Electrolyte and preparation method thereof, battery and electronic device

Abstract

The invention relates to an electrolyte and a preparation method thereof, a battery and an electronic device, the electrolyte comprises a lithium salt, a solvent and an additive, the solvent comprises a cyclic carbonate solvent, a low-viscosity solvent and a linear carbonate solvent; the low-viscosity solvent is selected from at least one of a carboxylic ester solvent and an ether solvent; wherein based on 100% of the total mass of the electrolyte, the mass percentage of the lithium salt is X%, the mass percentage of the cyclic carbonate solvent is Y%, the mass percentage of the low-viscosity solvent is Z%, and the mass percentage of the linear carbonate solvent is W%; wherein X, Y, Z and W satisfy the following conditions: 90 < = X + Y + Z + W < = 100, and Y < = Z < = W. The electrolyte disclosed by the invention has both interface stability and fast charging performance, and the battery comprising the electrolyte disclosed by the invention is excellent in high-temperature / normal-temperature high-power cycle performance and high in fast charging capacity.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion batteries, and in particular to an electrolyte and a preparation method thereof, a battery and an electronic device. Background Art

[0002] As the market's requirements for electric vehicle charging time are getting shorter and shorter, the requirements for lithium battery charging capacity are also gradually increasing. At present, there are two main ways to improve the fast charging capacity of lithium batteries from the electrolyte aspect in the existing technology: one is to increase the conductivity of the electrolyte to reduce the resistance inside the battery, thereby accelerating the migration speed of lithium ions and improving the charging efficiency; the second is to reduce the viscosity of the electrolyte to reduce the resistance when the electrolyte flows, which also helps to speed up the transmission speed of lithium ions. However, the solvents currently used to improve the conductivity and viscosity of the electrolyte are prone to cause battery bulging and damage the original negative electrode SEI interface. Based on this, some researchers have proposed adding some high interface protection additives. However, although this protects the negative electrode interface, it increases the interface impedance, which is not conducive to fast charging design. Some other literatures propose to increase the lithium salt content, and use high lithium salts to coordinate more free solvent molecules to reduce the solvent reaction activity, but high lithium salt content will cause viscosity and cost increases, which is obviously not suitable for existing commercial battery designs.

[0003] In addition, the existing electrolyte design of cyclic carbonate is generally twice or more than the lithium salt content. This is to ensure the full dissociation of lithium salts. However, too much cyclic carbonate itself also has certain interface problems, such as the co-embedding of PC into the graphite negative electrode, the easy reduction of EC / PC negative electrode and the safety issues of EC / PC. Summary of the invention

[0004] In view of this, the present application provides an electrolyte and a preparation method thereof, a battery and an electronic device to solve at least one problem existing in the background technology.

[0005] The present invention solves the above technical problems through the following technical solutions:

[0006] The first aspect of the present invention provides an electrolyte, the electrolyte comprising a lithium salt, a solvent and an additive, the solvent comprising a cyclic carbonate solvent, a low-viscosity solvent and a linear carbonate solvent; the low-viscosity solvent is selected from at least one of a carboxylate solvent and an ether solvent;

[0007] Wherein, based on the total mass of the electrolyte being 100%, the mass percentage of the lithium salt is X%, the mass percentage of the cyclic carbonate solvent is Y%, the mass percentage of the low-viscosity solvent is Z%, and the mass percentage of the linear carbonate solvent is W%;

[0008] Wherein, X, Y, Z and W satisfy the following conditions: 90≤X+Y+Z+W≤100, and Y≤Z≤W.

[0009] Preferably, X, Y, Z and W satisfy at least one of the following conditions (1) to (6):

[0010] (1) 0.5 ≤ Y / X ≤ 1.4;

[0011] (2)2≤Z / X≤3;

[0012] (3)2≤Z / Y≤4;

[0013] (4)2.5X≤Y+Z≤4.5X;

[0014] (5)10≤X≤15;

[0015] (6)30≤W≤55.

[0016] Preferably, X, Y, Z and W simultaneously satisfy the following conditions (1) to (4):

[0017] (1) 0.5 ≤ Y / X ≤ 1.4;

[0018] (2)2≤Z / X≤3;

[0019] (3)2≤Z / Y≤4;

[0020] (4)2.5X≤Y+Z≤4.5X.

[0021] Preferably, the lithium salt is selected from one or more of LiPF6, LiFSI, lithium tetrafluoroborate, lithium perchlorate, lithium difluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide and lithium difluorobis(oxalatophosphate).

[0022] Preferably, the cyclic carbonate solvent is selected from one or more of cyclic ethylene carbonate and its derivatives, cyclic propylene carbonate and its derivatives, fluorinated cyclic ethylene carbonate and its derivatives, and cyclic propylene carbonate and its derivatives.

[0023] Preferably, the carboxylic acid ester solvent is selected from one or more of ethyl formate and its derivatives, ethyl acetate and its derivatives, ethyl propionate and its derivatives, propyl acetate and its derivatives.

[0024] Preferably, the ether solvent is selected from one or more of ethylene glycol dimethyl ether and its derivatives, tetrahydrofuran and its derivatives, and dioxolane and its derivatives.

[0025] Preferably, the linear carbonate solvent is selected from one or more of diethyl carbonate and its derivatives, dimethyl carbonate and its derivatives, ethyl methyl carbonate and its derivatives.

