Secondary battery and device

Abstract

The application relates to a secondary battery and a device. The secondary battery of the application comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the electrolyte comprises a sulfur-containing additive, the positive electrode comprises a positive electrode active material layer, the positive electrode active material layer comprises a conductive agent, the content of the conductive agent in the positive electrode active material layer is A% based on the mass of the positive electrode active material layer, the positive electrode further comprises a solid electrolyte interface film on the surface of the positive electrode active material layer, the negative electrode comprises a negative electrode active material layer and a solid electrolyte interface film on the surface of the negative electrode active material layer, the mass percentage content of sulfur element in the negative electrode solid electrolyte interface film is Y1%, the mass percentage content of sulfur element in the positive electrode solid electrolyte interface film is Y2%, and 2.0 <= Y1+3*Y2 / A <= 8.5, so that the obtained secondary battery has better cycle performance, storage performance and safety performance at high temperature.

Description

Technical Field

[0001] This application relates to the field of energy storage. Specifically, this application relates to a secondary battery and device. Background Technology

[0002] Lithium-ion batteries have rapidly gained dominance in the 3C (computer, communication, and consumer electronics) sector, including mobile phones and laptops, as well as various electric vehicles, thanks to their numerous advantages.

[0003] In recent years, with the increasingly widespread application of lithium-ion rechargeable batteries, people have placed higher demands on their performance. How to achieve high safety and cycle performance in rechargeable batteries has become a pressing technical challenge. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a secondary battery and related apparatus. The secondary battery of this application effectively improves the cycle performance, storage performance, and safety performance by controlling the relationship between the sulfur content in the solid electrolyte interphase (CEI) film formed on the surface of the positive electrode active material layer, the sulfur content in the solid electrolyte interphase (SEI) film formed on the surface of the negative electrode active material layer, and the content of the conductive agent in the positive electrode active material layer.

[0005] The first aspect of this application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte, wherein...

[0006] The electrolyte includes sulfur-containing additives.

[0007] The positive electrode sheet includes a positive active material layer, which includes a conductive agent. Based on the mass of the positive active material layer, the content of the conductive agent is A%.

[0008] The positive electrode also includes a solid electrolyte interface film located on the surface of the positive electrode active material layer.

[0009] The negative electrode sheet includes a negative electrode active material layer and a solid electrolyte interface film located on the surface of the negative electrode active material layer.

[0010] Using X-ray photoelectron spectroscopy, the mass percentage of sulfur in the negative electrode solid electrolyte interface film is Y1%, and the mass percentage of sulfur in the positive electrode solid electrolyte interface film is Y2%, wherein 2.0≤Y1+3*Y2 / A≤8.5, 0.6<Y1<6.0, 0.4<Y2<2.2, and 0.5<A<4.5.

[0011] A second aspect of this application provides an apparatus comprising the secondary battery described in the first aspect.

[0012] The beneficial effects of this application are as follows:

[0013] The secondary battery of this application achieves a suitable relationship by controlling the sulfur content in the solid electrolyte interphase (CEI) film formed on the surface of the positive electrode active material layer, the sulfur content in the solid electrolyte interphase (SEI) film formed on the surface of the negative electrode active material layer, and the content of the conductive agent in the positive electrode active material layer. This results in the formation of more stable and denser CEI and SEI films on the positive and negative electrode surfaces, respectively. This effectively suppresses the continuous side reactions and electrolyte consumption caused by the contact between the electrolyte and the positive electrode active material, thereby extending the cycle life of the secondary battery and improving the kinetic performance of the positive electrode active material layer. Based on these improvements, the secondary battery of this application exhibits excellent cycle performance, storage performance, and safety performance at high temperatures. Detailed Implementation

[0014] For the sake of brevity, this application only specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0015] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0016] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0017] The term "C1-C6 alkyl" includes, but is not limited to: methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, etc.

[0018] The term "C1-C6 alkylene" includes, but is not limited to: methylene, ethylene, n-propylene, isopropylene, cyclopropylene, n-butylene, isobutylene, sec-butylene, tert-butylene, cyclobutylene, n-pentylene, isopentylene, neopentylene, cyclopentylene, methylenecyclopentylene, n-hexylene, isohexylene, and cyclohexylene.

