Electrolyte and battery containing the same

Abstract

The application provides an electrolyte and a battery containing the same, the electrolyte comprising a lithium salt, an organic solvent, a film-forming additive and a functional additive; the film-forming additive comprises fluoroethylene carbonate and vinylene carbonate; the mass proportion of the film-forming additive in the electrolyte is 9-16%; the functional additive comprises at least four of succinic anhydride, lithium difluorophosphate, tripropargyl phosphate, 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate and 1,3-propane sulfonic acid lactone; the mass proportion of the functional additive in the electrolyte is 0.5-3.8%; and the organic solvent does not contain vinyl carbonate. The electrolyte has high thermal stability, can effectively reduce the gas production of the battery at high temperature, further optimizes the cycle performance of the battery, makes the battery still have high capacity retention rate and capacity recovery rate after being stored at high temperature (60 DEG C) for a certain time, and has high cycle capacity retention rate at 25-40 DEG C.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to an electrolyte and a battery containing the same. BACKGROUND

[0002] The electrolyte of a lithium battery is a core component of a lithium ion battery, and is usually configured by an electrolyte lithium salt, a high-purity organic solvent and an electrolyte additive in a specific proportion under certain conditions, and serves as a medium for ion transmission and charge transfer to conduct lithium ions between the positive and negative electrodes. The electrolyte is a key to keeping the lithium battery with good performances such as high voltage level, high safety and high energy density.

[0003] Functional additives are the most economical and efficient method to improve the performance of batteries. By screening and proportioning a small amount of additives, the performance of the electrolyte can be greatly improved. In recent years, the electrolyte of a lithium ion battery has been the core direction of research. According to the mechanism, the additives can be divided into film-forming additives, high-voltage protection additives, low-temperature additives, safety additives (including flame-retardant additives and overcharge prevention additives). These additives can help the battery to achieve high energy density, long cycle life, high rate performance, wide temperature range and high safety, which is also the focus of the current market.

[0004] Among them, the safety performance of lithium ion batteries is paid more and more attention, and seeking additives to improve the safety performance of lithium ion batteries has become our primary task. When it comes to safety performance, the gas production problem in lithium batteries is a key factor affecting the safety performance of lithium batteries, and the gas production problem will also seriously affect the cycle performance of the battery. Gas production is one of the main side reactions in the process of lithium ion battery formation, high-temperature storage, cycling and repeated charging and discharging. Moreover, for high-nickel / high-silicon systems, the gas production problem is more serious, which further deteriorates the cycle life of high-nickel / high-silicon systems. Related technologies report that the gas produced at the electrode / electrolyte interface interferes between the negative and positive electrodes, leading to complex local reactions with other gas species, causing more side reactions at the interface. At the same time, relevant research has also found that the production and consumption of gas will lead to material surface degradation and an increase in negative electrode interfacial resistance, which will adversely affect the high-temperature storage and long-term cycling of the battery.

[0005] And in the battery cycle process, the electrolyte is also one of the main factors affecting the battery gas production performance. In the cycle process of the battery, with the change of the positive and negative electrode voltage, the electrolyte will tend to be oxidized / reduced on the surface of the highly delithiated positive electrode / fully lithiated negative electrode, resulting in gas production. Secondly, in the cycle process of the battery, the temperature inside the battery rises, or in the process of high temperature use, the crystal structure of the delithiated positive electrode material will change in a series of processes under the action of high temperature, and a part of high activity oxygen will be released in the process, and the active oxygen will oxidize the electrolyte to produce a large amount of gas. Therefore, how to develop an electrolyte with higher stability to reduce battery gas production, optimize battery safety performance and cycle performance has become one of the research focuses in the field of lithium batteries.

[0006] At present, by adding functional additives to the electrolyte, the stability of the electrolyte is further improved, and the battery performance is optimized, which has become the key research direction of the electrolyte. The research of lithium ion battery electrolyte functional additives mainly focuses on the following aspects: improving the stability of SEI film, improving the conductivity of electrolyte, improving the safety performance of battery(reducing gas production, etc.). But in the current electrolyte formula, there is usually only one or two kinds of electrolyte additives, so the performance improvement is often limited. With the increasing demand for lithium battery performance, developing an electrolyte formula with more excellent performance is an urgent problem to be solved. SUMMARY

[0007] In order to solve the problems and deficiencies in the prior art, the present application provides an electrolyte and a battery containing the same. The electrolyte has high thermal stability, can effectively reduce the gas production of the battery at high temperature, further optimize the cycle performance of the battery, make the battery still have high capacity retention rate and capacity recovery rate after storing for a certain time at high temperature(60℃), and have high cycle capacity retention rate at 25-40℃.

