Electrolyte and electrochemical apparatus comprising same

Abstract

Disclosed are an electrolyte and an electrochemical apparatus comprising the electrolyte. The electrolyte comprises a compound represented by formula I and a compound represented by formula II. The compound of formula I comprises at least two of a compound represented by formula I-A, a compound represented by formula I-B, and a compound represented by formula I-C, and at least comprises the compound represented by formula I-A. The compound represented by formula I-A at least contains a fluorine atom. The compound represented by formula I-B and the compound represented by formula I-C each contains at least one halogen atom. The electrolyte components can improve the cycling performance and the high-temperature storage performance of the electrochemical apparatus.

Description

Electrolyte and electrochemical device containing the same Technical Field

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

[0002] With the widespread application of electrochemical devices (e.g., lithium-ion batteries) in various electronic products, users have also put forward increasingly higher requirements for the performance of electrochemical devices, especially high-energy-density lithium-ion batteries. Currently, the main method to improve the energy density of lithium-ion batteries is to increase the charging voltage of lithium-ion batteries. However, when the charging voltage of lithium-ion batteries is increased, the higher charging voltage will accelerate the oxidative decomposition of the electrolyte by the high-valent transition metals in the positive electrode active material of the lithium-ion battery. The high-valent transition metals will obtain electron compensation from oxygen atoms, resulting in oxygen release, which in turn accelerates the decomposition of the electrolyte, resulting in increased gas production of the lithium-ion battery, affecting the room temperature cycle performance and high-temperature storage performance of the lithium-ion battery.

[0003] Summary of the Invention

[0004] In view of this, the present application provides an electrolyte and an electrochemical device containing the electrolyte, which has good oxidation resistance, can inhibit the oxidative decomposition of high-valent transition metals in the positive electrode active material, and can stabilize the high-valent transition metals in the positive electrode active material, thereby improving the room temperature cycle performance and high-temperature storage performance of the electrochemical device.

[0005] In a first aspect, the present application provides an electrolyte comprising a compound of formula I and a compound of formula II;

[0006] The compound of formula I includes at least two of the compound of formula IA, the compound of formula IB, and the compound of formula IC, and at least includes the compound of formula IA;

[0007] In Formula IA, R 11 、R 12 、R 13 、R 14 Each is independently selected from hydrogen, fluorine, and a substituted or unsubstituted C1-C3 alkyl group. When substituted, the substituent includes a halogen, and the compound represented by Formula IA contains at least one fluorine atom;

[0008] In some embodiments, R 11 、R 12 、R 13 、R 14Each is independently selected from hydrogen, fluorine, and a substituted or unsubstituted C1-C3 alkyl group. When substituted, the substituent includes a fluorine atom, and the compound represented by Formula IA contains at least one fluorine atom;

[0009] In Formula IB, R 15 、R 16 Each is independently selected from a substituted or unsubstituted C1-C5 alkyl group, wherein when substituted, the substituent comprises a halogen, and the compound represented by Formula IB contains at least one halogen atom;

[0010] In some embodiments, R 15 、R 16 Each is independently selected from a substituted or unsubstituted C1-C3 alkyl group, when substituted, the substituent includes a fluorine atom, and the compound represented by Formula IB contains at least one fluorine atom;

[0011] In formula IC, R 17 、R 18 Each is independently selected from a substituted or unsubstituted C1-C5 alkyl group, when substituted, the substituent includes a halogen, and the compound represented by Formula IC contains at least one halogen atom;

[0012] In formula IC, R 17 、R 18 Each is independently selected from a substituted or unsubstituted C1-C3 alkyl group, when substituted, the substituent includes a fluorine atom, and the compound represented by Formula IC contains at least one fluorine atom;

[0013] In Formula II, n is selected from an integer from 0 to 4, A 2 Selected from Any of the R 21 、R 22 、R 23 、R 24 Each independently selected from a covalent single bond, a C1-C5 alkylene group, a C2-C4 alkenylene group or Any of;

[0014] Among them, R 25 Any one selected from hydrogen, cyano, C1-C3 alkyl or C1-C3 alkyl substituted with cyano, R 26 、R 27 Each is independently selected from a covalent single bond or a C1-C3 alkylene group.

[0015] In the present application, by adding at least two of the compounds represented by formula IA, the compound represented by formula IB, and the compound represented by formula IC to the electrolyte, and at least including the compound represented by formula IA, the synergistic cooperation between the above compounds can improve the oxidation resistance of the electrolyte, which helps to inhibit the oxidative decomposition of the electrolyte. At the same time, the present application further adds the compound represented by formula II to the electrolyte containing the compound represented by formula I. The compound having the structure represented by formula II helps to stabilize the high-valent transition metal in the positive electrode active material. Through the mutual cooperation between the compound represented by formula I and the compound represented by formula II, the interface between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte can be stabilized, thereby inhibiting the gas production in the electrolyte, which helps to improve the cycle performance and high-temperature storage performance of the electrochemical device.

