Electrochemical device and electronic equipment

Abstract

The application discloses an electrochemical device and an electronic device. The electrochemical device comprises a negative electrode sheet and an electrolyte. The negative electrode sheet comprises a negative electrode active material, and the negative electrode active material contains a silicon-based material. The mass percentage of silicon in the silicon-based material is Z1%, and 0.1 < Z1 < 15 based on the mass of the negative electrode active material. The electrolyte comprises a compound of formula I and a substance A. The substance A is at least one selected from ethylene sulfite, ethylene sulfate, vinyl ethylene sulfite, trifluoromethyl phenyl sulfide or methylene methane disulfonate. The mass percentage of the compound of formula I is a%, and the mass percentage of the substance A is b% based on the mass of the electrolyte. 0.5 <= a / b <= 20, and 0.5 <= a <= 20. The electrochemical device has small volume expansion and low impedance growth during normal temperature cycling.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and more particularly to an electrochemical device and an electronic device. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density, high operating voltage, long cycle life, and environmental friendliness, making them widely used in portable electronic devices such as mobile phones, laptops, and cameras. They are also the preferred power source for future electric and hybrid vehicles. Currently, to improve the energy density of lithium-ion batteries, high-specific-capacity electrode materials are mainly used. Silicon-based materials, as a type of alloyed anode material, can provide ultra-high specific capacities up to 4200 mAh / g. However, silicon anodes undergo drastic volume expansion and contraction during lithium-ion insertion / extraction, leading to increased impedance. Summary of the Invention

[0003] In view of this, this application provides an electrochemical device and an electronic device, wherein the negative electrode of the electrochemical device is a silicon-containing negative electrode and the electrolyte of the electrochemical device contains a compound of formula I and substance A. By adjusting the types and contents of the three substances appropriately, the three substances can work together to suppress the volume expansion and impedance increase of the electrochemical device during room temperature cycling.

[0004] In a first aspect, this application provides an electrochemical device, which includes a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative electrode active material, which contains a silicon-based material. Based on the mass of the negative electrode active material, the mass percentage of silicon element in the silicon-based material is Z1%, where 0.1 < Z1 < 15. The electrolyte includes a compound of formula I.

[0005]

[0006] R is selected from fluorinated or unsubstituted C2-C6 alkyl groups, fluorinated or unsubstituted C6-C6 alkyl groups. 12 Nitrogen-containing heterocyclic groups, fluorine-substituted or unsubstituted C6-C 12Aryl. The electrolyte further comprises a substance A selected from at least one of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide or methanediyl dimethanesulfonate, the mass percentage of the compound of Formula I is a%, the mass percentage of the substance A is b%, 0.5≤a / b≤20, 0.5≤a≤20, based on the mass of the electrolyte. Preferably, the substance A is selected from at least two of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide or methanediyl dimethanesulfonate and contains at least vinyl sulfate. The present application can improve the volume expansion and impedance growth of the silicon-containing negative electrode electrochemical device in the room temperature cycling by regulating the content of silicon element in the silicon-based material within the above range, and simultaneously regulating the electrolyte to contain the compound of Formula I and the substance A, and the types and contents of the compound of Formula I and the types and contents of the substance A are also within the above range. The inventors have found that the regulation of the electrolyte to contain the compound of Formula I and the substance A and the contents and proportions thereof within the above range can form a relatively stable interface layer on the surface of the electrolyte and the mixed silicon-carbon negative electrode, thereby reducing the side reactions of the electrolyte on the surface of the negative electrode during the cycling, so as to inhibit the volume expansion and impedance growth of the battery in the room temperature cycling.

[0007] In some embodiments, the compound of Formula I comprises at least one of the following compounds:

[0008]

[0009] The compound of Formula I of the above type has a more optimal effect of inhibiting the volume expansion and impedance growth of the battery in the room temperature cycling when combined with the substance A and an appropriate amount of silicon element.

