Secondary battery and electronic device

Abstract

Provided is a secondary battery, comprising a positive electrode, a negative electrode and an electrolyte. The negative electrode comprises a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. The negative electrode mixture layer comprises graphite and a silicon-based material. The electrolyte comprises ethylene sulfate, 1,2,3-tris(2-cyanoethoxy)propane, and a nitrogen-containing lithium salt. The design can not only suppress lithium metal deposition and internal residual gas in secondary batteries, but also significantly improve the low-temperature cycle characteristics.

Description

Secondary batteries and electronic devices

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on April 1, 2024, with application number 202410384211.3 and invention name “Secondary Battery and Electronic Device”, the entire contents of which are incorporated by reference into this application. Technical Field

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

[0003] With the rapid development and continued growth of the new energy vehicle industry, the development of high-power, high-capacity, and highly safe battery systems is urgently needed. Silicon-based anode materials have garnered widespread attention and research due to their high theoretical specific capacity, low lithium insertion potential, abundant raw materials, non-toxicity, and environmental friendliness. They are expected to replace carbon anode materials as the next generation of high-performance lithium battery anode materials.

[0004] However, silicon-based anode materials experience significant volume expansion during repeated lithium insertion and removal, with volume changes reaching up to 400%. This leads to the fragmentation and pulverization of active particles, unstable and continuous growth of the surface SEI film structure, and severe electrode structural collapse. This rapidly degrades the electrochemical performance of the silicon anode, reducing battery capacity, cycle life, and coulombic efficiency. Furthermore, silicon's poor electrical conductivity increases internal resistance, significantly degrading battery cycle performance, especially at low temperatures. Summary of the Invention

[0005] The embodiments of the present application solve the problems existing in the prior art to some extent by adjusting the composition of the negative electrode and the components in the electrolyte used in the secondary battery.

[0006] The inventors of this application discovered that the negative electrode mixture layer includes graphite and silicon-based materials, and the electrolyte includes vinyl sulfate, 1,2,3-tris(2-cyanoethoxy)propane and nitrogen-containing lithium salt. This design can not only inhibit the lithium metal precipitation and internal residual gas of the secondary battery, but also significantly improve the low-temperature cycle characteristics, thereby completing this application.

[0007] In a secondary battery using silicon-carbon material for the negative electrode, it is important that the electrolyte contains (I) vinyl sulfate, (II) 1,2,3-tris(2-cyanoethoxy)propane and (III) nitrogen-containing lithium salt at the same time. Based on the quality of the electrolyte, it is especially important that the total content of the three is set to a specific range. Although the reason for suppressing lithium metal precipitation and internal residual gas in the secondary battery is still unclear, it is believed that the components (I) to (III) form a stable coating on the surface of the negative electrode during charging in the first cycle, which not only suppresses the growth of lithium dendrites, but also suppresses the damage to the negative electrode by the electrolyte during the charge and discharge cycle, and reduces the consumption of active lithium by decomposition and regeneration of the coating. As a result, not only can the lithium metal precipitation and internal residual gas in the secondary battery be suppressed, but the low-temperature cycle characteristics can also be significantly improved.

[0008] In another aspect of the present application, the present application provides an electronic device, which includes the secondary battery described in the present application.

[0009] The present application uses a specific negative electrode structure and electrolyte combination. This design not only suppresses lithium metal precipitation and internal residual gas in the secondary battery, but also significantly improves the low-temperature cycle characteristics.

[0010] 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

[0011] 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.

[0012] Unless expressly stated otherwise, the following terms used in this application have the meanings indicated below.

[0013] The present application uses a specific negative electrode structure and electrolyte combination. This design not only suppresses lithium metal precipitation and internal residual gas in the secondary battery, but also significantly improves the low-temperature cycle characteristics.

[0014] In one embodiment, the present application provides a secondary battery comprising a positive electrode, a negative electrode, and an electrolyte as described below.

[0015] I. Electrolyte

[0016] 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 vinyl sulfate, 1,2,3-tris(2-cyanoethoxy)propane, and a nitrogen-containing lithium salt.

[0017] Since the film formed by vinyl sulfate on the surface of silicon-carbon material is unstable and prone to decomposition at low temperatures, the inventors found that when the electrolyte also contains 1,2,3-tris(2-cyanoethoxy)propane and nitrogen-containing lithium salts, the decomposition of the film can be significantly reduced, the lithium metal precipitation and internal residual gas of the secondary battery can be inhibited, and the low-temperature cycle characteristics can be significantly improved.

[0018] Specifically, from the viewpoint of improving lithium metal precipitation in lithium ion batteries, the content of vinyl sulfate is 0.01 mass % or more, preferably 0.03 mass % or more, preferably 0.05 mass % or more, and more preferably 0.07 mass % or more, based on the mass of the electrolyte.