[0016] In some embodiments, the compound represented by Formula IA is selected from at least one of the following compounds:

[0017] In some embodiments, the compound represented by Formula IB is selected from at least one of the following compounds:

[0018] In some embodiments, the compound represented by Formula IC is selected from at least one of the following compounds:

[0019] In some embodiments, the compound represented by Formula II is selected from at least one of the following compounds:

[0020] In some embodiments, based on the mass of the electrolyte, the mass percentage of the compound represented by Formula IA is recorded as x1%, the sum of the mass percentages of the compound represented by Formula IB and the compound represented by Formula IC is recorded as x2%, the mass percentage of the compound represented by Formula II is recorded as y%, the sum of x1 and x2 is recorded as x, and the ratio of x to y is recorded as z, satisfying the following: 20 ≤ x ≤ 90. If the value of x is too small, the content of the compound represented by Formula I in the electrolyte is too low, and the effect of improving the oxidation resistance of the electrolyte is relatively limited. If the value of x is too large, the content of the compound represented by Formula I in the electrolyte is too high, which is not conducive to the dissociation of the lithium salt in the electrolyte and affects the kinetic performance of the electrochemical device. Preferably, the following: 80 ≤ x ≤ 90 is satisfied.

[0021] In some embodiments, the following condition is satisfied: 5≤z≤90. This is beneficial for improving the electrical performance of the electrochemical device, especially for improving the room temperature cycle performance and high temperature storage performance of the electrochemical device. Preferably, the following condition is satisfied: 80≤z≤90.

[0022] In some embodiments, the following condition is satisfied: 2 ≤ x2 / x1 ≤ 20. This facilitates the formation of an interfacial protective layer between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, further improving the oxidation resistance of the electrolyte. Preferably, the following condition is satisfied: 4 ≤ x2 / x1 ≤ 20.

[0023] In some embodiments, the following condition is satisfied: 0.5 ≤ y ≤ 5. When the content of the compound represented by Formula II is within the above range, it is more conducive to stabilizing the high-valent transition metal in the positive electrode active material. When combined with the compound represented by Formula I, it further improves the high-temperature storage performance of the electrochemical device. Preferably, the following condition is satisfied: 1 ≤ y ≤ 3.

[0024] In some embodiments, the electrolyte further comprises a compound of formula III, wherein the compound of formula III comprises a compound represented by formula III-A and / or a compound represented by formula III-B;

[0025] In formula III-A and formula III-B, m is selected from 0 or 1, A 31 、A 32 and A 33 Each independently selected from At least one of Indicates the binding site with the adjacent atoms;

[0026] R 31 、R 32 Each is independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C5 alkenyl, and when substituted, the substituent includes halogen;

[0027] R 33 and R 34 Each is independently selected from substituted or unsubstituted C1-C5 alkylene, substituted or unsubstituted C2-C5 alkenyl, and when substituted, the substituent includes halogen.

[0028] In some embodiments, R 31 、R 32 Each is independently selected from a substituted or unsubstituted C1-C3 alkyl group, a substituted or unsubstituted C2-C4 alkenyl group, and when substituted, the substituent includes a fluorine atom.

[0029] In some embodiments, R 33 and R 34 Each is independently selected from a substituted or unsubstituted C1-C3 alkylene group and a substituted or unsubstituted C2-C4 alkenyl group. When substituted, the substituent includes a fluorine atom.

[0030] In some embodiments, the compound of formula III is selected from at least one of the following compounds:

[0031] A compound of formula III is further added to the electrolyte of the present application. The compound of formula III is a compound containing a sulfur-oxygen double bond. The compound of formula III includes the compound shown in formula III-A and / or the compound shown in formula III-B. The compound having the structure shown in formula III-A and / or formula III-B has a strong antioxidant ability. It cooperates with other compounds in the electrolyte. On the one hand, it can improve the stability of the positive electrode interface. On the other hand, it can be reduced on the surface of the negative electrode to form a protective film, inhibit the decomposition of the electrolyte, further enhance the stability of the interface, and help improve the high-temperature full-discharge storage performance and room-temperature cycle performance of the electrochemical device.

[0032] In some embodiments, the weight percentage of the compound of Formula III is 0.1 wt % to 6 wt % based on the weight of the electrolyte. If the weight percentage of the compound of Formula III is too low, the effect of reducing side reactions is relatively limited. If the weight percentage of the compound of Formula III is too high, for example, greater than 6%, the electrolyte no longer significantly enhances the stability of the positive electrode interface and the negative electrode interface, and may also cause the electrolyte viscosity to be too high, affecting the kinetics and, in turn, the overall performance of the electrochemical device.

[0033] In some embodiments, the electrolyte further comprises a compound represented by Formula IV;

[0034] In Formula IV, R 41 is selected from substituted C1-C6 alkylene, substituted or unsubstituted C2-C6 alkenylene, and when substituted, the substituent is selected from C2-C6 alkenyl.

[0035] In some embodiments, R 41 is selected from substituted C1-C3 alkylene, substituted or unsubstituted C2-C4 alkenylene, and when substituted, the substituent is selected from C2-C4 alkenyl.

[0036] In some embodiments, the compound represented by Formula IV is selected from at least one of the following compounds:

[0037] The compound of formula IV is further added to the electrolyte of the present application. The compound of formula IV cooperates with other compounds in the electrolyte to enhance the film formation stability of the negative electrode solid interface film SEI. The use of the compound of formula IV can also increase the flexibility of the SEI film, further enhance the protection of the active material, reduce the probability of interfacial contact between the active material and the electrolyte, reduce the side reaction between the electrolyte and the active material, and thus reduce the impedance generated by the accumulation of by-products during the cycle.

