Electrolyte and electrochemical apparatus

Abstract

Provided are an electrolyte and an electrochemical device. The electrolyte comprises a compound represented by formula I and a compound represented by formula II. The compound represented by 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 electrolyte can improve the cycling performance and the high-temperature storage performance of the electrochemical apparatus, thereby ensuring that the electrochemical apparatus has good kinetic performance.

Description

Electrolyte and electrochemical device Technical Field

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

[0002] With the widespread application of electrochemical devices (e.g., lithium-ion batteries) in various electronic products, users have placed increasingly higher demands on 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 includes increasing the charging voltage of lithium-ion batteries. However, a higher charging voltage will accelerate the oxidative decomposition of the electrolyte by the high-valent transition metals in the positive electrode active material. The high-valent transition metals will obtain electron compensation from oxygen atoms, resulting in oxygen release, further accelerating the decomposition of the electrolyte, resulting in increased gas production in the lithium-ion battery, and affecting the 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, which have good oxidation resistance and can stabilize the high-valent transition metals in the positive electrode active material while taking into account the stability of the negative electrode interface, which is beneficial to improving the cycle performance and high-temperature storage performance of the electrochemical device, and ensuring that the electrochemical device has good kinetic performance.

[0005] In a first aspect, the present application provides an electrolyte, the 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 14 Each 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 independently selected from C1-C5 alkyl;

[0010] In some embodiments, in Formula IB, R 15 、R 16 Each independently selected from C1-C3 alkyl;

[0011] In formula IC, R 17 、R 18 Each independently selected from C1-C5 alkyl;

[0012] In some embodiments, in Formula IC, R 17 、R 18 Each independently selected from C1-C3 alkyl;

[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 the following; where 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.

[0014] 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 compound represented by formula IA in the electrolyte can form an interface protection layer between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte. At the same time, the introduction of the fluorinated substance represented by formula IA can improve the oxidation resistance of the electrolyte, and the introduction of the compound represented by formula IB and / or the compound represented by IC can reduce the viscosity of the electrolyte, which is beneficial to improving the kinetic properties of the electrolyte. At the same time, the compound represented by formula II is introduced. The compound represented by formula II can stabilize the high-valent transition metal in the positive electrode active material. Through the mutual synergistic cooperation between the compound represented by formula I and the compound represented by formula II, it is beneficial to stabilize the interface between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, thereby inhibiting gas production in the electrolyte, which is beneficial to improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0015] In some embodiments, the compound represented by Formula IA is selected from at least one of the following compounds: The inclusion of the compound represented by the above structural formula in the electrolyte is beneficial to further improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0016] In some embodiments, the compound represented by Formula IB is selected from 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, and butyl butyrate. Meeting the above conditions is beneficial for further improving the cycling performance and high-temperature storage performance of the electrochemical device.

[0017] In some embodiments, the compound represented by Formula IC is selected from at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and dipropyl carbonate. Meeting the above conditions is conducive to further improving the cycling performance and high-temperature storage performance of the electrochemical device.

[0018] In some embodiments, the compound represented by Formula II is selected from at least one of the following compounds: The inclusion of the compound represented by the above structural formula in the electrolyte is beneficial to further improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0019] In some embodiments, the compound represented by Formula II is selected from at least two of the above compounds. Meeting the above conditions is conducive to further improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0020] In some embodiments, the compound represented by Formula II is selected from at least three of the above compounds. Meeting the above conditions is conducive to further improving the cycling performance and high-temperature storage performance of the electrochemical device.

[0021] 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 ratio of x2 to x1 is denoted as x, and the ratio of x1 to y is denoted as z, and the following conditions are satisfied: 5 ≤ x1 ≤ 20. Meeting the above conditions is conducive to further improving the cycling performance and high-temperature storage performance of the electrochemical device. Preferably, 6 ≤ x1 ≤ 10.

