Electrolyte for power battery, preparation method therefor, power battery, and vehicle

Abstract

The present disclosure provides an electrolyte for a power battery and a preparation method therefor. The electrolyte comprises a lithium salt, a non-aqueous solvent, and a functional additive, wherein the functional additive comprises fluoroethylene carbonate, an unsaturated phosphate ester, and a siloxy compound.

Description

An electrolyte for a power battery and its preparation method, the power battery, and a vehicle.

[0001] Cross-references to related applications

[0002] This application is based on and claims priority to Chinese Patent Application No. 202411855977.1, filed on December 16, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure pertains to the field of battery manufacturing technology, and relates to an electrolyte, particularly to an electrolyte for a power battery and its preparation method, as well as a power battery and a vehicle containing the electrolyte. Background Technology

[0004] Lithium-ion batteries have become a popular energy storage system due to their high operating voltage, long lifespan, and environmental friendliness, and are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields. Summary of the Invention

[0005] The purpose of this disclosure is to provide an electrolyte for a power battery, its preparation method and application. By adding functional additives with specific components to the electrolyte, the fast charging and cycle performance of the power battery is significantly improved by leveraging the synergistic effect between fluoroethylene carbonate, unsaturated phosphate ester and siloxy compound, which is conducive to large-scale promotion and application.

[0006] In a first aspect, this disclosure provides an electrolyte for a power battery, comprising a lithium salt, a non-aqueous solvent, and a functional additive, wherein the functional additive comprises fluoroethylene carbonate (FEC), unsaturated phosphate esters, and siloxy compounds.

[0007] For silicon-based power batteries, due to the large volume expansion of silicon, the SEI (solid electrolyte interface) film of the silicon anode will rupture during cycling due to the continuous expansion of silicon, thus exposing a new interface. This disclosure can efficiently form an SEI film at the new interface by adding fluoroethylene carbonate to the electrolyte, thereby preventing other electrolyte components from being consumed on the silicon surface and improving the cycle performance of the battery.

[0008] Because fluoroethylene carbonate reacts with lithium salts at high temperatures to generate HF (hydrogen fluoride), which in turn damages the positive electrode interface, leading to an increase in positive electrode side reactions, consumption of active lithium, and cycle degradation; in response, this disclosure adds unsaturated phosphate to the electrolyte. Because its HOMO energy level (the energy level of the highest occupied molecular orbital) is much higher than that of the solvent molecules, it oxidizes on the positive electrode surface before the solvent molecules, forming a dense and robust CEI (positive electrode electrolyte interface) film, thereby preventing HF from damaging the positive electrode interface layer.

[0009] Since unsaturated phosphate esters form thicker films, they are prone to causing impedance growth. Therefore, this disclosure adds a siloxy compound to the electrolyte to react with lithium salt and slowly release lithium difluorophosphate. These lithium difluorophosphates compete with unsaturated anhydrides and work synergistically to form a thin and dense protective film, thereby reducing side reactions and balancing fast-charging performance.

[0010] In summary, this disclosure significantly improves the fast charging and cycle performance of power batteries by adding functional additives with specific components to the electrolyte, leveraging the synergistic effect between fluoroethylene carbonate, unsaturated phosphate esters, and siloxy compounds, which is beneficial for large-scale application.

[0011] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of the fluoroethylene carbonate is a%, where the value of a ranges from 1 to a ≤ 12.

[0012] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of the unsaturated phosphate ester is b%, where the value of b ranges from 0.01 to 0.5.

[0013] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of the siloxy compound is c%, where the value of c ranges from 0.01 to 1.

[0014] In some embodiments, the content relationship of the fluoroethylene carbonate, unsaturated phosphate ester and siloxy compound is: 2≤a / (b+c)≤22.

[0015] In some embodiments, the content relationship between the unsaturated phosphate ester and the siloxy compound is: 0.1 ≤ c / b ≤ 22.

[0016] In some embodiments, the chemical structural formula of the unsaturated phosphate ester is:

[0017] In the above formula, R1 and R2 are selected from substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C2-C4 alkenyl, substituted or unsubstituted C2-C4 alkynyl, respectively, and the substituents are selected from halogens.

