Electrolyte additive, electrolyte, and electrochemical device

Abstract

Provided are an electrolyte additive, an electrolyte, and an electrochemical device. The electrolyte additive comprises a compound represented by formula 1 and a compound represented by formula 2, wherein the compound represented by formula 2 is selected from at least one of a compound represented by formula 2-A and a compound represented by formula 2-B. By means of the above configuration, the compound represented by formula 1 and the compound represented by formula 2 are used in combination as the electrolyte additive, which is beneficial to forming a stable solid electrolyte interface film at a negative electrode interface and beneficial to forming a stable positive electrode electrolyte interface film at a positive electrode interface, thereby improving the stability of the positive electrode interface and the negative electrode interface, reducing side reactions between an electrolyte and electrode active materials, effectively inhibiting further decomposition of the electrolyte, reducing gas production, reducing the internal resistance growth rate of the electrochemical device, and improving the high-temperature cycle performance and the high-temperature storage performance of the electrochemical device.

Description

An electrolyte additive, an electrolyte, and an electrochemical device

[0001] This application claims priority to Chinese Patent Application No. 202410910196.1, filed on July 9, 2024, entitled "An Electrolyte Additive, Electrolyte and Electrochemical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical technology, and in particular to an electrolyte additive, an electrolyte, and an electrochemical device. Background Technology

[0003] Rechargeable electrochemical devices are considered one of the most attractive energy storage systems due to their advantages such as high operating voltage, long lifespan, and environmental friendliness. Today, electrochemical devices, such as lithium-ion batteries, are widely used in consumer electronics, power batteries, and energy storage batteries.

[0004] With the rapid development of the electrochemical device industry, the market has placed higher demands on the energy density and lifespan of electrochemical devices. Currently, to improve the energy density of electrochemical devices, the upper limit voltage of charging or the nickel content in the cathode material can be increased. However, traditional electrolyte systems are prone to decomposition under high voltage, and side reactions easily occur between the cathode material and the electrolyte, affecting the structural stability of the cathode active material. This also leads to excessive electrolyte consumption and gas generation, increasing the internal resistance of the electrochemical device and severely impacting its high-temperature cycling and storage performance. Therefore, reducing the rate of increase in internal resistance and improving the high-temperature cycling and storage performance of electrochemical devices have become urgent problems to be solved. Summary of the Invention

[0005] The purpose of this application is to provide an electrolyte additive, an electrolyte, and an electrochemical device to reduce the rate of increase in internal resistance of the electrochemical device and improve its high-temperature cycling performance and high-temperature storage performance. The specific technical solution is as follows:

[0006] A first aspect of this application provides an electrolyte additive comprising a compound of Formula 1 and a compound of Formula 2, wherein the compound of Formula 2 is selected from at least one of the compounds of Formula 2-A and Formula 2-B:

[0007] Where m and n are each independently selected from integers from 0 to 3, and m and n are not both 0, p is selected from integers from 1 to 5, R0 is selected from single bonds or methylene groups, R1 is selected from hydrogen, halogens, C1-C5 hydrocarbon groups, or C1-C5 haloalkyl groups, and R2, R3, and R4 are each independently selected from... One of the following: R5 and R6 are each independently selected from substituted or unsubstituted phenyl, substituted or unsubstituted imidazolyl, substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C5 alkenyl, C1-C5 alkoxy, substituted or unsubstituted C2-C5 alkoxyalkyl, substituted or unsubstituted C1-C5 carbonyl, substituted or unsubstituted C1-C5 cyano, and halogen. When substituted, the substituents are each independently selected from halogen and C1-C5 alkyl. R7 and R9 are each independently selected from halogen and substituted or unsubstituted C1-C5 alkyl. R8 is selected from substituted or unsubstituted phenylene, substituted or unsubstituted C1-C5 alkylene, C2-C5 alkenyl, C2-C5 alkoxyalkylene. When substituted, the substituents are each independently selected from halogen, hydroxyl, and phenyl. When used as an electrolyte additive, the compound shown in Formula 1 of this application can form an interfacial film at the interface between the positive and negative electrodes. However, to obtain a stable solid electrolyte interfacial film (SEI film) and a positive electrode electrolyte interfacial film (CEI film), a relatively large amount of the compound shown in Formula 1 is required. However, the film formation process is difficult to control. Adding too much of the compound shown in Formula 1 can easily lead to a large initial film-forming impedance, and the electrolyte interfacial film impedance increases with battery cycling, which in turn increases the internal resistance of the electrochemical device, affecting cycle life. To address this issue, this application uses the compound shown in Formula 1 and the compound shown in Formula 2 together as electrolyte additives. The compound shown in Formula 2 is preferred over the compound shown in Formula 1 and other electrolyte components at the negative electrode. The surface is reduced, forming a solid electrolyte interphase (SEI) film rich in alkyl sulfonates on the negative electrode surface, which improves the stability of the negative electrode interface. In addition, the preferential reduction of the compound of Formula 2 helps to inhibit the further reduction of the compound shown in Formula 1 and other components of the electrolyte at the negative electrode, which is conducive to the formation of a stable solid electrolyte interphase (SEI) film at the negative electrode interface. At the same time, it is also conducive to the formation of a stable positive electrode electrolyte interphase (CEI) film at the positive electrode interface, which improves the stability of the positive and negative electrode interfaces, reduces side reactions between the electrolyte and the electrode active materials, effectively inhibits further decomposition of the electrolyte, reduces gas production, reduces the rate of increase of internal resistance of the electrochemical device, and improves the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0008] In some embodiments of this application, the mass ratio of the compound shown in Formula 1 to the compound shown in Formula 2 is (0.1–16):1. By adjusting the mass ratio of the compound shown in Formula 1 to the compound shown in Formula 2 within the range of this application, it is beneficial to leverage the synergistic effect of the compound shown in Formula 1 and the compound shown in Formula 2, further improve the stability of the positive and negative electrode interface, further reduce side reactions between the electrolyte and electrode materials, reduce gas production, further reduce the rate of increase in internal resistance of the electrochemical device, and improve the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0009] In some embodiments of this application, the compound represented by Formula 1 is selected from at least one of the following compounds:

[0010] The electrolyte additive includes compounds of Formula 1 within the above-mentioned range, which is beneficial for forming a stable CEI film at the positive electrode interface, improving the stability of the positive electrode interface, thereby further improving the high-temperature cycle performance and high-temperature storage performance of the electrochemical device, and reducing internal resistance.

[0011] In some embodiments of this application, the compound shown in Formula 1 is selected from the compounds shown in Formula 1-1.

[0012] In some embodiments of this application, the compound represented by Formula 2-A is selected from at least one of the following compounds:

[0013] In some embodiments of this application, the compound represented by Formula 2-B is selected from at least one of the following compounds:

[0014] The electrolyte additive includes at least one of the compounds shown in Formula 2-A or Formula 2-B within the above-mentioned range. During the first charging process of the electrochemical device, the compound shown in Formula 2 is preferentially reduced on the negative electrode surface over the compound shown in Formula 1 and other electrolyte components, forming a solid electrolyte interphase (SEI) film rich in alkyl sulfonates on the negative electrode surface, thereby improving the stability of the negative electrode interface. In addition, the preferential reduction of the compound shown in Formula 2 helps to inhibit the further reduction of the compound shown in Formula 1 and other electrolyte components on the negative electrode. The compound shown in Formula 2 and the compound shown in Formula 1 work together to form a stable interfacial protective film on both the positive and negative electrodes, further improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device, and reducing the rate of increase of internal resistance of the electrochemical device.