[0008] According to a first aspect of the present application, an electrolyte is provided, comprising a lithium salt, an organic solvent, a film-forming additive, and a functional additive; the film-forming additive comprises fluoroethylene carbonate and vinylene carbonate; the mass fraction of the film-forming additive in the electrolyte is 9-16%; the functional additive comprises at least four of succinic anhydride, lithium difluorophosphate, tripropargyl phosphate, 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate, and 1,3-propane sulfone lactone; the mass fraction of the functional additive in the electrolyte is 0.5-3.8%; and the organic solvent does not contain vinyl carbonate. The mass fraction of the film-forming additive in the electrolyte may, for example, be 9%, 10%, 11%, 12%, 13%, 14%, 15%, or 16%; the mass fraction of the functional additive in the electrolyte may, for example, be 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, or 3.8%; and the above mass fractions are not limited to the listed values, and other values within the range are also applicable.

[0009] By using a certain proportion of film-forming additives and functional additives, the present application can form relatively stable SEI films (on the negative electrode side) and CEI films (on the positive electrode side), while inhibiting the oxidation-reduction reaction of the electrolyte on the positive and negative electrodes, effectively reducing battery gas production, battery ACR (alternating current resistance), DCR (direct current resistance), and Rct (interface impedance), and greatly improving high-temperature storage and cycle performance, especially for improving the high-temperature storage and cycle performance of high-nickel / high-silicon systems.

[0010] Specifically, fluoroethylene carbonate and vinylene carbonate are used as film-forming additives, and the use of these two additives can more effectively form stable negative SEI films and positive CEI films, improve the stability of the battery interface, and prevent internal short circuits.

[0011] Among the functional additives, succinic anhydride (SA) and lithium difluorophosphate (LiPO2F2) can reduce the battery ACR, and lithium difluorophosphate (LiPO2F2) is a lithium, phosphorus and fluorine containing additive, which can also effectively reduce the battery Rct and DCR. The battery performance is more related to the impedance (or resistance), so it is beneficial to improve the high-temperature storage and cycle performance. Tripropargyl phosphate (TPP) and 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate (DTD) can inhibit the battery gas production and reduce the battery ACR. At the same time, TPP is a new type of additive with the highest unsaturation, which is beneficial to improve the normal temperature, high-temperature cycle performance and high-temperature storage performance. Therefore, the above-mentioned SA, LiPO2F2, TPP, DTD and PS five kinds of functional additives can improve the electrolyte gas production, cycle performance and high-temperature storage performance. When at least four of the above-mentioned five kinds of additives are used together, not only can the stability of the negative electrode SEI film and the positive electrode CEI be further promoted, the gas production can be significantly inhibited, but also the battery ACR, DCR and Rct can be effectively reduced. Therefore, the electrolyte provided by the application can significantly improve the high-temperature storage and cycle performance of the battery. Specifically, at least four of the above-mentioned five kinds of additives are selected, and these additives participate in the chemical reactions of each other during the battery cycle process. On this basis, the matching of these additives can effectively reduce the side reactions during the battery cycle process, thereby improving the stability of the positive and negative electrode CEI and SEI film, reducing the gas production, reducing the battery ACR, DCR and Rct, and optimizing the battery cycle performance.

[0012] It should be further pointed out that in the electrolyte provided by the application, the content of the film-forming additive and the functional additive needs to be controlled within a certain range. Too much film-forming additive or functional additive will increase the interface impedance Rct. Too little film-forming additive is not conducive to film formation, which reduces the stability of the interface film. Too little functional additive cannot effectively inhibit the gas production, so it cannot effectively reduce the battery ACR, DCR and Rct, etc. The poor gas production inhibition effect is also not conducive to the stable lithium intercalation and deintercalation reaction of the battery, so it will cause the capacity stability to be poor and the battery cycle performance to be poor.

[0013] In addition, in the electrolyte provided by the present application, the organic solvent used is free of ethylene carbonate (EC), which can further effectively inhibit the interface side reaction of the electrolyte, reduce gas production, improve the stability of the positive and negative CEI, SEI films, and further improve the cycle stability of the positive and negative electrodes, especially in the high-nickel / high-silicon system, which is more obvious. This is because EC is less stable in the electrolyte, especially at high voltage, which produces more gas and is more unstable. Specifically, first, although the oxidation potential of the EC molecule is high, due to the catalysis of highly oxidized transition metal (TM) ions, especially nickel, the EC molecule is dehydrogenated on the surface of the layered oxide positive electrode at a lower potential. This process not only leads to the production of protons, but can further induce the decomposition of lithium salts such as lithium hexafluorophosphate to form hydrofluoric acid (HF), and also leads to the formation of spinel-like and rock salt-like phases at the positive electrode / electrolyte interface (CEI). In addition, the generated transition metal ions and HF can cross-influence the performance of the negative electrode such as graphite negative electrode. Second, the EC molecule is also prone to react with the oxygen released by the high-nickel positive electrode at high temperature, leading to catastrophic heat release and eventual safety hazards. In high-nickel positive electrodes, this problem is more serious because they tend to release more oxygen at low temperatures compared to low-nickel positive electrodes.

