Electrolyte and battery

Abstract

An electrolyte and a battery. The electrolyte comprises a lithium salt, an organic solvent, a first functional additive and a second functional additive, wherein the structural formula of the first functional additive is (I); and the structural formula of the second functional additive is a fluorine-substituted olefin, with the fluorine-substituted olefin comprising the following structural unit: (II), wherein R7 comprises a fluorine atom. In the electrolyte, by introducing two functional additives having a specific structure, and under the combined use of the two functional additives, stable growth of an interface SEI film of a negative electrode, especially a silicon negative electrode, can be promoted, thereby improving the interface stability of the negative electrode; in addition, gas production of a positive electrode can also be further reduced, thereby optimizing the interface stability of the positive electrode. Therefore, the electrolyte can further improve the electrochemical performance, such as the cycle performance and rate capability, of the battery.

Description

Electrolyte and battery

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 17, 2024, with application number 202411864465.1. The entire contents of the above application are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of lithium-ion batteries, and specifically relates to an electrolyte and a battery. Background Art

[0003] Graphite anodes are composed of planar layers of carbon atoms, which are attracted to each other by weak van der Waals forces. Within the layers, carbon atoms form planar six-membered rings in the form of sp2 hybridization. This structure gives graphite a high degree of structural stability and good electrical conductivity. The layered structure also makes graphite very conducive to the intercalation and deintercalation of lithium ions, which is one of the reasons for the successful commercialization of graphite anodes. Despite the advantages of high conductivity and stability, its theoretical specific capacity of 372 mAh / g is insufficient to meet the demand for high-capacity power batteries. The commercialization of batteries requires improving the specific energy of the battery while ensuring economy and safety.

[0004] Silicon is abundant in the earth's crust and widely distributed, and has a slightly higher potential platform than graphite (0.4 V, vs. Li / Li + ), there is no hidden danger of lithium plating, good safety, the highest theoretical specific capacity can reach 4200 mAh / g, and it is considered to be one of the most promising negative electrode materials.

[0005] Technical issues

[0006] Silicon anode materials will experience a volume expansion of nearly 300% during the process of lithium insertion and removal, resulting in problems such as particle crushing, electrical isolation and unstable SEI growth, which greatly limits the commercial application of silicon-based anodes. Silicon-based anode materials are mainly divided into silicon-carbon composites (Si / C) and silicon-oxygen anode materials (SiO x / C) are two major categories. The current mainstream direction is to use graphite as the matrix and dope 5% to 30% (mass fraction) of nano-silicon or SiO x Composition of composite negative electrode materials.

[0007] Technical Solutions

[0008] To address the shortcomings of silicon-based negative electrodes such as volume expansion and the resulting interface damage, introducing electrolyte additives into the electrolyte to promote the formation of SEI film and thus prevent electrolyte decomposition is a simple and cost-effective method.

[0009] According to a first aspect of the present application, an electrolyte is provided, comprising a lithium salt, an organic solvent, a first functional additive, and a second functional additive; the first functional additive has the structural formula:

[0010] The structural formula of the second functional additive is a fluorine-substituted olefin, and the fluorine-substituted olefin includes the following structural units: , wherein R7 includes a fluorine atom.

[0011] According to a second aspect provided by the present application, a battery is provided, comprising the above-mentioned electrolyte.

[0012] Beneficial effects

[0013] The present application provides an electrolyte and a battery. The electrolyte introduces two functional additives of specific structures. The combination of these two functional additives can promote the stable growth of the SEI film at the interface of the negative electrode, especially the silicon negative electrode, and improve the stability of the negative electrode interface. At the same time, it can also further reduce the gas production of the positive electrode and optimize the stability of the positive electrode interface. At the same time, the introduction of these two functional additives can further improve the stability of the electrolyte, so that it has good stability at both room temperature and high temperature, optimize the lithium ion transmission performance of the electrolyte and reduce the degree of side reactions between the electrolyte and the electrode material. Therefore, the electrolyte provided by the present application can further improve the electrochemical properties of the battery, such as the cycle performance and rate performance.

[0014] The battery prepared using the above electrolyte has effectively improved cycle performance and rate performance.

[0015] Other aspects will become apparent after reading and understanding the detailed description DETAILED DESCRIPTION

[0016] According to a first aspect of the present application, an electrolyte is provided, comprising a lithium salt, an organic solvent, a first functional additive, and a second functional additive; the first functional additive has the structural formula:

[0017] The structural formula of the second functional additive is a fluorine-substituted olefin, and the fluorine-substituted olefin includes the following structural units: , wherein R7 includes a fluorine atom.