[0015] In some embodiments of this application, the compound shown in Formula 2 is selected from the compounds shown in Formula 2-A10.

[0016] The second aspect of this application provides an electrolyte comprising a solvent, an electrolyte, and the electrolyte additives provided in the first aspect of this application.

[0017] In some embodiments of this application, the mass percentage of the compound shown in Formula 1 is C1% based on the mass of the electrolyte, 0.05 ≤ C1 ≤ 8; and / or, the mass percentage of the compound shown in Formula 2 is C2% based on the mass of the electrolyte, 0.1 ≤ C2 ≤ 5. Within the scope of this application, by adjusting the mass percentage of the compound shown in Formula 1 and / or the mass percentage of the compound shown in Formula 2 in the electrolyte, it is beneficial for the compound shown in Formula 2 to be preferentially reduced on the negative electrode surface compared to the compound shown in Formula 1 and other components of the electrolyte, forming a solid electrolyte interphase (SEI) film rich in alkyl sulfonate on the negative electrode surface, thereby improving the stability of the negative electrode interface and inhibiting the further reduction of the compound shown in Formula 1 and other components of the electrolyte at the negative electrode. This, in turn, is beneficial for the compound shown in Formula 1 to form a stable SEI film at the positive electrode interface, improving the stability of the positive electrode interface, effectively inhibiting further decomposition of the electrolyte, stabilizing the structural stability of the positive electrode material, and inhibiting the dissolution of transition metals in the positive electrode material layer. The compound shown in Formula 2 and the compound shown in Formula 1 work together to form a stable interfacial protective film at both the positive and negative electrodes, further improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device, and reducing the rate of increase of internal resistance of the electrochemical device.

[0018] In some embodiments of this application, the solvent is selected from at least one of cyclic carbonates, linear carbonates, and linear carboxylic esters; the cyclic carbonate is selected from at least one of ethylene carbonate and propylene carbonate; the linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the linear carboxylic ester is selected from at least one of ethyl acetate, ethyl butyrate, ethyl propionate, methyl propionate, propyl propionate, and propyl acetate; the mass percentage of the solvent is C3% based on the mass of the electrolyte, with 60 ≤ C3 ≤ 89%; and / or Alternatively, the electrolyte is selected from lithium salts or sodium salts; the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and bis(trifluoromethanesulfonyl)imide; the sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalate-borate), sodium difluorobis(oxalate-borate), sodium difluorobis(oxalate-phosphate), sodium tetrafluorooxalate-phosphate, and sodium 4,5-dicyano-2-trifluoromethyl-imidazolium; based on the mass of the electrolyte, the mass percentage of the electrolyte is C4%, 10≤C4≤18. The electrolyte including solvents within the above range and adjusting the mass percentage of the solvent within the scope of this application, and / or the electrolyte including electrolytes within the above range and adjusting the mass percentage of the electrolyte within the scope of this application, can give the electrolyte suitable viscosity, high ionic conductivity, and good electrochemical stability, further improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0019] In some embodiments of this application, the electrolyte may further include other electrolyte additives selected from at least one of lithium tetrafluoroborate and 1,3-propanesulfonate lactone; based on the mass of the electrolyte, the mass percentage of the other electrolyte additives is C5%, where 0.1 ≤ C5 ≤ 20. Including other electrolyte additives within the above range in the electrolyte, and controlling the mass percentage of these other electrolyte additives within the scope of this application, is beneficial for forming a stable interfacial film at the positive and / or negative electrodes, further improving the high-temperature cycling performance of the electrochemical device.

[0020] A third aspect of this application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte provided in the second aspect of this application. In some embodiments of this application, the negative electrode comprises a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. The negative electrode material layer comprises a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The electrochemical device satisfies relation I:

[0021] Among them, D 50 In the volume-based particle size distribution of the negative electrode active material particles, the particle size corresponding to 50% of the cumulative volume is measured from the smallest particle size, in μm; m is the adhesion force between the negative electrode material layer and the negative electrode current collector, in N / m; C2% is the mass percentage of the compound shown in Equation 2 based on the mass of the electrolyte. By controlling the particle size D of the negative electrode active material particles... 50 The adhesion force m between the negative electrode material layer and the negative electrode current collector, and the mass percentage C2 of the compound shown in Formula 2 satisfy the relationship Equation I. This is beneficial to improving the conductivity of electrons and ions of the negative electrode, and also to the formation of a stable SEI film by the compound of Formula 2 on the negative electrode, thereby improving the stability of the negative electrode interface. This further reduces the rate of increase of internal resistance of the electrochemical device and improves the high-temperature cycling performance and high-temperature expansion performance of the electrochemical device.

[0022] In some embodiments of this application, the electrochemical device satisfies at least one of the following conditions: (1) 7 μm ≤ D 50 ≤15μm; (2)3N / m≤m≤30N / m. When an electrochemical device meets at least one of the above conditions, it is beneficial to further reduce the rate of increase of internal resistance of the electrochemical device and improve the high-temperature cycling performance and high-temperature expansion performance of the electrochemical device.

[0023] The beneficial effects of this application are:

[0024] This application provides an electrolyte additive, an electrolyte, and an electrochemical device. The electrolyte additive includes compounds shown in Formula 1 and Formula 2, wherein the compound shown in Formula 2 is selected from at least one of the compounds shown in Formula 2-A and Formula 2-B. With the above configuration, when the compounds shown in Formula 1 and Formula 2 are used together as electrolyte additives, they facilitate the formation of a stable solid electrolyte interphase (SEI) film at the negative electrode interface and a stable positive electrode electrolyte interphase (CEI) film at the positive electrode interface. This improves the stability of the positive and negative electrode interfaces, reduces side reactions between the electrolyte and the electrode active materials, effectively inhibits further decomposition of the electrolyte, reduces gas production, decreases the rate of increase in internal resistance of the electrochemical device, and improves the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0025] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Detailed Implementation

[0026] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0027] It should be noted that, in the specific embodiments of this application, lithium-ion batteries and sodium-ion batteries are used as examples of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries and sodium-ion batteries.

[0028] A first aspect of this application provides an electrolyte additive comprising a compound of Formula 1 and a compound of Formula 2, wherein the compound of Formula 2 is selected from at least one of the compounds of Formula 2-A and Formula 2-B:

[0029] Where m and n are each independently selected from integers from 0 to 3, and m and n are not both 0, p is selected from integers from 1 to 5, R0 is selected from single bonds or methylene groups, R1 is selected from hydrogen, halogens, C1-C5 hydrocarbon groups, or C1-C5 haloalkyl groups, and R2, R3, and R4 are each independently selected from... One of the following: R5 and R6 are each independently selected from substituted or unsubstituted phenyl, substituted or unsubstituted imidazolyl, substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C5 alkenyl, C1-C5 alkoxy, substituted or unsubstituted C2-C5 alkoxyalkyl, substituted or unsubstituted C1-C5 carbonyl, substituted or unsubstituted C1-C5 cyano, and halogen. When substituted, the substituents are each independently selected from halogen and C1-C5 alkyl. R7 and R9 are each independently selected from halogen and substituted or unsubstituted C1-C5 alkyl. R8 is selected from substituted or unsubstituted phenylene, substituted or unsubstituted C1-C5 alkylene, C2-C5 alkenyl, C2-C5 alkoxyalkylene. When substituted, the substituents are each independently selected from halogen, hydroxyl, and phenyl. The halogens mentioned above are selected from at least one of fluorine, chlorine and bromine, preferably fluorine.