[0038] In some embodiments, the weight percentage of the compound represented by Formula IV is 0.01 wt % to 2 wt % based on the weight of the electrolyte. A too low weight percentage of the compound represented by Formula IV may not fully protect the interface and may have limited performance improvement on the electrochemical device. A too high weight percentage of the compound represented by Formula IV, for example, greater than 2%, may result in excessive interfacial impedance, affecting the overall performance of the electrochemical device.

[0039] In some embodiments, the electrolyte further comprises a compound represented by Formula V;

[0040] In Formula V, A 5 Selected from R 51 、R 52 、R 53 、R 54 are each independently selected from hydrogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C6-C 10 Aryl, R 55 The compound of formula V is further added to the electrolyte of the present application. The compound of formula V cooperates with other compounds in the electrolyte to further enhance the stability of the interface between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte.

[0041] In some embodiments, the compound represented by Formula V is selected from at least one of the following compounds:

[0042] In some embodiments, the mass percentage of the compound represented by Formula V is 0.01 wt % to 1 wt %. If the mass percentage of the compound represented by Formula V is too low, it may not fully protect the interface and may have limited performance improvement on the electrochemical device. If the mass percentage of the compound represented by Formula V is too high, for example, greater than 1%, it may result in excessively high interfacial impedance, which is not conducive to improving the overall performance of the electrochemical device.

[0043] In some embodiments, the mass ratio of the compound of formula III, the compound of formula IV, and the compound of formula V is (2-5):(1-2):(1-2). In this case, it is more conducive to improving the room temperature cycling performance and high temperature storage performance of the electrochemical device. Preferably, the mass ratio of the compound of formula III, the compound of formula IV, and the compound of formula V is (2-3):(1-2):(1-2).

[0044] In some embodiments, the electrolyte further comprises a boron-containing lithium salt, the boron-containing lithium salt being selected from at least one of lithium tetrafluoroborate, lithium dioxalatoborate, or lithium difluorooxalatoborate, and the mass percentage of the boron-containing lithium salt is 0.01 wt % to 1 wt % based on the mass of the electrolyte. The boron-containing lithium salt can form a film with other compounds in the electrolyte at the positive electrode interface, protecting the positive electrode interface and further improving the cycle performance of the electrochemical device. If the mass percentage of the boron-containing lithium salt is too low and insufficient to protect the positive electrode interface, its effect on improving the cycle is relatively limited; if the mass percentage of the boron-containing lithium salt is too high, for example, greater than 1%, the effect on improving the cycle is no longer significantly improved.

[0045] In a second aspect, the present application provides an electrochemical device, which includes the above-mentioned electrolyte.

[0046] The beneficial effects of the technical solutions provided by some embodiments of the present application include at least:

[0047] The present application provides an electrolyte and an electrochemical device comprising the electrolyte. The present application first introduces a compound represented by formula IA into the electrolyte. The compound represented by formula IA facilitates the formation of an interface protective layer between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte. Secondly, the present application further adds a compound represented by formula IB and / or formula IC to the electrolyte containing the compound represented by formula IA. The synergistic cooperation between the compound represented by IA and the compounds represented by formula IB and / or formula IC facilitates the improvement of the oxidation resistance of the electrolyte, thereby inhibiting the oxidative decomposition of the electrolyte. Finally, the present application further adds a compound represented by formula II to the electrolyte containing the compound represented by formula I. The compound having the structure represented by formula II facilitates the stabilization of the high-valent transition metal in the positive electrode active material. The present application stabilizes the interface between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, inhibits gas production in the electrolyte, and thereby improves the cycle performance and high-temperature storage performance of the electrochemical device through the mutual cooperation between the compound represented by formula I and the compound represented by formula II. DETAILED DESCRIPTION

[0048] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0049] electrolyte

[0050] In a first aspect, an embodiment of the present application provides an electrolyte, the electrolyte comprising a compound of formula I and a compound of formula II;

[0051] The compound of formula I includes at least two of the compound of formula IA, the compound of formula IB, and the compound of formula IC, and at least includes the compound of formula IA;

[0052] In Formula IA, R 11 、R 12 、R 13 、R 14 Each is independently selected from hydrogen, fluorine, and a substituted or unsubstituted C1-C3 alkyl group. When substituted, the substituent includes a halogen, and the compound represented by Formula IA contains at least one fluorine atom;

[0053] At least two of the compound represented by Formula IA, the compound represented by Formula IB, and the compound represented by Formula IC, and at least including the compound represented by Formula IA;

[0054] In some embodiments, R 15 、R 16 Each is independently selected from a substituted or unsubstituted C1-C3 alkyl group, when substituted, the substituent includes a fluorine atom, and the compound represented by Formula IB contains at least one fluorine atom;

[0055] In formula IC, R 17 、R 18 Each is independently selected from a substituted or unsubstituted C1-C5 alkyl group, when substituted, the substituent includes a halogen, and the compound represented by Formula IC contains at least one halogen atom;

[0056] In formula IC, R 17 、R 18 Each is independently selected from a substituted or unsubstituted C1-C3 alkyl group, when substituted, the substituent includes a fluorine atom, and the compound represented by Formula IC contains at least one fluorine atom;

[0057] In Formula II, n is selected from an integer from 0 to 4, A 2 Selected from Any of the R 21 、R 22 、R 23 、R 24 Each independently selected from a covalent single bond, a C1-C5 alkylene group, a C2-C4 alkenylene group or Any of;

[0058] Among them, R 25 Any one selected from hydrogen, cyano, C1-C3 alkyl or C1-C3 alkyl substituted with cyano, R 26 、R 27 Each is independently selected from a covalent single bond or a C1-C3 alkylene group.

