Electrochemical device and electric device

Abstract

The invention discloses an electrochemical device and a power utilization device, and belongs to the technical field of batteries. According to the electrochemical device provided by the invention, the first organic solvent and the first additive of proper types are selected in the electrolyte, meanwhile, the electrolyte further comprises fluoroethylene carbonate, and the first organic solvent, the first additive and the fluoroethylene carbonate interact with one another, so that the high-temperature resistance of the electrochemical device can be effectively improved; specifically, the obtained electrochemical device has good high-temperature cycle performance, high-temperature safety performance, high-temperature standing cycle performance and high-temperature storage performance.

Description

Technical Field

[0001] The present application relates to the technical field of energy storage technology, in particular to an electrochemical device and an electrical device. Background Art

[0002] In electrochemical devices, electrolytes play an important role, including conducting lithium ions, affecting the formation of the solid electrolyte interface (SEI) between the positive and negative electrodes, and ion transport within the electrodes. For different electrochemical device systems and different positive and negative electrode materials, the electrolyte should be rationally designed to achieve excellent battery performance. Conventional electrolytes undergo irreversible oxidative decomposition on the positive electrode surface under high voltage, leading to a series of side reactions such as gas generation, battery swelling, electrode structure destruction, transition metal dissolution, and increased polarization voltage, thereby causing the cycle performance of high-voltage positive electrode materials to degrade. The problem of electrolyte resistance to high-voltage oxidation has become a limiting factor in the development of high-energy-density lithium batteries, and the research of new high-voltage electrolyte systems is urgent. For example, for electrochemical devices using high-voltage positive electrodes (such as LiCoO2 systems above 4.53V) and silicon-based negative electrodes (such as silicon carbide), interface instability is a huge challenge. The positive electrode active material under high voltage is in a highly delithiated state, the layered structure is unstable, and transition metal extraction and oxygen precipitation are prone to occur, resulting in capacity loss and triggering many side reactions. The silicon in the silicon-based negative electrode will repeatedly undergo violent volume expansion and contraction during the lithium alloying process, causing the SEI to be destroyed.

[0003] Adding nitrile additives and negative electrode film-forming additives (such as fluoroethylene carbonate, FEC) to the electrolyte is considered to be an effective way to solve the above problems. Nitrile additives complex with transition metal ions to stabilize the positive electrode interface, while FEC negative electrode film-forming additives can generate a lithium fluoride-rich SEI with excellent mechanical properties to effectively alleviate the interface problems caused by the volume expansion of silicon-based materials. However, the positive and negative electrode interfaces based on high FEC electrolytes often exhibit poor thermal stability, which is related to the potential defluorination and acid production problem of FEC at high temperatures. In addition, the thermal stability of the solvent also profoundly affects the high-temperature performance of the electrolyte for high-voltage electrochemical devices. Solvents with poor thermal stability will cause many side reactions in the electrolyte at high temperature and high voltage, causing rapid capacity decay and gas production, and deteriorating the high-temperature performance of the electrochemical device.

[0004] Therefore, there is an urgent need to develop an electrolyte with excellent high-temperature performance, which is suitable for high-voltage system batteries, can alleviate the problem of poor high-temperature performance of the system batteries, and improve the performance of high-temperature cycling, high-temperature static cycling, high-temperature storage and high-temperature safety. Summary of the Invention

[0005] The purpose of this application is to solve the technical problem that the high-temperature performance of electrochemical devices in the prior art is poor, especially the poor high-temperature performance of high-voltage electrochemical device systems (such as lithium cobalt oxide-silicon based systems) with an operating voltage greater than 4.53V, and proposes an electrochemical device and an electrical device.

[0006] To achieve the above-mentioned object, in a first aspect of the present application, an electrochemical device is provided, wherein the electrochemical device comprises an electrolyte, wherein the electrolyte comprises a first organic solvent, a first additive, and fluoroethylene carbonate;

[0007] The structural formula of the first organic solvent is shown in Formula I, and the structural formula of the first additive is shown in Formula II;

[0008]

[0009] wherein R1 and R2 are each independently selected from a C1-C5 alkyl ester group, a C1-C5 alkyl group, and at least one of R1 and R2 is selected from a dimethyl ester, a methyl ethyl ester, or a methyl propyl ester;

[0010] R3 and R4 are independently selected from C1-C3 alkyl, hydrogen, fluorine, and cyano, wherein at least one of R3 and R4 is cyano.

[0011] As an embodiment of the present application, the electrochemical device further comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a silicon-based material, and the electrochemical device satisfies: 0.48≤A≤1.43

[0012] Where A = (a + b) / (c + d);

[0013] a% is the mass percentage of the first organic solvent based on the total mass of the electrolyte;

[0014] b% is the mass percentage of the first additive based on the total mass of the electrolyte;

[0015] c% is the mass percentage of fluoroethylene carbonate based on the total mass of the electrolyte;

[0016] d% is the mass percentage of the silicon-based material based on the total mass of the negative electrode active material layer.

[0017] As an embodiment of the present application, based on the total mass of the solvent, the mass percentage a% of the first organic solvent is 9%-30%.

[0018] As an embodiment of the present application, based on the total mass of the electrolyte, the mass percentage b% of the first additive is 0.1%-3%.

[0019] As an embodiment of the present application, based on the total mass of the electrolyte, the mass percentage c% of fluoroethylene carbonate is 8%-16%.

[0020] As an embodiment of the present application, based on the total mass of the negative electrode active material layer, the mass percentage d% of the silicon-based material is 10%-15%.

[0021] As an embodiment of the present application, R1 and R2 are each independently selected from methyl, ethyl, propyl, dimethyl ester, methyl ethyl ester, and methyl propyl ester.

[0022] As an embodiment of the present application, R3 and R4 are each independently selected from methyl, hydrogen, fluorine, and cyano.

[0023] As an embodiment of the present application, the electrolyte further includes a second organic solvent, and the second organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, 2,2-difluoroethyl acetate, ethyl propionate, and propyl propionate.

