Secondary battery and device

Abstract

A secondary battery and a device. The secondary battery comprises a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte comprises a sulfur-containing additive and a phosphorus-containing additive; and the negative electrode comprises a negative electrode active material layer and a solid electrolyte interface film located on the surface of the negative electrode active material layer. An X-ray photoelectron spectrometer is used for testing, the atomic percentage content of sulfur in the solid electrolyte interface film is S%, and the atomic percentage content of phosphorus is P%, where 2.5≤2S+P / 5≤10. According to the secondary battery, by controlling the content of sulfur atoms and phosphorus atoms in the solid electrolyte interface film formed on the surface of the negative electrode active material layer, the cycling performance, the storage performance and the safety performance of the secondary battery at high temperatures are improved while giving consideration to the low impedance thereof.

Description

Secondary batteries and devices

[0001] This application claims priority to Chinese patent application No. 202310687392.2, filed on June 12, 2023, with the invention name “Secondary Batteries and Devices”. The entire contents of the above Chinese patent application are incorporated into this application by reference. Technical Field

[0002] The present application relates to the field of energy storage, and in particular to a secondary battery and a device. Background Art

[0003] Lithium-ion batteries are widely used in our daily lives and high-tech fields. To meet people's needs, lithium-ion batteries must be developed towards higher energy density, greater safety, and longer lifespans. However, during the battery cycle, side reactions between the positive and negative electrodes and the electrolyte can easily occur. This can lead to a decrease in battery capacity and a significant reduction in cycle life, while also causing gas generation and battery volume expansion, thereby reducing battery safety.

[0004] Summary of the Invention

[0005] To address the current challenges of lithium-ion batteries, this application provides a secondary battery and related devices. By controlling the phosphorus and sulfur content of the solid electrolyte interface (SEI) film formed on the surface of the negative electrode active material layer, the secondary battery improves its high-temperature cycling performance, storage performance, and safety while maintaining low impedance.

[0006] A first aspect of the present application provides a secondary battery comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte comprises a sulfur-containing additive and a phosphorus-containing additive; the negative electrode comprises a negative electrode active material layer and a solid electrolyte interface film located on the surface of the negative electrode active material layer, and tested using an X-ray photoelectron spectrometer, the atomic percentage of sulfur in the solid electrolyte interface film is S%, and the atomic percentage of phosphorus is P%, wherein 2.5≤2S+P / 5≤10.

[0007] A second aspect of the present application provides a device, comprising the secondary battery according to the first aspect.

[0008] The beneficial effects of this application are:

[0009] The secondary battery of the present application controls the content of sulfur atoms and phosphorus atoms in the solid electrolyte interface film SEI formed on the surface of the negative electrode active material layer, making the SEI film denser and more stable, which can effectively slow down the erosion of the electrolyte on the electrode material, improve the interfacial lithium ion transmission capacity, reduce the interfacial impedance, and thus reduce the impedance of the secondary battery. At the same time, the SEI film with a specific content of sulfur atoms and phosphorus atoms can improve the cycle performance and safety performance of the lithium-ion secondary battery, especially the cycle performance and storage performance at high temperatures. DETAILED DESCRIPTION

[0010] For the sake of clarity, this application only specifically discloses certain numerical ranges. However, any lower limit may be combined with any upper limit to form an unspecified range; and any lower limit may be combined with other lower limits to form an unspecified range, and similarly, any upper limit may be combined with any other upper limit to form an unspecified range. In addition, each individually disclosed point or single value may itself serve as a lower limit or upper limit and be combined with any other point or single value, or with other lower limits or upper limits, to form an unspecified range.

[0011] Unless otherwise specified, the terms used in this application have the commonly understood meanings commonly understood by those skilled in the art. Unless otherwise specified, the numerical values ​​of the various parameters mentioned in this application can be measured using various measurement methods commonly used in the art (for example, they can be tested according to the methods given in the examples of this application).

[0012] A list of items connected by the term "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, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, 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 can contain a single component or multiple components. Item B can contain a single component or multiple components. Item C can contain a single component or multiple components.