[0010] In some embodiments, at least one of the following conditions is satisfied: (1) 0.1≤a / Z1≤6, (2) 0.3≤b≤8. Preferably, 4≤Z1≤5, 0.5≤b≤4. More preferably, 1≤b≤3, 2≤a / Z1≤3. The present application further regulates the values of the content of silicon element, the content of the compound of Formula I and the content of the substance A within the above range, so as to further improve the cycling performance of the electrochemical device at room temperature.

[0011] In some embodiments, the silicon-based material comprises at least one of silicon, silicon monoxide, silicon-carbon or silicon-oxygen-carbon ceramic particles, the silicon-carbon particles comprise a carbon skeleton, amorphous silicon dispersed in the carbon skeleton and a protective layer located on at least part of the surface of the carbon skeleton, the material of the protective layer comprises amorphous carbon, and the material of the carbon skeleton comprises at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon or hard carbon.

[0012] In some embodiments, the electrolyte comprises fluoroethylene carbonate and / or vinylene carbonate, the mass percentage of fluoroethylene carbonate is c1%, the mass percentage of vinylene carbonate is c2%, based on the mass of the electrolyte, and 12≤(c1+c2×60)≤25, 0.5≤(c1+c2×60) / Z1≤10. Preferably, 2.4≤(c1+c2×60) / Z1≤4.8. The electrolyte further comprises fluoroethylene carbonate and / or vinylene carbonate, and the content relationship thereof is within the above range, which can further improve the storage performance of the electrochemical device at high temperature, especially the inhibition of the storage volume expansion of the electrochemical device at high temperature, while taking into account the inhibition of the volume expansion of the electrochemical device at room temperature.

[0013] In some embodiments, the electrolyte comprises a dinitrile compound, the dinitrile compound is selected from at least one of butanedinitrile, hexanedinitrile, pentanedinitrile, ethylene glycol bis(propionitrile) ether or 1,4-dicyano-2-butene, the mass percentage of the dinitrile compound is d%, based on the mass of the electrolyte, and 0.1≤d≤5. By adding the dinitrile compound in the electrolyte, and the type and content of the dinitrile compound are within the range of the present application, the storage performance of the electrochemical device at high temperature can be further improved.

[0014] In some embodiments, the electrolyte comprises a trinitrile compound, the trinitrile compound is selected from at least one of 1,3,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanato)propane, 1,3,5-pentanetricarbonitrile or tricyanobenzene, the mass percentage of the trinitrile compound is e%, based on the mass of the electrolyte, and 1≤d / e≤2. Preferably, 1≤d≤5. The electrolyte further comprises the trinitrile compound, and the content of the trinitrile compound is also within the above range, which can further improve the effect of improving the storage performance of the electrochemical device at high temperature.

[0015] In some embodiments, the electrolyte further comprises substance B and vinylene carbonate, the substance B is selected from at least one of dimethyl carbonate, ethyl methyl carbonate or ethyl propionate, the mass percentage of the substance B is f%, based on the mass of the electrolyte, and 25≤f≤50, the mass percentage of the vinylene carbonate is g%, and 10≤g≤20. The electrolyte contains the above-mentioned substance B, and the content of the substance B is also within the range of the present application, and the substance B and the appropriate amount of vinylene carbonate can further improve the comprehensive performance of the electrochemical device, especially the electrochemical device has better room temperature and high temperature cycle capacity retention rate, and lower high temperature storage volume expansion rate. Preferably, 0.5≤f / g≤3.

[0016] In a second aspect, the present application provides an electronic device comprising the electrochemical device in any of the foregoing embodiments. Therefore, the electronic device provided by the present application has better room temperature performance.

[0017] The electrochemical device provided in the first aspect of this application exhibits small volume expansion and low impedance growth during room temperature cycling. Therefore, the electronic device provided in the second aspect of this application also exhibits small volume expansion and low impedance growth during room temperature cycling. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0019] It should be noted that, in the specific embodiments of this application, lithium-ion secondary batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion secondary batteries.

[0020] Lithium-ion secondary battery

[0021] It includes a negative electrode sheet and an electrolyte. The negative electrode sheet includes a negative current collector and a negative active material disposed on at least one surface of the negative current collector. The negative active material contains a silicon-based material. Based on the mass of the negative active material, the mass percentage of silicon element in the silicon-based material is Z1, where 0.1 < Z1 < 15. The electrolyte includes a compound of formula I.