[0014] Preferably, the mass ratio of fluoroethylene carbonate to vinylene carbonate in the film-forming additive is 5.8-6.5:1. For example, it can be 5.8:1, 6.0:1, 6.2:1, 6.4:1, 6.5:1, but is not limited to the listed values, and other values not listed in the value range are also applicable. Controlling the mass ratio of fluoroethylene carbonate to vinylene carbonate within the above range makes the negative electrode film and the positive electrode film more uniform and stable, thus more conducive to the stable lithium intercalation and deintercalation reactions of lithium ions, ensuring the capacity stability and cycle performance of the battery, especially the high-temperature cycle performance and high-temperature storage stability.

[0015] Preferably, the functional additive includes succinic anhydride, lithium difluorophosphate, tripropargyl phosphate, 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate, and 1,3-propane sulfone lactone. When the functional additive simultaneously contains the above 5 functional additives, it is more conducive to the high-temperature cycle performance and high-temperature storage performance of the electrolyte, and there is a more obvious synergistic effect when the 5 additives are used together, thus further optimizing the performance of the electrolyte.

[0016] Preferably, the mass ratio of succinic anhydride, lithium difluorophosphate, tripropargyl phosphate, 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate, 1,3-propane sultone is 0.2-0.4:0.5-0.9:0.55-0.85:0.6-1.0:0.15-0.30. For example, it can be 0.2:0.9:0.55:0.8:0.20, 0.3:0.75:0.70:0.75:0.25, 0.4:0.6:0.85:0.6:0.30, 0.3:0.5:0.65:0.75:0.25, 0.3:0.7:0.65:0.8:0.25, but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0017] Preferably, the mass ratio of succinic anhydride, lithium difluorophosphate, tripropargyl phosphate, 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate, 1,3-propane sultone is 0.3:0.7:0.65:0.8:0.25.

[0018] Preferably, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium tetrafluoroborate, lithium difluoro(oxalato)borate, lithium bistrifluoromethanesulfonylimide.

[0019] Preferably, the mass fraction of the lithium salt in the electrolyte is 9.5-14%. For example, it can be 9.5%, 10.0%, 11%, 12%, 13%, 14%, but is not limited to the listed values, and other values not listed within the value range are also applicable. If the lithium salt content is too low, it is not conducive to the power density, energy density, etc. of the battery; if the lithium salt content is too high, it can cause the electrolyte viscosity to be too high, the ionic conductivity to decrease, and the interfacial impedance to increase, which is not conducive to fast charging and cycle stability.

[0020] Preferably, the mass fraction of the organic solvent in the electrolyte is 57-78%; the organic solvent includes cyclic carbonate and linear carbonate; the mass ratio of the cyclic carbonate to the linear carbonate is 17-28:40-50. For example, the mass fraction of the organic solvent in the electrolyte can be 57%, 60%, 63%, 66%, 70%, 73%, 78%; the mass ratio of the cyclic carbonate to the linear carbonate can be 22:45, 17:50, 28:40; the above mass fraction or mass ratio is not limited to the listed values, and other values not listed within the value range are also applicable.

[0021] Preferably, the cyclic carbonate includes propylene carbonate; the linear carbonate includes at least one of methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, propyl propionate and ethyl propionate.

[0022] According to a second aspect of the present application, a battery is provided, characterized in that it comprises the electrolyte as described above.

[0023] Preferably, the battery further comprises a positive electrode sheet and a negative electrode sheet; the positive electrode active material in the positive electrode sheet comprises a ternary material; the negative electrode active material in the negative electrode sheet comprises a silicon-based material.

[0024] Preferably, in the silicon-based material, the mass fraction of silicon in the silicon-based material is 5-30%. For example, it can be 5%, 10%, 15%, 20%, 25%, or 30%, but is not limited to the listed values, and other values not listed within the value range are also applicable.

[0025] Preferably, the ternary material is a high-nickel ternary material; in the high-nickel ternary material, the molar content of nickel element in nickel-cobalt-manganese is not less than 80%. For example, it can be 80%, 85%, 90%, or 95%, but is not limited to the listed values, and other values not listed within the value range are also applicable. DETAILED DESCRIPTION

[0026] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, not all.

