; a diamond-like carbon film, the diamond-like carbon film being located on the side of the negative electrode active material layer away from the negative electrode current collector; the diamond-like carbon film comprising an organic compound containing heteroatoms, the heteroatoms being one or more selected from fluorine atoms, nitrogen atoms, sulfur atoms, boron atoms, silicon atoms, phosphorus atoms, chlorine atoms, bromine atoms, and iodine atoms.

[0037] In this application, carbon atoms serve as the core atoms, covalently bonded to heteroatoms (fluorine, nitrogen, sulfur, boron, silicon, phosphorus, chlorine, bromine, iodine, etc.) to form organic compounds containing heteroatoms. Compared to inorganic materials, organic compounds possess a certain degree of elasticity, and the interaction between carbon atoms and heteroatoms in the diamond-like carbon (DLC) film reduces the brittleness of the DLC film incorporating heteroatoms, thereby reducing the likelihood of cracks forming under stress due to volume changes in the negative electrode active material. This enhances the stability and durability of the DLC film, further improving its protective effect on the negative electrode. Consequently, the loss of the negative electrode during battery charging and discharging is reduced, effectively slowing down the rate of battery capacity decay and further extending the battery's cycle life.

[0038] Meanwhile, the diamond-like carbon film includes sp 2 Hybridized carbon and sp 3 Hybridized carbon. Diamond-like films include sp... 3 The presence of hybridized carbon indicates that diamond-like carbon films possess high mechanical strength and excellent electrochemical inertness, maintaining the stability of the overall electrode structure and reducing changes in the overall electrode volume caused by volume changes in the negative electrode active material during charge and discharge. Diamond-like carbon films include sp... 2 The presence of hybrid carbon indicates that diamond-like carbon (DLC) films possess high electron and active ion transport efficiency. Furthermore, DLC films may also prevent dendrites from penetrating the separator and improve internal thermal diffusion within the battery.

[0039] Therefore, in the diamond-like carbon film of the negative electrode sheet of this application, carbon atoms serve as the core atoms, and heteroatoms are bonded together through covalent bonds to form an organic compound containing heteroatoms; simultaneously, carbon atoms are sp 2 Hybrid states and sp 3 The carbon atoms exist in a hybrid state, with these different forms of carbon atoms interconnected by covalent bonds, forming the complex network structure of the diamond-like carbon (DLC) film. This gives the DLC film the high hardness of diamond, the conductivity of graphite, and the elasticity of organic compounds, resulting in a negative electrode with both excellent mechanical and electrochemical properties.

[0040] In some embodiments, the mass fraction of organic compounds is 10%-40% based on the total mass of the diamond-like carbon film.

[0041] In this application, the content of organic compounds in the diamond-like carbon film can be obtained by X-ray photoelectron spectroscopy (XPS).

[0042] XPS testing is a surface analysis technique that uses X-ray photoelectron spectrometer (XPS) to measure the energy distribution of photoelectrons emitted when an X-ray excites the sample surface, thereby determining the elemental composition and relative concentration of elements. The instrument used is an Axis Supra / Supra+ X-ray photoelectron spectrometer, conforming to standard GB / T 33502-2017.

[0043] Taking organic compounds containing fluorine atoms as an example, the specific operation process is as follows: turn on the X-ray source, irradiate the sample, photoelectrons escape from the sample surface, are analyzed by the electron energy analyzer and detected by the detector, and the photoelectron energy distribution data is collected to obtain the full spectrum and narrow spectrum.

[0044] The elements present in organic compounds can be identified by the peak positions in the full spectrum. For example, the F1s peak of fluorine typically appears around 685 eV-695 eV, while the C1s peak of carbon typically appears around 283 eV-290 eV. Therefore, the full spectrum indicates that organic compounds containing fluorine atoms contain both fluorine and carbon elements.

[0045] Furthermore, quantitative analysis is performed using various narrow spectrum parameters. For example, by analyzing the C1s narrow spectrum, peaks such as CF2 and CF3 can be identified; or by analyzing the F1s narrow spectrum, the chemical state of fluorine can be determined. In XPS spectra, the characteristic peak area of ​​each element is proportional to its content in the sample. Therefore, by performing peak fitting, peak area measurement, background correction, and normalization on the C1s or F1s spectra, the elemental content can be calculated based on the processed peak areas.

[0046] In this application, the fluorine atoms in the diamond-like carbon film mainly originate from organic compounds containing fluorine atoms. The content of organic compounds containing fluorine atoms in the diamond-like carbon film can be calculated using the following formula: Organic compound content = Fluorine element content / Molar ratio of fluorine atoms in each organic compound × 100%.

[0047] In this application, when the mass fraction of organic compounds exceeds 40%, it leads to an increase in the interfacial impedance within the cell, affecting the battery's kinetic performance. Therefore, by controlling the content of organic compounds in the diamond-like carbon film, it is beneficial to obtain better battery kinetic performance and further extend the battery's cycle life. As an example, based on the total mass of the diamond-like carbon film, the mass fraction of organic compounds can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, etc., or a range consisting of any two of the above values.

[0048] In this application, sp in diamond-like carbon film 2 Hybridized carbon and sp 3Hybridized carbon can also be obtained by X-ray photoelectron spectroscopy (XPS).

[0049] In some embodiments, the organic compound includes one or more of organofluorine, organonitrogen, and organosulfur.

