An electrolyte, a battery

Abstract

The application provides an electrolyte and a battery, the 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 structural formula of the second functional additive is a fluorine-substituted olefin, and the fluorine-substituted olefin comprises the following structural unit: wherein R7 comprises a fluorine atom. The electrolyte can promote the stable growth of the negative electrode interface SEI film, especially the silicon negative electrode interface SEI film, improve the stability of the negative electrode interface, further reduce the positive electrode gas production and optimize the stability of the positive electrode interface by introducing two specific structure functional additives and the collocation of the two functional additives. Therefore, the electrolyte provided by the application can further improve the electrochemical performance of the battery, such as the cycle performance and the rate performance.

Description

Technical Field

[0001] This application belongs to the field of lithium-ion battery technology, specifically relating to an electrolyte and a battery. Background Technology

[0002] Graphite anodes are composed of planar layered carbon atoms, with weak van der Waals forces attracting each other between layers. Within each layer, carbon atoms form planar six-membered rings in an sp2 hybrid configuration. This structure gives graphite high structural stability and good electrical conductivity. Furthermore, the layered structure facilitates lithium-ion insertion and extraction, which is one of the reasons for the successful commercialization of graphite anodes. Despite its advantages in high conductivity and stability, its theoretical specific capacity of 372 mAh / g is insufficient to meet our demand for high-capacity power batteries. The commercialization of batteries requires improving their specific energy while ensuring economic viability and safety.

[0003] Silicon is abundant and widely distributed in the Earth's crust, and has a slightly higher potential plateau than graphite (0.4V, vs. Li / Li). + Silicon anode materials, free from the risk of lithium plating, offer good safety and a theoretical specific capacity of up to 4200 mAh / g, making them one of the most promising anode materials. However, silicon anode materials experience nearly 300% volume expansion during lithium insertion / extraction, leading to problems such as particle fragmentation, electrical isolation, and unstable SEI growth, significantly limiting the commercial application of silicon-based anodes. Silicon-based anode materials are mainly divided into silicon-carbon composite materials (Si / C) and silicon-oxygen anode materials (SiO2). x The two main categories are graphite and silicon (SiO2). Currently, the mainstream approach is to use graphite as the matrix, doped with 5%–30% (mass fraction) nano-silicon or SiO2. x To form a composite negative electrode material.

[0004] To address the issues of volume expansion of silicon-based anodes and the resulting interface damage, introducing electrolyte additives into the electrolyte to promote the formation of the SEI film and thus prevent electrolyte decomposition is a simple, economical, and effective method. Summary of the Invention

[0005] To address the problems and shortcomings of existing technologies, this application provides an electrolyte and a battery. This electrolyte incorporates two functional additives with specific structures. The combined use of these two additives promotes the stable growth of the SEI film at the interface of the negative electrode, particularly the silicon negative electrode, improving the interface stability of the negative electrode. Simultaneously, it further reduces gas generation at the positive electrode, optimizing the interface stability of the positive electrode. Furthermore, the introduction of these two functional additives further enhances the stability of the electrolyte, giving it good stability at both room temperature and high temperature, optimizing the lithium-ion transport performance of the electrolyte, and reducing the degree of side reactions between the electrolyte and electrode materials. Therefore, the electrolyte provided by this application can further improve the electrochemical performance of the battery, such as cycle performance and rate performance.

[0006] According to a first aspect of this application, an electrolyte is provided, 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:

[0007] The second functional additive has the structural formula of a fluorinated olefin, which includes the following structural units: R7 includes fluorine atoms.

[0008] This application effectively improves the stability of the negative electrode interface and the positive electrode interface by introducing the above two functional additives with specific structures, improves the structural stability of the electrode material during cyclic charging and discharging, and optimizes the stability of the electrolyte, reducing its oxidation degree and side reaction degree. As a result, the cycle performance and rate performance of the battery prepared by it are significantly optimized.

