Secondary battery and electronic device

Abstract

The present application relates to a secondary battery and an electronic device. Specifically, provided is a secondary battery, which comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises an insulating layer and a positive electrode active material layer, which are arranged on a current collector; the insulating layer comprises an inorganic additive; and the electrolyte contains a fluorine-free chain carboxylic ester, ethylene sulfate and lithium difluorophosphate. The secondary battery can not only improve the lithium-ion acceptability at low temperatures, but can also inhibit the increase of low-temperature direct-current resistance and improve low-temperature output characteristics.

Description

Secondary batteries and electronic devices

[0001] Cross-references to related applications

[0002] This application is based on and claims priority to Chinese Patent Application No. 202410658437.8, filed on May 27, 2024, entitled "Secondary Battery and Electronic Device", the full disclosure of which is incorporated herein by reference. Technical Field

[0003] This application relates to the field of energy storage, specifically to a secondary battery and electronic device. Background Technology

[0004] With the rapid development of electronic products such as smartphones, tablets, and smart wearables, higher demands are being placed on the lifespan, battery life, and safety performance of secondary batteries, considering the varying usage time and operating temperatures of these products. As the charging cut-off voltage increases, the energy density of batteries has significantly improved. However, in existing technologies, as the secondary battery voltage increases, the cycle performance of high-voltage secondary batteries deteriorates. Even after using high-voltage positive electrode film-forming additives to improve cycle characteristics, low-temperature performance is greatly affected. Summary of the Invention

[0005] The embodiments of this application address, to some extent, the problems existing in the prior art by adjusting the composition of the positive electrode and the components of the electrolyte used in secondary batteries.

[0006] The inventors of this application have discovered that the positive electrode includes an insulating layer disposed on the current collector and a positive electrode active material layer. The insulating layer includes inorganic additives. The electrolyte consists of chain carboxylic acid esters, vinyl sulfate, and lithium difluorophosphate. This not only improves lithium-ion acceptance at low temperatures but also suppresses the increase in DC resistance at low temperatures and improves low-temperature output characteristics, thereby completing this application.

[0007] This application provides a secondary battery, comprising: a positive electrode, a negative electrode, and an electrolyte; the positive electrode comprises: an insulating layer and a positive electrode active material layer disposed on a current collector; the insulating layer comprises: an inorganic additive; the inorganic additive comprises: a metal element; the metal element in the inorganic additive comprises at least one selected from aluminum, magnesium, titanium, zirconium, niobium, indium, tungsten, tin, zinc, or antimony; the electrolyte contains a fluorine-free chain carboxylic acid ester, vinyl sulfate, and lithium difluorophosphate, wherein, based on the mass of the electrolyte, the total mass content of vinyl sulfate and lithium difluorophosphate is 0.02 wt% or more and 3.26 wt% or less, and the mass content of the fluorine-free chain carboxylic acid ester is 8.6 wt% or more and 65 wt% or less. Based on the mass of the electrolyte, the total mass content of (II) and (III) is more than 0.02 wt% and less than 3.26 wt%; the mass content of (I) is more than 8.6 wt% and less than 65 wt%, which is important for the stability of the positive electrode structure and significantly suppresses the increase of interface resistance at low temperature. This design can not only improve lithium ion acceptance at low temperature, but also suppress the increase of DC resistance at low temperature and improve the low temperature output characteristics.

[0008] In some embodiments, the total mass content of vinyl sulfate and lithium difluorophosphate is above 0.05 wt% and below 1.98 wt%, based on the mass of the electrolyte, which helps to further improve low-temperature performance.

[0009] In some embodiments, the mass content of fluorine-free chain carboxylic acid esters is 17.3 wt% or more and 52.6 wt% or less, based on the mass of the electrolyte, thereby improving low-temperature performance.

[0010] In some embodiments, the inorganic additive is selected from at least one of alumina, aluminum hydroxide, boehmite, magnesium oxide, magnesium hydroxide, titanium dioxide, zirconium dioxide, niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide, indium trioxide, tungsten trioxide, tin dioxide, zinc oxide, or antimony trioxide, thereby improving low-temperature performance.

[0011] In some embodiments, the fluorine-free chain carboxylic ester is selected from at least one of methyl acetate, ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, methyl neopentanoate, ethyl neopentanoate, n-propyl neopentanoate, methyl acrylate, ethyl acrylate, n-propyl acrylate, methyl methacrylate, ethyl methacrylate, or n-propyl methacrylate.