[0026] Preferably, the additive is selected from one or more of VC (vinylene carbonate), PS (1,3-propane sultone), PST (1,3-propylene sultone), TMSB (tris(trimethylsilyl)borate), TMSP (tris(trimethylsilyl)phosphate), FEC (fluoroethylene carbonate), DTD (ethylene sulfate), and MMDS (methylene methane disulfonate).

[0027] A second aspect of the present invention provides a battery, comprising the electrolyte provided by the first aspect of the present invention.

[0028] A third aspect of the present invention provides an electronic device, comprising the battery provided by the second aspect of the present invention.

[0029] The present invention provides an electrolyte and a preparation method thereof, a battery and an electronic device. To address the interface stability problem of commonly used solvents in existing fast-charging electrolytes, the present invention creatively designs the ratio of the contents of lithium salt, cyclic carbonate solvent and low-viscosity solvent by adjusting the ratio so that the solvent molecules are fully coordinated with the lithium salt and the number of free solvent molecules is minimized to improve the interface stability of the electrolyte. The low viscosity of the solution is ensured by designing that the content of the low-viscosity solvent is greater than the content of the cyclic carbonate solvent to meet the fast-charging requirements, thereby completing an electrolyte design that takes both interface stability and fast-charging performance into consideration, so that the battery including the electrolyte described in the present application has excellent high-temperature / normal-temperature high-cycle performance and strong fast-charging capability. DETAILED DESCRIPTION

[0030] In order to make the technical scheme and beneficial effects of the present invention more obvious and easy to understand, the following is described in detail by listing specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples without specifying specific conditions are usually based on conventional experimental conditions. The reagents and raw materials used in the present invention are commercially available unless otherwise specified.

[0031] In the following description, a large number of specific details are given to provide a more thorough understanding of the present application. However, it is obvious to those skilled in the art that the present application can be implemented without one or more of these details. In other examples, in order to avoid confusion with the present application, some technical features known in the art are not described; that is, all features of the actual embodiments are not described here, and well-known functions and steps are not described in detail.

[0032] The purpose of the terms used herein is only to describe specific embodiments and is not intended to be limiting of the present application. When used herein, the singular forms "one", "an" and "said / the" are also intended to include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "consisting of" and / or "comprising", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0033] In order to thoroughly understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solution of the present application. The preferred embodiments of the present application are described in detail below, but in addition to these detailed descriptions, the present application may also have other implementation methods.

[0034] Unless otherwise defined, technical and scientific terms used in this application have the same meanings as those in the technical field to which this application belongs.

[0035] If no specific techniques or conditions are specified in the following examples, the conventional techniques or conditions described in the literature in the art, or the conditions recommended by the product instructions and the manufacturer are generally used. The numerical ranges in the following examples all include the endpoint values.

[0036] [Electrolyte]

[0037] The first aspect of the present invention provides an electrolyte, the electrolyte comprising a lithium salt, a solvent and an additive, the solvent comprising a cyclic carbonate solvent, a low-viscosity solvent and a linear carbonate solvent; the low-viscosity solvent is selected from at least one of a carboxylate solvent and an ether solvent;

[0038] Wherein, based on the total mass of the electrolyte being 100%, the mass percentage of the lithium salt is X%, the mass percentage of the cyclic carbonate solvent is Y%, the mass percentage of the low-viscosity solvent is Z%, and the mass percentage of the linear carbonate solvent is W%;

[0039] Wherein, X, Y, Z and W satisfy the following conditions: 90≤X+Y+Z+W≤100, and Y≤Z≤W.

[0040] The present application is creatively designed by adjusting the ratio of lithium salt content X, cyclic carbonate solvent content Y and low-viscosity solvent content Z, so that the lithium salt is not completely dissociated and coordinated in the cyclic carbonate solvent, and a certain amount of low-viscosity solvent is subsequently coordinated, thereby weakening the activity of the low-viscosity solvent and the cyclic carbonate, minimizing the number of free solvent molecules as much as possible, improving the stability of the fast-charging electrolyte to the interface, and extending the cycle life; on the other hand, the viscosity of the electrolyte of the present application itself is reduced, but the conductivity is improved, which also makes the battery including the electrolyte described in the present application have excellent high-temperature / normal-temperature high-multiple cycle performance and strong fast-charging capability.

[0041] In the present application, the purpose of adding a cyclic carbonate solvent is to allow the lithium salt to be fully dissociated, improve the conductivity of the electrolyte, effectively prevent the content of free solvent molecules in the electrolyte, so as to improve the interface stability of the electrolyte, reduce the side reactions of the electrolyte, and thereby make the battery including the electrolyte described in the present application have excellent high temperature / normal temperature high-frequency cycle performance and strong fast charging capability.

[0042] When Y, Z and W satisfy Y≤Z≤W, the lithium salt can be fully dissociated, effectively preventing the content of free solvent molecules in the electrolyte, thereby improving the interface stability of the electrolyte, reducing the side reactions of the electrolyte, and thereby making the battery including the electrolyte described in the present application have excellent high temperature / normal temperature high-frequency cycle performance and strong fast charging capability.

