Secondary battery

Abstract

Provided in the present application is a secondary battery. The secondary battery comprises: a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a silicon-based negative electrode material; and the electrolyte comprises a first additive and a second additive, with the first additive comprising fluoroethylene carbonate, and the second additive comprising a compound as represented by formula I: formula I.

Description

Secondary batteries

[0001] Priority information

[0002] This disclosure claims priority and benefits to patent application No. 202411742098.8, filed with the China National Intellectual Property Administration on November 29, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of materials preparation, and more specifically, to secondary batteries. Background Technology

[0004] With continuous technological advancements and ever-increasing energy demands, the world is accelerating its transition to new energy technologies to address the rapid depletion of traditional energy sources. Against this backdrop, the booming development of the new energy vehicle industry has spurred rapid innovation in power battery technology. Simultaneously, with the rise of clean energy, rechargeable battery technology is also continuously improving, providing effective solutions for energy storage.

[0005] Most existing secondary batteries use graphite as the negative electrode material, with a specific capacity of 372 mAh g. -1 However, these limitations make it difficult to meet the higher specific energy requirements of rechargeable batteries. Issues such as energy density degradation and performance decline under high, low, or high pressure environments also hinder their development. Silicon, as one of the most promising anode materials, has attracted widespread attention from researchers both domestically and internationally. While using silicon-based materials can certainly improve battery energy density, they are prone to significant volume expansion during charge-discharge cycles, leading to continuous damage to the interfacial film, sustained electrolyte decomposition, and ultimately, a rapid decline in battery performance. Summary of the Invention

[0006] This application aims to at least partially address one of the technical problems in the related art. To this end, this application proposes a secondary battery that uses a silicon-based negative electrode material and has a dense and stable interface film, reducing side reactions in the battery and improving the battery's room temperature cycle performance, high temperature cycle performance, high temperature storage performance, and low temperature discharge performance.

[0007] This application proposes a secondary battery, which includes: a negative electrode and an electrolyte;

[0008] The negative electrode sheet includes a silicon-based negative electrode material;

[0009] The electrolyte includes a first additive and a second additive;

[0010] The first additive includes fluoroethylene carbonate;

[0011] The second additive includes the compound shown in Formula I:

[0012] R1, R2, and R3 each independently include any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkanes, R4-substituted phenyl, and R5-substituted benzyl.

[0013] R4 and R5 are each independently selected from any one of H, C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl, and C2-C4 fluoroalkenyl.

[0014] The secondary battery according to the embodiments of this application uses a silicon-based negative electrode material, which has a dense and stable interface film, reduces side reactions of the battery, and improves the battery's room temperature cycle performance, high temperature cycle performance, high temperature storage performance, and low temperature discharge performance.

[0015] 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. Detailed Implementation

[0016] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0017] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0018] 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 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 also expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​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, and ranges defined in this way can include endpoints a and b. 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.

[0019] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0020] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0021] 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.

[0022] This application proposes a secondary battery, which includes: a negative electrode and an electrolyte;

[0023] The negative electrode sheet includes a silicon-based negative electrode material;

[0024] The electrolyte includes a first additive and a second additive;

[0025] The first additive includes fluoroethylene carbonate;

[0026] The second additive includes the compound shown in Formula I:

[0027] in,

[0028] R1, R2, and R3 each independently include any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkanes, R4-substituted phenyl, and R5-substituted benzyl.

[0029] R4 and R5 are each independently selected from any one of H, C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl, and C2-C4 fluoroalkenyl.

[0030] The secondary battery according to the embodiments of this application uses a silicon-based negative electrode material, which has a dense and stable interface film, reduces side reactions of the battery, and improves the battery's room temperature cycle performance, high temperature cycle performance, high temperature storage performance, and low temperature discharge performance.

[0031] The principles by which this application achieves the aforementioned beneficial effects are explained in detail below:

[0032] The negative electrode of the secondary battery in this application contains silicon-based negative electrode material, which can significantly improve the energy density of the secondary battery. However, silicon-based materials are prone to huge volume expansion during charge and discharge, leading to pulverization of the battery material and a decrease in battery performance.