[0018] By introducing the above-mentioned two functional additives with specific structures, the present application effectively improves the stability of the negative electrode interface and the positive electrode interface, improves the structural stability of the electrode material during cyclic charge and discharge, and optimizes the stability of the electrolyte, reduces its degree of oxidation and side reactions, thereby significantly optimizing the cycle performance and rate performance of the battery prepared thereby.

[0019] Specifically, the first functional additive contains oxygen-containing silicon groups and sulfate groups. The oxygen-containing silicon groups can absorb residual water and impurities such as hydrofluoric acid that may be produced in the electrolyte, thereby removing water and inhibiting acid. The presence of water and hydrofluoric acid can trigger a series of adverse reactions, such as accelerating the decomposition of the electrolyte and corroding electrode materials, thereby affecting battery performance. After absorbing these impurities, the oxygen-containing silicon groups can effectively reduce their concentration in the electrolyte, reduce damage to the battery, reduce the battery's internal resistance, and improve the battery's charge and discharge efficiency and cycle life. Sulfate groups are prone to decomposition during the initial charge and discharge process of the battery. Their decomposition products can participate in the formation of a sulfur-containing SEI film, effectively improving the high-temperature performance of the electrolyte and battery. At the same time, they enhance the stability of the SEI film, prevent further contact and reaction between the electrolyte and the electrode material, prevent the dissolution of the electrode material and the continued decomposition of the electrolyte, thereby improving the battery's cycle stability and safety.

[0020] Secondly, the second functional additive contains vinyl and fluorine groups. During the first charge and discharge process of the battery, the vinyl group can polymerize into a film at the electrode material / electrolyte interface to form a polymer network structure, which is beneficial to improving the interface stability of the negative and positive electrodes, reducing interfacial side reactions, and providing structural stability of the electrode material during charge and discharge, thereby optimizing the battery's cycle performance and rate performance. In addition, this polymer film has excellent flexibility and can effectively alleviate the volume expansion effect of the silicon negative electrode while reducing gas production at the positive electrode. At the same time, this polymer network can increase the viscosity of the electrolyte and help inhibit the growth of lithium dendrites. The fluorine group has a lower Li+ solvation ability, which is beneficial to improving the battery's rate performance. At the same time, the fluorine group has a strong antioxidant capacity, which can increase the oxidation potential of the electrolyte, making it less susceptible to oxidation at high voltages, thereby effectively preventing the organic solvent and lithium salt components in the electrolyte from undergoing oxidative decomposition under high voltage or high temperature conditions, avoiding the increase in battery internal resistance, capacity decay and other deficiencies, and improving the stability and service life of the battery under high voltage and high temperature environments.

[0021] In one embodiment, in the first functional additive, R1, R2, R3, R4, R5, and R6 independently include an alkyl chain or a substituted alkyl chain; and in the second functional additive, R7 includes a fluorine-substituted alkyl chain.

[0022] In one embodiment, in the first functional additive, the number of carbon atoms in R1, R2, R3, R4, R5, and R6 does not exceed 4; in the second functional additive, the number of fluorine atoms in R7 is not less than 8. Ensuring that R1, R2, R3, R4, R5, R6, and R7 meet the above conditions can ensure that the first and second functional additives have good solubility in the electrolyte, and that these two materials can effectively improve the electrolyte and the battery. At the same time, it can take into account the combined effects of the two functional additives and other electrolyte components, so that the two functional additives and other electrolyte components exhibit better electrolyte performance, which is more conducive to the overall function of the electrolyte in the battery, thereby better optimizing the battery's electrochemical properties in various aspects, such as cycle performance and rate performance.

[0023] In one embodiment, R1, R2, R3, R4, R5, and R6 independently comprise —(CH2) n -CH3, n=0~4. Optionally, R1, R2, R3, R4, R5, and R6 independently include -(CH2) n -CH3, n = 0 to 3. Optionally, R1, R2, R3, R4, R5, and R6 independently include -CH3.

[0024] In one embodiment, the number of fluorine atoms in R7 of the second functional additive is no more than 14. Excessive fluorine atom content will reduce the solubility of the second functional additive, affecting its function in the electrolyte, and will also have a certain impact on other components in the electrolyte, ultimately causing a decrease in the overall performance of the electrolyte.