[0050] As an example, when the organic compound is an organofluorine compound, the fluorine atom exists in the form of an organic compound. The CF bond in organofluorine compounds has a high bond energy, which allows the diamond-like carbon (DLC) film to maintain structural stability under high-temperature conditions. The high electronegativity and strong electron-withdrawing effect of fluorine atoms enhance the chemical stability of the DLC film; simultaneously, the "shielding protection effect" of fluorine atoms on carbon atoms improves the thermal stability and chemical corrosion resistance of the DLC film. These properties work together to give the DLC film good stability and durability, which in turn can further improve the cycle life of the battery.

[0051] As an example, when the organic compound is organic nitrogen, organic nitrogen exists as nitrogen atoms in the form of an organic compound. In organic nitrogen, nitrogen atoms form CN bonds with carbon atoms. The lone pair electrons of the nitrogen atom in the CN bond can interact with the electron cloud of the carbon atom, forming an extended π-conjugated structure, thereby increasing the interlayer spacing between diamond-like carbon (DLC) film molecules. This increased interlayer spacing provides more free paths for electrons and active ions, reducing scattering and collisions, thus improving the transport efficiency of electrons and active ions. The improved electron and active ion transport rate allows the battery to complete charge transfer more quickly during charging, further enhancing the battery's fast-charging performance.

[0052] As an example, when the organic compound is organosulfur, the organosulfur exists as sulfur atoms in the form of an organic compound. In organosulfur, sulfur atoms form CS bonds with carbon atoms. Compared to C-C bonds, CS bonds have lower bond energies and longer bond lengths. CS bonds can undergo some deformation under external stress without breaking. This characteristic of CS bonds allows them to absorb and release energy through bond stretching or bending under thermal or mechanical stress, thereby reducing stress concentration within the material. Therefore, this elastic property allows diamond-like carbon (DLC) films to maintain structural integrity during multiple charge-discharge cycles, reducing stress-induced cracks or defects.

[0053] Furthermore, if the organic sulfur compounds also include disulfide bonds (SS bonds), the elasticity of these disulfide bonds is even better, which can further enhance the stability and durability of the diamond-like carbon (DLC) film. As a result, the DLC film can maintain its structural integrity during multiple charge-discharge cycles, allowing the battery to maintain a high capacity during long-term storage, thereby further improving the battery's storage life.

[0054] Understandably, battery performance can be further improved when the organic compound includes two or more of the following components: organic fluorine, organic nitrogen, and organic sulfur.

[0055] It is understandable that when the heteroatom is a boron atom, silicon atom, phosphorus atom, chlorine atom, bromine atom or iodine atom, the carbon atom can form a bond with the corresponding heteroatom to form an organic compound containing the corresponding heteroatom, thereby further improving the performance of the battery.

[0056] In some embodiments, the organic fluorine content is 15%-35% based on the total mass of the diamond-like carbon film; and / or, the organic nitrogen content is 5%-30% based on the total mass of the diamond-like carbon film; and / or, the organic sulfur content is 10%-25% based on the total mass of the diamond-like carbon film.

[0057] By controlling the content of organic fluorine in the diamond-like carbon (DLC) film, the cycle life of the battery can be further improved. As an example, based on the total mass of the DLC film, the mass fraction of organic fluorine can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, etc., or a range of any two of the above values. In this application, the content of organic fluorine can be obtained by X-ray photoelectron spectroscopy (XPS).

[0058] By controlling the organic nitrogen content in the diamond-like carbon (DLC) film, the fast-charging performance of the battery can be further improved. As an example, based on the total mass of the DLC film, the mass fraction of organic nitrogen can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range of any two of the above values. In this application, the organic nitrogen content can be obtained by X-ray photoelectron spectroscopy (XPS).

[0059] By controlling the organic sulfur content in the diamond-like carbon (DLC) film, the battery's storage life can be further improved. As an example, based on the total mass of the DLC film, the mass fraction of organic sulfur can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or a range of any two of the above values. In this application, the organic sulfur content can be obtained by X-ray photoelectron spectroscopy (XPS).

[0060] In some implementations, the thickness of the diamond-like carbon (DLC) film is 5 nm to 100 nm. When the thickness of the DLC film exceeds 100 nm, the transport path of active ions becomes longer, increasing the internal resistance of the battery; when the thickness of the DLC film is less than 5 nm, the DLC film is prone to damage during charging and discharging. Therefore, selecting an appropriate DLC film thickness aims to balance the durability of the DLC film with the cycle life of the battery.

[0061] In this application, the thickness of the diamond-like carbon film can be obtained by focusing ion beam transmission electron microscopy (FIB-TEM). Specifically, a dual-beam electron microscope (FIB, model: Thermo Fisher-Scios2 HiVac) is first used to thin the surface and side of the negative electrode sheet. Then, a TEM (Thermo Scientific-Talos F200S G2) is used to observe the surface film layer of the thinned sample. n test sites are selected, and the average thickness of the n test sites is measured and calculated to obtain the thickness of the diamond-like carbon film.

[0062] As an example, the thickness of the diamond-like carbon film can be 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm, 100nm, or a range of any two of the above values. In other embodiments, the thickness of the diamond-like carbon film is 10nm-50nm.

[0063] In some embodiments, the thickness of the negative electrode active material layer is 50 μm-90 μm. This optimizes the performance of the secondary battery. In this application, the thickness of the negative electrode active material layer can be measured using a micrometer. As an example, the thickness of the negative electrode active material layer can be 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm, 80 μm, 85 μm, 90 μm, or a range consisting of any two of the above values.