[0033] The addition of fluoroethylene carbonate (FEC) can decompose and polymerize on the electrode surface to form an elastic polymer film, significantly improving the cycle life of silicon-based anode materials and reducing volume expansion during charge and discharge. However, FEC performance deteriorates rapidly at high temperatures, readily defluorinating to form hydrofluoric acid (HF), which attacks the cathode material, causing transition metal ions to dissolve and resulting in a rapid decline in battery performance. Furthermore, the interfacial film formed by FEC becomes less stable at high temperatures, decomposing in large quantities. This leads to continuous decomposition and polymerization of FEC at the interface, producing an excessively thick interfacial film and a sharp increase in battery impedance.

[0034] During battery charging and discharging, the compound shown in Formula I exhibits preferential redox properties and inhibits solvent reduction, thereby reducing electrolyte decomposition. The stable interface constructed by fluorophosphate can effectively resist HF attack and reduce damage to the elastic interface film constructed by FEC. In addition, P=O, PO, and PF bonds can also complex transition metals, reducing the solubility of positive electrode transition metals in the electrolyte, inhibiting the catalytic effect of transition metal ions on the electrolyte, and preventing the reduction and deposition of transition metal ions on the negative electrode surface, thus improving the stability of both positive and negative electrode materials and reducing capacity loss of the positive electrode material.

[0035] Furthermore, the silicon-based structure exhibits a high ability to capture reactive oxygen species generated by the decomposition of electrode materials, enabling the construction of a stable interfacial film and improving its flexibility and smoothness. Moreover, the fluorophosphate structure combines with lithium salts to form fluorophosphate lithium salts, participating in the film formation process and providing LiF, Li3PO3, and Li... x PO y F z Various lithium salt inorganic components enhance the thermal stability and lithium-ion conduction performance of the interface film.

[0036] Overall, the silicon-based anode material, fluoroethylene carbonate, and the compound shown in Formula I work synergistically to construct a denser and more stable interfacial film, reduce side reactions in the secondary battery, and improve the battery's room temperature cycle performance, high temperature cycle performance, high temperature storage performance, and low temperature discharge performance.

[0037] According to embodiments of this application, the compound represented by Formula I includes at least one of compounds having the structures represented by Formulas 1 to 22:

[0038] (Compound 1, CAS number 2708941-25-5) (Compound 2, CAS number 4414-25-9) (Compound 3, CAS number 4414-27-1) (Compound 4, CAS number 6231-59-0) (Compound 5, CAS number 13683-39-1) (Compound 6, CAS number 6231-57-8) (Compound 7, CAS number 4414-26-0) (Compound 8, CAS number 4480-02-8) (Compound 9, CAS number 2577172-95-1) (Compound 10, CAS number 13683-40-4) (Compound 11, CAS No. 2577172-93-9) (Compound 12, CAS number 2708941-27-7) (Compound 13, CAS number 2287283-36-5) (Compound 14) (Compound 15) (Compound 16) (Compound 17) (Compound 18) (Compound 19, CAS number 1386-54-9) (Compound 20, CAS No. 2708941-26-6) (Compound 21, CAS number 6231-58-9) (Compound 22, CAS number 2577172-94-0).

[0039] The synthesis method of Equations 14-18 is as follows:

[0040] Compounds 14 to 18 were prepared according to the preparation method of Example 14 in patent CN114728992A, specifically, the dichlorophenylsilane in the reference document was replaced with the raw materials shown below.

[0041] The raw material is trivinylchlorosilane (1871-21-2);

[0042] The raw material is dimethylethynyl butylchlorosilane (2069196-19-4);

[0043] The raw material is dimethyl(trifluoropropylene)chlorosilane (89705-02-2);

[0044] The raw material is tris(pentafluoroethyl)chlorosilane (1620665-21-5);

[0045] The raw material is dimethyl(p-methylbenzyl)chlorosilane (1833-28-9).