[0022] In some embodiments, the following is satisfied: 60≤x2≤90. When the sum of the mass percentages of the compound represented by Formula IB and / or the compound represented by Formula IC is within the above range, it is more conducive to improving the kinetic properties of the electrolyte and can assist the compound represented by Formula I in improving the oxidation resistance of the electrolyte. Preferably, 65≤x2≤80

[0023] In some embodiments, the ratio x2 to x1 satisfies the following: 3 ≤ x ≤ 11. When the ratio of x2 to x1 is within this range, the synergistic effect between the compound represented by Formula IA, the compound represented by Formula IB, and the compound represented by Formula IC is enhanced, resulting in a more pronounced improvement in the oxidation resistance of the electrolyte. Preferably, x2 satisfies the following: 7 ≤ x ≤ 10.

[0024] In some embodiments, the following is satisfied: 1≤z≤20. This is more beneficial to the electrical performance of the electrochemical device, especially to improving the cycling performance and high-temperature storage performance of the electrochemical device. Preferably, 1≤z≤5.

[0025] In some embodiments, the electrolyte further comprises a compound represented by Formula III;

[0026] In formula III, m is selected from 0 or 1, A 31 and A 32 Each independently selected from Any of Represents the binding site with the adjacent atoms; R 31 、R 32 Each is independently selected from a covalent single bond, a substituted or unsubstituted C1-C5 alkylene group, a substituted or unsubstituted C2-C5 alkenylene group, and when substituted, the substituent includes a halogen. A compound shown in formula III is further added to the electrolyte of the present application. The compound shown in formula III is a compound containing a sulfur-oxygen double bond. The compound containing a sulfur-oxygen double bond having the structure shown in formula III has a strong antioxidant capacity. When combined 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 negative electrode surface to form a protective film, inhibiting the decomposition of the electrolyte, further enhancing the stability of the interface, and helping to improve the high-temperature full-discharge storage performance and cycle performance of the electrochemical device.

[0027] In some embodiments, R 31 、R 32 Each is independently selected from a covalent single bond, a substituted or unsubstituted C1-C3 alkylene group, and a substituted or unsubstituted C2-C4 alkenylene group. When substituted, the substituent includes a fluorine atom. Meeting the above conditions can further improve the cycling performance and high-temperature storage performance of the electrochemical device.

[0028] In some embodiments, the compound represented by Formula III is selected from at least one of the following compounds: Meeting the above conditions is conducive to further improving the cycle performance and high-temperature storage performance of electrochemical devices.

[0029] In some embodiments, the mass percentage of the compound represented by Formula III is 0.08 wt % to 5 wt %. Meeting the above conditions is more conducive to further improving the cycling performance and high-temperature storage performance of the electrochemical device. Preferably, the mass percentage of the compound represented by Formula III is 1 wt % to 5 wt %.

[0030] In some embodiments, the electrolyte further comprises a compound represented by Formula IV;

[0031] In Formula IV, R 41 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 byproducts during the cycle.

[0032] 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.

[0033] In some embodiments, the compound represented by Formula IV is selected from at least one of the following compounds: The inclusion of the compound represented by the above structural formula in the electrolyte is beneficial to further improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0034] In some embodiments, the weight percentage of the compound represented by Formula IV is 0.01 wt % to 2 wt %. Meeting the above conditions is more conducive to further improving the cycling performance and high-temperature storage performance of the electrochemical device. Preferably, the weight percentage of the compound represented by Formula IV is 0.01 wt % to 1.2 wt %.

[0035] In some embodiments, the electrolyte further comprises a compound represented by Formula V;

[0036] In Formula V, A 5 Independently selected 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.

[0037] In some embodiments, the compound represented by Formula V is selected from at least one of the following compounds: The inclusion of the compound represented by the above structural formula in the electrolyte is beneficial to further improving the cycle performance and high-temperature storage performance of the electrochemical device.

[0038] In some embodiments, the mass percentage of the compound represented by Formula V is 0.01 wt % to 1 wt %. Meeting the above conditions is more conducive to further improving the cycling performance and high-temperature storage performance of the electrochemical device. Preferably, the mass percentage of the compound represented by Formula V is 0.3 wt % to 1 wt %.