[0018] In some embodiments, the siloxy compound is selected from any one or a combination of at least two of the following compounds:

[0019] In some embodiments, the lithium salt includes any one or a combination of at least two of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium bis(fluorosulfonyl)imide (LiTFSI), lithium tetrafluoroborate, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethylsulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, or lithium tri(trifluoromethylsulfonyl)methyl.

[0020] In some embodiments, the non-aqueous solvent includes any one or a combination of at least two of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), or ethyl propyl carbonate (EPC).

[0021] In some embodiments, the electrolyte further includes improved additives.

[0022] In some embodiments, the improved additives include oxalate phosphate type additives and / or low-resistance additives.

[0023] In some embodiments, the oxalate phosphate type additive includes lithium difluorodioxalate phosphate (LiDFOP) and / or lithium tetrafluorooxalate phosphate (LiTFOP).

[0024] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of the oxalate phosphate additive is d%, where the value of d ranges from 0.1 to 1.5.

[0025] In some embodiments, the low-impedance additive includes lithium difluorophosphate and / or vinyl sulfate (DTD).

[0026] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of the low impedance additive is e%, where the value of e ranges from 0.1 to e ≤ 3.

[0027] In a second aspect, this disclosure provides a method for preparing an electrolyte as described in the first aspect, the method comprising: adding a functional additive and a lithium salt to a non-aqueous solvent in a protective gas atmosphere, and mixing them evenly to obtain an electrolyte for a power battery.

[0028] The protective gas includes nitrogen and / or an inert gas.

[0029] Thirdly, this disclosure provides a power battery containing an electrolyte as described in the first aspect.

[0030] Fourthly, this disclosure provides a vehicle that includes a power battery as described in the third aspect.

[0031] The embodiments disclosed herein have the following beneficial effects:

[0032] (1) For silicon-based power batteries, due to the large volume expansion of silicon, the SEI film of the silicon anode will rupture during the cycle due to the continuous expansion of silicon, thus exposing a new interface. This disclosure can efficiently form an SEI film at the new interface by adding fluoroethylene carbonate to the electrolyte, thereby preventing other electrolyte components from being consumed on the silicon surface and improving the cycle performance of the battery.

[0033] (2) Because fluoroethylene carbonate reacts with lithium salt to generate HF at high temperature, which in turn damages the positive electrode interface, leading to an increase in positive electrode side reactions, consumption of active lithium, and cycle deterioration; In response, this disclosure adds unsaturated phosphate to the electrolyte. Because its HOMO energy level is much higher than that of the solvent molecules, it oxidizes on the positive electrode surface before the solvent molecules, forming a dense and robust CEI film, thereby preventing HF from damaging the positive electrode interface layer.

[0034] (3) Since unsaturated phosphate esters form thicker films, they are prone to impedance growth. Therefore, this invention adds siloxy compounds to the electrolyte to react with lithium salts and slowly release lithium difluorophosphate. These lithium difluorophosphates compete with unsaturated anhydrides to form a thin and dense protective film, thereby reducing side reactions and balancing fast charging performance. Detailed Implementation

[0035] The technical solutions of this disclosure will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of this disclosure and should not be construed as specific limitations thereof.

[0036] As people have higher demands for driving range, it is necessary to eliminate range anxiety associated with electric vehicles. Therefore, it is urgent to develop lithium-ion battery systems with higher energy density.

[0037] Among currently known anode materials, silicon has the highest theoretical capacity (4200 mAh / g), far exceeding the 372 mAh / g of graphite anodes. Silicon-doped silicon-carbon anode materials can achieve capacities of 400-650 mAh / g. Therefore, the application of silicon has received widespread attention in order to further improve the energy density of lithium-ion batteries.

[0038] However, due to the large volume expansion of silicon (up to 300%), the SEI film on the silicon anode ruptures during cycling due to the continuous expansion of silicon, exposing a new interface to reform the SEI film. This leads to continuous consumption of the electrolyte, eventually causing the electrolyte to dry out and rapidly reducing cycle life. Furthermore, silicon has relatively low electrical conductivity. Therefore, improving the fast charging and cycle performance of power batteries is a pressing technical challenge for the industry.

[0039] Some embodiments of this disclosure provide an electrolyte for a power battery, comprising a lithium salt, a non-aqueous solvent, and functional additives, wherein the functional additives include fluoroethylene carbonate, unsaturated phosphate esters, and siloxy compounds.