[0012] In some embodiments, based on the mass of the electrolyte, the mass content of vinyl sulfate is 0.01 wt% or more and 1.67 wt% or less; or, based on the mass of the electrolyte, the mass content of lithium difluorophosphate is 0.01 wt% or more and 1.95 wt% or less, to improve lithium-ion acceptability.

[0013] In some embodiments, the electrolyte further comprises: other additives; the other additives include: at least one selected from 1,2-bis(difluorophosphoxy)ethane, compound of formula 1, compound of formula 2, vinylene carbonate, lithium fluorosulfonate, succinate, adiponitrile, 1,3,6-hexamethylenetricarbonate, 1,2,3-tris(2-cyanoethoxy)propane, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilane) phosphate, or tris(trimethylsilane) borate.

[0014] Formula 1 compound, The compound of Formula 2; based on the mass of the electrolyte, the mass content of other additives is more than 0.5 wt% and less than 7 wt%, which can improve the stability of the aforementioned coating at low temperature and increase the ion conduction rate of lithium ions, thereby further improving the low temperature performance.

[0015] In some embodiments, a tab is provided on one side of the current collector, and an insulating layer is provided on the edge surface of the current collector on the side with the tab. The insulating layer is used to improve the insulation of the positive electrode edge and the negative electrode edge, thereby improving the safety performance of the secondary battery, especially the insulation under high voltage.

[0016] In some embodiments, the secondary battery has a wound structure, with an insulating layer disposed on the surface of the end section along the length of the current collector, thereby improving the safety of the end section.

[0017] In another aspect of this application, an electronic device is provided that includes the secondary battery described in this application.

[0018] By using a specific combination of positive electrode structure and electrolyte, this application not only improves lithium-ion acceptance at low temperatures, but also suppresses the increase in DC resistance at low temperatures and enhances low-temperature output characteristics.

[0019] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Detailed Implementation

[0020] The embodiments of this application will be described in detail below. These embodiments should not be construed as limiting the scope of this application.

[0021] By using a specific combination of positive electrode structure and electrolyte, this application not only improves lithium-ion acceptance at low temperatures, but also suppresses the increase in DC resistance at low temperatures and enhances low-temperature output characteristics.

[0022] In one embodiment, this application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte as described below.

[0023] I. Electrolyte

[0024] The electrolyte in the secondary battery of this application includes an electrolyte and a solvent for dissolving the electrolyte.

[0025] In some embodiments, the electrolyte of this application includes (I) a fluorine-free chain carboxylic acid ester, (II) vinyl sulfate and (III) lithium difluorophosphate.

[0026] When an insulating layer is placed on the tab side or the end section of a secondary battery to improve its safety performance, the presence of inorganic additives in the insulating layer can easily catalyze the formation of a film of non-fluorinated chain carboxylic acid esters on the surface of the positive electrode active material, resulting in increased coating impedance and affecting the low-temperature characteristics of the secondary battery. The inventors discovered that when the electrolyte also contains vinyl sulfate and lithium difluorophosphate, the increase in coating impedance can be significantly suppressed. This not only improves lithium-ion acceptance at low temperatures but also suppresses the increase in low-temperature DC resistance and improves low-temperature output characteristics.

[0027] Examples of non-fluorinated chain carboxylic acid esters include: methyl acetate, ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, methyl neopentanoate, ethyl neopentanoate, n-propyl neopentanoate, and other saturated chain carboxylic acid esters; and methyl acrylate, ethyl acrylate, n-propyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, and other unsaturated chain carboxylic acid esters.

[0028] Among these, methyl acetate, ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl neopentanoate, ethyl neopentanoate, and n-propyl neopentanoate are preferred from the viewpoint of improving ionic conductivity by reducing electrolyte viscosity. Methyl acetate, ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate, and propyl propionate are more preferred, methyl acetate, methyl propionate, ethyl propionate, and propyl propionate are even more preferred, and methyl acetate, methyl propionate, ethyl propionate, and propyl propionate are particularly preferred.

[0029] Fluorine-free carboxylic esters can be used alone or in combination of two or more in any ratio.

