Secondary battery and electric device

Abstract

This application provides a secondary battery and an electrical device. The secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector, and the surface of the positive current collector is provided with a positive active material layer and an inorganic coating. The electrolyte includes additives, including at least one selected from lithium difluorophosphate, succinic anionyl nitrile, adiponitrile, 1,3,6-hexanetrionitrile, and 1,2,3-tris(2-oxyethoxy)propane. The inorganic coating has a unit area mass of Ag / m³. 2 Based on the electrolyte mass, the additive's mass percentage is B%, satisfying: 0.01 ≤ B / A ≤ 5. By selecting the above additives and adjusting B / A within the above range, it is beneficial to improve the high-temperature safety performance of secondary batteries under high voltage.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a secondary battery and power consumption device. Background Technology

[0002] In recent years, rechargeable batteries (such as lithium-ion batteries) have been widely used in smartphones, tablets, smart wearables, power tools and electric vehicles.

[0003] With the widespread application of rechargeable batteries, the market demands increasingly higher energy density and environmental performance requirements. For example, rechargeable batteries are required to maintain good high-temperature safety at high voltages (e.g., 4.7V or higher). Therefore, improving the high-temperature safety performance of rechargeable batteries under high voltage conditions has become an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and an electrical device to improve the high-temperature safety performance of the secondary battery under high voltage.

[0005] The specific technical solution is as follows:

[0006] This application provides a secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector, the surface of which is provided with a positive active material layer and an inorganic coating. The electrolyte includes an additive, which comprises at least one selected from lithium difluorophosphate, succinic anionyl nitrile, adiponitrile, 1,3,6-hexanetrionitrile, and 1,2,3-tris(2-oxyethoxy)propane. The inorganic coating has a unit area mass of Ag / m³. 2 Based on the mass of the electrolyte, the mass percentage of the additive is B%, satisfying: 0.01 ≤ B / A ≤ 5. By adopting the above-mentioned positive electrode structure and by synergistically selecting the above-mentioned electrolyte additives and synergistically controlling B / A within the above range, on the one hand, it is beneficial to reduce the side reactions between the positive electrode and the electrolyte, thereby improving the high-temperature safety performance of the secondary battery. It is also beneficial to improve the film formation quality of the positive electrolyte interphase (CEI) film and the negative electrolyte interphase (SEI) film, improve the wetting performance and flame retardant performance of the electrolyte, thereby improving the thermal stability and overcharge performance of the secondary battery. On the other hand, it is beneficial to improve the protective effect of the inorganic coating on the positive electrode, reduce the risk of short circuit in the secondary battery, and thus improve the high-temperature safety performance of the secondary battery under high voltage.

[0007] In some embodiments of this application, 1≤A≤20, which helps to reduce the risk of short circuit in the secondary battery and can reduce the energy density loss of the secondary battery.

[0008] In some embodiments of this application, 0.01≤B≤10 is beneficial to improving the thermal stability and overcharge performance of the secondary battery, and can reduce the kinetic losses of the secondary battery.

[0009] In some embodiments of this application, the inorganic coating is disposed on at least one surface of the current collector along the length direction of the positive electrode sheet. The length of the inorganic coating is W mm, where 5 ≤ W ≤ 300. When the length of the inorganic coating is W on at least one surface of the current collector, the protection of the positive electrode sheet can be further improved, the risk of short circuit in the secondary battery can be reduced, and the high-temperature safety performance of the secondary battery under high voltage can be improved.

[0010] In some embodiments of this application, the inorganic coating is disposed on two surfaces of the current collector along the length direction of the positive electrode sheet. The length of the inorganic coating on one surface of the current collector is W1, and the length of the inorganic coating on the other surface of the current collector is W2, where 5≤W1≤35 and 30≤W2≤300. The inorganic coating with lengths of W1 and W2 disposed on both sides of the current collector can further enhance the protection of the positive electrode sheet, reduce the risk of short circuit in the secondary battery, and thus improve the high-temperature safety performance of the secondary battery under high voltage.

[0011] In some embodiments of this application, the thickness of the inorganic coating is H μm along the thickness direction of the positive electrode sheet, where 1 ≤ H ≤ 20. This is beneficial for improving the protective effect of the inorganic coating on the positive electrode sheet, thereby improving the high-temperature safety performance of the secondary battery under high voltage.

[0012] In some embodiments of this application, the length of the inorganic coating accounts for 0.1% to 20% of the total length of the positive electrode sheet, which is beneficial to improve the protective effect of the inorganic coating on the positive electrode sheet, reduce the risk of short circuit in the secondary battery, and thus improve the high-temperature safety performance of the secondary battery under high voltage.