[0043] In certain embodiments, X and Y satisfy 0.5≤Y / X≤1.4, such as 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35 or 1.4, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Therefore, when X and Y satisfy the above range, it is possible to prevent the problem that the lithium salt cannot be fully dissociated due to the low content of the cyclic carbonate solvent, which seriously deteriorates the kinetic properties of the electrolyte; it is also possible to prevent the problem that the content of the cyclic carbonate solvent is too high, so that most of the lithium salt is coordinated with the cyclic carbonate solvent, resulting in a significant increase in the free solvent molecules of the low-viscosity solvent, a decrease in the stability of the electrolyte interface, and a significant increase in the side reactions of the electrolyte, thereby making the battery including the electrolyte described in the present application have excellent high temperature / normal temperature high-cycle performance and strong fast charging capability.

[0044] In some embodiments, X and Z satisfy 2≤Z / X≤3, such as 2, 2.05, 2.1, 2.15, 2.2, 2.25, 2.3, 2.35, 2.4, 2.45, 2.5, 2.55, 2.6, 2.65, 2.7, 2.75, 2.8, 2.85, 2.9, 2.95 or 3, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Thus, when X and Z meet the above range, it is possible to prevent the increase in electrolyte viscosity due to the low content of low viscosity solvent, thereby causing the problem of decreased conductivity of the electrolyte; it is also possible to prevent the problem of increased free solvent molecules in the electrolyte due to the inability of lithium salt to fully coordinate solvent molecules due to the high content of low viscosity solvent, decreased stability of the electrolyte interface, and further increased side reactions at high temperatures of the electrolyte, thereby making the battery including the electrolyte described in the present application have excellent high temperature / normal temperature high-frequency cycle performance and strong fast charging capability.

[0045] In certain embodiments, Z and Y satisfy 2≤Z / Y≤4, for example 2, 2.05, 2.1, 2.15, 2.2, 2.25, 2.3, 2.35, 2.4, 2.45, 2.5, 2.55, 2.6, 2.65, 2.7, 2.75, 2.8, 2.85, 2.9, 2.95, 3, 3.05, 3.1, 3.15, 3.2, 3.25, 3.3, 3.35, 3.4, 3.45, 3.5, 3.55, 3.6, 3.65, 3.7, 3.75, 3.8, 3.85, 3.9, 3.95 or 4, but are not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Therefore, when Y and Z satisfy the above ranges, the battery including the electrolyte described in the present application has excellent high temperature / normal temperature high-cycle performance and strong fast charging capability.

[0046] In certain embodiments, X, Y and Z satisfy 2.5X≤Y+Z≤4.5X, for example, Y+X=2.5X, Y+X=2.6X, Y+X=2.7X, Y+X=2.8X, Y+X=2.9X, Y+X=3X, Y+X=3.1X, Y+X=3.2X, Y+X=3.3X, Y+X=3.4X, Y+X=3.5X, Y+X=3.6X, Y+X=3.7X, Y+X=3.8X, Y+X=3.9X, Y+X=4.0X, Y+X=4.1X, Y+X=4.2X, Y+X=4.3X, Y+X=4.4X or Y+X=4.5X, but are not limited to the listed formulas, and other formulas not listed within the scope of the inequality are equally applicable. Therefore, when X, Y and Z meet the above conditions, the battery including the electrolyte described in the present application has excellent high temperature / normal temperature high-cycle performance and strong fast charging capability.

[0047] In some embodiments, the X satisfies 10≤X≤15, such as 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5 or 15, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable. Therefore, when the X satisfies the above range, it can prevent the problem that the lithium ion content of the electrolyte is significantly reduced due to the low lithium salt content, so that the electrolyte conductivity is reduced and the solvent molecules cannot be fully coordinated, resulting in an increase in the side reaction of the electrolyte; it can also prevent the problem that the lithium salt cannot be completely dissociated due to the high lithium salt content, and the electrolyte viscosity increases and causes the conductivity to decrease, thereby making the battery including the electrolyte described in the present application have excellent high temperature / normal temperature high-cycle performance and strong fast charging capability.

[0048] In some embodiments, the W satisfies 30≤W≤55, such as 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54 or 55, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable. Therefore, when the W satisfies the above range, the battery including the electrolyte described in the present application has excellent high temperature / normal temperature high-cycle performance and strong fast charging capability.

[0049] In certain embodiments, X, Y, Z and W satisfy at least one of the following conditions (1) to (6):

[0050] (1) 0.5 ≤ Y / X ≤ 1.4;

[0051] (2)2≤Z / X≤3;

[0052] (3)2≤Z / Y≤4;

[0053] (4)2.5X≤Y+Z≤4.5X;

[0054] (5)10≤X≤15;

[0055] (6)30≤W≤55.

[0056] In certain embodiments, X, Y, Z and W simultaneously satisfy the following conditions (1) to (4):

[0057] (1) 0.5 ≤ Y / X ≤ 1.4;

[0058] (2)2≤Z / X≤3;

[0059] (3)2≤Z / Y≤4;

[0060] (4)2.5X≤Y+Z≤4.5X.

[0061] In certain embodiments, X, Y, Z and W simultaneously satisfy the following conditions (1) to (6):

[0062] (1) 0.5 ≤ Y / X ≤ 1.4;

[0063] (2)2≤Z / X≤3;

[0064] (3)2≤Z / Y≤4;

[0065] (4)2.5X≤Y+Z≤4.5X;

[0066] (5)10≤X≤15;

[0067] (6)30≤W≤55.