[0013] The present application will be further described below in conjunction with specific embodiments. It should be understood that these specific embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0014] Primary and secondary batteries

[0015] The secondary battery provided in the present application includes a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte includes a sulfur-containing additive and a phosphorus-containing additive; the negative electrode includes a negative electrode active material layer and a solid electrolyte interface film located on the surface of the negative electrode active material layer. X-ray photoelectron spectrometer is used for testing. The atomic percentage of sulfur in the solid electrolyte interface film is S%, and the atomic percentage of phosphorus is P%, wherein 2.5≤2S+P / 5≤10. The sulfur atoms from the sulfur-containing additives in the negative electrode solid electrolyte interface film SEI (such as sulfur atoms in Li2S, Li2SO3, alkylsulfinic acid lithium salt RSO2Li, etc.) can improve the high-temperature stability of the SEI film, thereby improving the high-temperature storage performance and high-temperature cycle performance of the negative electrode. However, since sulfur is a poor conductor of lithium ions and electrons, when its content is high, it will affect the increase of battery impedance, increase battery polarization, and accelerate the attenuation of battery capacity during the cycle. The phosphorus atoms from the phosphorus-containing additives in the SEI (such as LiP x F y 、Li x PO y F z Phosphorus atoms in the electrolyte (such as phosphorus atoms in the electrolyte) can improve the conductivity of lithium ions and electrons, reduce interfacial impedance, and thus reduce the impedance of secondary batteries, but the high-temperature performance of phosphorus-containing additives is poor.

[0016] In this application, the atomic percentage of sulfur refers to the molar percentage of sulfur atoms in the solid electrolyte membrane to all atoms excluding hydrogen atoms. The atomic percentage of phosphorus refers to the molar percentage of phosphorus atoms in the solid electrolyte membrane to all atoms excluding hydrogen atoms.

[0017] In some embodiments, 2S+P / 5 is 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8, 7, 7.2, 7.5, 7.8, 8, 8.2, 8.5, 8.8, 9, 9.2, 9.5, 9.8, 10 or a range consisting of any two of these values. In some embodiments, 3≤2S+P / 5≤10. When 2S+P / 5 is too high, the sulfur and phosphorus content in the SEI film is large, which increases the active sites on the negative electrode surface, consumes more lithium, and cannot suppress the continuous decomposition of the electrolyte, thereby affecting the cycle performance of the battery. When 2S+P / 5 is too low, there are too few active sites on the negative electrode surface, resulting in poor electrode interface kinetics and increased polarization, which in turn affects the cycle performance of the battery.

[0018] In some embodiments, 0.1≤S≤8. In some embodiments, S is 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8, 7, 7.2, 7.5, 7.8, 8, or a range consisting of any two of these values. In some embodiments, 0.5≤S≤5. In other embodiments, 1≤S≤4.

[0019] In some embodiments, 0.1≤P≤15. In some embodiments, P is 0.2, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 5, 5.2, 5.5, 5.8, 6, 6.2, 6.5, 6.8, 7, 7.2, 7.5, 7.8, 8, 8.2, 8.5, 8.8, 9, 9.2, 9.5, 9.8, 10, 10.2, 10.5, 10.8, 11, 11.2, 11.5, 11.8, 12, 12.2, 12.5, 12.8, 13, 13.2, 13.5, 13.8, 14, 14.2, 14.5, 14.8, 15, or a range consisting of any two of these values. In some embodiments, 0.5≤P≤10. In other embodiments, 2≤P≤10.

[0020] In some embodiments, the phosphorus-containing additive includes at least one selected from lithium phosphate salts. The phosphorus-containing additive can improve the composition and structure of the interface film, reduce the interfacial impedance, and more effectively exert the above effects, thereby further improving the cycle performance and storage performance of the secondary battery.

[0021] In some embodiments, the phosphorus-containing additive includes at least one selected from lithium difluorobis(oxalatophosphate) (LiDFOP), lithium tetrafluorobis(oxalatophosphate) (LiTFOP), lithium trioxalatophosphate (LiTOP), and lithium difluorophosphate (LiDFP). In other embodiments, the phosphorus-containing additive includes lithium difluorobis(oxalatophosphate) and / or lithium difluorophosphate.

