Electrolyte and battery

Abstract

Disclosed in the present application are an electrolyte and a battery, the electrolyte comprising a lithium salt, an organic solvent, a first additive and a second additive; the first additive is represented by formula I, and the second additive comprises at least one of 1,3-propane sultone, 1,3-propene sultone, ethylene sulfate, methylene methanedisulfonate and a compound represented by formula II; in formula I, R1, R2, R3, R4, R5, R6, R7 and R8 are each independently selected from any one of hydrogen, halogen, alkyl and haloalkyl. Introducing both the first additive and the second additive into the electrolyte can improve the cycle performance and the high and low temperature performance of lithium batteries, thereby prolonging the service life.

Description

Electrolyte and battery

[0001] Priority information

[0002] This application claims priority to and the benefit of the filing date of the patent application with the China National Intellectual Property Office, filed on June 4, 2024, with the patent application number 202410717168.8, and incorporates it herein in its entirety by reference. TECHNICAL FIELD

[0003] The present application belongs to the field of batteries, and in particular, relates to electrolyte and battery. BACKGROUND

[0004] Lithium batteries, such as lithium ion batteries, are widely used in various fields, such as portable electronic devices, electric vehicles, etc., due to their excellent specific capacity, stable cycle performance and rate performance. With the continuous development of battery products, the requirements for their performance are also constantly improving. For example, there is an increasing demand for lithium ion batteries with long cycle life, low cost and wide working temperature. SUMMARY

[0005] The present application aims to solve one of the related technical problems to some extent. To this end, one object of the present application is to propose an electrolyte and battery, in which the first additive and the second additive are introduced to improve the cycle performance and high and low temperature performance of the lithium battery, and prolong the service life.

[0006] The first aspect of the present application proposes an electrolyte, comprising: a lithium salt, an organic solvent, a first additive and a second additive, the first additive is shown as formula I, and the second additive comprises at least one of 1,3-propane sulfone, 1,3-propylene sulfone, ethylene sulfate, methane disulfide methylene, a compound shown as formula II,

[0007] In formula I, R1, R2, R3, R4, R5, R6, R7 and R8 are independently selected from any one of hydrogen, halogen, alkyl and halogenated alkyl.

[0008] The electrolyte of the present application comprises a first additive and a second additive shown in formula I. The first additive, lithium bisalicylate borate, can form a stable SEI film with appropriate lithium ion and boron content on the surface of the negative electrode of the battery, which can effectively reduce the consumption of irreversible lithium ions in the battery, weaken the transmission resistance of lithium ions in low temperature environment, increase the migration rate of lithium ions in the SEI film, and significantly reduce the active site radicals in the electrolyte, thereby obtaining excellent low temperature discharge and cycle performance. On the other hand, the oxidation potential of the first additive is low, and it is easy to be oxidized on the surface of the positive electrode to form a CEI film rich in boron element, which is beneficial to reduce the dissolution of transition metal ions in the positive electrode, inhibit the side reaction at the positive electrode interface, and maintain the good stability of the electrolyte. That is, the first additive introduced into the electrolyte can decompose and form an effective passivation layer on the surface of the positive and negative electrodes, prevent parasitic side reactions of the electrolyte, and thus improve the coulombic efficiency, long cycle stability and high and low temperature performance of the battery. On this basis, the introduction of the second additive is beneficial to further form inorganic lithium salt (such as lithium sulfate or lithium alkyl sulfonate LiOSO2-R, etc.) on the surface of the negative electrode, optimize the composition of the SEI film, further improve the interface stability of the negative electrode and the high temperature cycle performance of the battery. Moreover, the first additive will be reduced in preference to the second additive and organic solvents, and the use of the first additive and the second additive together is beneficial to achieving better cycle performance and high and low temperature performance of the battery on the basis of reducing the overall amount of the additive, and has lower interface impedance, prolonging the service life. In summary, the addition of the electrolyte to the lithium battery can improve the cycle performance and high and low temperature performance of the battery, and prolong the service life.

[0009] In some embodiments, the alkyl group is C 1-8 alkyl group, the haloalkyl group is C 1-8 haloalkyl group. Thus, it is beneficial to further reduce the amount of the first additive in the electrolyte on the basis of better improving the cycle performance and high and low temperature performance of the battery.

[0010] In some embodiments, the first additive comprises at least one of the compounds shown in formula A-1 to formula A-8:

[0011] Thus, the cycle performance and high and low temperature performance of the battery can be effectively improved.

[0012] In some embodiments, the content of the first additive is 0.1wt%-4wt% based on the total mass of the electrolyte. In this way, it is not only conducive to improving the cycle performance and high-low temperature performance of the battery, but also conducive to avoiding the adverse effects on the performance of the electrolyte when the amount of the first additive exceeds the upper limit of its solubility in the electrolyte.

[0013] In some embodiments, the content of the second additive is 0.1wt%-5wt%. In this way, it is conducive to better improving the cycle performance and high-low temperature performance of the battery.