[0064] In some embodiments, the projected area of ​​the diamond-like carbon film on the negative electrode active material layer is greater than or equal to the area of ​​the negative electrode active material layer. Therefore, the diamond-like carbon film can further isolate the negative electrode active material layer from the electrolyte.

[0065] 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.).

[0066] In some embodiments, the negative electrode active material layer includes a negative electrode active material, which may be a negative electrode active material known in the art for use in batteries.

[0067] In some embodiments, the negative electrode active material includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. As an example, silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0068] In some embodiments, the negative electrode active material layer may optionally include a binder. The binder may include one or more 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).

[0069] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0070] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0071] In some embodiments, the secondary battery proposed in this application further includes a positive electrode, an electrolyte, and a separator. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of ions between the positive and negative electrode. The separator, disposed between the positive and negative electrode, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0072] [Positive electrode plate]

[0073] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including a positive active material.

[0074] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0075] 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.).

[0076] 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.

[0077] 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 / 3Mn 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 0.25O2 (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 One or more of the following: 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] In some embodiments, the transition metal in the sodium transition metal oxide can be one or more 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 xMO2, wherein M includes one or more of Ti, V, Mn, Co, Ni, Fe, Zn, V, Zr, Ce, Cr, and Cu, and 0 < x ≤ 1.

[0083] 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 one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include one or more of P, S, and Si; n represents (YO4). n- The price state.

[0084] 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 one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y may include one or more of P, S, and Si, where n represents (YO4). n- The valence state of halogens can include one or more of F, Cl, and Br.

[0085] 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 one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, Y may include one or more 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 one or more of F, Cl, and Br.

[0086] 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 one or more of V, Fe, Mn and Ni), and Na3(VO4) y )2(PO4)2F 3-2y One or more of (0≤y≤1).

[0087] In some embodiments, Prussian blue compounds may contain sodium ions, transition metal ions, and cyanide ions (CN).- A class of compounds. Transition metals can include one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce.

[0088] 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 one or more of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0089] 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.

[0090] 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.

[0091] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0092] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0093] 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.

[0094] [Electrolytes]

[0095] 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.

[0096] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0097] In some embodiments, the electrolyte salt may include one or more 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.

[0098] In some embodiments, the solvent may include one or more of the following: 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.

[0099] 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.

[0100] [Isolation membrane]

[0101] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0102] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may 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 may be the same or different, without particular limitation.

[0103] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0104] [Rechargeable Battery]

[0105] 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.

[0106] 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.

[0107] 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 3 This is an example of a square-structured secondary battery 5.

[0108] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 through 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 according to specific practical needs.

[0109] [Battery Module]

[0110] 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 according to the application and capacity of the battery module.

[0111] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple batteries 5 can be fixed in place using fasteners.

[0112] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of batteries 5 are received.

[0113] [Battery Pack]

[0114] 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 according to the application and capacity of the battery pack.

[0115] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

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

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

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

[0119] S200, A diamond-like film is formed on the side of the negative electrode active material layer away from the negative electrode current collector. The diamond-like film includes an organic compound containing heteroatoms, which include one or more of fluorine atoms, nitrogen atoms, and sulfur atoms.

[0120] In some embodiments, the method for forming a diamond-like film includes one or more of plasma chemical vapor deposition, plasma-enhanced chemical vapor deposition, and microwave plasma chemical vapor deposition.

[0121] Plasma chemical vapor deposition (PCVD) involves ionizing a source gas to form plasma under a high-frequency or DC electric field. Using plasma as an energy source, an appropriate amount of reactive gas is introduced, and the reactive gas is activated by plasma discharge, thereby causing a chemical reaction on the substrate surface to generate a solid thin film.

[0122] Plasma-enhanced chemical vapor deposition (PECVD) generates plasma by applying a voltage to electrodes embedded in a low-pressure gas environment. High-energy electrons and ions in the plasma activate the reactive gas, causing it to dissociate into active groups. These active groups then undergo a chemical reaction on the substrate surface, forming a solid thin film.

[0123] Microwave plasma chemical vapor deposition (MPCVD) uses microwave energy to excite gas molecules, generating high-density plasma, which causes the reactive gas to dissociate into active groups, thereby forming a solid film on the substrate surface.

[0124] In some embodiments, the method of forming a diamond-like carbon film includes introducing a first gas source and a second gas source; wherein the first gas source comprises substituted or unsubstituted C1-C. 13 Hydrocarbons; the second gas source includes one or more of the following: fluorine-containing gas source, nitrogen-containing gas source, and sulfur-containing gas source.

[0125] Thus, the first gas source (such as methane or acetylene) dissociates into highly chemically reactive carbon plasma under plasma excitation, mainly containing carbon radicals and carbon ions. The second gas source (such as methane CF4, nitrogen N2, ammonia NH3, sulfur dioxide SO2, etc.) forms highly chemically reactive heteroatom plasma under plasma excitation, mainly including one or more of fluorine-containing radicals, nitrogen-containing radicals, and sulfur-containing radicals.

[0126] Among them, some carbon radicals or carbon ions in the carbon plasma will move towards sp 2 Hybridized carbon (such as planar triangular structures) and sp 3 Hybridized carbon (e.g., tetrahedral structure) transformation, sp 2 Hybridized carbon tends to form graphitic structures, sp 3 Hybridized carbon is closer to the diamond structure. In another part of the carbon plasma, carbon radicals or carbon ions combine with fluorine-containing, nitrogen-containing, or sulfur-containing radicals in the heteroatom plasma to form organic compounds containing heteroatoms, such as organofluorine, organonitrogen, or organosulfur compounds. 2 Hybridized carbon, sp 3 Hybridized carbon and organic compounds containing heteroatoms are deposited together on the surface of the negative electrode active material layer to form a diamond-like film.

