Secondary battery and electronic apparatus

Abstract

A secondary battery and an electronic apparatus. Specifically, the secondary battery comprises a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises: lithium cobalt oxide, a binder, and an inorganic additive. The electrolyte comprises: lithium difluorophosphate, a sulfur-oxygen double bond-containing compound and 1,2,3-tris(2-cyanoethoxy)propane. The present invention can not only improve penetration resistance and warping suppression of a positive electrode, but can also improve the service life and low-temperature direct-current resistance characteristics of a high-potential area of a secondary battery.

Description

Secondary batteries and electronic devices Technical Field

[0001] The present application relates to the field of energy storage, and in particular to a secondary battery and an electronic device. Background Art

[0002] The rapid development of electronic products such as smartphones, tablets, and smart wearables has placed higher demands on the service life and safety of secondary batteries, taking into account the varying usage times and operating temperatures of these products. The batteries for the new generation of high-end electronic products have been upgraded to high-voltage cells with a charge cutoff voltage of 4.4V. As the charge cutoff voltage increases, the battery's energy density significantly improves. However, in existing technologies, the cycling performance of high-voltage secondary batteries deteriorates as the secondary battery voltage increases. While using high-voltage cathode film-forming additives to improve cycling characteristics significantly impacts low-temperature performance.

[0003] Summary of the Invention

[0004] The embodiments of the present application solve the problems existing in the prior art to some extent by adjusting the composition of the positive electrode used in the secondary battery and the components in the electrolyte.

[0005] The inventors of this application discovered that the positive electrode includes lithium cobalt oxide, a binder and an inorganic additive, and the electrolyte includes lithium difluorophosphate, 1,3-propane sultone and 1,2,3-tris(2-cyanoethoxy)propane, which can not only improve the positive electrode's penetration resistance and warping suppression, but also improve the life of the secondary battery in the high potential region and the low-temperature DC resistance characteristics, thereby completing this application.

[0006] In a secondary battery whose positive electrode includes lithium cobalt oxide, a binder, and an inorganic additive, the electrolyte simultaneously contains (I) lithium difluorophosphate, (II) a sulfur-oxygen double bond compound, and (III) 1,2,3-tris(2-cyanoethoxy)propane. Based on the mass of the electrolyte, the total content of (I), (II), and (III) is greater than 1.71% by mass and less than 8.25% by mass. It is important that the content of (II) is greater than 0.01% by mass and less than 2.95% by mass. In particular, it is critical that the total content of (I) to (III) is set within a specific range, which is very critical for the stability of the positive electrode structure and significantly suppresses the increase in interface resistance under high voltage. This design can not only improve the positive electrode's penetration resistance and warping suppression, but also improve the life of the secondary battery in the high potential region and the low-temperature DC resistance characteristics.

[0007] In another aspect of the present application, the present application provides an electronic device, which includes the secondary battery described in the present application.

[0008] The present application uses a specific positive electrode composition and electrolyte combination, which can not only improve the positive electrode's penetration resistance and warping suppression, but also improve the life of the secondary battery in the high potential region and the low-temperature DC resistance characteristics.

[0009] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the following description through implementation of the embodiments of the present application. DETAILED DESCRIPTION

[0010] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the present application.

[0011] Unless expressly stated otherwise, the following terms used in this application have the meanings indicated below.

[0012] The present application uses a specific positive electrode composition and electrolyte combination, which can not only improve the positive electrode's penetration resistance and warping suppression, but also improve the life of the secondary battery in the high potential region and the low-temperature DC resistance characteristics.

[0013] In one embodiment, the present application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte as described below.

[0014] I. Electrolyte

[0015] The electrolyte used in the secondary battery of the present application includes an electrolyte and a solvent for dissolving the electrolyte. In some embodiments, the electrolyte of the present application includes (I) lithium difluorophosphate, (II) a sulfur-oxygen double bond compound, and (III) 1,2,3-tris(2-cyanoethoxy)propane.

[0016] When 1,2,3-tris(2-cyanoethoxy)propane is used to stabilize the surface structure of the positive electrode material, the film formed by 1,2,3-tris(2-cyanoethoxy)propane on the surface of the positive electrode material is relatively thick, especially in the presence of inorganic additives, which catalyzes the film formation of 1,2,3-tris(2-cyanoethoxy)propane, causing the film impedance to increase, affecting the life and low-temperature characteristics of the secondary battery. The inventors found that when the electrolyte also contains lithium difluorophosphate and a sulfur-oxygen double bond compound, the increase in the impedance of the film can be significantly suppressed, thereby not only improving the positive electrode's penetration resistance and warpage suppression, but also improving the life and low-temperature DC resistance characteristics of the secondary battery's high potential region.

[0017] Specifically, from the viewpoint of improving the positive electrode penetration resistance characteristics of the secondary battery, based on the mass of the electrolyte, the content of lithium difluorophosphate is 0.01% by mass or more, preferably 0.04% by mass or more, preferably 0.06% by mass or more, more preferably 0.08% by mass or more. In addition, as the upper limit of the content of lithium difluorophosphate, from the viewpoint of improving the low-temperature DC resistance, the content of lithium difluorophosphate is 2% by mass or less, preferably 1.8% by mass or less, more preferably 1.3% by mass or less, further preferably 1.1% by mass or less, and particularly preferably 0.9% by mass or less. When within the above range, it helps to further improve the low-temperature DC resistance.