[0024] As an embodiment of the present application, the electrolyte further includes a second additive, which includes at least one of 1,3-propane sultone, vinyl sulfate, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate.

[0025] As an embodiment of the present application, the mass percentage of the second additive is 0.1%-20% based on the total mass of the electrolyte.

[0026] As an embodiment of the present application, the electrolyte further includes a lithium salt, and the mass percentage of the lithium salt is 8%-25% based on the total mass of the electrolyte; the lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, bistrifluoromethanesulfonyl imide lithium salt, and lithium bisfluorosulfonyl imide.

[0027] As an implementation scheme of the present application, the viscosity of the electrolyte is 10 mPa·s-15 mPa·s.

[0028] In a second aspect of the present application, the present application provides an electrical device comprising the electrochemical device described in the present application.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] The present application provides an electrochemical device that can effectively improve the high-temperature resistance of the electrochemical device by selecting suitable types of a first organic solvent and a first additive in the electrolyte, and also including fluoroethylene carbonate in the electrolyte. The interaction between the three can effectively improve the high-temperature resistance of the electrochemical device; specifically, the electrochemical device has good high-temperature cycle performance, high-temperature safety performance, high-temperature static cycle performance and high-temperature storage performance. DETAILED DESCRIPTION

[0031] To make the purpose, technical solutions, and advantages of the embodiments of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0032] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0033] In this application, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe a feature or characteristic, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges subsumed therein.

[0034] In one embodiment of the present application, the present application provides an electrochemical device, the electrochemical device comprising an electrolyte, the electrolyte comprising a first organic solvent, a first additive, and fluoroethylene carbonate;

[0035] The structural formula of the first organic solvent is shown in Formula I, and the structural formula of the first additive is shown in Formula II;

[0036]

[0037] wherein R1 and R2 are each independently selected from a C1-C5 alkyl ester group, a C1-C5 alkyl group, wherein at least one of R1 and R2 is selected from a dimethyl ester, a methyl ethyl ester, or a methyl propyl ester;

[0038] R3 and R4 are independently selected from C1-C3 alkyl, hydrogen, fluorine, and cyano, wherein at least one of R3 and R4 is cyano.

[0039] The present application introduces a first organic solvent and a first additive of a specific structure into the electrolyte, and simultaneously adds fluoroethylene carbonate into the electrolyte. The components in the electrolyte can interact with each other, effectively stabilize the electrode interface, and alleviate excessive volume expansion of the electrochemical device during the cycle process or under high temperature conditions, thereby effectively improving the high-temperature cycle performance, high-temperature storage performance, and high-temperature safety performance of the electrochemical device.

[0040] Specifically, in the first aspect, the present application selects a substance with a structure as shown in Formula I as the first organic solvent, which has better thermal stability and a higher flash point than the organic solvents conventionally used in electrolytes; the first organic solvent selected in the present application is more polar than the conventional organic solvents used in electrolytes, and has a stronger interaction with lithium salts, which can assist in the dissociation of lithium salts and thus improve the ionic conductivity of the electrolyte; in addition, the first organic solvent selected in the present application has a lower viscosity and excellent solubility, which can improve the thermal stability of the electrolyte while also taking into account excellent electrochemical properties.

[0041] Secondly, the present application selects a substance with a structure as shown in Formula II as the first additive, which has the functions of stabilizing the positive electrode interface and forming a film at the negative electrode. Its molecular formula matrix is ​​an ethylene carbonate solvent commonly used in electrolytes that can form a film at the negative electrode. Subsequently, by introducing different groups into the ethylene carbonate cyclic molecule, the first additive exhibits the multifunctionality of simultaneously regulating the positive and negative electrode interfaces; for example, when the positive electrode active material layer includes lithium cobalt oxide, the introduced cyano group can improve the problem of cobalt precipitation at the positive electrode, and can preferentially cause the organic solvent to undergo a reduction film-forming reaction on the negative electrode side to form a solid electrolyte interface with high mechanical properties and stability; the first additive of this structure can simultaneously exhibit the functions of FEC and nitrile additives, and has excellent high-temperature stability.

[0042] On the third aspect, the electrolyte proposed in the present application can be used in combination with a first organic solvent and a first additive, both of which have excellent thermal stability and can significantly improve the high-temperature performance of the electrochemical device. In addition, the first organic solvent is a dibasic ester structure, which has more carbonyl polar functional groups than monobasic esters, and the first organic solvent with a linear structure can more easily enter the deep solvation shell layer, which can reduce the steric hindrance brought by the cyclic carbonate solvent and the first additive, and reduce the lithium ion solvation / desolvation energy barrier increased by the introduction of the first additive, that is, the first organic solvent and the first additive can be used in combination to synergistically regulate the solvation structure, so that the lithium ions have stronger solvation / desolvation thermodynamics and exhibit excellent reaction kinetics.

[0043] Fourthly, the introduction of fluoroethylene carbonate in the electrolyte can have a relatively excellent negative electrode film-forming effect under the action of the first organic solvent and the first additive, and can assist the first organic solvent and the first additive in regulating the solvation structure, so that the lithium ions have strong solvation / desolvation thermodynamics and exhibit excellent reaction kinetics.

[0044] In one embodiment, the electrochemical device further comprises a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a silicon-based material, and the electrochemical device satisfies: 0.48≤A≤1.43

[0045] Where A = (a + b) / (c + d);

[0046] a% is the mass percentage of the first organic solvent based on the total mass of the electrolyte;

[0047] b% is the mass percentage of the first additive based on the total mass of the electrolyte;

[0048] c% is the mass percentage of fluoroethylene carbonate based on the total mass of the electrolyte;

[0049] d% is the mass percentage of the silicon-based material based on the total mass of the negative electrode active material layer.

[0050] Exemplarily, the silicon-based material includes silicon carbide, silicon monoxide, and the like.