[0022] In some embodiments, the sulfur-containing additive comprises at least one selected from sulfonates, sulfates, and sulfites. The sulfur-containing additive can improve the composition and structure of the interface film, allowing it to more effectively exert the above-mentioned effects, thereby further improving the cycle performance and storage performance of the secondary battery.

[0023] In some embodiments, the sulfonate comprises at least one compound of Formula I-1,

[0024] In formula I-1, Q1 and Q2 are independently selected from C1-C6 alkylene groups.

[0025] In some embodiments, Q1 and Q2 are independently selected from C1-C4 alkylene, such as methylene, ethylene or propylene. In some embodiments, the sulfonate comprises at least one of methylene methyl disulfonate (MMDS), ethylene ethyl disulfonate and propylene methyl disulfonate.

[0026] In some embodiments, the sulfonate comprises at least one of the compounds shown in Formula I-2,

[0027] In formula I-2, R1 and R2 are independently selected from a hydrogen atom or a C1-C6 alkyl group, and Q3 is selected from a C1-C6 alkylene group and a C2-C6 alkenylene group.

[0028] In some embodiments, in formula I-2, R1 and R2 are independently selected from a hydrogen atom or a C1-C4 alkyl group, and Q3 is selected from a C1-C4 alkylene group and a C2-C4 alkenylene group.

[0029] In some embodiments, the sulfonate ester includes at least one of 1,3-propane sultone (PS), 1-propylene-1,3-sultone (PST), and 1,4-butane sultone (BS).

[0030] In some embodiments, the sulfate ester comprises at least one of the compounds shown in Formula I-3,

[0031] In formula I-3, R3, R4, R5, and R6 are independently selected from a hydrogen atom or a C1-C6 alkyl group, and Q4 is absent or selected from a C1-C6 alkylene group.

[0032] In some embodiments, in formula I-3, R3, R4, R5, and R6 are independently selected from a hydrogen atom or a C1-C4 alkyl group, and Q4 is absent or selected from a C1-C4 alkylene group.

[0033] In some embodiments, in formula I-3, R3, R4, R5, and R6 are independently selected from hydrogen atom, methyl, ethyl, n-propyl, or isopropyl, and Q4 is absent.

[0034] In some embodiments, the sulfate ester includes at least one of diethyl sulfate (DTD), 4-methylethylene sulfate (PCS), 4-ethylethylene sulfate (PES), 4-propylethylene sulfate (PEGLST), and propylene sulfate (TS).

[0035] In some embodiments, the sulfite comprises at least one of the compounds shown in Formula I-4,

[0036] In formula I-4, R7, R8, R9, R 10 Q5 is independently selected from a hydrogen atom or a C1-C6 alkyl group, Q5 is absent or Q5 is selected from a C1-C6 alkylene group.

[0037] In some embodiments, in Formula I-4, R7, R8, R9, R 10 Q5 is independently selected from a hydrogen atom or a C1-C4 alkyl group, Q5 is absent or Q5 is selected from a C1-C4 alkylene group.

[0038] In some embodiments, the sulfite comprises ethylene sulfite (DTO).

[0039] In some embodiments, the sulfite comprises at least one of the compounds shown in Formula I-5,

[0040] In formula I-5, R 11 and R 12 Independently selected from C1-C6 alkyl.

[0041] In some embodiments, in Formula I-5, R 11 and R 12 In some embodiments, the sulfite comprises at least one of dimethyl sulfite (DMS) and diethyl sulfite (DES).

[0042] In some embodiments, the content of the phosphorus-containing additive is 0.01-4.5 g per 100 g of negative electrode active material. In some embodiments, the content of the phosphorus-containing additive is 0.1 g, 0.3 g, 0.5 g, 0.7 g, 0.9 g, 1 g, 1.2 g, 1.4 g, 1.6 g, 1.8 g, 2 g, 2.2 g, 2.4 g, 2.6 g, 2.8 g, 3.2 g, 3.5 g, 3.8 g, 4 g, 4.2 g, 4.5 g, or a range consisting of any two of these values ​​per 100 g of negative electrode active material. In some embodiments, the content of the phosphorus-containing additive is 0.05-4 g per 100 g of negative electrode active material. In some embodiments, the content of the phosphorus-containing additive is 0.1-3 g per 100 g of negative electrode active material.