[0046] The compound shown in Formula I can effectively reduce the impedance of the battery interface, improve the stability, flexibility and ionic conductivity of the interface, reduce the decomposition of the electrolyte and the generation of hydrofluoric acid (HF), thereby reducing the corrosion of the positive electrode material, improving its stability, and reducing the capacity loss caused by material corrosion, thus better improving the battery's cycle performance, high-temperature storage performance and low-temperature discharge performance.

[0047] According to embodiments of this application, the mass ratio of the first additive to the second additive is (4-79):1, for example, it can be 4:1, 6:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, or 79:1. A mass ratio of the first additive to the second additive satisfying the above conditions helps to further improve the stability, flexibility, and ionic conductivity of the interfacial film, reduce interfacial impedance, better reduce electrolyte decomposition and hydrofluoric acid (HF) generation, thereby mitigating corrosion of the positive electrode material, improving its stability, and reducing capacity loss due to material corrosion, thus better improving the battery's cycle performance, high-temperature storage performance, and low-temperature discharge performance.

[0048] According to embodiments of this application, the mass percentage of the first additive in the electrolyte is 3% to 15%, for example, 3%, 5%, 6%, 8%, 10%, 12%, or 15%, preferably 6% to 10%. When the content of the first additive meets the above conditions, a stable and elastic interface film can be formed on the positive electrode surface of the battery. This interface film can effectively reduce the interfacial impedance of the battery and improve its cycle stability, high-temperature storage performance, and low-temperature discharge performance.

[0049] According to embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the second additive is 0.05% to 5%, for example, 0.05%, 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 3%, 4%, or 5%, preferably 0.5% to 2.5%. The content of the compound shown in Formula I, satisfying the above conditions, helps to form a more stable and flexible interface film on the surfaces of the positive and negative electrodes of the battery. This not only reduces interface impedance and improves the ionic conductivity of the battery, but also effectively protects the electrode materials and reduces capacity loss caused by electrolyte decomposition and metal ion dissolution. Furthermore, the compound shown in Formula I can reduce electrolyte decomposition and inhibit HF generation, thereby reducing corrosion of internal battery components and improving the battery's thermal stability and safety. This further improves the battery's cycle stability, high-temperature storage performance, and low-temperature discharge performance.

[0050] According to embodiments of this application, the mass percentage of silicon in the silicon-based anode material is 1% to 50%, for example, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, or 50%, preferably 4% to 30%. Since silicon has a high theoretical specific capacity and can store more lithium ions, the silicon content in the silicon-based anode material meeting the above conditions can significantly improve the energy density of the battery. Simultaneously, it helps to balance the volume expansion during charging and discharging, reducing material cracking and pulverization, thereby enhancing the cycle stability and extending the battery's lifespan. Furthermore, it can improve the conductivity of the anode material, accelerate the insertion and extraction speed of lithium ions, and improve the battery's charge and discharge efficiency and power performance.

[0051] According to embodiments of this application, the silicon-based anode material includes at least one of silicon oxide compounds, silicon-carbon composites, and silicon alloys. Exemplarily, silicon oxide compounds include SiO, SiO2, etc., silicon-carbon composites include CVD silicon@porous carbon (mass ratio of (0.1-10):1), etc., and silicon alloys include composite materials containing silicon and lithium.

[0052] According to embodiments of this application, the method for synthesizing the silicon-based anode includes: chemical vapor deposition, plasma evaporation and condensation, and mechanical grinding.

[0053] The principle of preparing silicon-based anode materials by chemical vapor deposition is as follows: the silicon source material is vaporized and decomposed through a gas-phase chemical reaction at high temperature, and then the gas is embedded into the matrix material and condensed to form silicon-carbon composite materials and silicon oxides.

[0054] The principle of preparing silicon-based anode materials by plasma evaporation and condensation is as follows: silicon raw materials are evaporated at high temperature through plasma generation, and the generated gas enters the matrix material and then condenses to form silicon-carbon composite materials and silicon oxides.

[0055] The principle of preparing silicon-based anode materials by mechanical grinding is as follows: The mixed raw materials (silicon, carbon, and possibly metal) are placed in a ball mill and milled under an inert atmosphere. During the milling process, the silicon material is ground to the nanoscale through mechanical force, and then uniformly mixed and refined with other materials. This ultimately forms silicon-carbon composites, silicon oxide compounds, and silicon alloys.