[0127] As an example, C1-C without substitution 13 Hydrocarbons can include unsubstituted C1-C 13 Alkanes, unsubstituted C2-C 13 Alkenes, unsubstituted C2-C 13 Alkynes, unsubstituted C5-C 13 Alicyclic hydrocarbons, unsubstituted C6-C 13 One or more of aromatic hydrocarbons.

[0128] Specifically, non-substitutable C1-C 13 Alkanes may include one or more of the following: methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane, isohexane, neohexane, n-heptane, isoheptane, neoheptane, n-octane, isooctane, neooctane, n-nonane, isononane, neononane, n-decane, isodecane, neodecane, n-undecane, isoundecane, neoundecane, n-dodecane, isododecane, neododecane, n-tridecane, isotridecane, and neotridecane.

[0129] Unsubstituted C2-C 13 Olefins may include one or more of the following: ethylene, propylene, 1-butene, 2-butene, isobutene, 1-pentene, 2-pentene, isopentene, 1-hexene, 2-hexene, isohexene, 1-heptene, 2-heptene, isoheptene, 1-octene, 2-octene, isooctene, 1-nonene, 2-nonene, isononene, 1-decene, 2-decene, isodecanene, 1-undecene, 2-undecene, isoundecene, 1-dodecene, 2-dodecene, isododecene, 1-tetracene, 2-tetracene, isotetracene, 1-tetracene, 2-tetracene, isotetracene, 1-tetracene, isotetracene.

[0130] Unsubstituted C2-C 13 Alkynes may include one or more of the following: acetylene, propyne, 1-butyne, 2-butyne, 1-pentyne, 2-pentyne, 1-hexyne, 2-hexyne, 1-heptyne, 2-heptyne, 1-octyne, 2-octyne, 1-nonyne, 2-nonyne, 1-decyne, 2-decyne, 1-undecanyne, 2-undecanyne, 1-dodecyne, 2-dodecyne, 1-tetaneyne, 2-tetaneyne, 1-tetaneyne, 2-tetaneyne, 1-tetaneyne, 2-tetaneyne.

[0131] No substitute C5-C 13 Alicyclic hydrocarbons may include one or more of cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclononane, cyclodecane, cycloundecane, cyclododecane, and cyclotridecane.

[0132] Unreplaceable C6-C 13 Aromatic hydrocarbons may include one or more of benzene, toluene, o-xylene, m-xylene, p-xylene, o-trimethylene, m-trimethylene, p-trimethylene, o-tetramethylene, m-tetramethylene, p-tetramethylene, o-pentane, m-pentane, p-pentane, o-hexamethylene, m-hexamethylene, p-hexamethylene, o-heptamethylene, m-heptamethylene, and p-heptamethylene.

[0133] For the replacement C1-C 13 Hydrocarbons, which can be understood as C1-C 13 One or more hydrogen atoms in a hydrocarbon are replaced by other atoms or groups. Substituents can include halogens (such as F, Cl, Br, I), hydroxyl groups (-OH), amino groups (-NH2), carboxyl groups (-COOH), sulfonic acid groups (-SO3H), etc.

[0134] In some embodiments, the fluorine-containing gas source includes one or more of fluorinated hydrocarbons, fluorinated siloxanes, and fluorinated silanes.

[0135] As an example, fluorinated hydrocarbons may include one or more of the following: carbon tetrafluoride, hexafluoroethane, octafluoropropane, decafluorobutane, tetrafluoroethylene, hexafluoropropylene, octafluorobutene, trifluoromethane, tetrafluoroethane, trifluoroethane, 1,1,1,2,3,3-hexafluoropropane, 1,1,1,2,2,3,3,3-octafluoropropane, perfluorobutyne, perfluorobutadiene, 1-fluoropropene, 1,2-difluoropropene, 1,3-difluoropropene, 1,2,3-trifluoropropene, trifluoromethane, difluoromethane, monofluoromethane, trifluoroethane, difluoroethane, monofluoroethane, perfluoropropane, perfluorobutane, perfluoropentane, perfluorohexane, perfluoroheptane, perfluorooctane, perfluorononane, perfluorodecane, perfluoroundecane, perfluorododecane, and perfluorotridecane.

[0136] As an example, fluorinated silanes may include one or more of silicon tetrafluoride, trifluoromethylsilane, heptafluoropropyltrichlorosilane, fluorinated phenylsilane, and bis(trifluoromethyl)silane fluoride.

[0137] As an example, fluorinated siloxanes may include one or more of hexafluorodisiloxane, trifluoromethylsilanetrimethoxy, bistrifluoromethylsilanedimethoxy, trifluoromethylsilanetriethoxy, 1,3,5-tris(3,3,3-trifluoropropyl)-1,3,5-trimethylcyclotrisiloxane, and 1,3,5,7-tetra(3,3,3-trifluoropropyl)-1,3,5,7-tetrasiloxane.

[0138] In some embodiments, the nitrogen source includes one or more of nitrogen, ammonia, nitrogen oxides, nitrogen hydrocarbons, and nitrogen-containing siloxanes.