[0025] In one embodiment, the structural formula of the fluorine-substituted olefin contains at least two alkenyl groups.

[0026] In one embodiment, in the structural formula of the fluorine-substituted olefin, at least one end is an alkenyl group.

[0027] In one embodiment, in the structural formula of the fluorine-substituted olefin, both ends of the fluorine-substituted olefin are alkenyl groups.

[0028] In one embodiment, the first functional additive includes bis(trimethylsilyl) sulfate, and the second functional additive includes 1,6-divinylperfluorohexane. When the first and second functional additives are the aforementioned two substances, the combination of the two substances works best. Furthermore, the electrolyte prepared with the two additives and other electrolyte components exhibits improved performance, further facilitating overall battery performance optimization.

[0029] Among them, the structural formula of bis(trimethylsilyl) sulfate is , CAS number is 18306-29-1. The structural formula of 1,6-divinylperfluorohexane is , CAS number is 1800-91-5.

[0030] In one embodiment, when the first functional additive includes bis(trimethylsilyl) sulfate, the mass proportion of the first functional additive in the electrolyte is 0.5~4wt%; when the second functional additive includes 1,6-divinylperfluorohexane, the mass proportion of the second functional additive in the electrolyte is 0.2~2wt%.

[0031] In one embodiment, the organic solvent includes at least one of a fluorinated solvent and an ether solvent. Further, the electrolyte provided in the present application also introduces a fluorinated solvent and / or an ether solvent. The fluorinated solvent and / or an ether solvent can further improve the solubility of the above-mentioned two functional additives in the electrolyte, contribute to the performance of the two functional additives, and promote the interaction of the two functional additives with other electrolyte components, thereby further improving the overall performance of the electrolyte and the battery. Moreover, the fluorinated solvent has high chemical stability, can increase the oxidation potential of the electrolyte, effectively prevent the organic solvent and lithium salt components in the electrolyte from oxidative decomposition under high voltage or high temperature conditions, avoid the increase in battery internal resistance, capacity decay and other deficiencies, improve the stability and service life of the battery under high voltage and high temperature environments, and the fluorinated solvent helps to reduce the interfacial tension between the electrode and the electrolyte, promote the rapid transmission of lithium ions between the electrode and the electrolyte, and improve the rate performance of the battery. The ether solvent has a relatively low viscosity, which is conducive to reducing the viscosity of the overall electrolyte, facilitating the rapid migration of lithium ions, etc. therein, improving the ionic conductivity of the electrolyte, and thus improving the charge and discharge performance of the battery.

[0032] In one embodiment, the fluorinated solvent is at least one of trifluoropropylene carbonate (TFPC), difluoromethyl acetate (MFA), difluoroethyl acetate (EFA), and trifluoroethyl methyl carbonate (FEMC).

[0033] In one embodiment, the ether solvent includes at least one of ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), and tetrahydrofuran (THF).

[0034] In one embodiment, the organic solvent includes a fluorinated solvent and an ether solvent. When the organic solvent includes both a fluorinated solvent and an ether solvent, the two organic solvents can further promote the solubility of other components in the electrolyte while taking into account the low-temperature and high-temperature stability of the electrolyte, further improving the performance and synergistic effect of each component in the electrolyte, optimizing the performance of the electrolyte, and thus further improving the cycle performance and rate performance of the battery. Optionally, when the organic solvent includes a fluorinated solvent and an ether solvent, the volume ratio of the fluorinated solvent to the ether solvent is 5-40:5-40.

[0035] In one embodiment, when the organic solvent includes a fluorinated solvent and an ether solvent, the fluorinated solvent includes trifluoroethyl methyl carbonate, and the ether solvent includes ethylene glycol dimethyl ether. Optionally, the volume ratio of trifluoroethyl methyl carbonate to ethylene glycol dimethyl ether is 5-40:5-40. The combination of these fluorinated solvents and ether solvents further enhances the overall performance of the electrolyte, further optimizing battery performance.

[0036] In one embodiment, the organic solvent further comprises at least one of linear carbonate and cyclic carbonate.

[0037] In one embodiment, the linear carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC).

[0038] In one embodiment, the cyclic carbonate includes at least one of ethylene carbonate (EC), fluoroethylene carbonate (FEC), and propylene carbonate (PC).