[0068] In certain embodiments, the lithium salt is selected from one or more of LiPF6, LiFSI, lithium tetrafluoroborate, lithium perchlorate, lithium difluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide, and lithium difluorobis(oxalatophosphate).

[0069] In certain embodiments, the cyclic carbonate solvent is selected from one or more of cyclic ethylene carbonate and its derivatives, cyclic propylene carbonate and its derivatives, fluorinated cyclic ethylene carbonate and its derivatives, and cyclic propylene carbonate and its derivatives.

[0070] In certain embodiments, the cyclic carbonate solvent is selected from one or more of cyclic ethylene carbonate, cyclic propylene carbonate, fluorinated cyclic ethylene carbonate, and cyclic propylene carbonate.

[0071] In certain embodiments, the carboxylate solvent is selected from one or more of ethyl formate and its derivatives, ethyl acetate and its derivatives, ethyl propionate and its derivatives, and propyl acetate and its derivatives.

[0072] In certain embodiments, the carboxylate solvent is selected from one or more of ethyl formate, ethyl acetate, ethyl propionate, and propyl acetate.

[0073] In certain embodiments, the ether solvent is selected from one or more of ethylene glycol dimethyl ether and its derivatives, tetrahydrofuran and its derivatives, and dioxolane and its derivatives.

[0074] In certain embodiments, the ether solvent is selected from one or more of ethylene glycol dimethyl ether, tetrahydrofuran, and dioxolane.

[0075] In certain embodiments, the low viscosity solvent is selected from one or more of ethyl formate, ethyl acetate, ethyl propionate, propyl acetate, methyl acetate, ethylene glycol dimethyl ether, tetrahydrofuran, and dioxolane.

[0076] In certain embodiments, the linear carbonate solvent is selected from one or more of diethyl carbonate and its derivatives, dimethyl carbonate and its derivatives, ethyl methyl carbonate and its derivatives.

[0077] In certain embodiments, the linear carbonate solvent is selected from one or more of diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0078] In certain embodiments, the additive is selected from one or more of VC (vinylene carbonate), PS (1,3-propane sultone), PST (1,3-propylene sultone), TMSB (tris(trimethylsilyl)borate), TMSP (tris(trimethylsilyl)phosphate), FEC (fluoroethylene carbonate), DTD (ethylene sulfate), and MMDS (methylene methane disulfonate).

[0079] In certain embodiments, the additive is selected from one or more of VC (vinylene carbonate), PS (1,3-propane sultone), DTD (diethylene sulfate) and MMDS (methylene methane disulfonate).

[0080] In certain embodiments, the additive is selected from a mixture of VC (vinylene carbonate), PS (1,3-propane sultone), DTD (vinyl sulfate) and MMDS (methylene methane disulfonate).

[0081] [Battery]

[0082] A second aspect of the present invention provides a battery, comprising the electrolyte provided by the first aspect of the present invention.

[0083] In some embodiments, the battery may be a secondary battery or a primary battery, preferably a secondary battery. For example, the battery may be a lithium-ion battery, but is not limited thereto. The battery structure of the present application includes but is not limited to a soft-pack lithium-ion battery, a square hard-shell battery, or a cylindrical hard-shell battery.

[0084] In some embodiments, the battery further comprises a positive electrode sheet, a negative electrode sheet and a separator. Typically, the battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator, and the separator is disposed between the positive electrode sheet and the negative electrode sheet. During the battery charge and discharge process, active ions are embedded and removed back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and mainly plays the role of preventing the positive / negative electrode from short-circuiting, while allowing ions to pass through.

[0085] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode current collector may be aluminum foil, copper foil, titanium foil, nickel foil, iron foil, zinc foil, etc. The positive electrode active material layer includes a positive electrode active material. The positive electrode active material suitable for the present invention may be various known positive electrode active materials that can be used for lithium ion batteries, which can reversibly embed and deintercalate lithium ions. The positive electrode active material may be selected from a composite oxide containing lithium and at least one selected from cobalt, manganese, nickel and iron, preferably a composite oxide containing lithium. The lithium-containing composite oxide is preferably LiM x O y and LiM x PO4, wherein M is a combination of one or more transition metals, 0<x≤3, 0<y≤4. Examples of positive electrode active materials include lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese aluminum oxide, lithium iron phosphate (LiFePO4), etc. In some embodiments, the positive electrode active material includes NCM (811).

[0086] The positive electrode active material layer may also include one or two selected from a conductive agent and a binder. The conductive agent is used to improve the conductivity of the electrode. Examples of the conductive agent of the positive electrode include one or more of conductive carbon black, carbon fiber (CF), acetylene black, Ketjen black, graphene and carbon nanotubes. The binder of the positive electrode improves the bonding performance between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of the binder of the positive electrode include at least one of a fluorine-containing resin, a polypropylene resin, a fiber-type binder, a rubber-type binder and a polyimide-type binder. In some embodiments, the conductive agent in the positive electrode active material layer is conductive carbon black and single-walled carbon nanotubes, and the binder is polyvinylidene fluoride. The mass ratio of each component in the positive electrode active material layer can be conventional.

[0087] The positive electrode active material layer is obtained by coating a positive electrode slurry containing various components of the positive electrode active material layer and a solvent onto a positive electrode current collector, and then rolling and slitting. The solvent of the positive electrode slurry can be N-methylpyrrolidone (NMP).