[0059] In some embodiments, the compound of Formula IA is selected from at least one of the following compounds:

[0060] In some embodiments, the compound of Formula IB is selected from at least one of the following compounds:

[0061] In some embodiments, the compound of formula IC is selected from at least one of the following compounds:

[0062] In some embodiments, the compound represented by Formula II is selected from at least one of the following compounds:

[0063] In some embodiments, based on the mass of the electrolyte, the mass percentage of the compound represented by Formula IA is denoted as x1%, the sum of the mass percentages of the compound represented by Formula IB and the compound represented by Formula IC is denoted as x2%, the mass percentage of the compound represented by Formula II is denoted as y%, the sum of x1 and x2 is denoted as x, and the ratio of x to y is denoted as z, satisfying: 20≤x≤90. Exemplarily, the value range of x is 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or a range consisting of any two of the foregoing values.

[0064] In some embodiments, the following condition is satisfied: 2≤x2 / x1≤20. For example, x2 / x1 is 2, 3, 4, 6, 8, 10, 15, 20, or a range consisting of any two of the above values.

[0065] In some embodiments, 0.5≤y≤5 is satisfied. For example, the value range of y is 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, or a range consisting of any two of the above values.

[0066] In some embodiments, 5≤z≤90 is satisfied. For example, the value range of z is 5, 10, 15, 20, 25, 30, 50, 60, 75, 80, 85, 90, or a range consisting of any two of the above values.

[0067] In some embodiments, the electrolyte further comprises a compound of formula III, wherein the compound of formula III comprises a compound represented by formula III-A and / or a compound represented by formula III-B;

[0068] In formula III-A and formula III-B, m is selected from 0 or 1, A 31 、A 32 and A 33 Each independently selected from At least one of Indicates the binding site with the adjacent atoms;

[0069] R 31 、R 32 Each is independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C5 alkenyl, and when substituted, the substituent includes halogen;

[0070] R 33 and R 34 Each is independently selected from substituted or unsubstituted C1-C5 alkylene, substituted or unsubstituted C2-C5 alkenyl, and when substituted, the substituent includes halogen.

[0071] In some embodiments, the compound of formula III is selected from at least one of the following compounds:

[0072] In some embodiments, the electrolyte further comprises a compound represented by Formula IV;

[0073] In Formula IV, R 41 is selected from substituted C1-C6 alkylene, substituted or unsubstituted C2-C6 alkenylene, and when substituted, the substituent is selected from C2-C6 alkenyl.

[0074] In some embodiments, the compound represented by Formula IV is selected from at least one of the following compounds:

[0075] In some embodiments, the electrolyte further comprises a compound represented by Formula V;

[0076] In Formula V, A 5 Selected from R 51 、R 52 、R 53 、R 54 are each independently selected from hydrogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C6-C 10 Aryl, R 55 is selected from substituted or unsubstituted C1-C6 alkylene groups, and when substituted, the substituents include halogen.

[0077] In some embodiments, the compound represented by Formula V is selected from at least one of the following compounds:

[0078] In some embodiments, the weight percentage of the compound of formula III is 0.1 wt % to 6 wt % based on the weight of the electrolyte. For example, the weight percentage of the compound of formula III is 0.1 wt %, 0.5 wt %, 0.8 wt %, 1 wt %, 2 wt %, 3 wt %, 4 wt %, 5 wt %, 6 wt %, or a range consisting of any two of the foregoing values.

[0079] In some embodiments, the weight percentage of the compound represented by Formula IV is 0.01 wt % to 2 wt % based on the weight of the electrolyte. For example, the weight percentage of the compound represented by Formula IV is 0.01 wt %, 0.05 wt %, 0.08 wt %, 0.1 wt %, 0.2 wt %, 0.3 wt %, 0.5 wt %, 1 wt %, 1.5 wt %, 2 wt %, or a range consisting of any two of the foregoing values.

[0080] In some embodiments, the mass percentage of the compound represented by Formula V is 0.01 wt % to 1 wt %. For example, the mass percentage of the compound represented by Formula V is 0.01 wt %, 0.05 wt %, 0.08 wt %, 0.1 wt %, 0.2 wt %, 0.3 wt %, 0.5 wt %, 1 wt %, or a range consisting of any two of the foregoing values.

[0081] In some embodiments, the mass ratio of the compound of formula III, the compound of formula IV, and the compound of formula V is (2-5):(1-2):(1-2). For example, the mass ratio of the compound of formula III, the compound of formula IV, and the compound of formula V is (1.8-2.2):(0.8-1.2):(0.8-1.2).