[0051] In one embodiment, the silicon-based material is silicon carbide, which is a material having silicon particles as a core and a carbon layer as an outer layer, or a material having silicon loaded on a carbon matrix.

[0052] Silicon-based materials are a commonly added negative electrode active material in the field of electrochemical devices. They have high energy density, high safety and fast charging capabilities. The present application has found that selecting a silicon-based material in the negative electrode active material layer in the electrolyte system of the present application can effectively alleviate the drastic volume expansion and contraction of silicon in the silicon-based material in the conventional electrochemical device during the lithium alloying process, thereby alleviating the destruction of SEI. At the same time, the electrochemical device of the present application satisfies the relationship of 0.48≤(a+b) / (c+d)≤1.43 by regulating the mass percentage of the first organic solvent, the first additive and the fluoroethylene carbonate in the electrolyte and the mass percentage of the silicon-based material in the negative electrode active material layer. When the silicon-based material (such as silicon carbide) is included in the negative electrode active material layer, the obtained electrochemical device also has excellent high temperature performance, specifically, good high temperature cycle performance, high temperature static cycle performance, high temperature storage performance and high temperature impact resistance. In particular, when the upper limit of the operating voltage of the electrochemical device is 4.55V, good high temperature performance can also be achieved.

[0053] Specifically, the present application controls the mass percentages of the first organic solvent, the first additive, and fluoroethylene carbonate in the electrolyte and the mass percentages of the silicon-based material in the negative electrode active material layer to satisfy a certain relationship. The first organic solvent and the first additive are used to respectively improve the thermal stability of the electrolyte and the positive and negative electrode interfaces, while controlling the relationship between the added amounts of fluoroethylene carbonate and the silicon-based material. This can effectively control the overall dynamics of the electrolyte and the electrochemical device within a reasonable range, thereby effectively improving the high-temperature cycle performance, static cycle performance, high-temperature storage performance, high-temperature impact resistance, and safety performance of the electrochemical device.

[0054] Illustratively, A can be any point value or any two point range values ​​between 0.48-1.43, such as 0.48, 0.49, 0.5, 0.52, 0.55, 0.58, 0.6, 0.62, 0.65, 0.68, 0.7, 0.72, 0.75, 0.78, 0.8, 0.82, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1, 1.02, 1.05, 1.08, 1.1, 1.12, 1.15, 1.18, 1.2, 1.22, 1.25, 1.28, 1.3, 1.32, 1.35, 1.38, 1.4, 1.43 or any value therebetween.

[0055] In one embodiment, 0.75≤A≤1. For example, A may be 0.75, 0.76, 0.78, 0.8, 0.82, 0.84, 0.86, 0.88, 0.9, 0.92, 0.94, 0.96, 0.98, 1, or any value therebetween.

[0056] The research in this application found that when the mass percentage of the first organic solvent, the first additive and the fluoroethylene carbonate in the electrolyte and the mass percentage of the silicon-based material in the negative electrode active material layer are further selected to satisfy 0.75≤(a+b) / (c+d)≤1, the overall performance of the obtained electrochemical device is better.

[0057] In one embodiment, based on the total mass of the electrolyte, the mass percentage a% of the first organic solvent is 9%-30%.

[0058] It should be noted that, based on the total mass of the electrolyte, the mass percentage a% of the first organic solvent is obtained by testing with gas chromatography and normalizing the solvent.

[0059] Exemplarily, based on the total mass of the electrolyte, the mass percentage a% of the first organic solvent can be any point value between 9% and 30% or any two point range values, for example, it can be 9%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30% or any value therebetween.

[0060] In one embodiment, based on the total mass of the electrolyte, the mass percentage a% of the first organic solvent is 15%-20%, for example, 15%, 16%, 17%, 18%, 19%, 20% or any value therebetween.

[0061] The present application study found that selecting a first organic solvent with a specific structure of the present application can effectively improve the thermal stability of the electrolyte. Further, when the mass percentage of the first organic solvent is selected to be 9%-30%, especially 15%-20%, it is possible to control the viscosity and kinetics of the electrolyte within a suitable range while improving the high-temperature stability of the electrolyte, thereby ensuring the cycle performance of the prepared electrochemical device, that is, the overall performance of the obtained electrochemical device is better. If too much first organic solvent is used (>30%), the viscosity of the electrolyte is too high, the kinetics decreases and the conductivity decreases, and the high-temperature cycle retention rate and high-temperature storage performance will deteriorate to a certain extent.

[0062] In one embodiment, based on the total mass of the electrolyte, the mass percentage b% of the first additive is 0.1%-3%.

[0063] It should be noted that, based on the total mass of the electrolyte, the mass percentage b% of the first additive is obtained by gas chromatography testing.

[0064] Exemplarily, based on the total mass of the electrolyte, the mass percentage b% of the first additive can be any point value between 0.1% and 3% or any two point range values, for example, it can be 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.6%, 2.8%, 3% or any value therebetween.

[0065] In one embodiment, based on the total mass of the electrolyte, the mass percentage b% of the first additive is 1.5%-2%, for example, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, or any value therebetween.

[0066] The present application study found that the addition of the first additive can improve the thermal stability of the positive and negative electrode interfaces, thereby improving the high-temperature comprehensive performance of the electrochemical device. At the same time, the amount of the first additive added will also affect the cycle performance of the electrochemical device. When the mass percentage of the first additive is further selected to be 0.1%-3%, especially 1.5%-2%, the high-temperature comprehensive performance of the electrochemical device is even better. If the first additive is too high (>3%), although the expansion rate can be further improved, due to the inherent high intermolecular force of the first additive, the viscosity of the electrolyte will increase significantly, which will deteriorate the kinetics to a certain extent, thereby reducing the high-temperature cycle retention rate to a certain extent.

[0067] In one embodiment, based on the total mass of the electrolyte, the mass percentage c% of fluoroethylene carbonate is 8%-16%.

[0068] It should be noted that the mass percentage c% of fluoroethylene carbonate based on the total mass of the electrolyte is obtained by gas chromatography.