[0013] In some embodiments of this application, the inorganic coating comprises an inorganic material and a binder. Based on the mass of the inorganic coating, the inorganic material comprises 70% to 80% by mass, and the binder comprises 20% to 30% by mass. The inorganic material comprises at least one of alumina, magnesium oxide, calcium oxide, magnesium hydroxide, boehmite, or zirconium oxide, and the binder comprises at least one of polyvinylidene fluoride, polypropylene, or polyacrylate. This improves the interfacial adhesion between the inorganic coating and the positive electrode current collector, thereby enhancing the high-temperature safety performance of the secondary battery under high voltage.

[0014] In some embodiments of this application, the Dv99 of the inorganic material is 0.5 μm to 2 μm, which is beneficial to improve the mixing uniformity of the inorganic material and the binder, improve the interfacial adhesion performance between the inorganic coating and the positive electrode current collector, and thus improve the high-temperature safety performance of the secondary battery under high voltage.

[0015] In some embodiments of this application, the secondary battery satisfies at least one of the following conditions:

[0016] (1) Along the length of the positive electrode sheet, the length of the inorganic coating is W mm, 40≤W≤160;

[0017] (2) Along the thickness direction of the positive electrode sheet, the thickness of the inorganic coating is H μm, 3≤H≤14.

[0018] By controlling W and H within the above range, it is beneficial to further improve the protective effect of the inorganic coating on the positive electrode sheet, thereby further improving the high-temperature safety performance of the secondary battery under high voltage.

[0019] In some embodiments of this application, the secondary battery satisfies at least one of the following conditions:

[0020] (1) 2≤A≤14;

[0021] (2) 0.02 ≤ B ≤ 7.5;

[0022] (3) 0.2 ≤ B / A ≤ 3.

[0023] By controlling A, B, and B / A within the above range, it is beneficial to further improve the protective effect of the inorganic coating on the positive electrode sheet, reduce the risk of short circuit in the secondary battery, and also to obtain a more uniform CEI film and SEI film, ensuring the transport of lithium ions in the lithium-ion battery, reducing impedance, and thus further improving the high-temperature safety performance of the secondary battery under high voltage.

[0024] The second aspect of this application provides an electrical device that includes a secondary battery as described in any of the foregoing embodiments. The secondary battery provided by this application has good high-temperature safety performance under high voltage, and the resulting electrical device has good high-temperature safety performance under high voltage.

[0025] This application provides a secondary battery and an electrical device, wherein the surface of the positive current collector of the positive electrode sheet in the secondary battery is provided with a positive electrode active material layer and an inorganic coating; the electrolyte of this application includes additives, which include at least one selected from lithium difluorophosphate, succinic anionyl nitrile, adiponitrile, 1,3,6-hexanetrionitrile, and 1,2,3-tris(2-oxyethoxy)propane; the inorganic coating has a unit area mass of Ag / m³. 2Based on the quality of the electrolyte, the mass percentage of the additive is B%, satisfying: 0.01 ≤ B / A ≤ 5. This application, by adopting the above-mentioned positive electrode structure and systematically selecting the above-mentioned electrolyte additives, and synergistically controlling B / A within the above range, on the one hand, helps to reduce side reactions between the positive electrode and the electrolyte, reduce inorganic spillage, improve the warping deformation of the secondary battery, thereby improving the high-temperature safety performance of the secondary battery. It also helps to improve the film formation quality of the CEI and SEI films, improve the wetting and flame-retardant properties of the electrolyte, reduce the redox decomposition of the electrolyte at the positive and negative electrode interfaces, improve lithium-ion transport, reduce impedance, thereby improving the thermal stability and overcharge performance of the secondary battery. On the other hand, it helps to improve the protective effect of the inorganic coating on the positive electrode, reduce the risk of short circuits in the secondary battery, and thus improve the high-temperature safety performance of the secondary battery under high voltage.

[0026] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0027] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0028] It should be noted that the application uses lithium-ion batteries as an example of secondary batteries to explain this application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0029] The inventors discovered that current lithium-ion batteries are prone to thermal runaway when used in extreme environments such as continuous high temperatures. The reasons may be that the electrolyte is prone to redox decomposition reaction with the positive electrode plate under high temperature and high pressure (for example, temperature above 85°C and voltage above 4.48V), which damages the CEI film on its surface. This causes the impedance of the lithium-ion battery to increase continuously, resulting in local deformation, warping, or short circuit of the lithium-ion battery.

[0030] In view of the above, the first aspect of this application provides a secondary battery, which includes a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode includes a positive current collector, the surface of which is provided with a positive active material layer and an inorganic coating. The electrolyte includes additives, including at least one selected from lithium difluorophosphate, succinic anionyl nitrile, adiponitrile, 1,3,6-hexanetrionitrile, and 1,2,3-tris(2-oxyethoxy)propane. The inorganic coating has a unit area mass of Ag / m³. 2Based on the mass of the electrolyte, the mass percentage of the additive is B%, satisfying: 0.01 ≤ B / A ≤ 5. In one embodiment of this application, 0.2 ≤ B / A ≤ 3. By adopting the above-mentioned positive electrode structure and by synergistically selecting the above-mentioned electrolyte additives and synergistically controlling B / A within the above range, this application, on the one hand, helps to reduce side reactions between the positive electrode and the electrolyte, thereby improving the high-temperature safety performance of the secondary battery, and also helps to improve the film formation quality of the CEI film and SEI film, improve the wetting performance and flame retardant performance of the electrolyte, thereby improving the thermal stability and overcharge performance of the secondary battery; on the other hand, it helps to improve the protective effect of the inorganic coating on the positive electrode, reduce the risk of short circuit in the secondary battery, and thus improve the high-temperature safety performance of the secondary battery under high voltage.