[0082] In some embodiments, the electrolyte further includes a boron-containing lithium salt, which is selected from at least one of lithium tetrafluoroborate, lithium dioxalatoborate, or lithium difluorooxalatoborate. Based on the mass of the electrolyte, the mass percentage of the boron-containing lithium salt is 0.01 wt % to 1 wt %.

[0083] Illustratively, the mass percentage of the boron-containing lithium salt is 0.01 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.3 wt%, 0.5 wt%, 0.8 wt%, 1 wt% or a range consisting of any two of the above values.

[0084] In some embodiments, the electrolyte may further include other non-aqueous organic solvents and electrolyte salts; the other non-aqueous organic solvents may include at least one of carbonate solvents, carboxylate solvents, ether solvents, or other aprotic solvents.

[0085] Examples of the carbonate-based solvent include at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, or butylene carbonate.

[0086] Examples of carboxylate solvents include at least one of methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, γ-butyrolactone, valerolactone, and butyrolactone.

[0087] Examples of the ether solvent include at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, and bis-2,2,2-trifluoroethyl ether.

[0088] The electrolyte salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the electrolyte salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2, abbreviated as LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2)) (abbreviated as LiFSI), lithium hexafluorocesium oxide (LiCsF6), lithium perchlorate (LiClO4), and lithium trifluoromethanesulfonate (LiCF3SO3).

[0089] In some embodiments, the weight percentage of the electrolyte salt is 10% to 20% based on the mass of the electrolyte. If the electrolyte salt concentration is too low, the ionic conductivity of the electrolyte will be low, which will affect the rate and cycle performance of the electrochemical device. If the electrolyte salt concentration is too high, the electrolyte viscosity will be too high, which will affect the rate performance of the electrochemical device. Alternatively, the weight percentage of the electrolyte salt is 12% to 19%.

[0090] electrochemical devices

[0091] A second aspect of an embodiment of the present application provides an electrochemical device, which includes a shell and an electrode assembly. The shell is used to encapsulate the electrode assembly. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte of the first aspect mentioned above.

[0092] Positive electrode

[0093] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode active material layer can be located on one side or both sides of the positive electrode current collector.

[0094] In some embodiments, the positive electrode current collector may be aluminum foil or other positive electrode current collectors commonly used in the art, for example, aluminum alloy foil or a composite current collector (such as a composite current collector with a metal layer disposed on the surface of a polymer layer).

[0095] In some embodiments, the thickness of the positive electrode current collector may be 1 μm to 200 μm. The present application has no particular limitation on the thickness of the positive electrode current collector, as long as the purpose of the present application can be achieved.

[0096] In some embodiments, the positive electrode active material layer may be coated only on a partial area of ​​the positive electrode current collector.

[0097] In some embodiments, the thickness of the positive electrode active material layer may be 10 μm to 500 μm. The present application has no particular limitation on the thickness of the positive electrode active material layer, as long as the purpose of the present application can be achieved.

[0098] In some embodiments, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes LiCoO2, LiNiO2, LiMn2O4, LiCo 1-y MyO2、LiNi 1-y MyO2、LiMn 2-y MyO4、LiNi x Co y Mn z M 1-x-y-z O2, wherein M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, and 0≤y≤1, 0≤x≤1, 0≤z≤1, x+y+z≤1.

[0099] In some embodiments, the positive electrode active material may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, or lithium nickel manganese oxide, and the above positive electrode active materials may be doped and / or coated.

[0100] In some embodiments, the positive electrode active material layer also includes a binder and a conductive agent; the binder may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene; the conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, flake graphite, graphene, carbon nanotubes or carbon fibers.

[0101] In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer may be 70 to 98: 1 to 15: 1 to 15. It is understood that the present application does not particularly limit the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer, and those skilled in the art may select the mass ratio according to actual needs, as long as the purpose of the present application can be achieved.

[0102] Negative electrode

[0103] The negative electrode may include a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer may be disposed on one side or both sides of the negative electrode current collector. In some embodiments, the negative electrode current collector may be at least one of copper foil, aluminum foil, nickel foil, or a carbon-based current collector. In some embodiments, the thickness of the negative electrode current collector may be 1 μm to 200 μm. In some embodiments, the negative electrode active material layer may be coated only on a partial area of ​​the negative electrode current collector. In some embodiments, the thickness of the negative electrode active material layer may be 10 μm to 500 μm. It should be understood that these are merely exemplary and other suitable thicknesses may be used.

[0104] In some embodiments, the negative electrode active material layer includes a negative electrode active material. In some embodiments, the negative electrode active material in the negative electrode active material layer includes at least one of lithium metal, natural graphite, artificial graphite, or a silicon-based material. In some embodiments, the silicon-based material includes at least one of silicon, a silicon oxide, a silicon carbon compound, or a silicon alloy.

[0105] In some embodiments, the negative electrode active material layer may further include a conductive agent and / or a binder. The conductive agent in the negative electrode active material layer may include at least one of carbon black, acetylene black, Ketjen black, flake graphite, graphene, carbon nanotubes, carbon fibers, or carbon nanowires. In some embodiments, the binder in the negative electrode active material layer may include at least one of carboxymethyl cellulose CMC, polyacrylic acid, polyacrylic acid salt, polyacrylate, polyvinyl pyrrolidone, polyaniline, polyimide, polyamide-imide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. It should be understood that the materials disclosed above are only exemplary, and the negative electrode active material layer may be made of any other suitable material. In some embodiments, the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode active material layer may be 80-99:0.5-10:0.5-10. It should be understood that this is only exemplary and is not intended to limit the present application.