[0027] Embodiment 1

[0028] 1. Composition of the electrolyte

[0029] The electrolyte in this embodiment includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sulfonic acid lactone (PS), and the mass ratio of LiFP6, PC, DMC, FEC, VC, SA, LiPO2F2, TPP, DTD, and PS is 12.3:25:47:11.2:1.8:0.3:0.7:0.65:0.8:0.25.

[0030] 2. Preparation of the battery

[0031] The battery used in this embodiment is a soft package battery with a rating of 3.3 Ah, which is assembled into an electric core by a positive plate, a separator, and a negative plate, and then the electric core is transferred into a shell, followed by injecting the electrolyte in this embodiment, forming, and constant volume to obtain the battery of this embodiment.

[0032] In the positive plate in this embodiment, the positive active material is ternary material NCM811, and the positive formula is (mass ratio): ternary material NCM811: binder polyvinylidene fluoride (PVDF): conductive agent carbon black (SP) = 97:1.6:1.4; the positive current collector is an aluminum foil of 12 μm.

[0033] In the negative plate of this embodiment, the negative active material is a silicon-carbon material (with a silicon mass fraction of 10%), and the negative formula is (mass ratio): silicon-carbon material: water-based binder PAA (polyacrylic acid): conductive agent carbon nanotube = 96:3:1; wherein the solid content of the water-based binder is 39.4%, and the negative current collector is a copper foil of 6 μm.

[0034] And the separator of this embodiment adopts a 12 μm ceramic coated PE separator.

[0035] Example 2

[0036] 1. Composition of electrolyte

[0037] The electrolyte in this embodiment includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sulfonic acid lactone (PS), and the mass ratio of LiFP6, PC, DMC, FEC, VC, SA, LiPO2F2, TPP, DTD, and PS is 12.3:25:47:11.2:1.8:0.2:0.9:0.8:0.65:0.15.

[0038] 2. Preparation of battery

[0039] The preparation of the battery in this embodiment is consistent with that of Example 1.

[0040] Example 3

[0041] 1. Composition of electrolyte

[0042] The electrolyte in this example includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sulfone lactone (PS), and the mass ratio of LiFP6, PC, DMC, FEC, VC, SA, LiPO2F2, TPP, DTD, and PS is 12.3:25:47:11.2:1.8:0.4:0.5:0.55:0.95:0.3.

[0043] 2. Preparation of the battery

[0044] The preparation of the battery in this example is identical to that of Example 1.

[0045] Example 4

[0046] 1. Composition of the electrolyte

[0047] The electrolyte in this example includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sulfone lactone (PS), and the mass ratio of LiFP6, PC, DMC, FEC, VC, LiPO2F2, TPP, DTD, and PS is 12.3:25:47:11.2:1.8:0.788:0.731:0.900:0.281.

[0048] 2. Preparation of the battery

[0049] The preparation of the battery in this example is identical to that of Example 1.

[0050] Example 5

[0051] 1. Composition of the electrolyte

[0052] The electrolyte in this example includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), tripropargyl phosphate (TPP), 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sulfone lactone (PS), and the mass ratio of LiFP6, PC, DMC, FEC, VC, SA, TPP, DTD, and PS is 12.3:25:47:11.2:1.8:0.405:0.878:1.08:0.337.

[0053] 2. Preparation of the battery

[0054] The preparation of the battery in this example is consistent with that of Example 1.

[0055] Example 6

[0056] 1. Composition of the electrolyte

[0057] The electrolyte in this example includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sulfone lactone (PS), and the mass ratio of LiFP6, PC, DMC, FEC, VC, SA, LiPO2F2, DTD, and PS is 12.3:25:47:11.2:1.8:0.395:0.922:1.054:0.329.

[0058] 2. Preparation of the battery

[0059] The preparation of the battery in this example is consistent with that of Example 1.

[0060] Example 7

[0061] 1. Composition of the electrolyte

[0062] The electrolyte in this example includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), 1,3-propane sulfone lactone (PS), and the mass ratio of LiFP6, PC, DMC, FEC, VC, SA, LiPO2F2, TPP, and PS is 12.3:25:47:11.2:1.8:0.426:0.995:0.924:0.355.

[0063] 2. Preparation of the battery

[0064] The preparation of the battery in this example is identical to that of Example 1.