[0018] In some embodiments, the additive comprises one or more compounds containing sulfur-oxygen double bonds. Examples of the compounds containing sulfur-oxygen double bonds may include, but are not limited to, one or more of the following: cyclic sulfates, chain sulfates, chain sulfonates, cyclic sulfonates, chain sulfites, and cyclic sulfites.

[0019] Examples of the cyclic sulfate may include, but are not limited to, one or more of the following: ethylene glycol sulfate, 1,2-propylene glycol sulfate, 1,3-propylene glycol sulfate, 1,2-butanediol sulfate, 1,3-butanediol sulfate, 1,4-butanediol sulfate, 1,2-pentanediol sulfate, 1,3-pentanediol sulfate, 1,4-pentanediol sulfate, 1,5-pentanediol sulfate, and the like.

[0020] Examples of the chain sulfate ester may include, but are not limited to, one or more of the following: dimethyl sulfate, ethyl methyl sulfate, diethyl sulfate, and the like.

[0021] Examples of the chain sulfonate may include, but are not limited to, one or more of the following: methyl fluorosulfonate, ethyl trifluoromethanesulfonate, methyl methanesulfonate, ethyl methanesulfonate, butyl dimethanesulfonate, methyl 2-(methylsulfonyloxy)propionate, and ethyl 2-(methylsulfonyloxy)propionate.

[0022] Examples of the cyclic sulfonate ester may include, but are not limited to, one or more of the following: 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 2-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1-propylene-1,3-sultone, 2-propylene-1,3-sultone, 1-fluoro-1-propylene-1,3-sultone, 2-fluoro-1-propylene-1,3-sultone, 3-fluoro-1-propylene-1,3-sultone, 1-Fluoro-2-propylene-1,3-sultone, 2-Fluoro-2-propylene-1,3-sultone, 3-Fluoro-2-propylene-1,3-sultone, 1-methyl-1-propylene-1,3-sultone, 2-methyl-1-propylene-1,3-sultone, 3-methyl-1-propylene-1,3-sultone, 1-methyl-2-propylene-1,3-sultone, 2-methyl-2-propylene-1,3-sultone, 3-methyl-2-propylene-1,3-sultone, 1,4-butanesultone, 1,5-pentanesultone, methylene methanedisulfonate and ethylene methanedisulfonate, etc.

[0023] Examples of the chain sulfite may include, but are not limited to, one or more of the following: dimethyl sulfite, ethyl methyl sulfite, diethyl sulfite, and the like.

[0024] Examples of the cyclic sulfite may include, but are not limited to, one or more of the following: 1,2-ethylene glycol sulfite, 1,2-propylene glycol sulfite, 1,3-propylene glycol sulfite, 1,2-butylene glycol sulfite, 1,3-butylene glycol sulfite, 1,4-butylene glycol sulfite, 1,2-pentanediol sulfite, 1,3-pentanediol sulfite, 1,4-pentanediol sulfite, 1,5-pentanediol sulfite, and the like.

[0025] The sulfur-oxygen double bond-containing compound may be one or more. Preferably, the compound is at least one of ethylene glycol sulfate, dimethyl sulfate, ethyl trifluoromethanesulfonate, 1,3-propane sultone, 1-methyl-1,3-propane sultone, 1-propylene-1,3-sultone, methylene methanedisulfonate, ethylene methanedisulfonate, diethyl sulfite, dimethyl sulfite, or 1,2-propylene glycol sulfite.

[0026] Specifically, from the perspective of improving the positive electrode penetration resistance, the content of the sulfur-oxygen double bond compound is 0.01% by mass or more, preferably 0.1% by mass or more, preferably 0.5% by mass or more, and more preferably 0.6% by mass or more, based on the mass of the electrolyte. In addition, as the upper limit of the content of the sulfur-oxygen double bond compound, from the perspective of improving the low-temperature DC resistance, the content of the sulfur-oxygen double bond compound is 2.95% by mass or less, preferably 2.6% by mass or less, more preferably 1.8% by mass or less, further preferably 1.3% by mass or less, and particularly preferably 1.2% by mass or less. When within the above range, it helps to further improve the low-temperature DC resistance.

[0027] Specifically, from the viewpoint of improving the high voltage cycle characteristics of the secondary battery, based on the mass of the electrolyte, the content of 1,2,3-tris(2-cyanoethoxy)propane is 0.5% by mass or more, preferably 1,2,3-tris(2-cyanoethoxy)propane has a content of 1.2% by mass or more, preferably 1.8% by mass or more, and more preferably 2.2% by mass or more. In addition, as the upper limit of the content of 1,2,3-tris(2-cyanoethoxy)propane, from the viewpoint of suppressing the increase in positive electrode penetration resistance, the content of 1,2,3-tris(2-cyanoethoxy)propane is 5% by mass or less, preferably 4.8% by mass or less, more preferably 4.5% by mass or less, further preferably 3.8% by mass or less, and particularly preferably 3.5% by mass or less. When within the above range, it helps to further suppress the increase in positive electrode penetration resistance.