[0009] Specifically, firstly, the primary functional additive contains oxygen-containing silicon groups and sulfate ester groups. The oxygen-containing silicon groups can absorb residual moisture and impurities such as hydrofluoric acid that may be generated in the electrolyte, thus acting as a dehydrator and acid suppressant. The presence of moisture and hydrofluoric acid can trigger a series of adverse reactions, such as accelerating electrolyte decomposition 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, minimizing damage to the battery, reducing internal resistance, and improving charge / discharge efficiency and cycle life. The sulfate ester groups are prone to decomposition during the first charge / discharge process. 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, while also enhancing the stability of the SEI film. This prevents further contact and reaction between the electrolyte and electrode materials, preventing the dissolution of electrode materials and the continuous decomposition of the electrolyte, thereby improving the battery's cycle stability and safety.

[0010] Secondly, the secondary functional additive contains vinyl and fluorine groups. During the initial charge and discharge of the battery, vinyl groups can polymerize at the electrode material / electrolyte interface to form a polymer network structure, which is beneficial for improving the stability of the negative and positive electrode interface, reducing interfacial side reactions, and providing structural stability of the electrode materials during charge and discharge, thereby optimizing the battery's cycle performance and rate performance. Furthermore, this polymer film has excellent flexibility, effectively mitigating the volume expansion effect of the silicon negative electrode while reducing gas generation at the positive electrode. Simultaneously, this polymer network can increase the viscosity of the electrolyte, helping to suppress lithium dendrite growth. Fluorine groups have lower Li+ solvation capability, which is beneficial for improving battery rate performance. At the same time, fluorine groups have strong antioxidant capabilities, increasing the oxidation potential of the electrolyte and making it less susceptible to oxidation at high voltages. This effectively prevents the oxidative decomposition of organic solvents and lithium salts in the electrolyte under high voltage or high temperature conditions, avoiding problems such as increased internal resistance and capacity decay, and improving the battery's stability and lifespan under high voltage and high temperature environments.

[0011] Preferably, in the first functional additive, R1, R2, R3, R4, R5, and R6 independently comprise alkyl chains or substituted alkyl chains; in the second functional additive, R7 comprises a fluorinated substituted alkyl chain.

[0012] Preferably, in the first functional additive, the number of carbon atoms in R1, R2, R3, R4, R5, and R6 does not exceed 4; and 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 guarantees good solubility of both the first and second functional additives in the electrolyte, while also ensuring that these two materials effectively improve the electrolyte and battery performance. Simultaneously, it allows for the synergistic effect of these two functional additives with other electrolyte components, resulting in better electrolyte performance and a more favorable overall effect of the electrolyte in the battery. This leads to better optimization of the battery's cycle performance, rate performance, and other electrochemical properties.

[0013] Preferably, R1, R2, R3, R4, R5, and R6 independently include —(CH2). n -CH3, n = 0 to 4. Preferably, R1, R2, R3, R4, R5, and R6 independently include -(CH2). n -CH3, n = 0 to 3. Preferably, R1, R2, R3, R4, R5, and R6 independently include -CH3.

[0014] Preferably, in the second functional additive, R7 contains no more than 14 fluorine atoms. Excessive fluorine content will reduce the solubility of the second functional additive, affecting its function in the electrolyte. It will also negatively impact other components in the electrolyte, ultimately leading to a decline in the overall performance of the electrolyte.

[0015] Preferably, the fluorinated olefin contains at least two alkenyl groups in its structural formula.

[0016] Preferably, in the structural formula of the fluorinated olefin, at least one end is an alkenyl group.

[0017] Preferably, in the structural formula of the fluorinated olefin, the two ends of the fluorinated olefin are alkenyl groups.

[0018] Preferably, the first functional additive includes bis(trimethylsilyl)sulfate; the second functional additive includes 1,6-divinylperfluorohexane. When the first and second functional additives are each one of the above two substances, their combined effect is optimal, and the electrolyte prepared from them with other electrolyte components exhibits better performance, which is more conducive to optimizing the overall battery performance.