[0039] 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. This is more conducive to improving the 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.

[0040] In some embodiments, the electrolyte further includes 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. Meeting the above conditions is more conducive to further improving the cycle performance and high-temperature storage performance of the electrochemical device. Preferably, the mass percentage of the boron-containing lithium salt is 0.3 wt % to 1 wt %. 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.

[0041] In a second aspect, the present application provides an electrochemical device, which includes the above-mentioned electrolyte.

[0042] The beneficial effects of the technical solutions provided by some embodiments of the present application include at least:

[0043] The present application provides an electrolyte and an electrochemical device. The present application first introduces a compound represented by Formula IA into the electrolyte. The compound represented by Formula IA is conducive to forming an interface protective layer between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, and the fluorinated substance represented by Formula IA can improve the oxidation resistance of 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 introduction of the compound represented by Formula IB and / or Formula IC can reduce the viscosity of the electrolyte and improve the dynamics of the electrolyte. The synergistic cooperation between the compound represented by IA and the compound represented by Formula IB and / or Formula IC is further conducive to improving the oxidation resistance of the electrolyte. The present application adds a compound represented by Formula II to the electrolyte containing the compound represented by Formula I. The cyano group in the compound represented by Formula II can stabilize the high-valent transition metal. The present application stabilizes the interface between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, through the mutual cooperation between the compound represented by Formula I and the compound represented by Formula II, inhibits gas production in the electrolyte, and thereby improves the cycle performance and high-temperature storage performance of the electrochemical device. DETAILED DESCRIPTION

[0044] 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.

[0045] electrolyte

[0046] 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;

[0047] 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;

[0048] 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;

[0049] In some embodiments, R 11 、R 12 、R 13 、R 14are each 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;

[0050] In Formula IB, R 15 、R 16 Each independently selected from C1-C5 alkyl;

[0051] In some embodiments, in Formula IB, R 15 、R 16 Each independently selected from C1-C3 alkyl;

[0052] In formula IC, R 17 、R 18 Each independently selected from C1-C5 alkyl;

[0053] In some embodiments, in Formula IC, R 17 、R 18 Each independently selected from C1-C3 alkyl;

[0054] 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 the following; where 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.

[0055] In some embodiments, the compound of Formula IA is selected from at least one of the following compounds:

[0056] In some embodiments, the compound of formula IB is selected from at least one of methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate (EP), propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, or butyl butyrate.

[0057] In some embodiments, the compound represented by Formula IC is selected from at least one of dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, and dipropyl carbonate.

[0058] In some embodiments, the compound represented by Formula II is selected from at least one of the following compounds:

[0059] In some embodiments, the compound represented by Formula II is selected from at least two of the above compounds.

[0060] In some embodiments, the compound of Formula II is selected from at least three of the above compounds.

[0061] 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 ratio of x2 to x1 is recorded as x, and the ratio of x1 to y is recorded as z, satisfying: 5≤x1≤20. Exemplarily, the value range of x1 is 5, 6, 8, 10, 12, 14, 15, 16, 18, 20, or a range consisting of any two of the above values. If the value of x1 is too small, the content of the compound represented by Formula IA in the electrolyte is too small, and the effect of improving the oxidation resistance of the electrolyte is relatively limited. If the value of x1 is too large, the content of the compound represented by Formula IA in the electrolyte is too high, which is not conducive to the dissociation of the lithium salt in the electrolyte.

[0062] In some embodiments, the condition 60≤x2≤90 is satisfied. For example, the value range of x2 is 60, 65, 70, 75, 80, 85, 88, 90, or a range consisting of any two of the above values.

[0063] In some embodiments, 3≤x≤11 is satisfied. For example, the value range of x is 3, 4, 5, 6, 7, 8, 8, 9, 9, 10, 11, or a range consisting of any two of the above values.

[0064] In some embodiments, 1≤z≤20 is satisfied. For example, the value range of x is 1, 2, 3, 5, 8, 10, 12, 15, 18, 20, or a range consisting of any two of the above values.