[0031] In some embodiments of this application, 1 ≤ A ≤ 20. In another embodiment of this application, 2 ≤ A ≤ 14. In yet another embodiment of this application, 2 ≤ A ≤ 8. For example, A can be 1 g / m³. 2 3.1g / m 2 5.2g / m 2 7.6g / m 2 10g / m 2 14.5g / m 2 20g / m 2 It can be any value within a range consisting of any two of these values. By adjusting A within the above range, it is beneficial to improve the protective effect of the inorganic coating on the positive electrode, reduce the risk of short circuits in the secondary battery, and reduce the energy density loss of the secondary battery.

[0032] In some embodiments of this application, 0.01 ≤ B ≤ 10. In another embodiment of this application, 0.02 ≤ B ≤ 7.5. In yet another embodiment of this application, 0.02 ≤ B ≤ 6. For example, B can be 0.01, 1.2, 2.4, 3.6, 4.7, 7.3, 8.5, 10, or any two of these values. By adjusting B within the above ranges, it is beneficial to improve the thermal stability and overcharge performance of the secondary battery, and to reduce the kinetic losses of the secondary battery.

[0033] In some embodiments of this application, 100 ≤ C ≤ 500. In another embodiment of this application, 200 ≤ C ≤ 400. For example, C can be 100, 200, 300, 400, 500, or any two of these values. By adjusting C within the above range, it is beneficial to improve the interfacial adhesion between the inorganic coating and the positive electrode current collector, reduce the risk of inorganic powder falling off the surface of the positive electrode current collector, and thus improve the high-temperature safety performance of the secondary battery under high voltage.

[0034] In some embodiments of this application, the length of the inorganic coating accounts for 0.1% to 20% of the total length of the positive electrode sheet. In another embodiment of this application, the length of the inorganic coating accounts for 0.1% to 10% of the total length of the positive electrode sheet. In yet another embodiment of this application, the length of the inorganic coating accounts for 1% to 15% of the total length of the positive electrode sheet. For example, the length of the inorganic coating can account for 0.1%, 1%, 1.5%, 3%, 5%, 7%, 13%, 16%, 20%, or any two of these values. By adjusting the proportion of the length of the inorganic coating to the total length of the positive electrode sheet, it is beneficial to improve the protective effect of the inorganic coating on the positive electrode sheet, reduce the risk of short circuit in the secondary battery, and thus improve the high-temperature safety performance of the secondary battery under high voltage. The length of the inorganic coating can be adjusted according to the overall size of the electrode assembly. When the overall size of the electrode assembly is small, the total length of the positive electrode sheet it contains is short, and the length of the inorganic coating is short. When the overall size of the electrode assembly is large, the length of the positive electrode sheet it contains is long, and the length of the inorganic coating is long.

[0035] In some embodiments of this application, the inorganic coating is disposed on at least one surface of the current collector along the length direction of the positive electrode sheet, and the length of the inorganic coating is W mm, where 5 ≤ W ≤ 300. In some embodiments of this application, 5 ≤ W ≤ 160. In some embodiments of this application, 40 ≤ W ≤ 160. In some embodiments of this application, 120 ≤ W ≤ 300. For example, W can be 5, 25, 55, 120, 140, 180, 220, 255, 270, 300, or a value within a range of any two of these values. When the length of the inorganic coating is W on at least one surface of the current collector, the protection of the positive electrode sheet can be further improved, the risk of short circuit in the secondary battery can be reduced, and thus the high-temperature safety performance of the secondary battery under high voltage can be improved.

[0036] In some embodiments of this application, the inorganic coating is disposed on two surfaces of the current collector along the length of the positive electrode sheet. The length of the inorganic coating on one surface of the current collector is W1, and the length of the inorganic coating on the other surface is W2, where 5 ≤ W1 ≤ 35 mm and 20 ≤ W2 ≤ 300 mm. In some embodiments of this application, 5 ≤ W1 ≤ 35 mm and 20 ≤ W2 ≤ 150 mm. In some embodiments of this application, 5 ≤ W1 ≤ 35 mm and 120 ≤ W2 ≤ 300 mm. Distributing inorganic coatings of lengths W1 and W2 on both sides of the current collector significantly improves the protection of the positive electrode sheet, reduces the risk of short circuits in the secondary battery, and thus improves the high-temperature safety performance of the secondary battery under high voltage.