[0030] The inventors discovered that the electrolyte additive includes both the compound shown in Formula 1 and the compound shown in Formula 2. During the initial charging of the electrochemical device, the compound shown in Formula 2 is preferentially reduced on the negative electrode surface compared to the compound shown in Formula 1 and other electrolyte components, forming a solid electrolyte interphase (SEI) film rich in sulfonate esters. This improves the stability of the negative electrode interface and effectively inhibits further reduction of the compound shown in Formula 1 and other electrolyte components on the negative electrode surface. During further charging, the compound shown in Formula 1 can be oxidized on the positive electrode surface, forming a stable positive electrode electrolyte interphase (CEI) film. This helps to inhibit further decomposition of the electrolyte, improve the structural stability of the positive electrode material, and suppress the dissolution of transition metals in the positive electrode material layer. Therefore, the synergistic effect of the compound shown in Formula 1 and the compound shown in Formula 2 can significantly improve the high-temperature cycling performance and high-temperature storage performance of the electrochemical device, and reduce the rate of increase in internal resistance of the electrochemical device.

[0031] In some embodiments of this application, the mass ratio of the compound shown in Formula 1 to the compound shown in Formula 2 is (0.1–16):1. For example, the mass ratio of the compound shown in Formula 1 to the compound shown in Formula 2 can be 0.1:1, 0.5:1, 0.8:1, 1:1, 3:1, 5:1, 8:1, 10:1, 12:1, 15:1, 16:1, or a range consisting of any two of these values. By adjusting the mass ratio of the compound shown in Formula 1 to the compound shown in Formula 2 within the range of this application, it is beneficial to leverage the synergistic effect of the compound shown in Formula 1 and the compound shown in Formula 2, further improving the stability of the positive and negative electrode interfaces, further reducing side reactions between the electrolyte and electrode materials, reducing gas production, further reducing the rate of increase in internal resistance of the electrochemical device, and improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0032] In some embodiments of this application, the compound represented by Formula 1 is selected from at least one of the following compounds:

[0033] The electrolyte additive includes compounds of Formula 1 within the above-mentioned range, which is beneficial for forming a stable CEI film at the positive electrode interface, improving the stability of the positive electrode interface, effectively inhibiting further decomposition of the electrolyte, stabilizing the structural stability of the positive electrode material, inhibiting the dissolution of transition metals in the positive electrode material layer, thereby further improving the high-temperature cycle performance and high-temperature storage performance of the electrochemical device, and reducing the rate of increase of internal resistance of the electrochemical device.

[0034] In some embodiments of this application, the compound shown in Formula 1 is selected from the compounds shown in Formula 1-1. Electrolyte additives including compounds shown in Formula 1-1 are more conducive to the formation of a stable CEI film at the positive electrode interface, improving the stability of the positive electrode interface, effectively inhibiting further decomposition of the electrolyte, stabilizing the structural stability of the positive electrode material, inhibiting the dissolution of transition metals in the positive electrode material layer, thereby further improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device, and reducing the rate of increase in internal resistance of the electrochemical device.

[0035] In some embodiments of this application, the compound represented by Formula 2-A is selected from at least one of the following compounds:

[0036] In some embodiments of this application, the compound represented by Formula 2-B is selected from at least one of the following compounds:

[0037] The electrolyte additive includes at least one of the compounds shown in Formula 2-A or Formula 2-B within the aforementioned range. During the initial charging process of the electrochemical device, the compound shown in Formula 2 has lower steric hindrance and some electron-withdrawing groups, which facilitates its preferential reduction at the negative electrode surface compared to the compound shown in Formula 1 and other electrolyte components. This results in the formation of a solid electrolyte interphase (SEI) film rich in alkyl sulfonates at the negative electrode surface. Compared to the cyclic structure, the compound shown in Formula 2 has a chain structure, which avoids the formation of an unstable SEI film containing unsaturated bonds (C=C and C≡C) sulfonates during reduction. Furthermore, the lithium alkyl sulfonate component helps improve the stability of the negative electrode interface, thereby enhancing high-temperature cycling performance and high-temperature storage performance. In addition, the preferential reduction of the compound shown in Formula 2 helps inhibit the further reduction of the compound shown in Formula 1 and other electrolyte components at the negative electrode. The compounds shown in Formula 2 and Formula 1 work together to form a stable interfacial protective film at both the positive and negative electrodes, further improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device and reducing the rate of increase in internal resistance of the electrochemical device.

[0038] In some embodiments of this application, the compound shown in Formula 2 is selected from the compound shown in Formula 2-A10. The electrolyte additive including the compound shown in Formula 2-A10 is more conducive to the formation of a solid electrolyte interphase (SEI) film rich in alkyl sulfonates on the negative electrode surface, improving the stability of the negative electrode interface, inhibiting further reduction of the compound shown in Formula 1 and other electrolyte components at the negative electrode, and the compound shown in Formula 2 and the compound shown in Formula 1 work together to form a stable interfacial protective film at both the positive and negative electrodes, further improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device, and reducing the rate of increase in internal resistance of the electrochemical device. Simultaneously, the imidazole group of the compound shown in Formula 2-A10 contains a nitrogen atom with a lone pair of electrons, making the compound exhibit weak Lewis basicity in the electrolyte, which can effectively inhibit the increase in electrolyte acidity and moisture content.

[0039] The second aspect of this application provides an electrolyte comprising a solvent, an electrolyte, and the electrolyte additives provided in the first aspect of this application. The electrolyte, including the electrolyte additives within the scope of this application, is applied to an electrochemical device, which helps improve the stability of the positive and negative electrode interface, reduces side reactions between the electrolyte and the electrode active materials, effectively suppresses excessive electrolyte consumption, reduces gas generation, decreases the rate of increase in internal resistance of the electrochemical device, and improves the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0040] In some embodiments of this application, the mass percentage of the compound shown in Formula 1 is C1% based on the mass of the electrolyte, where 0.05 ≤ C1 ≤ 8. For example, the mass percentage C1% of the compound shown in Formula 1 can be 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or a range of any two of these values. By controlling the mass percentage of the compound shown in Formula 1 in the electrolyte within the range of this application, it is beneficial to form a stable CEI film at the positive electrode interface, improve the stability of the positive electrode interface, effectively inhibit further decomposition of the electrolyte, stabilize the structural stability of the positive electrode material, inhibit the dissolution of transition metals in the positive electrode material layer, further improve the high-temperature cycling performance and high-temperature storage performance of the electrochemical device, and reduce the rate of increase of internal resistance of the electrochemical device.

[0041] In some embodiments of this application, the mass percentage of the compound shown in Formula 2 is C2% based on the mass of the electrolyte, where 0.1 ≤ C2 ≤ 5. For example, the mass percentage C2% of the compound shown in Formula 2 can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, or a range of any two of these values. By controlling the mass percentage of the compound shown in Formula 2 in the electrolyte within the range of this application, it is beneficial for the compound shown in Formula 2 to be preferentially reduced on the negative electrode surface compared to the compound shown in Formula 1 and other components of the electrolyte, forming a solid electrolyte interphase (SEI) film rich in alkyl sulfonates on the negative electrode surface. This improves the stability of the negative electrode interface and results in lower impedance. It also effectively inhibits further reduction of the compound shown in Formula 1 and other components of the electrolyte at the negative electrode. The compound shown in Formula 2 and the compound shown in Formula 1 work together to form a stable interfacial protective film on both the positive and negative electrodes, further improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device, and reducing the rate of increase in internal resistance of the electrochemical device.