[0019] The term "C2-C6 alkenyl" includes, but is not limited to: vinylidene, n-propenylidene, isopropenylidene, n-but-2-enylidene, n-but-3-enylidene, n-hex-3-enylidene, etc.

[0020] The present application will be further described below with reference to specific embodiments. It should be understood that these specific embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0021] Primary and secondary batteries

[0022] The secondary battery provided in this application includes a positive electrode, a negative electrode, and an electrolyte, wherein the electrolyte includes a sulfur-containing additive; wherein the positive electrode includes a positive active material layer and a solid electrolyte interface film located on the surface of the positive active material layer, and based on the mass of the positive active material layer, the content of conductive agent in the positive active material layer is A%.

[0023] The negative electrode sheet includes a negative electrode active material layer and a solid electrolyte interface film located on the surface of the negative electrode active material layer.

[0024] X-ray photoelectron spectroscopy (XPS) analysis revealed that the sulfur content (Y) in the negative electrode solid electrolyte interface film was 1% by mass, and the sulfur content (Y) in the positive electrode solid electrolyte interface film was 2% by mass.

[0025] Among them, 2.0≤Y1+3*Y2 / A≤8.5, 0.6<Y1<6.0, 0.4<Y2<2.2, 0.5<A<4.5.

[0026] Sulfur in the positive electrode solid electrolyte interphase (CEI) and negative electrode solid electrolyte interphase (SEI) membranes can improve the high-temperature stability of the CEI and SEI membranes, respectively, thus improving the high-temperature storage and cycling performance of the positive and negative electrodes. However, since sulfur is a poor conductor of lithium ions and electrons, a high sulfur content can affect the kinetic performance of the electrodes, thereby impacting the electrochemical performance of the battery. The inventors of this application have discovered that by limiting the relationship between the sulfur content in the positive electrode solid electrolyte interphase (CEI) and the negative electrode solid electrolyte interphase (SEI) membranes and the content of the conductive agent in the positive electrode within the aforementioned range, on the one hand, the CEI / SEI membranes become denser and more stable, effectively suppressing the continuous side reactions and electrolyte consumption caused by the contact between the electrolyte and the positive and negative electrode active materials, thereby extending the cycle life of the secondary battery. On the other hand, an appropriate conductive agent content in the CEI membrane can mitigate the deterioration of electrode kinetic performance caused by the presence of sulfur, improve the kinetic characteristics of lithium ion transport at the interface, and achieve a significant improvement in the performance of the secondary battery.

[0027] In some embodiments, 2.0 ≤ Y1 + 3 * Y2 / A ≤ 8.5 is a range of 2.0, 3.0, 4.0, 5.0, 6.5, 7.5, 8, 8.5, or any two of the above values. In some embodiments, 3.0 ≤ Y1 + 3 * Y2 / A ≤ 6.0.

[0028] In some embodiments, 0.6 ≤ Y1 ≤ 6.0; in other embodiments, Y1 is a range of 0.6, 0.7, 1.0, 2.3, 3.5, 4.0, 5.0, 6.0, or any two of the above values. In some embodiments, 1.0 ≤ Y1 ≤ 4.0.

[0029] In some embodiments, 0.4 ≤ Y2 ≤ 2.2; in other embodiments, Y2 is a range of 0.4, 0.5, 0.6, 0.7, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, or any two of the above values. In some embodiments, 0.5 ≤ Y2 ≤ 1.8.

[0030] In some embodiments, 0.5 ≤ A ≤ 4.5. In some embodiments, A is a range of 0.5, 0.8, 1.0, 1.5, 2.0, 3.0, 4.0, 4.5, or any two of the above values. In some embodiments, 1.0 ≤ A ≤ 3.0.

