Electrolyte and electrochemical device

Abstract

The invention provides an electrolyte and an electrochemical device. The electrolyte comprises at least one of compounds shown in the formula I and a polycyano compound; in the formula, R1, R2, R3 and R4 are independently selected from a hydrogen atom, a fluorine atom, a cyano group, a methanesulfonic acid group, an ethyl sulfonic acid group, a propyl sulfonic acid group and an unsubstituted or fluorine-atom-substituted alkyl group of C1 to C3. Based on the total mass of the electrolyte, the mass content of the compound in the formula I is A, the mass content of the polycyano compound is B, 0.01% < = A < = 5%, and 0.1% < = B < = 10%. The electrochemical device has good cycle performance and high-temperature storage performance.

Description

Technical Field

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

[0002] Lithium-ion batteries offer significant advantages, including high energy density, miniaturization, and lightweight design. They are widely used in mobile phones, laptops, tablets, drones, electric vehicles, power tools, and power storage systems. Typically, a lithium-ion battery consists of a positive electrode, a negative electrode, and an electrolyte. The electrolyte is responsible for maintaining ion transport between the positive and negative electrodes and a stable interface, enabling the lithium-ion battery to operate reliably.

[0003] In order to form a stable interface in lithium-ion batteries, film-forming additives are usually added to the electrolyte. However, film-forming additives usually form a high-impedance interface film on the surface of the positive electrode or negative electrode. Although the formed interface film is conducive to the stable operation of the lithium-ion battery, the interface film makes ion conduction more difficult, which will lead to limited cycle performance of the lithium-ion battery. Summary of the Invention

[0004] The purpose of the present application is to provide an electrolyte and an electrochemical device to improve the cycle performance and high-temperature storage performance of the electrochemical device.

[0005] It should be noted that in the invention content of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries. The specific technical solutions are as follows:

[0006] A first aspect of the present application provides an electrolyte comprising at least one compound of formula I and a polycyano compound;

[0007]

[0008] Among them, R 1 、R 2 、R 3 and R 4Each is independently selected from a hydrogen atom, a fluorine atom, a cyano group, a methylsulfonic acid group, an ethylsulfonic acid group, a propylsulfonic acid group, and an alkyl group of C1 to C3 that is unsubstituted or substituted with a fluorine atom. Based on the total mass of the electrolyte, the mass content of the compound of formula I is A, and the mass content of the polycyano compound is B, 0.01%≤A≤5%, 0.1%≤B≤10%. The compound of formula I and the polycyano compound are used in combination in the electrolyte. When the values of A and B are within the above ranges, the polycyano compound can form a network structure through cross-linking of alkyl chains, thereby improving the adsorption of the compound of formula I at the positive electrode interface and the oxidation resistance of the electrolyte at the positive electrode interface at high temperatures, stabilizing the adsorption of the compound of formula I at the positive electrode interface, and facilitating the combination of the compound of formula I with the transition metal element at the positive electrode interface through its adsorption, thereby inhibiting the catalytic decomposition of the electrolyte by the transition metal at the positive electrode interface, thereby improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0009] In one embodiment of the present application, the polycyano compound comprises at least one of a compound of formula II-A, a compound of formula II-B, a compound of formula II-C, or a compound of formula II-D;

[0010]

[0011] Among them, R 5 is selected from C2 to C7 alkylene or C2 to C4 alkenylene; R 6 is selected from C3 to C6 alkylene or C3 to C6 alkenylene; n is selected from 2 or 3; when n=2, R 7 is a C2 to C6 alkylene group; when n=3, R 7 When the polycyano compound includes the above compound, the high temperature storage performance of the electrochemical device can be further improved.

[0012] In one embodiment of the present application, 0.1%≤A≤3%. When the value of A is within the above range, the compound of Formula I has a more suitable mass content, which can further improve the cycle performance and high-temperature storage performance of the electrochemical device.

[0013] In one embodiment of the present application, 0.1%≤B≤5%. When the value of B is within the above range, the polycyano compound has a more appropriate mass content, which can further improve the cycle performance and high-temperature storage performance of the electrochemical device.

[0014] In one embodiment of the present application, 0.02≤A / B≤30, preferably, 0.1≤A / B≤10. When the value of A / B is within the above range, the mass contents of the compound of formula I and the polycyano compound are more matched, and the polycyano compound can form a network structure through alkyl chain cross-linking, thereby improving the adsorption of the compound of formula I at the positive electrode interface and the oxidation resistance of the positive electrode interface electrolyte at high temperature, stabilizing the adsorption of the compound of formula I at the positive electrode interface, and facilitating the combination of the compound of formula I with the transition metal element at the positive electrode interface through its adsorption, thereby inhibiting the catalytic decomposition of the electrolyte by the transition metal at the positive electrode interface, thereby further improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0015] In one embodiment of the present application, the compound of formula I comprises at least one of the following compounds:

[0016]

[0017] When the compound of formula I includes the above-mentioned compound, the high-temperature storage performance of the electrochemical device can be improved while the cycle performance of the electrochemical device is improved.

[0018] In one embodiment of the present application, the compound of formula II-A comprises at least one of the following compounds:

[0019]

[0020]

[0021] When the compound of formula II-A includes the above-mentioned compound, it can synergistically act with the compound of formula I to promote the formation of a CEI film rich in sulfur and nitrogen elements, improve the stability of the CEI film, reduce the consumption of the electrolyte due to side reactions, and improve the high-temperature storage performance of the electrochemical device.

[0022] In one embodiment of the present application, the compound of formula II-B comprises at least one of the following compounds:

[0023]

[0024] When the compound of formula II-B includes the above-mentioned compound, the stability of the positive electrode interface can be further enhanced, thereby improving the high-temperature storage performance of the electrochemical device.