[0019] The structural formula of bis(trimethylsilyl)sulfate is as follows: The CAS number is 18306-29-1. The structural formula of 1,6-divinylperfluorohexane is: The CAS number is 1800-91-5.

[0020] Preferably, when the first functional additive includes bis(trimethylsilyl)sulfate, the mass percentage of the first functional additive in the electrolyte is 0.5 to 4 wt%; when the second functional additive includes 1,6-divinylperfluorohexane, the mass percentage of the second functional additive in the electrolyte is 0.2 to 2 wt%.

[0021] Preferably, the organic solvent includes at least one of fluorinated solvents and ether solvents. Furthermore, the electrolyte provided in this application also incorporates fluorinated solvents and / or ether solvents. These solvents can further improve the solubility of the two functional additives mentioned above in the electrolyte, facilitating the performance of these additives and promoting their interaction with other electrolyte components, thereby further improving the overall performance of the electrolyte and the battery. Moreover, fluorinated solvents have high chemical stability, increasing the oxidation potential of the electrolyte and effectively preventing the oxidative decomposition of organic solvents and lithium salts in the electrolyte under high voltage or high temperature conditions. This avoids problems such as increased battery internal resistance and capacity decay, improving the battery's stability and lifespan under high voltage and high temperature environments. Furthermore, fluorinated solvents help reduce the interfacial tension between the electrode and the electrolyte, promoting rapid lithium ion transport between the electrode and the electrolyte, and improving the battery's rate performance. Ether solvents have relatively low viscosity, which helps reduce the overall viscosity of the electrolyte, facilitating the rapid migration of lithium ions and improving the ionic conductivity of the electrolyte, thereby enhancing the battery's charge and discharge performance.

[0022] Preferably, the fluorinated solvent is at least one selected from propylene trifluorocarbonate (TFPC), methyl difluoroacetate (MFA), ethyl difluoroacetate (EFA), and trifluoroethyl methyl carbonate (FEMC).

[0023] Preferably, the ether solvent includes at least one of ethylene glycol dimethyl ether (DME), 1,3-dioxolane (DOL), and tetrahydrofuran (THF).

[0024] Preferably, the organic solvent includes fluorinated solvents and ether solvents. When the organic solvent includes both fluorinated solvents and ether solvents, these two organic solvents can further promote the solubility of other components in the electrolyte, while also taking into account the low-temperature and high-temperature stability of the electrolyte. This can further improve the performance of each component in the electrolyte and their synergistic effect, optimizing the performance of the electrolyte, thereby further improving the cycle performance and rate performance of the battery. Preferably, when the organic solvent includes fluorinated solvents and ether solvents, the volume ratio of the fluorinated solvent to the ether solvent is 5-40:5-40.

[0025] Preferably, the organic solvent includes a fluorinated solvent and an ether solvent, wherein the fluorinated solvent includes trifluoroethyl methyl carbonate and the ether solvent includes ethylene glycol dimethyl ether. Preferably, the volume ratio of trifluoroethyl methyl carbonate to ethylene glycol dimethyl ether is 5–40:5–40. Selecting the above-mentioned combination of fluorinated solvents and ether solvents further improves the overall performance of the electrolyte and is more conducive to further optimizing battery performance.

[0026] Preferably, the organic solvent further includes at least one of linear carbonates and cyclic carbonates.

[0027] Preferably, the linear carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), and methyl propyl carbonate (MPC).

[0028] Preferably, the cyclic carbonate includes at least one of ethylene carbonate (EC), fluoroethylene carbonate (FEC), and propylene carbonate (PC).

[0029] Preferably, the organic solvents include fluorinated solvents, ether solvents, linear carbonates, and cyclic carbonates. Preferably, the volume ratio of the fluorinated solvent, ether solvent, linear carbonate, and cyclic carbonate is 40–60:10–30:5–40:5–40.

[0030] Preferably, the organic solvents include 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. Preferably, 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.

[0031] Preferably, the lithium salt comprises at least one of lithium hexafluorophosphate, lithium trifluoromethanesulfonylimide, lithium tetrafluoroborate, lithium perchlorate, lithium difluorosulfonylimide, and lithium dioxalateborate.