[0139] As an example, nitrogen-containing oxides may include one or more of nitric oxide, nitrogen dioxide, nitrous oxide, dinitrogen trioxide, dinitrogen tetroxide, and dinitrogen pentoxide.

[0140] As an example, nitrogen-containing hydrocarbons may include one or more of the following: methylamine, ethylamine, propylamine, n-propylamine, isopropylamine, butylamine, n-butylamine, isobutylamine, sec-butylamine, tert-butylamine, pentylamine, n-pentylamine, isopentylamine, sec-pentylamine, tert-pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, trimethylamine, dimethylamine, methylamine, acetonitrile, propionitrile, butyronitrile, n-butyronitrile, isobutyronitrile, pentylamine, n-pentylamine, isopentylamine, sec-pentylamine, tert-pentylamine, hexylamine, heptylamine, octylamine, diazomethane, azobenzene, azidomethane, and azidoethane.

[0141] As an example, nitrogen-containing siloxanes may include one or more of hexamethylcyclotrisilazane, hexaphenylcyclotrisilazane, tetramethylcyclotetrasilazane, tetramethylcyclotetrasiloxane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane.

[0142] In some embodiments, the sulfur-containing gas source includes one or more of sulfur vapor, sulfur-containing oxides, sulfur-containing hydrocarbons, and sulfur-containing siloxanes.

[0143] As an example, sulfur-containing oxides may include one or more of sulfur dioxide, sulfur trioxide, sulfurous acid, and sulfuric acid.

[0144] As an example, sulfur-containing hydrocarbons may include one or more of the following: methanethiol, ethanethiol, benzenethiophenol, propanethiol, butanethiol, dimethyl sulfide, ethanethiol, benzene sulfide, propanethiophenol, butanethiophenol, dimethyl disulfide, diethyl disulfide, phenyl disulfide, propyl disulfide, butyl disulfide, methyl polysulfide, ethyl polysulfide, phenyl polysulfide, propyl polysulfide, butyl polysulfide, methanesulfonic acid, benzenesulfonic acid, ethanesulfonic acid, p-toluenesulfonic acid, 2-aminobenzenesulfonic acid, ethanethioic acid, ethanethioate, benzenethioic acid, benzenethioate, propanethioic acid, thiophene, thiazole, benzothiophene, thienothiazole, thienothiophene, alliin, diallyl sulfide, diphenyl sulfide, methyl thiophene, and methyl thiophene.

[0145] As an example, sulfur-containing siloxanes may include one or more of the following: bis(2,4,6,8-tetramethylcyclotetrasiloxane) sulfide, bis(1,1,1,3,3-pentamethyldisiloxane-3-yl) sulfide, bis(3-(triethoxysilane)propyl)tetrasulfide, 4,4'-diaminodiphenyl disulfide, 3-(triethoxysilane)propylthiol, 3-(triethoxysilane)propylthiocyano, 3-(triethoxysilane)propyl isocyanate, 3-(triethoxysilane)propylphenyl sulfide, 3-(triethoxysilane)propyl vinyl sulfide, and 3-(triethoxysilane)propyl polysulfide.

[0146] In some embodiments, the flow rate ratio of the first gas source and the second gas source is (0.1-100):1. Therefore, by controlling the flow rate ratio of the first gas source and the second gas source, the content of organic compounds in the diamond-like carbon film can be controlled.

[0147] As an example, the flow ratio of the first gas source and the second gas source can be 0.1:1, 0.5:1, 1:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 65:1, 70:1, 75:1, 80:1, 85:1, 90:1, 95:1, 100:1, or a range of any two of the above values.

[0148] In some embodiments, the plasma-enhanced chemical vapor deposition (PECVD) method satisfies at least one of the following conditions: the power of the PECVD method is 10W-5000W; the ventilation time of the PECVD method is 1min-60min.

[0149] Here, power refers to the power applied during plasma generation, and gas permeation time is the time from the start of introducing reactive gas into the reaction chamber to the cessation of introducing reactive gas during the deposition process. By controlling the power and gas permeation time in plasma-enhanced chemical vapor deposition, the thickness and quality of diamond-like carbon (DLC) films can be controlled.

[0150] As an example, the power of plasma-enhanced chemical vapor deposition can be 10W, 50W, 100W, 200W, 400W, 600W, 800W, 1000W, 1200W, 1400W, 1600W, 1800W, 2000W, 2200W, 2400W, 2600W, 2800W, 3000W, 3200W, 3400W, 3600W, 3800W, 4000W, 4200W, 4400W, 4600W, 4800W, 5000W, etc., or a range of any two of the above values.

[0151] As an example, the ventilation time for plasma-enhanced chemical vapor deposition can be 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min, or a range of any two of the above values.

[0152] In a third aspect, this application provides an electrical device, including a secondary battery as described in the first aspect of this application, or a secondary battery prepared using the method described in the second aspect of this application. Thus, the secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0153] As an electrical device, batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0154] Figure 8This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0155] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can be powered by a battery.

[0156] Example

[0157] 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.

[0158] Example 1

[0159] (1) Preparation of negative electrode sheet

[0160] S100. The negative electrode active material artificial graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC-Na) are thoroughly mixed in a deionized water solvent system at a weight ratio of 96.82:0.53:1.95:0.7, and then coated onto both surfaces of a copper foil. After the copper foil is dried, it is cold-pressed to obtain a negative electrode sheet with a negative electrode active material layer.