[0065] In some embodiments, the electrolyte further comprises a compound represented by Formula III;

[0066] In formula III, m is selected from 0 or 1, A 31 and A 32 Each independently selected from Any of Represents the binding site with the adjacent atoms; R 31 、R 32 Each is independently selected from a covalent single bond, a substituted or unsubstituted C1-C5 alkylene group, a substituted or unsubstituted C2-C5 alkenylene group, and when substituted, the substituent includes halogen.

[0067] In some embodiments, R 31 、R 32 Each is independently selected from a covalent single bond, a substituted or unsubstituted C1-C3 alkylene group, a substituted or unsubstituted C2-C4 alkenylene group, and when substituted, the substituent includes a fluorine atom.

[0068] In some embodiments, the compound represented by Formula III is selected from at least one of the following compounds:

[0069] In some embodiments, the mass percentage of the compound shown in Formula III is 0.08wt% to 5wt%. Exemplarily, the mass percentage of the compound shown in Formula III is 0.08wt%, 0.1wt%, 0.5wt%, 0.8wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt% or a range consisting of any two of the above values. In the electrolyte, if the mass percentage of the compound shown in Formula III is too low, the effect of reducing side reactions is relatively limited. If the mass percentage of the compound shown in Formula III is too high, for example, greater than 5%, the enhancing effect of the compound shown in Formula III on the stability of the positive electrode interface and the negative electrode interface is no longer significantly improved, and the viscosity of the electrolyte may be too large, affecting the kinetics and the performance of the electrochemical device.

[0070] In some embodiments, the electrolyte further comprises a compound represented by Formula IV;

[0071] 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.

[0072] 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.

[0073] In some embodiments, the compound represented by Formula IV is selected from at least one of the following compounds:

[0074] In some embodiments, the mass percentage of the compound shown in Formula IV is 0.01wt% to 2wt%. Exemplarily, the mass percentage of the compound shown in Formula IV is 0.01wt%, 0.05wt%, 0.08wt%, 0.1wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt% or a range consisting of any two of the above values. In the electrolyte, if the mass percentage of the compound shown in Formula IV is too low, it will not fully protect the interface and will have limited effect on improving the performance of the electrochemical device; if the mass percentage of the compound shown in Formula IV is too high, for example, greater than 2%, it will result in excessive interfacial impedance, affecting the performance of the electrochemical device.

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

[0076] In Formula V, A 5 Independently selected 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 mass percentage of the compound shown in Formula V is 0.01wt% to 1wt%. Exemplarily, the mass percentage of the compound shown in Formula V is 0.01wt%, 0.05wt%, 0.08wt%, 0.1wt%, 0.3wt%, 0.5wt%, 0.8wt%, 1wt% or a range consisting of any two of the above values. In the electrolyte, the mass percentage of the compound shown in Formula V is too low to fully protect the interface and has limited performance improvement on the electrochemical device. The mass percentage of the compound shown in Formula V is too high, for example, greater than 1%, which will result in excessive interfacial impedance and affect the performance of the electrochemical device.

[0079] 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.

[0080] 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 %.

[0081] 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.

[0082] 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 ethers or other aprotic solvents. Examples of ether solvents 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.

[0083] 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).

[0084] 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%.

[0085] electrochemical devices

[0086] 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.

[0087] Positive electrode

[0088] 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.

[0089] 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).

[0090] 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.

[0091] In some embodiments, the positive electrode active material layer may be coated only on a partial area of ​​the positive electrode current collector.

[0092] 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.

[0093] 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.

[0094] 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.

[0095] In some embodiments, the positive electrode active material layer also includes a binder and a conductive agent, and 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.

[0096] 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.

[0097] Negative electrode

[0098] 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.

[0099] 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.

[0100] 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.

[0101] Isolation film

[0102] 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.

[0103] 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.

[0104] case

[0105] 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.