[0031] In some embodiments, the porosity of the positive electrode is Z1%, and the porosity of the negative electrode is Z2%, wherein 30 ≤ Z1 ≤ 45 and / or 20 ≤ Z2 ≤ 40. When the Z1 value is too small, i.e., the porosity of the positive electrode is small, the ability of the positive electrode to absorb electrolyte is reduced, the electrolyte is difficult to wet, and the polarization of the secondary battery will increase during cycling, thus affecting its cycle performance. When the porosity of the positive electrode is too large, the conductivity of the electrode also decreases, which will reduce the utilization rate of the secondary battery and affect the electrochemical performance and energy density of the secondary battery. In some embodiments, the value of Z1 is 30, 33, 35, 37, 40, 43, 45, or any value between them. In some embodiments, 30 ≤ Z1 ≤ 40.

[0032] In some embodiments, the porosity of the negative electrode sheet is Z2%, where 20 ≤ Z2 ≤ 40. In some embodiments, Z is 20, 22, 25, 28, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, or any value between them. In some embodiments, 30 ≤ Z2 ≤ 40.

[0033] By controlling the porosity of the positive and negative electrode sheets within a suitable range, it is beneficial for the electrolyte to fully wet the electrodes, which in turn facilitates the formation of a dense and stable solid electrolyte interface film on the positive and negative electrode surfaces.

[0034] In this application, the porosity of the positive electrode sheet and the porosity of the negative electrode sheet can be adjusted by conventional technical means in the field according to the characteristics of the selected active material, such as controlling the electrode sheet rolling pressure, rolling temperature, and rolling speed.

[0035] In some embodiments, the conductive agent includes at least one of carbon nanotubes, acetylene black, graphene, conductive carbon black, Ketjen black, conductive fibers, and conductive polymers.

[0036] In some embodiments, the conductive agent content in the positive electrode active material layer satisfies 0.5 ≤ A ≤ 4.5. To ensure good charge-discharge performance of the positive electrode, a certain amount of conductive agent is usually added during electrode fabrication to reduce electrode contact resistance and accelerate electron mobility. Simultaneously, the conductive agent improves electrode processability, promotes electrolyte wetting of the electrode, and effectively increases the migration rate of lithium ions in the electrode material, reducing polarization, thereby improving electrode charge-discharge efficiency and lithium battery lifespan. Excessive conductive agent content results in high positive electrode electronic conductivity, low electrode resistance, and facilitates the formation of sulfur-containing additives on the CEI film, but leads to low initial efficiency and low battery energy density. Conversely, insufficient conductive agent content results in low positive electrode electronic conductivity, high electrode resistance, poor electrode conductivity, low cell capacity utilization, and poor battery kinetics.

[0037] In some embodiments, the conductive agent includes carbon nanotubes, with the carbon nanotubes comprising A1% of the conductive agent by mass, where 30 ≤ A1 ≤ 100. That is, the conductive agent contains a certain proportion of carbon nanotubes. Because carbon nanotubes have a linear contact with the active material, they exhibit extremely high conductivity, thereby enabling rapid charge and discharge, significantly improving electrode conductivity, and enhancing rate performance. Simultaneously, the presence of carbon nanotubes can more effectively mitigate the deterioration of electrode kinetics caused by the presence of a sulfur-containing solid electrolyte interface film on the surface of the positive electrode. Furthermore, the introduction of a certain proportion of carbon nanotubes can reduce the amount of conductive agent used in the positive electrode, increasing the battery's energy density and improving key technical indicators such as battery thermal stability and cycle life.

[0038] In some embodiments, the sulfur-containing additive includes at least one selected from sulfonates, sulfates, and sulfites. These sulfur-containing additives can improve the composition and structure of the interfacial film, enabling it to more effectively exert the aforementioned effects, thereby further improving the cycle performance and storage performance of the secondary battery.

[0039] In some embodiments, the sulfur-containing additive includes at least one of the sulfonates shown in Formula I-1.

[0040]

[0041] In Formula I-1, Q1 and Q2 are independently selected from C1-C6 alkylene groups.

[0042] In some embodiments, Q1 and Q2 are independently selected from C1-C4 alkylene groups, such as methylene or ethylene. In some embodiments, the sulfur-containing additive includes at least one of methylene disulfonate (MMDS) and ethyl disulfonate.

[0043] In some embodiments, the sulfur-containing additive includes at least one of the sulfonates shown in Formula I-2.