[0030] Specifically, from the viewpoint of improving low-temperature resistance, based on the electrolyte quality, the mass content of fluorine-free carboxylic acid esters (the total amount in two or more cases) can be 8.6 wt% or more, preferably 10.3 wt% or more, more preferably 13.7 wt% or more, further preferably 21.9 wt% or more, particularly preferably 23.4 wt% or more, and can also be 65 wt% or less, preferably 52.6 wt% or less, more preferably 47.3 wt% or less.

[0031] Specifically, from the viewpoint of improving lithium-ion acceptability, based on the electrolyte mass, the mass content of vinyl sulfate is 0.01 wt% or more, preferably 0.02 wt% or more, more preferably 0.04 wt% or more, and more preferably 0.08 wt% or more. Furthermore, as an upper limit for the mass content of vinyl sulfate, from the viewpoint of improving low-temperature DC resistance, the mass content of vinyl sulfate is 1.67 wt% or less, preferably 1.59 wt% or less, more preferably 1.45 wt% or less, further preferably 1.23 wt% or less, and particularly preferably 0.88 wt% or less. When within the above ranges, it helps to further improve the increase in low-temperature DC resistance.

[0032] Specifically, from the viewpoint of improving lithium-ion acceptability, based on the electrolyte mass, the lithium difluorophosphate mass content is 0.01 wt% or more, preferably 0.05 wt% or more, more preferably 0.07 wt% or more, and even more preferably 0.11 wt% or more. Furthermore, as an upper limit for the lithium difluorophosphate mass content, from the viewpoint of improving low-temperature output, the lithium difluorophosphate mass content is 1.95 wt% or less, preferably 1.87 wt% or less, more preferably 1.59 wt% or less, even more preferably 1.22 wt% or less, and particularly preferably 0.93 wt% or less. When within the above ranges, it helps to further improve low-temperature output.

[0033] Furthermore, from the viewpoint of improving lithium-ion acceptability, based on the electrolyte mass, the total mass content of (II) and (III) is 0.02 wt% or more, preferably 0.05 wt% or more. Moreover, as an upper limit for the total mass content of (II) and (III), from the viewpoint of improving electrochemical characteristics at low temperatures, the total mass content of (II) and (III) is 3.26 wt% or less, preferably 2.81 wt% or less.

[0034] In some embodiments, the total mass content of (II) and (III) is a wt%, where a is 0.02, 0.05, 0.09, 0.13, 0.19, 0.29, 0.46, 0.68, 1.17, 1.57, 1.98, 2.38, 2.81, 3.26, or within a range consisting of any two of the above values. When within the above range, it helps to further improve the increase in low-temperature DC resistance.

[0035] In addition, the electrolyte may also include at least one of the following: 1,2-bis(difluorophosphoxy)ethane, compound of formula 1, compound of formula 2, vinylene carbonate, lithium fluorosulfonate, succinate, adiponitrile, 1,3,6-hexamethylenetricarbonate, 1,2,3-tris(2-cyanoethoxy)propane, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilane) phosphate, and tris(trimethylsilane) borate.

[0036] Formula 1 compound, Compound of Formula 2.

[0037] The inventors also unexpectedly discovered that other additives can improve the stability of the aforementioned coating at low temperatures and increase the ion conductivity of lithium ions, thereby further improving the low-temperature resistance increase characteristic. These other additives can be just one type or two or more.

[0038] Specifically, from the viewpoint of improving lithium-ion conductivity in the aforementioned coating, based on the electrolyte mass, the mass content of other additives is 0.01 wt% or more, preferably 0.1 wt% or more, more preferably 0.3 wt% or more, and even more preferably 0.5 wt% or more. Furthermore, as an upper limit for the mass content of other additives, from the viewpoint of improving the increase in low-temperature DC resistance, the mass content of other additives is 10 wt% or less, preferably 9 wt% or less, more preferably 8 wt% or less, further preferably 7 wt% or less, and particularly preferably 5 wt% or less. When within the above ranges, it helps to further improve the characteristics of increasing low-temperature DC resistance.

[0039] In some embodiments, the electrolyte in the electrode solution is not particularly limited, and any substance known as an electrolyte can be used. The mass of the electrolyte is not particularly limited, as long as it does not impair the effectiveness of this application. For example, the lithium salt used in the electrolyte of this application includes lithium hexafluorophosphate, and the mass content of lithium hexafluorophosphate is 9% to 15 wt%, preferably 9% to 13 wt%, and more preferably 9% to 12 wt%, based on the mass of the electrolyte. By setting the content within the above range, the increase in low-temperature DC resistance can be improved.