[0025] In one embodiment of the present application, the compound of formula II-C includes at least one of the following compounds:

[0026]

[0027] When the compound of formula II-C includes the above-mentioned compound, it can synergistically act with the compound of formula I to promote the formation of a CEI film rich in sulfur and nitrogen elements, further improving the high-temperature storage performance of the electrochemical device.

[0028] In one embodiment of the present application, the electrolyte further comprises fluoroethylene carbonate, and the mass content of the fluoroethylene carbonate is F, based on the total mass of the electrolyte, and 0.01%≤F≤15%. When the electrolyte comprises fluoroethylene carbonate and the value of F is within the above range, the high-temperature storage performance of the electrochemical device can be improved while also improving the cycling performance of the electrochemical device.

[0029] In one embodiment of the present application, 0.005 ≤ F / (A+B) ≤ 100, preferably, 0.01 ≤ F / (A+B) ≤ 50. When the value of F / (A+B) is within the above range, the mass content of fluoroethylene carbonate, the compound of formula I, and the polycyano compound matches, thereby further improving the cycling performance and high-temperature storage performance of the electrochemical device.

[0030] In one embodiment of the present application, the electrolyte further comprises a compound of formula III, which comprises at least one of the following compounds:

[0031]

[0032] When the compound of formula III includes the above-mentioned compound, the compound of formula III is a fluorocarboxylate compound. The compound of formula III has lower viscosity and higher oxidation resistance, and can partially replace carbonate solvents. Further introducing the compound of formula III on the basis of introducing the compound of formula I and the polycyano compound can further improve the cycle performance and high-temperature storage performance of the electrochemical device.

[0033] In one embodiment of the present application, the mass content of the compound of formula III is C, based on the total mass of the electrolyte, and 10%≤C≤50%. When the value of C is within the above range, the compound of formula III has a suitable mass content, which can further improve the stability of the electrolyte at the positive electrode interface and reduce the decomposition of the electrolyte during the cycle, thereby further improving the cycle performance of the electrochemical device.

[0034] In one embodiment of the present application, 1≤C / (A+B)≤200. When the value of C / (A+B) is within the above range, the mass content of the compound of formula III matches that of the compound of formula I and the polycyano compound. On the one hand, the compound of formula III can provide a weaker solvation structure, promote the participation of the compound of formula I and the polycyano compound in the solvation shell of lithium ions, improve the film-forming ability of the compound of formula I and the polycyano compound at the positive electrode interface and the negative electrode interface, and further improve the high-temperature storage performance of the electrochemical device; in addition, it can also make the compound of formula III more stably present at the negative electrode interface, and the viscosity of the compound of formula III itself is low, which can further improve the cycle performance of the electrochemical device.

[0035] A second aspect of the present application provides an electrochemical device, comprising the electrolyte of any one of the aforementioned embodiments. The electrochemical device of the present application has good cycle performance and high-temperature storage performance.

[0036] Beneficial effects of this application:

[0037] The present application provides an electrolyte and an electrochemical device, wherein the electrolyte includes at least one of the compounds of formula I and a polycyano compound. Based on the total mass of the electrolyte, the mass content of the compound of formula I is A, the mass content of the polycyano compound is B, 0.01%≤A≤5%, 0.1%≤B≤10%. When the electrolyte contains the compound of formula I and the polycyano compound, and the values of A and B are within the scope of the present application, the polycyano compound can form a network structure through alkyl chain cross-linking, thereby improving the adsorption of the compound of formula I at the positive electrode interface and the oxidation resistance of the electrolyte at the positive electrode interface at high temperature, stabilizing the adsorption of the compound of formula I at the positive electrode interface, facilitating the binding of the compound of formula I to the transition metal element at the positive electrode interface through its adsorption, inhibiting the catalytic decomposition of the electrolyte by the transition metal at the positive electrode interface, thereby improving the cycle performance and high-temperature storage performance of the electrochemical device. DETAILED DESCRIPTION

[0038] The following will be combined with the embodiments of the present application to clearly and completely describe the technical solutions in this application. Obviously, the embodiments described are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0039] It should be noted that, in the specific embodiments of the present application, a lithium-ion battery is used as an example of an electrochemical device to explain the present application, but the electrochemical device of the present application is not limited to a lithium-ion battery.

[0040] A first aspect of the present application provides an electrolyte comprising at least one compound of formula I and a polycyano compound;

[0041]

[0042] Among them, R 1 、R 2 、R 3 and R 4 Each is independently selected from a hydrogen atom, a fluorine atom, a cyano group, a methylsulfonic acid group, an ethylsulfonic acid group, a propylsulfonic acid group, and a C1 to C3 alkyl group which is unsubstituted or substituted with a fluorine atom; the substitution may be full or partial. The C1 to C3 alkyl group may be a methyl group, an ethyl group, or a propyl group. 1 and R 4 Represents a single substituent, with R 1 and R 4 The other substituent of the attached carbon atom is a hydrogen atom. A polycyano compound is a compound containing two or more cyano functional groups. Based on the total mass of the electrolyte, the mass content of the compound of formula I is A, and the mass content of the polycyano compound is B, 0.01% ≤ A ≤ 5%, 0.1% ≤ B ≤ 10%; preferably, 0.1% ≤ A ≤ 3%, 0.1% ≤ B ≤ 5%. For example, the value of A can be 0.01%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range consisting of any two of the above values; the value of B can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of the above values.