[0037] In some embodiments of this application, the thickness of the inorganic coating along the thickness direction of the positive electrode sheet is H μm, where 1 ≤ H ≤ 20. In another embodiment of this application, 3 ≤ H ≤ 14. In yet another embodiment of this application, 3 ≤ H ≤ 9. For example, H can be 1, 3, 5, 7, 11, 15, 17, 20, or any two of these values. By adjusting H within the above range, it is beneficial to improve the protective effect of the inorganic coating on the positive electrode sheet, reduce the risk of short circuit in the secondary battery, and thus improve the high-temperature safety performance of the secondary battery under high voltage. In some embodiments of this application, an inorganic coating is provided on both surfaces of the positive current collector, and the thickness of the inorganic coating can be the thickness of the inorganic coating on either side of the positive current collector.

[0038] In some embodiments of this application, the inorganic coating comprises an inorganic material and a binder. Based on the mass of the inorganic coating, the inorganic material comprises 70% to 80% by mass, and the binder comprises 20% to 30% by mass. The inorganic material includes at least one of alumina, magnesium oxide, calcium oxide, magnesium hydroxide, boehmite, or zirconium oxide, and the binder includes at least one of polyvinylidene fluoride, polypropylene, or polyacrylate. By controlling the mass percentage and type of the inorganic material and binder within the scope of this application, it is beneficial to improve the interfacial adhesion performance between the inorganic coating and the positive electrode current collector, thereby improving the high-temperature safety performance of the secondary battery under high voltage.

[0039] In some embodiments of this application, the Dv99 of the inorganic material is from 0.5 μm to 2 μm. By controlling the Dv99 of the inorganic material within the range of this application, it is beneficial to improve the mixing uniformity of the inorganic material and the binder during the preparation of the inorganic coating, and to improve the interfacial adhesion performance between the inorganic coating and the positive electrode current collector, thereby improving the high-temperature safety performance of the secondary battery under high voltage. In this application, Dv99 refers to the particle size value that reaches 99% of the volumetric particle size from the smallest particle size side in the volumetric particle size distribution.

[0040] The secondary battery described in this application is not particularly limited and may include devices in which an electrochemical reaction occurs. For example, the secondary battery may include, but is not limited to, lithium-ion secondary batteries or sodium-ion secondary batteries.

[0041] This application does not impose any particular limitation on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, the positive electrode current collector may include aluminum foil or aluminum alloy foil, etc. The positive electrode active material layer of this application includes a positive electrode active material. The positive electrode active material includes lithium and at least one transition metal. For example, the positive electrode active material may include lithium transition metal composite oxide and lithium transition metal phosphate compound, and the lithium transition metal composite oxide may include, but is not limited to, LiCoO2, LiMn2O4, LiNi. 0.5 Mn 0.5 O2, LiNi0.85 Co 0.10 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.45 Co 0.10 Al 0.45 O2, LiMn 1.8 Al 0.2 O4 and LiMn 1.5 Ni 0.5 At least one of O4, etc., and the lithium-containing transition metal phosphate compound may include, but is not limited to, at least one of LiFePO4, Li3Fe2(PO4)3, LiFeP2O7, LiCoPO4, etc. In the present application, there is no particular limitation on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm. The thickness of the single-sided positive electrode active material layer is 30 μm to 120 μm. Among them, the thickness of the inorganic coating is less than or equal to the thickness of the positive electrode active material layer. The positive electrode active material layer of the present application may further include a conductive agent and a binder.

[0042] The present application has no particular limitation on the negative electrode sheet, as long as the object of the present application can be achieved. For example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on at least one surface of the negative electrode current collector. The present application has no particular limitation on the negative electrode current collector, as long as the object of the present application can be achieved. For example, the negative electrode current collector may include copper foil, copper alloy foil, nickel foil, titanium foil, nickel foam or copper foam, etc. The negative electrode active material layer of the present application includes a negative electrode active material. The present application has no particular limitation on the type of the negative electrode active material, as long as the object of the present application can be achieved. For example, the negative electrode active material may include natural graphite, artificial graphite, mesophase microcarbon microbeads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiO x (0 < x ≤ 2) or metallic lithium, etc., at least one of them. In the present application, there is no particular limitation on the thickness of the negative electrode current collector and the negative electrode active material layer, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 12 μm, and the thickness of the single-sided negative electrode active material layer is 30 μm to 130 μm. In the present application, the negative electrode active material layer may be provided on one surface in the thickness direction of the negative electrode current collector, or may be provided on both surfaces in the thickness direction of the negative electrode current collector. It should be noted that the "surface" here may be the entire area of the negative electrode current collector, or may be a partial area of the negative electrode current collector, and the present application has no particular limitation, as long as the object of the present application can be achieved.

[0043] The negative electrode active material layer of this application may further include a conductive agent and a binder. This application does not impose any particular limitations on the conductive agent and binder, as long as they achieve the purpose of this application. For example, the conductive agent may include at least one of acetylene black, amorphous carbon, conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, carbon dots, or graphene. The binder may include at least one of polyacrylamide, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyamide-imide, styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), waterborne acrylic resin, carboxymethyl cellulose (CMC), or sodium carboxymethyl cellulose (CMC-Na).