[0106] Isolation film

[0107] The separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Polyethylene and polypropylene are particularly effective in preventing short circuits and can improve battery stability through the shutdown effect. In some embodiments, the separator has a thickness ranging from approximately 3 μm to 500 μm.

[0108] In some embodiments, the isolation membrane surface may further include a porous layer disposed on at least one surface of the isolation membrane. The porous layer includes at least one of inorganic particles or a binder. The inorganic particles are selected from at least one of aluminum oxide (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium oxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (Y2O3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the isolation membrane have a diameter ranging from approximately 0.01 μm to 1 μm. The binder of the porous layer is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer on the surface of the isolation membrane can improve the heat resistance, oxidation resistance and electrolyte wetting performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the electrode.

[0109] case

[0110] The shell can be a hard shell or a flexible shell. For example, the hard shell is made of metal, and the flexible shell is made of metal plastic film, such as aluminum plastic film, steel plastic film, etc.

[0111] The electrochemical device of the present application is not particularly limited and may include any device in which an electrochemical reaction occurs. In some embodiments, the electrochemical device may include, but is not limited to, a lithium-ion battery. The electrode assembly in the electrochemical device is a wound electrode assembly or a stacked electrode assembly. In some embodiments, the electrochemical device is a lithium-ion battery, but the present application is not limited thereto. In some embodiments of the present application, taking a lithium-ion battery as an example, the positive electrode, the separator, and the negative electrode are wound or stacked in sequence to form an electrode assembly, which is then encapsulated in, for example, an aluminum-plastic film housing, injected with an electrolyte, formed, and encapsulated to form a lithium-ion battery. The prepared lithium-ion battery is then subjected to performance testing. Those skilled in the art will understand that the above-described method for preparing an electrochemical device, such as a lithium-ion battery, is merely an example. Other methods commonly used in the art may be adopted without departing from the disclosure of the present application.

[0112] The present application will be further described below using a lithium-ion battery as an example of an electrochemical device and in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0113] The following examples and comparative examples are given to illustrate the embodiments of the present application in more detail. Unless otherwise stated, the parts, contents, percentages and ratios listed are all based on weight.

[0114] Preparation of positive electrode

[0115] The positive electrode active material, lithium cobalt oxide (LiCoO2), conductive carbon black (conductive carbon black), and binder (polyvinylidene fluoride (PVDF)) were dissolved in an N-methylpyrrolidone (NMP) solution at a weight ratio of 97.9:0.9:1.2 to form a positive electrode slurry. A 13μm aluminum foil was used as the positive electrode current collector. The positive electrode slurry was coated on the positive electrode current collector and dried, cold pressed, and cut to obtain the positive electrode. The compacted density of the positive electrode was 4.15g / cm 3 .

[0116] Preparation of negative electrode sheet

[0117] The negative electrode active material, artificial graphite, the binder, styrene-butadiene rubber (SBR), and the thickener, sodium carboxymethyl cellulose (CMC), were dissolved in deionized water at a weight ratio of 97.4:1.4:1.2 to form a negative electrode slurry. A 10μm thick copper foil was used as the negative electrode current collector. The negative electrode slurry was coated on the negative electrode current collector, dried, cold pressed, and cut to obtain the negative electrode. The compacted density of the negative electrode was 1.8g / cm 3 .

[0118] Preparation of isolation membrane

[0119] The base material of the isolation membrane is 5μm thick polyethylene PE. A 2μm thick alumina ceramic layer is coated on one side of the isolation membrane base material. Finally, 2.5mg / 1540.25mm is coated on both sides of the isolation membrane coated with a single layer of ceramic layer. 2 The binder is polyvinylidene fluoride (PVDF), which is dried. The porosity of the separator is 39%.

[0120] Preparation of electrolyte

[0121] In an environment with a water content of less than 10 ppm, the compound of Formula IA, the compound of Formula IB, the compound of Formula IC, or other non-aqueous organic solvent is mixed in a certain mass ratio, and then an appropriate amount of the compound of Formula II is added and mixed uniformly. The electrolyte salt LiPF6 is dissolved in the mixed solvent and mixed uniformly to form an electrolyte solution, wherein the mass percentage of LiPF6 is 12.5% ​​based on the mass of the electrolyte solution. The difference between Examples 1 to 16 and Comparative Example 1 lies in the type and / or content of the compound of Formula IA, the compound of Formula IB, the compound of Formula IC, or the compound of Formula II used in the electrolyte solution, as shown in Table 1. The corresponding abbreviations of some of these compounds are as follows: diethyl carbonate DEC, ethyl propionate EP.

[0122] The difference between Example 17 to Example 35 and Example 5 is that, on the basis of the electrolyte of Example 5, Examples 17 to Example 35 further add the compound represented by Formula III, the compound represented by Formula IV and / or the compound represented by Formula V, as shown in Table 2 for details.

[0123] The difference between Example 36 to Example 39 and Example 5 is that Examples 33 to Example 36 further add boron lithium salts to the electrolyte of Example 5, as shown in Table 3 for details.