[0065] Example 8

[0066] 1. Composition of the electrolyte

[0067] The electrolyte in this example includes lithium hexafluorophosphate (LiFP6), lithium bisfluorosulfonylimide (LiFSI), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sulfone (PS), LiFP6, LiFSI, PC, EMC, DEC, FEC, VC, SA, LiPO2F2, TPP, DTD, PS, the mass ratio of LiFP6, LiFSI, PC, EMC, DEC, FEC, VC, SA, LiPO2F2, TPP, DTD, PS being 8.3:4:25:20:27:11.2:1.8:0.3:0.7:0.65:0.8:0.25.

[0068] 2. Preparation of the battery

[0069] The preparation of the battery in this example is identical to that of Example 1.

[0070] Example 9

[0071] 1. Composition of the electrolyte

[0072] The electrolyte in this example includes lithium hexafluorophosphate (LiFP6), lithium bisfluorosulfonylimide (LiFSI), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sulfone (PS), LiFP6, LiFSI, PC, EMC, DEC, FEC, VC, SA, LiPO2F2, TPP, DTD, PS, the mass ratio of LiFP6, LiFSI, PC, EMC, DEC, FEC, VC, SA, LiPO2F2, TPP, DTD, PS being 8.3:4:25:20:27:11.2:1.8:0.3:0.7:0.65:0.8:0.25.

[0073] 2. Preparation of the battery

[0074] The preparation of the battery in this example is identical to that of Example 1.

[0075] Example 10

[0076] 1. Composition of the electrolyte

[0077] The electrolyte in this example includes lithium hexafluorophosphate (LiFP6), lithium tetrafluoroborate (LiBF4), propylene carbonate (PC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sulfone (PS), LiFP6, LiBF4, PC, EMC, DMC, FEC, VC, SA, LiPO2F2, TPP, DTD, PS in a mass ratio of 7.3:5:25:22:25:11.2:1.8:0.3:0.7:0.65:0.8:0.25.

[0078] 2. Preparation of the battery

[0079] The battery in this example was prepared in the same manner as in Example 1.

[0080] Comparative Example 1

[0081] 1. Composition of the electrolyte

[0082] The electrolyte in this comparative example includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), LiFP6, PC, DMC, FEC, VC in a mass ratio of 11.8:30:47:10:1.2.

[0083] 2. Preparation of the battery

[0084] The battery in this comparative example was prepared in the same manner as in Example 1.

[0085] Comparative Example 2

[0086] 1. Composition of the electrolyte

[0087] This comparative example differs from Example 4 in that propylene carbonate (PC) is replaced with ethylene carbonate (EC). The rest is the same as Example 4.

[0088] 2. Preparation of the battery

[0089] The battery in this comparative example was prepared in the same manner as in Example 4.

[0090] Comparative Example 3

[0091] 1. Composition of the electrolyte

[0092] This comparative example differs from Example 1 in that propylene carbonate (PC) is replaced with ethylene carbonate (EC). The rest is the same as Example 1.

[0093] 2. Preparation of the battery

[0094] The preparation of the battery in this comparative example was identical to that of Example 1.

[0095] Comparative Example 4

[0096] 1. Composition of the electrolyte

[0097] The electrolyte in this comparative example included lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), LiFP6, PC, DMC, FEC, VC, SA, LiPO2F2, TPP in a mass ratio of 12.3:25:47:11.2:1.8:0.491:1.145:1.064.

[0098] 2. Preparation of the battery

[0099] The preparation of the battery in this comparative example was identical to that of Example 1.

[0100] Comparative Example 5

[0101] 1. Composition of the electrolyte

[0102] The electrolyte in this comparative example included lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), tripropargyl phosphate (TPP), 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sultone (PS), LiFP6, PC, DMC, FEC, VC, TPP, DTD, PS in a mass ratio of 12.3:25:47:11.2:1.8:1.032:1.271:0.397.

[0103] 2. Preparation of the battery

[0104] The preparation of the battery in this comparative example was identical to that of Example 1.

[0105] Comparative Example 6

[0106] 1. Composition of the electrolyte

[0107] The electrolyte in this comparative example includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), 1,3,2-dioxazolthiophene-2,2-dioxide / vinylsulfate (DTD), LiFP6, PC, DMC, FEC, VC, LiPO2F2, DTD, and the mass ratio of LiFP6, PC, DMC, FEC, VC, LiPO2F2, and DTD is 12.3:25:47:11.2:1.8:1.4:1.3.

[0108] 2. Preparation of the battery

[0109] The preparation of the battery in this comparative example is in accordance with Example 1.

[0110] Comparative Example 7

[0111] 1. Composition of the electrolyte

[0112] The electrolyte in this comparative example includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), 1,3-propane sulfone lactone (PS), and the mass ratio of LiFP6, PC, DMC, FEC, VC, SA, and PS is 12.3:25:47:11.2:1.8:1.47:1.23.