[0044] The negative electrode sheet of this application may further include a base coating layer, which is located between the negative electrode current collector and the negative electrode active material layer, and is disposed on at least a portion of the surface of the negative electrode current collector. The base coating layer includes a conductive agent and a binder. The conductive agent includes at least one of carbon fiber, Ketjen black, acetylene black, carbon nanotubes, and graphene; the binder includes at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene, styrene-butadiene rubber, acrylate, or epoxy resin. In this application, the thickness of the base coating layer is from 0.1 μm to 2.0 μm. A base coating layer of appropriate thickness can conduct electrons and also increase the adhesion between the active material layer and the current collector. During cycling, it reduces the peeling of the active material layer, thereby causing the secondary battery to exhibit a trend of reduced charge transfer impedance and improved kinetics, and improving the high-temperature safety performance of the secondary battery under high voltage.

[0045] This application does not impose any particular limitation on the separator, as long as it can achieve the purpose of this application. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, 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 used. Optionally, a surface treatment layer may be 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 polymers and inorganic materials. For example, the inorganic layer includes inorganic particles and a binder. There are no particular limitations on the inorganic particles, and they may be selected from 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 adhesive is not particularly limited and can be selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polyhexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polymethyl methacrylate. The polymer layer includes a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or polyvinylidene fluoride-hexafluoropropylene. In this application, the thickness of the separator is not particularly limited, as long as it achieves the purpose of this application; for example, the thickness of the separator can be from 5 μm to 50 μm.

[0046] In this application, the electrolyte may also contain other additives, including at least one of 1,3-propanesulfonate lactone, glutaronitrile, and lithium tetrafluoroborate. The mass percentage of the other additives is from 0.01% to 20% based on the mass of the electrolyte.

[0047] In this application, the electrolyte further includes an organic solvent and a lithium salt. Based on the mass of the electrolyte, the organic solvent comprises 60% to 90% by mass, and the lithium salt comprises 8% to 15% by mass. This application does not impose any particular limitation on the types of organic solvents and lithium salts, as long as they achieve the purpose of this application. For example, the organic solvent may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents. The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), methyl n-propyl carbonate, ethyl n-propyl carbonate, and di n-propyl carbonate. The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). The aforementioned fluorocarbonate compounds may include, but are not limited to, at least one of the following: fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, fluoro-2-methylethylene carbonate, fluoro-methylethylene carbonate, 1,2-difluoro-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate, bis(fluoromethyl)carbonate, bis(difluoromethyl)carbonate, bis(trifluoromethyl)carbonate, bis(2-fluoroethyl)carbonate, bis(2,2-difluoroethyl)carbonate, bis(2,2,2-trifluoroethyl)carbonate, 2-fluoroethylmethylcarbonate, 2,2-difluoroethylmethylcarbonate, or 2,2,2-trifluoroethylmethylcarbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of chain carboxylic acid ester compounds or fluorocarboxylic acid ester compounds. The aforementioned chain carboxylic acid ester compounds may include, but are not limited to, at least one of methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, sec-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate (PP), isopropyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, methyl isobutyrate, ethyl isobutyrate, methyl valerate, ethyl valerate, methyl pivalate, or ethyl pivalate. The aforementioned fluorocarboxylic acid ester compounds may include, but are not limited to, at least one of methyl trifluoroacetate, ethyl trifluoroacetate, propyl trifluoroacetate, butyl trifluoroacetate, or 2,2,2-trifluoroethyl trifluoroacetate. The aforementioned ether compounds may include, but are not limited to, at least one of chain ethers or cyclic ethers.The aforementioned chain ethers may include, but are not limited to, at least one of dimethoxymethane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, diethoxymethane, 1,1-diethoxyethane, 1,2-diethoxyethane, ethoxymethoxymethane, 1,1-ethoxymethoxyethane, or 1,2-ethoxymethoxyethane. The aforementioned cyclic ethers may include, but are not limited to, at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 2-methyl-1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, or dimethoxypropane. The aforementioned other organic solvents may include, but are not limited to, at least one of phosphorus-containing organic solvents, sulfur-containing organic solvents, and aromatic fluorine-containing solvents. The aforementioned phosphorus-containing organic solvents may include, but are not limited to, at least one of trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene phosphate, ethylene phosphate, triphenyl phosphate, trimethyl phosphite, triethyl phosphite, triphenyl phosphite, tri(2,2,2-trifluoroethyl) phosphate, or tri(2,2,3,3,3-pentafluoropropyl) phosphate. The aforementioned sulfur-containing organic solvents may include, but are not limited to, at least one of sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethyl sulfone, diethyl sulfone, ethyl methyl sulfone, methylpropyl sulfone, dimethyl sulfoxide, methyl methanesulfonate, ethyl methanesulfonate, methyl ethanesulfonate, ethyl ethanesulfonate, dimethyl sulfate, diethyl sulfate, and dibutyl sulfate. The aforementioned aromatic fluorine-containing solvents may include, but are not limited to, at least one of fluorobenzene, difluorobenzene, trifluorobenzene, tetrafluorobenzene, pentafluorobenzene, hexafluorobenzene, and trifluoromethylbenzene. For example, lithium salts may include, but are not limited to, at least one of LiTFSI, LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate.