[0022]

[0023] R is selected from fluorinated or unsubstituted C2-C6 alkyl groups, fluorinated or unsubstituted C6-C6 alkyl groups. 12 Nitrogen-containing heterocyclic groups, fluorine-substituted or unsubstituted C6-C 12Aryl. The electrolyte further comprises a substance A selected from at least one of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide, or methylene methane disulfonate, the mass percentage of the compound of Formula I is a%, the mass percentage of the substance A is b%, 0.5≤a / b≤20, 0.5≤a≤20, 0.1≤a / Z1≤6, 0.3≤b≤8, based on the mass of the electrolyte. Preferably, the substance A is selected from at least two of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide, or methylene methane disulfonate and contains at least vinyl sulfate. By regulating the content of silicon element in the silicon-based material and regulating the electrolyte to contain the compound of Formula I and the substance A, and the content of the compound of Formula I and the substance A is also in the above range, the volume expansion and impedance growth of the electrochemical device under normal temperature cycling can be improved. Illustratively, the value of a can be 0.5, 1, 2, 5, 6, 8, 10, 12, 14, 15, 17, 18, 20, or a range consisting of any two of the above values. Illustratively, the value of a / b can be 0.5, 1.3, 3.2, 4.4, 5.2, 7.2, 8.5, 9.9, 11.4, 13.9, 14.4, 16.1, 17.1, 19.4, 20, or a range consisting of any two of the above values. Illustratively, the value of a / Z1 can be 0.1, 0.2, 0.8, 1.1, 1.4, 1.9, 2.0, 2.7, 2.8, 3, 3.4, 3.7, 4.1, 4.5, 4.7, 5, 6, or a range consisting of any two of the above values. Illustratively, the value of b can be 0.3, 0.5, 1.0, 1.3, 1.6, 2.0, 2.5, 2.7, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.6, 4.9, 5, 5.5, 6, 6.5, 7.5, 8, or a range consisting of any two of the above values. Illustratively, the value of Z1 can be 4, 4.3, 4.5, 4.6, 4.8, 5, or a range consisting of any two of the above values.

[0024] In some embodiments, the compound of Formula I includes at least one of the following compounds:

[0025]

[0026] The compound of Formula I of the above kind is more conducive to synergistically improving the volume expansion and impedance growth of the electrochemical device under normal temperature cycling with other substances.

[0027] In some embodiments, the electrolyte comprises fluoroethylene carbonate and / or vinylene carbonate, the mass percentage of fluoroethylene carbonate is c1%, the mass percentage of vinylene carbonate is c2%, based on the mass of the electrolyte, and 12≤(c1+c2x60)≤25, 2.4≤(c1+c2x60) / Z1≤4.8. The electrolyte contains fluoroethylene carbonate and / or vinylene carbonate, and the content of fluoroethylene carbonate and / or vinylene carbonate is in the above range, which can better improve the volume expansion of the electrochemical device at room temperature and also take into account the lower impedance increase. Exemplarily, the value of (c1+c2x60) can be 12, 12.4, 13.4, 14.8, 16.0, 16.7, 17.0, 18.3, 19.7, 20.4, 21.6, 22.6, 23.0, 24.7, 25, or a range composed of any two of the above values. Exemplarily, the value of (c1+c2x60) / Z1 can be 0.5, 1.5, 2.4, 2.6, 2.8, 3, 3.2, 3.6, 3.8, 4, 4.2, 4.4, 4.6, 4.8, 6, 8.5, 10, or a range composed of any two of the above values.

[0028] In some embodiments, the electrolyte comprises a dinitrile compound, the dinitrile compound is selected from at least one of butanedinitrile, hexanedinitrile, pentanedinitrile, ethylene glycol bis(propionitrile) ether, or 1,4-dicyano-2-butene, the mass percentage of the dinitrile compound is d%, based on the mass of the electrolyte, and 0.1≤d≤5. The electrolyte contains the dinitrile compound of the above type and content, which is conducive to further improving the high-temperature storage performance of the electrochemical device. Exemplarily, the value of d can be 0.1, 0.3, 0.6, 1.1, 1.3, 1.6, 2.2, 2.5, 2.8, 3.4, 3.6, 4, 4.4, 5, or a range composed of any two of the above values.