[0019] Furthermore, from the viewpoint of suppressing internal residual gas, the upper limit of the vinyl sulfate content is 3% by mass or less, preferably 2.87% by mass or less, more preferably 2.11% by mass or less, further preferably 1.34% by mass or less, and particularly preferably 0.79% by mass or less.

[0020] In some embodiments, the vinyl sulfate content is set to a1% by mass, where a1 is 0.01, 0.03, 0.05, 0.07, 0.12, 0.16, 0.28, 0.35, 0.79, 1.34, 2.11, 2.87, or 3, or within a range consisting of any two of the foregoing values, for example, 0.01 to 0.07, 0.01 to 0.12, 0.03 to 0.35, 0.07 to 1.34, 0.05 to 0.28, 0.12 to 0.35, 0.16 to 1.34, 0.35 to 2.11, 0.79 to 2.87, or 0.12 to 3. When within the foregoing ranges, this helps further suppress internal residual gas.

[0021] Specifically, from the viewpoint of improving lithium metal precipitation in lithium ion batteries, the content of 1,2,3-tris(2-cyanoethoxy)propane is 0.3% by mass or more, preferably 0.6% by mass or more, preferably 0.8% by mass or more, and more preferably 1.2% by mass or more, based on the mass of the electrolyte.

[0022] Furthermore, from the viewpoint of suppressing internal residual gas, the upper limit of the content of 1,2,3-tris(2-cyanoethoxy)propane is 5% by mass or less, preferably 4.9% by mass or less, more preferably 4.2% by mass or less, further preferably 3.5% by mass or less, and particularly preferably 2.1% by mass or less.

[0023] In some embodiments, the content of 1,2,3-tris(2-cyanoethoxy)propane is set to a2% by mass, where a2 is 0.3, 0.6, 0.8, 1.2, 1.7, 1.9, 2.1, 3.5, 4.2, 4.9, or 5, or within a range consisting of any two of the foregoing values, for example, 0.3 to 1.9, 0.6 to 2.1, 0.8 to 3.5, 1.2 to 4.2, 1.7 to 4.9, or 1.2 to 5. When within the foregoing ranges, it helps to further suppress internal residual gas.

[0024] In some embodiments, the nitrogen-containing lithium salt includes LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethanedisulfonyl imide lithium, cyclic 1,3-perfluoropropanedisulfonyl imide lithium, LiN(CF3SO2)(C4F9SO2), 4,5-dicyano-2-trifluoromethylimidazole lithium salt, 4,5-dicyano-2-pentafluoroethylimidazole lithium salt, 2,4,5-tricyano At least one of tricyanobenzimidazole lithium salt, 5,6-dicyano-2-trifluoromethylbenzimidazole lithium salt, 5,6-dicyano-2-pentafluoroethylbenzimidazole lithium salt, 2,5,6-tricyanobenzimidazole lithium salt, 4,7-dicyano-2-trifluoromethylbenzimidazole lithium salt, 4,7-dicyano-2-pentafluoroethylbenzimidazole lithium salt, 2,4,7-tricyanobenzimidazole lithium salt, 4,5,6,7-tetracyano-2-trifluoromethylbenzimidazole lithium salt, 4,5,6,7-tetracyano-2-pentafluoroethylbenzimidazole lithium salt, and 2,4,5,6,7-pentacyanobenzimidazole lithium salt. Due to the excellent stability of the formed film, the battery performance is further improved. As (III) nitrogen-containing lithium salt, there can be only one kind or more than two kinds.

[0025] In some embodiments, the nitrogen-containing lithium salt is preferably at least one of LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, and LiN(C2F5SO2)2.

[0026] Specifically, from the viewpoint of improving lithium metal precipitation in lithium ion batteries, the content of the nitrogen-containing lithium salt is 0.2% by mass or more, preferably 0.6% by mass or more, preferably 0.8% by mass or more, and more preferably 1.1% by mass or more, based on the mass of the electrolyte.

[0027] In addition, as the upper limit of the content of the nitrogen-containing lithium salt, from the viewpoint of suppressing internal residual gas, the content of the nitrogen-containing lithium salt is 3 mass % or less, preferably 2.8 mass % or less, more preferably 2.4 mass % or less, further preferably 2.1 mass % or less, and particularly preferably 1.7 mass % or less.

[0028] In some embodiments, the content of the nitrogen-containing lithium salt is set to a3% by mass, where a3 is 0.2, 0.6, 0.7, 0.8, 1.1, 1.9, 2.1, 2.4, 2.8, 3, or within a range consisting of any two of the foregoing values, for example, 0.2 to 1.9, 0.6 to 3, 0.7 to 2.8, 0.8 to 2.1, 1.1 to 2.8, 0.2 to 1.1, or 0.2 to 0.8. When within the foregoing ranges, the precipitation of lithium metal is further improved.

[0029] Furthermore, from the viewpoint of suppressing internal residual gas, the total content of (I), (II) and (III) is 1.26% by mass or more, preferably 2.5% by mass or more, based on the mass of the electrolyte.