[0048] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the secondary battery. Furthermore, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the secondary battery. The packaging bag is any packaging bag known in the art, and this application does not limit its use.

[0049] The second aspect of this application provides an electrical device comprising the secondary battery described in the foregoing embodiments. This application does not specifically limit the electronic device; it can be any electronic device known in the prior art. For example, the electronic device may include, but is not limited to: laptop computers, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CD-ROMs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0050] Example

[0051] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0052] Test methods and equipment :

[0053] Inorganic particle size testing:

[0054] The Dv99 of inorganic materials was tested using a particle size analyzer.

[0055] Short-circuit deformation rate test:

[0056] The lithium-ion battery was left to stand at 25°C for 30 minutes. Then, it was charged at a constant current rate (C) of 0.5 to a voltage of 4.7V, followed by constant voltage charging at 4.7V to a current of 0.05C. After standing for 60 minutes, the thickness of the lithium-ion battery was measured and recorded as T1. Next, the lithium-ion battery was left to stand at 25°C for 30 minutes. A 100mΩ current wire was connected to the tab position, causing an external short circuit. After 1 hour, the thickness of the lithium-ion battery was measured and recorded as T2. The short-circuit deformation rate is calculated as [(T2-T1) / T1] × 100%.

[0057] Overcharge deformation rate test:

[0058] The lithium-ion battery was left to stand at 25°C for 30 minutes. Then, it was charged at a constant current of 0.5C to a voltage of 4.7V, followed by constant voltage charging at 4.7V to a current of 0.05C. After standing for 60 minutes, the thickness of the lithium-ion battery was measured and recorded as T3. Next, it was charged at a constant current of 0.1C for 60 minutes, followed by a 30-minute stand. This process was repeated five times to bring the lithium-ion battery to 150% state of charge (SOC). The thickness of the lithium-ion battery was then measured and recorded as T4. The overcharge deformation rate is calculated as [(T4-T3) / T3] × 100%.

[0059] Voltage drop test:

[0060] At 25℃, the lithium-ion battery was charged at a constant current of 1C to a voltage of 4.7V, then charged at a constant voltage of 4.7V to a current of 0.05C, and then discharged at a constant current of 1C to a voltage of 3.2V. After standing for 5 minutes, the voltage was measured and recorded as the voltage before storage. Then, the battery was stored at -20℃ for 24 hours, and the voltage was measured again and recorded as the voltage after storage. Voltage drop = voltage before storage - voltage after storage.

[0061] Thermal stability test:

[0062] The lithium-ion battery was left to stand at 25°C for 30 minutes to reach a constant temperature. The initial thickness was measured and recorded as T0. Then, the temperature was increased to 130°C at a rate of 5°C / min and held at 130°C for 30 minutes. After cooling to room temperature, the thickness of the lithium-ion battery was measured and recorded as T5. The thermal stability deformation rate = [(T5-T0) / T0]×100%.

[0063] Example 1-1

[0064] <Preparation of the positive electrode>

[0065] Lithium cobalt oxide (LiCoO2), a positive electrode active material, Super-P, a conductive agent, and polyvinylidene fluoride (PVDF) binder were mixed at a mass ratio of 97:1:2. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry with a solid content of 70 wt%. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil used as a positive electrode current collector. The aluminum foil was dried at 120°C for 1 hour to obtain a single-sided positive electrode active material layer with a thickness of 80 μm. The above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After cold pressing, cutting, and welding of tabs, the sheet was dried under vacuum at 120°C for 1 hour to obtain a positive electrode sheet with dimensions of 74 mm (width) × 854 mm (length) and an empty foil area at the tail for current collection.

[0066] Alumina (Dv99 of 0.7 μm) and PVDF binder were mixed at a mass ratio of 80:20, and N-methylpyrrolidone (NMP) was added. The mixture was stirred evenly under vacuum to obtain an inorganic coating slurry with a solid content of 30 wt%. The inorganic coating slurry was then uniformly coated onto one surface (defined as surface a, and the other surface of the current collector as surface b) of the positive electrode sheet at the tail end of the positive electrode sheet. The surface was then dried at 120 °C for 1 hour to obtain a positive electrode sheet with an inorganic coating on one surface (surface a) of the current collector. The length of the inorganic coating was 95 mm, and the thickness of the inorganic coating was 1.5 μm.