[0088] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode current collector may be aluminum foil, copper foil, titanium foil, nickel foil, iron foil, zinc foil, etc. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material may include a material capable of reversibly embedding / de-embedding lithium ions, lithium metal, lithium metal alloy, a material capable of doping / de-doping lithium, or a transition metal oxide. Examples of negative electrode active materials include lithium metal, structured lithium metal, graphite (e.g., natural graphite, artificial graphite), mesophase carbon balls, hard carbon, soft carbon, silicon, silicon-oxygen materials (e.g., silicon dioxide, silicon oxide), silicon-carbon composite materials (Si / C composite materials), Li-Sn alloys, Li-Sn-O alloys, spinel-structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy, etc. In some embodiments, the negative electrode active material comprises graphite.

[0089] The negative electrode active material layer may also include one or two selected from a conductive agent and a binder. The conductive agent is used to improve the conductivity of the electrode. Examples of negative electrode conductive agents include conductive carbon black, conductive graphite, vapor deposited carbon fiber (VGCF), carbon nanotubes, graphene, etc. The binder of the negative electrode improves the bonding performance between the negative electrode active material particles and between the negative electrode active material particles and the current collector. Examples of negative electrode binders include polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC-Na), cyclodextrin, gelatin, polyvinyl alcohol, polyacrylate, acrylonitrile multipolymer, etc. In some embodiments, the conductive agent in the negative electrode active material layer is acetylene black, and the binder is styrene butadiene rubber and sodium carboxymethyl cellulose. The mass ratio of each component in the negative electrode active material layer can be conventional.

[0090] The negative electrode active material layer is obtained by coating the negative electrode slurry containing the components of the negative electrode active material layer and a solvent onto the negative electrode current collector, and then rolling and slitting. The solvent of the negative electrode slurry can be a conventional solvent in the art, such as deionized water.

[0091] In certain embodiments, the separator can be a polymer porous separator, an inorganic porous separator or a polymer-inorganic composite porous separator. The polymer porous separator includes a single-layer polymer porous separator and a multi-layer polymer porous separator.

[0092] The battery of the present application also includes a packaging shell for accommodating a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, as well as other components known in the art in lithium-ion batteries, and the present application does not limit the above-mentioned other components. The present application does not specifically limit the packaging shell, and it can be a packaging shell known in the art, as long as it can achieve the purpose of the present application.

[0093] The present invention has no special limitation on the method for preparing the battery, and the technical scheme for preparing the negative electrode material into a battery such as a secondary battery, which is well known to those skilled in the art, can be adopted.

[0094] It should be understood that, since the battery provided in the present application includes the electrolyte described in the first aspect of the present invention, the beneficial effects of the electrolyte described in any of the above embodiments are applicable to the battery.

[0095] [Electronic devices]

[0096] A third aspect of the present invention provides an electronic device, comprising the battery provided by the second aspect of the present invention.

[0097] The use of the 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 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 TVs, 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, drones, and lithium-ion capacitors.

[0098] It should be understood that, since the electronic device provided in the present application includes the battery described in the second aspect of the present invention, the beneficial effects of the electrolyte described in any of the above embodiments are applicable to the electronic device.

[0099] The method of the present invention is described below by means of specific examples. It should be understood that these examples are used to illustrate the basic principles, main features and advantages of the present invention, and the present invention is not limited to the scope of the following examples; the implementation conditions adopted in the examples can be further adjusted according to specific requirements, and the implementation conditions not specified are usually the conditions in routine experiments.

[0100] Example

[0101] Example 1 provides an electrolyte that takes into account both interface stability and fast charging performance, and the preparation method thereof is: in a glove box filled with inert gas (H2O <10ppm, O2 <5ppm), a lithium salt (LiPF6), a cyclic carbonate solvent (EC), a low viscosity solvent (EA), a linear carbonate solvent (EMC) and additives (VC, PS, DTD and MMDS) are mixed in a ratio of 12:12:30:43:3 to obtain the electrolyte that takes into account both interface stability and fast charging performance.

[0102] The preparation methods of the electrolytes provided in Examples 2 to 11 and Comparative Examples 1 to 9 are the same as those in Example 1, except that in each example or comparative example, the specific selection and component proportions of the lithium salt, cyclic carbonate solvent, low viscosity solvent and linear carbonate solvent are different, as shown in Table 1.

[0103] Table 1

[0104]

[0105]

[0106] (EC is ethylene carbonate; PC is propylene carbonate; EA is ethyl acetate; MA is methyl acetate; DMC is dimethyl carbonate; EMC is ethyl methyl carbonate; VC is vinylene carbonate; PS is 1,3-propane sultone; DTD is vinyl sulfate; MMDS is methylene disulfonate)

[0107] Preparation of batteries

[0108] 1. Preparation of positive electrode sheet: The positive electrode active material NCM (811), the binder polyvinylidene fluoride (PVDF), the conductive carbon black and the single-walled carbon nanotube are mixed in a weight ratio of 97.2:1.5:1.2:0.1, N-methylpyrrolidone (NMP) is added, and the mixture is stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is evenly coated on the current collector aluminum foil; the coated aluminum foil is baked in an oven with 5 different temperature gradients, and then dried in an oven at 120°C for 8 hours, and then rolled and cut to obtain the desired positive electrode sheet.