[0028] Furthermore, from the viewpoint of improving low-temperature DC resistance, the total content of (I), (II) and (III) is 1.71% by mass or more, preferably 2.25% by mass or more, based on the mass of the electrolyte. Furthermore, from the viewpoint of improving electrochemical properties in a low-temperature environment, the upper limit of the total content of (I), (II) and (III) is 8.25% by mass or less, preferably 8.2% by mass or less, and preferably 7% by mass or less.

[0029] In some embodiments, the combined content of (I), (II), and (III) is a mass %, where a is 1.71, 2.14, 2.58, 3.2, 3.4, 4.51, 5.2, 7, 7.8, 8.25, or within a range consisting of any two of these values. When within this range, the low-temperature DC resistance is further improved.

[0030] In addition, the electrolyte may further include a first compound, such as 1,2-bis(difluorophosphine)ethane, fluoroethylene carbonate, vinylene carbonate, lithium fluorosulfonate, succinonitrile, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilyl)phosphate or at least one of tris(trimethylsilyl)borate. The inventors also unexpectedly discovered that the first compound can improve the stability of the aforementioned film at high voltage and increase the ion conductivity rate of lithium ions, thereby further improving the low-temperature DC resistance characteristics. The above-mentioned first compound may be only one or more than two.

[0031] Specifically, from the perspective of improving the conduction of lithium ions in the aforementioned coating, the content of the first compound is 0.01% by mass or more, preferably 0.1% by mass or more, preferably 0.3% by mass or more, and more preferably 0.5% by mass or more, based on the mass of the electrolyte. In addition, as the upper limit of the content of the first compound, from the perspective of improving low-temperature DC resistance, the content of the first compound is 10% by mass or less, preferably 9% by mass or less, more preferably 8% by mass or less, further preferably 7% by mass or less, and particularly preferably 5% by mass or less. When within the above range, it helps to further improve the low-temperature DC resistance characteristics.

[0032] In some embodiments, the electrolyte is not particularly limited, and any substance known as an electrolyte can be used arbitrarily. The quality of the electrolyte is not particularly limited, as long as it does not damage the effect of the present application. For example, the lithium salt used in the electrolyte of the present application includes lithium hexafluorophosphate, and the content of lithium hexafluorophosphate is 9 to 15% by mass based on the mass of the electrolyte, preferably 9 to 13% by mass, and more preferably 9 to 12% by mass. By setting it to the above content range, the life of the high potential region and the low-temperature DC resistance characteristics can be improved in a more balanced manner.

[0033] In some embodiments, the electrolyte further comprises any non-aqueous solvent known in the art as a solvent for the electrolyte. In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, linear carbonates, cyclic carboxylates, linear carboxylates, cyclic ethers, linear ethers, phosphorus-containing organic solvents, and sulfur-containing organic solvents.

[0034] II. Positive electrode

[0035] The positive electrode includes a positive electrode current collector and a positive electrode mixture layer disposed on the surface of the positive electrode current collector. The positive electrode mixture layer contains a positive electrode active material, and the positive electrode mixture layer can be one or more layers. The positive electrode mixture layer includes a positive electrode active material layer, and optionally includes a primer layer or an edge layer. The primer layer is located between the current collector and the positive electrode active material layer, and the edge layer is disposed at the edge of the current collector and is parallel to the positive electrode active layer. The positive electrode active material is any substance that can reversibly insert and release lithium ions.

[0036] For example, as the positive electrode active material for a secondary battery, a composite metal oxide of lithium containing one or more selected from the group consisting of cobalt, manganese, and nickel, 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.

[0037] 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), LiNi 1 / 2 Mn 3 / 2 O4, LiFePO4, LiMnPO4, and LiMn 1-x FexPO4 (0.01 < x < 1), and more preferably two or more. A part of these composite metal oxides of lithium or lithium-containing olivine-type phosphates can be substituted with other elements. For example, 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 or carbon material containing these elements.

[0038] For example, the positive electrode contains lithium cobaltate having a first element. The first element includes at least one of a lanthanum element, a yttrium element, a cerium element, a tungsten element, or a strontium element. From the viewpoint of improving the high-temperature cycle characteristics of the lithium ion battery, based on the mass of lithium cobaltate, the content of any one of the first elements is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and still more preferably 0.05% by mass or more. In addition, as the upper limit of the content of the first element, the content of any one of the first elements is 1% by mass or less, preferably 0.5% by mass or less, more preferably 0.3% by mass or less, further preferably 0.15% by mass or less, and particularly preferably 0.1% by mass or less.

[0039] As the voltage during charging, from the viewpoint of increasing the 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.

[0040] The conductive agent of the positive electrode is not particularly limited as long as it is an electron-conducting material that does not cause chemical changes. Examples include graphites such as natural graphite (e.g., flaky graphite) or artificial graphite, and carbon blacks such as acetylene black, Ketjen black, channel black, furnace black, lamp black, or thermal black. In addition, graphite and carbon black may be appropriately mixed for use. The amount of the conductive agent added to the positive electrode mixture is preferably 1 to 10% by mass, particularly preferably 1.5 to 5% by mass.