[0029] In some embodiments, the electrolyte comprises a trinitrile compound, the trinitrile compound is selected from at least one of 1,3,6-hexanetricarbonitrile, 1,2,3-tris(2-cyanato)propane, 1,3,5-pentanetricarbonitrile, or tricyanobenzene, the mass percentage of the trinitrile compound is e%, based on the mass of the electrolyte, and 1≤d / e≤2. The electrolyte contains the trinitrile compound of the above type and content, which has a more optimal effect of improving the high-temperature storage performance of the electrochemical device. Exemplarily, the value of d / e can be 1, 1.1, 1.3, 1.5, 1.8, 2, or a range composed of any two of the above values.

[0030] In some embodiments, the electrolyte further comprises a substance B selected from at least one of dimethyl carbonate, ethyl methyl carbonate or ethyl propionate, and ethylene carbonate, the mass percentage of the substance B is f%, 25≤f≤50, and the mass percentage of the ethylene carbonate is g%, 10≤g≤20, based on the mass of the electrolyte. In this case, the comprehensive performance of the electrochemical device is relatively optimal, i.e., the normal-temperature cycle, high-temperature cycle and high-temperature storage are all relatively optimal. Exemplarily, the value of f can be 25, 28, 30, 32, 35, 38, 40, 45, 50 or a range formed by any two of the above values. Exemplarily, the value of g can be 10, 12, 13, 15, 18, 19, 20 or a range formed by any two of the above values. Exemplarily, the value of f / g can be 0.5, 0.6, 0.8, 0.9, 1.2, 1.3, 1.5, 1.8, 2.0, 2.1, 2.3, 2.4, 2.8, 2.9, 3 or a range formed by any two of the above values.

[0031] The thickness of the negative electrode current collector is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, the thickness of the negative electrode current collector is 5 μm to 12 μm. The negative electrode current collector is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, it can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a foamed nickel, a foamed copper or a composite current collector, etc.

[0032] The negative electrode material layer can further include a binder and a thickening agent, and the kind of the binder and the thickening agent is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the binder can include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene butadiene rubber or acrylated styrene butadiene rubber; and the thickening agent can include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0033] The negative electrode material layer can further include a conductive agent. The type of the conductive agent is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the conductive agent can include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, a metal material, or a conductive polymer. The mass ratio of the negative electrode active material, the conductive agent, the binder, and the thickening agent in the negative electrode active layer is not particularly limited in the present application, and can be selected by a person skilled in the art according to actual needs as long as the purpose of the present application can be achieved. Optionally, the negative electrode sheet can further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode active layer. The composition of the conductive layer is not particularly limited in the present application, and can be a commonly used conductive layer in the art. For example, the conductive layer includes a conductive agent and a binder. The conductive agent and the binder in the conductive layer are not particularly limited in the present application, and can be at least one of the conductive agent and the binder in the negative electrode active layer described above.

[0034] Others

[0035] The lithium ion secondary battery further includes a positive electrode sheet, and the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector. The positive electrode current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved, and for example, can include an aluminum foil, an aluminum alloy foil, or a composite current collector (for example, a composite current collector in which a metal layer is disposed on the surface of a polymer layer).

[0036] The thickness of the positive electrode current collector is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 13 μm.

[0037] The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material is not particularly limited in the present application as long as the purpose of the present application can be achieved. For example, the positive electrode active material can include a composite metal oxide containing one or two or more selected from the group consisting of cobalt, manganese, and nickel, and a lithium-containing olivine-type phosphate containing one or two or more selected from iron, cobalt, nickel, and manganese. These positive electrode active materials can be used alone or in combination of two or more.