[0056] According to an embodiment of this application, the mass percentage of silicon in the silicon-based anode material is A, the mass percentage of the first additive in the electrolyte is B, and the mass percentage of the second additive in the electrolyte is C. A, B, and C satisfy the following:

[0057] For example, The values ​​can be 18, 25, 30, 45, 50, 60, 70, 80, 90, 100, or 112.

[0058] Meeting the above conditions (A, B, and C) can reduce the volume expansion of silicon-based materials during charging and discharging, reduce electrolyte decomposition, decrease the solubility of positive electrode transition metals in the electrolyte, inhibit the catalytic effect of transition metal ions on the electrolyte, and prevent the reduction and deposition of transition metal ions on the negative electrode surface. This improves the stability of both positive and negative electrode materials, reduces capacity loss in the positive electrode material, constructs a stable interface film, enhances the flexibility and smoothness of the interface film, and improves its thermal stability and lithium-ion conductivity. Therefore, a denser and more stable interface film is constructed, reducing side reactions in the secondary battery and improving the battery's room temperature cycle performance, high temperature cycle performance, high temperature storage performance, and low temperature discharge performance.

[0059] According to embodiments of this application, the electrolyte further comprises a lithium salt, which includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), and lithium di(fluorooxalateborate).

[0060] According to embodiments of this application, the mass percentage of the lithium salt in the electrolyte is 12% to 17%, for example, 12%, 13%, 14%, 15%, 16%, or 17%. Thus, the lithium salt meets the above conditions, which contributes to the efficient migration and stable transport of ions in the electrolyte, thereby improving the battery's charge-discharge efficiency and power density. Furthermore, it helps maintain the chemical stability of the electrolyte, reducing side reactions during high-voltage charging, such as electrolyte decomposition and gas generation, which helps extend the battery's cycle life and improve its safety.

[0061] According to embodiments of this application, the electrolyte further comprises a solvent, which includes at least one of propylene carbonate, ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate, wherein the combination of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, and diethyl carbonate is preferred. This provides good ionic conductivity, maintains efficient lithium-ion transport between the positive and negative electrodes, and helps stabilize the electrode interface, reduce side reactions, and further improve the battery's cycle stability, high-temperature storage performance, and low-temperature discharge performance.

[0062] According to embodiments of this application, the solvent includes ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (DEC), and diethyl carbonate (EMC);

[0063] The mass ratio of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (DEC), and diethyl carbonate (EMC) is (1–5):(1–5):(2–8):(1–5), for example, 1:1:2:1, 1.5:1.5:5:2, 2:2:6:3, 4:3:6:2, or 5:2:8:5. This provides good ionic conductivity, maintains efficient lithium-ion transport between the positive and negative electrodes, helps stabilize the electrode interface, reduces side reactions, and further improves the battery's cycle stability, high-temperature storage performance, and low-temperature discharge performance.

[0064] According to embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the solvent is 10% to 80%, for example, 10%, 20%, 30%, 40%, 50%, 60%, 70%, or 80%. This provides good ionic conductivity, maintains efficient lithium-ion transport between the positive and negative electrodes, and helps stabilize the electrode interface, reduce side reactions, and further improve the battery's cycle stability, high-temperature storage performance, and low-temperature discharge performance.

[0065] According to an embodiment of this application, the negative electrode sheet includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer is disposed on at least one side surface of the negative electrode current collector, and the negative electrode active material layer includes a silicon-based negative electrode material.

[0066] According to an embodiment of this application, the negative electrode active material layer includes a binder.

[0067] According to embodiments of this application, the adhesive may include 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).

[0068] According to embodiments of this application, the negative electrode active material layer may optionally include a conductive agent. 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.

[0069] According to embodiments of this application, the negative electrode active material layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0070] According to embodiments of this application, the negative electrode current collector can be a metal foil or a composite current collector. For example, aluminum or copper foil can 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 can be formed by forming a metal material (aluminum, copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0071] According to embodiments of this application, a negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0072] According to an embodiment of this application, the battery further includes a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector, the positive active material layer including the positive active material.