[0030] Furthermore, the upper limit of the total content of (I), (II), and (III) is 6.07 mass % or less, preferably 5.66 mass % or less, from the viewpoint of improving electrochemical characteristics in a low-temperature environment.

[0031] In some embodiments, the total content of (I), (II), and (III) is a mass % based on the mass of the electrolyte, and a is 1.26, 1.46, 1.86, 2.36, 2.56, 3.21, 3.55, 3.99, 4.16, 4.54, 5.31, 5.56, 5.66, 6.07, or within a range consisting of any two of the foregoing values, for example, 1.26 to 3.31, 1.46 to 3.55, 1.86 to 5.31, 2.36 to 5.66, 1.26 to 4.16, or 2.56 to 6.07. When within the foregoing ranges, it helps to further suppress internal residual gas.

[0032] In addition, the electrolyte may also include other nitrile compounds. The inventors have also unexpectedly discovered that other nitrile compounds can reduce the impedance of the aforementioned coating, enhance lithium ion charge transfer, and improve initial resistance and low-temperature performance.

[0033] Other nitrile compounds include at least one of succinonitrile, adiponitrile, ethylene glycol bis(propionitrile), 1,3,5-pentanetricarboxylic acid nitrile, 1,2,3-propanetricarboxylic acid nitrile, 1,2,6-hexanetricarboxylic acid nitrile, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane or 1,2,5-tris(cyanoethoxy)pentane.

[0034] The other nitrile compounds may be one or more, for example, succinonitrile and adiponitrile, or succinonitrile and ethylene glycol di(propionitrile) ether, or adiponitrile and ethylene glycol di(propionitrile) ether.

[0035] Specifically, from the viewpoint of improving lithium metal precipitation of lithium ion batteries, based on the mass of the electrolyte, the content of other nitrile compounds is 0.3% by mass or more, preferably the content of other nitrile compounds is 0.6% by mass or more, preferably 0.9% by mass or more, more preferably 1.4% by mass or more.

[0036] In addition, as the upper limit of the content of other nitrile compounds, from the viewpoint of suppressing internal residual gas, the content of other nitrile compounds is 8% by mass or less, preferably 7.9% by mass or less, more preferably 7.1% by mass or less, further preferably 6.2% by mass or less, and particularly preferably 5.3% by mass or less.

[0037] In some embodiments, the total content of other nitrile compounds is b% by mass, and b is 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.4, 1.5, 2, 2.5, 3, 3.5, 3.9, 4, 4.6, 5.3, 6.2, 7.1, 7.9, 8, or within a range consisting of any two of the above values, for example, 0.3 to 5.3, 0.6 to 4.6, 0.9 to 3.9, 0.4 to 2, 0.45 to 4.6, 0.8 to 2.5, 1.4 to 3.9, 2.5 to 8, 0.9 to 6.2, 0.45 to 5.3, or 0.6 to 1.4. When within the above ranges, it helps to further suppress internal residual gas.

[0038] In addition, the electrolyte may further include a first substance. The inventors have unexpectedly discovered that the first substance can inhibit the decomposition and regeneration of the aforementioned film during the charge and discharge process, thereby further improving the low-temperature performance.

[0039] The first substance includes at least one of lithium monofluorophosphate, lithium difluorophosphate, 1,2-bis(difluorophosphine)ethane, vinylene carbonate, lithium fluorosulfonate, 1,3-propane sultone, 1,3-propylene sultone, 1,3-propylene glycol cyclic sulfate, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilyl)phosphate, and tris(trimethylsilyl)borate.

[0040] The first substance may be one or more, including, for example, lithium monofluorophosphate and lithium difluorophosphate, lithium monofluorophosphate and lithium fluorosulfonate, lithium monofluorophosphate and 1,3-propane sultone, lithium fluorosulfonate and 1,3-propane sultone, lithium difluorophosphate and 1,3-propane sultone, tris(trimethylsilyl)phosphate and lithium difluorophosphate, or tris(trimethylsilyl)borate and lithium difluorophosphate.

[0041] Specifically, from the viewpoint of suppressing internal residual gas, based on the mass of the electrolyte, the content of the first substance is 0.3 mass % or more, preferably the content of the first substance is 0.6 mass % or more, preferably the content of the first substance is 0.9 mass % or more, preferably 1.6 mass % or more, and more preferably 2.8 mass % or more.

[0042] In addition, as the upper limit of the content of the first substance, from the viewpoint of suppressing internal residual gas, the content of the first substance is 10 mass % or less, preferably 9.7 mass % or less, more preferably 8.2 mass % or less, further preferably 7.1 mass % or less, and particularly preferably 6.7 mass % or less.