[0043] In some embodiments, the content of the sulfur-containing additive is 0.1-6 g per 100 g of negative electrode active material. In some embodiments, the content of the sulfur-containing additive is 0.2 g, 0.4 g, 0.6 g, 0.8 g, 1 g, 1.2 g, 1.4 g, 1.6 g, 1.8 g, 2 g, 2.2 g, 2.4 g, 2.6 g, 2.8 g, 3.2 g, 3.5 g, 3.8 g, 4 g, 4.2 g, 4.5 g, 4.8 g, 5 g, 5.2 g, 5.5 g, 5.8 g, 6 g, or a range consisting of any two of these values ​​per 100 g of negative electrode active material. In some embodiments, the content of the sulfur-containing additive is 0.1-5 g per 100 g of negative electrode active material. In some embodiments, the content of the sulfur-containing additive is 0.2-4 g per 100 g of negative electrode active material.

[0044] In some embodiments, the electrolyte further includes other additives, and the other additives include at least one of vinylene carbonate, vinyl ethylene carbonate, tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, fluoroethylene carbonate, difluoroethylene carbonate, trifluoropropylene carbonate, 2,2,2-trifluoromethyl ethyl carbonate, 2,2,2-trifluorodiethyl carbonate, tris(trifluoroethyl) phosphate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0045] In some embodiments, the electrolyte further includes an electrolyte lithium salt, and the lithium salt is selected from at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethylsulfonyl (LiOTf), lithium bis(fluorosulfonyl)imide (LiFSI), lithium (trifluoromethylsulfonyl)(perfluorobutylsulfonyl)imide (LiFNFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonic acid)imide (LiBETI), lithium bis(oxalatoborate) (LiBOB), lithium bis(fluoromalonate)borate (LiBFMB), lithium 4,5-dicyano-2-(trifluoromethyl)imidazolium (LiTDI), and lithium difluorooxalatoborate (LiDFOB).

[0046] In some embodiments, the lithium salt comprises lithium hexafluorophosphate. In some embodiments, the concentration of the lithium hexafluorophosphate is 0.3-1.2 mol / L, wherein the concentration represents the number of moles of lithium hexafluorophosphate contained in a unit volume of the electrolyte.

[0047] In some embodiments, the electrolyte further comprises a solvent. In some embodiments, the solvent comprises at least one of a linear carbonate, a cyclic carbonate, and a carboxylate.

[0048] In some embodiments, the linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methylpropyl carbonate, ethylpropyl carbonate and fluorinated linear carbonate. In some embodiments, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate and butylene carbonate. In some embodiments, the carboxylate is selected from at least one of methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, gamma-butyrolactone and fluorinated carboxylate.

[0049] In some embodiments, the solvent includes linear carbonate and / or cyclic carbonate, and based on the mass of the solvent, the mass content of the linear carbonate and / or cyclic carbonate is more than 90%, for example more than 95%, more than 98%. In some embodiments, the solvent does not include carboxylate. In some embodiments, the solvent does not include ether.

[0050] In some embodiments, the negative electrode includes a negative electrode active material layer, and the negative electrode active material includes a silicon-based material. The silicon-based material includes at least one of silicon, silicon alloys, silicon oxides, and silicon carbon compounds. In some embodiments, the silicon-based material is a silicon oxide and / or a silicon carbon compound. The "silicon oxide" in this application can be a single substance or a mixture, as long as its average chemical formula conforms to SiO x , x=0.5-1.5, that’s it.

[0051] In some embodiments, the negative electrode active material further comprises a mixture of at least one of a carbon-based material, a tin-based material, a phosphorus-based material, and metallic lithium. The carbon-based material comprises at least one of graphite, soft carbon, hard carbon, carbon nanotubes, and graphene. The tin-based material comprises at least one of tin, tin oxide, and a tin alloy. The phosphorus-based material comprises phosphorus and / or a phosphorus complex.

[0052] In some embodiments, the mass content (g%) of the silicon-based material, based on the mass of the negative electrode active material, satisfies the following: 10 ≤ g ≤ 100. 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 a range consisting of two of these values. In some embodiments, 10 ≤ g ≤ 50. In other embodiments, 12 ≤ g ≤ 35.