[0073] According to embodiments of this application, the positive electrode active material includes lithium iron phosphate, nickel-cobalt-manganese ternary materials, or lithium cobalt oxide.

[0074] The positive electrode active material includes LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, and LiNi. x Co y Mn z M 1-x-y-z O2, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4 and Li2Mn 1-x At least one of O4, M is selected from at least one of Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B and F, 0≤a<0.2, 0≤x<1.

[0075] For example, 0≤a≤0.19, 0.05≤a≤0.15, 0.08≤a≤0.13, 0.1≤a≤0.12; 0≤x≤0.9, 0.1≤x≤0.8, 0.2≤x≤0.7, 0.3≤x≤0.6, 0.4≤x≤0.5, etc.

[0076] Understandable, Li1+a Mn 1-x M x O2, LiCo 1-x M x O2 and LiFe 1-x M x In PO4, the choice of M in each chemical formula is independent and does not affect each other; they can be the same or different. Similarly, in the list of positive electrode active materials above, the choices of a and x are also mutually exclusive and do not affect each other; they can be the same or different.

[0077] According to embodiments of this application, the positive electrode current collector may include a metal foil or a composite positive electrode current collector. For example, the metal foil may be aluminum foil. The composite positive electrode current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. For example, the composite negative electrode current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.).

[0078] According to embodiments of this application, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0079] According to embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0080] According to embodiments of this application, a 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, and binder, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive current collector, and obtaining the positive electrode sheet after drying, cold pressing, and other processes.

[0081] According to an embodiment of this application, the secondary battery further includes a separator. The separator is disposed between the positive electrode and the negative electrode, mainly serving to prevent short circuits between the positive and negative electrodes, while allowing ions to pass through.

[0082] 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.

[0083] According to embodiments of this application, the material of the separator may include one or more of polyolefins, aromatic polyamides, polytetrafluoroethylene, and polyethersulfone. Further, the separator may include one or both of polyethylene and polypropylene. Moreover, the separator may be obtained by sequentially stacking multiple layers of materials; for example, the separator may include sequentially stacked polypropylene layers, polyethylene layers, and polypropylene layers.

[0084] According to embodiments of this application, the thickness of the separator can be 9μm-12μm, for example, 9μm, 10μm, 11μm, 12μm, etc.

[0085] The following will explain the solution of this application with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of 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 the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0086] Example 1

[0087] 1. Preparation of electrolyte

[0088] In an argon-filled glove box (moisture < 10 ppm, oxygen < 1 ppm), EC, PC, DEC, and EMC were mixed thoroughly in a mass ratio of 1.5:1.5:5:2 to obtain an organic solvent. 50% of the organic solvent was then mixed with 10% FEC, 1% Compound 2, and 12.5% ​​LiPF6, and the mixture was brought to a final volume of 100% with the remaining organic solvent to obtain the electrolyte. The percentages are based on the total mass of the electrolyte.

[0089] 2. Preparation of the positive electrode sheet

[0090] Lithium cobalt oxide (CCO), polyvinylidene fluoride (PVDF), acetylene black, and single-arm carbon nanotubes (SWCNTs) were mixed in a mass ratio of 96.3:1.2:2:0.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 68 wt%. The slurry was then uniformly stirred under vacuum to obtain the positive electrode slurry. This slurry was uniformly coated onto both surfaces of a 16 μm thick aluminum foil used as a positive electrode current collector. The foil was then baked in an oven at 2200 mm / min at 90°C, 100°C, and 85°C sequentially, followed by drying at 120°C to obtain a positive electrode sheet with a double-sided coating of the positive electrode material. After cutting and welding the tabs, a positive electrode sheet with a size of 558 mm × 55 mm was obtained for later use. The compaction density of the positive electrode material layer was 3.4 g / cm³. 3 The thickness of the single-sided positive electrode material layer is 59 μm.