[0043] In some embodiments, the total content of the first substance is c mass %, and c is 0.3, 0.35, 0.4, 0.45, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.5, 1.6, 2, 2.5, 2.8, 3, 3.5, 3.9, 4, 4.5, 5, 5.5, 6, 6.5, 7.1, 7.5, 8.2, 8.6, 9, 9.3, 9.7, 10, or within a range consisting of any two of the above values, for example, 0.3 to 10, 0.45 to 7.5, 0.6 to 9.7, 5.5 to 9.7, 6 to 8.6, 2.8 to 6.5, 1 to 6.5, 0.7 to 7.1, 1.5 to 9.3, 0.45 to 3.9, or 0.7 to 4.5. When within the above ranges, it helps to further suppress internal residual gas.

[0044] In some embodiments, the electrolyte is not particularly limited, and any known electrolyte can be used. The quality of the electrolyte is not particularly limited as long as it does not impair the effects of the present application.

[0045] For example, the lithium salt used in the electrolyte of the present application includes lithium hexafluorophosphate, and the content of lithium hexafluorophosphate is 9-15% by mass, preferably 9-13% by mass, and more preferably 9-12% by mass, based on the mass of the electrolyte. By setting the content within this range, a more balanced improvement in lithium metal precipitation and improved low-temperature discharge characteristics can be achieved.

[0046] 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.

[0047] In some embodiments, the non-aqueous solvent includes, but is not limited to, one or more of the following: cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, cyclic ethers, chain ethers, phosphorus-containing organic solvents, and sulfur-containing organic solvents.

[0048] II. Negative Electrode

[0049] 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.

[0050] 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.

[0051] Carbon-based negative electrode active materials

[0052] Here, the carbon-based negative electrode active material refers to an active material having a carbon-based skeleton into which lithium can be inserted. Examples of the carbon-based negative electrode active material include carbonaceous materials and graphite materials.

[0053]

Carbonaceous materials

[0054] Examples of carbonaceous materials include easily graphitized carbon and non-graphitizable carbon having amorphous structures 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.

[0055]

Graphite material

[0056] 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.

[0057]

Metal-based negative electrode active materials

[0058] 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 a lithium-ion secondary battery.

[0059]

Silicon-based negative electrode active material

[0060] Examples of silicon-based negative electrode active materials, that is, silicon-based materials in this application, include silicon (Si), alloys containing silicon, SiO x (SiO x In the above, there is no special requirement for the value range of x, as long as it can constitute naturally existing or artificially synthesized silicon oxide, the value of x can be an integer value or a non-integer value, for example, the value range of x can be 1≤x<2), a composite of silicon-based material and conductive carbon formed by coating or compounding the silicon-based material with conductive carbon.

[0061] From the viewpoint of improving battery capacity, silicon-carbon materials, for example, porous carbon-supported silicon composite materials are preferred.

[0062] The negative electrode active material may be used alone or in combination of two or more at any ratio.

[0063] Volume average particle size of active substance

[0064] Here, 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, internal residual gas can be effectively suppressed. If the volume average particle size of the negative electrode active material is below the upper limit, lithium metal precipitation in the resulting battery can be effectively suppressed.

[0065] Weight per unit area of ​​negative electrode mixture layer

[0066] Specifically, from the viewpoint of improving electrochemical characteristics in a low-temperature environment, the mass per unit area of ​​the negative electrode mixture layer is 4.5 mg / cm 2 Above, preferably 5.1 mg / cm 2 Above, preferably 5.5 mg / cm 2 More than 6.2 mg / cm 2 above.

[0067] In addition, the upper limit of the mass per unit area of ​​the negative electrode mixture layer is 12.5 mg / cm from the viewpoint of suppressing internal residual gas. 2 Below, preferably 11.2 mg / cm 2 Below, more preferably 10.5 mg / cm 2 Below, more preferably 9.3 mg / cm 2 Below, particularly preferably 8.1 mg / cm 2 the following.

[0068] In some embodiments, the mass per unit area of ​​the negative electrode mixture layer is w mg / cm 2 , w is 4.5, 4.8, 5.1, 5.3, 5.5, 6.2, 7.8, 8.1, 9.3, 10.5, 11.2, 12.3, 12.5, or within a range consisting of any two of the above values, for example, 4.5 to 9.3, 4.8 to 12.3, 5.1 to 8.1, 5.3 to 10.5, 5.5 to 12.3, 6.2 to 11.2, 7.8 to 12.5, 8.1 to 10.5, 9.3 to 12.5, 5.3 to 9.3, 6.2 to 8.1. When within the above ranges, it helps to further suppress internal residual gas.

[0069] Furthermore, from the perspective of suppressing internal short-circuit heat generation, the aforementioned a / w is 0.2 or greater and 1.011 or less. In some embodiments, a / w is 0.2, 0.225, 0.35, 0.457, 0.488, 0.506, 0.544, 0.561, 0.617, 0.637, 0.673, 0.713, 0.868, 0.993, 1.011, or within a range consisting of any two of these values. For example, a / w is 0.2 to 0.713, 0.35 to 0.673, 0.457 to 0.993, 0.225 to 0.637, or 0.673 to 1.011. Within the above ranges, a / w further helps suppress internal residual gas.