[0109] 2. Preparation of negative electrode sheets: A certain proportion of negative electrode active material graphite, thickener sodium carboxymethyl cellulose (CMC-Na), binder styrene-butadiene rubber, and conductive agent acetylene black are mixed in a weight ratio of 97:1:1:1, deionized water is added, and negative electrode slurry is obtained under the action of a vacuum mixer; the negative electrode slurry is evenly coated on a high-strength carbon-coated copper foil to obtain an electrode sheet; the obtained electrode sheet is dried at room temperature and then transferred to an oven at 80°C for drying for 10 hours, and then rolled and cut to obtain a negative electrode sheet.

[0110] 3. Preparation of batteries: The positive electrode sheet, separator (9-micron thick PP film), and negative electrode sheet prepared by the above method are stacked in order to ensure that the separator is between the positive and negative electrode sheets to play an isolating role. The bare battery cell is placed in an aluminum-plastic film outer package. The electrolyte prepared according to Examples 1 to 11 and Comparative Examples 1 to 9 of the present application is respectively injected into the dried battery. After packaging, standing, forming, shaping, and capacity division, batteries with Examples 1 to 11 and Comparative Examples 1 to 9 as electrolytes are obtained.

[0111] Electrochemical performance test

[0112] The batteries prepared according to the above preparation method using Examples 1-11 and Comparative Examples 1-9 as electrolytes were subjected to room temperature high rate cycle tests and high temperature high rate cycle tests respectively:

[0113] 1. High-frequency cycle test at room temperature: At 25°C, charge to 4.25V at 2C constant current, then discharge to 2.5V at 2C constant current, record the discharge capacity at this time as the initial discharge capacity; repeat the above operation until the discharge capacity drops to 80% of the initial discharge capacity, the test is terminated, and the number of cycles at this time is recorded.

[0114] 2. High temperature and high cycle test: At 45°C, charge to 4.25V at 2C constant current, and then discharge to 2.5V at 2C constant current, record the discharge capacity at this time as the initial discharge capacity; repeat the above operation until the discharge capacity drops to 80% of the initial discharge capacity, the test is terminated, and the number of cycles at this time is recorded. The relevant test results are shown in Table 2.

[0115] Table 2

[0116]

[0117]

[0118] The lithium salt (LiPF6) content X, the cyclic carbonate solvent (EC) content Y, the low viscosity solvent (EA) content Z and the linear carbonate solvent (EMC) content W in the electrolyte provided in Example 1 simultaneously satisfy 90≤X+Y+Z+W≤100, Y≤Z≤W, 0.5≤Y / X≤1.4, 2≤Z / X≤3, 2≤Z / Y≤4, 2.5X≤Y+Z≤4.5X, 10≤X≤15 and 30≤W≤55. It can be seen from Table 2 that the battery prepared with Example 1 as the electrolyte has extremely excellent cycle numbers in both the room temperature high-multiple cycle test (25℃-2C) and the high temperature high-multiple cycle test (45℃-2C).

[0119] The electrolyte provided in Example 2 also satisfies 90≤X+Y+Z+W≤100, Y≤Z≤W, 0.5≤Y / X≤1.4, 2≤Z / X≤3, 2≤Z / Y≤4, 2.5X≤Y+Z≤4.5X, 10≤X≤15 and 30≤W≤55, wherein the ratio of the cyclic carbonate solvent (EC) to the lithium salt (LiPF6) content Y / X=0.5. It can be seen from Table 2 that the battery prepared with Example 2 as the electrolyte has a certain influence on the high-frequency cycle at room temperature of 25℃-2C, which is due to the reduction of the EC content, which leads to a certain limitation in the dissociation of the lithium salt.

[0120] The electrolyte provided in Example 3 also satisfies 90≤X+Y+Z+W≤100, Y≤Z≤W, 0.5≤Y / X≤1.4, 2≤Z / X≤3, 2≤Z / Y≤4, 2.5X≤Y+Z≤4.5X, 10≤X≤15 and 30≤W≤55, wherein the ratio of the cyclic carbonate solvent (EC) to the lithium salt (LiPF6) content Y / X=1.4. As can be seen from Table 2, since both EC and EA have increased relative to Example 1, the lithium salt is fully dissociated, so the battery prepared with Example 3 as the electrolyte is less affected by the 25℃-2C room temperature cycle. However, due to the increase of EC and EA, the free solvent content in the electrolyte has also increased to a certain extent, resulting in a decrease in the stability of the electrolyte interface, causing the battery to have side reactions at high temperatures, thereby affecting the high temperature cycle of the battery.

[0121] The electrolyte provided in Example 4 also satisfies 90≤X+Y+Z+W≤100, Y≤Z≤W, 0.5≤Y / X≤1.4, 2≤Z / X≤3, 2≤Z / Y≤4, 2.5X≤Y+Z≤4.5X, 10≤X≤15 and 30≤W≤55, wherein the ratio of the low viscosity solvent (EA) to the lithium salt (LiPF6) content Z / X=2. It can be seen from Table 2 that due to the reduction of EA content relative to Example 1, the viscosity of the electrolyte increases, which in turn causes its kinetic performance to be limited, which has a certain impact on the 25℃-2C room temperature high-frequency cycle of the battery prepared using Example 4 as the electrolyte, but has little impact on the high-temperature cycle.