[0069] Exemplarily, based on the total mass of the electrolyte, the mass percentage c% of fluoroethylene carbonate can be any point value between 8% and 16% or any two point range values, such as 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16% or any value therebetween.

[0070] In one embodiment, the mass percentage c% of fluoroethylene carbonate is 10%-12% based on the total mass of the electrolyte, for example, 10%, 10.2%, 10.5%, 10.8%, 11%, 11.2%, 11.5%, 11.8%, 12%, or any value therebetween.

[0071] The research in this application found that the addition of fluoroethylene carbonate in an appropriate addition amount range can interact with the first additive to jointly maintain the thermal stability of the positive and negative electrode interfaces and improve the high-temperature performance of the electrolyte. In particular, when the mass percentage of fluoroethylene carbonate is further selected to be 10%-12%, the overall performance of the resulting electrochemical device is better.

[0072] In one embodiment, based on the total mass of the negative electrode active material layer, the mass percentage d% of the silicon-based material is 10%-15%.

[0073] It should be noted that the mass percentage d% of the silicon-based material, based on the total mass of the negative electrode active material layer, is obtained through elemental analysis.

[0074] For example, based on the total mass of the negative electrode active material layer, the mass percentage d% of the silicon-based material can be any point value between 10% and 15% or any two point range values, such as 10%, 11%, 12%, 13%, 14%, 15% or any value therebetween.

[0075] In one embodiment, the mass percentage d% of the silicon-based material, based on the total mass of the negative electrode active material layer, is 12%-13%. For example, it can be 12%, 12.1%, 12.2%, 12.3%, 12.4%, 12.5%, 12.6%, 12.7%, 12.8%, 12.9%, 13%, or any value therebetween.

[0076] The present application study found that the mass percentage of the silicon-based material in the negative electrode active material layer affects its interaction with the fluoroethylene carbonate and the first additive in the electrolyte. If the mass percentage of the silicon-based material increases, the amount of fluoroethylene carbonate added to the electrolyte must also be increased relatively to maintain good cycle performance of the electrochemical device. However, the increase in fluoroethylene carbonate will inevitably reduce the amount of the first additive added, thereby damaging the high-temperature performance of the electrolyte to a certain extent, and rapid decay will occur in the later cycles; therefore, when the mass percentage of the silicon-based material is further selected to be 10%-15%, especially 12%-13%, based on the total mass of the negative electrode active material layer, the overall performance of the resulting electrochemical device is better.

[0077] In one embodiment, R1 and R2 are independently selected from methyl, ethyl, propyl, dimethyl, methylethyl, and methylpropyl.

[0078] For example, the first organic solvent may be a compound represented by Formula III, Formula IV, Formula V, etc.;

[0079]

[0080] The present application study found that when R1 and R2 are further selected from methyl, ethyl, propyl, dimethyl, methyl ethyl, and methyl propyl, they have higher thermal stability than conventional monoester solvents, a boiling point of over 200°C, are not easy to volatilize, and have a higher flash point; in addition, their structure is more complex, their polarity is greater, their interaction with lithium salts is stronger, and they can better assist in the dissociation of lithium salts, thereby improving the ionic conductivity of the electrolyte; at the same time, they are more likely to enter the deep solvation shell of lithium ions, reducing the solvent steric hindrance of the deep solvation shell, thereby helping to regulate the solvation structure, reducing the solvation / desolvation energy barrier of lithium ions, and obtaining faster solvation / desolvation thermodynamics, thereby accelerating the reaction kinetics and increasing the reaction rate; in addition, the first organic solvent of the above-mentioned structural type has a lower viscosity and excellent solubility, which can improve the thermal stability of the electrolyte while also taking into account excellent electrochemical properties.

[0081] In one embodiment, R3 and R4 are independently selected from methyl, hydrogen, fluorine, and cyano.

[0082] For example, the first additive may be a compound represented by Formula VI, Formula VII, Formula VIII, etc.;

[0083]

[0084] The present application found that the first additive is further selected as a substance with the above structure, that is, a cyano group is introduced into the first additive, so that the first additive exhibits multifunctionality. On the one hand, the cyano functional group has a good complexation with metal ions, especially metal ions conventionally used in the positive electrode active material layer, such as cobalt ions. The force of complexation with cobalt ions can effectively improve the cobalt precipitation problem of the positive electrode in the high-voltage lithium battery system. Therefore, the first additive of this type of structure has the function of stabilizing the positive electrode interface; on the other hand, the cyano functional group has an electron-withdrawing effect. Compared with ethylene carbonate, the electron cloud density on the carbonyl group of the first additive provided by this application is lower, and it is more easily absorbed by Li + The attack causes a ring-opening reaction. Furthermore, the LUMO energy level (the lowest unoccupied molecular orbital, which determines a substance's resistance to reduction) of the first additive is lowered due to the electron-withdrawing effect of the cyanide group, resulting in a higher reduction potential. This allows the first additive to undergo a reduction film-forming reaction on the negative electrode side before ethylene carbonate, forming a mechanically stable solid electrolyte interface (SEI), making it an ideal negative electrode film-forming additive. Importantly, the first additive generally exhibits excellent thermal stability, significantly improving the stability of the positive and negative electrode interfaces at high temperatures, thereby enhancing the high-temperature performance of the electrolyte.

[0085] In one embodiment, the electrolyte further includes a second organic solvent, and the second organic solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DEC), 2,2-difluoroethyl acetate (DFEA), ethyl propionate (EP), and propyl propionate (PP).

[0086] In one embodiment, the mass percentage of the second organic solvent is 70%-90% based on the total mass of the electrolyte.

[0087] Illustratively, based on the total mass of the electrolyte, the mass percentage of the second organic solvent can be any point value between 70% and 90% or any two points in the range, such as 70%, 72%, 80%, 85%, 90% or any value therebetween.

[0088] In one embodiment, the electrolyte further includes a second additive, and the second additive includes at least one of 1,3-propane sultone (PS), dithiothreitol (DTD), tris(trimethylsilyl)borate (TMSB), and tris(trimethylsilyl)phosphate (TMSP).