[0053] In some embodiments, the negative electrode active material layer further comprises 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, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon.

[0054] 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, artificial 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.

[0055] In some embodiments, the negative electrode further includes a negative electrode current collector, and the negative electrode current collector 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.

[0056] In some embodiments, the negative electrode has a compaction density of 1.5-1.8 g / cm 3 In some embodiments, the negative electrode has a compacted density of 1.5 g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 , 1.65g / cm 3 , 1.7g / cm 3 , 1.75g / cm 3 , 1.8g / cm 3 In this application, the electrode compaction density can be adjusted according to the characteristics of the selected active material by conventional technical means in the art, such as controlling the electrode rolling pressure, rolling temperature, rolling speed and rolling times.

[0057] In some embodiments, the surface density of the negative electrode is 6-10 mg / cm 2 In some embodiments, the surface density of the negative electrode is 6 mg / cm 2 、6.5mg / cm 2 , 7mg / cm 2 , 7.5mg / cm 2 , 8mg / cm 2 , 8.5mg / cm 2 , 9mg / cm 2, 9.5mg / cm 2 、10mg / cm 2 Or a range consisting of any two of these values. In some embodiments, the surface density of the negative electrode sheet is 7-10 mg / cm 2 In this application, the surface density of the electrode on a single side can be adjusted according to the characteristics of the selected active material by conventional technical means in the art, such as coating knife surface thickness, coating temperature, and coating speed.

[0058] In some embodiments, the positive electrode includes a positive electrode active material layer, and the positive electrode active material includes at least one selected from lithium nickel transition metal oxides. In some embodiments, the chemical formula of the lithium nickel transition metal oxide is as follows: LiNi m Co n A (1-m-n) O2, wherein A is selected from at least one of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver or niobium, 0.5≤m≤1, 0≤n≤0.5, and m+n≤1.

[0059] In some embodiments, m is 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or a range consisting of any two of these values. In some embodiments, n is 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or a range consisting of any two of these values.

[0060] In some embodiments, the lithium nickel transition metal oxide includes at least one of NCA, NCM111, NCM523, NCM622, NCM811, Ni90, Ni92, or Ni95.

[0061] In some embodiments, the positive electrode active material may also include at least one phosphate compound, the chemical formula of which is LiMn k B (1-k) PO4, wherein 0≤k≤1, and the B element is selected from at least one of iron, cobalt, magnesium, calcium, zinc, chromium, or lead. In some embodiments, k is 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, or a range consisting of any two of these values. In some embodiments, the phosphate compound includes lithium iron phosphate, LiMn 0.6 Fe 0.4 PO4 or LiMn 0.8 Fe 0.2 At least one of PO4.

[0062] In some embodiments, the positive electrode active material layer further includes a binder, and optionally a conductive agent. 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.

[0063] 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, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin or nylon, etc.

[0064] 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, artificial 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.

[0065] In some embodiments, the positive electrode further includes a positive electrode 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 prepared by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0066] In some embodiments, a separator is provided between the positive and negative electrodes to prevent short circuits. The material and shape of the separator that can be used in the embodiments of the present application are not particularly limited and can be any material disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material that is stable to the electrolyte of the present application.

[0067] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer includes at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film can be used.

[0068] A surface treatment layer is provided 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 a polymer and an inorganic layer.

[0069] The inorganic layer includes inorganic particles and a binder, wherein the inorganic particles include at least one of aluminum oxide, 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 vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.

[0070] The polymer layer includes a polymer, and the polymer material includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0071] In some embodiments, the preparation method of the secondary battery includes providing an electrode assembly, injecting, packaging and forming. In some embodiments, the temperature of the formation is 40°C to 50°C, for example, 41°C, 42°C, 43°C, 44°C, 45°C, 46°C, 47°C, 48°C or 49°C. In some embodiments, the pressure of the formation is 150kgf to 250kgf, for example, 160kgf, 170kgf, 180kgf, 190kgf, 200kgf, 210kgf, 220kgf, 230kgf or 240kgf. In some embodiments, the charging current of the formation is 0.05C-0.1C, and the discharge current of the formation is 0.1C-0.3C.