[0042] In some embodiments of this application, the mass percentage of the compound shown in Formula 1 is C1% based on the mass of the electrolyte, where 0.05 ≤ C1 ≤ 8; and the mass percentage of the compound shown in Formula 2 is C2% based on the mass of the electrolyte, where 0.1 ≤ C2 ≤ 5. By adjusting the mass percentages of the compounds shown in Formula 1 and Formula 2 in the electrolyte within the scope of this application, it is advantageous for the compound shown in Formula 2 to be preferentially reduced on the negative electrode surface compared to the compound shown in Formula 1 and other components of the electrolyte, forming a solid electrolyte interphase (SEI) film rich in alkyl sulfonates on the negative electrode surface. This improves the stability of the negative electrode interface and inhibits further reduction of the compound shown in Formula 1 and other components of the electrolyte at the negative electrode. Consequently, it is advantageous for the compound shown in Formula 1 to form a stable SEI film at the positive electrode interface, improving the stability of the positive electrode interface, effectively inhibiting further decomposition of the electrolyte, stabilizing the structural stability of the positive electrode material, and inhibiting the dissolution of transition metals in the positive electrode material layer. The compound shown in Formula 2 and the compound shown in Formula 1 work together to form a stable interfacial protective film at both the positive and negative electrodes, further improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device, and reducing the rate of increase in internal resistance of the electrochemical device.

[0043] In some embodiments of this application, the solvent is selected from at least one of cyclic carbonates, linear carbonates, and linear carboxylic acid esters; the cyclic carbonate is selected from at least one of ethylene carbonate and propylene carbonate; the linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the linear carboxylic acid ester is selected from at least one of ethyl acetate, ethyl butyrate, ethyl propionate, methyl propionate, propyl propionate, and propyl acetate; based on the mass of the electrolyte, the mass percentage of the solvent is C3%, 60≤C3≤89. For example, the value of the mass percentage of the solvent C3% can be 60%, 65%, 70%, 75%, 80%, 85%, 89%, or a range consisting of any two of these values. The electrolyte includes solvents within the above range, and by controlling the mass percentage of the solvent within the scope of this application, the electrolyte can have suitable viscosity, high ionic conductivity, and good electrochemical stability, which can further improve the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0044] In some embodiments of this application, the electrolyte is selected from lithium salts or sodium salts; the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and bis(trifluoromethanesulfonyl)imide; the sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalate-borate), sodium difluorobis(oxalate-borate), sodium difluorobis(oxalate-phosphate), sodium tetrafluorooxalate phosphate, and sodium 4,5-dicyano-2-trifluoromethyl-imidazolium; based on the mass of the electrolyte, the mass percentage of the electrolyte is C4%, where 10 ≤ C4 ≤ 18. For example, the mass percentage of the electrolyte C4% can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, or a range of any two of these values. The electrolyte includes electrolytes within the above-mentioned range, and by adjusting the mass percentage of the electrolyte within the scope of this application, the electrolyte can have high ionic conductivity and good electrochemical stability, which can further improve the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0045] In some embodiments of this application, the solvent is selected from at least one of cyclic carbonates, linear carbonates, and linear carboxylic esters; the cyclic carbonate is selected from at least one of ethylene carbonate and propylene carbonate; the linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the linear carboxylic ester is selected from at least one of ethyl acetate, ethyl butyrate, ethyl propionate, methyl propionate, propyl propionate, and propyl acetate; based on the mass of the electrolyte, the mass percentage of the solvent is C3%, 60≤C3≤89; The electrolyte is selected from lithium salts or sodium salts; the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and bis(trifluoromethanesulfonyl)imide; the sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalato)borate, sodium difluorobis(oxalato)borate, sodium difluorobis(oxalato)phosphate, sodium tetrafluorooxalatophosphate, and sodium 4,5-dicyano-2-trifluoromethyl-imidazolium; based on the mass of the electrolyte, the mass percentage of the electrolyte is C4%, 10≤C4≤18. The electrolyte includes solvents within the above range and the mass percentage of the solvent is controlled within the scope of this application. The electrolyte includes electrolytes within the above range and the mass percentage of the electrolyte is controlled within the scope of this application, which can make the electrolyte have suitable viscosity, high ionic conductivity, and good electrochemical stability, and can further improve the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0046] In some embodiments of this application, the electrolyte may further include other electrolyte additives selected from at least one of lithium tetrafluoroborate and 1,3-propanesulfonate lactone; based on the mass of the electrolyte, the mass percentage of the other electrolyte additives is C5%, where 0.1 ≤ C5 ≤ 20. For example, the mass percentage C5% of the other additives can be 0.1%, 1%, 2%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, or a range consisting of any two of these values. Including other electrolyte additives within the above range in the electrolyte, and controlling the mass percentage of these other electrolyte additives within the scope of this application, is beneficial for forming a stable interfacial film at the positive and negative electrodes, further improving the high-temperature cycling performance of the electrochemical device.

[0047] A third aspect of this application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte provided in the second aspect of this application. The electrochemical device, including the electrolyte within the scope of this application, is beneficial for improving the stability of the positive and negative electrode interface, reducing side reactions between the electrolyte and the electrode active materials, effectively suppressing excessive electrolyte consumption, reducing gas generation, decreasing the rate of increase in internal resistance of the electrochemical device, and improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0048] In some embodiments of this application, the negative electrode sheet includes a negative current collector and a negative electrode material layer disposed on at least one surface of the negative current collector. The negative electrode material layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The electrochemical device satisfies relation I:

[0049] Among them, D 50 In the volume-based particle size distribution of the negative electrode active material particles, the particle size corresponding to 50% of the cumulative volume, measured from the smallest particle size, is expressed in μm; m is the adhesion force between the negative electrode material layer and the negative electrode current collector, expressed in N / m; C2% is the mass percentage of the compound shown in Equation 2, based on the mass of the electrolyte. The value of Equation I can be 0.02, 0.05, 0.1, 0.3, 0.5, 0.8, 1, 1.2, 1.3, 1.5, or a range of any two of these values. By adjusting D... 50 The relationship between C1, C2, and C2 satisfies Equation I, which is beneficial to improving the conductivity of electrons and ions of the negative electrode sheet. It also helps the compound of Equation 2 to form a stable SEI film on the negative electrode, improves the stability of the negative electrode interface, thereby further reducing the growth rate of internal resistance of the electrochemical device and improving the high-temperature cycling performance and high-temperature expansion performance of the electrochemical device.

[0050] In some embodiments of this application, 7μm≤D 50 ≤15μm. For example, D 50 The value can be 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or a range of any two of these values. The particle size D of the negative electrode active material can be adjusted. 50 Within the scope of this application and satisfying relation I, the negative electrode active material has suitable active sites, and the active metal ions (e.g., Li) + Na + The shorter transport path within the negative electrode active material particles and the fewer side reactions between the negative electrode active material and the electrolyte are beneficial for reducing the rate of increase in internal resistance of the electrochemical device and improving the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0051] In some embodiments of this application, 3 N / m ≤ m ≤ 30 N / m. For example, the value of m can be 3 N / m, 5 N / m, 10 N / m, 13 N / m, 15 N / m, 18 N / m, 20 N / m, 23 N / m, 25 N / m, 28 N / m, 30 N / m, or a range of any two of these values. The adhesion force m between the negative electrode material layer and the negative electrode current collector is within the range of this application and satisfies Relationship I. The active metal ions (e.g., Li) + Na +The transmission path is shorter and the negative electrode has good electron and ion conduction capabilities, which improves the kinetic and cycle performance of the electrochemical device.