[0113] 2. Preparation of the battery

[0114] The preparation of the battery in this comparative example is in accordance with Example 1.

[0115] Comparative Example 8

[0116] 1. Composition of the electrolyte

[0117] The electrolyte in this comparative example includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), 1,3,2-dioxazolthiophene-2,2-dioxide / vinylsulfate (DTD), 1,3-propane sulfone lactone (PS), and the mass ratio of LiFP6, PC, DMC, FEC, SA, LiPO2F2, TPP, DTD, and PS is 12.3:25:47:13:0.3:0.7:0.65:0.8:0.25.

[0118] 2. Preparation of the battery

[0119] The preparation of the battery in this comparative example is in accordance with Example 1.

[0120] Comparative Example 9

[0121] 1. Composition of electrolyte

[0122] The electrolyte in this comparative example includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), 1,3,2-dioxazolthiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sulfone (PS), and the mass ratio of LiFP6, PC, DMC, FEC, VC, SA, LiPO2F2, TPP, DTD, and PS is 12.3:25.59:48.11:11.8:1.8:0.044:0.104:0.096:0.119:0.037.

[0123] 2. Preparation of battery

[0124] The preparation of the battery in this comparative example is identical to that of Example 1.

[0125] Comparative Example 10

[0126] 1. Composition of electrolyte

[0127] The electrolyte in this comparative example includes lithium hexafluorophosphate (LiFP6), propylene carbonate (PC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinic anhydride (SA), lithium difluorophosphate (LiPO2F2), tripropargyl phosphate (TPP), 1,3,2-dioxazolthiophene-2,2-dioxide / vinyl sulfate (DTD), 1,3-propane sulfone (PS), and the mass ratio of LiFP6, PC, DMC, FEC, VC, SA, LiPO2F2, TPP, DTD, and PS is 12.3:24.549:46.151:11.2:1.8:0.445:1.037:0.963:1.185:0.37.

[0128] 2. Preparation of battery

[0129] The preparation of the battery in this comparative example is identical to that of Example 1.

[0130] Test Example

[0131] 1. Experimental construction method

[0132] The batteries prepared in all the above examples and comparative examples were tested for performance before and after 60°C storage (including water volume of the battery before storage, ACR, capacity, water volume of the battery after storage, gas generation rate, ACR increment, capacity retention rate, capacity recovery rate), normal temperature (25°C) cycle performance (including DCR, cycle capacity retention rate), and high temperature (45°C) cycle performance (including DCR, cycle capacity retention rate). The specific testing methods are as follows.

[0133] (1) Performance test before and after 60°C storage

[0134] The battery after the capacity grading was charged to 4.2V at 0.5C, and then constant voltage charged to 0.05C. After the battery reached the full charge state, the battery voltage was tested at room temperature after 2h standing, and the battery volume was measured in silicone oil using the Archimedes principle, and then the battery was placed in a 60°C oven for 7 days. The ACR (alternation current resistance) and water volume of the battery were tested before and after storage, and the capacity before storage was also tested. Then the battery was discharged to 3.0V at 0.5C, and then charged to 4.2V at 0.5C, and then constant voltage charged to 0.05C, and then discharged to 3.0V at 0.5C for 3 times. Then the gas generation rate, capacity retention rate, and capacity recovery rate after storage were tested.

[0135] The specific operation of testing the ACR of the battery before and after storage is as follows: Alternation Current Resistance (ACR) is tested by a sinusoidal current signal to test the voltage response in different frequency ranges, to obtain the alternation current impedance of the battery under the corresponding time constant. The graph is called the alternation current impedance spectrum, and the main equipment for testing is an electrochemical workstation, which can obtain electrochemical impedance (EIS). ACR@1000Hz: the resistance measured at about 1000Hz is considered as ohmic resistance (RΩ), and the commonly used testing equipment is an alternation current resistance meter. The ACR of the battery before and after 60°C storage for 7 days was tested according to the above operation.

[0136] The specific operation of testing the capacity of the battery before storage is as follows: before 60°C storage for 7 days, the battery was discharged at 0.5C rate to a cut-off voltage of 3.0V, and the discharge capacity at that time was recorded.

[0137] The specific operation of testing the capacity retention rate of the battery after storage is as follows: after 60°C storage for 7 days, the battery was discharged at 0.5C rate, and the discharge capacity a at a cut-off voltage of 3.0V was recorded. The calculation method of the capacity retention rate after storage is the percentage of the discharge capacity a after storage to the capacity of the battery after the capacity grading.