[0043] The inventors have found that the sulfolane structure of the compound of Formula I has a high dielectric constant and can participate in the solvation process of lithium ions while dissociating lithium salts. By adjusting the sulfolane substituent structure, the formation of a solid electrolyte interface (SEI) film can be promoted, and the stability of the negative electrode interface between the electrolyte and the negative electrode sheet can be improved, thereby improving the cycle performance of the electrochemical device; on the other hand, the sulfolane structure of the compound of Formula I has high oxidation resistance, and the sulfur-oxygen bond therein can be combined with the metal ions at the positive electrode interface between the electrolyte and the positive electrode sheet, thereby improving the stability of the positive electrode interface and improving the high-temperature storage performance of the electrochemical device; the polycyano compound has high oxidation resistance and can also be combined with the metal ions on the positive electrode interface, which can promote the formation of a positive electrode electrolyte interface (CEI) film rich in sulfur and nitrogen elements, thereby further improving the high-temperature storage performance of the electrochemical device. When the mass content A of the compound of formula I is too high, for example, greater than 5%, it will lead to an increase in the impedance of the negative electrode interface and reduce the cycle performance of the electrochemical device. When the mass content A of the compound of formula I is too low, for example, less than 0.01%, it has a low effect on promoting the formation of CEI and SEI films, and the improvement of the high-temperature storage performance and cycle performance of the electrochemical device is small. When the mass content B of the polycyano compound is too high, for example, greater than 10%, due to the high viscosity of the polycyano compound, it will reduce the ionic conductivity of the electrolyte and reduce the cycle performance of the electrochemical device. When the mass content B of the polycyano compound is too low, for example, less than 0.1%, the synergistic effect between the polycyano compound and the compound of formula I is not obvious, and the improvement of the high-temperature storage performance and cycle performance of the electrochemical device is small. When the electrolyte contains a compound of formula I and a polycyano compound, and the values of A and B are within the scope of this application, the compound of formula I can generate a compound containing a SO3 structure by reduction decomposition at the negative electrode interface. SO3 has high thermal stability, which is beneficial to improving the stability of the negative electrode interface. In addition, the compound of formula I can combine with the transition metal element at the positive electrode interface through its adsorption effect, thereby inhibiting the catalytic decomposition of the electrolyte by the transition metal at the positive electrode interface. However, as the temperature rises, the molecular thermal motion intensifies, and the adsorption of the compound of formula I at the positive electrode interface will decrease, resulting in oxidation of the electrolyte, while the polycyano compound has a stronger adsorption effect at the positive electrode interface, which can improve the oxidation resistance of the electrolyte at the positive electrode interface, and its alkyl chain can be cross-linked to form a network structure, stabilizing the adsorption of the compound of formula I at the positive electrode interface, thereby improving the cycle performance and high temperature storage performance of the electrochemical device. In this application, "high temperature" refers to a temperature ≥85°C.

[0044] In one embodiment of the present application, the polycyano compound comprises at least one of a compound of formula II-A, a compound of formula II-B, a compound of formula II-C, or a compound of formula II-D;

[0045]

[0046] Among them, R 5 is selected from C2 to C7 alkylene or C2 to C4 alkenylene; R 6 is selected from C3 to C6 alkylene or C3 to C6 alkenylene; n is selected from 2 or 3; when n=2, R 7 is a C2 to C6 alkylene group; when n=3, R 7 It is a C3 to C6 alkylene group. The C2 to C7 alkylene group can be an ethylene group, a propylene group, a butylene group, a pentylene group, a hexylene group or a heptylene group. The C2 to C4 alkenylene group can be an ethenylene group, a propenylene group or a butenylene group. The C3 to C6 alkylene group can be a propylene group, a butylene group, a pentylene group or a hexylene group. The C3 to C6 alkenylene group can be a propenylene group, a butenylene group, a pentenylene group or a hexenylene group. The C2 to C6 alkylene group can be an ethylene group, a propylene group, a butylene group, a pentylene group or a hexylene group. The C3 to C6 alkylene group can be a propylene group, a butylene group, a pentylene group or a hexylene group. When the polycyano compound includes the above-mentioned compound, the polycyano compound has a high oxidation resistance, can combine with the metal ions on the positive electrode interface, and synergistically with the compound of formula I can promote the formation of a CEI film rich in sulfur and nitrogen elements, thereby further improving the high-temperature storage performance of the electrochemical device.

[0047] In one embodiment of the present application, 0.02≤A / B≤30, preferably, 0.1≤A / B≤10. For example, the value of A / B can be 0.02, 0.1, 1, 5, 10, 15, 20, 25, 30 or a range consisting of any two of the above values. When the value of A / B is within the above range, the mass content of the compound of formula I and the polycyano compound is more matched, and the polycyano compound can form a network structure through cross-linking of alkyl chains, thereby improving the adsorption of the compound of formula I at the positive electrode interface and the oxidation resistance of the positive electrode interface electrolyte at high temperature, stabilizing the adsorption of the compound of formula I at the positive electrode interface, and facilitating the compound of formula I to combine with the transition metal element at the positive electrode interface through its adsorption, thereby inhibiting the catalytic decomposition of the electrolyte by the transition metal at the positive electrode interface, thereby further improving the cycle performance and high temperature storage performance of the electrochemical device.

[0048] In one embodiment of the present application, the compound of formula I comprises at least one of the following compounds:

[0049]

[0050]

[0051] When the compound of formula I includes the above-mentioned compound, the sulfolane structure of the compound of formula I has a higher dielectric constant and can participate in the solvation process of lithium ions while dissociating the lithium salt. By adjusting the sulfolane substituent structure, the formation of the SEI film can be promoted, and the stability of the negative electrode interface between the electrolyte and the negative electrode plate can be improved, thereby further improving the cycle performance of the electrochemical device; on the other hand, the sulfolane structure of the compound of formula I has higher oxidation resistance, and the sulfur-oxygen bond therein can be combined with the metal ions on the positive electrode interface between the electrolyte and the positive electrode plate, thereby improving the stability of the positive electrode interface, thereby further improving the high-temperature storage performance of the electrochemical device.