[0040] For silicon-based power batteries, due to the large volume expansion of silicon, the SEI film of the silicon anode will rupture during cycling due to the continuous expansion of silicon, thus exposing a new interface. This disclosure can efficiently form an SEI film at the new interface by adding fluoroethylene carbonate to the electrolyte, thereby preventing other electrolyte components from being consumed on the silicon surface and improving the cycle performance of the battery.

[0041] Because fluoroethylene carbonate reacts with lithium salts at high temperatures to generate HF, which in turn damages the cathode interface, leading to an increase in cathode side reactions, consumption of active lithium, and cycle degradation; in response, this disclosure adds unsaturated phosphate to the electrolyte. Because its HOMO energy level is much higher than that of solvent molecules, it oxidizes on the cathode surface before solvent molecules, forming a dense and robust CEI film, thereby preventing HF from damaging the cathode interface layer.

[0042] Since unsaturated phosphate esters form thicker films, they are prone to causing impedance growth. Therefore, this disclosure adds a siloxy compound to the electrolyte to react with lithium salt and slowly release lithium difluorophosphate. These lithium difluorophosphates compete with unsaturated anhydrides and work synergistically to form a thin and dense protective film, thereby reducing side reactions and balancing fast-charging performance.

[0043] In summary, this disclosure significantly improves the fast charging and cycle performance of power batteries by adding functional additives with specific components to the electrolyte, leveraging the synergistic effect between fluoroethylene carbonate, unsaturated phosphate esters, and siloxy compounds, which is beneficial for large-scale application.

[0044] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of the fluoroethylene carbonate is a%, where the value of a ranges from 1 to a to 12. For example, a can be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] In this disclosure, fluoroethylene carbonate, as a film-forming additive, can form a stable SEI film on the surface of a silicon anode, thereby reducing electrolyte decomposition and consumption. Because it reacts with lithium salts at high temperatures to generate HF, its content range needs to be strictly limited. If the content is too low, a protective film cannot be effectively formed; if the content is too high, it will damage the positive electrode interface.

[0046] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of the unsaturated phosphate ester is b%, where the value of b ranges from 0.01 to 0.5. For example, b can be 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, or 0.5, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0047] This disclosure avoids excessively high battery impedance while forming a CEI film by precisely controlling the content range of unsaturated phosphate esters. When the content is too low, a dense and robust CEI film cannot be formed to prevent HF from damaging the positive electrode interface layer; when the content is too high, the CEI film becomes too thick, resulting in excessively high battery impedance.

[0048] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of the siloxy compound is c%, where the value of c ranges from 0.01 to 1. For example, c can be 0.01, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] This disclosure optimizes the competitive synergistic effect between lithium difluorophosphate and unsaturated anhydride by precisely controlling the content range of siloxy compounds, thereby controlling costs while ensuring battery performance and achieving a balance between battery performance and economy.

[0050] In some embodiments, the content relationship of the fluoroethylene carbonate, unsaturated phosphate and siloxy compound is: 2≤a / (b+c)≤22, for example, a / (b+c)=2, 4, 6, 8, 10, 12, 14, 16, 18, 20 or 22, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0051] This disclosure optimizes the synergistic effect among the three additives by precisely controlling the content ratio of fluoroethylene carbonate, unsaturated phosphate, and siloxy compounds, thereby achieving optimal electrochemical performance. When the ratio is too high, the unsaturated phosphate and siloxy compounds provide insufficient protection for the interface, while fluoroethylene carbonate generates a high content of HF, resulting in an unstable positive electrode interface and side reactions in the electrolyte at the positive electrode interface, leading to poor high-temperature cycling performance. When the ratio is too low, i.e., the content of fluoroethylene carbonate is too low, there is insufficient protection for the silicon negative electrode interface, resulting in poor high-temperature cycling performance.

[0052] In some embodiments, the content relationship between the unsaturated phosphate ester and the siloxy compound is: 0.1 ≤ c / b ≤ 22, for example, c / b can be 0.1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20 or 22, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0053] This disclosure achieves a balance between CEI film stability and battery impedance control by precisely controlling the content ratio of unsaturated phosphate esters and silicon oxide compounds, thereby contributing to further improvements in battery fast-charging performance and cycle stability. When the ratio is too high, the content of unsaturated phosphate esters is much greater than that of silicon oxide compounds, leading to phosphate esters dominating the competition and forming a high-resistance interface film, resulting in excessively high battery impedance. When the ratio is too low, silicon oxide compounds dominate, resulting in an insufficiently dense protective film and deteriorating cycle performance.