[0044]

[0045] In Formula I-2, R1, R2, and R3 are independently selected from hydrogen atoms or C1-C6 alkyl groups, and Q3 is absent or selected from C1-C6 alkylene groups or C2-C6 alkenyl groups.

[0046] In some embodiments, in Formula I-2, R1, R2, and R3 are independently selected from hydrogen atoms or C1-C4 alkyl groups, and Q3 is absent or selected from C1-C4 alkylene groups or C2-C4 alkenyl groups.

[0047] In some embodiments, the sulfur-containing additive includes at least one of 1,3-propanesulfonyl lactone (1,3-PS), 1-propylene-1,3-sulfonyl lactone (PST), and 1,4-butanesulfonyl lactone (1,4-BS).

[0048] In some embodiments, the sulfur-containing additive includes at least one of the sulfate ester compounds represented by Formula II.

[0049]

[0050] In Formula II, R5, R6, R7, and R8 are independently selected from hydrogen atoms or C1-C6 alkyl groups, and Q4 is absent or selected from C1-C6 alkylene groups.

[0051] In some embodiments, in Formula II, R5, R6, R7, and R8 are independently selected from hydrogen atoms or C1-C4 alkyl groups, and Q4 is absent or selected from C1-C4 alkylene groups.

[0052] In some embodiments, in Formula II, R5, R6, R7, and R8 are independently selected from hydrogen atoms, methyl, ethyl, n-propyl, or isopropyl, and Q4 is absent.

[0053] In some embodiments, the sulfur-containing additive includes at least one of vinyl sulfate (DTD), 4-methyl ethylene sulfate (PCS), 4-ethyl ethylene sulfate (PES), 4-propyl ethylene sulfate (PEGLST), and propylene sulfate (TS).

[0054] In some embodiments, the sulfur-containing additive includes at least one of the sulfites represented by formula III-1.

[0055]

[0056] In Equation III-1, R9, R 10 R 11 R 12 It is independently selected from hydrogen atoms or C1-C6 alkyl groups, and Q5 is absent or selected from C1-C6 alkylene groups.

[0057] In some implementations, in formula III-1, R9, R 10 R 11 R 12 Q5 is independently selected from hydrogen atoms or C1-C4 alkyl groups, and Q5 is absent or selected from C1-C4 alkylene groups.

[0058] In some embodiments, the sulfur-containing additive is ethylene sulfite (DTO).

[0059] In some embodiments, the sulfur-containing additive includes at least one of the sulfites shown in Formula III-2.

[0060]

[0061] In Equation III-2, R 13 and R 14 It is independently selected from C1-C6 alkyl groups.

[0062] In some implementations, in formula III-2, R 13 and R 14 The sulfur-containing additive is independently selected from C1-C4 alkyl groups. In some embodiments, the sulfur-containing additive includes at least one of dimethyl sulfite (DMS) and diethyl sulfite (DES).

[0063] In some embodiments, the content of the sulfur-containing additive is 0.01-2g per 100g of positive electrode active material. In some embodiments, the mass content of the sulfur-containing additive is 0.01g, 0.1g, 0.5g, 1g, 1.2g, 1.5g, 1.8g, 2.0g, or any value between these values, per 100g of positive electrode active material. In some embodiments, the mass content of the sulfur-containing additive is 0.1-1.8g per 100g of positive electrode active material.

[0064] In some embodiments, the electrolyte further includes at least one of cyclic carbonates containing carbon-carbon double bonds, silyl-containing phosphates, silyl-containing borates, nitrile compounds, and pyridinium propanesulfonate. In some embodiments, the other additives are selected from at least one of vinylene carbonate (VC), ethylene ethylene carbonate, tris(trimethylsilane) phosphate, tris(trimethylsilane) borate, succinic anionyl, adiponitrile, glutaronitrile, and hexanetrionitrile.

[0065] In some embodiments, the mass content of the other additives is 0.05%-10% based on the mass of the electrolyte. In some embodiments, the mass content of the other additives is 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 6%, 7%, 8%, 9%, 10%, or any value between them. In some embodiments, the mass content of the other additives is 0.1%-5%.