[0124] Preparation of lithium-ion electrons

[0125] The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The electrodes are then wound to form an electrode assembly. The electrode assembly is then placed in an aluminum-plastic film package, dehydrated at 80°C, and then injected with the aforementioned electrolyte and packaged. The lithium-ion battery is then produced through a series of processes, including formation, degassing, and trimming.

[0126] Performance testing:

[0127] (1) 25℃ cycle performance test:

[0128] At 25°C, the lithium-ion battery was charged at 0.5C to 4.5V, then charged at 4.5V to 0.05C at constant voltage. It was then discharged at 1C to 3.0V, and then cycled 800 times using a 0.5C charge and 1C discharge cycle. The discharge capacity at the third cycle was used as the benchmark, and the capacity retention rate was used as an indicator to evaluate the cycling performance of the lithium-ion battery.

[0129] Cycle capacity retention rate = discharge capacity at the 800th cycle / discharge capacity at the 3rd cycle × 100%.

[0130] (2) High temperature storage performance test:

[0131] The lithium-ion battery was charged at 25°C at a constant current of 0.5C to 4.5V, then charged at a constant voltage to a current of 0.05C. The thickness of the lithium-ion battery was measured and recorded as d0. The battery was placed in an 85°C oven for 8 hours, and the thickness at this time was monitored and recorded as d.

[0132] The thickness expansion rate (%) of the lithium-ion battery after high-temperature storage for 4 hours = (d-d0) / d0×100%. If the thickness expansion rate exceeds 50%, the test is stopped.

[0133] Table 1 Parameters of Examples 1-16 and Comparative Example 1

[0134] Note: “*” indicates that the number of cycles cannot reach 800.

[0135] By comparing Examples 1 to 16 in Table 1 with Comparative Example 1, it can be seen that the synergistic combination of the compound of Formula IA, the compound of Formula IB, and / or the compound of Formula IC with the compound of Formula II can significantly improve the room temperature cycling performance and high temperature storage performance of lithium-ion batteries. In Comparative Example 1, which contains only Formula I-1 (the compound represented by Formula IA), without the addition of the compound of Formula IB and the compound of Formula IC, and without the addition of the compound of Formula II, it cannot reach 800 cycles at room temperature, and its thickness expansion rate at high temperature is greater than 50%. In contrast, in Examples 1 to 16, by adjusting the content of the compound of Formula IA, the compound of Formula IB, and / or the compound of Formula IC, and the compound of Formula II within an appropriate range, it is possible to achieve a capacity retention rate of more than about 70% after 800 cycles at room temperature, and its thickness expansion rate at high temperature is also less than about 45%. In particular, Examples 5 and 6 each achieve a capacity retention rate of more than 77% after 800 cycles at room temperature, and their thickness expansion rate at high temperature is also less than 38%. Example 16 and Example 6 are parallel examples, and it can be seen that other compounds in Formula IA can also achieve similar effects as Example 6. It can be seen that the combination of the compound of Formula IA, the compound of Formula IB, and / or the compound of Formula IC is beneficial for improving the oxidation resistance of the electrolyte, and the compound of Formula II can stabilize the transition metal surface. The synergistic combination of the compound of Formula I and the compound of Formula II can suppress the continuous consumption of the electrolyte. When the content of the compound of Formula IA, the compound of Formula IB, the compound of Formula IC, and the compound of Formula II is within the range of this application, the cycling performance and high-temperature storage performance of the electrochemical device are better. The content of each compound is the mass percentage calculated based on the total mass of the electrolyte.

[0136] Table 2 Parameters of Example 5 and Examples 17-35

[0137] Examples 17 to 35 in Table 2 are all based on the electrolyte of Example 5, further adding at least one of the compounds of Formula III, Formula IV, and Formula V. It can be seen from the data in Table 2 that the addition of the compounds of Formula III, Formula IV, and Formula V to the electrolyte of Example 5 can further improve the room temperature cycle performance and high temperature storage performance of the electrochemical device. This is because the compound of Formula III can form an interface protective layer between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, and the compound of Formula IV and Formula V can polymerize to form a protective layer, which is beneficial for suppressing electrolyte consumption and gas production. In particular, Example 33 is based on the electrolyte of Example 5 and simultaneously adds appropriate amounts of the compound of Formula III, Formula IV, and Formula V. Combined with Table 2, the capacity retention rate of Example 33 after 800 cycles at room temperature is as high as 83.7%, and its thickness expansion rate at high temperature is also significantly reduced to 29.1%. The compounds of Formula III, Formula IV, and Formula V act synergistically to strengthen and stabilize the beneficial effects of the protective layer, thereby obtaining improved cycle and high temperature storage performance. Example 34 and Example 35 are both parallel examples of Example 33. The difference between them and Example 33 is that the types of the compound of Formula III, the compound of Formula IV and the compound of Formula V are changed, and similar effects as Example 33 can be achieved.

[0138] Table 3 Parameters of Example 5 and Examples 36-39

[0139] Examples 36 to 39 in Table 3 all further added boron-based lithium salts to the electrolyte of Example 5. Comparison of Example 5 and Examples 36-39 shows that the addition of boron-based lithium salts to the electrolyte of Example 5 can further improve the room temperature cycling performance of lithium-ion batteries.