[0161] S200. The negative electrode sheet with the negative electrode active material layer is placed in the PECVD reaction chamber. The first gas source, acetylene (C2H2), and the second gas source, tetrafluoromethane (CF4), are introduced into the reaction chamber respectively. The inlet flow rate of the first gas source is controlled at 150 sccm and the discharge power is 600W. The inlet flow rate of the second gas source is controlled at 15 sccm and the discharge power is 100W. After C2H2 and CF4 are excited into a plasma state, a film-forming reaction occurs on the surface of the negative electrode sheet. After both the first and second gas sources are circulated for 4 minutes, a diamond-like film is formed on the surface of the negative electrode active material layer.

[0162] (2) Preparation of positive electrode sheet

[0163] The positive electrode active material lithium iron phosphate, conductive agent 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 97.2:0.7:2.1 to form a uniform positive electrode slurry. The positive electrode slurry is coated on both surfaces of the positive electrode current collector aluminum foil, and then dried, cold-pressed, slit, and cut to obtain the positive electrode sheet.

[0164] (3) Separating membrane

[0165] A 12μm thick polyethylene film was selected as the separator.

[0166] (4) Preparation of electrolyte

[0167] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent; sodium hexafluorophosphate (NaPF6) was dissolved in the above mixed solvent and stirred until homogeneous, with a molar concentration of 1 mol / L, to form an electrolyte.

[0168] (5) Battery manufacturing

[0169] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation, forming a battery cell. The bare cell is then placed in an outer package, filled with the prepared electrolyte, and sealed to obtain a secondary battery.

[0170] The battery preparation methods in Examples 2-13 are the same as in Example 1, and the specific parameter differences are detailed in Table 1.

[0171] Table 1

[0172]

[0173] Example 14

[0174] The difference between Example 14 and Example 1 is that a diamond-like film is formed by magnetron sputtering; specifically, graphite is used as the target material, the sputtering power of magnetron sputtering is 1000W, the sputtering time is 4min, and only the second gas source CF4 is introduced during the magnetron sputtering process.

[0175] Example 15

[0176] The difference between Example 15 and Example 1 is that the second gas source is fluorine gas (F2), and the plasma auxiliary power supply is not turned on when the second gas source is introduced.

[0177] Example 16

[0178] The difference between Example 16 and Example 1 is that the second gas source is nitrogen (N2).

[0179] Example 17

[0180] The difference between Example 17 and Example 1 is that the second gas source is nitrogen (NH3).

[0181] Example 18

[0182] The difference between Example 18 and Example 1 is that the second gas source is sulfur vapor.

[0183] Example 19

[0184] The difference between Example 19 and Example 1 is that the second gas source is sulfur dioxide (SO2).

[0185] Comparative Example 1

[0186] The difference between Comparative Example 1 and Example 1 is that no second gas source is introduced.

[0187] Structural characterization and performance testing

[0188] 1. Thickness of diamond-like carbon film

[0189] The thickness of the diamond-like carbon film can be measured using focused ion beam transmission electron microscopy (FIB-TEM). Specifically, a dual-beam electron microscope (FIB, Thermo Fisher Scientific-Scios2 HiVac) was first used to thin the surface and sides of the negative electrode sheet. Then, a TEM microscope (Thermo Scientific-Talos F200S G2) was used to observe the processed sample. The observation results of Example 1 are as follows: Figure 1 As shown. By Figure 1 It can be seen that region A exhibits a layered structure and is graphite, the negative electrode active material; region B is a diamond-like film.

[0190] Select n test sites in region B, measure and calculate the average thickness of the diamond-like carbon film at the n test sites, and obtain the thickness of the diamond-like carbon film.

[0191] 2. Detection of diamond-like carbon film composition

[0192] The composition of diamond-like carbon (DLC) films can be determined using X-ray photoelectron spectroscopy (XPS). XPS is a surface analysis technique that measures the energy distribution of photoelectrons emitted when an X-ray excites the sample surface to obtain the elemental composition of the sample surface and determine the relative concentration of elements. Testing instrument: Axis Supra / Supra+ X-ray photoelectron spectrometer, reference standard GB / T 33502-2017.

[0193] XPS analysis was performed on the diamond-like carbon film of Example 1. The chemical state spectrum of C element in Example 1 is shown in the reference image. Figure 2 .

[0194] Depend on Figure 2 As shown, the value at 284.8 eV is sp. 2 The hybrid carbon peak (used as a reference for charge correction) is sp at 285.2 eV. 3The hybrid carbon peaks are observed, with a CF2 peak at 294.4 eV and a CF3 peak at 295.8 eV. Therefore, the diamond-like carbon film simultaneously includes sp... 2 Hybridized carbon, sp 3 Organic compounds containing hybrid carbon and fluorine atoms.

[0195] In XPS spectra, the characteristic peak area of ​​each element is proportional to the content of that element in the sample. Therefore, by performing peak fitting, peak area measurement, background correction, normalization, and other processing on the C1s spectrum, the element content can be calculated based on the processed peak area.

[0196] Depend on Figure 2 It is known that fluorine atoms in diamond-like carbon (DLC) films mainly originate from organic compounds containing fluorine atoms. The content of organic compounds containing fluorine atoms in DLC films can be calculated using the following formula: Organic compound content = Fluorine element content / Molar ratio of fluorine atoms in each organic compound × 100%.