[0054] In some embodiments, the chemical structural formula of the unsaturated phosphate ester is:

[0055] In the above formula, R1 and R2 are selected from substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C2-C4 alkenyl, substituted or unsubstituted C2-C4 alkynyl, respectively, and the substituents are selected from halogens.

[0056] Specifically, the unsaturated phosphate esters used in some embodiments are selected from any one or a combination of at least two of the following compounds:

[0057] In some embodiments, the siloxy compound is selected from any one or a combination of at least two of the following compounds:

[0058] In some embodiments, the lithium salt comprises any one or a combination of at least two of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethanesulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, or lithium tri(trifluoromethanesulfonyl)methyl. Typical but non-limiting combinations include combinations of lithium hexafluorophosphate and lithium difluorophosphate, and combinations of lithium difluorophosphate and lithium difluorooxalate borate. Combinations of lithium difluorooxalate borate and lithium difluorosulfonyl imide, combinations of lithium difluorosulfonyl imide and lithium tetrafluoroborate, combinations of lithium tetrafluoroborate and lithium dioxalate borate, combinations of lithium dioxalate borate and lithium hexafluoroantimonyate, combinations of lithium hexafluoroantimonyate and lithium hexafluoroarsenate, combinations of lithium hexafluoroarsenate and lithium di(trifluoromethanesulfonyl)imide, combinations of lithium di(trifluoromethanesulfonyl)imide and lithium di(pentafluoroethylsulfonyl)imide, or combinations of lithium di(pentafluoroethylsulfonyl)imide and lithium tri(trifluoromethanesulfonyl)methyl.

[0059] In some embodiments, the non-aqueous solvent includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, or ethyl propyl carbonate. Typical but non-limiting combinations include combinations of ethylene carbonate and propylene carbonate, combinations of propylene carbonate and methyl ethyl carbonate, combinations of methyl ethyl carbonate and diethyl carbonate, combinations of diethyl carbonate and dimethyl carbonate, combinations of dimethyl carbonate and dipropyl carbonate, combinations of dipropyl carbonate and methyl propyl carbonate, or combinations of methyl propyl carbonate and ethyl propyl carbonate.

[0060] In some embodiments, the electrolyte further includes improved additives.

[0061] In some embodiments, the improved additives include oxalate phosphate type additives and / or low-resistance additives.

[0062] In some embodiments, the oxalate phosphate type additive includes lithium difluorodioxalate phosphate and / or lithium tetrafluorooxalate phosphate.

[0063] In this disclosure, the oxalate phosphate type additive can react at both the positive and negative electrodes, further enhancing interfacial stability and thus significantly improving the high-temperature cycle performance of the battery.

[0064] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of the oxalate phosphate additive is d%, where the value of d ranges from 0.1 to 1.5. For example, d can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4 or 1.5, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0065] In some embodiments, the low-impedance additive includes lithium difluorophosphate and / or vinyl sulfate.

[0066] In this disclosure, the low-impedance additive can form a low-impedance stable interface film at the positive electrode interface, which not only reduces positive electrode polarization, but also prevents side reactions of the electrolyte at the positive electrode interface, thereby significantly improving battery impedance and high-temperature cycle performance.

[0067] In some embodiments, the total mass of the electrolyte is used as the calculation basis, and the content of the low-resistance additive is e%, where the value of e is in the range of 0.1≤e≤3, for example, e can be 0.1, 0.5, 1, 1.5, 2, 2.5 or 3, but is not limited to the listed values, and other unlisted values ​​within this range are also applicable.

[0068] Some embodiments of this disclosure provide a method for preparing the above-mentioned electrolyte, comprising: adding functional additives and lithium salts to a non-aqueous solvent in a protective gas atmosphere, and mixing them evenly to obtain an electrolyte for a power battery.

[0069] The protective gas includes nitrogen and / or an inert gas.

[0070] Some embodiments of this disclosure provide a power battery containing the above-described electrolyte.