[0039] In one embodiment, the organic solvent comprises a fluorinated solvent, an ether solvent, a linear carbonate, and a cyclic carbonate. Optionally, the volume ratio of the fluorinated solvent, the ether solvent, the linear carbonate, and the cyclic carbonate is 40-60:10-30:5-40:5-40.

[0040] In one embodiment, the organic solvent comprises dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, ethylene carbonate, trifluoroethyl methyl carbonate, and ethylene glycol dimethyl ether; the volume ratio of dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, ethylene carbonate, trifluoroethyl methyl carbonate, and ethylene glycol dimethyl ether is 5-15:30-50:5-15:5-15:5-30:5-30. Alternatively, the volume ratio of dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, ethylene carbonate, trifluoroethyl methyl carbonate, and ethylene glycol dimethyl ether is 10:40:10:10:15:15.

[0041] In one embodiment, the lithium salt includes at least one of lithium hexafluorophosphate, lithium trifluoromethanesulfonyl imide, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl imide), and lithium bis(oxalatoborate).

[0042] In one embodiment, the concentration of the lithium salt in the electrolyte is 1-1.5 mol / L.

[0043] According to a second aspect provided by the present application, a battery is provided, comprising the above-mentioned electrolyte.

[0044] In order to enable people in this technical field to better understand the solution of this application, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments.

[0045] Example 1

[0046] 1. Composition and preparation of electrolyte

[0047] The electrolyte in this embodiment includes lithium salt, an organic solvent, a first functional additive, and a second functional additive.

[0048] The lithium salt is lithium hexafluorophosphate (LiPF6), and the concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L.

[0049] The first functional additive is bis(trimethylsilyl) sulfate, and its weight ratio in the electrolyte is 2.2 wt%. The second functional additive is 1,6-divinylperfluorohexane, and its weight ratio in the electrolyte is 1.1 wt%.

[0050] The organic solvent includes dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), ethylene carbonate (EC), trifluoroethyl methyl carbonate (FEMC), and ethylene glycol dimethyl ether (DME), with the volume ratio of dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, ethylene carbonate, trifluoroethyl methyl carbonate, and ethylene glycol dimethyl ether being 10:40:10:10:15:15. The electrolyte is prepared according to the following steps: Under an argon atmosphere, the above-mentioned lithium salt, functional additives, and film-forming additives are uniformly mixed in the organic solvent, and stirring is performed at low temperature during the mixing process.

[0051] 2. Preparation of batteries

[0052] Preparation of lithium-ion batteries

[0053] (1) Preparation of positive electrode

[0054] The ternary material NCM (LiNi 0.9 Co 0.05 Mn 0.05 O2) positive electrode active material, binder PVDF (polyvinylidene fluoride), conductive agent SP (conductive carbon black Super-P) are mixed and stirred evenly in a mass ratio of 96:1.8:2.2 to obtain positive electrode slurry, and then the positive electrode slurry is coated on aluminum foil through a coating process, and the positive electrode sheet is obtained after vacuum drying and cold pressing processes.

[0055] (2) Preparation of negative electrode sheet

[0056] Silicon-carbon negative electrode material (silicon content of 40~60wt%), conductive agent SP (conductive carbon black Super-P), SWCNT (single-walled carbon nanotube) and binder PAA (polyacrylic acid) are mixed and stirred in a mass ratio of 83.5:8:0.5:8 to obtain a negative electrode slurry. The solid content is controlled at 30%. The negative electrode slurry is then coated on copper foil through a coating process, and the negative electrode sheet is obtained after vacuum drying and cold pressing processes.

[0057] (3) Selection of electrolyte

[0058] The electrolyte prepared in this example was used.

[0059] (4) Selection of isolation membrane

[0060] Polyethylene (PE) + ceramics are selected as the separator for lithium-ion batteries.

[0061] (5) Preparation of lithium-ion batteries

[0062] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive and negative electrode sheets to serve as an isolation. The bare battery cell is placed in an outer packaging shell, and after drying, the electrolyte is injected. After vacuum packaging, standing, forming, shaping and other processes, a soft-pack lithium-ion battery is obtained.

[0063] Example 2

[0064] The difference between this embodiment and embodiment 1 is that in the prepared electrolyte, the first functional additive is adjusted to ; The rest is consistent with Example 1.

[0065] Example 3

[0066] The difference between this embodiment and embodiment 1 is that in the prepared electrolyte, the second functional additive is adjusted to ; The rest is consistent with Example 1.