[0197] 3. Battery performance testing

[0198] (1) Cyclic performance test

[0199] Test method: At 60℃, the battery is first charged to 3.65V with a constant current of 0.5C, then further charged to 0.05C with a constant voltage of 3.65V, and finally discharged to 2.5V with 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 is subjected to multiple charge-discharge cycles in the above manner to obtain the number of cycles in which the discharge capacity is 80% of the discharge capacity of the first cycle. The more cycles, the longer the cycle life of the secondary battery.

[0200] (2) Charging time

[0201] At 25℃, the secondary battery was charged and discharged for the first time at a current of 0.33C (where 1C represents the current value corresponding to the theoretical capacity of the secondary battery being completely discharged within 1 hour). The specific steps included: charging the secondary battery at a constant current of 0.33C to the upper limit cutoff voltage, and then charging at a constant voltage until the current ≤0.05C; letting the secondary battery stand for 5 minutes, and then discharging it at a constant current of 0.33C to the lower limit cutoff voltage, and recording the actual discharge capacity C0 of the secondary battery.

[0202] The secondary battery was sequentially charged at different charging rates: 0.5C0, 0.8C0, 1.2C0, 1.5C0, 2.0C0, 2.5C0, 3.0C0, 4.0C0, and 5.0C0, using a constant current to the upper cutoff voltage or the negative electrode potential dropping to 0V (whichever comes first). After each charge, it was discharged at 0.33C0 to the lower cutoff voltage. The negative electrode potential corresponding to charging the secondary battery to 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% SOC (SOC represents the State of Charge of the secondary battery) at different charging rates was recorded.

[0203] Plot the charge rate-negative electrode potential curves for different states of charge (SOCs). Linearly fit these curves to obtain the charge rate corresponding to a negative electrode potential of 0V under different SOCs. This charge rate is the charging window for that SOC. The charging windows for different SOCs are denoted as C. 10％SOC C 20％SOC C 30％SOC C 40％SOC C 50％SOC C 60％SOC C 70％SOC C 80％SOC .

[0204] According to the formula (60 / C) 20％SOC +60 / C 30％SOC +60 / C 40％SOC +60 / C 50％SOC +60 / C 60％SOC +60 / C 70％SOC +60 / C 80％SOC The charging time T for the secondary battery to charge from 10% SOC to 80% SOC is calculated by multiplying the original charge by 10%. The shorter the charging time, the better the fast charging performance of the secondary battery.

[0205] (3) Storage performance test

[0206] Test method: At 25℃, the battery is charged at a constant current rate of 0.33C to a voltage of 3.65V, then charged at a constant voltage of 3.65V until the current is less than or equal to 0.05C. After that, it is left to stand for 10 minutes, and then discharged at a constant current rate of 0.1C to a voltage of 2V (the capacity of this step is marked as C2). The secondary battery was then charged at a constant current rate of 0.33C to a voltage of 3.65V, and then charged at a constant voltage of 3.65V until the current was less than or equal to 0.05C. At this point, the secondary battery was fully charged and stored at 60℃ for 60 days. Then, the secondary battery was transferred to a 25℃ environment and discharged at a constant current rate of 0.33C to a voltage of 2V. Finally, it was charged at a constant current rate of 0.1C to a voltage of 3.65V, and then charged at a constant voltage of 3.65V until the current was less than or equal to 0.05C. After that, it was left to stand for 10 minutes, and then discharged at a constant current rate of 0.1C to a voltage of 2V (the capacity at this step is marked as C90). The reversible capacity retention rate of the secondary battery during storage was calculated as R2 = C90 ÷ C2 × 100%. The larger the value of R2, the better the storage performance.

[0207] The test results of the diamond-like carbon film and battery in Examples 1-15 and Comparative Example 1 are shown in Table 2.

[0208] Table 2

[0209]

[0210]

[0211] As shown in Table 2, the batteries obtained in Examples 1-13 all exhibit good cycle life. Examples 1-13, through plasma-enhanced chemical vapor deposition, can increase the organic fluorine content in the diamond-like carbon (DLC) film, which not only reduces the brittleness of the DLC film but also improves its stability under high-temperature conditions, thereby further enhancing the battery's cycle life.

[0212] In contrast, Example 14 uses magnetron sputtering to introduce organic fluorine into a diamond-like carbon film. However, the efficiency of magnetron sputtering is lower than that of plasma-enhanced chemical vapor deposition, resulting in a lower organic fluorine content in the diamond-like carbon film of Example 14 compared to Examples 1-13. The number of cycles in Example 14 is also less than that in Examples 1-13, indicating that the cycle performance of the battery in Example 14 is worse than that in Examples 1-13.

[0213] In Example 15, the introduction of fluorine gas was not assisted by plasma, which prevented the introduction of a large amount of organic fluorine into the diamond-like carbon (DLC) film. Furthermore, XPS testing revealed that the DLC film of Example 15 contained a significant amount of elemental fluorine. Elemental fluorine readily reacts with components such as the electrolyte in the battery, leading to the consumption of active materials and the generation of gas, thus damaging the battery's internal structure and increasing internal resistance. Therefore, the large amount of elemental fluorine in the DLC film of Example 15 actually worsened the battery's cycle performance, resulting in a lower cycle performance than Comparative Example 1.

[0214] Comparative Example 1 did not introduce a second gas source, and the diamond-like membrane of Comparative Example 1 did not contain organic fluorine. The number of cycles in Comparative Example 1 was less than that in Examples 1-14, indicating that the cycle performance of the battery in Comparative Example 1 was worse than that in Examples 1-14.