[0072] In some embodiments, the formation comprises: charging to 4.2V at 0.05C current and standing for 60 minutes, then charging to 4.2V at 0.1C current, and then discharging to 3.0V at 0.2C current, at a temperature of 40°C-50°C, such as 45°C, and a pressure of 150kgf-250kgf, such as 200kgf.

[0073] 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.

[0074] In some embodiments, the secondary battery may include an outer packaging, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0075] In some embodiments, the shape of the secondary battery is not particularly limited, and it can be cylindrical, square, or any other shape.

[0076] In some embodiments, the present application also provides a battery module. The battery module includes the aforementioned secondary battery. The battery module of the present application utilizes the aforementioned secondary battery and therefore has at least the same advantages as the aforementioned secondary battery. The battery module of the present application may include multiple secondary batteries, the specific number of which can be adjusted based on the application and capacity of the battery module.

[0077] In some embodiments, the present application further provides a battery pack comprising the above-mentioned battery module. The number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0078] 2. Device

[0079] The present application also provides a device comprising at least one of the above-mentioned secondary battery, battery module or battery pack.

[0080] In some embodiments, the device includes, but is not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, power storage systems, etc. To meet the device's requirements for high power and high energy density of secondary batteries, a battery pack or battery module may be used.

[0081] In other embodiments, the device may be a mobile phone, a tablet computer, a laptop computer, etc. The device is usually required to be lightweight and thin, and may use a secondary battery as a power source.

[0082] Example

[0083] Test Method

[0084] 1. Battery impedance test

[0085] Discharge the lithium-ion battery at 1C constant current to 2.5V at 25±2°C, then charge it to 4.25V at 0.5C constant current. Charge it to 0.05C at 4.25V, then discharge it to 50% SOC at 1C constant current. Let it rest for 60 minutes, and record the voltage U1 after the rest. Discharge it at 2C constant current for 10 seconds, and record the voltage U2 after the discharge. The 2C current is recorded as I, and let it rest for 60 minutes. Calculate the battery's discharge DCR at 50% SOC using the formula DCR = (U1-U2) / I.

[0086] 2. Battery high temperature cycle performance test

[0087] At 45°C, the lithium-ion battery was charged at a constant current of 0.5C to 4.25V, then charged at a constant voltage of 0.05C at 4.25V, and then discharged at a constant current of 1C to 2.5V. After 400 charge and discharge cycles, the capacity retention after the 400th cycle at 45°C was calculated according to the following formula: discharge capacity after the 400th cycle / discharge capacity in the first cycle × 100%.

[0088] 3. Battery thickness change rate test at 60℃ storage

[0089] A lithium-ion battery was discharged at a constant current of 1C to 2.5V at 25°C, then charged at a constant current of 0.5C to 4.25V. Then, it was charged at a constant voltage of 0.05C at 4.25V. 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 placed in an oven at 60°C and stored at a constant voltage of 4.25V for 30 days. The thickness after 30 days was recorded as b. The thickness expansion ratio was calculated as (b a) / a × 100%.

[0090] 4. Test of atomic percentage of sulfur and phosphorus in SEI film

[0091] The lithium-ion battery was discharged at a current of 0.1C to 2.5V. The battery was then disassembled in an argon-filled glove box to obtain the electrode sheets. The resulting negative electrode sheets were cut into 8mm x 8mm test samples and soaked and cleaned in a low-boiling-point dimethyl carbonate (DMC) solvent for half an hour. After complete drying, they were attached to the XPS sample stage with the surface of the negative electrode active material layer facing away from the current collector facing upward. Measurements were performed without exposure to the atmosphere. The specific test conditions and steps are as follows:

[0092] Single crystal spectroscopy AlKα radiation was used, and as the X-ray spot, an elliptical form of 1000×1750 μm with an output of 10 KV and 22 mA was used, data when the sputter etching time was 0 seconds was selected, 284.8 eV was used for neutral carbon C1s, and as for data processing such as peak differentiation, 3-point smoothing, peak area measurement, background subtraction, and peak synthesis were used to calculate the atomic percentage content of sulfur and phosphorus.