[0066] In some embodiments, the electrolyte further includes an electrolyte lithium salt selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluorosulfonyl (LiTf), lithium bis(fluorosulfonyl)imide (LiFSI), lithium (trifluoromethanesulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonic acid)imide (LiBETI), lithium bis(oxalate borate)borate (LiBOB), lithium bis(fluoromalonic acid)borate (LiBFMB), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium) (LiTDI), and lithium difluorooxalate borate (LiDFOB).

[0067] In some embodiments, the electrolyte further includes a solvent. In some embodiments, the solvent includes at least one selected from chain carbonates, cyclic carbonates, and carboxylic acid esters.

[0068] In some embodiments, the chain carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and fluorinated chain carbonates. In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, and butenyl carbonate. In some embodiments, the carboxylic acid ester is selected from at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, and fluorinated carboxylic acid esters.

[0069] In some embodiments, the positive electrode active material includes at least one selected from lithium nickel oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium nickel manganese cobalt magnesium oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate. In some embodiments, the nickel-cobalt ternary material includes at least one selected from NCA, NCM111, NCM523, NCM622, NCM811, Ni90, Ni92, or Ni95.

[0070] In some embodiments, the positive electrode active material layer further includes a binder. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material and the current collector.

[0071] In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0072] In some embodiments, the positive electrode sheet further includes a positive current collector, which can be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0073] In some embodiments, the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, or a mixture of a silicon-based material and at least one material selected from carbon-based materials, tin-based materials, phosphorus-based materials, and lithium metal.

[0074] In some embodiments, the silicon-based material includes at least one selected from silicon, silicon alloys, silicon oxides, and silicon carbide compounds. In some embodiments, the carbon-based material includes at least one selected from graphite, soft carbon, hard carbon, carbon nanotubes, and graphene. In some embodiments, the tin-based material includes at least one selected from tin, tin oxides, and tin alloys. In some embodiments, the phosphorus-based material includes phosphorus and / or phosphorus complexes.

[0075] In some embodiments, the mass content (g%) of the silicon-based material satisfies the following condition: 10 ≤ g ≤ 100, based on the mass of the negative electrode active material. In some embodiments, g is 11, 13, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or any value between them.

[0076] In some embodiments, the negative electrode active material layer further includes a binder and a conductive agent. In some embodiments, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc.

[0077] In some embodiments, the conductive agent includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0078] In some embodiments, the negative electrode further includes a negative electrode current collector, which includes: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or any combination thereof.

[0079] In some embodiments, a separator is provided between the positive and negative electrodes to prevent short circuits. The material and shape of the separator used in the embodiments of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0080] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0081] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0082] The inorganic layer comprises inorganic particles and a binder. The inorganic particles include at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder includes at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0083] The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0084] In some embodiments, the method for preparing the secondary battery includes providing electrode assemblies, liquid injection, encapsulation, and formation. In some embodiments, the formation temperature is between 25°C and 50°C, for example, 25°C, 28°C, 30°C, 35°C, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C, or 49°C.

[0085] In some embodiments, the formation includes: charging to 4.25V at different current densities under conditions of a temperature of 40°C-50°C (e.g., 45°C) and a pressure of 150 kgf-250 kgf (e.g., 210 kgf), followed by discharging to 2.5V at the same current density. The current densities are from 0.01C to 1C, for example, 0.05C, 0.1C, 0.2C, 0.33C, and 0.5C.

[0086] In some embodiments, the secondary battery is a lithium secondary battery or a sodium secondary battery. In some embodiments, the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery.

[0087] In some embodiments, the secondary battery may include an outer packaging, which may be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging may also be a soft pack, such as a pouch. The soft pack may be made of plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0088] In some embodiments, the shape of the secondary battery is not particularly limited; it can be cylindrical, square, or any other arbitrary shape.

[0089] In some embodiments, this application also provides a battery module. This battery module includes the aforementioned secondary battery. The battery module of this application uses the aforementioned secondary battery, and therefore has at least the same advantages as the aforementioned secondary battery. The battery module of this application can contain multiple secondary batteries, and the specific number can be adjusted according to the application and capacity of the battery module.