[0089] In one embodiment, the mass percentage of the second additive is 0.1%-20% based on the total mass of the electrolyte.

[0090] It should be noted that the mass percentage of the second additive based on the total mass of the electrolyte is obtained by gas chromatography testing.

[0091] Exemplarily, based on the total mass of the electrolyte, the mass percentage of the second additive can be any point value between 0.1% and 20% or any two point range values, such as 0.1%, 1%, 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20% or any value therebetween.

[0092] In one embodiment, the electrolyte includes lithium salt, and the mass percentage of the lithium salt is 8%-25% based on the total mass of the electrolyte.

[0093] It should be noted that the mass percentage of lithium salt based on the total mass of the electrolyte is obtained by gas chromatography testing.

[0094] Illustratively, based on the total mass of the electrolyte, the mass percentage of the lithium salt can be any point value between 8% and 25% or any two point range values, such as 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 25% or any value therebetween.

[0095] In one embodiment, the lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiDFP), lithium difluorobis(oxalatophosphate) (LiODFP), lithium tetrafluorooxalatophosphate (LiOTFP), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl imide) (LiTFSI), and lithium bis(fluorosulfonyl imide) (LiFSI).

[0096] In one embodiment, the electrolyte viscosity is 10 mPa·s-15 mPa·s.

[0097] It should be noted that the method for testing the viscosity of the electrolyte is as follows: the electrochemical device with the folded edges cut open is centrifuged to obtain the electrolyte, and the viscosity of the electrolyte is tested using a vibration / rotation viscometer.

[0098] Exemplarily, the viscosity value of the electrolyte may be any point value or any two point range value between 10mPa·s-15mPa·s, such as 10mPa·s, 11mPa·s, 12mPa·s, 13mPa·s, 14mPa·s, 15mPa·s or any value therebetween.

[0099] The present application has found that by adding the above-mentioned first organic solvent, first additive, fluoroethylene carbonate and other substances in the present application, and further controlling the viscosity value of the electrolyte within the above-mentioned range, the viscosity value is appropriate, which can achieve good dynamic performance and high-temperature static cycle performance of the electrochemical device.

[0100] In one embodiment, the electrochemical device further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer comprises lithium cobalt oxide.

[0101] The research in this application found that including lithium cobalt oxide in the positive electrode active material layer can realize the preparation of high-voltage high-voltage positive electrodes (above 4.53V), and under the electrochemical device system given in this application, it can effectively alleviate the problem of interface instability of high-voltage electrochemical devices, and alleviate the problem that the LiCoO2 positive electrode at high voltage is in a highly delithiation state, the layered structure is unstable, cobalt is released and oxygen is precipitated, resulting in capacity loss and triggering many side reactions, thereby helping to achieve excellent high-temperature performance of high-voltage electrochemical devices.

[0102] In one embodiment, the positive electrode active material layer further includes a positive electrode conductor and a positive electrode binder.

[0103] The present application has no limitation on the selection of the positive electrode conductive agent, and any known positive electrode conductive agent can be used, such as conductive carbon black (SuperP).

[0104] The present application has no limitation on the selection of the positive electrode binder, and any known positive electrode binder can be used, such as polyvinylidene fluoride (PVDF).

[0105] In one embodiment, the negative electrode active material layer further includes a negative electrode active material, a negative electrode conductive agent, a negative electrode thickener, and a negative electrode binder.

[0106] The present application has no limitation on the selection of the negative electrode active material, and any known negative electrode active material can be used, such as graphite, silicon carbide (SiC), etc.

[0107] The present application has no limitation on the selection of the negative electrode conductive agent, and any known negative electrode conductive agent can be used, such as carbon nanotubes (CNT / SWCNT).

[0108] The present application has no limitation on the selection of the negative electrode thickener, and any known negative electrode thickener can be used, such as carboxymethyl cellulose (CMC).

[0109] The present application has no limitation on the selection of the negative electrode binder, and any known negative electrode binder can be used, such as polyacrylic acid (PAA).

[0110] In one embodiment, a separator of an electrochemical device is disposed between a positive electrode and a negative electrode.

[0111] The present application has no limitation on the diaphragm, and any known diaphragm can be used.

[0112] Illustratively, the diaphragm includes any one of a polyethylene diaphragm, a polypropylene diaphragm, a polyvinylidene fluoride diaphragm, and a multi-layer composite film.

[0113] In one embodiment of the present application, the present application provides an electrical device, which includes the electrochemical device described in the present application.

[0114] Example 1

[0115] The present invention provides an electrochemical device, wherein a method for preparing the electrochemical device comprises the following steps:

[0116] (1) Preparation of electrolyte

[0117] In an argon-filled glove box, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) are mixed in a mass ratio of EC:PC:DEC:PP=10:20:30:20 to obtain a second organic solvent, and then 20% of the first organic solvent (dibasic ester solvent A1) based on the total mass of the electrolyte is added, and then 10% of lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte is slowly added to the mixed solution, and finally 10% of fluoroethylene carbonate (FEC) based on the total weight of the electrolyte, 3% of the second additive difluoroethylene carbonate (DFEC), 1% of the second additive vinyl sulfate (DTD), 1% of the second additive adiponitrile (ADN, dinitriles), 1.5% of the second additive 1,3,6-hexanetrinitrile (HTCN, ternary nitriles), and 1.5% of the first additive B1 are added, and the mixture is stirred uniformly to obtain an electrolyte;

[0118] (2) Preparation of positive electrode sheet

[0119] The positive electrode material (LiCoO2, Xiamen Tungsten New Energy), the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) were thoroughly stirred and mixed in an N-methylpyrrolidone solvent (NMP) at a mass ratio of 97:2:1 to obtain a positive electrode slurry. The positive electrode slurry was coated on a current collector aluminum foil, dried at 85°C, and then cold pressed. After trimming and striping, the positive electrode was dried at 85°C under vacuum for 6 hours, and the tabs were welded to obtain the positive electrode sheets.