[0052] In one embodiment of the present application, the compound of formula II-A comprises at least one of the following compounds:

[0053]

[0054] When the compound of formula II-A includes the above-mentioned compound, it can synergistically act with the compound of formula I to promote the formation of a CEI film rich in sulfur and nitrogen elements, improve the stability of the CEI film, reduce the consumption of the electrolyte due to side reactions, and thus improve the high-temperature storage performance of the electrochemical device.

[0055] In one embodiment of the present application, the compound of formula II-B comprises at least one of the following compounds:

[0056]

[0057] When the compound of formula II-B includes the above-mentioned compound, the compound of formula II-B can complex with the high-valent metal ions in the positive electrode active material to stabilize the positive electrode interface, and synergistically act with the compound of formula I to promote the formation of a CEI film rich in sulfur and nitrogen elements, further enhancing the stability of the positive electrode interface, thereby improving the high-temperature storage performance of the electrochemical device.

[0058] In one embodiment of the present application, the compound of formula II-C includes at least one of the following compounds:

[0059]

[0060] When the compound of formula II-C includes the above-mentioned compound, the compound of formula II-C has high oxidation resistance, can combine with metal ions on the positive electrode interface, and synergistically act with the compound of formula I to promote the formation of a CEI film rich in sulfur and nitrogen elements, thereby further improving the high-temperature storage performance of the electrochemical device.

[0061] In one embodiment of the present application, the electrolyte further comprises fluoroethylene carbonate, and the mass content of fluoroethylene carbonate is F based on the total mass of the electrolyte, and 0.01%≤F≤15%. For example, the value of F can be 0.01%, 1%, 3%, 5%, 7%, 9%, 11%, 13%, 15% or a range consisting of any two of the above values. Fluoroethylene carbonate has good reducing properties. When the electrolyte comprises fluoroethylene carbonate and the value of F is within the above range, a LiF-rich SEI film can be formed at the negative electrode interface. The combination of fluoroethylene carbonate and the compound of formula I is applied to the electrolyte to improve the stability of the negative electrode interface; at the same time, the combination of fluoroethylene carbonate and polycyano compounds is applied to the electrolyte to reduce the corrosion of HF generated by the decomposition of fluoroethylene carbonate on the positive electrode interface, thereby improving the high-temperature storage performance of the electrochemical device while improving the cycle performance of the electrochemical device.

[0062] In one embodiment of the present application, 0.005≤F / (A+B)≤100, preferably, 0.01≤F / (A+B)≤50. For example, the value of F / (A+B) can be 0.005, 0.01, 1, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 or a range consisting of any two of the above values. When the value of F / (A+B) is within the above range, the mass content of fluoroethylene carbonate matches that of the compound of formula I and the polycyano compound, and fluoroethylene carbonate can improve the film-forming ability of the compound of formula I at the negative electrode interface by adjusting the solvation structure of the compound of formula I, thereby effectively suppressing the negative effects of the polycyano compound at the negative electrode interface; in addition, fluoroethylene carbonate itself can also form polycarbonate to participate in negative electrode film formation, and promote the stable distribution of the decomposition products of the compound of formula I at the negative electrode interface through polymer cross-linking, thereby further improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0063] In one embodiment of the present application, the electrolyte further comprises a compound of formula III, which comprises at least one of the following compounds:

[0064]

[0065] When the compound of formula III includes the above-mentioned compound, the compound of formula III is a fluorocarboxylate compound. The compound of formula III has lower viscosity and higher oxidation resistance, and can partially replace carbonate solvents. Further introducing the compound of formula III on the basis of introducing the compound of formula I and the polycyano compound can further improve the stability of the electrolyte at the positive electrode interface, reduce the decomposition of the electrolyte during the cycle, thereby further improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0066] In one embodiment of the present application, the mass content of the compound of formula III is C, based on the total mass of the electrolyte, 10%≤C≤50%. For example, the value of C can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or a range consisting of any two of the above values. When the value of C is within the above range, the compound of formula III has a suitable mass content, which can further improve the stability of the electrolyte at the positive electrode interface, reduce the decomposition of the electrolyte during the cycle, and thus further improve the cycle performance of the electrochemical device.

[0067] In one embodiment of the present application, 1≤C / (A+B)≤200. For example, the value of C / (A+B) can be 1, 10, 20, 40, 60, 80, 100, 120, 140, 160, 180, 200 or a range consisting of any two of the above values. When the value of C / (A+B) is within the above range, the compound of formula III, the compound of formula I and the polycyano compound have a more suitable mass content, and the mass content of the compound of formula III matches that of the compound of formula I and the polycyano compound. On the one hand, the compound of formula III can provide a weaker solvation structure, promote the compound of formula I and the polycyano compound to participate in the solvation shell of lithium ions, improve the film-forming ability of the compound of formula I and the polycyano compound at the positive electrode interface and the negative electrode interface, and further improve the high temperature storage performance of the electrochemical device; in addition, it can also make the compound of formula III more stably present at the negative electrode interface, and the viscosity of the compound of formula III itself is low, which can further improve the cycle performance of the electrochemical device.

[0068] In the present application, the features of the different components contained in the above-mentioned electrolyte can be combined, and the implementation methods covered by the above-mentioned combination are all within the protection scope of the present application.

[0069] In the present application, the electrolyte also includes a lithium salt. The present application has no particular restrictions on the lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalatoborate) (LiBOB) or lithium difluoroborate. The present application has no particular restrictions on the mass content of the lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass content of the lithium salt is 8% to 15%.

[0070] In the present application, the electrolyte also includes a non-aqueous solvent. The present application has no particular restrictions on the non-aqueous solvent, as long as it can achieve the purpose of the present application. For example, the non-aqueous solvent may include but is not limited to at least one of a carbonate compound, a carboxylate compound, an ether compound, or other organic solvents.