[0032] Preferably, the concentration of the lithium salt in the electrolyte is 1 to 1.5 mol / L.

[0033] According to a second aspect of this application, a battery is provided, comprising the aforementioned electrolyte. The battery prepared using the aforementioned electrolyte exhibits effectively improved cycle performance and rate capability. Detailed Implementation

[0034] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments.

[0035] Example 1

[0036] 1. Composition and preparation of electrolyte

[0037] The electrolyte in this embodiment includes lithium salt, organic solvent, first functional additive, and second functional additive.

[0038] The lithium salt is lithium hexafluorophosphate (LiPF6), and the concentration of lithium hexafluorophosphate in the electrolyte is 1 mol / L.

[0039] The first functional additive is bis(trimethylsilyl)sulfate, and its mass percentage in the electrolyte is 2.2 wt%. The second functional additive is 1,6-divinylperfluorohexane, and its mass percentage in the electrolyte is 1.1 wt%.

[0040] The organic solvents include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC), ethylene carbonate (EC), trifluoroethyl methyl carbonate (FEMC), and diethylene glycol dimethyl ether (DME), with a volume ratio of 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 mixed evenly in the organic solvent, with low-temperature stirring during the mixing process.

[0041] 2. Battery manufacturing

[0042] Preparation of lithium-ion batteries

[0043] (1) Preparation of positive electrode

[0044] Ternary material NCM (LiNi) 0.9 Co 0.05 Mn 0.05 O2) positive electrode active material, binder PVDF (polyvinylidene fluoride), and conductive agent SP (conductive carbon black Super-P) are mixed and stirred evenly at a mass ratio of 96:1.8:2.2 to obtain positive electrode slurry. Then, the positive electrode slurry is coated onto aluminum foil through a coating process, and after vacuum drying and cold pressing, a positive electrode sheet is obtained.

[0045] (2) Preparation of negative electrode

[0046] Silicon-carbon anode material (silicon content 40-60 wt%), conductive agent SP (Super-P conductive carbon black), SWCNT (single-walled carbon nanotubes), and binder PAA (polyacrylic acid) are mixed and stirred evenly 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 onto copper foil through a coating process. After vacuum drying and cold pressing, a negative electrode sheet is obtained.

[0047] (3) Selection of electrolyte

[0048] The electrolyte prepared using this embodiment.

[0049] (4) Selection of the separator

[0050] Polyethylene (PE) + ceramic was chosen as the separator for lithium-ion batteries.

[0051] (5) Preparation of lithium-ion batteries

[0052] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The bare cell is placed in the outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a soft-pack lithium-ion battery is obtained.

[0053] Example 2

[0054] The difference between this embodiment and Embodiment 1 is that the first functional additive in the prepared electrolyte is adjusted to... The rest is the same as in Example 1.

[0055] Example 3

[0056] The difference between this embodiment and Embodiment 1 is that the second functional additive in the prepared electrolyte is adjusted to... The rest is the same as in Example 1.

[0057] Example 4

[0058] The difference between this embodiment and Embodiment 1 is that the second functional additive in the prepared electrolyte is adjusted to... The rest is the same as in Example 1.

[0059] Example 5

[0060] The difference between this embodiment and Embodiment 1 is that the second functional additive in the prepared electrolyte is adjusted to... The rest is the same as in Example 1.

[0061] Example 6

[0062] The difference between this embodiment and Example 1 is that the second functional additive in the prepared electrolyte is adjusted to 1,4-divinylperfluorobutane, whose structural formula is [insert structural formula here]. The rest is the same as in Example 1.

[0063] Example 7

[0064] The difference between this embodiment and Embodiment 1 is that the mass percentage of the first functional additive in the prepared electrolyte is adjusted to 0.3 wt%; the rest is the same as in Embodiment 1.