[0090] In some embodiments, this application also provides a battery pack that includes the aforementioned battery modules. The number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0091] II. Apparatus

[0092] This application also provides an apparatus comprising at least one of the above-described secondary batteries, battery modules, or battery packs.

[0093] In some embodiments, the device includes, but is not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems. To meet the device's requirements for high power and high energy density in secondary batteries, battery packs or battery modules may be used.

[0094] In other embodiments, the device may be a mobile phone, tablet computer, laptop computer, etc. This device typically requires a slim and lightweight design and may use a rechargeable battery as its power source.

[0095] Examples and Comparative Examples

[0096] Example 1

[0097] The preparation steps for the positive electrode, negative electrode, electrolyte, separator, and battery are described below. The positive electrode active material is LiNi. 0.6 Co 0.2 Mn 0.2 O2; the negative electrode active material is a composite material of artificial graphite and silicon oxide (silicon oxide / graphite = 10 / 90), and the coating density is determined according to the battery size, capacity design, and the capacity of the positive and negative electrode materials. The positive electrode preparation steps are: [The text abruptly ends here, likely due to an incomplete sentence or missing information.] 0.6 Co 0.2 Mn 0.2 O2, conductive agent carbon nanotubes / acetylene black, binder polyvinylidene fluoride (PVDF), and LiNi by weight ratio 0.6 Co 0.2 Mn 0.2 After being thoroughly homogenized in an N-methylpyrrolidone (NMP) solvent system, O2:CNT / Super-P:PVDF = 96:1 / 1:2 was coated onto a 12μm thick aluminum-coated current collector, dried, and rolled to obtain the positive electrode sheet.

[0098] The steps for preparing the negative electrode sheet are as follows: Silicon-oxygen (SiO2) is used as the negative electrode active material. x A mixture of graphite composite (0.5≤x≤1.5), conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMCNa), and polyacrylic acid (PAA) in a weight ratio of 96:1:1.5:1:0.5 was thoroughly homogenized in deionized water and then coated onto the surface of an 8μm thick copper current collector. After drying, rolling, and slitting, the negative electrode sheet was obtained.

[0099] The diaphragm is a three-layer composite PP / PE / PP membrane.

[0100] Electrolyte preparation: In a glove box filled with argon (H2O < 0.1 ppm, O2 < 0.1 ppm), lithium salt LiPF6 and solvent EC:EMC:DEC = 3:5:2 were mixed evenly in a certain ratio to prepare a 1M solution. Finally, sulfur-containing compound additives from Table 1 were added and stirred evenly to obtain the lithium-ion battery electrolyte of Example 1.

[0101] Lithium-ion battery fabrication: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets, and then wound to obtain a bare cell; the bare cell is placed in an aluminum-plastic film outer packaging, and the prepared lithium-ion power battery electrolyte is injected into a fully dried silicon-artificial graphite / LiNi alloy. 0.6 Co 0.2 Mn 0.2 In O2 batteries, the batteries undergo formation according to the formation steps shown in Table 1, followed by aging and capacity testing, finally yielding a soft-pack battery with a rated capacity of approximately 4Ah.

[0102] Examples 2 to 16 and Comparative Examples 1 to 7

[0103] Examples 2 to 16 and Comparative Examples 1 to 7 were based on Example 1 and were achieved by adjusting the type and content of additives in the electrolyte, the type and content of conductive agents in the positive electrode active material layer, the proportion of CNTs, the formation conditions, and the porosity of the positive and negative electrode sheets (wherein the porosity was achieved by adjusting factors such as the positive electrode roll pressing line load, roll gap size, rolling load, and roll pressing speed during the preparation process). Specific adjustment measures and detailed data are shown in Table 1.

[0104] Table 1

[0105]

[0106]

[0107] Test methods

[0108] 1. Electrode porosity determination

[0109] Porosity was determined using a mercury porosimeter. Specifically, the dried electrode sample was cut into thin strips of a certain size. The apparent volume of the electrode coating was measured using a micrometer. Apparent volume = coating thickness * sample length * sample width. The electrode was then degassed under vacuum and wound into a sample cell, ensuring the sample volume was 40-70% of the effective volume of the sample tube to guarantee measurement accuracy. The pore volume of the sample, i.e., the volume of mercury injected into the sample, was then measured using a mercury porosimeter. Porosity = pore volume / apparent volume.