[0071] Above-mentioned carbonate compound can include but not limited to linear carbonate compound or cyclic carbonate compound.Above-mentioned linear carbonate compound can include but not limited to at least one in dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC) or methyl ethyl carbonate (MEC).Above-mentioned cyclic carbonate compound can include but not limited to at least one in ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC).Above-mentioned carboxylate compound can include but not limited to at least one in methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, gamma-butyrolactone, decanolactone, valerolactone or caprolactone. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include but are not limited to at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate or trioctyl phosphate. The present application does not particularly limit the content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0072] The present application has no particular limitation on the mass content of the non-aqueous solvent in the electrolyte, as long as the purpose of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass content of the non-aqueous solvent is 5% to 91.89%.

[0073] In one embodiment of the present application, the electrolyte may include a compound of Formula I, a polycyano compound, a lithium salt, and a non-aqueous solvent. The mass contents of the compound of Formula I, the polycyano compound, and the lithium salt are as described above, and the mass content of the non-aqueous solvent is 70% to 91.89%. An electrochemical device including the above electrolyte has good cycling performance and high-temperature storage performance.

[0074] In one embodiment of the present application, the electrolyte may include a compound of formula I, a polycyano compound, fluoroethylene carbonate, a lithium salt, and a non-aqueous solvent. The mass contents of the compound of formula I, the polycyano compound, fluoroethylene carbonate, and the lithium salt are as described above, and the mass content of the non-aqueous solvent is 55% to 91.88%. An electrochemical device including the above electrolyte has good cycle performance and high-temperature storage performance.

[0075] In one embodiment of the present application, the electrolyte may include a compound of Formula I, a polycyano compound, a compound of Formula III, a lithium salt, and a non-aqueous solvent. The mass contents of the compound of Formula I, the polycyano compound, the compound of Formula III, and the lithium salt are as described above, and the mass content of the non-aqueous solvent is 20% to 81.89%. An electrochemical device including the above electrolyte has good cycling performance and high-temperature storage performance.

[0076] In one embodiment of the present application, the electrolyte may include a compound of formula I, a polycyano compound, fluoroethylene carbonate, a compound of formula III, a lithium salt, and a non-aqueous solvent. The mass contents of the compound of formula I, the polycyano compound, fluoroethylene carbonate, the compound of formula III, and the lithium salt are as described above, and the mass content of the non-aqueous solvent is 5% to 81.88%. An electrochemical device including the above electrolyte has good cycle performance and high-temperature storage performance.

[0077] A second aspect of the present application provides an electrochemical device, comprising the electrolyte of any one of the aforementioned embodiments. The electrochemical device of the present application has good cycle performance and high-temperature storage performance.

[0078] In the present application, the electrochemical device also includes a positive electrode sheet, which includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of the surface of the positive electrode current collector or a partial area of the surface of the positive electrode current collector. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0079] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0080] The positive electrode material layer includes a positive electrode active material. The present application has no particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to at least one of lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate.

[0081] The positive electrode material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, the binder may include at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene butadiene copolymer (styrene-butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose or potassium hydroxymethyl cellulose, and the conductive agent may include at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fiber, flake graphite or graphene. The conductive carbon black may be at least one of acetylene black, Super P or Ketjen black. The carbon nanotubes may be at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes. The carbon fiber may be at least one of vapor-grown carbon fiber (VGCF) or nanocarbon fiber. The present application does not particularly limit the mass ratio of the positive electrode active material, conductive agent and binder in the positive electrode material layer. Those skilled in the art may select according to actual needs, as long as the purpose of the present application can be achieved.

[0082] The thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited in this application, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer is 30 μm to 120 μm.

[0083] Optionally, the positive electrode sheet may further include a conductive layer positioned between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and may be any commonly used conductive layer in the art. The conductive layer includes a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer; for example, the conductive layer may be at least one of the aforementioned conductive agents and binders.

[0084] In the present application, the electrochemical device further includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The aforementioned "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on both surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire area of the negative electrode current collector surface, or it can be a partial area of the negative electrode current collector surface. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0085] The present application has no particular restrictions on the negative electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foam nickel, foam copper or a composite current collector. For example, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, etc.

[0086] The negative electrode material layer includes a negative electrode active material. The present application has no particular limitation on the negative electrode active material, as long as the purpose of the present application can be achieved. For example, the negative electrode active material may include but is not limited to natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 or at least one of Li-Al alloys.

[0087] In some embodiments of the present application, the negative electrode material layer may further include a conductive agent and a binder. The present application does not particularly limit the types of the conductive agent and binder, as long as they can achieve the purpose of the present application. For example, they can be at least one of the above-mentioned conductive agents and binders. The present application does not particularly limit the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as they can achieve the purpose of the present application.

[0088] The present application does not particularly limit the thickness of the negative electrode material layer, as long as it can achieve the purpose of this application. For example, the thickness of the single-sided negative electrode material layer is 30 μm to 120 μm. The present application does not particularly limit the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0089] Optionally, the negative electrode sheet may further include a conductive layer positioned between the negative electrode current collector and the negative electrode material layer. The present application does not particularly limit the composition of the conductive layer, and it may be any conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and for example, it may be at least one of the above-mentioned conductive agents and binders.

[0090] In the present application, the electrochemical device also includes a diaphragm. The present application has no particular restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane, or a spun membrane.

[0091] In some embodiments of the present application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0092] Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The present application is not particularly limited to inorganic particles. For example, inorganic particles can include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application is not particularly limited to binders. For example, the binder can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0093] In the present application, the thickness of the separator is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0094] The electrochemical device of the present application also includes a packaging bag for containing the positive electrode sheet, separator, negative electrode sheet, and electrolyte, as well as other components of the electrochemical device known in the art. This application does not limit these other components. This application does not specifically limit the packaging bag and can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0095] The present application does not particularly limit the type of electrochemical device, which may include any device that undergoes an electrochemical reaction. In the present application, the electrochemical device may include, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery, or a lithium ion polymer secondary battery (lithium ion polymer battery).