[0038] As such a lithium composite metal oxide, for example, LiCoO2, LiMn2O4, LiNiO2, LiCoO2(0.01 < x < 1), LiNiO2(x + y + z = 1), Li2MnO3, and a solid solution of LiMO2(M is a transition metal such as Co, Ni, Mn, Fe, etc.) can be suitably listed. 1-x Ni x O2(0.01 < x < 1), LiNiO2(x + y + z = 1), Li2MnO3, and a solid solution of LiMO2(M is a transition metal such as Co, Ni, Mn, Fe, etc.) can be suitably listed. x MnyCo z O2(x + y + z = 1), Li2MnO3, and a solid solution of LiMO2(M is a transition metal such as Co, Ni, Mn, Fe, etc.) can be suitably listed. 1 / 2 Mn 3 / 2O4, LiFePO4, LiMnPO4, and LiMn 1-x Fe x PO4(0.01 < x < 1), more preferably two or more. A part of these complex metal oxides with lithium or olivine-type lithium-containing phosphates can be substituted with other elements, or a part of cobalt, nickel, manganese, 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 carbon material. The thickness of the positive electrode active material layer is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the thickness of the positive electrode active material layer is 30 μm to 120 μm.

[0039] The positive electrode active material layer can further include a conductive agent and a binder, and the type of the conductive agent and the binder is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the conductive agent can include, but is not limited to, at least one of conductive carbon black, carbon nanotube (CNT), carbon fiber, ketjen black, graphene, metal material, or conductive polymer. The binder can include, but is not limited to, at least one of polyacrylic acid, polyacrylate, acrylate polymer, polyvinyl alcohol, polyvinylidene fluoride, polytetrafluoroethylene, or vinylidene-hexafluoropropylene copolymer.

[0040] The mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer is not particularly limited in the present application, and a person skilled in the art can select according to actual needs, as long as the object of the present application can be achieved.

[0041] The lithium ion secondary battery further includes a separator, which is used to separate the positive electrode sheet and the negative electrode sheet, prevent internal short circuit of the secondary battery, allow electrolyte ions to pass freely, and not affect the electrochemical charging and discharging process. The separator is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) based on polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid; and the type of the separator can include at least one of woven film, non-woven film, microporous film, composite film, calendered film, or spunlaced film.

[0042] In the present application, the separator can include a base material and a surface treatment layer. The base material can be a nonwoven fabric or a composite film having a porous structure, and the material of the base material can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. Optionally, a surface treatment layer is provided on at least one surface of the base material, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited in the present application, and for example, can include at least one of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is not particularly limited in the present application, and for example, can be at least one of the aforementioned binders. The polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene).

[0043] In the present application, the separator has a pore diameter of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm. 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 rate characteristics and energy density of the secondary battery can be ensured.

[0044] The electrochemical device of the present application also includes a packaging bag for containing the positive electrode sheet, the separator, the negative electrode sheet, and the electrolyte, and other components known in the art, which are not limited in the present application. The packaging bag is not particularly limited in the present application, and can be a packaging bag known in the art, as long as the purpose of the present application can be achieved.

[0045] The lithium ion secondary battery can be prepared according to a conventional method in the art. Illustratively, the positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to serve as a separator, to obtain an electrode assembly, which can also be obtained by winding. The electrode assembly is placed in a packaging case, an electrolyte is injected and sealed to obtain a secondary battery. The structure of the lithium ion secondary battery is not particularly limited, and can be a coin-type battery, a cylindrical battery, a prismatic battery, or a pouch-type battery, etc. having a single layer or multiple layers of separators.

[0046] The lithium ion secondary battery of the present application is not particularly limited in its use, and can be used for any electronic device known in the art. In some embodiments, the lithium ion battery of the present application can be used for, but not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copying machines, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini-disc players, transceivers, electronic organizers, calculators, memory cards, portable audio players, radios, backup power supplies, motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game machines, timepieces, power tools, flashlights, cameras, home-use large storage batteries, and lithium ion capacitors, etc.

[0047] Hereinafter, the embodiments of the present application will be described more specifically by citing examples and comparative examples. The listed parts, percentages and ratios are all based on mass unless otherwise stated.