[0215] The test results of the diamond-like carbon film and battery in Examples 16-17 and Comparative Example 1 are shown in Table 3.

[0216] Table 3

[0217]

[0218] As shown in Table 3, the batteries obtained in Examples 16-17 all have shorter charging times. Examples 16-17, through plasma-enhanced chemical vapor deposition, can increase the content of organic nitrogen in the diamond-like carbon film, which can not only reduce the brittleness of the diamond-like carbon film, but also improve the transmission efficiency of electrons and active ions, thereby further improving the fast charging performance of the battery.

[0219] In contrast, Comparative Example 1 did not introduce a second gas source, and the diamond-like carbon film of Comparative Example 1 did not contain organic nitrogen. The charging time of Comparative Example 1 was longer than that of Examples 16-17, indicating that the fast charging performance of the battery in Comparative Example 1 was worse than that of Examples 16-17.

[0220] The test results of the diamond-like carbon film and battery in Examples 18-19 and Comparative Example 1 are shown in Table 4.

[0221] Table 4

[0222]

[0223] As shown in Table 4, the batteries obtained in Examples 18-19 all exhibit high reversible capacity retention rates. Examples 18-19, through plasma-enhanced chemical vapor deposition, can increase the organic sulfur content in the diamond-like carbon (DLC) film, which not only reduces the brittleness of the DLC film but also improves its structural integrity during long-term storage, thereby further enhancing the battery's storage life.

[0224] In contrast, Comparative Example 1 does not have a second gas source, the diamond-like carbon film of Comparative Example 1 does not contain organic sulfur, and the R2 of Comparative Example 1 is less than that of Examples 18-19, indicating that the storage life of the battery in Comparative Example 1 is worse than that of Examples 18-19.

[0225] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, characterized in that, Includes a negative electrode sheet, wherein the negative electrode sheet comprises: Negative electrode current collector; A negative electrode active material layer, wherein the negative electrode active material layer is located on at least one side of the negative electrode current collector; A diamond-like carbon (DLC) film is located on the side of the negative electrode active material layer away from the negative electrode current collector; the DLC film includes an organic compound containing heteroatoms, wherein the heteroatoms include one or more of fluorine atoms, nitrogen atoms, sulfur atoms, boron atoms, silicon atoms, phosphorus atoms, chlorine atoms, bromine atoms, and iodine atoms.

2. The secondary battery according to claim 1, characterized in that, Based on the total mass of the diamond-like carbon film, the mass fraction of the organic compound is 10%-40%.

3. The secondary battery according to any one of claims 1-2, characterized in that, The organic compounds include one or more of organic fluorine, organic nitrogen, and organic sulfur.

4. The secondary battery according to claim 3, characterized in that, Based on the total mass of the diamond-like carbon film, the mass fraction of the organic fluorine is 15%-35%; and / or, Based on the total mass of the diamond-like carbon film, the mass fraction of the organic nitrogen is 5%-30%; and / or, Based on the total mass of the diamond-like carbon film, the mass fraction of the organic sulfur is 10%-25%.

5. The secondary battery according to any one of claims 1-4, characterized in that, The thickness of the diamond-like carbon film is 5nm-100nm.

6. The secondary battery according to claim 5, characterized in that, The thickness of the diamond-like carbon film is 10nm-50nm.

7. The secondary battery according to any one of claims 1-6, characterized in that, The negative electrode active material layer includes a negative electrode active material, which includes one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

8. The secondary battery according to any one of claims 1-7, characterized in that, The thickness of the negative electrode active material layer is 50μm-90μm.

9. A method for preparing a secondary battery, characterized in that, This includes preparing a negative electrode sheet, wherein preparing the negative electrode sheet includes: A negative electrode sheet containing a negative electrode active material layer is formed on at least one side of the negative electrode current collector; A diamond-like carbon film is formed on the side of the negative electrode active material layer away from the negative electrode current collector. The diamond-like carbon film includes an organic compound containing heteroatoms, which include one or more of fluorine atoms, nitrogen atoms, sulfur atoms, boron atoms, silicon atoms, phosphorus atoms, chlorine atoms, bromine atoms, and iodine atoms.

10. The method according to claim 9, characterized in that, The method for forming diamond-like carbon films includes one or more of plasma chemical vapor deposition, plasma-enhanced chemical vapor deposition, and microwave plasma chemical vapor deposition.

11. The method according to claim 10, characterized in that, The method for forming a diamond-like carbon film includes introducing a first gas source and a second gas source; wherein... The first gas source includes substituted or unsubstituted C1-C 13 Hydrocarbons; The second gas source includes one or more of the following: fluorine-containing gas source, nitrogen-containing gas source, and sulfur-containing gas source.

12. The method according to claim 11, characterized in that, The fluorine-containing gas source includes one or more of fluorinated hydrocarbons, fluorinated siloxanes, and fluorinated silanes; and / or, The nitrogen-containing gas source includes one or more of nitrogen, ammonia, nitrogen-containing oxides, nitrogen-containing hydrocarbons, and nitrogen-containing siloxanes; and / or, The sulfur-containing gas source includes one or more of the following: sulfur vapor, sulfur oxides, sulfur hydrocarbons, and sulfur siloxanes.

13. The method according to any one of claims 11-12, characterized in that, The flow rate ratio of the first gas source to the second gas source is (0.1-100):

1.

14. An electrical appliance, characterized in that, The secondary battery includes any one of claims 1-8, or the secondary battery prepared by any one of claims 9-13.

Images