[0070] The weight per unit area of ​​the negative electrode mixture layer is the mass of the negative electrode mixture layer (mg) relative to the area of ​​the negative electrode mixture layer (cm 2 ) ratio. The mass and area of ​​the negative electrode mixture layer are determined as follows: a test piece of appropriate size is cut from the negative electrode, and its area is measured as S1 and its mass as W0. The negative electrode current collector is then peeled from the negative electrode and its mass W1 is measured. The mass of the negative electrode mixture layer is calculated from (W0-W1): weight per unit area = (W0-W1) / S1. If the selected negative electrode has a double-sided mixture layer, the weight per unit area = (W0-W1) / (S1×2).

[0071] Examples of a method for peeling the negative electrode mixture layer include immersing the negative electrode mixture layer in a solvent capable of dissolving or swelling the negative electrode mixture layer, and wiping the negative electrode mixture layer with a cloth or the like.

[0072] The weight per unit area of ​​the negative electrode mixture layer can be adjusted using known methods. For example, when the negative electrode mixture layer is formed by coating, the weight can be adjusted by varying the solid content concentration of the coating solution used to form the negative electrode mixture layer, the number of coating passes, the gap between the coating liquid inlet of the coating machine, and the like. The weight per unit area of ​​the negative electrode mixture layer can be increased by increasing the solid content concentration, increasing the number of coating passes, or increasing the gap. The weight per unit area of ​​the negative electrode mixture layer can be decreased by decreasing the solid content concentration, reducing the number of coating passes, or decreasing the gap.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] III. Positive electrode

[0077] The positive electrode includes a positive electrode current collector and a positive electrode mixture layer disposed on a surface of the positive electrode current collector.

[0078] The positive electrode mixture layer contains a positive electrode active material, which can be one layer or multiple layers. The positive electrode active material is any substance that can reversibly intercalate and deintercalate lithium ions.

[0079] For example, as a positive electrode active material for lithium ion batteries, 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.

[0080] As such lithium composite metal oxides, suitable examples include 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), solid solution of Li2MnO3 and LiMO2 (M is a transition metal such as Co, Ni, Mn, Fe), LiNi 1 / 2 Mn3 / 2 One or more of 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 with lithium or olivine-type phosphates containing lithium can be substituted with other elements, or a part of cobalt, nickel, manganese, and iron can be substituted with one or two 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.

[0081] For example, the positive electrode contains lithium cobaltate having at least three elements among aluminum, magnesium, titanium, zirconium, lanthanum, iridium, cerium, and tungsten. From the viewpoint of improving the resistance characteristics during high-temperature storage of the lithium-ion battery, based on the mass of lithium cobaltate, the content of any one of the foregoing elements is preferably 0.01% by mass or more, preferably 0.03% by mass or more, more preferably 0.05% by mass or more. In addition, as the upper limit of the content of the foregoing element, the content of any one of the foregoing 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.

[0082] If a lithium composite metal oxide that operates at a high charging voltage is used, the electrochemical characteristics are likely to deteriorate in a high-temperature environment due to the reaction with the non-aqueous electrolyte during charging, but in the lithium-ion battery described in the present application, the deterioration of these electrochemical characteristics can be suppressed.

[0083] 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.

[0084] The conductive agent of the positive electrode is not particularly limited as long as it is an electron-conductive material that does not cause a chemical change. Examples include natural graphite (such as flake graphite), artificial graphite, etc., graphite, acetylene black, Ketjen black, channel black, furnace black, lamp black, or carbon black such as thermal cracking carbon black. In addition, graphite and carbon black can be appropriately mixed and used. The addition amount of the conductive agent in the positive electrode mixture is preferably 1 to 10% by mass, and particularly preferably 1.5 to 5% by mass.

[0085] [[ID=Z18]]The type of the binder of the positive electrode is not particularly limited and can be selected from the binders of the negative electrode described above.

[0086] The positive electrode can be made as follows: the above-mentioned positive electrode active material is mixed with a conductive agent and a binder, a high-boiling point solvent such as 1-methyl-2-pyrrolidone is added thereto and kneaded to form a positive electrode mixture slurry, which is then coated on an aluminum foil of a current collector, etc., dried, and pressed to form a positive electrode mixture layer, thereby making a positive electrode.

[0087] 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.

[0088] 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.

[0089] To reduce the electronic contact resistance between the positive electrode current collector and the positive electrode mixture layer, the surface of the positive electrode current collector may include a conductive additive or a conductive coating. Examples of conductive additives include, but are not limited to, carbon and precious metals such as gold, platinum, and silver. Examples of conductive coatings include a mixture layer containing an inorganic oxide, a conductive agent, and a binder.