[0110] 2. Capacity

[0111] After formation and aging, the battery cell is charged to 4.2V at a constant current and constant voltage of 0.33C, and then discharged to 2.5V at a constant current of 0.33C. This 0.33C charge and discharge cycle is repeated 3 times, and the discharge capacity of the third cycle is recorded, which is the cell's capacity.

[0112] 3. XPS Test

[0113] The lithium-ion battery was discharged to 2.5V at 0.1C, and the electrode sheets were obtained by disassembling the lithium-ion battery in an argon-filled glove box. The obtained electrode sheets were cut into 8mm × 8mm test samples, and then immersed and cleaned in low-boiling-point dimethyl carbonate (DMC) solvent for half an hour. After being completely dried, they were pasted onto the XPS sample stage with the surface of the positive electrode active material layer facing upwards, and measurements were performed without exposure to the atmosphere. The specific test conditions and procedures are as follows:

[0114] Single-crystal AlKα spectroscopy was used. For X-ray points, elliptical shapes of 1000×1750μm with outputs of 10kV and 22mA were used. Data was selected at a sputtering etching time of 0 seconds. For neutral carbon C1s, 284.8eV was used. For data processing, such as peak differentiation, three-point smoothing, peak area measurement, background subtraction, and peak synthesis were used to calculate the mass percentage of each component.

[0115] 4. First-time effectiveness test

[0116] The battery cells, after being de-capacitated, are discharged to 2.5V at a constant current of 1C under conditions of 25℃, and then charged to 2.5V under a constant current and constant voltage of 0.5C.

[0117] At 4.2V, record the charging capacity Q1. Then, discharge to 2.5V under 1C constant current conditions and record the discharge capacity Q2. First efficiency: Discharge capacity Q2 / Charge capacity Q1 × 100%.

[0118] 5. Cyclic capacity retention test

[0119] At 45°C, the above lithium-ion battery was charged to 4.2V under 1C constant current and constant voltage conditions, and then discharged to 2.5V under 1C constant current conditions. After 400 charge-discharge cycles, the capacity retention rate after the 400th cycle at 45°C was calculated using the following formula: Discharge capacity after the 400th cycle / Discharge capacity of the first cycle × 100%.

[0120] Thickness change rate at 6.60℃

[0121] The battery was discharged to 2.5V at 0.5C at 25℃, then charged to 4.2V at 0.5C, and finally charged at a constant voltage of 0.05C at 4.2V. The thickness of the battery at this point was measured using a PPG soft-pack battery thickness gauge and recorded as 'a'. The battery was then placed in an oven and stored at a constant voltage of 4.2V at 60℃ for 30 days. The thickness after 30 days was recorded as 'b'. The formula for calculating the thickness expansion rate is: (ba) / a × 100%.

[0122] Test Results

[0123] Table 2

[0124]

[0125]

[0126] While some exemplary embodiments of this application have been described and illustrated, this application is not limited to the disclosed embodiments. Rather, those skilled in the art will recognize that modifications and changes may be made to the described embodiments without departing from the spirit and scope of this application as described in the appended claims.

Claims

1. A secondary battery, comprising: Positive electrode, negative electrode, and electrolyte; The electrolyte includes sulfur-containing additives. The positive electrode sheet includes a positive active material layer, which includes a conductive agent. Based on the mass of the positive active material layer, the content of the conductive agent is A%. The positive electrode also includes a solid electrolyte interface film located on the surface of the positive electrode active material layer. The negative electrode sheet includes a negative electrode active material layer and a solid electrolyte interface film located on the surface of the negative electrode active material layer. Using X-ray photoelectron spectroscopy at a sputtering etching time of 0 seconds, the mass percentage of sulfur in the negative electrode solid electrolyte interface film was determined to be Y1%, and the mass percentage of sulfur in the positive electrode solid electrolyte interface film was determined to be Y2%. Among them, 2.0≤Y1+3*Y2 / A≤8.5, 0.6<Y1<6.0, 0.4<Y2<2.2, 0.5<A<4.5; The sulfur-containing additives include at least one of sulfonates, sulfates, and sulfites; The formation temperature of the secondary battery is 25℃-50℃, and the formation current is 0.01C-1C.