[0067] Example 4

[0068] The difference between this embodiment and embodiment 1 is that in the prepared electrolyte, the second functional additive is adjusted to ; The rest is consistent with Example 1.

[0069] Example 5

[0070] The difference between this embodiment and embodiment 1 is that in the prepared electrolyte, the second functional additive is adjusted to ; The rest is consistent with Example 1.

[0071] Example 6

[0072] The difference between this embodiment and embodiment 1 is that in the prepared electrolyte, the second functional additive is adjusted to 1,4-divinylperfluorobutane, whose structural formula is ; The rest is consistent with Example 1.

[0073] Example 7

[0074] This embodiment differs from Example 1 in that, in the prepared electrolyte, the mass proportion of the first functional additive in the electrolyte is adjusted to 0.3 wt %; the rest is the same as Example 1.

[0075] Example 8

[0076] This embodiment differs from Embodiment 1 in that, in the prepared electrolyte, the mass proportion of the second functional additive in the electrolyte is adjusted to 2.5 wt %; the rest is the same as in Embodiment 1.

[0077] Example 9

[0078] This embodiment differs from Example 1 in that the prepared electrolyte does not contain a fluorinated solvent, i.e., does not contain trifluoroethyl methyl carbonate, and the volume ratio of dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, ethylene carbonate, and ethylene glycol dimethyl ether is 10:40:10:10:15; the rest is the same as Example 1.

[0079] Example 10

[0080] This embodiment differs from Example 1 in that the prepared electrolyte does not contain an ether solvent, i.e., does not contain ethylene glycol dimethyl ether, and the volume ratio of dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, ethylene carbonate, and trifluoroethyl methyl carbonate is 10:40:10:10:15; the rest is consistent with Example 1.

[0081] Example 11

[0082] This embodiment differs from Example 1 in that, in the prepared electrolyte, in the organic solvent, the volume ratio of trifluoroethyl methyl carbonate and ethylene glycol dimethyl ether is 2:28, that is, the volume ratio of dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, ethylene carbonate, trifluoroethyl methyl carbonate, and ethylene glycol dimethyl ether is 10:40:10:10:2:28; the rest is consistent with Example 1.

[0083] Example 12

[0084] This embodiment differs from Example 1 in that, in the prepared electrolyte, the ether solvent is replaced with tetrahydrofuran, that is, ethylene glycol dimethyl ether is replaced with tetrahydrofuran, and the volume ratio of dimethyl carbonate, ethyl methyl carbonate, fluoroethylene carbonate, ethylene carbonate, trifluoroethyl methyl carbonate: tetrahydrofuran is 10:40:10:10:15:15; the rest is the same as Example 1.

[0085] Example 13

[0086] This embodiment differs from Example 1 in that, in the prepared electrolyte, fluoroethylene carbonate (FEC) is replaced by propylene carbonate (PC), and the volume ratio of dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, ethylene carbonate, trifluoroethyl methyl carbonate: ethylene glycol dimethyl ether is 10:40:10:10:15:15; the rest is the same as Example 1.

[0087] Comparative Example 1

[0088] This comparative example is different from Example 1 in that the prepared electrolyte does not contain the first functional additive and the second functional additive, that is, does not contain bis(trimethylsilyl) sulfate and 1,6-divinylperfluorohexane; the rest is consistent with Example 1.

[0089] Comparative Example 2

[0090] This comparative example is different from Example 1 in that the prepared electrolyte does not contain the first functional additive, that is, does not contain bis(trimethylsilyl) sulfate; the rest is the same as Example 1.

[0091] Comparative Example 3

[0092] This comparative example is different from Example 1 in that the prepared electrolyte does not contain the second functional additive, that is, does not contain 1,6-divinylperfluorohexane; the rest is consistent with Example 1.

[0093] Comparative Example 4

[0094] The difference between this comparative example and Example 1 is that in the prepared electrolyte, the first functional additive is replaced by ; The rest is consistent with Example 1.

[0095] Comparative Example 5

[0096] The difference between this comparative example and Example 1 is that in the prepared electrolyte, the second functional additive is replaced by ; The rest is consistent with Example 1.

[0097] Comparative Example 6

[0098] The difference between this comparative example and Example 1 is that the second functional additive is replaced by ; The rest is consistent with Example 1.