[0071] In some embodiments, the power battery includes a positive electrode, a negative electrode, a separator, and the electrolyte described above.

[0072] In some embodiments, the positive electrode includes a positive current collector and a positive active material layer on its surface, the positive active material layer including a positive active material and a conductive agent.

[0073] In some embodiments, the negative electrode includes a negative electrode current collector and a layer of negative electrode active material on its surface.

[0074] Some embodiments of this disclosure provide a vehicle that includes the aforementioned power battery.

[0075] The numerical range described in this disclosure includes not only the point values ​​listed above, but also any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of brevity, this disclosure will not exhaustively list the specific point values ​​included in the range.

[0076] Examples 1-8

[0077] This set of embodiments provides an electrolyte for a power battery and its preparation method. The specific preparation method includes: mixing EC, PC and EMC in an argon atmosphere at a volume ratio of 15:15:70 to obtain an anhydrous solvent; then adding FEC, unsaturated phosphate ester and siloxy compound to the anhydrous solvent according to the conditions in Table 1 below, followed by adding LiPF6, and using the total mass of the electrolyte as the calculation basis, the content of LiPF6 is 12.5%.

[0078] Table 1

[0079] The chemical structural formulas of compounds 1-8 and compound AC in Table 1 above are shown in Table 2 below.

[0080] Table 2

[0081] Examples 9-23

[0082] This set of embodiments provides an electrolyte for a power battery and its preparation method. The specific preparation method includes: mixing EC, PC and EMC in an argon atmosphere at a volume ratio of 15:15:70 to obtain an anhydrous solvent; then adding FEC, unsaturated phosphate ester and siloxy compound to the anhydrous solvent according to the conditions of Example 1 in Table 1 above; then adding oxalate phosphate type additive and / or low impedance additive according to the conditions in Table 3 below; finally adding LiPF6, and using the total mass of the electrolyte as the calculation basis, the content of LiPF6 is 12.5%.

[0083] Table 3

[0084] Examples 24-29

[0085] This set of embodiments provides an electrolyte for a power battery and its preparation method. The specific preparation method includes: mixing EC, PC and EMC in an argon atmosphere at a volume ratio of 15:15:70 to obtain an anhydrous solvent; then adding FEC, unsaturated phosphate ester and siloxy compound to the anhydrous solvent according to the conditions in Table 4 below, followed by adding LiPF6, and using the total mass of the electrolyte as the calculation basis, the content of LiPF6 is 12.5%.

[0086] Table 4

[0087] Comparative Examples 1-3

[0088] This group provides an electrolyte and its preparation method, respectively. The specific preparation method includes: mixing EC, PC and EMC in an argon atmosphere at a volume ratio of 15:15:70 to obtain an anhydrous solvent; then adding one or two of FEC, unsaturated phosphate ester or siloxy compound to the anhydrous solvent according to the conditions in Table 5 below, followed by adding LiPF6, and using the total mass of the electrolyte as the calculation basis, the content of LiPF6 is 12.5%.

[0089] Table 5

[0090] Silicon-based power batteries were prepared using the electrolytes obtained in Examples 1-29 and Comparative Examples 1-3, respectively, and the specific steps included:

[0091] (1) Cathode preparation: LiNi 0.8 Co 0.1 Mn 0.1 (NCM811), conductive carbon (SP), carbon nanotubes (CNTs) and polyvinylidene fluoride (PVDF) were mixed in N-methylpyrrolidone solvent at a mass ratio of 96:1:0.5:2.5 and stirred evenly to obtain a positive electrode slurry. Aluminum foil was used as the positive electrode current collector, and the positive electrode current collector coated with the positive electrode slurry was baked at 120°C for 1 hour. Then, it was cold-pressed, cut into sheets and slit to obtain the positive electrode.

[0092] (2) Anode preparation: Artificial graphite and SiO (mass ratio of 95:5), conductive carbon, single-walled carbon nanotubes, sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA) and styrene-butadiene rubber (SBR) are mixed in deionized water at a mass ratio of 96.05:1.2:0.05:0.3:1.7:0.7 and stirred evenly to obtain anode slurry; copper foil is used as anode current collector, and the anode current collector coated with anode slurry is baked at 120°C for 1 hour, and then cold-pressed, cut and slit in sequence to obtain anode.