[0014] In some embodiments, the content of the first additive is 0.5wt%-2wt% based on the total mass of the electrolyte. In this way, it is conducive to better improving the cycle performance and high-low temperature performance of the battery on the basis of a lower amount of the first additive.

[0015] In some embodiments, the second additive includes methylene methane disulfonate and / or a compound represented by Formula II. In this way, it is conducive to better improving the cycle performance and high-low temperature performance of the battery.

[0016] In some embodiments, the content of the second additive is 0.2wt%-2wt% based on the total mass of the electrolyte. In this way, it is conducive to further improving the negative electrode interface stability and high-temperature cycle performance.

[0017] In some embodiments, the electrolyte further includes at least one of vinylene carbonate, fluoroethylene carbonate, and vinyl ethylene carbonate. In this way, it is conducive to further improving the interface stability of the negative electrode plate and further improving the room temperature cycle performance of the battery.

[0018] In some embodiments, the electrolyte further includes at least one of tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, and triallyl phosphate. In this way, it is conducive to further improving the stability of the electrolyte.

[0019] In some embodiments, the electrolyte further includes at least one of an acid anhydride additive and a nitrile additive. In this way, it is conducive to further improving the interface stability of the positive electrode plate.

[0020] In some embodiments, the total content of the second additive, the vinylene carbonate, the fluoroethylene carbonate, the vinyl ethylene carbonate, the tris(trimethylsilyl)borate, the tris(trimethylsilyl)phosphate, the triallyl phosphate, the acid anhydride additive, and the nitrile additive is not more than 5wt% based on the total mass of the electrolyte.

[0021] In some embodiments, the total content of the first additive, the vinylene carbonate, the fluoroethylene carbonate, and the vinyl ethylene carbonate is not more than 4 wt% based on the total mass of the electrolyte.

[0022] In some embodiments, the second additive is at least one of vinylene carbonate, fluoroethylene carbonate, and vinyl ethylene carbonate, and the total content of the first additive and the second additive is not more than 4 wt% based on the total mass of the electrolyte. This is beneficial for further improving the stability of the negative electrode interface and the cycling performance at room temperature.

[0023] In some embodiments, the lithium salt comprises at least one of LiPF6, LiAsF6, LiClO4, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2, and LiPF4C2O4.

[0024] In some embodiments, the content of the lithium salt is 8 wt% to 20 wt% based on the total mass of the electrolyte.

[0025] In some embodiments, the organic solvent comprises a cyclic organic solvent and / or a chain organic solvent, the cyclic organic solvent comprises at least one of vinyl carbonate, propylene carbonate, γ-butyrolactone, sulfolane, fluoroethylene carbonate, and the chain organic solvent comprises at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and 2,2-difluoroethyl acetate.

[0026] In some embodiments, the content of the organic solvent is 71 wt% to 91.3 wt% based on the total mass of the electrolyte.

[0027] The second aspect of the present application provides a battery comprising the electrolyte of the first aspect. Thus, the battery has good cycling performance, high and low temperature performance, and a long service life.

[0028] In some embodiments, the battery further comprises a positive electrode active material and a negative electrode active material, the positive electrode active material comprises LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M xPO4, Li2Mn 1-x O4, wherein M comprises at least one selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, F, 0≤a≤0.2, 0≤x<1; and / or, the negative active material comprises at least one of graphite, silicon-carbon composite material, silicon material, lithium metal, lithium titanate.

[0029] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter in the description. BRIEF DESCRIPTION OF DRAWINGS

[0030] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings.

[0031] FIG. 1 is a graph showing the change rate of the content of the unit voltage interval (dQ / dV) with respect to the voltage after the electrolyte configured with the compound described in A-1 as the first additive and vinyl carbonate (VC) as the other additive is used in a battery, and the battery is formed.

[0032] FIG. 2 is a graph showing the current density with respect to the voltage in the intrinsic LSV test of the compound described in A-1 according to an embodiment of the present application. DETAILED DESCRIPTION

[0033] The embodiments of the present application are described in detail below, which are intended to explain the present application and cannot be understood as a limitation of the present application.

[0034] The technical solution of the present application is completed by the inventors based on the following findings: the electrolyte, as an important component of the lithium secondary battery, has an important influence on the comprehensive performance of the battery. The additive is an important component of the electrolyte, and a suitable additive can significantly improve at least one of the coulombic efficiency, the cycle performance, the high and low temperature performance, etc. of the battery. In view of the problems that the battery may have insufficient stability of the positive and negative electrodes, decomposition of the electrolyte, etc., the battery is prone to have poor low-temperature discharge performance, poor cycle stability, short service life, etc. during operation, which can be improved by selecting a suitable additive. The inventors found that selecting lithium bisalicylate borate and at least one of 1, 3-propane sulfone lactone, 1, 3-propylene sulfone lactone, vinyl sulfate, methanedi sulfonate methylene, and the compound shown in formula II as an additive component can improve the long cycle performance and high and low temperature performance (such as discharge performance) of the lithium ion battery, which is beneficial to prolong the service life of the battery.