[0041] The positive electrode binder includes at least one of polyvinylidene fluoride, polyacrylonitrile, or polyacrylic acid. From the perspective of improving the positive electrode's penetration resistance and the high-temperature cycle stability of the secondary battery, polyacrylonitrile is preferred.

[0042] From the perspective of improving the positive electrode's penetration resistance and suppressing positive electrode warpage, the positive electrode binder may further include a dispersant, which includes at least one of triethylene glycol-di-methacrylate, triethylene glycol bis(2-ethylhexanoate), triethylene glycol-di-benzoate, di(2-(2-butoxyethoxy)ethyl) adipate, or tetraethylene glycol bis(2-ethylhexanoate). The dispersant, when combined with the components of the positive electrode and the electrolyte of the present application, is also beneficial for improving the positive electrode's penetration resistance and suppressing positive electrode warpage.

[0043] From the perspective of improving the positive electrode's penetration resistance and suppressing positive electrode warpage, the inorganic additives contained in the positive electrode include at least one of aluminum, magnesium, titanium, zirconium, niobium, indium, tungsten, tin, zinc, and antimony.

[0044] Specifically, the inorganic additive may be at least one of an inorganic metal oxide and an inorganic metal hydroxide, such as 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.

[0045] The inorganic additive may be included in any one or more of the active material layer, the undercoat layer, or the edge layer. From the perspective of improving battery life, it is preferably included in the edge layer; from the perspective of suppressing positive electrode warping, it is preferably included in the undercoat layer.

[0046] There are three ways to make the positive electrode:

[0047] Method 1: Inorganic additives are included in the active material layer

[0048] The above-mentioned positive electrode active material, inorganic additives, conductive agents such as acetylene black and carbon black, and binders such as polyvinylidene fluoride or polyacrylonitrile are mixed, and a high-boiling point solvent such as 1-methyl-2-pyrrolidone is added and kneaded to form a slurry, which is then coated on an aluminum foil of a current collector, dried, and pressed to form a positive electrode.

[0049] Method 2: Inorganic additives are included in the base coat

[0050] Inorganic additives are mixed with conductive agents such as acetylene black and carbon black, and binders such as polyvinylidene fluoride or polyacrylonitrile, deionized water is added and mixed evenly to form a slurry, which is then coated on the aluminum foil of the current collector and dried to form a primer layer.

[0051] The above-mentioned positive electrode active material is mixed with a conductive agent such as acetylene black, carbon black, and a binder such as polyvinylidene fluoride or polyacrylonitrile, and a high-boiling point solvent such as 1-methyl-2-pyrrolidone is added and kneaded to form a slurry, which is then applied to a primer layer, dried, and pressed to form a positive electrode.

[0052] Method 3: Inorganic additives are included in the edge layer

[0053] An inorganic additive is mixed with a conductive agent such as acetylene black, carbon black, and a binder such as polyvinylidene fluoride or polyacrylonitrile, and deionized water is added thereto and mixed evenly to prepare a slurry 1.

[0054] The above-mentioned positive electrode active material is mixed with a conductive agent such as acetylene black or carbon black, and a binder such as polyvinylidene fluoride or polyacrylonitrile, and a high boiling point solvent such as 1-methyl-2-pyrrolidone is added thereto and kneaded to prepare slurry 2 .

[0055] Slurry 1 and slurry 2 are coated in parallel on the aluminum foil of the current collector, with slurry 1 located at one or two outer edges of slurry 2 (along the coating direction), and then dried and pressed to form a positive electrode.

[0056] The density of the positive electrode excluding the current collector is usually 3.5 g / cm 3 In order to further increase the capacity of the battery, it is preferably 3.8 g / cm 3 More than 4 g / cm 3 More preferably, 4.1 g / cm 3 In addition, as its upper limit, it is preferably 4.6 g / cm 3 the following.

[0057] The type of positive electrode current collector is not particularly limited and can be any known material suitable for use as a positive electrode current collector. Examples of positive electrode current collectors include, but are not limited to, metal 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 metal material. In some embodiments, the positive electrode current collector is aluminum.

[0058] III. Negative electrode

[0059] The negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on a surface of the negative electrode current collector. The negative electrode mixture layer contains a negative electrode active material. In some embodiments, the charge 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.

[0060] The negative electrode active material is not particularly limited, and examples thereof include carbon-based negative electrode active materials, metal-based negative electrode active materials, and negative electrode active materials obtained by combining these.

[0061] Carbon-based negative electrode active materials

[0062] Here, the carbon-based negative electrode active material refers to an active material having a carbon-based skeleton that can insert lithium. Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite materials.

[0063] Examples of carbonaceous materials include easily graphitized carbon and non-graphitizable carbon having an amorphous structure, such as glassy carbon. Examples of easily graphitized carbon include carbon materials obtained from petroleum or coal using tar pitch as a raw material. Specific examples include coke, mesocarbon microbeads (MCMB), mesophase pitch-based carbon fibers, and pyrolysis vapor-grown carbon fibers. Examples of non-graphitizable carbon include phenolic resin sintered bodies, polyacrylonitrile-based carbon fibers, quasi-isotropic carbon, furfuryl alcohol resin sintered bodies (PFA), and hard carbon.