[0093] (3) Preparation of the isolation membrane: A polyethylene film with a thickness of 7 μm is used as the isolation membrane, and a boehmite ceramic layer with a thickness of 2 μm is coated on its surface.

[0094] (4) Battery assembly: The positive electrode, separator and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrodes to play a role in isolation. The side coated with boehm ceramic layer is aligned with the positive electrode. Then the cells are stacked and placed in an aluminum-plastic film. After drying at 80°C, the obtained electrolyte is injected. The cells are then processed through vacuum sealing, settling, formation and shaping to complete the preparation of the silicon system power battery.

[0095] Performance testing

[0096] (1) Fast charging performance evaluation: The power batteries corresponding to the electrolytes obtained in the above examples and comparative examples were placed in a 55°C constant temperature chamber and left to stand for 30 minutes. They were charged to 4.25V at a constant charging rate of 2C, then charged at a constant voltage to a charging rate of 0.05C, left to stand for 5 minutes, and then discharged at a constant discharge rate of 1C to 3.0V. The following steps were repeated 200 times: The power batteries corresponding to the electrolytes obtained in the above examples and comparative examples were placed in a 25°C constant temperature chamber and left to stand for 30 minutes. They were charged to 4.25V at a constant charging rate of 1 / 3C, then charged at a constant voltage to a charging rate of 0.05C, left to stand for 10 minutes, then discharged at a constant discharge rate of 1 / 3C for 1.5 hours, left to stand for 60 minutes. The voltage at the end of the standing period was recorded as voltage V1. The 4C constant current discharge was recorded for 10 seconds (the sampling time interval was 0.1 seconds). The end current was recorded as I, and the end voltage was recorded as V2. The DCR was calculated as (V1-V2) / I.

[0097] (2) High-temperature cycling test: The power batteries corresponding to the electrolytes obtained in the above examples and comparative examples were placed in a 55°C constant temperature chamber and left to stand for 30 minutes. They were then charged at a constant charging rate of 2C to 4.25V, and then charged at a constant voltage to a charging rate of 0.05C. After standing for 5 minutes, they were discharged at a constant discharge rate of 1.0C to 3.0V, and the capacity was recorded as D0. Cyclic tests were performed according to the following steps:

[0098] (2.1) Let stand for 5 minutes;

[0099] (2.2) Charge at a constant charging rate of 1C to 4.25V, and then charge at a constant voltage to a charging rate of 0.05C;

[0100] (2.3) Let stand for 5 minutes;

[0101] (2.4) Discharge to 3.0V at a constant discharge rate of 1C;

[0102] (2.5) Repeat steps (2.1) to (2.4) 600 times, with a recording capacity of D1.

[0103] Calculate the cycle capacity retention rate (%) of the power battery = (D1-D0) / D0×100%.

[0104] The fast charging performance and high-temperature cycling test results of the electrolytes obtained in Examples 1-29 and Comparative Examples 1-3 are shown in Table 6 below.

[0105] Table 6

[0106] As shown in Table 5:

[0107] (1) In Examples 1-8, FEC, unsaturated phosphate esters and siloxy compounds were added to the electrolyte as functional additives, and the fast charging performance and high temperature cycling performance of the resulting power batteries remained at a high level.

[0108] (2) Based on Example 1, Examples 9-12 added oxalate phosphate type additives to the electrolyte, Examples 13-16 added low impedance additives to the electrolyte, and Examples 17-23 added both oxalate phosphate type additives and low impedance additives to the electrolyte. The fast charging performance and high-temperature cycle performance of the resulting power batteries were further improved. This is because: the oxalate phosphate type additive can react at the positive and negative electrodes, further improving the interface stability, thereby significantly improving the high-temperature cycle performance of the battery; the low impedance additive can form a low impedance stable interface film at the positive electrode interface, which not only reduces positive electrode polarization, but also prevents side reactions of the electrolyte at the positive electrode interface, thereby significantly improving the battery impedance and high-temperature cycle performance; at the same time, the addition of oxalate phosphate type additives and low impedance additives can significantly improve the high-temperature cycle performance and impedance performance. The two work together at the positive electrode interface to strengthen the protection of the positive electrode interface. As the content of oxalate phosphate and low impedance additives continues to increase, the improvement effect is suppressed to a certain extent.