2. The secondary battery according to claim 1, characterized in that, 3≤Y1+3*Y2 / A≤6.

3. The secondary battery according to claim 1 or 2, characterized in that, Y1, Y2, and A meet at least one of the following conditions: (a) 1.0 ≤ Y1 ≤ 4.0, (b) 0.5 ≤ Y² ≤ 1.8 (c) 1.0≤A≤3.

0.

4. The secondary battery according to claim 1 or 2, characterized in that, The conductive agent includes at least one of carbon nanotubes, acetylene black, graphene, Ketjen black, conductive fibers, and conductive polymers.

5. The secondary battery according to claim 1 or 2, characterized in that, The conductive agent includes carbon nanotubes, and the mass percentage of the carbon nanotubes in the conductive agent is A1%, where 30≤A1≤100.

6. The secondary battery according to claim 1 or 2, characterized in that, The porosity of the positive electrode is Z1%, and the porosity of the negative electrode is Z2%, wherein 30≤Z1≤45, and / or 20≤Z2≤40.

7. The secondary battery according to claim 1 or 2, characterized in that, The content of the sulfur-containing additive is 0.01-2g per 100g of positive electrode active material.

8. The secondary battery according to claim 7, characterized in that, The content of the sulfur-containing additive is 0.1-1.8g per 100g of positive electrode active material.

9. The secondary battery according to claim 8, characterized in that, The sulfur-containing additive satisfies at least one of the following conditions (i) to (iii): (i) The sulfonate comprises at least one of the compounds shown in Formula I-1 and Formula I-2, Equation I-1, Formula I-2 In Formula I-1, Q1 and Q2 are independently selected from C1-C6 alkylene groups; in Formula I-2, R1, R2, and R3 are independently selected from hydrogen atoms or C1-C6 alkyl groups; Q3 is absent or Q3 is selected from C1-C6 alkylene groups or C2-C6 alkenyl groups. (ii) The sulfate ester includes at least one of the compounds represented by Formula II, Formula II In Formula II, R5, R6, R7, and R8 are independently selected from hydrogen atoms or C1-C6 alkyl groups, and Q4 is absent or selected from C1-C6 alkylene groups; (iii) The sulfite comprises at least one of the compounds shown in Formula III-1 and Formula III-2. Formula III-1, Formula III-2 In Equation III-1, R9, R 10 R 11 R 12 Independently selected from hydrogen atoms or C1-C6 alkyl groups, Q5 is absent or Q5 is selected from C1-C6 alkylene groups, in formula III-2, R 13 and R 14 It is independently selected from C1-C6 alkyl groups.

10. The secondary battery according to claim 8, characterized in that, The sulfur-containing additive satisfies at least one of the following conditions (iv) to (vi): (iv) The sulfonate comprises at least one of methylene disulfonate, ethyl disulfonate, propylene disulfonate, 1,3-propane sulpholactone, 1-propene-1,3-sulfonate lactone and 1,4-butane sulpholactone. (v) The sulfate ester includes at least one of vinyl sulfate, 4-methylethylene sulfate, 4-ethylethylene sulfate, 4-propylethylene sulfate and propylene sulfate; (vi) The sulfite includes at least one of ethyl sulfite, dimethyl sulfite and diethyl sulfite.

11. The secondary battery according to claim 1 or 2, characterized in that, The positive electrode active material layer includes a positive electrode active material, which includes at least one of lithium nickel oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, lithium nickel manganese cobalt magnesium oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium iron phosphate, and lithium manganese iron phosphate; and / or The negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, or a mixture of a silicon-based material and at least one material selected from carbon-based materials, tin-based materials, phosphorus-based materials, and lithium metal, and based on the mass of the negative electrode active material, the mass content of the silicon-based material in g% satisfies: 10 ≤ g ≤ 100.

12. An apparatus comprising a secondary battery according to any one of claims 1-11.

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