[0064] Furthermore, examples of graphite materials include natural graphite and artificial graphite. Examples of artificial graphite include artificial graphite obtained by heat-treating carbon containing graphitized carbon at 2800°C or higher, graphite MCMB obtained by heat-treating MCMB at 2000°C or higher, and graphite mesophase pitch-based carbon fibers obtained by heat-treating mesophase pitch-based carbon fibers at 2000°C or higher. Furthermore, in the present application, natural graphite (amorphous-coated natural graphite) at least a portion of its surface is coated with amorphous carbon may be used as the carbon-based negative electrode active material.

[0065] In addition, the metal-based negative electrode active material is an active material containing a metal, generally referring to an active material having an element capable of inserting lithium or alloying with lithium in the structure, an element inserted into lithium or alloyed with lithium, and a theoretical current capacity of 500 mAh / g or more per unit mass. As a metal-based negative electrode active material, for example, lithium metal, a single metal that can form a lithium alloy (such as Ag, Al, Ba, Bi, Cu, Ga, Ge, In, Ni, P, Pb, Sb, Si, Sn, Sr, Zn, Ti, etc.) and its alloys, and their oxides, sulfides, nitrides, silicides, carbides, phosphides, etc. can be used. Among them, as a metal-based negative electrode active material, an active material containing silicon (silicon-based negative electrode active material) is preferably used. This is because the use of a silicon-based negative electrode active material can increase the capacity of the secondary battery.

[0066] Examples of silicon-based negative electrode active materials include silicon (Si), alloys containing silicon, SiO, and SiO. x , a composite of silicon-containing material and conductive carbon in which a silicon-containing material is coated or composited with conductive carbon.

[0067] From the viewpoint of improving battery capacity, silicon-carbon materials, for example, porous carbon-supported silicon composite materials are preferred.

[0068] The negative electrode active material may be used alone or in combination of two or more at any ratio.

[0069] The volume average particle size of the negative electrode active material is preferably 1 μm or greater, more preferably 5 μm or greater, and preferably 30 μm or less, more preferably 20 μm or less. If the volume average particle size of the negative electrode active material is above the lower limit, heat generation during internal short circuits can be effectively suppressed. If the volume average particle size of the negative electrode active material is below the upper limit, an increase in the initial resistance of the resulting battery can be effectively suppressed.

[0070] The negative electrode mixture layer may further include a negative electrode binder. The negative electrode binder can improve the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. The type of negative electrode binder is not particularly limited, as long as it is a material that is 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, fluororesins, polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. When an aqueous solvent is used to prepare the negative electrode mixture slurry, the negative electrode binder includes, but is not limited to, carboxymethyl cellulose (CMC) or its salt, styrene-butadiene rubber (SBR), polyacrylic acid (PAA) or its salt, polyvinyl alcohol, and the like.

[0071] As a current collector for retaining the negative electrode active material, any known current collector can be used. Examples of negative electrode current collectors include, but are not limited to, metal materials such as copper, nickel, stainless steel, and nickel-plated steel. In some embodiments, the negative electrode current collector is copper.

[0072] The negative electrode can be prepared by applying a negative electrode mixture slurry containing a negative electrode active material, a resin binder, etc. on a negative electrode current collector, drying it, and then rolling it to form a negative electrode mixture layer on both sides of the negative electrode current collector.

[0073] IV. Isolation membrane

[0074] To prevent short circuits, a separator is usually provided between the positive electrode and the negative electrode. In this case, the electrolyte of the present application is usually used by permeating the separator.

[0075] There is no particular restriction on the material and shape of the isolation membrane, as long as the effect of the present application is not significantly impaired. The isolation membrane may be a resin, glass fiber, inorganic substance, etc. formed of a material that is stable to the electrolyte of the present application. In some embodiments, the isolation membrane includes a porous sheet or a non-woven fabric-like material with excellent liquid retention. Examples of materials for resin or glass fiber isolation membranes 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 materials of the above-mentioned isolation membranes can be used alone or in any combination.

[0076] The isolation film may also be a material formed by laminating the above materials, and examples thereof include, but are not limited to, a three-layer isolation film formed by laminating polypropylene, polyethylene, and polypropylene in this order.

[0077] Examples of inorganic materials include, but are not limited to, oxides such as aluminum oxide and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates (e.g., barium sulfate, calcium sulfate, etc.) The inorganic material may be in the form of, but is not limited to, particles or fibers.

[0078] The separator may be in the form of a thin film, examples of which include, but are not limited to, nonwoven fabrics, woven fabrics, and microporous membranes. In the thin film form, the separator has a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. In addition to the aforementioned standalone thin film separators, separators may also be used: separators formed by forming a composite porous layer containing the aforementioned inorganic particles on the surface of the positive and / or negative electrode using a resin binder. For example, a separator formed by forming a porous layer of aluminum oxide particles, 90% of which have a particle size of less than 1 μm, on both sides of the positive electrode using a fluororesin as a binder.

[0079] 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 range, insulation and mechanical strength can be ensured, and the DC resistance characteristics and energy density of the secondary battery can be ensured.

[0080] The present application further provides an electronic device, which includes the secondary battery according to the present application.