[0120] (3) Preparation of negative electrode sheet

[0121] The negative electrode active material artificial graphite (Gr) and silicon carbide material (SiC, Shenzhen BTR), conductive agent carbon nanotubes (CNT), binder polyacrylic acid (PAA), and thickener sodium carboxymethyl cellulose (CMC) were thoroughly stirred and mixed in a deionized water solvent at a mass ratio of 97:1:1:1 to obtain a negative electrode slurry, wherein the mass ratio of the negative electrode active material Gr to SiC was controlled to be 88:12; the negative electrode slurry was coated on a current collector copper foil, dried at 85°C and then cold pressed, and then trimmed and slit, and then dried at 85°C under vacuum for 12 hours, and the tabs were welded to obtain the negative electrode sheet;

[0122] (4) Preparation of isolation membrane

[0123] A polyethylene (PE) porous polymer film is used as a separator;

[0124] (5) Preparation of soft-pack lithium batteries

[0125] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the positive and negative sheets, and then wound to produce a bare cell with a designed capacity of 5.0Ah and a voltage range of 3.0-4.55V. The bare cell is encapsulated in an aluminum-plastic film outer packaging and then baked in an 85°C vacuum oven for 48 hours. The dried battery is then injected with electrolyte, with a designed injection coefficient of 1.4g / Ah. After encapsulation, static rest, formation, shaping, and volume separation, followed by a second sealing process, the average electrolyte retention coefficient is 1.2g / Ah, resulting in an electrochemical device.

[0126] Examples 2-4

[0127] The embodiments of the present application provide an electrochemical device, which differs from Embodiment 1 in that the amount of the first organic solvent added is adjusted to achieve the parameters in Table 1. In Embodiments 2-4, if the mass percentage of the first organic solvent is increased on the basis of Embodiment 1, the mass percentage of PP in the second organic solvent is correspondingly reduced; conversely, if the mass percentage of the first organic solvent is reduced on the basis of Embodiment 1 in Embodiments 2-4, the mass percentage of PP in the second organic solvent is correspondingly increased.

[0128] Examples 5-7

[0129] The embodiment of the present application provides an electrochemical device, which differs from embodiment 1 in that the amount of the first additive is adjusted to achieve the parameters in Table 1, and the changed amount of the first additive is replaced by a second organic solvent of a corresponding mass percentage.

[0130] Examples 8-10

[0131] The embodiment of the present application provides an electrochemical device, which differs from Example 1 in that the amount of fluoroethylene carbonate added is adjusted to achieve the parameters in Table 1, and the changed amount of fluoroethylene carbonate is replaced by a second organic solvent with a corresponding mass percentage.

[0132] Examples 11-13

[0133] The embodiment of the present application provides an electrochemical device, which differs from Example 1 in that the amount of silicon carbide added is adjusted to achieve the parameters in Table 1.

[0134] Examples 14-15

[0135] This embodiment of the present application provides an electrochemical device, which differs from Example 1 in that the type of the first organic solvent is adjusted to achieve the parameters in Table 1.

[0136] Examples 16-17

[0137] This embodiment of the present application provides an electrochemical device, which differs from Example 1 in that the type of the first additive is adjusted to achieve the parameters in Table 1.

[0138] Example 18

[0139] The embodiment of the present application provides an electrochemical device, which differs from embodiment 1 in that the type and amount of the second additive are adjusted to achieve the parameters in Table 1.

[0140] Example 19

[0141] This embodiment of the present application provides an electrochemical device, which differs from Example 1 in that the type and amount of lithium salt added are adjusted to achieve the parameters in Table 1.

[0142] Examples 20-21

[0143] The embodiment of the present application provides an electrochemical device, which differs from Example 1 in that the addition amounts of the first organic solvent, the first additive, fluoroethylene carbonate, the second organic solvent, and silicon carbide are adjusted to achieve the parameters in Table 1.

[0144] Example 22

[0145] This embodiment of the present application provides an electrochemical device, which differs from Example 1 in that graphite is used instead of silicon carbide to achieve the parameters in Table 1.

[0146] Comparative Example 1

[0147] The comparative example of the present application provides an electrochemical device, which differs from Example 1 in that the first organic solvent and the first additive are not introduced to achieve the parameters in Table 1.

[0148] Comparative Example 2

[0149] The comparative example of the present application provides an electrochemical device, which differs from Example 1 in that the first organic solvent is not introduced and the amount of the second organic solvent is supplemented to achieve the parameters in Table 1.

[0150] Comparative Example 3

[0151] The comparative example of the present application provides an electrochemical device, which differs from Example 1 in that the first additive is not introduced and the amount of the second organic solvent is supplemented to achieve the parameters in Table 1.

[0152] Comparative Example 4

[0153] The comparative example of the present application provides an electrochemical device, which differs from Example 1 in that fluoroethylene carbonate is not introduced and the amount of the second organic solvent is supplemented to achieve the parameters in Table 1.

[0154] Comparative Example 5

[0155] The comparative example of the present application provides an electrochemical device, which differs from Example 1 in that the first organic solvent is not introduced and PP is used to supplement the parameters in Table 1.