[0099] Test Case

[0100] 1. Experimental Construction Method

[0101] The batteries prepared in all the above examples and comparative examples were tested on the LAND battery testing system of Wuhan Jinnuo Electronics Co., Ltd. at room temperature (25°C), with the charge and discharge voltage limited to 2.5V-4.2V. The specific testing methods for initial efficiency, cycle and rate performance are as follows:

[0102] 1) First Coulomb efficiency

[0103] At 25°C, the battery was charged to 4.2 V at a constant current and constant voltage rate of 0.33C and allowed to stand for 10 minutes. Then, the battery was discharged to 2.5 V at a constant current rate of 0.33C and allowed to stand for 10 minutes. The first coulombic efficiency of the battery was calculated.

[0104] First coulombic efficiency (%) = total capacity of the battery for the first discharge at 0.33C / total capacity of the battery for the first charge at 0.33C × 100%.

[0105] 2) Capacity retention rate after 1000 cycles at room temperature 1C / 1C

[0106] At 25°C, the battery was charged to 4.2 V at a constant current and constant voltage rate of 1C, with a cut-off current of 0.05C, and allowed to stand for 10 minutes. The battery was then discharged to 2.5 V at a constant current rate of 1C and allowed to stand for 10 minutes. This was considered one charge and discharge cycle. The battery was charged and discharged for 1000 cycles according to the above method, and the capacity retention rate after 1000 cycles of charge and discharge at 1C / 1C was calculated.

[0107] The capacity retention rate (%) of the battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the battery.

[0108] 3) Capacity retention rate at 45℃ 1C / 1C cycle for 1000 cycles

[0109] At 45°C, the battery was charged to 4.2 V at a constant current and constant voltage rate of 1C, with a cut-off current of 0.05C, and allowed to stand for 10 minutes. The battery was then discharged to 2.5 V at a constant current rate of 1C and allowed to stand for 10 minutes. This was considered one charge and discharge cycle. The battery was charged and discharged for 1000 cycles according to the above method, and the capacity retention rate after 1000 cycles of charge and discharge at 1C / 1C was calculated.

[0110] The capacity retention rate (%) of the battery after N cycles = (discharge capacity at the Nth cycle / initial discharge capacity) × 100%, where N is the number of cycles of the battery.

[0111] 4) Room temperature 6C rate performance - constant current charging ratio

[0112] At 25°C, the battery was discharged at a constant current rate of 1C to 2.5 V and allowed to stand for 10 minutes. The battery was then charged at a constant current and constant voltage rate of 6C to 4.2 V with a cut-off current of 0.05C and allowed to stand for 10 minutes. The constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 of the battery were recorded. The constant current charging ratio of 6C rate charging was calculated according to the following formula: constant current charging ratio of 6C rate charging = constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2 × 100%.

[0113] 2. Experimental Results

[0114] The relevant performance test results of the batteries prepared in all the above examples and comparative examples are shown in Table 1.

[0115] Table 1 Relevant performance test results of batteries prepared in Examples and Comparative Examples

[0116]

[0117] As can be seen from Table 1, the battery prepared using the electrolyte provided in this application can exhibit excellent performance in the battery cycle, and thus can effectively optimize the electrochemical properties of the battery such as the initial efficiency, room temperature and high temperature cycle performance, and 6C constant current charging ratio. It is an electrolyte with excellent performance. For details, please refer to Examples 1 to 13.

[0118] Comparative Example 1, which did not contain the first and second functional additives, Comparative Example 2, which did not contain the first functional additive, and Comparative Example 3, which did not contain the second functional additive, all resulted in a decline in various aspects of battery performance. This demonstrates that the specific functional additives introduced in this application have a significant impact on further improving electrolyte performance, thereby further optimizing battery performance.

[0119] In Comparative Example 4, there is no sulfate group in the first functional additive, there is no fluorine atom in the second functional additive in Comparative Example 5, and there is no olefin group in the second functional additive in Comparative Example 6. This causes the first functional additive or the second functional additive to have an effect in the electrolyte, and therefore cannot effectively improve the overall performance of the electrolyte, ultimately leading to a decrease in the stability of the silicon negative electrode interface and the positive electrode interface, causing the battery performance in all aspects to decline.