[0067] <Preparation of Negative Electrode Sheets>

[0068] Acetylene black, styrene-butadiene rubber (SBR) binder, and carboxymethyl cellulose (CMC) thickener were mixed in a mass ratio of 50:45:5. Deionized water was added, and the mixture was stirred under vacuum to obtain a negative electrode undercoating slurry with a solid content of 30 wt%. The negative electrode undercoating slurry was uniformly coated onto one surface of a copper foil with a thickness of 8 μm. The copper foil was dried at 120 °C to obtain a negative electrode undercoating with a thickness of 1 μm. The above steps were then repeated on the other surface of the copper foil to obtain a negative electrode current collector with a double-sided negative electrode undercoating.

[0069] Then, artificial graphite, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC-Na) binder were mixed at a mass ratio of 97.4:1.2:1.4, and deionized water was added. A negative electrode slurry with a solid content of 75 wt% was obtained under vacuum stirring. The negative electrode slurry was uniformly coated onto one surface of the negative electrode current collector containing the negative electrode conductive layer. The copper foil was dried at 120°C to obtain a negative electrode active material layer with a single-sided thickness of 100 μm. The above steps were repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. After cold pressing, cutting, and slitting, the sheet was dried under vacuum at 120°C for 1 hour to obtain a negative electrode sheet with dimensions of 76 mm × 867 mm.

[0070] <Preparation of Electrolyte>

[0071] In an argon-atmospheric glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propyl propionate (PP), and diethyl carbonate (DEC) were mixed in a 1:1:1 mass ratio to obtain an organic solvent. Lithium salt LiPF6 and lithium difluorophosphate were then added to the organic solvent to obtain the electrolyte. The mass percentage of LiPF6 was 12.5%, the mass percentage of lithium difluorophosphate was 0.15%, and the remainder was the organic solvent. The mass percentages of each substance were calculated based on the mass of the electrolyte.

[0072] <Preparation of the separating membrane>

[0073] A porous polyethylene film with a thickness of 7μm is used.

[0074] <Preparation of Lithium-ion Batteries>

[0075] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and baked to remove moisture. Electrolyte is then injected into the aluminum-plastic film packaging bag. After vacuum sealing, settling, formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0076] Examples 1-2 to Examples 1-16

[0077] Except for adjusting the thickness of the inorganic coating to adjust the unit area mass of the inorganic coating according to Table 1 in the <Preparation of Positive Electrode Sheet>, and adjusting the type and content of electrolyte additives according to Table 1 in the <Preparation of Electrolyte>, with the content of LiPF6 remaining unchanged and the content of organic solvent changing accordingly, the rest is the same as in Example 1-1.

[0078] Examples 2-1 to 2-6

[0079] Except for adjusting the length of the inorganic coating in <Preparation of the Positive Electrode>, the rest is the same as in Examples 1-2. The length of the inorganic coating on side a is shown in Table 2.

[0080] Examples 2-7 to Examples 2-8

[0081] Except for adjusting the dimensions of the positive electrode to 163mm × 2275mm and the negative electrode to 167mm × 2283mm in the <Preparation of Positive Electrode> section, as well as the length of the inorganic coating, the rest is the same as in Examples 1-2. The length of the inorganic coating on side a is shown in Table 2.

[0082] Examples 2-9

[0083] Except for adjustments to the preparation of the inorganic coating in <Preparation of the Positive Electrode>, the rest is the same as in Examples 1-2. The preparation of the inorganic coating is as follows: Alumina (Dv99 is 0.7μm) and binder PVDF are mixed at a mass ratio of 80:20, N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly under vacuum to obtain an inorganic coating slurry with a solid content of 30wt%. The inorganic coating slurry is first uniformly coated on surface a of the positive current collector aluminum foil at the tail of the positive electrode sheet, and dried at 120°C for 1 hour. Then, the above steps are repeated on surface b of the positive electrode sheet. After drying, a positive electrode sheet with inorganic coatings on both surfaces of the current collector is obtained. The lengths of the inorganic coatings on surfaces a and b are shown in Table 2.

[0084] Example 2-10

[0085] Except for adjusting the dimensions of the positive electrode to 163mm × 2275mm and the negative electrode to 167mm × 2283mm in the <Preparation of Positive Electrode> section, and the lengths of the inorganic coatings on the a and b sides of the positive current collector, the rest are the same as in Examples 2-9. The lengths of the inorganic coatings on the a and b sides are shown in Table 2.

[0086] Examples 2-11 to 2-14

[0087] Except for adjusting the thickness of the inorganic coating in the <Preparation of Positive Electrode Sheet> section, the rest is the same as in Examples 1-2. The thickness of the inorganic coating is shown in Table 2.

[0088] Examples 3-1 to 3-7

[0089] Except for adjusting the type and content of inorganic materials, Dv99, and type and content of binder according to Table 3 in the <Preparation of Positive Electrode>, the rest is the same as in Example 1-1.

[0090] Comparative Example 1

[0091] Except for adjusting the type and content of electrolyte additives according to Table 1 in <Electrolyte Preparation>, keeping the content of LiPF6 unchanged, and changing the content of organic solvent accordingly, the rest is the same as in Examples 1-2.