[0065] Example 8

[0066] The difference between this embodiment and Embodiment 1 is that the mass percentage of the second functional additive in the prepared electrolyte is adjusted to 2.5 wt%; the rest is the same as in Embodiment 1.

[0067] Example 9

[0068] The difference between this embodiment and Example 1 is that the electrolyte prepared does not contain fluorinated solvents, i.e., it 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 in Example 1.

[0069] Example 10

[0070] The difference between this embodiment and Example 1 is that the electrolyte prepared does not contain ether solvents, i.e., it 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 the same as in Example 1.

[0071] Example 11

[0072] The difference between this embodiment and Example 1 is that in the prepared electrolyte, the volume ratio of trifluoroethyl methyl carbonate to ethylene glycol dimethyl ether in the organic solvent is 2:28, that is, the volume ratio of dimethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, ethylene carbonate, trifluoroethyl methyl carbonate, and ethylene glycol dimethyl ether is 10:40:10:10:2:28; the rest is the same as in Example 1.

[0073] Example 12

[0074] The difference between this embodiment and Example 1 is that the ether solvent in the prepared electrolyte is replaced with tetrahydrofuran, that is, ethylene glycol dimethyl ether is replaced with tetrahydrofuran, and the volume ratio of dimethyl carbonate, methyl ethyl carbonate, fluoroethylene carbonate, ethylene carbonate, trifluoroethyl methyl carbonate and tetrahydrofuran is 10:40:10:10:15:15; the rest is the same as in Example 1.

[0075] Example 13

[0076] The difference between this embodiment and Example 1 is that in the prepared electrolyte, fluoroethylene carbonate (FEC) is replaced with propylene carbonate (PC), and the volume ratio of dimethyl carbonate, methyl ethyl carbonate, propylene carbonate, ethylene carbonate, trifluoroethyl methyl carbonate, and ethylene glycol dimethyl ether is 10:40:10:10:15:15; the rest is the same as in Example 1.

[0077] Comparative Example 1

[0078] The difference between this comparative example and Example 1 is that the electrolyte prepared does not contain the first functional additive and the second functional additive, that is, it does not contain bis(trimethylsilyl)sulfate and 1,6-divinylperfluorohexane; otherwise, it is the same as Example 1.

[0079] Comparative Example 2

[0080] The difference between this comparative example and Example 1 is that the electrolyte prepared does not contain the first functional additive, i.e., it does not contain bis(trimethylsilyl)sulfate; otherwise, it is the same as Example 1.

[0081] Comparative Example 3

[0082] The difference between this comparative example and Example 1 is that the electrolyte prepared does not contain the second functional additive, i.e., it does not contain 1,6-divinylperfluorohexane; otherwise, it is the same as Example 1.

[0083] Comparative Example 4

[0084] The difference between this comparative example and Example 1 is that the first functional additive in the prepared electrolyte is replaced with... The rest is the same as in Example 1.

[0085] Comparative Example 5

[0086] The difference between this comparative example and Example 1 is that the second functional additive in the prepared electrolyte is replaced with... The rest is the same as in Example 1.

[0087] Comparative Example 6

[0088] The difference between this comparative example and Example 1 is that the second functional additive in the prepared electrolyte is replaced with... The rest is the same as in Example 1.

[0089] Test case

[0090] 1. Experimental Construction Method

[0091] The batteries prepared in all the above embodiments and comparative examples were tested at room temperature (25°C) on the LAND battery testing system of Wuhan Jinno Electronics Co., Ltd., with the charge and discharge voltage limited to 2.5V to 4.2V. The specific test methods for performance such as first-efficiency, cycle life, and rate capability are as follows:

[0092] 1) First Coulomb efficiency

[0093] At 25°C, the battery was charged at a constant current and constant voltage of 0.33C to 4.2V, allowed to stand for 10 minutes, and then discharged at a constant current of 0.33C to 2.5V, allowed to stand for 10 minutes. The initial coulombic efficiency of the battery was then calculated.

[0094] Initial coulombic efficiency (%) = Total capacity of battery during initial discharge at 0.33C / Total capacity of battery during initial charge at 0.33C × 100%.