[0090] The positive electrode can be made by forming a positive electrode mixture layer containing a positive electrode active material and a binder on a current collector. The positive electrode using the positive electrode active material can be manufactured by conventional methods, that is, the positive electrode active material and the binder, as well as the conductive material and thickener as needed, are dry-mixed to form a sheet, and the resulting sheet is press-bonded to the positive electrode current collector; or these materials are dissolved or dispersed in a liquid medium to form a slurry, and the slurry is applied to the positive electrode current collector and dried to form a positive electrode mixture layer on the current collector, thereby obtaining the positive electrode.

[0091] IV. Isolation membrane

[0092] 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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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 films. 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 above-mentioned independent thin film separators, separators may also be used: separators formed by forming a composite porous layer containing the above-mentioned inorganic particles on the surface of the positive electrode and / or negative electrode using a resin-based binder. For example, a separator formed by forming a porous layer on both sides of the positive electrode using fluororesin as a binder with aluminum oxide particles having a particle size of 90% less than 1 μm.

[0097] The thickness of the separator is arbitrary. In some embodiments, the separator has a thickness greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the separator has a thickness less than 50 μm, less than 40 μm, or less than 30 μm. When the separator has a thickness within the above range, insulation and mechanical strength can be ensured, and the rate characteristics and energy density of the secondary battery can be ensured.

[0098] The present application further provides an electronic device, which includes the secondary battery according to the present application.

[0099] 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.

[0100] 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.

[0101] Example

[0102] Examples of the secondary battery of the present application are shown below, but the present application is not limited to these examples.

[0103] Lithium-ion battery production

[0104] A positive electrode mixture paste 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 was then added to a solution of 1.5% by mass of polyacrylonitrile dissolved in 1-methyl-2-pyrrolidone and mixed. This paste was applied to one side of aluminum foil (current collector), dried, pressurized, and then cut to the desired size to produce the positive electrode.

[0105] Separately, a negative electrode mixture paste was prepared by mixing 96% by mass of the negative electrode active material listed in Table 1-1 with 2% by mass of styrene-butadiene rubber. This was then added to a solution of 2% by mass of 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 a desired size to produce the negative electrode. The mass per unit area of ​​the negative electrode mixture layer was adjusted by controlling the coating thickness.

[0106] The positive electrode and negative electrode prepared as above are each connected to a wire. They are stacked via a polypropylene porous membrane with a thickness of 10 μm. In addition, LiPF6 as a supporting electrolyte is dissolved in a solution containing (I) vinyl sulfate, (II) 1,2,3-tris(2-cyanoethoxy)propane, (III) nitrogen-containing lithium salt, 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), other nitrile compounds, and the first substance are as shown in Tables 1 and 2, and the content of LiPF6 is 14%.

[0107] 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 to form a lithium-ion battery. This lithium-ion battery was in the form of a bag, 35mm wide, 48mm high, and 5mm thick.

[0108] Table 1

[0109] Table 1 shows the positive and negative electrode materials of the prepared lithium-ion battery and some component codes of the electrolyte, and the detailed compositions are shown in Tables 1-1, 1-2, and 1-3 respectively.

[0110] The values ​​in () in the above table are all mass %

[0111] Table 1-1 Positive electrode

[0112] Table 1-2 Negative electrode

[0113] Table 1-3 Electrolyte

[0114] Test Method

[0115] Lithium metal precipitation suppression

[0116] At -10°C, the secondary batteries prepared in the examples and comparative examples were charged and discharged five times using a constant current method (CCCV charging at 0.05C cutoff) at 1.5C to a cell voltage of 4.6V, and then discharged at the same rate (CC discharge) to a cell voltage of 3.0V. Finally, at 25°C, they were charged using a constant current method at 0.2C to a cell voltage of 4.6V.

[0117] After the above-described operation, the battery cell of the lithium-ion secondary battery is disassembled, the negative electrode is removed, and the proportion of lithium metal deposited (Li metal deposited portion) on the entire negative electrode surface is calculated through image processing. The smaller the proportion of Li metal deposited portion on the entire negative electrode surface, the more lithium metal deposition in the negative electrode of the lithium-ion secondary battery is suppressed.

[0118] A: The proportion of Li metal precipitation on the negative electrode surface is less than 2%;

[0119] B: The proportion of Li metal precipitation on the entire negative electrode surface is greater than 2% and less than 5%;

[0120] C: The proportion of Li metal precipitation on the entire negative electrode surface is greater than 5% and less than 10%;

[0121] D: The ratio of the Li metal deposited portion to the entire negative electrode surface is 10% or more.