[0096] The preparation process of the electrochemical device of the present application is well known to those skilled in the art and is not particularly limited in the present application. For example, it may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly with a wound structure, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain an electrochemical device; or stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire stacked structure with tape to obtain an electrode assembly with a stacked structure, placing the electrode assembly in a packaging bag, injecting an electrolyte into the packaging bag and sealing it to obtain an electrochemical device. In addition, an overcurrent protection element, a guide plate, etc. may also be placed in the packaging bag as needed to prevent pressure rise and overcharging and discharging inside the electrochemical device.

[0097] The third aspect of the present application provides an electronic device, which includes the electrochemical device according to any of the aforementioned embodiments. Therefore, the electronic device provided by the present application has good performance.

[0098] The present application does not particularly limit the type of electronic device, and it can be any electronic device known in the prior art. In some embodiments of the present application, the electronic device can include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0099] Example

[0100] The following examples and comparative examples are provided to more specifically illustrate the embodiments of the present invention. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0101] Test methods and equipment:

[0102] Electrolyte composition test:

[0103] The lithium-ion battery was discharged at 0.5C to 3V and then disassembled to obtain the positive and negative electrode sheets. The positive and negative electrode sheets were placed in a centrifuge tube and centrifuged to obtain an electrolyte. The centrifuged electrolyte was then analyzed using gas chromatography-mass spectrometry (GC-MS) to determine the mass content of various substances (e.g., the compound of formula I, the polycyano compound, fluoroethylene carbonate, and the compound of formula III) in the electrolyte.

[0104] Cyclic performance test:

[0105] The test temperature is 25°C. The lithium-ion battery is charged at a constant current of 0.5C to 4.5V, then charged at a constant voltage of 4.5V to 0.025C. After standing for 5 minutes, it is discharged at a constant current of 0.5C to 3.0V. The discharge capacity obtained in this step is the initial capacity. Following the above steps, the charge and discharge cycle test is performed. The discharge capacity at each step is compared to the initial capacity to obtain the discharge capacity retention rate at each step. The number of cycles at 25°C at which the discharge capacity retention rate reaches 90% is recorded.

[0106] The cycling performance of a lithium-ion battery is characterized by the number of cycles at 25°C at which the discharge capacity retention rate reaches 90%. The higher the number of cycles at 25°C at which the discharge capacity retention rate reaches 90%, the better the cycling performance of the lithium-ion battery.

[0107] High temperature storage performance test:

[0108] Place the lithium-ion battery in a 25°C constant temperature environment and let it sit for 30 minutes to allow the lithium-ion battery to reach a constant temperature of 25°C. Charge the lithium-ion battery at a constant current of 0.5C to 4.5V. Then charge it at a constant voltage of 4.5V to a current of 0.025C. At this point, the lithium-ion battery reaches a full charge state. Record the thickness of the lithium-ion battery at this time as the initial thickness H0. Transfer the fully charged lithium-ion battery to an 85°C constant temperature box and store it for 24 hours. Record the thickness of the lithium-ion battery after 24 hours of storage at 85°C, H1.

[0109] High-temperature storage thickness expansion ratio (%) = (H1-H0) / H0×100%.

[0110] The high-temperature storage thickness expansion rate is used to characterize the high-temperature storage performance of lithium-ion batteries. The lower the high-temperature storage thickness expansion rate, the better the high-temperature storage performance of the lithium-ion battery.

[0111] Example 1-1

[0112] <Preparation of negative electrode sheet>

[0113] The negative electrode active material, artificial graphite, the binder, styrene butadiene rubber, and the conductive agent, acetylene black, were mixed in a mass ratio of 97.4:1.4:1.2. Deionized water was added as the negative electrode solvent to prepare a slurry with a solid content of 45 wt%. The mixture was stirred evenly in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was evenly coated on one surface of a 6 μm thick negative electrode current collector copper foil and dried at 120°C to obtain a negative electrode sheet coated with a negative electrode material layer on one side. The coating weight of the negative electrode material layer was 142 mg / 1540.25 mm 2 . Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode material layer. After drying at 120°C, cold pressing, cutting and welding the tabs, a negative electrode sheet with a specification of 78mm×875mm is obtained for use. Among them, the thickness of the single-sided negative electrode material layer after cold pressing is 54.5μm; the compaction density of the negative electrode material layer after cold pressing is 1.70g / cm 3 .

[0114] <Preparation of positive electrode sheet>

[0115] The positive electrode active material LiCoO2, the conductive agent Super P, and the binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2, and N-methylpyrrolidone (NMP) was added as the positive electrode solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the positive electrode slurry was obtained. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm and dried at 120℃ to obtain a positive electrode sheet with a single-sided positive electrode material layer. The coating weight of the positive electrode material layer was 267.8mg / 1540.25mm 2 . Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. After drying at 120°C, cold pressing, cutting and welding the tabs, a positive electrode sheet with a specification of 74mm×867mm is obtained for use. Among them, the thickness of the single-sided positive electrode material layer after cold pressing is 42μm; the compaction density of the positive electrode material layer after cold pressing is 4.15g / cm 3 .

[0116] <Preparation of Electrolyte>

[0117] In an argon atmosphere glove box with a water content of less than 10 ppm, dimethyl carbonate, diethyl carbonate, and ethylene carbonate were mixed in a mass ratio of 1:1:1 to obtain an organic solvent. A compound of formula I-1, a polycyano compound of formula II-A-1, and a lithium salt of lithium hexafluorophosphate (LiPF6) were then added to the organic solvent, and stirred to obtain an electrolyte. Based on the mass of the electrolyte, the mass content A of the compound of formula I was 1.5%, the mass content B of the polycyano compound was 3%, the mass content of the lithium salt was 12.5%, and the mass content of the organic solvent was 83%.