[0122] The electrolyte provided in Example 5 also satisfies 90≤X+Y+Z+W≤100, Y≤Z≤W, 0.5≤Y / X≤1.4, 2≤Z / X≤3, 2≤Z / Y≤4, 2.5X≤Y+Z≤4.5X, 10≤X≤15 and 30≤W≤55, wherein the ratio of the low viscosity solvent (EA) to the lithium salt (LiPF6) is Z / X=3. As can be seen from Table 2, due to the increase in EA content compared with Example 1, the free solvent molecules of the low viscosity solvent increase, resulting in a decrease in the interfacial stability of the electrolyte, and the strengthening of the high temperature side reaction, which has a certain impact on the 45°C-2C high temperature and high-frequency cycle of the battery prepared with Example 5 as the electrolyte, but has little impact on the normal temperature cycle.

[0123] The electrolyte provided in Example 6 also satisfies 90≤X+Y+Z+W≤100, Y≤Z≤W, 0.5≤Y / X≤1.4, 2≤Z / X≤3, 2≤Z / Y≤4, 2.5X≤Y+Z≤4.5X, 10≤X≤15 and 30≤W≤55, wherein the lithium salt (LiPF6) content X=10. It can be seen from Table 2 that due to the reduction of the lithium salt content in the electrolyte, the lithium ion content of the electrolyte is reduced, so that the conductivity of the battery prepared with Example 6 as the electrolyte is affected to some extent, but the overall performance is still relatively excellent.

[0124] The electrolyte provided in Example 7 also satisfies 90≤X+Y+Z+W≤100, Y≤Z≤W, 0.5≤Y / X≤1.4, 2≤Z / X≤3, 2≤Z / Y≤4, 2.5X≤Y+Z≤4.5X, 10≤X≤15 and 30≤W≤55, wherein the lithium salt (LiPF6) content X=15. As can be seen from Table 2, although the lithium salt content in the electrolyte increases, since all the proportions are satisfied at the same time, the overall performance of the battery prepared using Example 7 as the electrolyte is affected, but the impact is small.

[0125] Compared with Example 1, the electrolyte provided in Example 8 replaces the lithium salt from LiPF6 to LIFSI, the electrolyte provided in Example 9 replaces the cyclic carbonate solvent from EC to PC, the electrolyte provided in Example 10 replaces the low viscosity solvent from EA to MA, and the electrolyte provided in Example 11 replaces the linear carbonate solvent from EMC to DEC. The batteries prepared with the electrolytes provided in the above examples have little difference in high temperature and room temperature high-cycle performance from Example 1, and both show excellent electrochemical performance.

[0126] The ratio of the cyclic carbonate solvent (EC) to the lithium salt (LiPF6) in the electrolyte provided in Comparative Example 1 is Y / X < 0.5, which does not meet the requirements. As can be seen from Table 2, the battery prepared with Comparative Example 1 as the electrolyte cannot meet the ratio requirements of this application due to the large reduction in EC content, resulting in the inability to fully dissociate the lithium salt, which seriously deteriorates the kinetic properties of the electrolyte and significantly deteriorates the overall performance of the battery.

[0127] The ratio of the cyclic carbonate solvent (EC) to the lithium salt (LiPF6) in the electrolyte provided in Comparative Example 2 is Y / X>1.4, which does not meet the requirements. As can be seen from Table 2, due to the large increase in the EC content, the ratio requirement of the present application can no longer be met, so that most of the lithium salt is coordinated with EC, resulting in a significant increase in the free molecules of the EA solvent, resulting in a decrease in the interfacial stability of the electrolyte, causing a significant increase in the side reactions of the electrolyte, and thus causing the cycle performance of the battery prepared with Comparative Example 2 as the electrolyte to be seriously deteriorated.

[0128] The ratio of the low viscosity solvent (EA) to the lithium salt (LiPF6) in the electrolyte provided in Comparative Example 3, Z / X < 2, does not meet the requirements. As can be seen from Table 2, since the EA content is reduced too much to meet the ratio requirements of this application, the viscosity of the electrolyte increases, causing the conductivity of the electrolyte to decrease, and further causing the cycle performance of the battery prepared with Comparative Example 3 as the electrolyte to deteriorate seriously.

[0129] The ratio of the low viscosity solvent (EA) to the lithium salt (LiPF6) in the electrolyte provided in Comparative Example 4 is Z / X>3, which does not meet the requirements. As can be seen from Table 2, due to the large increase in the EA content, the ratio requirement of the present application can no longer be met, resulting in the inability of the lithium salt to fully coordinate the solvent molecules, resulting in an increase in the free solvent molecules in the electrolyte, resulting in a decrease in the stability of the electrolyte interface, causing a further increase in side reactions at high temperatures, and thus causing the cycle performance of the battery prepared using Comparative Example 4 as the electrolyte to be seriously deteriorated.

[0130] The lithium salt (LiPF6) content X in the electrolyte provided in Comparative Example 5 is less than 10, which does not meet the requirements. As can be seen from Table 2, the lithium salt content in the electrolyte is reduced too much to meet the ratio requirements of this application, resulting in a significant reduction in the lithium ion content of the electrolyte, which makes the electrolyte conductivity decrease while the solvent molecules cannot be fully coordinated, resulting in an increase in side reactions, and further causing the cycle performance of the battery prepared using Comparative Example 5 as the electrolyte to deteriorate seriously.