[0156] a, b, c, d, A, the type of the first organic solvent, the type of the first additive and the second additive, the mass percentage e of the second additive in the electrolyte, the type and molar concentration M of the lithium salt in the electrochemical devices in the Examples and Comparative Examples are shown in Table 3;

[0157] Wherein, the first organic solvent A1 is a compound represented by formula III, the first organic solvent A2 is a compound represented by formula IV, and the first organic solvent A3 is a compound represented by formula V;

[0158]

[0159] The first additive B1 is a compound represented by formula VI, the first additive B2 is a compound represented by formula VII, and the first additive B3 is a compound represented by formula VIII;

[0160]

[0161] The second additive is a mixture formed using the additive mass ratios shown in Table 1;

[0162] Lithium salt 1 is lithium hexafluorophosphate, and lithium salt 2 is lithium bis(fluorosulfonyl)imide;

[0163] Table 1

[0164] Second additive package type Mass ratio of additives used 1 DFEC:DTD:ADN:HTCN=3:1:1:0 2 DFEC:DTD:ADN:HTCN=3:1:1:1.5

[0165] Table 2

[0166]

[0167]

[0168] The performance tests of the electrochemical devices prepared in the examples and comparative examples include the following aspects:

[0169] 1. High temperature cycle performance test: In a 45°C environment, the divided battery is charged to 4.55V at a constant current and constant voltage of 0.7C, with a cut-off current of 0.05C, and then discharged to 3.0V at a constant current of 0.5C. This cycle is repeated 300 times. After the cycle, the capacity retention rate and thickness expansion rate at the 300th week are calculated. The calculation formula is as follows:

[0170] 300th cycle capacity retention rate (%) = (300th cycle discharge capacity / first cycle discharge capacity) × 100%;

[0171] Thickness expansion rate at the 300th cycle = (thickness at the 300th cycle at full charge / thickness at the first cycle at full charge) × 100;

[0172] 2. Static cycle performance test: In a 45°C environment, charge the divided battery to 4.55V at a constant current and constant voltage of 0.7C, with a cut-off current of 0.05C. Let it stand for 24 hours in a fully charged state, and then discharge it to 3.0V at a constant current of 0.5C. Repeat this cycle for 120 times. After the cycle, calculate the capacity retention rate and thickness expansion rate at the 120th cycle. The calculation formula is as follows:

[0173] 120th cycle capacity retention rate (%) = (120th cycle discharge capacity / first cycle discharge capacity) × 100%;

[0174] Thickness expansion rate at the 120th cycle = (thickness at the 120th cycle in full charge state / thickness at the first cycle in full charge state) × 100%;

[0175] 3. 85℃ / 24h high temperature storage test: The battery is placed at room temperature and charged and discharged once at 0.5C (3.0V-4.55V), and the discharge capacity C0 of the battery before storage is recorded. The battery is then charged to a full charge state of 4.55V (100% SOC) using constant current and constant voltage. The battery is placed in an 85℃ constant temperature box and stored for 24h. After storage, the battery is removed and allowed to cool at room temperature for 24h. The battery is then discharged again at a constant current of 0.5C to 3.0V. The discharge capacity C1 of the battery after storage is recorded. The capacity retention rate of the battery after storage at 85℃ for 24h is calculated using the following formula:

[0176] Capacity retention after storage at 85°C for 24 hours = C1 / C0 × 100%;

[0177] 4. Thermal shock performance test: Under 25℃ ambient conditions, discharge the battery to 3.0V at a given current of 0.2C; let it sit for 5 minutes; charge it to 4.55V at a charging current of 0.2C. When the battery cell voltage reaches 4.55V, change to 4.55V constant voltage charging until the charging current ≤ the cut-off current of 0.05C; after standing for 1 hour, place the battery cell in an oven, increase the oven temperature to 132±2℃ at a rate of 5±2℃ / min, and keep it for 60 minutes before stopping. The judgment standard is that the battery cell does not catch fire or explode;

[0178] 5. Electrolyte viscosity test: Under 25°C environmental conditions, take 100mL of electrolyte into a beaker, insert the viscosity tester probe into the electrolyte, let it stand for 1 minute, and record the viscosity tester reading.

[0179] The results are shown in Table 3;

[0180] Table 3

[0181]

[0182]

[0183] From the results of Examples 1-22 in Table 4, it can be seen that the electrolyte prepared by using dibasic ester as the first organic solvent and nitrile ethylene carbonate as the first additive can enable the electrochemical device to exhibit excellent high-temperature comprehensive performance.

[0184] Compared to Comparative Examples 1 and 5 where the first organic solvent is not used, the thermal stability of the electrolyte is significantly improved after the first organic solvent is added in Examples 1-22, and the high-temperature cycle and high-temperature static cycle retention rates of the electrochemical device are improved, indicating that the dibasic ester solvent has better high-temperature performance than the monobasic ester solvent. From the results of Examples 1, 14, and 15, it can be seen that the A1 dibasic ester solvent exhibits better overall performance than A2 and A3, because compared to the A2 and A3 solvents, the carbon chain length of A1 is relatively short and the viscosity is relatively low. Adding an appropriate amount to the electrolyte will not significantly deteriorate the high-temperature cycle retention rate; and from the results of Examples 1-4, it can be seen that excessive use of the A1 solvent may deteriorate certain electrolyte dynamics, resulting in a slight decrease in the high-temperature cycle retention rate. If the use amount is too low, the electrolyte cannot be given good thermal stability, and the static cycle retention rate decreases.

[0185] Compared to the case where the first additive is not used in Comparative Example 3, the thickness expansion rate of the electrochemical device prepared after adding the first additive in Examples 1-22 is significantly reduced during high-temperature cycling and high-temperature static cycling, and the pass rate of the 132°C thermal shock test is improved. From the results of Examples 1, 16, and 17, it can be seen that B1 nitrile ethylene carbonate has the best comprehensive improvement on the electrochemical device compared to B2 and B3. Because compared to B2, the B1 additive has no methyl electron-donating group on the molecular ring, and the ring-opening film formation is relatively easier. Compared with B3, the B1 additive has no fluorine-substituted group and does not cause the problem of defluorination and acid production at high temperature. In addition, the viscosity of the electrolyte after introducing B1 is relatively lower than that of B2 and B3, and the kinetics are better. If too much or too little B1 additive is used, as in the results of Examples 1, 5, 6, and 7, it is not conducive to the comprehensive performance of the battery. Excessive addition of B1 additive increases the content of nitrile additives in the electrolyte as a whole, increases the overall viscosity, and deteriorates the kinetics. Too little addition of B1 additive cannot achieve the ideal film-forming effect and cannot achieve the effect of improving the expansion rate.