[0095] 2) Capacity retention rate after 1000 cycles at room temperature (1°C) / 1°C

[0096] At 25°C, the battery was charged at a constant current and constant voltage of 1C to 4.2V, with a cutoff current of 0.05C. After resting for 10 minutes, the battery was discharged at a constant current of 1C to 2.5V and then rested for 10 minutes. This constitutes one charge-discharge cycle. The battery was charged and discharged for 1000 cycles using the above method. The capacity retention rate after 1000 charge-discharge cycles at 1C / 1C was calculated.

[0097] The capacity retention rate (%) of a battery after N cycles = (discharge capacity of the Nth cycle / initial discharge capacity) × 100%, where N is the number of battery cycles.

[0098] 3) Capacity retention rate after 1000 cycles at 45℃ (1C / 1C)

[0099] At 45°C, the battery is charged at a constant current and constant voltage of 1C to 4.2V, with a cutoff current of 0.05C. After resting for 10 minutes, the battery is discharged at a constant current of 1C to 2.5V and then rested for 10 minutes. This constitutes one charge-discharge cycle. The battery is charged and discharged for 1000 cycles using the above method. The capacity retention rate after 1000 charge-discharge cycles at 1C / 1C is calculated.

[0100] The capacity retention rate (%) of a battery after N cycles = (discharge capacity of the Nth cycle / initial discharge capacity) × 100%, where N is the number of battery cycles.

[0101] 4) Room temperature 6C rate performance - constant current charge ratio

[0102] At 25℃, the battery was discharged at a constant current rate of 1C to 2.5V, left to stand for 10 minutes, and then charged at a constant current and constant voltage rate of 6C to 4.2V with a cutoff current of 0.05C. After standing for 10 minutes, the constant current charging capacity Q1 and the total constant current and constant voltage charging capacity Q2 were recorded. The constant current charging ratio at the 6C rate was calculated using the following formula: 6C rate charging constant current charging ratio = constant current charging capacity Q1 / total constant current and constant voltage charging capacity Q2 × 100%.

[0103] 2. Experimental Results

[0104] The relevant performance test results of the batteries prepared in all the above embodiments and comparative examples are shown in Table 1.

[0105] Table 1. Performance test results of batteries prepared in the examples and comparative examples.

[0106]

[0107]

[0108] As shown in Table 1, the battery prepared using the electrolyte provided in this application exhibits excellent performance during battery cycling. Therefore, it can effectively optimize the electrochemical performance of the battery, such as initial efficiency, room temperature and high temperature cycling performance, and 6C constant current charge ratio. It is a high-performance electrolyte, as detailed in Examples 1 to 13.

[0109] Comparative Example 1, which lacks both the first and second functional additives, Comparative Example 2, which lacks the first functional additive, and Comparative Example 3, which lacks the second functional additive, all resulted in a decline in battery performance in various aspects. This demonstrates that the specific functional additives introduced in this application have a significant impact on further improving electrolyte performance, thereby enabling further optimization of battery performance.

[0110] The first functional additive in Comparative Example 4 lacks a sulfate ester group, the second functional additive in Comparative Example 5 lacks a fluorine atom, and the second functional additive in Comparative Example 6 lacks an alkenyl group. These factors all affect the effectiveness of the first or second functional additive in the electrolyte, thus failing to effectively improve the overall performance of the electrolyte. Ultimately, this leads to a decrease in the stability of the silicon anode and cathode interfaces, resulting in a decline in the battery's performance in various aspects.

[0111] Further comparing Examples 1 and 2, in Example 2, the alkyl chain linked after the Si atom in the first functional additive is too long. Comparing Examples 1 and Examples 3, 4, 5, and 6, in Example 3, the second functional additive has only one alkenyl group; in Example 4, the second functional additive has only one alkenyl group and only seven fluorine atoms, and the alkenyl group is not at either end; in Example 5, the second functional additive has only one alkenyl group, and the alkenyl group is not at either end; in Example 6, the second functional additive has one alkynyl group at each end and eight fluorine atoms. Compared to Example 1, the structure of the first or second functional additive in Examples 2-6 has changed to some extent, resulting in a decrease in performance. Furthermore, it can be seen from Examples 3, 4, and 5 that the battery performance in Examples 4 and 5 is worse than that in Example 3. This indicates that functional additives with alkenyl groups at both ends are more beneficial for improving the performance of the electrolyte, thereby improving battery performance.