[0052] In some embodiments of this application, 7μm≤D 50 ≤15μm, 3N / m≤m≤30N / m. By adjusting D 50 The values ​​of m and m are within the range of this application and satisfy relation I, which can further improve the conductivity of electrons and ions of the negative electrode, and are conducive to the formation of a stable SEI film on the negative electrode by the compound of formula 2, thereby improving the stability of the negative electrode interface, thereby further reducing the internal resistance growth rate of the electrochemical device and improving the high-temperature cycling performance and high-temperature expansion performance of the electrochemical device.

[0053] In some embodiments of this application, the mass percentage X% of the negative electrode binder is 1% to 4% based on the mass of the negative electrode material layer.

[0054] Generally, the adhesion force *m* between the negative electrode material layer and the negative electrode current collector can be adjusted by changing the mass percentage of the negative electrode binder in the negative electrode material layer. Under otherwise unchanged conditions, increasing the mass percentage of the negative electrode binder increases the adhesion force *m* between the negative electrode material layer and the negative electrode current collector; decreasing the mass percentage of the negative electrode binder decreases the adhesion force *m* between the negative electrode material layer and the negative electrode current collector.

[0055] This application does not impose any particular limitation on the type of negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Graphite may include, but is not limited to, at least one of natural graphite or artificial graphite; the aforementioned silicon-based materials may include, but are not limited to, at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, or silicon alloys; the aforementioned tin-based materials may include at least one of elemental tin, tin oxide compounds, or tin alloys.

[0056] In this application, the negative electrode active material can be obtained by purchase, and in conjunction with the "particle size D of the negative electrode active material" provided in this application... 50 "Test", select the desired D 50 The negative electrode active material.

[0057] In this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the negative electrode current collector, or only a portion of the surface area; this application has no particular limitation, as long as the purpose of this application is achieved. This application has no particular limitation on the negative electrode current collector, as long as the purpose of this application is achieved; for example, the negative electrode current collector can be copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, foamed nickel or foamed copper, aluminum foil, or a composite negative electrode current collector. The aforementioned composite negative electrode current collector can be a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The material of the polymer material base layer can be, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). The material of the metal layer can be, but is not limited to, at least one of copper, copper alloy, nickel, or nickel alloy. This application does not impose any particular limitation on the thickness of the negative electrode material layer and the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided negative electrode material layer can be from 50 μm to 180 μm, and the thickness of the negative electrode current collector can be from 3 μm to 10 μm.

[0058] This application does not impose any particular limitation on the types of negative electrode conductive agents and negative electrode binders, as long as they can achieve the purpose of this application. For example, the negative electrode conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fibers. The aforementioned carbon nanotubes may include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The aforementioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. For example, the negative electrode binder may include, but is not limited to, at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), sodium carboxymethyl cellulose (CMC), polymethyl methacrylate (PMAA), or carboxymethyl chitosan (CMCS).

[0059] In this application, the electrochemical device includes a positive electrode sheet, which includes a positive current collector and a positive electrode material layer disposed on at least one surface of the positive current collector. The phrase "positive electrode material layer disposed on at least one surface of the positive current collector" means that the positive electrode material layer can be disposed on one surface of the positive current collector along its thickness direction, or on two surfaces of the positive current collector along its thickness direction. It should be noted that "surface" here can refer to the entire surface of the positive current collector or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved. This application does not impose any particular limitation on the positive current collector, as long as the purpose of this application is achieved; for example, the positive current collector can be an aluminum foil, an aluminum alloy foil, or a composite positive current collector. The aforementioned composite positive electrode current collector can be a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The material of the polymer material base layer can be, but is not limited to, at least one of polypropylene (PP), polyethylene terephthalate (PET), or polybutylene terephthalate (PBT). The material of the metal layer can be, but is not limited to, at least one of aluminum, aluminum alloy, nickel, or nickel alloy. This application does not impose any particular limitation on the thickness of the positive electrode material layer and the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the single-sided positive electrode material layer can be from 50 μm to 250 μm, and the thickness of the positive electrode current collector can be from 7 μm to 15 μm.

[0060] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular limitation on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium iron phosphate, lithium manganese iron phosphate, LiCoO2, and LiNi. x Co y Mn z O2 (0≤x,y,z≤1, x+y+z=1), lithium-rich manganese-based materials (xLi2MnO3·(1-x)LiAO2, where A can be Ni, Co, or Mn), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4), Na 0.44 At least one of MnO2, P2 layered NaMO2 (M is one, two or three of Ni, Mn, and Fe), NaFePO4, Na4Fe3(PO4)2P2O7, Na3V2(PO4)3, Na3V2(PO4)2F3, Na2Fe(CN)6 or Na2MnFe(CN)6.

[0061] The positive electrode material layer may further include a positive electrode conductive agent and a positive electrode binder. This application does not impose any particular limitation on the types of positive electrode conductive agents and positive electrode binders, as long as they achieve the purpose of this application. For example, the positive electrode conductive agent may include, but is not limited to, at least one of superconducting carbon black (Super P), acetylene black, Ketjen black, carbon nanotubes, graphene, or carbon fiber. For example, the positive electrode binder may include, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, or fluorinated acrylate resin. This application does not impose any particular limitation on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0062] In this application, the electrochemical device also includes a diaphragm. There are no particular limitations on the diaphragm, as long as it achieves the purpose of this application. For example, the diaphragm material may include, but is not limited to, at least one of polyethylene (PE), polypropylene (PP), glass fiber, polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), and polyamide (PA). The type of diaphragm may include at least one of woven membrane, nonwoven fabric, microporous membrane, composite membrane, rolled membrane, or spun membrane. In this application, there are no particular limitations on the thickness of the diaphragm, as long as it achieves the purpose of this application; for example, the thickness of the diaphragm may be from 4 μm to 20 μm.

[0063] In this application, the electrochemical device also includes a housing for accommodating the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of secondary batteries. This application does not limit the scope of these other components. This application does not impose any particular limitation on the housing; it can be a housing known in the art, as long as it achieves the purpose of this application. For example, the housing can be a rigid housing or a flexible housing. The material of the rigid housing can be metal; this application does not limit the type of metal and can use known metal rigid housings, as long as they achieve the purpose of this application. The flexible housing can be a metal-plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0064] The electrochemical device described in this application is not particularly limited and may include any device in which an electrochemical reaction occurs. In one embodiment of this application, the electrochemical device may include, but is not limited to, lithium-ion secondary batteries (lithium-ion batteries), sodium-ion secondary batteries (sodium-ion batteries), etc.

[0065] The preparation process of the electrochemical device described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the preparation process of the electrochemical device may include, but is not limited to, the following steps: stacking the positive electrode, separator, and negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode, separator, and negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain an electrochemical device. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0066] Example

[0067] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0068] Test methods and equipment:

[0069] Anode active material particle size D 50 Test

[0070] The negative electrode active material to be tested was ultrasonicated together with 1% ethyl phenyl polyethylene glycol (Nonidet p40) dispersant for 1 minute, and then the particle size distribution was measured using a laser particle size analyzer (Malvin MS300). In the volume-based particle size distribution of the negative electrode active material, starting from the smallest particle size, the particle size reaching 50% of the volumetric accumulation is D. 50 .