[0131] The lithium salt (LiPF6) content X>15 in the electrolyte provided in Comparative Example 6 does not meet the requirements. As can be seen from Table 2, the lithium salt content in the electrolyte has increased too much to meet the ratio requirements of this application, resulting in the inability to completely dissociate the lithium salt, and the increase in electrolyte viscosity causes the conductivity to decrease, which in turn leads to a serious deterioration in the cycle performance of the battery prepared using Comparative Example 6 as the electrolyte.

[0132] The electrolyte provided in Comparative Example 7 reduces the content of the low-viscosity solvent to 0 compared with Example 1. Compared with Example 1, the cycle performance of the battery prepared with the electrolyte provided in Comparative Example 7 is reduced by nearly half.

[0133] The electrolyte cyclic carbonate solvent (EC) content Y, low viscosity solvent (EA) content Z and linear carbonate solvent (EMC) content W provided in Comparative Example 8 do not meet the requirement of Y<Z<W. Since the ratio requirement of the present application is not met, there are certain free solvent molecules in the electrolyte, resulting in decreased stability of the electrolyte interface. Therefore, it can be seen from Table 2 that the cycle performance of the battery prepared with the electrolyte provided in Comparative Example 8 is significantly deteriorated.

[0134] Compared with Example 1, the electrolyte provided in Comparative Example 9 reduces the content of the cyclic carbonate solvent to 0, causing the lithium salt to be unable to fully dissociate, thereby resulting in a decrease in conductivity, and the free solvent content is relatively high, resulting in a decrease in electrolyte interface stability, which significantly increases electrolyte side reactions. Therefore, it can be seen from Table 2 that the cycle performance of the battery prepared with the electrolyte provided in Comparative Example 9 is significantly deteriorated.

[0135] It should be understood that the above embodiments are exemplary and are not intended to include all possible implementations included in the claims. Various modifications and changes may be made on the basis of the above embodiments without departing from the scope of the present disclosure. Similarly, the various technical features of the above embodiments may be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments only express several implementations of the present invention and do not limit the scope of protection of the patent of the present invention.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises a lithium salt, a solvent and an additive, wherein the solvent comprises a cyclic carbonate solvent, a low-viscosity solvent and a linear carbonate solvent; the low-viscosity solvent is selected from at least one of a carboxylate solvent and an ether solvent; Wherein, based on the total mass of the electrolyte being 100%, the mass percentage of the lithium salt is X%, the mass percentage of the cyclic carbonate solvent is Y%, the mass percentage of the low-viscosity solvent is Z%, and the mass percentage of the linear carbonate solvent is W%; Wherein, X, Y, Z and W satisfy the following conditions: 90≤X+Y+Z+W≤100, and Y≤Z≤W.

2. The electrolyte according to claim 1, characterized in that The X, Y, Z and W satisfy at least one of the following conditions (1) to (6): (1) 0.5 ≤ Y / X ≤ 1.4; (2)2≤Z / X≤3; (3)2≤Z / Y≤4; (4)2.5X≤Y+Z≤4.5X; (5)10≤X≤15； (6)30≤W≤55。 3. The electrolyte according to claim 1, characterized in that The X, Y, Z and W simultaneously satisfy the following conditions (1) to (4): (1) 0.5 ≤ Y / X ≤ 1.4; (2)2≤Z / X≤3; (3)2≤Z / Y≤4; (4)2.5X≤Y+Z≤4.5X.

4. The electrolyte according to any one of claims 1 to 3, characterized in that The lithium salt is selected from one or more of LiPF6, LiFSI, lithium tetrafluoroborate, lithium perchlorate, lithium difluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonyl)imide and lithium difluorobis(oxalatophosphate).

5. The electrolyte according to any one of claims 1 to 3, characterized in that The cyclic carbonate solvent is selected from one or more of cyclic ethylene carbonate and its derivatives, cyclic propylene carbonate and its derivatives, fluorinated cyclic ethylene carbonate and its derivatives, and cyclic propylene carbonate and its derivatives.

6. The electrolyte according to any one of claims 1 to 3, characterized in that The carboxylate solvent is selected from one or more of ethyl formate and its derivatives, ethyl acetate and its derivatives, ethyl propionate and its derivatives, propyl acetate and its derivatives; and / or, The ether solvent is selected from one or more of ethylene glycol dimethyl ether and its derivatives, tetrahydrofuran and its derivatives, and dioxolane and its derivatives.

7. The electrolyte according to any one of claims 1 to 3, characterized in that The linear carbonate solvent is selected from one or more of diethyl carbonate and its derivatives, dimethyl carbonate and its derivatives, ethyl methyl carbonate and its derivatives.

8. The electrolyte according to any one of claims 1 to 3, characterized in that The additive is selected from one or more of VC (vinylene carbonate), PS (1,3-propane sultone), PST (1,3-propylene sultone), TMSB (tris(trimethylsilyl)borate), TMSP (tris(trimethylsilyl)phosphate), FEC (fluoroethylene carbonate), DTD (ethylene sulfate), and MMDS (methylene methane disulfonate).

9. A battery, characterized in that: The battery comprises the electrolyte according to any one of claims 1-8.

10. An electronic device, characterized in that: The electronic device comprises the battery as claimed in claim 9.

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