[0118] <Diaphragm>

[0119] A polyethylene (PE) porous membrane with a thickness of 5 μm (supplied by Celgard) was used.

[0120] <Preparation of lithium-ion batteries>

[0121] The prepared positive electrode sheet, separator, negative electrode sheet, and separator are stacked in order, with the separator positioned between the positive and negative electrode sheets to act as a barrier. The electrodes are then wound to form an electrode assembly. The electrode assembly is packaged in an aluminum-plastic film bag and dried in an 85°C vacuum oven for 12 hours to remove moisture. The prepared electrolyte is then injected and the lithium-ion battery is produced through vacuum packaging, resting, formation, shaping, and capacity testing.

[0122] Example 1-2 to Example 1-23

[0123] The preparation parameters were the same as in Example 1-1 except that they were adjusted according to Table 1. When the mass content of at least one of the compound of Formula I and the polycyano compound changes, the mass content of the organic solvent changes accordingly, while the mass ratio of the organic solvent components remains unchanged and the mass content of the lithium salt remains unchanged.

[0124] Example 2-1 to Example 2-18

[0125] The preparation process was the same as Example 1-1, except that fluoroethylene carbonate and / or the compound of Formula III were added in the preparation of the electrolyte solution and the relevant preparation parameters were adjusted according to Table 2. When the mass content of at least one of the compound of Formula I, the polycyano compound, fluoroethylene carbonate, or the compound of Formula III changes, the mass content of the organic solvent changes accordingly, the mass ratio of the organic solvent components remains unchanged, and the mass content of the lithium salt remains unchanged.

[0126] Comparative Examples 1 to 3

[0127] The process was the same as Example 1-1, except that the compound of Formula I and / or the polycyano compound was not added in the preparation of the electrolyte. When the mass content of at least one of the compound of Formula I or the polycyano compound changes, the mass content of the organic solvent changes accordingly, while the mass ratio of the organic solvent components remains unchanged and the mass content of the lithium salt remains unchanged.

[0128] Comparative Examples 4 to 6

[0129] The preparation parameters were the same as in Example 1-1 except that they were adjusted according to Table 1. When the mass content of at least one of the compound of Formula I and the polycyano compound changes, the mass content of the organic solvent changes accordingly, while the mass ratio of the organic solvent components remains unchanged and the mass content of the lithium salt remains unchanged.

[0130] The preparation parameters and performance tests of each embodiment and comparative example are shown in Table 1 and Table 2.

[0131] Table 1

[0132]

[0133]

[0134] Note: (1) The “ / ” in Table 1 indicates that the corresponding preparation parameters or substances do not exist. (2) Taking Example 1-16 as an example, the “Type of Compound of Formula I” is “Formula I-1 + Formula I-2”, and the “Mass Content of Compound of Formula I” is “1 + 0.5”, indicating that the compound of Formula I includes the compound of Formula I-1 and the compound of Formula I-2. Based on the total mass of the electrolyte, the mass content of the compound of Formula I-1 is 1%, and the mass content of the compound of Formula I-2 is 0.5%. The same applies to other examples.

[0135] As can be seen from Examples 1-1 to 1-23 and Comparative Examples 1 to 6, the electrolytes of the lithium ion batteries in the examples of the present application contain a compound of formula I and a polycyano compound, and the mass content A of the compound of formula I and the mass content B of the polycyano compound are controlled within the range of the present application. The obtained lithium ion batteries have a low high-temperature storage thickness expansion rate and a high number of cycles with a discharge capacity retention rate of 90% at the end of the cycle, indicating that the lithium ion batteries in the examples of the present application have good high-temperature storage performance and cycle performance. However, the electrolytes in Comparative Examples 1 to 3 are not within the scope of the present application, and the mass content of the compound of formula I and / or the polycyano compound in Comparative Examples 4 to 6 is not within the scope of the present application. The obtained lithium ion batteries have a high high-temperature storage thickness expansion rate and a low number of cycles with a discharge capacity retention rate of 90% at the end of the cycle, indicating that the lithium ion batteries in Comparative Examples 1 to 6 have poor high-temperature storage performance and cycle performance.

[0136] It can be seen from Examples 1-1 to 1-5 that when the mass content A of the compound of Formula I is less than 5%, as A increases, the number of cycles at which the cycle-end discharge capacity retention rate of the lithium ion battery is 90% first increases and then decreases, and the high-temperature storage thickness expansion first decreases and then increases; when the mass content A of the compound of Formula I is ≥5%, the high-temperature storage thickness expansion rate of the lithium ion battery decreases, and at the same time, the number of cycles at which the cycle-end discharge capacity retention rate is 90% decreases.

[0137] The A / B ratio generally affects the high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1 to 1-10, when the A / B ratio is adjusted within the range of this application, the resulting lithium-ion batteries have a lower high-temperature storage thickness expansion rate and a higher number of cycles with a 90% discharge capacity retention rate. This indicates that the lithium-ion batteries of the present application examples have improved high-temperature storage performance and good cycling performance.

[0138] The type of compound of Formula I generally affects the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-11, and 1-16, when the type of compound of Formula I is adjusted within the scope of this application, the resulting lithium-ion batteries exhibit a lower high-temperature storage thickness expansion rate and a higher number of cycles with a 90% discharge capacity retention rate, indicating that the high-temperature storage performance and cycling performance of the lithium-ion batteries of the examples of this application are improved.

[0139] The type of polycyano compound generally affects the high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1, 1-17, and 1-23, when the type of polycyano compound is adjusted within the scope of this application, the resulting lithium-ion batteries have a low high-temperature storage thickness expansion rate and a high number of cycles with a 90% discharge capacity retention rate. This demonstrates that the lithium-ion batteries of the present application examples have improved high-temperature storage performance and good cycling performance.