[0092] Comparative Example 2

[0093] Except for adjusting the thickness of the inorganic coating to adjust the unit area mass of the inorganic coating according to Table 1 in <Preparation of Positive Electrode Sheet>, and adjusting the type and content of electrolyte additives according to Table 1 in <Preparation of Electrolyte>, with the content of LiPF6 remaining unchanged and the content of organic solvent changing accordingly, the rest is the same as in Examples 1-2.

[0094]

[0095]

[0096] As can be seen from Examples 1-1 to 1-16 and Comparative Examples 1 to 2, by adopting the positive electrode structure of this application and by selecting electrolyte additives within the scope of this application and synergistically regulating B / A within the scope of this application, the overcharge deformation rate, short-circuit deformation rate, voltage drop and thermal stability deformation rate of the obtained lithium-ion battery are significantly reduced, indicating that the lithium-ion battery of this application has excellent high-temperature safety performance under high voltage.

[0097] Table 2

[0098]

[0099] As can be seen from Examples 2-1 to 2-10, by adjusting the length of the inorganic coating along the positive electrode sheet within the scope of this application, the resulting lithium-ion battery exhibits lower overcharge deformation rate, short-circuit deformation rate, voltage drop, and thermal stability deformation rate, indicating that the lithium-ion battery has good high-temperature safety performance under high voltage. As can be seen from Examples 1-2 and Examples 2-11 to 2-14, by adjusting the thickness of the inorganic coating within the scope of this application, the lithium-ion battery not only exhibits good high-temperature safety performance under high voltage but also ensures high energy density.

[0100] Table 3

[0101]

[0102] The types and contents of inorganic substances and binders usually affect the high-temperature safety performance of lithium-ion batteries under high voltage. As can be seen from Examples 3-1 to 3-7, by adjusting the above parameters within the application range, the overcharge deformation rate, short-circuit deformation rate, voltage drop and thermal stability deformation rate of lithium-ion batteries are low, thus lithium-ion batteries have good high-temperature safety performance under high voltage.

[0103] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0104] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application are included within the scope of protection of this application.

Claims

1. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, the positive electrode sheet comprising a positive electrode current collector, wherein, The surface of the positive current collector is provided with a positive active material layer and an inorganic coating. Along the length direction of the positive electrode sheet, the inorganic coating is provided on at least one surface of the positive current collector at the tail of the positive electrode sheet. The electrolyte includes additives, which include at least one of lithium difluorophosphate, succinic acid, adiponitrile, 1,3,6-hexanetrionitrile, and 1,2,3-tris(2-oxyethoxy)propane. The inorganic coating has a unit area mass of A g / m³. 2 Based on the mass of the electrolyte, the mass percentage of the additive is B%, satisfying: 0.01≤B / A≤5.

2. The secondary battery according to claim 1, wherein 1≤A≤20。 3. The secondary battery according to claim 1, wherein 0.01≤B≤10。 4. The secondary battery according to claim 1, wherein Along the thickness direction of the positive electrode sheet, the thickness of the inorganic coating is H μm, where 1 ≤ H ≤ 20.

5. The secondary battery according to claim 1, wherein Along the length of the positive electrode sheet, the length of the inorganic coating accounts for 0.1% to 20% of the total length of the positive electrode sheet.

6. The secondary battery according to claim 1, wherein Along the length of the positive electrode sheet, the length of the inorganic coating is W mm, where 5 ≤ W ≤ 300.

7. The secondary battery according to claim 1, wherein The inorganic coating is disposed on two surfaces of the positive current collector at the tail of the positive electrode sheet, wherein the length of the inorganic coating on one surface of the positive current collector is W1, and the length of the inorganic coating on the other surface of the positive current collector is W2, 5≤W1≤35, 30≤W2≤300.

8. The secondary battery according to claim 1, wherein The inorganic coating comprises an inorganic material and a binder. Based on the mass of the inorganic coating, the inorganic material has a mass percentage content of 70% to 80%, and the binder has a mass percentage content of 20% to 30%. The inorganic material includes at least one of alumina, magnesium oxide, calcium oxide, magnesium hydroxide, boehmite, or zirconium oxide. The binder includes at least one of polyvinylidene fluoride, polypropylene, or polyacrylate. The Dv99 of the inorganic material is 0.5 μm to 2 μm.

9. The secondary battery according to any one of claims 1 to 8, wherein The secondary battery satisfies at least one of the following conditions: (1) Along the length of the positive electrode sheet, the length of the inorganic coating is W mm, 40≤W≤160; (2) Along the thickness direction of the positive electrode sheet, the thickness of the inorganic coating is H μm, 3≤H≤14; （3）2≤A≤14； （4）0.02≤B≤7.5； (5) 0.2≤B / A≤3.

10. An electrical device comprising a secondary battery as described in any one of claims 1 to 9.

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