[0071] Test of the adhesion force m between the negative electrode material layer and the negative electrode current collector

[0072] After formation, shaping, and capacity testing, the lithium-ion battery was fully discharged to 2V at a constant current of 0.5C and then disassembled to obtain the negative electrode sheet. The negative electrode sheet was cleaned three times with dimethyl carbonate (DMC) and then placed in an oven at 80℃ for 24 hours. A 180° peel test was then performed using a tensile testing machine to measure the adhesion between the negative electrode material layer and the negative electrode current collector. The specific testing was conducted according to the national standard GB / T2790-1995, "Test Method for 180° Peel Strength of Adhesives".

[0073] High-temperature cycling performance test and internal resistance growth rate test

[0074] The lithium-ion battery was placed in a 45℃ constant temperature chamber and allowed to stand for 30 minutes. Then, it was charged at a constant current of 1C to a voltage of 3.6V, followed by constant voltage charging at 3.6V to a current of 0.05C. Finally, it was discharged at a constant current of 1C to a voltage of 2V. This constitutes one charge-discharge cycle, which was repeated 2000 times. The maximum discharge capacity of the first three charge-discharge cycles was recorded as Q1, and the AC internal resistance of the lithium-ion battery after the third cycle was recorded as ACR1. After 2000 cycles, the discharge capacity of the lithium-ion battery was recorded as Q2, and the AC internal resistance was recorded as ACR2. The charge-discharge cycle test instrument was a Xinwei BTS, and the AC internal resistance test instrument was a battery internal resistance meter.

[0075] Capacity retention rate (%) = Q2 / Q1 × 100%; The capacity retention rate is used to evaluate the high-temperature cycle performance of lithium-ion batteries. The higher the capacity retention rate, the better the high-temperature cycle performance of lithium-ion batteries.

[0076] Internal resistance growth rate (%) = [(ACR2 / ACR1)-1]×100%.

[0077] High-temperature storage performance test

[0078] The lithium-ion battery was placed in an environment of 25°C and charged to 3.6V with a constant current of 1C. Then it was charged to 0.05C with a constant voltage of 3.6V. The thickness of the lithium-ion battery was measured and recorded as d0. After that, the lithium-ion battery was placed in a constant temperature chamber of 70°C and left to stand for 15 days. The surface condition of the lithium-ion battery was observed.

[0079] Judgment criteria: If the lithium-ion battery cell is separated from the aluminum-plastic film packaging bag, i.e., in a non-vacuum state, then the lithium-ion battery is judged to be producing gas.

[0080] The test methods for the high-temperature cycling performance, internal resistance growth rate, and high-temperature storage performance of sodium-ion batteries in Examples 1-26 are the same as those for the lithium-ion batteries described above.

[0081] Example 1-1

[0082] <Preparation of Electrolyte>

[0083] In an inert atmosphere with a water content of less than 0.1 ppm and an oxygen content of less than 1 ppm, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and ethyl acetate (EA) were mixed in a mass ratio of 3:6:1 to obtain a base solvent. Then, lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), the compound shown in Formula 1-1, and the compound shown in Formula 2-A10 were added to the base solvent and mixed thoroughly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentages of LiPF6, LiFSI, the compound shown in Formula 1-1, and the compound shown in Formula 2-A10 were 9%, 5%, 1%, and 0.5%, respectively, with the remainder being 84.5% base solvent.

[0084] <Preparation of Negative Electrode Sheets>

[0085] Graphite (negative electrode active material), acetylene black (conductive agent), sodium carboxymethyl cellulose (CMC) (binder), and styrene-butadiene rubber (SBR) were mixed in a mass ratio of 95:2:2:1 (based on the mass of the negative electrode material layer, the mass percentage of sodium carboxymethyl cellulose (CMC) is 2%). Deionized water was added as a solvent to prepare a slurry with a solid content of 49 wt%. After uniform mixing in a vacuum mixer, the negative electrode slurry was obtained. The negative electrode slurry was uniformly coated onto one surface of a 9 μm thick copper foil current collector and dried at 90 °C to obtain a negative electrode sheet with a single-sided negative electrode material layer. The coating weight of the negative electrode material layer was 8 mg / mm². 2 Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 85°C, it is rolled, then slit and welded with tabs to obtain a negative electrode sheet with a size of 74mm×59mm for later use. The thickness of the single-sided negative electrode material layer is 111μm.

[0086] <Preparation of the positive electrode>

[0087] Lithium iron phosphate (LiFePO4), the positive electrode active material, acetylene black, and polyvinylidene fluoride (PVDF), the positive electrode conductive agent, were mixed in a mass ratio of 96:2:2. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 55 wt%. After vacuum stirring, the slurry was obtained. The positive electrode slurry was uniformly coated onto one surface of a 12 μm thick aluminum foil used as a positive electrode current collector and dried at 90 °C to obtain a single-sided coated positive electrode sheet with a coating weight of 17 mg / mm². 2Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After drying at 85°C, it is rolled, then slit and welded with tabs to obtain a positive electrode sheet with a size of 70mm×55mm for later use. The thickness of the positive electrode material layer on one side is 158μm.

[0088] <Preparation of the diaphragm>

[0089] A 10μm thick polyethylene (PE) porous membrane (provided by Shenzhen Xingyuan Material Technology Co., Ltd.) was used as the separator.

[0090] <Preparation of Lithium-ion Batteries>

[0091] The prepared positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to obtain the electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 85°C. The electrolyte prepared above is then injected, and the battery undergoes vacuum sealing, settling, formation, and shaping processes to obtain a lithium-ion battery with a rated capacity of 2Ah. The formation process involves a 48-hour settling period, a maximum formation voltage of 3.6V, a formation temperature of 45°C, and a formation pressure of 300 kgf.

[0092] Examples 1-2 to 1-25

[0093] Except for <Preparation of Electrolyte>, where the types of compounds shown in Formula 1 or Formula 2 are adjusted according to Table 1, the rest is the same as in Examples 1-1.

[0094] Examples 1-26

[0095] Except for the following steps: in the <Preparation of Electrolyte>, lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) electrolytes are replaced with sodium hexafluorophosphate (NaPF6), and the mass percentage of NaPF6 electrolyte is 14% based on the mass of the electrolyte; in the <Preparation of Negative Electrode>, graphite is replaced with hard carbon as the negative electrode active material; and in the <Preparation of Positive Electrode>, NaFePO4 is replaced with NaFePO4 as the positive electrode active material, a sodium-ion battery is prepared. The rest of the preparation is the same as in Example 1-1.

[0096] Examples 2-1 to 2-11

[0097] Except for the section on "Preparation of Electrolyte," where the mass percentage of the compound shown in Formula 1 or Formula 2 is adjusted according to Table 2, the rest is the same as in Examples 1-1. When the content of the compound shown in Formula 1 or Formula 2 changes, the mass percentage of the base solvent changes accordingly, while the mass percentage of the electrolyte remains unchanged.

[0098] Examples 2-12 to 2-15

[0099] Except for the negative electrode active material with the corresponding particle size D50 selected according to Table 2 in the <Preparation of Negative Electrode Sheet>, the rest is the same as in Example 1-1.

[0100] Examples 2-16 to 2-19

[0101] Except for adjusting the mass percentage of the negative electrode binder in the <Preparation of the Negative Electrode Sheet>, which changes the mass percentage of the negative electrode active material accordingly, the rest is the same as in Example 1-1.