[0081] The use of the secondary battery of the present 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 the present application can be used for, but not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

[0082] The preparation of a secondary battery is described below with reference to specific embodiments. Those skilled in the art will understand that the preparation method described in this application is only an example, and any other suitable preparation method is within the scope of this application.

[0083] Example

[0084] Examples of the secondary battery of the present application are shown below, but the present application is not limited to these examples.

[0085] Production of secondary batteries

[0086] Production of positive electrode:

[0087] Method 1: Inorganic additives are included in the active material layer

[0088] A positive electrode slurry was prepared by mixing 97% of the positive electrode active material listed in Table 1-1, 0.5% of the inorganic additive listed in Table 1-1, and 1.0% of acetylene black. The mixture was then added to a solution prepared by dissolving 1.5% of the binder listed in Table 1-1 in 1-methyl-2-pyrrolidone. The mixture was then applied to both sides of aluminum foil, dried, pressurized, and cut to the desired size to produce the positive electrode.

[0089] Method 2: Inorganic additives are included in the base coat

[0090] Mix 65% by mass of the inorganic additive in Table 1-1, 20% by mass of acetylene black, and 15% by mass of the binder in Table 1-1 (if a dispersant is used, adjust the ratio to 12% by mass of the binder and 3% by mass of the dispersant in Table 1-1), add deionized water and mix evenly, make a slurry, apply it on both sides of the aluminum foil, and dry it to form a primer layer.

[0091] A positive electrode slurry was prepared by mixing 97% by mass of the positive electrode active material listed in Table 1-1 with 1.5% by mass of acetylene black. This mixture was then added to a solution prepared by dissolving 1.5% by mass of the binder listed in Table 1-1 in 1-methyl-2-pyrrolidone. This slurry was applied to the surface of the undercoat layer, dried, pressurized, and then cut to a desired size to produce the positive electrode.

[0092] Method 3: Inorganic additives are included in the edge layer

[0093] Mix 65 mass% of the inorganic additives in Table 1-1, 20 mass% of acetylene black, and 15 mass% of the binder in Table 1-1 (if a dispersant is used, adjust the amount to 12 mass% of the binder and 3 mass% of the dispersant in Table 1-1), add deionized water and mix evenly to form a positive electrode slurry 1, apply it to the edge of the aluminum foil with the pole ear side, dry it, and form an edge layer.

[0094] The positive electrode active material (97% by mass) and acetylene black (1.5% by mass) listed in Table 1-1 were mixed and added to a solution prepared by dissolving 1.5% by mass of the binder (1.5% by mass) listed in Table 1-1 in 1-methyl-2-pyrrolidone. This mixture was mixed to prepare positive electrode slurry 2. Slurries 1 and 2 were applied parallel to each other on aluminum foil, with slurry 1 positioned at the outer edge of slurry 2 (along the direction of the applied foil). After drying and pressurizing, the slurry was cut to the specified size to produce the positive electrode.

[0095] Negative electrode production:

[0096] A negative electrode paste was prepared by mixing 96% artificial graphite and 96% silicon carbon (90:10 mass ratio) with 2% styrene-butadiene rubber as the negative electrode active materials. This paste was then added to a solution of 2% lithium carboxymethyl cellulose dissolved in deionized water. This paste was then applied to one side of a copper foil (current collector), dried, pressurized, and cut to the desired size to produce the negative electrode.

[0097] Battery production:

[0098] The positive electrode and negative electrode prepared as above are each connected to a wire. The layers are stacked via a polypropylene porous membrane having a thickness of 10 μm to obtain a laminate. In addition, LiPF6 as a supporting electrolyte is dissolved in a solution comprising (I) lithium difluorophosphate, (II) a sulfur-oxygen double bond compound and (III) 1,2,3-tris(2-cyanoethoxy)propane and propyl propionate, ethyl propionate, ethylene carbonate and propylene carbonate (mass ratio 2.3:2:1.2:0.9). Based on 100 parts by mass of the total mass of the non-aqueous electrolyte, the contents and components of (I) to (III) and the first compound are as shown in Table 1-2, and the content of LiPF6 is 14%.

[0099] The stacked body was then placed in an aluminum laminate case along with 3.2g of electrolyte. The opening of the case was heat-sealed, and the battery was completed through formation and capacity testing. This secondary battery was in the form of a bag, 35mm wide, 48mm high, and 5mm thick.

[0100] Tables 1-1 and 1-2 show the positive electrode active material, inorganic additives, binder, and electrolyte component codes of the prepared secondary batteries. The positive electrode active material is lithium cobalt oxide containing the first element, and the mass content of the first element is calculated based on the mass of the positive electrode active material.

[0101] The abbreviation code of polyvinylidene fluoride is PVDF, the abbreviation of polyacrylonitrile is PAN, and the abbreviation of polyacrylic acid is PAA;

[0102] Dispersants: triethylene glycol-di-methacrylate code A1, triethylene glycol bis(2-ethylhexanoate code A2, triethylene glycol-di-benzoate code A3, di(2-butoxyethoxyethyl) adipate code A4, tetraethylene glycol-di-2-ethylhexanoate code A5.