[0109] (3) Based on Example 1, Examples 24-29 respectively adjusted the contents of FEC, unsaturated phosphate ester and siloxy compound to outside the specified range, which ultimately led to different degrees of adverse effects on the fast charging performance and high temperature cycling performance of the power battery.

[0110] (4) Based on Example 1, no unsaturated phosphate ester was added in Comparative Example 1, no silicon oxy compound was added in Comparative Example 2, and no FEC was added in Comparative Example 3. Ultimately, all of these resulted in significant adverse effects on the fast charging performance and high-temperature cycling performance of the power battery.

[0111] Therefore, this disclosure demonstrates that by adding functional additives with specific components to the electrolyte, and by leveraging the synergistic effect between fluoroethylene carbonate, unsaturated phosphate esters, and siloxy compounds, the fast charging and cycle performance of power batteries is significantly improved, which is conducive to large-scale promotion and application.

[0112] The applicant declares that the above description is only a specific implementation of this disclosure, but the protection scope of this disclosure is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this disclosure fall within the protection and disclosure scope of this disclosure.

Claims

1. An electrolyte for a power battery, comprising a lithium salt, a non-aqueous solvent, and a functional additive, wherein the functional additive comprises fluoroethylene carbonate, unsaturated phosphate, and a siloxy compound.

2. The electrolyte according to claim 1, wherein, Using the total mass of the electrolyte as the calculation basis, the content of the fluoroethylene carbonate is a%, where the value of a ranges from 1 to a ≤ 12; and / or Using the total mass of the electrolyte as the calculation basis, the content of the unsaturated phosphate ester is b%, where the value of b ranges from 0.01 to 0.5; and / or The total mass of the electrolyte is used as the calculation basis, and the content of the siloxy compound is c%, where the value of c ranges from 0.01 to 1.

3. The electrolyte according to claim 2, wherein, The content relationship of the fluoroethylene carbonate, the unsaturated phosphate ester, and the siloxy compound is: 2 ≤ a / (b+c) ≤ 22; and / or The content relationship between the unsaturated phosphate ester and the siloxy compound is: 0.1≤c / b≤22.

4. The electrolyte according to any one of claims 1-3, wherein, The chemical structural formula of the unsaturated phosphate ester is: In the above formula, R1 and R2 are selected from substituted or unsubstituted C1-C4 alkyl, substituted or unsubstituted C2-C4 alkenyl, substituted or unsubstituted C2-C4 alkynyl, respectively, and the substituents are selected from halogens.

5. The electrolyte according to any one of claims 1-4, wherein, The siloxy compound is selected from any one or a combination of at least two of the following compounds:

6. The electrolyte according to any one of claims 1-5, wherein, The lithium salt comprises any one or a combination of at least two of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium bis(oxalate borate), lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(trifluoromethanesulfonyl)imide, lithium di(pentafluoroethylsulfonyl)imide, or lithium tri(trifluoromethanesulfonyl)methyl; and / or The non-aqueous solvent includes any one or a combination of at least two of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, or ethyl propyl carbonate.

7. The electrolyte according to any one of claims 1-6, wherein, The electrolyte also includes improved additives; The improved additives include oxalate phosphate type additives and / or low impedance additives.

8. The electrolyte according to claim 7, wherein, The oxalate phosphate type additive includes lithium difluorodioxalate phosphate and / or lithium tetrafluorooxalate phosphate; and / or The total mass of the electrolyte is used as the calculation basis, and the content of the oxalate phosphate additive is d%, where the value of d ranges from 0.1 to 1.

5.

9. The electrolyte according to claim 7 or 8, wherein, The low-resistance additive includes lithium difluorophosphate and / or vinyl sulfate; and / or The total mass of the electrolyte is used as the calculation basis, and the content of the low impedance additive is e%, where the value of e ranges from 0.1 to e ≤ 3.

10. A method for preparing the electrolyte according to any one of claims 1-9, the method comprising: In a protective gas atmosphere, functional additives and lithium salts are added to a non-aqueous solvent and mixed evenly to obtain the electrolyte for the power battery. The protective gas includes nitrogen and / or an inert gas.

11. A power battery, the power battery comprising the electrolyte as described in any one of claims 1-9.

12. A vehicle comprising the power battery as claimed in claim 11.

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