[0048] Example 1-1

[0049] (I) Preparation of lithium ion battery

[0050] <Preparation of negative electrode sheet>

[0051] The Si / C composite material (carbon nanohole loaded Si), artificial graphite, negative electrode binder lithium polyacrylate (PAA-Li), and negative electrode conductive agent carbon nanotube were mixed in a mass ratio of 20:70:7:3, deionized water was added, and the mixture was uniformly mixed under the action of a vacuum stirrer to obtain a negative electrode slurry with a solid content of 30 wt%. The negative electrode slurry was uniformly coated on one side surface of a negative electrode current collector copper foil with a thickness of 12 μm, dried at 120°C, and a negative electrode sheet with a single-side coated negative electrode material layer with a coating thickness of 143 μm was obtained. The above steps were repeated on the other side surface of the copper foil to obtain a negative electrode sheet with a double-side coated negative electrode material layer, which was then cold-pressed and cut to obtain a negative electrode sheet with a specification of 78 mm x 875 mm. The content of silicon element in the silicon-based material based on the mass of the negative electrode active material is shown in Table 1.

[0052] <Preparation of positive electrode sheet>

[0053] The positive electrode active material lithium cobaltate (LiCoO2), conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 97:1.4:1.6, N-methyl pyrrolidone (NMP) was added as a solvent, and a slurry with a solid content of 75 wt% was prepared. After uniform stirring in a vacuum stirrer, a positive electrode slurry was obtained. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, and dried at 85°C to obtain a positive electrode tab with a single-sided coated positive electrode material layer with a coating thickness of 110 μm. Then, the above steps were repeated on the other surface of the aluminum foil to obtain a positive electrode tab with a double-sided coated positive electrode material layer. After coating, the positive electrode tab was cold-pressed and cut into a specification of 74 mm x 867 mm for use. The cold-pressed positive electrode material layer had a compacted density of 4.15 g / cm3 3 .

[0054] <Preparation of electrolyte>

[0055] In an argon atmosphere glove box with a water content of less than 10 ppm, propylene carbonate (PC), propyl propionate (PP), and diethyl carbonate (DEC) were mixed in a mass ratio of 2:3:5 to obtain a base solvent, and then formula I-1 (a compound of formula I), vinyl sulfate (substance A), and lithium hexafluorophosphate were added to the base solvent and mixed uniformly to obtain an electrolyte. The mass percentage of lithium hexafluorophosphate was 12.5% based on the mass of the electrolyte, and the contents of the compound of formula I and substance A are shown in Table 1, and the balance was the base solvent.

[0056] <Separator>

[0057] A porous polyethylene (PE) film with a thickness of 5 μm was used.

[0058] <Preparation of lithium ion battery>

[0059] The positive electrode tab, separator, negative electrode tab, and separator prepared above were stacked in order, with the separator between the positive electrode tab and the negative electrode tab to act as a barrier, and then wound to obtain an electrode assembly. After welding the tabs, the electrode assembly was placed in an aluminum-plastic film packaging bag and dried in a vacuum oven at 85°C for 12 h to remove water, and then the electrolyte prepared above was injected. After vacuum packaging, standing, formation, shaping, and capacity testing procedures, a lithium ion battery was obtained.

[0060] Examples 1-2 to 1-39

[0061] Except for adjusting the relevant preparation parameters according to Table 1, the rest was the same as Example 1-1.

[0062] Examples 2-1 to 2-7

[0063] Based on the electrolyte of Example 1-6, the substances in Table 2 were also added to the base solvent during preparation, with the balance being the base solvent, and the rest being the same as Example 1-6.

[0064] Examples 3-1 to 3-5

[0065] Based on the electrolyte of Example 2-7, the substances in Table 3 were also added to the base solvent during preparation, with the balance being the base solvent, and the rest being the same as Example 1-1.

[0066] Comparative Examples 1 to 7

[0067] Except for adjusting the relevant preparation parameters according to Table 1, the rest was the same as Example 1-1.