[0122] Reduction of residual gas

[0123] After the electrolyte was injected into the secondary batteries prepared in the examples and comparative examples, they were left to stand at a temperature of 25°C for 5 hours. Next, they were charged at a temperature of 25°C and 0.2C using a constant current method until the battery cell voltage reached 4.6V, and then aged at a temperature of 60°C for 12 hours. Thereafter, the electrode parts (positive electrode, separator and negative electrode) of the battery cell were pressurized at 25kPa for 1 minute, and then the gas retention area on the electrode was measured using an ultrasonic inspection system ("NAUT21" manufactured by JAPAN PROBE). The gas retention area ratio (%) was obtained by dividing the gas retention area by the electrode area, and the evaluation was performed according to the following criteria. The smaller the gas retention area ratio, the less residual gas in the secondary battery.

[0124] A: The gas retention area ratio is greater than 0% and less than 5%;

[0125] B: The gas retention area ratio is 5% or more and less than 10%;

[0126] C: The gas retention area ratio is 10% or more and less than 15%;

[0127] D: The gas retention area ratio is 15% or more.

[0128] Low temperature cycle characteristics

[0129] The secondary batteries prepared in the examples and comparative examples were charged and discharged at a charge rate of 0.5C to 4.6V and at a discharge rate of 0.5C to 3.0V at a temperature of 25°C, and the initial capacity C0 was measured. Furthermore, the same charge and discharge operation was repeated at a temperature of -15°C, and the capacity C1 after 50 cycles was measured. Then, the capacity retention rate ΔC = (C1 / C0) × 100 (%) was calculated, and the evaluation was performed according to the following criteria. The higher the value of the capacity retention rate, the less the decrease in discharge capacity, indicating that the cycle characteristics at low temperatures (i.e., low-temperature cycle characteristics) are better.

[0130] A: Capacity retention rate ΔC is above 45%;

[0131] B: Capacity retention rate ΔC is 40% or more and less than 45%;

[0132] C: Capacity retention rate ΔC is 35% or more and less than 40%;

[0133] D: Capacity retention rate ΔC is less than 35%.

[0134] Table 2

[0135] In Table 2, a1 represents the content of (I) vinyl sulfate, a2 represents the content of (II) lithium difluorophosphate, a3 represents the content of (III) nitrogen-containing lithium salt, a represents the total content of (I), (II), and (III), and w represents the mass per unit area of ​​the negative electrode mixture layer (unit: mg / cm 2 ), b represents the total content of other nitrile compounds, and c represents the total content of the first substance.

[0136] In a secondary battery using silicon-carbon material for the negative electrode, the electrolyte simultaneously contains (I) vinyl sulfate, (II) 1,2,3-tris(2-cyanoethoxy)propane, and (III) a nitrogen-containing lithium salt. During the initial cycle charge, components (I) to (III) form a stable coating on the surface of the negative electrode, which not only inhibits the growth of lithium dendrites, but also inhibits the damage of the electrolyte to the negative electrode during the charge and discharge cycle, and reduces the consumption of active lithium by decomposition and regeneration of the coating. This not only inhibits the precipitation of lithium metal and internal residual gas in the secondary battery, but also significantly improves the low-temperature cycle characteristics.

[0137] In particular, when the electrolyte also contains other nitrile compounds, the impedance of the aforementioned coating can be reduced, lithium ion charge transfer can be improved, the initial resistance can be further suppressed, and the low-temperature cycle performance of the lithium-ion battery can be significantly improved.

[0138] In particular, when the electrolyte further contains the first substance, the inventors unexpectedly discovered that the first substance can inhibit the decomposition of the aforementioned film during the charge and discharge cycle and suppress the internal residual gas.

[0139] References throughout this specification to “an embodiment,” “part of an embodiment,” “one embodiment,” “another example,” “an example,” “a specific example,” or “a portion of an example” mean that at least one embodiment or example in this application includes the specific features, structures, materials, or characteristics described in that embodiment or example. Therefore, descriptions appearing throughout this 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 this application. In addition, the specific features, structures, materials, or characteristics in this application may be combined in any suitable manner in one or more embodiments or examples.

[0140] 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, characterized in that: The negative electrode includes a negative electrode current collector and a negative electrode mixture layer formed on the negative electrode current collector. The negative electrode mixture layer includes graphite and silicon-based materials. The unit area mass of the negative electrode mixture layer is 4.5 mg / cm 2 Above and 12.5 mg / cm 2 the following; The electrolyte contains (I) vinyl sulfate, (II) 1,2,3-tris(2-cyanoethoxy)propane, and (III) a nitrogen-containing lithium salt, wherein the total content of (I), (II), and (III) is greater than or equal to 1.26 mass % and less than or equal to 6.07 mass % based on the mass of the electrolyte.