[0103] Table 1-1 Positive electrode

[0104] The values ​​in the above table are all in mass %

[0105] Table 1-2 Electrolyte

[0106] The values ​​in () in the above table are all mass %

[0107] The abbreviations in the above table represent the following substances:

[0108] Test Method

[0109] Positive electrode penetration resistance

[0110] The prepared positive electrode was immersed in an electrolyte solution at a temperature of 60°C. After 12 hours, the immersed positive electrode was removed, appropriately cleaned with diethyl carbonate (DEC), and gently wiped with a tissue. In addition, as the electrolyte, a solution prepared by dissolving LiPF6 at a concentration of 14% by mass in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a ratio of EC:EMC = 3:7 (mass ratio at 25°C) was used.

[0111] The positive electrode was then clamped with a gold-plated fixture and pressed at 10 MPa. Using the terminals attached to the gold-plated fixture and a multichannel potentiostat, the voltage was measured when a current of 10 mA was passed. The voltage was read after 10 minutes. The volume resistivity (ρ) (Ω·cm) was calculated based on the calculated resistance value and the thickness and area of ​​the positive electrode, and evaluated using the following criteria. A lower volume resistivity (ρ) indicates lower penetration resistance.

[0112] A: Volume resistivity ρ is less than 90Ω·cm;

[0113] B: Volume resistivity ρ is 90 Ω·cm or more and less than 180 Ω·cm;

[0114] C: Volume resistivity ρ is 180 Ω·cm or more and less than 270 Ω·cm;

[0115] D: Volume resistivity ρ is 270 Ω·cm or more.

[0116] Positive electrode warpage suppression

[0117] A narrow strip with a size of 2 cm in width (coating width direction) × 5 cm in length (coating direction) was cut from the positive electrode as a test piece. The test piece was placed on a horizontal plane with the positive electrode total layer side facing downward. Then, a laser displacement meter (Keyence Corporation "LJV-7080") was used to measure the height (warping amount) of the width end of the test piece from the horizontal plane when the center of the width direction of the two ends of the length direction of the test piece was pressed from above to the horizontal plane, and the evaluation was performed according to the following benchmarks. The smaller the warping amount, the more the warping of the positive electrode can be suppressed.

[0118] A: The warpage is less than 1.2mm;

[0119] B: Warpage is greater than 1.2mm and less than 1.6mm;

[0120] C: Warpage is greater than 1.6mm and less than 2mm;

[0121] D: The warping is greater than 2 mm, or the positive electrode mixture layer has cracks.

[0122] High potential life characteristics

[0123] For the secondary battery produced, the operation of charging to 4.7V at 0.2C and discharging to 3.0V was repeated three times at 25°C. Subsequently, the operation of charging at 1C until the battery voltage reached 4.7V and discharging at 1C until the battery voltage reached 3.0V was repeated 100 times at 45°C. The ratio of the discharge capacity at the 100th discharge to the discharge capacity at the first discharge was then calculated and evaluated according to the following criteria. The larger the discharge capacity ratio, the better the high-potential life characteristics.

[0124] A: Ratio is more than 85%;

[0125] B: The ratio is 80% or more and less than 85%;

[0126] C: Ratio is 75% or more and less than 80%;

[0127] D: The ratio is 70% or more and less than 75%;

[0128] E: ratio is less than 70%.

[0129] Low temperature DC resistance characteristics

[0130] The prepared secondary battery was charged at 140 mA at 25°C to a 50% state of charge (SOC). It was then discharged at 140 mA for 20 seconds and charged at 140 mA for 20 seconds at -20°C. The voltage change during discharge was recorded as ΔV0.2. The same test was then repeated at 350 mA, 700 mA, and 1050 mA to determine ΔV0.5, ΔV1.0, and ΔV1.5.

[0131] Next, a graph was drawn with the discharge current value on the X-axis and ΔV on the Y-axis to find an approximate straight line passing through the intercept zero point. The slope of the approximate straight line was used as the direct current resistance (DCR), and the evaluation was performed according to the following criteria.

[0132] A: DCR is less than 0.5Ω;

[0133] B: DCR is greater than 0.5Ω and less than 0.8Ω;

[0134] C: DCR is greater than 0.8Ω and less than 1.2Ω;

[0135] D: DCR is 1.2Ω or more.

[0136] Test results

[0137] Table 2-1

[0138] Table 2-2

[0139] Table 2-3

[0140] In a secondary battery whose positive electrode includes lithium cobalt oxide, a binder, and an inorganic additive, the electrolyte simultaneously contains (I) lithium difluorophosphate, (II) a sulfur-oxygen double bond compound and (III) 1,2,3-tris(2-cyanoethoxy)propane, and the total content of (I), (II) and (III) is greater than 1.71 mass% and less than 8.25 mass%; the total content of the sulfur-oxygen double bond compound is greater than 0.01 mass% and less than 2.95 mass%, which is very critical to the stability of the positive electrode structure and significantly suppresses the increase in interface resistance under high voltage. This design can not only improve the positive electrode's penetration resistance and warping suppression, but also improve the life of the secondary battery in the high potential region and the low-temperature DC resistance characteristics.

[0141] When the positive electrode binder further includes triethylene glycol-di-methacrylate, triethylene glycol bis(2-ethylhexanoate), triethylene glycol-di-benzoate, di(2-butoxyethoxyethyl) adipate or tetraethylene glycol-di-2-ethylhexanoate, the secondary battery performance can be further improved.