[0040] In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the art that can be used as a solvent for an electrolyte. In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylic esters, cyclic ethers, chain ethers, phosphorus-containing organic solvents, and sulfur-containing organic solvents.

[0041] II. Positive electrode

[0042] The positive electrode includes a positive electrode current collector and a positive electrode mixture layer provided on the positive electrode current collector. The positive electrode mixture layer contains positive electrode active materials, and the positive electrode mixture layer can be one layer or multiple layers. The positive electrode mixture layer includes a positive electrode active material layer and an insulating layer. The insulating layer can be provided on the edge surface of the current collector on the side with the tab, that is, the insulating layer is located on the tab side. Or the insulating layer is provided on the surface of the end section in the length direction of the current collector of the wound secondary battery, that is, the insulating layer is located on the end section. The insulating layer is used to improve the insulation between the positive electrode edge and the negative electrode edge, thereby improving the safety performance of the secondary battery, especially the insulation at high voltages. The positive electrode active material is any substance that can reversibly intercalate and deintercalate lithium ions.

[0043] For example, as the positive electrode active material for a secondary battery, a composite metal oxide containing one or more selected from the group consisting of cobalt, manganese, and nickel and lithium, or a lithium-containing olivine-type phosphate containing one or more selected from iron, cobalt, nickel, and manganese is used. These positive electrode active materials can be used alone or in combination of two or more.

[0044] As such a lithium composite metal oxide, for example, those selected from LiCoO2, LiMn2O4, LiNiO2, LiCo 1-x Ni x O2 (0.01 < x < 1), LiNi x Mn y Co z O2 (x + y + z = 1), a solid solution of Li2MnO3 and LiMO2 (M is a transition metal such as Co, Ni, Mn, Fe, etc.), LiNi 1 / 2 Mn 3 / 2 O4, LiFePO4, LiMnPO4, and LiMn 1-x FexPO4 (0.01 < x < 1) are preferably one or more, more preferably two or more. A part of these composite metal oxides with lithium or lithium-containing olivine-type phosphates can be substituted with other elements, or a part of cobalt, nickel, manganese, and iron can be substituted with one or more elements selected from Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W, and Zr, or coated with a compound containing these other elements or a carbon material.

[0045] Regarding the voltage during charging, from the perspective of high voltage, the positive electrode potential is preferably 4.4 V (vs. Li / Li+) or more, more preferably 4.5 V (vs. Li / Li+) or more, and particularly preferably 4.6 V (vs. Li / Li+) or more.

[0046] There are no particular restrictions on the conductive agent used in the positive electrode, as long as it is an electron-conducting material that does not cause chemical changes. Examples include natural graphite (flake graphite, etc.), artificial graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal cracking black, etc. Furthermore, graphite and carbon black can be appropriately mixed. The preferred amount of conductive agent added to the positive electrode mixture is 1 to 10 wt% by mass, particularly preferably 1.5 to 5 wt% by mass.

[0047] The binder for the positive electrode includes at least one of polyvinylidene fluoride, polyacrylonitrile, and polyacrylic acid. From the viewpoint of improving lithium-ion acceptance and reducing the low-temperature DC resistance of the secondary battery, polyacrylonitrile is preferred.

[0048] From the perspective of mitigating the increase in DC resistance at low temperatures, inorganic additives are included in the insulating layer. The metallic elements in these inorganic additives include at least one of aluminum, magnesium, titanium, zirconium, niobium, indium, tungsten, tin, zinc, and antimony.

[0049] Specifically, the inorganic additive can be at least one of inorganic metal oxides and inorganic metal hydroxides. Examples include aluminum oxide, aluminum hydroxide, boehmite, magnesium oxide, magnesium hydroxide, titanium dioxide, zirconium dioxide, niobium monoxide, niobium dioxide, niobium trioxide, niobium pentoxide, indium trioxide, tungsten trioxide, tin dioxide, zinc oxide, and antimony trioxide.

[0050] The positive electrode is made in the following way:

[0051] Inorganic additives, conductive agents such as acetylene black and carbon black, and binders such as polyvinylidene fluoride or polyacrylonitrile are mixed together, and deionized water is added and mixed evenly to form slurry 1.

[0052] The above-mentioned positive electrode active material, conductive agents such as acetylene black and carbon black, and binders such as polyvinylidene fluoride or polyacrylonitrile are mixed together, and high-boiling-point solvents such as 1-methyl-2-pyrrolidone are added and kneaded to prepare slurry 2.