[0106] The electrochemical device of the present application is not particularly limited and may include any device that undergoes an electrochemical reaction. 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, separator, and negative electrode are sequentially wound or stacked into an electrode assembly, which is then encapsulated in, for example, an aluminum-plastic film casing, injected with an electrolyte, and then formed and packaged to produce 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 employed without departing from the disclosure of the present application.

[0107] 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.

[0108] 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.

[0109] Preparation of positive electrode

[0110] 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 .

[0111] Preparation of negative electrode sheet

[0112] 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 .

[0113] Preparation of isolation membrane

[0114] 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%.

[0115] Preparation of electrolyte

[0116] 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 after uniform mixing, an electrolyte solution is formed, wherein the mass percentage of LiPF6 is 12.5% ​​based on the mass of the electrolyte solution. The difference between Examples 1 to 17 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: ethylene carbonate EC, propylene carbonate PC.

[0117] The difference between Examples 18 to 35 and Example 1 is that, on the basis of the electrolyte of Example 1, Examples 18 to 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.

[0118] The difference between Example 36 to Example 39 and Example 1 is that Examples 33 to Example 36 further add boron lithium salts on the basis of the electrolyte of Example 1, as shown in Table 3 for details.

[0119] Preparation of lithium-ion electrons

[0120] 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.

[0121] Performance test:

[0122] (1) 45℃ cycle performance test:

[0123] At 45°C, the lithium-ion battery was charged at 1C to 4.5V, then charged at 4.5V to 0.05C at a constant voltage. It was then discharged at 0.5C to 3.0V, and then cycled 200 times using a 1C charge and 0.5C discharge cycle. The discharge capacity at the third cycle was used as the benchmark, and the capacity retention rate was used as the indicator for evaluating the cycling performance of the lithium-ion battery.

[0124] Cycle capacity retention rate = discharge capacity at the 200th cycle / discharge capacity at the 3rd cycle × 100%.

[0125] (2) High temperature storage performance test:

[0126] The lithium-ion battery was charged at 25°C at a constant current of 0.5C to 4.55V, and then charged at a constant voltage to a current of 0.05C. The thickness of the lithium-ion battery was tested and recorded as d0. The battery was placed in a 60°C oven for 4 hours. The thickness at this time was monitored and recorded as d. The thickness expansion rate (%) of the lithium-ion battery after high-temperature storage for 4 hours = (d-d0) / d0×100%. The thickness expansion rate exceeded 50%, and the test was stopped.

[0127] Table 1 Parameters of Examples 1-17 and Comparative Example 1

[0128] Note: “*” indicates that the number of cycles cannot reach 200.

[0129] Comparing Examples 1 to 17 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 cycling performance and high-temperature storage performance of lithium-ion batteries. The electrolyte of Comparative Example 1, containing only the compound of Formula I without the compound of Formula II, failed to cycle 200 times at 45°C, and its thickness expansion rate at high temperatures exceeded 50%. In contrast, in Examples 1 to 17, by adding the compound of Formula IA, the compound of Formula IB, and / or the compound of Formula IC, and the compound of Formula II to the electrolyte, and adjusting the contents of the compound of Formula IA, the compound of Formula IB, and / or the compound of Formula IC, and the compound of Formula II to appropriate ranges, the prepared lithium-ion batteries achieved a capacity retention rate of greater than approximately 70% after 200 cycles at 45°C, and a thickness expansion rate of less than 50% at high temperatures. In particular, Example 15, the electrolyte in Example 15 contains three compounds of Formula II. By adjusting the content of the three compounds of Formula II to be appropriate, it is more conducive to synergizing with the compound of Formula I. Example 15 has a capacity retention rate of 78.9% after 200 cycles at 45°C, and its thickness expansion rate at high temperature is only 7.5%. In the electrolytes of Examples 12 to 14, the compounds of Formula II are all a combination of multiple compounds, and similar effects as Example 15 can be achieved. Examples 16 to 17 are parallel examples of Example 1. The only difference between them and Example 1 is that the type of compound of Formula I is changed, and similar results as Example 1 can be obtained. The compound of formula IA can form a protective layer between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, thereby improving the oxidation resistance of the electrolyte. The introduction of the compound of formula IB and / or the compound of formula IC is beneficial to improving the kinetics of the electrochemical device. At the same time, the compound represented by formula II is introduced. The compound represented by formula II can stabilize the high-valent transition metal in the positive electrode active material. Through the mutual synergistic cooperation between the compound represented by formula I and the compound represented by formula II, it is beneficial to stabilize the interface between the positive electrode and the electrolyte, and between the negative electrode and the electrolyte, thereby inhibiting gas production in the electrolyte, and improving the cycle performance and high-temperature storage performance of the lithium-ion battery. 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 cycle performance and high-temperature storage performance of the electrochemical device are better.