[0102] Examples 2-20 to 2-24

[0103] Except for adjusting the relevant parameters according to Table 2, the rest is the same as in Examples 1-1. Among them, in the <Preparation of Negative Electrode Sheet>, when the mass percentage of the negative electrode binder changes, the mass percentage of the negative electrode active material changes accordingly; when the content of the compound shown in Formula 1 or the compound shown in Formula 2 changes, the mass percentage of the base solvent changes accordingly, while the mass percentage of the electrolyte remains unchanged.

[0104] Examples 2-25 to 2-28

[0105] Except for the section on "Preparation of Electrolyte," where the mass percentage (C5%) and types of other electrolyte additives are adjusted according to Table 2, the rest is the same as in Examples 1-1. Specifically, when the C5% content of other electrolyte additives changes, the mass percentage of the base solvent changes accordingly, while the mass percentage of the electrolyte remains unchanged. In Table 2, LiBF4 is lithium tetrafluoroborate, and PS is 1,3-propanesulfonate lactone.

[0106] Example 2-29

[0107] Except for <Preparation of Electrolyte>, where lithium bis(fluorosulfonyl)imide (LiFSI) is replaced with lithium hexafluorophosphate (LiPF6), and the total mass percentage of lithium hexafluorophosphate (LiPF6) is 14% based on the mass of the electrolyte, the rest is the same as in Example 1-1.

[0108] Examples 2-30

[0109] Except for the adjustment of the amount of lithium bis(fluorosulfonyl)imide (LiFSI) added in the <Electrolyte Preparation> section, the mass percentage of lithium bis(fluorosulfonyl)imide (LiFSI) is 1% based on the mass of the electrolyte; otherwise, it is the same as in Examples 1-1. Specifically, when the mass percentage of lithium bis(fluorosulfonyl)imide (LiFSI) changes, the mass percentage of the base solvent changes accordingly, while the mass percentage of lithium hexafluorophosphate (LiPF6) remains unchanged, i.e., the mass percentage of the electrolyte C4% is 10%.

[0110] Example 2-31

[0111] Except for the adjustment of the amount of lithium hexafluorophosphate (LiPF6) added in the <Electrolyte Preparation> section, the mass percentage of lithium hexafluorophosphate (LiPF6) is 13% based on the mass of the electrolyte; otherwise, it is the same as in Example 1-1. Specifically, when the mass percentage of lithium hexafluorophosphate (LiPF6) changes, the mass percentage of the base solvent changes accordingly, while the mass percentage of lithium bis(fluorosulfonyl)imide (LiFSI) remains unchanged, i.e., the mass percentage of the electrolyte (C4%) is 18%.

[0112] Example 2-32

[0113] Except for the preparation of the electrolyte, in which the solvent is adjusted to propylene carbonate (PC), dimethyl carbonate (DMC), and ethyl butyrate (EB) in a mass ratio of 3:6:1, the rest is the same as in Example 1-1.

[0114] Comparative Examples 1 to 5

[0115] Except for adjusting the content of compounds shown in Formula 1 and / or Formula 2 according to Table 1 in the section on <Preparation of Electrolyte>, the rest are the same as...

[0116] The same applies to Examples 1-1. However, when the content of the compound shown in Formula 1 or Formula 2 changes, the mass percentage of the base solvent changes accordingly, while the mass percentage of the electrolyte remains unchanged. In Table 1, vinyl sulfate is abbreviated as DTD, and 1,3-propanesulfonate lactone is abbreviated as PS.

[0117] The preparation and performance parameters of each embodiment and comparative example are shown in Tables 1 and 2.

[0118] Table 1 Note: In Table 1, " / " indicates that the corresponding preparation parameters or substances do not exist.

[0119] As can be seen from Examples 1-1 to 1-26 and Comparative Examples 1 to 5, the electrolytes of the electrochemical devices in each embodiment of this application include compounds shown in Formula 1 and Formula 2 within the scope of this application. However, the electrochemical devices in the comparative examples do not simultaneously satisfy the above characteristics. The electrochemical devices obtained in the examples have a high capacity retention rate, a small internal resistance growth rate, and no gas generation during storage, indicating that the electrochemical devices have good high-temperature cycling performance, high-temperature storage performance, and a small internal resistance growth rate.

[0120] The types of compounds shown in Formula 1 affect the high-temperature cycling performance, high-temperature storage performance, and internal resistance growth rate of the electrochemical device. As can be seen from Examples 1-1 to 1-10 and Comparative Example 2, when the electrolyte includes the compounds shown in Formula 1 within the scope of this application, the resulting electrochemical device has a high capacity retention rate, a small internal resistance growth rate, and no gas generation during storage, indicating that the electrochemical device has good high-temperature cycling performance, high-temperature storage performance, and a small internal resistance growth rate.

[0121] The types of compounds shown in Formula 2 affect the high-temperature cycling performance, high-temperature storage performance, and internal resistance growth rate of the electrochemical device. As can be seen from Examples 1-1, 1-11 to 1-25, Comparative Example 1, and Comparative Example 4 to 5, when the electrolyte includes the compounds shown in Formula 2 within the scope of this application, the resulting electrochemical device has a high capacity retention rate, a small internal resistance growth rate, and no gas generation during storage, indicating that the electrochemical device has good high-temperature cycling performance, high-temperature storage performance, and a small internal resistance growth rate.

[0122] Table 2

[0123] The mass ratio of the compound shown in Formula 1 to the compound shown in Formula 2 affects the high-temperature cycling performance, high-temperature storage performance, and internal resistance growth rate of the electrochemical device. As can be seen from Examples 1-1, 2-1 to 2-11, by adjusting the mass ratio of the compound shown in Formula 1 to the compound shown in Formula 2 in the electrolyte within the range specified in this application, the obtained electrochemical device exhibits a higher capacity retention rate, a smaller internal resistance growth rate, and no gas generation during storage, indicating that the electrochemical device has good high-temperature cycling performance, high-temperature storage performance, and a smaller internal resistance growth rate. Compared with Examples 1-1, 2-2 to 2-4, Example 2-1 has a mass ratio of less than 0.1 for the compound shown in Formula 1 to the compound shown in Formula 2, resulting in a slightly lower capacity retention rate and a slightly larger internal resistance growth rate, thus providing a weaker improvement to the high-temperature cycling performance and high-temperature storage performance of the electrochemical device. Compared with Examples 1-1, 2-2 to 2-4, Examples 2-5 have a mass ratio of the compound shown in Formula 1 to the compound shown in Formula 2 greater than 16. Their capacity retention rate is slightly lower, their internal resistance growth rate is slightly higher, and their improvement on the high-temperature cycling performance and high-temperature storage performance of the electrochemical device is weaker.

[0124] The mass percentage C1% of the compound shown in Formula 1 affects the high-temperature cycling performance, high-temperature storage performance, and internal resistance growth rate of the electrochemical device. As can be seen from Examples 1-1, 2-1 to 2-5, by adjusting the mass percentage C1% of the compound shown in Formula 1 within the range of this application, the obtained electrochemical device has a high capacity retention rate, a small internal resistance growth rate, and no gas generation during storage, indicating that the electrochemical device has good high-temperature cycling performance, high-temperature storage performance, and a small internal resistance growth rate.

[0125] The mass percentage C2% of the compound shown in Formula 2 affects the high-temperature cycling performance, high-temperature storage performance, and internal resistance growth rate of the electrochemical device. As can be seen from Examples 1-1, 2-6 to 2-11, by adjusting the mass percentage C2% of the compound shown in Formula 2 within the range of this application, the obtained electrochemical device has a high capacity retention rate, a small internal resistance growth rate, and no gas generation during storage, indicating that the electrochemical device has good high-temperature cycling performance, high-temperature storage performance, and a small internal resistance growth rate.