[0091] 3. Preparation of negative electrode sheet

[0092] A mixture of CVD silicon@porous carbon (CVD silicon to porous carbon mass ratio 1:1) containing 10% silicon as the negative electrode active material, sodium carboxymethyl cellulose (CMC-Na) as the thickener, styrene-butadiene rubber as the binder, acetylene black as the conductive agent, and single-arm carbon nanotubes (SWCNTs) in a mass ratio of 94.94:1.5:2:1.5:0.06 was prepared with deionized water as a solvent to form a slurry with a solid content of 49 wt%. The mixture was then vacuum-stirred to obtain the negative electrode slurry. This negative electrode slurry was uniformly coated onto both surfaces of a 9 μm thick copper foil used as the negative electrode current collector and dried at 85°C to obtain a negative electrode sheet with a double-sided coating of the negative electrode material layer. After cutting and welding the tabs, a negative electrode sheet with a size of 708 mm × 59 mm was obtained for later use. The compaction density of the negative electrode material layer was 1.6 g / cm³. 3 The thickness of the single-sided negative electrode material layer is 47 μm.

[0093] The differences between Examples 2-51 and Comparative Examples 1-5 and Example 1 are shown in Table 1, wherein:

[0094] The difference between Example 42 and Example 1 is that the second additive is replaced with compound 1 and compound 2 in a mass ratio of 1:1.

[0095] The difference between Example 48 and Example 1 is that the positive electrode active material is changed to lithium nickel manganese oxide, and the preparation method of the positive electrode sheet is as follows:

[0096] Lithium nickel manganese oxide (LiN), polyvinylidene fluoride (PVDF), acetylene black, and single-arm carbon nanotubes (SWCNTs) were mixed in a mass ratio of 96.3:1.2:2:0.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 68 wt%. The slurry was then uniformly stirred under vacuum to obtain the positive electrode slurry. The positive electrode slurry was uniformly coated onto both surfaces of a 16 μm thick aluminum foil current collector. The foil was then baked in an oven at 2200 mm / min at 90°C, 100°C, and 85°C sequentially, followed by drying at 120°C to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After cutting and welding tabs, positive electrode sheets with dimensions of 558 mm × 55 mm were obtained for later use. The compaction density of the positive electrode material layer was 3.4 g / cm³. 3 The thickness of the single-sided positive electrode material layer is 59 μm.

[0097] The difference between Comparative Example 1 and Example 1 is that no second additive is added, and the mass ratio of the first additive is changed to 11%.

[0098] The difference between Comparative Example 2 and Example 1 is that the first additive is not added, and the mass ratio of the second additive is changed to 11%.

[0099] The difference between Comparative Example 3 and Example 1 is that compound 2 is replaced with tetramethylsilane.

[0100] The difference between Comparative Example 4 and Example 1 is that fluoroethylene carbonate is replaced with vinylene carbonate (VC).

[0101] The difference between Comparative Example 5 and Example 48 is that no second additive is added, and the mass percentage of the first additive is changed to 11%.

[0102] Test case

[0103] Impedance, cycle life, and high / low temperature performance tests were conducted on the lithium-ion batteries prepared in Examples 1-51 and Comparative Examples 1-5, respectively. The test method for lithium cobalt oxide batteries is as follows. The test method for lithium nickel manganese oxide batteries differs from that for lithium cobalt oxide batteries in that the charging cutoff voltage is 4.8V and the discharging cutoff voltage is 3V. The test results are shown in Table 1.

[0104] 1. Room temperature cycling performance test

[0105] The lithium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1.0C to 4.4V, followed by constant voltage charging at 4.4V until the cutoff current reached 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1.0C to 2.75V, and this discharge capacity was recorded as C1. This process was repeated for 500 cycles, and the discharge capacity C2 after 500 cycles was recorded. The cycle capacity retention rate of the lithium-ion battery was calculated. The cycle capacity retention rate at room temperature = C2 / C1 × 100%.