[0093] Example 1

[0094] The positive electrode preparation steps are: LiNi 0.9 Co 0.05 Mn 0.05 O2, conductive agent carbon nanotube / acetylene black, binder polyvinylidene fluoride PVDF, by weight proportion LiNi 0.9 Co 0.05 Mn 0.05O2﹕CNT / Super-P﹕PVDF=95﹕2.0 / 1.0﹕2 was fully homogenized in N-methylpyrrolidone NMP solvent system, coated on a 12μm thick aluminum-coated current collector, dried and roll-pressed to obtain a positive electrode sheet.

[0095] The negative electrode preparation steps are: the negative electrode active material silicon oxide (SiO x , 0.5≤x≤1.5)-graphite composite (the mass ratio of silicon oxide to graphite in the composite is 14:86), conductive agent acetylene black, binder styrene-butadiene rubber SBR, thickener sodium carboxymethyl cellulose CMCNa, and polyacrylic acid PAA are fully homogenized in deionized water in a weight ratio of 96:2:1.5:1:0.5, and then coated on the surface of an 8μm thick copper current collector. After drying, rolling, and slitting, the negative electrode sheet is obtained.

[0096] Diaphragm: PP / PE / PP three-layer composite diaphragm.

[0097] Preparation of the electrolyte: In an argon-filled glove box (H2O <0.1ppm, O2 <0.1ppm), the lithium salt LiPF6 and the solvent EC / DEC / EMC = 25 / 20 / 55 were mixed uniformly in a certain proportion to form a 1M solution. Finally, the sulfur-containing additive (0.435gDTD relative to 100g negative electrode active material) and the phosphorus-containing additive (0.435gLiDFP relative to 100g negative electrode active material) in the amount shown in Table 1 were added according to the mass of the negative electrode active material. After stirring, the lithium ion battery electrolyte of Example 1 was obtained.

[0098] Preparation of lithium-ion batteries: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator located between the positive and negative electrode sheets, and then wound to obtain a bare battery cell; the bare battery cell is placed in an aluminum-plastic film outer packaging, and after being fully dried, the prepared lithium-ion battery electrolyte is injected. The battery is left at 45°C for 48 hours, formed in a high-temperature fixture (formation conditions are: temperature 45°C, pressure 210kgf, 0.05C current charging to 4.2V and standing for 60 minutes, then 0.1C charging to 4.2V, and then 0.2C discharge to 3.0V, and this is repeated twice) and secondary sealing, and then conventional capacity division is carried out to finally obtain a lithium-ion battery with a rated capacity of ~4Ah.

[0099] Examples 2 to 16 and Comparative Examples 1 to 8

[0100] Examples 2 to 16 and Comparative Examples 1 to 8 are achieved on the basis of Example 1 by adjusting the type and content of additives in the electrolyte, the compaction density and single-sided surface density of the negative electrode sheet (wherein the compaction density of the negative electrode sheet is adjusted by controlling the negative electrode roller pressing pressure, and the single-sided surface density of the negative electrode sheet is adjusted by controlling the coating knife surface thickness). Specific adjustment measures and detailed data are shown in Table 1.

[0101] Example 17

[0102] Example 17 is based on Example 6, except that the lithium salt is adjusted by replacing the 1M LiPF6 lithium salt with a combined lithium salt of 0.3M LiPF6 and 0.7M LiFSI.

[0103] Table 1

[0104] The battery performance test results of Examples 1-17 and Comparative Examples 1-7 are shown in Table 2.

[0105] Table 2 *: Indicates that the battery capacity retention rate is less than 60% at a certain cycle before 400 cycles.

[0106] Although some exemplary embodiments of the present application have been illustrated and described, the present application is not limited to the disclosed embodiments. On the contrary, those skilled in the art will recognize that some modifications and changes may be made to the described embodiments without departing from the spirit and scope of the present application as described in the appended claims.

Claims

1. A secondary battery comprising a positive electrode, a negative electrode and an electrolyte, in, The electrolyte includes a sulfur-containing additive and a phosphorus-containing additive; The negative electrode 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 an X-ray photoelectron spectrometer to test, the atomic percentage of sulfur in the solid electrolyte interface film is S%, and the atomic percentage of phosphorus is P%, wherein 2.5≤2S+P / 5≤10.