[0068] (ii) Test method

[0069] 1. Test of silicon element content

[0070] The lithium ion battery discharged at 0.5C to 3.0V was disassembled, and the negative electrode sheet was taken out, soaked in dimethyl carbonate (DMC) for 20 minutes, and then rinsed with DMC and acetone in turn. Then the negative electrode sheet was placed in an oven and baked at 80°C for 12 hours to obtain the negative electrode sheet. The negative electrode sheet was placed in a vacuum oven at 100°C for 24 hours, 1g of powder sample of negative electrode material layer on the negative electrode sheet was scraped off with a blade, and then the mass percentage content of silicon element in the negative electrode material layer was tested using an ICP (Inductively coupled plasma) analyzer.

[0071] 2. Cycle performance test

[0072] The lithium ion battery was placed in a constant temperature test box at 25°C / 45°C, and allowed to stand for 30 minutes to reach constant temperature. It was charged at 0.5C constant current to 4.45V, then charged at constant voltage to a current of 0.025C, and allowed to stand for 5 minutes. It was discharged at 0.5C constant current to 3.0V, and the initial discharge capacity C1, initial thickness D1, and initial impedance I1 were recorded. The same step was repeated for 500 cycles, and the discharge capacity C2, thickness D2, and impedance I2 after 500 cycles were recorded, and the cycle capacity retention rate of the lithium ion battery was calculated.

[0073] Normal temperature / high temperature cycle capacity retention rate = C2 / C1 x 100%

[0074] Normal temperature cycle volume expansion rate = D2 / D1 x 100%, and normal temperature impedance growth rate = I2 / I1 x 100%.

[0075] 3. High temperature storage test

[0076] The lithium ion battery was placed in a constant temperature environment of 25°C and rested for 30 min, so that the lithium ion battery reached a constant temperature state of 25°C. It was charged at 0.5C constant current to 4.5V, and charged at 4.5V constant voltage to a current of 0.025C. The thickness of the lithium ion battery at this time was recorded as the initial thickness H0. The lithium ion battery was transferred to a constant temperature oven at 60°C and stored for 30 days. During this period, the thickness of the lithium ion battery was tested and recorded every 6 days. The test thickness recorded after 30 days was the storage thickness H1.

[0077] The high-temperature storage volume expansion rate = (H1-H0) / H0x100%.

[0078] Table 1

[0079]

[0080]

[0081]

[0082] Note: " / " in the table means that there is no relevant parameter.

[0083] In combination with Table 1, compared with Example 1-1, the mass ratio (a / b) of the compound of formula I and substance A in the electrolyte of Comparative Examples 1-2 is not in the appropriate range, the content a of the compound of formula I in the electrolyte of Comparative Example 3 is not in the appropriate range, the content of silicon element in the negative electrode sheet of Comparative Examples 4-5 is not in the appropriate range, the electrolyte of Comparative Example 6 does not contain substance A, and the electrolyte of Comparative Example 7 does not contain the compound of formula I. As can be seen from Table 1, the normal temperature performance of the lithium ion battery corresponding to Comparative Examples 1-7 is not as good as that of the lithium ion battery of Example 1-1. In particular, the volume expansion rate of the lithium ion battery of Comparative Examples 1-7 at normal temperature is all above 17.9%, and the highest can be up to 23.3%. The impedance growth rate of the lithium ion battery of Comparative Examples 1-7 at normal temperature is also as high as above 76.4%, and the highest can be up to 85.3%. The content of silicon element in the lithium ion battery of Example 1-1 is appropriate, and the electrolyte contains the compound of formula I and substance A of appropriate type and mass ratio. The volume expansion rate of the lithium ion battery of Example 1-1 at normal temperature is only 14.3%, and the impedance growth rate is reduced to 74.8%.

[0084] In particular, further regulating the content of silicon element in the silicon-based material and the content of the compound of formula I and substance A in the electrolyte in the preferred range is conducive to the synergistic effect among the three, which can further inhibit the volume expansion and impedance growth of the electrochemical device at normal temperature.

[0085] Table 2

[0086]

[0087]

[0088] As can be seen in combination with Table 2, further adding fluoroethylene carbonate and / or vinylene carbonate to the electrolyte containing the compound of Formula I and the substance A, and regulating the content of the fluoroethylene carbonate and / or vinylene carbonate in the above range, thus, can further improve the high-temperature performance of the lithium ion battery while taking into account the room-temperature cycling performance, especially inhibiting the volume expansion of the lithium ion battery at high temperature.