[0138] The specific procedure for testing the battery capacity recovery rate after storage is as follows: After storing at 60℃ for 7 days, after completing the capacity retention process, charge the battery at 0.5C to 4.2V and then discharge it to 3.0V. The discharge capacity at this time is the discharge capacity b recorded in the recovery rate record. The capacity recovery rate is calculated as the percentage of the discharge capacity b after storage to the calibrated discharge capacity.

[0139] The specific procedure for testing the gas production rate of the battery after storage is as follows: The water volume of the battery cell was tested before and after storage at 60℃ for 7 days, and the water volumes before and after were recorded as V1 and V2. The gas production rate was calculated as S1 = (V2 - V1) / V1.

[0140] (2) Cyclic performance test at room temperature (25℃) and at high temperature (45℃)

[0141] After capacity grading, the batteries were charged to 4.2V at 1.0C in a constant temperature chamber at (25±2)℃ and (45±2)℃ respectively, then switched to constant voltage charging to 0.05C. After resting for 10 minutes, they were discharged to 3.0V at 1.0C for room temperature and high temperature cycle tests (cycle capacity retention rate). Discharge DC internal resistance (DCR) tests were performed before the room temperature and high temperature cycle tests and after every 100 cycles.

[0142] The cycle capacity retention rate is calculated as: discharge capacity at 100th cycle / discharge capacity at the first cycle.

[0143] The specific test procedure for DCR is as follows: the absolute value of the difference between the stop voltage recorded after discharging a 50% SOC cell at 1C for 10 seconds and the stop voltage after discharging for 10 seconds, divided by the 1C current.

[0144] 2. Experimental Results

[0145] The results of the battery preparations in all the above embodiments and comparative examples regarding performance tests before and after storage at 60°C, cycle performance tests at room temperature (25°C), and cycle performance tests at high temperature (45°C) are shown in Tables 1, 2, and 3, respectively.

[0146] Table 1. Performance test results of batteries in the examples and comparative examples before and after storage at 60°C.

[0147]

[0148]

[0149] Table 2 shows the battery cycle performance test results at room temperature (25°C) for the examples and comparative examples.

[0150]

[0151]

[0152] Table 3. Test results of battery high temperature (45℃) cycle performance in examples and comparative examples

[0153]

[0154]

[0155] From the above table 1, table 2, table 3, it can be seen that the use of the electrolyte formula provided by the application can effectively improve the high temperature storage performance of the battery and the cycle performance at room temperature and high temperature. The performance data of examples 1-10 can be referred to. In table 1, it can be seen that after the battery is stored at 60℃ for 7 days, the gas production rate can be controlled to be not higher than 128%, the capacity retention rate is not less than 90.3%, and the capacity recovery rate is not less than 93.2%. From table 2, it can be seen that after the battery is cycled at room temperature of 25℃ for 1000 cycles, the DCR growth rate is low, and the capacity retention rate after 1000 cycles can reach not less than 90.4%. From table 3, it can be seen that after the battery is cycled at high temperature of 45℃ for 1000 cycles, the DCR growth rate is also low, and the capacity retention rate after 1000 cycles can reach not less than 82.4%.

[0156] The battery in comparative example 1 does not contain functional additives, and after the battery is stored at 60℃ for 7 days, the gas production rate increases obviously, and the DCR value of the battery under high temperature cycle at 45℃ is large, and the capacity retention rate after 1000 cycles is significantly reduced, which shows that the additive provided by the application can effectively reduce the gas production of the battery, and at the same time reduce the DCR of high temperature cycle, and improve the high temperature cycle life.

[0157] The electrolyte in comparative examples 2 and 3 contains ethylene carbonate (EC), because EC is not stable, especially at high temperature, and EC can easily react with the functional additive provided by the application or other components of the electrolyte to cause some adverse side reactions that are not conducive to the stability of the battery, resulting in an obvious increase in the gas production rate of the battery after being stored at 60℃ for 7 days, and the DCR value of the battery under high temperature cycle at 45℃ is large, and the capacity retention rate after 1000 cycles is reduced. At the same time, because EC itself is not stable at room temperature, the capacity retention rate of the battery after 1000 cycles at room temperature of 25℃ is also decreased.

[0158] Comparative Examples 4 and 5 contain only 3 functional additives, and Comparative Examples 6 and 7 contain only 2 functional additives, which results in an increase in the gas generation rate of the battery after 7 days of storage at 60°C or a decrease in the capacity retention rate and the capacity recovery rate. At the same time, this also results in a decrease in the capacity retention rate of the battery after 1000 cycles at room temperature of 25°C or after 1000 cycles at high temperature of 45°C, and a higher DCR at high temperature of 45°C. This shows that only 2 or 3 functional additives are not conducive to the overall stability of the electrolyte, and cannot effectively inhibit the gas generation of the battery or effectively improve the cycle performance of the battery at room temperature and high temperature.