2. The secondary battery according to claim 1, It is characterized in that 0.1≤S≤8, and / or, 0.1≤P≤15.

3. The secondary battery according to claim 1 or 2, It is characterized in that 0.5≤S≤5, and / or, 0.5≤P≤10.

4. The secondary battery according to claim 1 or 2, It is characterized in that The content of the phosphorus-containing additive is 0.01-4.5 g per 100 g of the negative electrode active material.

5. The secondary battery according to claim 1 or 2, It is characterized in that The content of the sulfur-containing additive is 0.1-6 g per 100 g of the negative electrode active material.

6. The secondary battery according to claim 1 or 2, It is characterized in that The compaction density of the negative electrode is 1.5-1.8 g / cm 3 and / or, The single surface density of the negative electrode is 6-10 mg / cm 2 .

7. The secondary battery according to claim 1 or 2, It is characterized in that The phosphorus-containing additive includes at least one selected from lithium phosphate salts, and / or the sulfur-containing additive includes at least one selected from sulfonates, sulfates and sulfites, wherein: The sulfonate ester includes at least one of the compounds represented by Formula I-1 and Formula I-2, In Formula I-1, Q 1 and Q 2 independently selected from C1-C6 alkylene, in Formula I-2, R 1 , R 2 are independently selected from hydrogen atom or C1-C6 alkyl, Q 3 Selected from C1-C6 alkylene, C2-C6 alkenylene; The sulfate ester includes at least one of the compounds shown in formula I-3, In Formula I-3, R 3 , R 4 , R 5 , R 6 are independently selected from hydrogen atom or C1-C6 alkyl, Q 4 Not present or Q 4 Selected from C1-C6 alkylene; The sulfite comprises at least one of the compounds represented by formula I-4 and formula I-5, In Formula I-4, R 7 , R 8 , R 9 , R 10 are independently selected from hydrogen atom or C1-C6 alkyl, Q 5 Not present or Q 5 is selected from C1-C6 alkylene, in formula I-5, R 11 and R 12 Independently selected from C1-C6 alkyl.

8. The secondary battery according to claim 7, It is characterized in that The phosphorus-containing additive comprises at least one selected from lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, lithium trioxalate phosphate and lithium difluorophosphate; and / or, The sulfonate ester includes at least one of methylene disulfonate, ethylene disulfonate, propylene disulfonate, 1,3-propane sultone, 1-propylene-1,3-sultone and 1,4-butane sultone, The sulfate ester includes at least one of vinyl sulfate, 4-methylethylene sulfate, 4-ethylethylene sulfate, 4-propylethylene sulfate and propylene sulfate, The sulfite includes at least one of ethylene sulfite, dimethyl sulfite and diethyl sulfite.

9. The secondary battery according to claim 1 or 2, It is characterized in that The electrolyte includes a lithium salt, the lithium salt includes lithium hexafluorophosphate, and the concentration of the lithium hexafluorophosphate is 0.3-1.2 mol / L; and / or, The electrolyte includes a solvent, and the solvent includes a linear carbonate and / or a cyclic carbonate. Based on the mass of the solvent, the mass content of the linear carbonate and / or the cyclic carbonate is greater than 90%.

10. The secondary battery according to claim 1 or 2, It is characterized in that The negative electrode comprises at least one silicon-based material selected from silicon, silicon alloys, silicon oxide compounds and silicon carbon compounds, and the mass content g% of the silicon-based material satisfies: 10≤g≤100 based on the mass of the negative electrode active material; and / or, The positive electrode comprises an active material selected from lithium nickel transition metal oxides, wherein the chemical formula of the lithium nickel transition metal oxide is LiNi m Co n A (1-m-n) O 2 As shown, wherein A is selected from at least one of manganese, aluminum, magnesium, chromium, calcium, zirconium, molybdenum, silver or niobium, 0.5≤m≤1, 0≤n≤0.5, m+n≤1.

11. A device comprising the secondary battery according to any one of claims 1 to 10.

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