[0142] When the electrolyte further contains a first compound such as 1,2-bis(difluorophosphine)ethane, fluoroethylene carbonate, vinylene carbonate, lithium fluorosulfonate, succinonitrile, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilyl)phosphate, and tris(trimethylsilyl)borate, further improved lifespan in the high potential region and low-temperature DC resistance characteristics are obtained.

[0143] References throughout the specification to “an embodiment,” “some embodiments,” “one embodiment,” “another example,” “an example,” “a specific example,” or “a portion of an example” mean that at least one embodiment or example in the present application includes the specific features, structures, materials, or characteristics described in that embodiment or example. Therefore, descriptions appearing throughout the specification, such as, for example, “in some embodiments,” “in an embodiment,” “in one embodiment,” “in another example,” “in an example,” “in a specific example,” or “an example,” are not necessarily references to the same embodiment or example in the present application. In addition, the specific features, structures, materials, or characteristics in the present application may be combined in any suitable manner in one or more embodiments or examples.

[0144] Although illustrative embodiments have been shown and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions, and modifications may be made to the embodiments without departing from the spirit, principles, and scope of the present application.

Claims

1. A secondary battery comprising: A positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode comprises lithium cobalt oxide, a binder, and an inorganic additive, and the metal element in the inorganic additive comprises at least one of aluminum, magnesium, titanium, zirconium, niobium, indium, tungsten, tin, zinc, or antimony; The electrolyte contains (I) lithium difluorophosphate, (II) a sulfur-oxygen double bond compound, and (III) 1,2,3-tris(2-cyanoethoxy)propane, wherein the total content of (I), (II), and (III) is greater than or equal to 1.71% by mass and less than or equal to 8.25% by mass based on the mass of the electrolyte; and the content of the sulfur-oxygen double bond compound is greater than or equal to 0.01% by mass and less than or equal to 2.95% by mass. 2 . The secondary battery according to claim 1 , wherein the total content of (I), (II) and (III) is 1.98 mass % or more and 5.8 mass % or less. 3 . The secondary battery according to claim 1 , wherein the total content of (I), (II) and (III) is 3.2% by mass or more and 7.8% by mass or less. 4 . The secondary battery according to claim 1 , wherein the binder comprises at least one of polyvinylidene fluoride, polyacrylonitrile, or polyacrylic acid.

5. The secondary battery according to claim 1, wherein the binder further comprises a dispersant, the dispersant comprising at least one of triethylene glycol-di-methacrylate, triethylene glycol bis(2-ethylhexanoate), triethylene glycol-di-benzoate, di(2-(2-butoxyethoxy)ethyl)adipate, or tetraethylene glycol bis(2-ethylhexanoate). 6 . The secondary battery according to claim 1 , wherein the sulfur-oxygen double bond-containing compound is at least one selected from cyclic sulfate, chain sulfate, chain sulfonate, cyclic sulfonate, chain sulfite, or cyclic sulfite.

7. The secondary battery according to any one of claims 1 to 5, wherein the sulfur-oxygen double bond-containing compound is at least one selected from the group consisting of ethylene glycol sulfate, dimethyl sulfate, ethyl trifluoromethanesulfonate, 1,3-propane sultone, 1-methyl-1,3-propane sultone, 1-propylene-1,3-sultone, methylene methanedisulfonate, ethylene methanedisulfonate, diethyl sulfite, dimethyl sulfite, and 1,2-propylene glycol sulfite.

8. The secondary battery according to any one of claims 1 to 5, wherein the mass of the lithium difluorophosphate is 0.01 mass % or more and 2 mass % or less based on the mass of the electrolyte; The mass of the sulfur-oxygen double bond compound is greater than or equal to 0.1 mass % and less than or equal to 1.8 mass % based on the mass of the electrolyte; The mass of the 1,2,3-tris(2-cyanoethoxy)propane is 0.5 mass % or more and 5 mass % or less based on the mass of the electrolyte solution.

9. The secondary battery according to any one of claims 1 to 5, wherein The electrolyte further includes a first compound, the first compound including at least one of 1,2-bis(difluorophosphine)ethane, fluoroethylene carbonate, vinylene carbonate, lithium fluorosulfonate, succinonitrile, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilyl)phosphate, or tris(trimethylsilyl)borate.

10. The secondary battery according to any one of claims 1 to 5, wherein the lithium cobalt oxide includes a first element, the first element including at least one of lanthanum, yttrium, cerium, tungsten, or strontium; and a content of any one of the first elements is greater than or equal to 0.01% by mass and less than or equal to 1% by mass based on the mass of the lithium cobalt oxide.

11. The secondary battery according to any one of claims 1 to 5, wherein The positive electrode includes a primer layer and an active material layer disposed on a current collector, and the inorganic additive is contained in the active material layer or the primer layer.

12. The secondary battery according to any one of claims 1 to 5, wherein The positive electrode includes an edge layer and an active material layer disposed on a current collector, and the inorganic additive is contained in the edge layer. 13 . An electronic device comprising the secondary battery according to claim 1 .

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