2. The secondary battery according to claim 1, wherein The nitrogen-containing lithium salts include LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,2-perfluoroethanedisulfonyl imide lithium, cyclic 1,3-perfluoropropanedisulfonyl imide lithium, LiN(CF3SO2)(C4F9SO2), 4,5-dicyano-2-trifluoromethylimidazole lithium salt, 4,5-dicyano-2-pentafluoroethylimidazole lithium salt, 2,4,5-tricyanoimidazole At least one of lithium salt, 5,6-dicyano-2-trifluoromethylbenzimidazole lithium salt, 5,6-dicyano-2-pentafluoroethylbenzimidazole lithium salt, 2,5,6-tricyanobenzimidazole lithium salt, 4,7-dicyano-2-trifluoromethylbenzimidazole lithium salt, 4,7-dicyano-2-pentafluoroethylbenzimidazole lithium salt, 2,4,7-tricyanobenzimidazole lithium salt, 4,5,6,7-tetracyano-2-trifluoromethylbenzimidazole lithium salt, 4,5,6,7-tetracyano-2-pentafluoroethylbenzimidazole lithium salt, and 2,4,5,6,7-pentacyanobenzimidazole lithium salt.

3. The secondary battery according to claim 1 or 2, characterized in that The mass per unit area of ​​the negative electrode mixture layer is 5.1 mass % or more and 11.2 mass % or less.

4. The secondary battery according to claim 1 or 2, characterized in that The nitrogen-containing lithium salt includes at least one of LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, and LiN(C2F5SO2)2.

5. The secondary battery according to claim 1 or 2, characterized in that The mass of the vinyl sulfate is greater than or equal to 0.01 mass % and less than or equal to 3 mass % based on the mass of the electrolyte; The mass of the 1,2,3-tris(2-cyanoethoxy)propane is greater than or equal to 0.3 mass % and less than or equal to 5 mass % based on the mass of the electrolyte; The mass of the nitrogen-containing lithium salt is 0.2 mass % or more and 3 mass % or less based on the mass of the electrolyte.

6. The secondary battery according to claim 1 or 2, characterized in that The sum of the mass of the vinyl sulfate, 1,2,3-tris(2-cyanoethoxy)propane, and the nitrogen-containing lithium salt is 1.86 mass % or more and 5.66 mass % or less based on the mass of the electrolyte.

7. The secondary battery according to claim 1 or 2, characterized in that: The mass per unit area of ​​the negative electrode mixture layer is 4.5 mg / cm 2 Above and 12.5 mg / cm 2 the following; Based on the mass of the electrolyte, the sum of the masses of the vinyl sulfate, 1,2,3-tris(2-cyanoethoxy)propane and the nitrogen-containing lithium salt is a, the unit area of ​​the negative electrode mixture layer is w, and a and w satisfy: a / w is greater than or equal to 0.2 and less than or equal to 1.

011.

8. The secondary battery according to claim 1 or 2, characterized in that: The electrolyte further comprises other nitrile compounds, and the other nitrile compounds include at least one of succinonitrile, adiponitrile, ethylene glycol bis(propionitrile), 1,3,5-pentanetricarboxylic acid nitrile, 1,2,3-propanetricarboxylic acid nitrile, 1,3,6-hexanetricarboxylic acid nitrile, 1,2,6-hexanetricarboxylic acid nitrile, 1,2,4-tris(2-cyanoethoxy)butane, 1,1,1-tris(cyanoethoxymethylene)ethane, 1,1,1-tris(cyanoethoxymethylene)propane, 3-methyl-1,3,5-tris(cyanoethoxy)pentane, 1,2,7-tris(cyanoethoxy)heptane, 1,2,6-tris(cyanoethoxy)hexane, and 1,2,5-tris(cyanoethoxy)pentane; The content of the other nitrile compound is 0.3% by mass or more and 8% by mass or less based on the mass of the electrolyte.

9. The secondary battery according to claim 8, characterized in that The content of the other nitrile compound is 0.6% by mass or more and 7.1% by mass or less based on the mass of the electrolyte.

10. The secondary battery according to claim 8, wherein The content of the other nitrile compound is 1.4 mass % or more and 6.2 mass % or less based on the mass of the electrolyte.

11. The secondary battery according to claim 1 or 2, characterized in that: The electrolyte further includes a first substance, the first substance including at least one of lithium monofluorophosphate, lithium difluorophosphate, 1,2-bis(difluorophosphine)ethane, vinylene carbonate, lithium fluorosulfonate, 1,3-propane sultone, 1,3-propylene sultone, 1,3-propylene glycol cyclic sulfate, fluorobenzene, cyclohexylbenzene, biphenyl, tris(trimethylsilyl)phosphate, and tris(trimethylsilyl)borate; The content of the first substance is 0.3 mass % or more and 10 mass % or less based on the mass of the electrolyte.

12. The secondary battery according to claim 11, wherein The content of the first substance is 0.6 mass % or more and 9.7 mass % or less based on the mass of the electrolyte.

13. The secondary battery according to claim 11, wherein The content of the first substance is 1.6 mass % or more and 7.1 mass % or less based on the mass of the electrolyte. 14 . An electronic device comprising the secondary battery according to claim 1 .

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