[0112] Comparing Examples 1 and 7 and 8, the first functional additive in Example 7 was too small, and the second functional additive in Example 8 was too large. Both of these resulted in a decrease in battery performance. This shows that further controlling the amount of the first and second functional additives within a specific range is more conducive to improving the overall performance of the electrolyte, and thus further improving the performance of the battery.

[0113] Comparing Examples 1 and 9-13, the organic solvent in Example 9 did not contain a fluorinated solvent; the organic solvent in Example 10 did not contain an ether solvent; the volume ratio of fluorinated solvent to ether solvent in the organic solvent in Example 11 was 2:28; the ether solvent in the organic solvent in Example 12 was tetrahydrofuran; and in Example 13, fluoroethylene carbonate (FEC) was replaced with propylene carbonate (PC). All of these factors led to a decrease in battery performance in various aspects. In particular, Examples 9 and 10, which did not contain specific fluorinated solvents or specific ether solvents, showed a more significant decrease in battery performance compared to Examples 11 and 12. Furthermore, replacing FEC with PC in Example 13 also resulted in a more significant decrease in battery performance. This may be because it is detrimental to the interaction of solutes, leading to a more pronounced decrease in electrolyte performance and consequently a more significant decrease in battery performance.

[0114] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application, but such modifications or substitutions are all within the scope of protection of this application.

Claims

1. An electrolyte, characterized in that: Including lithium salts, organic solvents, primary functional additives, and secondary functional additives; The structural formula of the first functional additive is: Among them, R1, R2, R3, R4, R5, and R6 independently include alkyl chains or substituted alkyl chains; the number of carbon atoms in R1, R2, R3, R4, R5, and R6 does not exceed 4; The second functional additive is a fluorinated olefin, which comprises the following structural units: — R7 includes a fluorinated alkyl chain, and the number of fluorine atoms in R7 is not less than 8; in the structural formula of the fluorinated olefin, at least one end is an alkenyl group. The electrolyte is used in batteries containing silicon anodes.

2. The electrolyte as described in claim 1, characterized in that: The first functional additive comprises bis(trimethylsilyl)sulfate; the second functional additive comprises 1,6-divinylperfluorohexane; The first functional additive has a mass percentage of 0.5-4 wt% in the electrolyte; the second functional additive has a mass percentage of 0.2-2 wt% in the electrolyte.

3. The electrolyte as described in claim 1, characterized in that: The organic solvent includes at least one of fluorinated solvents and ether solvents; The fluorinated solvent is at least one of the following: trifluoropropylene carbonate, difluoromethyl acetate, difluoroethyl acetate, and trifluoroethylmethyl carbonate. The ether solvent includes at least one of ethylene glycol dimethyl ether, 1,3-dioxolane, and tetrahydrofuran.

4. The electrolyte as described in claim 1, characterized in that: The organic solvents include fluorinated solvents and ether solvents; The volume ratio of the fluorinated solvent to the ether solvent is 5~40:5~40.

5. The electrolyte according to any one of claims 1-4, characterized in that: The organic solvent also includes at least one of linear carbonates and cyclic carbonates; The linear carbonate includes at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propyl carbonate. The cyclic carbonates include at least one of ethylene carbonate, fluoroethylene carbonate, and propylene carbonate.

6. The electrolyte as described in claim 5, characterized in that: The organic solvent includes fluorinated solvents, ether solvents, the linear carbonate, and the cyclic carbonate, wherein 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.

7. A battery, characterized in that: Includes the electrolyte as described in any one of claims 1 to 6.

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