[0053] Slurry 1 and slurry 2 are coated in parallel onto the aluminum foil of the current collector, then dried and pressurized to form the positive electrode.

[0054] The density of the positive electrode active material layer is typically 3.5 g / cm³. 3 In order to further improve the battery capacity, a value of 3.8 g / cm³ is preferred. 3 The above, more preferably 4g / cm 3 The above is further optimized to 4.1 g / cm³. 3 That's all. Furthermore, as an upper limit, 4.6 g / cm³ is preferred. 3 the following.

[0055] There are no particular limitations on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors may include, but are not limited to, metallic materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper. In some embodiments, the positive electrode current collector is a metallic material. In some embodiments, the positive electrode current collector is aluminum foil.

[0056] III. Negative electrode

[0057] The negative electrode includes a negative electrode current collector and a negative electrode additive layer disposed on the surface of the negative electrode current collector, the negative electrode additive layer containing a negative electrode active material. In some embodiments, the rechargeable capacity of the negative electrode active material is greater than the discharge capacity of the positive electrode active material to prevent unintentional deposition of lithium metal on the negative electrode during charging.

[0058] Furthermore, there are no particular limitations on the negative electrode active material; examples include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials that combine these elements.

[0059] Carbon-based anode active materials

[0060] Here, carbon-based anode active materials refer to active materials with carbon as the main framework that can insert lithium. Examples of carbon-based anode active materials include carbonaceous materials and graphitic materials.

[0061] Examples of carbonaceous materials include easily graphitized carbon and non-graphitized carbon with a similar amorphous structure, such as glassy carbon. Among easily graphitized carbons, examples include carbon materials derived from petroleum or coal using tar pitch as a raw material. Specific examples include coke, mesophase carbon microspheres (MCMB), mesophase pitch-based carbon fibers, and pyrolysis-grown carbon fibers. Furthermore, examples of non-graphitized carbons include phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), and hard carbon.

[0062] Furthermore, examples of graphitic materials include natural graphite and artificial graphite. Among these, examples of artificial graphite include: artificial graphite formed by heat-treating carbon containing easily graphitizable carbon primarily at temperatures above 2800°C; graphitic MCMB formed by heat-treating MCMB at temperatures above 2000°C; and graphitic mesophase pitch-based carbon fiber formed by heat-treating mesophase pitch-based carbon fiber at temperatures above 2000°C. Additionally, in this application, natural graphite (amorphously coated natural graphite) can be used as the carbon-based negative electrode active material, where at least a portion of its surface is coated with amorphous carbon.

[0063] Furthermore, metal-based anode active materials are active materials containing metals, generally referring to active materials whose structure contains elements capable of intercalating into or alloying with lithium, and whose theoretical current capacity per unit mass is 500 mAh / g or more when intercalated into or alloyed with lithium. Examples of metal-based anode active materials include: lithium metal, elemental metals capable of forming lithium alloys (e.g., Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and their alloys, as well as their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. Among these, active materials containing silicon (silicon-based anode active materials) are preferred as metal-based anode active materials. This is because using silicon-based anode active materials enables high-capacity secondary batteries.

[0064] Examples of silicon-based anode active materials include: silicon (Si), silicon-containing alloys, silicon oxides, and silicon-containing materials coated or composited with conductive carbon.

[0065] From the perspective of improving battery capacity, silicon-carbon materials are preferred, such as composites of porous carbon-supported silicon.

[0066] In addition, the negative electrode active material can be used alone, or two or more can be used in any ratio.

[0067] The negative electrode mixture layer may also include a negative electrode binder. The negative electrode binder improves the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. There are no particular limitations on the type of negative electrode binder, as long as it is a material stable to the electrolyte or the solvent used in electrode manufacturing. In some embodiments, the negative electrode binder includes a resin binder. Examples of resin binders include, but are not limited to, fluoropolymers, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, etc. When preparing the negative electrode mixture slurry using an aqueous solvent, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salts, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salts, polyvinyl alcohol, etc.

[0068] As the current collector for retaining the active material of the negative electrode, any known current collector can be used. Examples of negative electrode current collectors include, but are not limited to, metallic materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper foil.