[0140] The above are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. An electrolyte, characterized in that: The electrolyte comprises a compound of formula I and a compound of formula II; The compound of formula I includes at least two of the compound of formula IA, the compound of formula IB and the compound of formula IC, and at least includes the compound of formula IA; In Formula IA, R 11 , R 12 , R 13 , R 14 Each is independently selected from hydrogen, fluorine, a substituted or unsubstituted C1-C3 alkyl group, when substituted, the substituent includes a halogen, and the compound represented by Formula IA contains at least one fluorine atom; In Formula IB, R 15 , R 16 Each is independently selected from a substituted or unsubstituted C1-C5 alkyl group, when substituted, the substituent includes a halogen, and the compound represented by formula IB contains at least one halogen atom; In formula IC, R 17 , R 18 Each is independently selected from a substituted or unsubstituted C1-C5 alkyl group, when substituted, the substituent includes a halogen, and the compound represented by formula IC contains at least one halogen atom; In Formula II, n is selected from an integer from 0 to 4, A 2 Selected from Any of the R 21 , R 22 , R 23 , R 24 Each independently selected from a covalent single bond, a C1-C5 alkylene group, a C2-C4 alkenylene group or Any of; Among them, R 25 Any one selected from hydrogen, cyano, C1-C3 alkyl or C1-C3 alkyl substituted with cyano, R 26 , R 27 Each is independently selected from a covalent single bond or a C1-C3 alkylene group.

2. The electrolyte according to claim 1, characterized in that The compound represented by formula IA is selected from at least one of the following compounds:

3. The electrolyte according to claim 1, characterized in that The compound represented by formula IB is selected from at least one of the following compounds:

4. The electrolyte according to claim 1, characterized in that The compound represented by formula IC is selected from at least one of the following compounds:

5. The electrolyte according to claim 1, characterized in that The compound represented by formula II is selected from at least one of the following compounds:

6. The electrolyte according to claim 1, characterized in that Based on the mass of the electrolyte, the mass percentage of the compound represented by formula IA is denoted as x1%, the sum of the mass percentages of the compound represented by formula IB and the compound represented by formula IC is denoted as x2%, the mass percentage of the compound represented by formula II is denoted as y%, the sum of x1 and x2 is denoted as x, and the ratio of x to y is denoted as z, satisfying at least one of the following conditions: (1) 20≤x≤90; (2) 2≤x2 / x1≤20; (3) 0.5≤y≤5; (4) 5≤z≤90.

7. The electrolyte according to claim 1, characterized in that The electrolyte further comprises a compound of formula III, wherein the compound of formula III comprises a compound of formula III-A and / or a compound of formula III-B; In formula III-A and formula III-B, m is selected from 0 or 1, A 31 , A 32 and A 33 Each independently selected from At least one of represents the binding site with the neighboring atoms; R 31 , R 32 Each is independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C5 alkenyl, and when substituted, the substituent includes halogen; R 33 and R 34 Each is independently selected from substituted or unsubstituted C1-C5 alkylene, substituted or unsubstituted C2-C5 alkenyl, and when substituted, the substituent includes halogen.

8. The electrolyte according to claim 7, characterized in that The compound of formula III is selected from at least one of the following compounds:

9. The electrolyte according to claim 7, characterized in that The electrolyte further comprises a compound represented by formula IV; In Formula IV, R 41 is selected from substituted C1-C6 alkylene, substituted or unsubstituted C2-C6 alkenylene, and when substituted, the substituent is selected from C2-C6 alkenyl.

10. The electrolyte according to claim 9, characterized in that The compound represented by formula IV is selected from at least one of the following compounds:

11. The electrolyte according to claim 9, characterized in that The electrolyte further comprises a compound represented by formula V; In Formula V, A 5 Selected from R 51 , R 52 , R 53 , R 54 are each independently selected from hydrogen, substituted or unsubstituted C1-C6 alkyl, substituted or unsubstituted C6-C 10 Aryl, R 55 Selected from substituted or unsubstituted C1-C6 alkylene groups, when substituted, the substituents include halogen.

12. The electrolyte according to claim 11, characterized in that The compound represented by formula V is selected from at least one of the following compounds:

13. The electrolyte according to claim 11, characterized in that Based on the quality of the electrolyte, at least one of the following conditions is met: (1) The mass percentage of the compound of formula III is 0.1wt% to 6wt%; (2) The mass percentage of the compound represented by formula IV is 0.01wt% to 2wt%; (3) The mass percentage of the compound represented by formula V is 0.01wt% to 1wt%.

14. The electrolyte according to claim 11, characterized in that The mass ratio of the compound represented by formula III, the compound represented by formula IV and the compound represented by formula V is (2-5):(1-2):(1-2).

15. The electrolyte according to claim 1, characterized in that The electrolyte also includes a boron-containing lithium salt; The boron-containing lithium salt is selected from at least one of lithium tetrafluoroborate, lithium dioxalatoborate or lithium difluorooxalatoborate; Based on the mass of the electrolyte, the mass percentage of the boron-containing lithium salt is 0.01wt% to 1wt%.

16. An electrochemical device, characterized in that: The electrochemical device comprises the electrolyte according to any one of claims 1 to 15.

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