[0126] The relationship between the particle size D50 of the negative electrode active material, the adhesion force m between the negative electrode material layer and the negative electrode current collector, and the mass percentage C2% of the compound shown in Formula 2 affects the high-temperature cycling performance, high-temperature storage performance, and internal resistance growth rate of the electrochemical device. Examples 1-1, 2-6 to 2-24 show that by adjusting the values ​​of D50, m, and C2 to satisfy Formula I, the obtained electrochemical device exhibits a high capacity retention rate, a small internal resistance growth rate, and no gas generation during storage, indicating good high-temperature cycling performance, high-temperature storage performance, and a small internal resistance growth rate. Examples 2-21 to 2-24 show that the values ​​of D50, m, and C2 do not satisfy Formula I, resulting in a lower capacity retention rate, a higher internal resistance growth rate, and gas generation during storage, indicating a weak improvement in the high-temperature cycling performance and high-temperature storage performance of the electrochemical device.

[0127] The mass percentage content and type of other electrolyte additives can affect the high-temperature cycling performance, high-temperature storage performance and internal resistance growth rate of the electrochemical device. As can be seen from Examples 1-1, 2-25 to 2-28, the electrolyte includes other additives within the scope of this application, and the mass percentage content is controlled within the scope of this application. The resulting electrochemical device has a high capacity retention rate, a small internal resistance growth rate, and no gas generation during storage, indicating that the electrochemical device has good high-temperature cycling performance, high-temperature storage performance and a small internal resistance growth rate.

[0128] The type and mass percentage of electrolytes affect the high-temperature cycling performance, high-temperature storage performance, and internal resistance growth rate of electrochemical devices. As can be seen from Examples 1-1, 2-29 to 2-31, the electrolytes include electrolytes within the scope of this application, and by adjusting their mass percentage within the scope of this application, the resulting electrochemical devices have a high capacity retention rate, a small internal resistance growth rate, and no gas generation during storage. This indicates that the electrochemical devices have good high-temperature cycling performance, high-temperature storage performance, and a small internal resistance growth rate.

[0129] The type and mass percentage of the solvent affect the high-temperature cycling performance, high-temperature storage performance, and internal resistance growth rate of the electrochemical device. As can be seen from Examples 1-1, 2-1 to 2-32, the electrolyte includes solvents within the scope of this application, and the mass percentage of the electrolyte is controlled within the scope of this application. The resulting electrochemical device has a high capacity retention rate, a small internal resistance growth rate, and no gas generation during storage, indicating that the electrochemical device has good high-temperature cycling performance, high-temperature storage performance, and a small internal resistance growth rate.

[0130] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. An electrolyte additive comprising a compound of Formula 1 and a compound of Formula 2, wherein the compound of Formula 2 is selected from at least one of the compounds of Formula 2-A and Formula 2-B: Where m and n are each independently selected from integers from 0 to 3, and m and n are not both 0, p is selected from integers from 1 to 5, R0 is selected from single bonds or methylene groups, R1 is selected from hydrogen, halogens, C1-C5 hydrocarbon groups, or C1-C5 haloalkyl groups, and R2, R3, and R4 are each independently selected from... One of them; R5 and R6 are each independently selected from substituted or unsubstituted phenyl, substituted or unsubstituted imidazolyl, substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C5 alkenyl, C1-C5 alkoxy, substituted or unsubstituted C2-C5 alkoxyalkyl, substituted or unsubstituted C1-C5 carbonyl, substituted or unsubstituted C1-C5 cyano, and halogen. When substituted, the substituents are each independently selected from halogen and C1-C5 alkyl. R7 and R9 are each independently selected from halogens, substituted or unsubstituted C1-C5 alkyl groups, and R8 is selected from substituted or unsubstituted phenylene, substituted or unsubstituted C1-C5 alkylene, C2-C5 alkenylene, C2-C5 alkyneylene, and C2-C5 alkoxyalkylene. When substituted, the substituents are each independently selected from halogens, hydroxyl groups, and phenyl groups.

2. The electrolyte additive according to claim 1, wherein, The mass ratio of the compound shown in Formula 1 to the compound shown in Formula 2 is (0.1–16):

1.

3. The electrolyte additive according to claim 1 or 2, wherein, The compound represented by Formula 1 is selected from at least one of the following compounds:

4. The electrolyte additive according to claim 3, wherein, The compound shown in Formula 1 is selected from the compounds shown in Formula 1-1.

5. The electrolyte additive according to claim 1 or 2, wherein, The compound represented by Formula 2-A is selected from at least one of the following compounds:

6. The electrolyte additive according to claim 1 or 2, wherein, The compound represented by Formula 2-B is selected from at least one of the following compounds:

7. The electrolyte additive according to claim 5, wherein, The compound shown in Formula 2 is selected from the compound shown in Formula 2-A10.

8. An electrolyte comprising a solvent, an electrolyte, and an electrolyte additive according to any one of claims 1 to 7.

9. The electrolyte according to claim 8, wherein, Based on the mass of the electrolyte, the mass percentage of the compound shown in Formula 1 is C1%, 0.05≤C1≤8; and / or, based on the mass of the electrolyte, the mass percentage of the compound shown in Formula 2 is C2%, 0.1≤C2≤5.

10. The electrolyte according to any one of claims 8 to 9, wherein, The solvent is selected from at least one of cyclic carbonates, linear carbonates, and linear carboxylic acid esters; the cyclic carbonate is selected from at least one of ethylene carbonate and propylene carbonate; the linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; the linear carboxylic acid ester is selected from at least one of ethyl acetate, ethyl butyrate, ethyl propionate, methyl propionate, propyl propionate, and propyl acetate; based on the mass of the electrolyte, the mass percentage of the solvent is C3%, 60≤C3≤89; and / or, the electrolyte... The electrolyte is selected from lithium or sodium salts; the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and bis(trifluoromethanesulfonyl)imide; the sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, sodium bis(oxalate-borate), sodium difluorobis(oxalate-borate), sodium difluorobis(oxalate-phosphate), sodium tetrafluorooxalate-phosphate, and sodium 4,5-dicyano-2-trifluoromethyl-imidazolium; based on the mass of the electrolyte, the mass percentage of the electrolyte is C4%, 10≤C4≤18.

11. The electrolyte according to any one of claims 8 to 9, further comprising other electrolyte additives selected from at least one of lithium tetrafluoroborate and 1,3-propanesulfonate lactone; wherein the other electrolyte additives have a mass percentage of C5% based on the mass of the electrolyte, and 0.1 ≤ C5 ≤ 20.

12. An electrochemical device comprising a positive electrode, a negative electrode, a diaphragm, and an electrolyte according to any one of claims 8 to 11; The negative electrode sheet includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The negative electrode material layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The electrochemical device satisfies relation I: in, D 50 The particle size distribution of the negative electrode active material particles, measured from the smallest particle size to the particle size corresponding to 50% of the cumulative volume, is expressed in μm; m is the bonding force between the negative electrode material layer and the negative electrode current collector, expressed in N / m; C2% is the mass percentage of the compound shown in Formula 2 based on the mass of the electrolyte.

13. The electrochemical device according to claim 12, wherein at least one of the following conditions is satisfied: (1)7μm≤D 50 ≤15μm; (2) 3N / m≤m≤30N / m.

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