[0106] 2. High-temperature cycling performance test

[0107] The lithium-ion battery was placed in a 45°C constant temperature test chamber and left to stand for 60 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1.0C to 4.4V, followed by constant voltage charging at 4.4V until the cutoff current reached 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1.0C to 2.75V, and this discharge capacity was recorded as C3. This process was repeated for 300 cycles, and the discharge capacity C4 after 300 cycles was recorded. The cycle capacity retention rate of the lithium-ion battery was calculated. High-temperature cycle capacity retention rate = C4 / C3 × 100%.

[0108] 3. High-temperature storage performance test

[0109] The lithium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1.0C to 4.4V, followed by constant voltage charging at 4.4V until the cutoff current was 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1.0C to 2.75V, and the discharge capacity was recorded as C5. After 28 days, the lithium-ion battery was removed, and its thickness was measured and recorded as h2. It was then discharged at a constant current of 1.0C to 2.75V, and the discharge capacity was recorded as C6. It was then charged again at a constant current of 1.0C to 4.4V, followed by constant voltage charging at 4.4V until the cutoff current was 0.05C. The thickness of the lithium-ion battery was measured and recorded as h1. Finally, the lithium-ion battery was transferred to a 60°C static temperature storage chamber. Capacity retention rate = C6 / C5 × 100%.

[0110] 4. Low-temperature discharge test

[0111] The lithium-ion battery was placed in a 25°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 1.0C to 4.4V, followed by constant voltage charging at 4.4V until the cutoff current was 0.05C. After standing for 5 minutes, it was discharged at a constant current of 1.0C to 2.75V, and this discharge capacity was recorded as C7. The lithium-ion battery was then charged at a constant current of 1.0C to 4.4V, followed by constant voltage charging at 4.4V until the cutoff current was 0.05C. After standing for 5 minutes, it was transferred to a -20°C constant temperature chamber and left to stand for 4.5 hours to allow it to reach a constant temperature. Finally, it was discharged at a constant current of 1.0C to 2.75V, and this discharge capacity was recorded as C8. The low-temperature discharge capacity retention rate of the lithium-ion battery was calculated as C8 / C7 × 100%.

[0112] The results are shown in Table 1. It can be seen that the battery performance of Examples 1–47 and 49–51 is generally better than that of Comparative Examples 1–4, and the performance of Example 48 is better than that of Comparative Example 5. This indicates that the silicon-based anode material, fluoroethylene carbonate, and the compound shown in Formula I work synergistically to construct a denser and more stable interfacial film, reduce side reactions in the secondary battery, and improve the battery's room temperature cycle performance, high temperature cycle performance, high temperature storage performance, and low temperature discharge performance.

[0113] Comparing Examples 2-4, 6-7, 20, 21, and 49-51, a silicon content of 1%–50% in the silicon-based anode material significantly improves the battery's energy density. Simultaneously, it helps balance volume expansion during charge and discharge, reducing material cracking and pulverization, thereby enhancing cycle stability and extending battery life. Furthermore, it improves the conductivity of the anode material, accelerates lithium-ion insertion and extraction, and enhances charge / discharge efficiency and power performance. A higher silicon content leads to material volume expansion and decreased battery life, while a lower silicon content, although improving electrochemical performance, results in lower energy density. Examples 3 and 21 have lower silicon content; although their cycle performance and low-temperature discharge performance are stronger, their energy density is slightly lower, with Example 21 being inferior to Example 3. Examples 4, 6, and 7 show that Example 7 has superior overall battery performance. Therefore, a silicon content of 4%–30% yields the best results.

[0114] Comparing Examples 1, 8-11, 22, and 23, the first additive in the electrolyte, with a mass ratio of 3% to 15%, can form a stable and elastic interfacial film on the positive electrode surface of the battery. This interfacial film can effectively reduce the interfacial impedance of the battery and improve its cycle stability, high-temperature storage performance, and low-temperature discharge performance. If the amount of the first additive is too high, it will produce a thicker interfacial film, resulting in higher battery impedance. Furthermore, excessive dosage will increase its decomposition gas production, leading to an incomplete interfacial film that fails to fully protect the electrode, thus degrading battery performance. A mass ratio of 6% to 10% for the first additive yields the best results.