[0069] The negative electrode can be prepared by coating a negative electrode slurry containing negative electrode active material, resin binder, etc. onto the negative electrode current collector, drying it, and then calendering it to form a negative electrode slurry layer on both sides of the negative electrode current collector, thereby obtaining the negative electrode.

[0070] IV. Separating membrane

[0071] To prevent short circuits, a separator is typically placed between the positive and negative electrodes. In this case, the electrolyte of this application is typically used after penetrating into the separator.

[0072] There are no particular limitations on the material and shape of the separator, as long as it does not significantly impair the effectiveness of this application. The separator may be a resin, glass fiber, inorganic material, or other material formed from a material stable to the electrolyte of this application. In some embodiments, the separator includes a porous sheet or non-woven fabric-like material with excellent liquid retention properties. Examples of materials for resin or glass fiber separators may include, but are not limited to, polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc. In some embodiments, the polyolefin is polyethylene or polypropylene. In some embodiments, the polyolefin is polypropylene. The above-mentioned separator materials can be used alone or in any combination.

[0073] The separator can also be a material formed by laminating the above-mentioned materials, examples of which include, but are not limited to, a three-layer separator formed by laminating polypropylene, polyethylene, and polypropylene in that order.

[0074] Examples of inorganic materials may include, but are not limited to, oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.). Inorganic materials may be in, but are not limited to, particulate or fibrous forms.

[0075] The separator can be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, microporous membranes, etc. In the form of a thin film, the pore size of the separator is 0.01 μm to 1 μm, and the thickness is 5 μm to 50 μm. In addition to the above-mentioned independent thin film separator, the following separator can also be used: a separator formed by using a resin-based adhesive to form a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode, for example, a separator formed by using fluororesin as an adhesive to form a porous layer of alumina particles with a particle size of less than 1 μm on both sides of the positive electrode.

[0076] The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the separator is less than 50 μm, less than 40 μm, or less than 30 μm. When the thickness of the separator is within the above ranges, insulation and mechanical strength can be ensured, and the DC resistance characteristics and energy density of the secondary battery can be improved.

[0077] This application also provides an electronic device that includes a secondary battery as described in this application.

[0078] The application of the secondary battery in this application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, the secondary battery of this application can be used in, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, 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, household large-capacity batteries, and lithium-ion capacitors, etc.

[0079] The preparation of secondary batteries is described below with reference to specific embodiments. Those skilled in the art will understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0080] Example

[0081] The following are examples of non-aqueous electrolytes of this application, but this application is not limited to these examples.

[0082] Manufacturing of secondary batteries

[0083] The production of the positive electrode:

[0084] Mix 65 wt% of the inorganic additives in Table 1 with 15 wt% of acetylene black and 20 wt% of the binder polyvinylidene fluoride, add deionized water and mix evenly to prepare positive electrode slurry 1.

[0085] A solution was prepared by mixing 97 wt% lithium cobalt oxide positive electrode active material and 1.5 wt% acetylene black, and dissolving 1.5 wt% polyacrylonitrile (a binder) in 1-methyl-2-pyrrolidone, and then mixing the mixture to prepare positive electrode slurry 2. Slurry 1 can be coated on the tab side or at the end of the coating process. Slurries 1 and 2 are coated parallel to each other on an aluminum foil. The coated aluminum foil is then dried, pressurized, and cut to the specified size to fabricate the positive electrode.

[0086] Negative electrode fabrication:

[0087] A negative electrode slurry was prepared by mixing 96 wt% artificial graphite and silicon carbon (mass ratio 90:10) and 2 wt% styrene-butadiene rubber, and adding the mixture to a solution obtained by dissolving 2 wt% lithium carboxymethyl cellulose in deionized water. This negative electrode slurry was then coated onto one side of a copper foil, dried, pressurized, and cut to the specified size to fabricate the negative electrode.

[0088] Battery making:

[0089] The positive and negative electrodes prepared as described above are each connected to a wire. They are then stacked via a 10 μm thick polypropylene porous membrane. Furthermore, LiPF6, serving as the electrolyte, is dissolved in a solution containing (I) a non-fluorinated carboxylic acid ester, (II) ethylene sulfate, and (III) lithium difluorophosphate, as well as ethylene carbonate and propylene carbonate (mass ratio 1:1.2). Based on 100 parts by mass of the total non-aqueous electrolyte, the contents and composition of (I) to (III), and other additives are shown in Table 2, and the mass content of LiPF6 is 13 wt%.