[0186] Compared to the case where FEC is not used in Comparative Example 4, the electrochemical device cycle attenuation obtained after adding a sufficient amount of FEC in Examples 1-22 can be well maintained, and no serious capacity drop occurs. From the results of Examples 1, 8, 9, and 10, it can be seen that when FEC is used in excess, a series of high-temperature performances will deteriorate. This is caused by the defluorination and acid production of FEC at high temperatures, which causes interface damage. When the amount of FEC used is too small, the high-temperature long cycle of the electrochemical device will be significantly attenuated, while the static cycle will be improved to a certain extent. This is because although the low FEC content improves the acid production problem and improves the static cycle and high-temperature storage performance, in the late stage of the long cycle, the FEC content cannot be replenished in time to repair the damaged SEI, resulting in a deterioration in the retention rate.

[0187] Example 22 is a case where silicon carbide material is not introduced into the negative electrode, that is, in the LCO-Gr system, the electrolyte used in the present application can enable the electrochemical device to exhibit excellent high-temperature comprehensive performance, and the cycle capacity retention rate and expansion rate are better than those of other embodiments. However, considering that the graphite negative electrode is less prone to material expansion and corresponding interface deterioration problems than the silicon-doped negative electrode, considering the cost and benefit, it is not necessary to introduce the first solvent and the first additive into the high-voltage graphite system. This embodiment shows that the electrolyte proposed in the present application has good compatibility with electrochemical device systems, especially in high-voltage electrochemical device systems, it can also help achieve good comprehensive performance of the electrochemical device. In addition, by comparing the results of Examples 1, 11, 12, and 13, it can be seen that when the silicon carbide material content in the negative electrode reaches 20%, the electrochemical device prepared in the present application can still provide excellent cycle performance with a retention rate of over 75% for 300 high-temperature cycles and a retention rate of over 70% for 120 static cycles. There is no capacity drop, and good high-temperature safety performance can be maintained. This fully demonstrates that the electrolyte proposed in the present application has good application prospects in high-energy density systems. However, considering that the expansion deterioration caused by 20% silicon carbide content is too serious, combined with the comparison of benefits of different ratios, the present application prefers 12% doping as the optimal ratio.

[0188] It can be seen from Examples 1-19 and Examples 20-21 that when A is not within the preferred range given in this application, the various performance tests of the obtained product show a certain degree of deterioration. Therefore, the reasonable regulation of various factors of the electrolyte and the negative electrode in this application helps the electrochemical device to achieve the best comprehensive performance, and effectively improves the high-temperature cycle performance, static cycle performance, high-temperature storage performance and high-temperature safety performance of the electrochemical device.

[0189] Finally, it should be noted that the above embodiments are intended to illustrate the technical solutions of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present application.

Claims

1. An electrochemical device comprising an electrolyte, characterized in that: The electrolyte includes a first organic solvent, a first additive and fluoroethylene carbonate; The structural formula of the first organic solvent is shown in Formula I, and the structural formula of the first additive is shown in Formula II; wherein R1 and R2 are each independently selected from a C1-C5 alkyl ester group, a C1-C5 alkyl group, wherein at least one of R1 and R2 is selected from a dimethyl ester, a methyl ethyl ester, or a methyl propyl ester; R3 and R4 are independently selected from C1-C3 alkyl, hydrogen, fluorine, and cyano, wherein at least one of R3 and R4 is cyano.

2. The electrochemical device according to claim 1, wherein The electrochemical device further comprises a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer comprising a silicon-based material, and the electrochemical device satisfies the following conditions: 0.48≤A≤1.43; Where A = (a + b) / (c + d); a% is the mass percentage of the first organic solvent based on the total mass of the electrolyte; b% is the mass percentage of the first additive based on the total mass of the electrolyte; c% is the mass percentage of fluoroethylene carbonate based on the total mass of the electrolyte; d% is the mass percentage of the silicon-based material based on the total mass of the negative electrode active material layer.

3. The electrochemical device according to claim 2, characterized in that At least one of the following is met: (1) Based on the total mass of the electrolyte, the mass percentage a% of the first organic solvent is 9%-30%; (2) Based on the total mass of the electrolyte, the mass percentage b% of the first additive is 0.1%-3%; (3) Based on the total mass of the electrolyte, the mass percentage c% of fluoroethylene carbonate is 8%-16%; (4) Based on the total mass of the negative electrode active material layer, the mass percentage d% of the silicon-based material is 10%-15%.

4. The electrochemical device according to claim 1, wherein Said R1 and R2 are each independently selected from methyl, ethyl, propyl, dimethyl ester, methyl ethyl ester, methyl propyl ester; And / or, R3 and R4 are each independently selected from methyl, hydrogen, fluorine, and cyano.

5. The electrochemical device according to claim 1, wherein The electrolyte further includes a second organic solvent, wherein the second organic solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, 2,2-difluoroethyl acetate, ethyl propionate, and propyl propionate; And / or, the electrolyte further includes a second additive, and the second additive includes at least one of 1,3-propane sultone, vinyl sulfate, tris(trimethylsilyl)borate, and tris(trimethylsilyl)phosphate.

6. The electrochemical device according to claim 5, characterized in that Based on the total mass of the electrolyte, the mass percentage of the second additive is 0.1%-20%.

7. The electrochemical device according to claim 1, wherein The electrolyte further comprises a lithium salt, wherein the mass percentage of the lithium salt is 8% to 25% based on the total mass of the electrolyte; The lithium salt includes at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate, bistrifluoromethanesulfonyl imide lithium salt, and lithium bisfluorosulfonyl imide.

8. The electrochemical device according to claim 1, wherein The viscosity of the electrolyte is 10 mPa·s-15 mPa·s.

9. The electrochemical device according to claim 1, wherein The electrochemical device further includes a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode active material layer includes lithium cobalt oxide.

10. An electrical device, characterized in that: The electrochemical device comprises the electrochemical device according to any one of claims 1 to 9.

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