[0089] In particular, when the electrolyte further contains the dinitrile compound and the trinitrile compound, and the types and contents of the dinitrile compound and the trinitrile compound are also appropriate, the effect of improving the room-temperature performance and the high-temperature performance of the lithium ion battery is more optimal, especially being able to further inhibit the volume expansion rate of the lithium ion battery at room-temperature cycling and improve the storage volume expansion rate of the lithium ion battery at high temperature.

[0090] Table 3

[0091]

[0092] In combination with Table 3, when an appropriate amount of substance B is further added to the electrolyte, and an appropriate amount of vinylene carbonate is further added, the comprehensive performance of the electrochemical device is better, and the improvement of the room-temperature cycling capacity rate, the high-temperature cycling capacity rate, and the high-temperature storage volume expansion rate is more obvious.

[0093] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electrochemical device, characterized in that, The electrochemical device includes a negative electrode and an electrolyte; The negative electrode sheet includes a negative electrode active material, which contains silicon-based material. Based on the mass of the negative electrode active material, the mass percentage of silicon element in the silicon-based material is Z1%, where 0.1 < Z1 < 15. The electrolyte includes a compound of formula I; Wherein, R is selected from fluorinated or unsubstituted C2-C6 alkyl groups, fluorinated or unsubstituted C6-C6 alkyl groups. 12 Nitrogen-containing heterocyclic groups, fluorine-substituted or unsubstituted C6-C 12 Aryl; The electrolyte also includes substance A, which is selected from at least one of vinyl sulfite, vinyl sulfate, vinyl vinyl sulfite, trifluoromethyl phenyl sulfide, or methane disulfonate. Based on the mass of the electrolyte, the mass percentage of compound I is a%, the mass percentage of substance A is b%, 0.5 ≤ a / b ≤ 20, and 0.5 ≤ a ≤ 20.

2. The electrochemical device according to claim 1, characterized in that, The compound of formula I includes at least one of the following compounds:

3. The electrochemical device according to claim 1, characterized in that, At least one of the following conditions must be met: (1) 0.1 ≤ a / Z1 ≤ 6; (2)0.3≤b≤8。 4. The electrochemical device according to any one of claims 1 to 3, characterized in that, The electrolyte comprises fluoroethylene carbonate and / or vinylene carbonate; Based on the mass of the electrolyte, the mass percentage of the fluoroethylene carbonate is c1%, and the mass percentage of the vinylene carbonate is c2%, satisfying: 12≤(c1+c2×60)≤25.

5. The electrochemical device according to claim 4, characterized in that, 0.5≤(c1+c2×60) / Z1≤10.

6. The electrochemical device according to claim 4, characterized in that, The electrolyte includes dinitrile compounds; The dinitrile compound is selected from at least one of butadionitrile, adiponitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether or 1,4-dicyano-2-butene; Based on the mass of the electrolyte, the mass percentage of the dinitrile compound is d%, 0.1≤d≤5.

7. The electrochemical device according to claim 6, characterized in that, The electrolyte includes trinitrile compounds; The trinitrile compound is selected from at least one of 1,3,6-hexanetrionitrile, 1,2,3-tris(2-cyanoxy)propane, 1,3,5-pentanetricarbonitrile, or tricyanobenzene; Based on the mass of the electrolyte, the mass percentage of the trinitrile compound is e%, 1≤d / e≤2.

8. The electrochemical device according to any one of claims 1 to 3, characterized in that, The electrolyte also includes substance B and ethylene carbonate; The substance B is selected from at least one of dimethyl carbonate, ethyl methyl carbonate, or ethyl propionate. Based on the mass of the electrolyte, the mass percentage of substance B is f%, 10≤f≤50, and the mass percentage of ethylene carbonate is g%, 10≤g≤20.

9. The electrochemical device according to claim 8, characterized in that, 0.5≤f / g≤3.

10. An electronic device, characterized in that, The electronic device includes the electrochemical device according to any one of claims 1 to 9.

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