[0120] Further comparing Example 1 and Example 2, the alkyl chain linked behind the Si atom in the first functional additive in Example 2 is too long; comparing Example 1 with Examples 3, 4, 5, and 6, there is only one alkenyl group in the second functional additive in Example 3, only one alkenyl group in the second functional additive in Example 4, and only 7 fluorine atoms, and the alkenyl group is not at both ends. There is only one alkenyl group in the second functional additive in Example 5, and the alkenyl group is not at both ends. In Example 6, there is an alkynyl group at both ends of the second functional additive, and 8 fluorine atoms. Compared with Example 1, the structure of the first functional additive or the second functional additive in Examples 2 to 6 has changed to a certain extent, resulting in a decrease in performance. It can also be further seen from Examples 3, 4, and 5 that the battery performance in Examples 4 and 5 is even worse than that in Example 3, which shows that functional additives with alkenyl groups at both ends of the structural formula are more conducive to improving the performance of the electrolyte, and thus improving the battery performance.

[0121] Comparing Example 1 with Examples 7 and 8, the first functional additive in Example 7 is too little, and the second functional additive in Example 8 is too much, which both result in a decrease in battery performance. This shows that further controlling the amount of the first functional additive and the second functional additive within a specific range is more conducive to improving the overall performance of the electrolyte, thereby further improving the performance of the battery.

[0122] Comparing Examples 1 and 9-13, Example 9 contained no fluorinated solvents, Example 10 contained no ether solvents, Example 11 contained a fluorinated solvent to ether solvent volume ratio of 2:28, Example 12 contained tetrahydrofuran as the ether solvent, and Example 13 replaced fluoroethylene carbonate (FEC) with propylene carbonate (PC) as the organic solvent. These factors all led to a decrease in battery performance across various dimensions. In particular, the absence of specific fluorinated solvents and ether solvents in Examples 9 and 10 led to a more significant decrease in battery performance compared to Examples 11 and 12. Furthermore, the replacement of FEC with PC in Example 13 also resulted in a more pronounced decrease in battery performance. This is likely due to the reduced solute interaction, which resulted in a more pronounced decrease in electrolyte performance and, consequently, battery performance.

[0123] The above embodiments are only used to illustrate the technical solutions of the present application and are not intended to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the technical solutions of the present application can be modified or replaced by equivalents, but these modifications or replacements are all within the scope of protection of the present application.

Claims

1. An electrolyte comprising a lithium salt, an organic solvent, a first functional additive, and a second functional additive; The structural formula of the first functional additive is: ； The second functional additive is a fluorine-substituted olefin, and the fluorine-substituted olefin includes the following structural units: , wherein R7 includes a fluorine atom.

2. The electrolyte according to claim 1, wherein In the first functional additive, R1, R2, R3, R4, R5, and R6 independently comprise an alkyl chain or a substituted alkyl chain; In the second functional additive, R7 includes a fluorine-substituted alkyl chain.

3. The electrolyte according to claim 2, wherein In the first functional additive, the number of carbon atoms in R1, R2, R3, R4, R5, and R6 does not exceed 4; In the second functional additive, the number of fluorine atoms in R7 is not less than 8.

4. The electrolyte according to any one of claims 1 to 3, wherein In the structural formula of the fluorine-substituted olefin, at least one end is an alkenyl group.

5. The electrolyte according to claim 1, wherein The first functional additive includes bis(trimethylsilyl) sulfate; the second functional additive includes 1,6-divinylperfluorohexane; The first functional additive accounts for 0.5-4 wt % by weight in the electrolyte; the second functional additive accounts for 0.2-2 wt % by weight in the electrolyte.

6. The electrolyte according to claim 1, wherein The organic solvent includes at least one of a fluorinated solvent and an ether solvent; The fluorinated solvent is at least one of trifluoropropylene carbonate, difluoromethyl acetate, difluoroethyl acetate, and trifluoroethyl methyl carbonate; The ether solvent includes at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, and tetrahydrofuran.

7. The electrolyte according to claim 1, wherein The organic solvent includes a fluorinated solvent and an ether solvent; The volume ratio of the fluorinated solvent to the ether solvent is 5-40:5-40.

8. The electrolyte according to any one of claims 6 or 7, wherein The organic solvent further comprises at least one of a linear carbonate and a cyclic carbonate; The linear carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate; The cyclic carbonate includes at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate.

9. The electrolyte according to claim 8, wherein The organic solvent includes the fluorinated solvent, the ether solvent, the linear carbonate, and the cyclic carbonate, and the volume ratio of the fluorinated solvent, the ether solvent, the linear carbonate, and the cyclic carbonate is 40-60:10-30:5-40:5-40.

10. A battery comprising the electrolyte according to any one of claims 1 to 9.

Images