[0115] Comparing Examples 13-17, 12, and 18, the mass percentage of the second additive in the electrolyte is 0.05%–5%, which helps to form a more stable and flexible interfacial film on the surfaces of the positive and negative electrodes of the battery. This not only reduces interfacial impedance and improves the ionic conductivity of the battery, but also effectively protects the electrode materials and reduces capacity loss caused by electrolyte decomposition and metal ion dissolution. Furthermore, the compound shown in Formula I can reduce electrolyte decomposition and inhibit HF generation, thereby reducing corrosion of internal battery components and improving the battery's thermal stability and safety. This further improves the battery's cycle stability, high-temperature storage performance, and low-temperature discharge performance. Excessive addition of the second additive increases battery impedance and causes decomposition at high temperatures, producing gas and leading to a decrease in battery performance. A mass percentage of 0.5%–2.5% for the second additive yields the best results.

[0116] Table 1

[0117] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A secondary battery, characterized in that, include: Negative electrode plate and electrolyte; The negative electrode sheet includes a silicon-based negative electrode material; The electrolyte includes a first additive and a second additive; The first additive includes fluoroethylene carbonate; The second additive includes the compound shown in Formula I: R1, R2, and R3 each independently include any one of H, F, C1-C4 alkyl, C1-C4 fluoroalkyl, C2-C4 alkenyl, C2-C4 fluoroalkenyl, C2-C4 alkynyl, C5-C7 cycloalkanes, R4-substituted phenyl, and R5-substituted benzyl. R4 and R5 are each independently selected from any one of H, C1-C4 alkyl, C2-C4 alkenyl, C2-C4 alkynyl, C1-C4 fluoroalkyl, and C2-C4 fluoroalkenyl.

2. The secondary battery according to claim 1, characterized in that, The compound represented by Formula I includes at least one of the compounds having the structures shown in Formulas 1 to 22:

3. The secondary battery according to claim 1, characterized in that, The mass ratio of the first additive to the second additive is (4-79):

1.

4. The secondary battery according to claim 1, characterized in that, The mass percentage of the first additive in the electrolyte is 3% to 15%. And / or, the mass percentage of the second additive in the electrolyte is 0.05% to 5%; And / or, the silicon element in the silicon-based anode material accounts for 1% to 50% by mass.

5. The secondary battery according to claim 1, characterized in that, The mass percentage of the first additive in the electrolyte is 6% to 10%; And / or, the mass percentage of the second additive in the electrolyte is 0.5% to 2.5%; And / or, the silicon element in the silicon-based anode material accounts for 4% to 30% by mass.

6. The secondary battery according to any one of claims 1-5, characterized in that, The silicon-based anode material has a mass percentage of silicon (A), the electrolyte has a mass percentage of the first additive (B), and the electrolyte has a mass percentage of the second additive (C). A, B, and C satisfy the following:

7. The secondary battery according to claim 1, characterized in that, The silicon-based anode material includes at least one of silicon oxides, silicon-carbon composites, and silicon alloys.

8. The secondary battery according to claim 7, characterized in that, The methods for synthesizing the silicon-based anode include: chemical vapor deposition, plasma evaporation and condensation, and mechanical grinding.

9. The secondary battery according to claim 1, characterized in that, The electrolyte further comprises: lithium salt; The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium tetrafluoroborate, lithium hexafluoroarsenate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(oxalateborate), and lithium di(fluorooxalateborate). And / or, the lithium salt in the electrolyte accounts for 12% to 17% of the total mass.

10. The secondary battery according to claim 1, characterized in that, The electrolyte further includes: a solvent; The solvent includes at least one of propylene carbonate, methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, fluoroethylene carbonate, γ-butyrolactone, sulfolane, methyl formate, ethyl formate, propyl formate, butyl formate, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, and butyl butyrate. And / or, the solvent in the electrolyte accounts for 10% to 80% by mass.

11. The secondary battery according to claim 10, characterized in that, The solvents include ethylene carbonate, propylene carbonate, methyl ethyl carbonate, and diethyl carbonate; The mass ratio of ethylene carbonate, propylene carbonate, methyl ethyl carbonate and diethyl carbonate is (1-5):(1-5):(2-8):(1-5).

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