[0090] The laminated body and 3.2g of electrolyte are then placed inside an aluminum-plastic film. The opening of the casing is heat-sealed, and a secondary battery is manufactured through formation, capacity testing, and other steps. The secondary battery is a pouch-shaped structure with a width of 35mm, a height of 48mm, and a thickness of 5mm.

[0091] Table 1 Positive electrode insulation layer configuration

[0092] Table 2 Electrolytes

[0093] The values ​​in parentheses above are all in wt%, and a is the total mass content of (II) and (III).

[0094] The abbreviations in the table above represent the following substances:

[0095] Test methods

[0096] Lithium-ion acceptance at low temperatures

[0097] After the secondary battery was left to stand at 25°C for 24 hours, it was charged at a constant current of 1.0C for 1 hour at 25°C, and the room temperature charging capacity (C0) was measured. Then, at 25°C, it was discharged at a constant current of 0.1C until it reached 3V, at which point the discharge was stopped. Next, at -20°C, it was charged at a constant current of 1.0C for 1 hour, and the low temperature charging capacity (C1) was measured. The ratio of C1 to C0 (C1 / C0) was then calculated and evaluated using the following criteria. A higher C1 / C0 value indicates better lithium-ion acceptance of the secondary battery at low temperatures.

[0098] A: C1 / C0 is greater than 0.65 and less than 1;

[0099] B: C1 / C0 is greater than 0.5 and less than 0.65;

[0100] C: C1 / C0 is less than 0.5.

[0101] Low-temperature DC resistance (-20℃)

[0102] The secondary battery was charged at 140mA to 50% State of Charge (SOC) at 25°C. Then, it was discharged at 140mA for 20 seconds and charged at 140mA for 20 seconds at -20°C. The voltage change during discharge was recorded as ΔV0.2. Next, the same test was performed with the 140mA replaced by 350mA, 700mA, and 1050mA, respectively, and the voltage changes were calculated and recorded as ΔV0.5, ΔV1.0, and ΔV1.5, respectively.

[0103] Next, plot the discharge current value on the X-axis and ΔV on the Y-axis to find an approximate straight line passing through the zero intercept point. The slope of this approximate straight line is the direct current resistance (DCR), and it is evaluated according to the following criteria.

[0104] A: DCR is less than 0.7Ω;

[0105] B: DCR is 0.7Ω or higher and less than 1Ω;

[0106] C: DCR is greater than 1Ω and less than 1.2Ω;

[0107] D: DCR is above 1.2Ω.

[0108] Low temperature output characteristics

[0109] The secondary battery was left to stand at 25°C for 24 hours. Then, it was charged at 0.1C for 5 hours at 25°C, and the voltage V0 was measured. Next, it was discharged at 1C at -10°C, and the voltage V1 was measured 15 seconds after the start of discharge. The voltage change ΔV was calculated as ΔV = V0 - V1. The smaller the value of this voltage change ΔV, the better the low-temperature output characteristics, and it was evaluated according to the following criteria.

[0110] A: Voltage change ΔV is less than 350mV;

[0111] B: Voltage change ΔV is greater than 350mV and less than 500mV;

[0112] C: Voltage change ΔV is greater than 500mV.

[0113] Test Results

[0114] Table 3-1

[0115] Table 3-2

[0116] In a secondary battery comprising an insulating layer disposed on a current collector and a positive electrode active material layer, wherein the insulating layer comprises inorganic additives, the electrolyte contains (I) a fluorine-free chain carboxylic acid ester, (II) ethylene sulfate and (III) lithium difluorophosphate, wherein, based on the mass of the electrolyte, the total content of (II) and (III) is 0.02 wt% or more and 3.26 wt% or less; the content of (I) is 8.6 wt% or more and 65 wt% or less, which is important and crucial for the stability of the positive electrode structure, significantly suppressing the increase of interfacial resistance at low temperatures. This design not only improves the lithium-ion acceptability of the secondary battery at low temperatures, but also suppresses the increase of DC resistance at low temperatures and improves the low-temperature output characteristics.

[0117] Excellent secondary battery characteristics were obtained when the insulating layer was located on the tab side or the end section. In particular, when the insulating layer was located on the end section, it had a further effect on improving low-temperature characteristics.