[0140] Table 2

[0141]

[0142] Note: “ / ” in Table 2 indicates that there is no corresponding preparation parameter or substance.

[0143] The electrolyte also includes fluoroethylene carbonate. The mass content F of fluoroethylene carbonate generally affects the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1 and 2-1 to 2-9, when the mass content F of fluoroethylene carbonate is within the range of this application, the resulting lithium-ion batteries have a low high-temperature storage thickness expansion rate and a high number of cycles with a discharge capacity retention rate of 90%, demonstrating that the lithium-ion batteries of the present application examples have excellent high-temperature storage performance and cycling performance.

[0144] The value of F / (A+B) generally affects the cycling performance and high-temperature storage performance of lithium-ion batteries. As can be seen from Examples 1-1 and 2-1 to 2-9, when the value of F / (A+B) is within the range of this application, the resulting lithium-ion batteries have a low high-temperature storage thickness expansion rate and a high number of cycles with a 90% discharge capacity retention rate, indicating that the lithium-ion batteries of the present application examples have good high-temperature storage performance and cycling performance.

[0145] The electrolyte also includes a compound of Formula III. The mass content C of the compound of Formula III generally affects the cycling performance of the lithium-ion battery. As can be seen from Examples 1-1, 2-10, and 2-15, when the mass content C of the compound of Formula III is within the range of this application, the resulting lithium-ion battery has a low high-temperature storage thickness expansion rate and a high number of cycles with a discharge capacity retention rate of 90%. This indicates that the lithium-ion batteries of the examples of this application have improved cycling performance and good high-temperature storage performance.

[0146] The electrolyte also includes a compound of Formula III. The type of Formula III compound generally affects the cycling performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-16, and 2-17, when the type of Formula III compound falls within the scope of this application, the resulting lithium-ion batteries exhibit a low high-temperature storage thickness expansion rate and a high number of cycles with a discharge capacity retention rate of 90%. This demonstrates that the lithium-ion batteries of the present application examples have improved cycling performance and good high-temperature storage performance.

[0147] The C / (A+B) value generally affects the cycling performance of lithium-ion batteries. As can be seen from Examples 1-1 and 2-10 to 2-17, when the C / (A+B) value is within the range of this application, the resulting lithium-ion batteries have a low high-temperature storage thickness expansion rate and a high number of cycles with a 90% discharge capacity retention rate. This indicates that the lithium-ion batteries of the present application examples have improved cycling performance and good high-temperature storage performance.

[0148] The composition of the electrolyte generally affects the storage and cycling performance of lithium-ion batteries. As can be seen from Examples 1-1, 2-4, 2-16, and 2-18, when the electrolyte simultaneously includes the compound of Formula I, the polycyano compound, the fluoroethylene carbonate, and the compound of Formula III, the resulting lithium-ion batteries have a lower high-temperature storage thickness expansion rate and a higher number of cycles with a discharge capacity retention rate of 90%, demonstrating that the lithium-ion batteries of the present examples have excellent high-temperature storage and cycling performance.

[0149] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article comprising a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, or article.

[0150] Each embodiment in this specification is described in a related manner. The same or similar parts between the embodiments can be referred to each other. Each embodiment focuses on the differences from other embodiments.

[0151] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. An electrolyte comprising at least one compound of formula I and a polycyano compound; in, R 1 、R 2 、R 3 and R 4 Each is independently selected from a hydrogen atom, a fluorine atom, a cyano group, a methylsulfonate group, an ethylsulfonate group, a propylsulfonate group, and a C1 to C3 alkyl group which is unsubstituted or substituted with a fluorine atom; Based on the total mass of the electrolyte, the mass content of the compound of formula I is A, the mass content of the polycyano compound is B, 0.01%≤A≤5%, 0.1%≤B≤10%.

2. The electrolyte according to claim 1, wherein The polycyano compound includes at least one of a compound of formula II-A, a compound of formula II-B, a compound of formula II-C or a compound of formula II-D; Among them, R 5 is selected from C2 to C7 alkylene or C2 to C4 alkenylene; R 6 is selected from C3 to C6 alkylene or C3 to C6 alkenylene; n is selected from 2 or 3; when n=2, R 7 is a C2 to C6 alkylene group; when n=3, R 7 It is a C3 to C6 alkylene group.

3. The electrolyte according to claim 1, wherein The electrolyte satisfies at least one of the following conditions: (1)0.1％≤A≤3％； (2)0.1％≤B≤5％； (3)0.02≤A / B≤30.

4. The electrolyte according to claim 3, wherein 0.1≤A / B≤10.

5. The electrolyte according to claim 1, wherein The compound of formula I includes at least one of the following compounds:

6. The electrolyte according to claim 2, wherein The compound of formula II-A includes at least one of the following compounds:

7. The electrolyte according to claim 2, wherein The compound of formula II-B includes at least one of the following compounds:

8. The electrolyte according to claim 2, wherein The compound of formula II-C includes at least one of the following compounds:

9. The electrolyte according to claim 1, wherein The electrolyte further comprises fluoroethylene carbonate. Based on the total mass of the electrolyte, the mass content of the fluoroethylene carbonate is F, and 0.01%≤F≤15%.

10. The electrolyte according to claim 9, wherein 0.005≤F / (A+B)≤100.

11. The electrolyte according to claim 10, wherein 0.01≤F / (A+B)≤50.

12. The electrolyte according to claim 1, wherein The electrolyte further comprises a compound of formula III, wherein the compound of formula III comprises at least one of the following compounds:

13. The electrolyte according to claim 12, wherein Based on the total mass of the electrolyte, the mass content of the compound of formula III is C, 10%≤C≤50%.

14. The electrolyte according to claim 13, wherein 1≤C / (A+B)≤200. 15 . An electrochemical device comprising the electrolyte according to claim 1 .

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