[0159] Comparative Example 8 contains only one film-forming additive FEC, and the stability of the film formed on the positive and negative electrodes of the battery decreases, thus resulting in an increase in the gas generation rate of the battery after 7 days of storage at 60°C or a decrease in the capacity retention rate and the capacity recovery rate. At the same time, due to the decrease in the stability of the film formed on the positive and negative electrodes, the capacity retention rate of the battery after 1000 cycles at room temperature of 25°C or after 1000 cycles at high temperature of 45°C decreases, and the DCR at high temperature of 45°C is higher.

[0160] The functional additives in Comparative Examples 9 and 10 are too much or too little, respectively, which is not conducive to the performance of the battery. Too much functional additive will increase the interfacial impedance Rct, and too little functional additive will not effectively inhibit the gas generation, thus cannot effectively reduce the ACR, DCR and Rct of the battery. Ultimately, this results in an increase in the gas generation rate of the battery after 7 days of storage at 60°C or a decrease in the capacity retention rate and the capacity recovery rate, and a significant decrease in the capacity retention rate of the battery after 1000 cycles at room temperature of 25°C or after 1000 cycles at high temperature of 45°C.

[0161] Further comparison of Examples 1 and 4-8 shows that Examples 4-8 contain only 4 functional additives, which are worse than Example 1 in terms of the gas generation rate, capacity retention rate and capacity recovery rate after 7 days of storage at 60°C, and the DCR at room temperature of 25°C, after 1000 cycles at room temperature of 25°C, after 1000 cycles at high temperature of 45°C, and after 1000 cycles at high temperature of 45°C. This shows that when the 5 functional additives in Example 1 are used together, the high-temperature cycle performance and high-temperature storage performance of the electrolyte are improved, which may be because the 5 additives together have a more obvious synergistic effect, thus further optimizing the performance of the electrolyte.

[0162] Comparing Example 1 with Examples 9-10, we can find that changing the organic solvent or the type of lithium salt in the electrolyte will inevitably affect the performance of the battery, which shows that further optimizing the combination of organic solvents, lithium salts and additives is more conducive to the cycle performance of the battery.

[0163] The above examples are only used to illustrate the technical solutions of the present application and not to limit the protection scope of the present application. Although the present application is described in detail with reference to the above examples, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently, and these modifications or replacements are within the protection scope of the present application.

Claims

1. An electrolyte, characterized by: The lithium salt, the organic solvent, the film forming additive, and the functional additive; The film forming additive comprises fluoroethylene carbonate and vinylene carbonate; the mass percentage of the film forming additive in the electrolyte is 9-16%; The functional additive comprises succinic anhydride, lithium difluorophosphate, tripropargyl phosphate, 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate, and 1,3-propane sulfonic acid lactone; the mass ratio of the succinic anhydride, the lithium difluorophosphate, the tripropargyl phosphate, the 1,3,2-dioxazolothiophene-2,2-dioxide / vinyl sulfate, and the 1,3-propane sulfonic acid lactone is 0.2-0.4:0.5-0.9:0.55-0.85:0.6-1.0:0.15-0.30; The mass percentage of the functional additive in the electrolyte is 0.5-3.8%; The organic solvent does not contain vinyl carbonate.

2. The electrolyte of claim 1, wherein: In the film forming additive, the mass ratio of the fluoroethylene carbonate to the vinylene carbonate is 5.8-6.5:

1.

3. The electrolyte of claim 1, wherein: The lithium salt comprises at least one of lithium hexafluorophosphate, lithium bisfluorosulfonylimide, lithium tetrafluoroborate, lithium difluoro oxalate borate, and lithium bis-trifluoromethanesulfonimide.

4. The electrolyte of claim 1, wherein: The mass fraction of the lithium salt in the electrolyte is 9.5-14%.

5. The electrolyte of claim 1, wherein: The mass fraction of the organic solvent in the electrolyte is 57-78%.

6. The electrolyte of claim 1, wherein: The organic solvent comprises cyclic carbonate and linear carbonate; the mass ratio of the cyclic carbonate to the linear carbonate is 17-28:40-50.

7. The electrolyte of claim 6, wherein: The cyclic carbonate comprises propylene carbonate. The linear carbonate comprises at least one of methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, propyl propionate, and ethyl propionate.

8. A battery, characterized by: The electrolyte comprises the electrolyte according to any one of claims 1-7.

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