[0118] When the electrolyte also contains at least one of other additives such as 1,2-bis(difluorophosphoxy)ethane, compound of formula 1, compound of formula 2, vinylene carbonate, lithium fluorosulfonate, succinate, adiponitrile, 1,3,6-hexamethylenetricarbonate, 1,2,3-tris(2-cyanoethoxy)propane, vinyl sulfate, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilane)phosphate, and tris(trimethylsilane)borate, the increase in low-temperature DC resistance and the improvement of low-temperature output characteristics are further suppressed.

[0119] Throughout this specification, references to "embodiment," "partial embodiment," "one embodiment," "another example," "example," "specific example," or "partial example" mean that at least one embodiment or example in this application includes a specific feature, structure, material, or characteristic described in that embodiment or example. Therefore, descriptions appearing throughout this specification, such as "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a specific example," or "example," do not necessarily refer to the same embodiments or examples in this application. Furthermore, specific features, structures, materials, or characteristics in this application can be combined in any suitable manner in one or more embodiments or examples.

[0120] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A secondary battery, characterized in that, Comprising: a positive electrode, a negative electrode, and an electrolyte solution; the positive electrode includes an insulating layer and a positive electrode active material layer provided on a current collector; the insulating layer includes an inorganic additive; the inorganic additive includes a metal element; the metal element in the inorganic additive includes at least one of aluminum, magnesium, titanium, zirconium, niobium, indium, tungsten, tin, zinc, or antimony; the electrolyte solution contains a chain carboxylic acid ester not containing fluorine, a vinylsulfate, and lithium difluorophosphate, wherein the total mass content of the vinylsulfate and the lithium difluorophosphate is 0.02% by mass or more and 3.26% by mass or less based on the mass of the electrolyte solution, and the mass content of the chain carboxylic acid ester not containing fluorine is 8.6% by mass or more and 65% by mass or less.

2. The secondary battery according to claim 1, characterized by The total mass content of the vinylsulfate and the lithium difluorophosphate is 0.05% by mass or more and 1.98% by mass or less based on the mass of the electrolyte solution.

3. The secondary battery according to claim 1, characterized by The mass content of the chain carboxylic acid ester not containing fluorine is 17.3% by mass or more and 52.6% by mass or less based on the mass of the electrolyte solution.

4. The secondary battery according to claim 1, characterized by The inorganic additive is selected from at least one of aluminum oxide, aluminum hydroxide, boehmite, magnesium oxide, magnesium hydroxide, titanium dioxide, zirconium dioxide, niobium monoxide, niobium dioxide, di-niobium trioxide, di-niobium pentoxide, di-indium trioxide, tungsten trioxide, tin dioxide, zinc oxide, or di-antimony trioxide.

5. The secondary battery according to any one of claims 1 to 4, characterized by The chain carboxylic acid ester not containing fluorine is selected from at least one of methyl acetate, ethyl acetate, n-propyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, methyl pivalate, ethyl pivalate, n-propyl pivalate, methyl acrylate, ethyl acrylate, n-propyl acrylate, methyl methacrylate, ethyl methacrylate, or n-propyl methacrylate.

6. The secondary battery according to any one of claims 1 to 4, characterized by The mass content of the vinylsulfate is 0.01% by mass or more and 1.67% by mass or less based on the mass of the electrolyte solution; or, the mass content of the lithium difluorophosphate is 0.01% by mass or more and 1.95% by mass or less based on the mass of the electrolyte solution.

7. The secondary battery according to any one of claims 1 to 4, characterized by The electrolyte further includes: other additives; the other additives include: at least one of 1,2-bis(difluorophosphoryl)ethane, a compound of formula 1, a compound of formula 2, vinylene carbonate, lithium fluorosulfonate, butanedinitrile, hexanedinitrile, 1,3,6-hexanetrinitrile, 1,2,3-tris(2-cyanoethoxy)propane, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilyl)phosphate, or tris(trimethylsilyl)borate; The mass content of the other additive is 0.5% by mass or more and 7% by mass or less based on the mass of the electrolyte solution.

8. The secondary battery according to any one of claims 1 to 4, characterized by One side of the current collector is provided with a tab, and the insulating layer is provided on the edge surface of the current collector having the tab side.

9. The secondary battery according to any one of claims 1 to 4, characterized by The secondary battery has a jelly-roll structure, and the insulating layer is provided on the surface of the current collector at the end of the length direction.

10. An electronic device, comprising: Comprising: The secondary battery according to any one of claims 1 to 9.