[0130] Table 2 Parameters of Example 1 and Examples 18-35

[0131] Examples 18 to 35 in Table 2 are all based on the electrolyte of Example 1, 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 1 can further improve the 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 cooperates with each other and helps to inhibit electrolyte consumption and gas production. In particular, Example 34 is based on the electrolyte of Example 1, and Example 34 is based on the addition of appropriate amounts of the compound of Formula III, Formula IV, and Formula V. Combined with Table 2, the capacity retention rate of Example 34 after 200 cycles at 45°C is as high as 85.7%, and its thickness expansion rate at high temperature is also significantly reduced to 12.6%. Example 35 is a parallel example of Example 34. The difference between it 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 to those of Example 34 can be achieved.

[0132] Table 3 Parameters of Example 1 and Examples 36-39

[0133] Examples 36 to 39 in Table 3 all further added boron-based lithium salts to the electrolyte of Example 1. Comparison of Example 1 with Examples 36-39 shows that adding boron-based lithium salts to the electrolyte of Example 1 can further improve the cycle performance of lithium-ion batteries.

[0134] 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 independently selected from C1-C5 alkyl; In formula IC, R 17 , R 18 Each independently selected from C1-C5 alkyl; 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 methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate or butyl butyrate: The compound represented by formula IC is at least one selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and dipropyl carbonate.

4. 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:

5. 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 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 ratio of x2 to x1 is recorded as x, and the ratio of x1 to y is recorded as z, and at least one of the following conditions is satisfied: (I) 5≤x1≤20; (II) 60≤x2≤90; (III) 3≤x≤11; (IV) 1≤z≤20.

6. The electrolyte according to claim 5, characterized in that Satisfies at least one of the following conditions: (i) 6≤x1≤10; (ii) 65≤x2≤80; (iii) 7≤x≤10; (iv) 1≤z≤5.

7. The electrolyte according to claim 1, characterized in that The electrolyte further comprises a compound represented by formula III; In Formula III, m is selected from 0 or 1, A 31 and A 32 Each independently selected from Any of represents the binding site with the neighboring atoms; R 31 , R 32 Each is independently selected from a covalent single bond, a substituted or unsubstituted C1-C5 alkylene group, a substituted or unsubstituted C2-C5 alkenylene group, and when substituted, the substituent includes halogen.

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

9. The electrolyte according to claim 1, 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 1, characterized in that The electrolyte further comprises a compound represented by formula V; In Formula V, A 5 Independently selected 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 any one of claims 1 to 12, characterized in that The electrolyte satisfies at least one of the following conditions: (1) The electrolyte comprises a compound represented by formula III, and the mass percentage of the compound represented by formula III is 0.08wt% to 5wt% based on the mass of the electrolyte; (2) The electrolyte comprises a compound represented by Formula IV, and the mass percentage of the compound represented by Formula IV is 0.01wt% to 2wt% based on the mass of the electrolyte; (3) The electrolyte comprises a compound represented by Formula V, and the mass percentage of the compound represented by Formula V is 0.01 wt % to 1 wt % based on the mass of the electrolyte. (4) The electrolyte comprises the compound represented by formula III, the compound represented by formula IV and the compound represented by formula V. Based on the mass of the electrolyte, 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.

14. 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%.

15. An electrochemical device, characterized in that: The electrochemical device comprises the electrolyte according to any one of claims 1 to 14.

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