[0035] In view of the above, the first aspect of the present application provides an electrolyte, comprising: a lithium salt, an organic solvent, a first additive and a second additive, the first additive is shown as formula I, the second additive comprises at least one of 1,3-propane sultone, 1,3-propene sultone, ethylene sulfate, methane dithioate methylene, a compound shown as formula II,

[0036] In formula I, R1, R2, R3, R4, R5, R6, R7, R8 are independently selected from any one of hydrogen, halogen, alkyl and haloalkyl.

[0037] It should be noted that in formula I, R1, R2, R3, R4, R5, R6, R7, R8 can be completely the same, or different or not completely the same. For example, taking R1 to R8 including haloalkyl as an example, when there are at least two haloalkyl groups in R1 to R8 in formula I, the number of carbon atoms of the at least two haloalkyl groups can be the same or different, and the number of halogen substitutions and the type of halogen in the at least two haloalkyl groups can be the same or different. It can be understood that the halogen refers to the elements of VIIA, such as one or more of F, Cl, Br, I; the haloalkyl group can be an alkyl group partially substituted by halogen or completely substituted by halogen.

[0038] The electrolyte of the present application comprises a first additive and a second additive shown in formula I. The first additive, lithium bisalicylate borate, can form a stable SEI film with suitable lithium ion and boron element content on the surface of the negative electrode of the battery, which can effectively reduce the consumption of irreversible lithium ions in the battery, weaken the transmission resistance of lithium ions in low temperature environment, increase the migration rate of lithium ions in the SEI film, and significantly reduce the active site radicals in the electrolyte, thereby reducing the negative effects caused by the active site radicals, so as to obtain excellent low temperature discharge and cycle performance. On the other hand, the oxidation potential of the first additive is low, and it is easy to be oxidized on the surface of the positive electrode to form a CEI film rich in boron element, which is beneficial to reduce the dissolution of transition metal ions in the positive electrode, inhibit the side reaction at the positive electrode interface, and maintain the good stability of the electrolyte. That is, the first additive introduced into the electrolyte can decompose on the surface of the positive and negative electrodes and form an effective passivation layer to prevent parasitic side reactions of the electrolyte, thereby improving the coulombic efficiency, long cycle stability and high and low temperature performance of the battery. Further, the effect of lithium bisalicylate borate on improving the high temperature cycle performance of the battery is limited, and by using it in combination with the second additive, an inorganic lithium salt (such as lithium sulfate or lithium alkylsulfonate LiOSO2-R, etc.) can be further formed as a bottom buffer layer on the surface of the negative electrode, which can improve the integrity of the organic polymer layer formed by lithium bisalicylate borate at high temperature, optimize the composition of the SEI film, that is, a gradient structure model of polymer-inorganic salt-negative active material layer (such as graphite layer) can be formed, the organic polymer phase has mechanical elasticity when lithium ions are inserted and extracted, and the inorganic salt phase can isolate the direct contact between the organic polymer layer and the high-activity negative active material layer (such as the graphite layer), while producing higher ionic conductivity. Therefore, by using the second additive in combination with the first additive, the interface stability of the negative electrode can be further improved and the high temperature cycle performance of the battery can be improved. In addition, the first additive will be reduced before the second additive and the organic solvent, and the use of the first additive in combination with the second additive can help to achieve better cycle performance and high and low temperature performance of the battery on the basis of reducing the overall amount of additives, and has lower interface impedance, prolonging the service life. That is, the first additive and the second additive cooperate with each other to further improve the performance of the battery.

[0039] In summary, the electrolyte can improve the cycle performance and high and low temperature performance of the battery, and prolong the service life when added to the lithium battery.

[0040] In some embodiments of the present application, the number of carbon atoms in the alkyl group and the haloalkyl group can be independently selected as appropriate, for example, the alkyl group can be C 1.8 The alkyl group may, for example, include a methyl group, and the haloalkyl group can be C 1-8haloalkyl groups, such as fluoromethyl groups, etc. The satisfaction of the given conditions is conducive to further reducing the amount of the first additive added in the electrolyte, reducing the risk of increased impedance and decreased ion transport performance that can be caused by a high overall amount of the additive, on the basis of better improvement effects on the cycle performance and high and low temperature performance of the battery.

[0041] In some embodiments of the present application, the halogen can include fluorine elements, and / or the haloalkyl group can include fluorinated alkyl groups. The increase in the fluorine content in the first additive shown in Formula I is conducive to further improving the improvement effect on the stability of the positive and negative electrode interfaces and reducing the direct current impedance of the battery. The introduction of fluorine substituents or fluorinated alkyl groups in the first additive shown in Formula I is conducive to further forming lithium fluoride in the SEI film during formation, inhibiting the growth of Li dendrites and the occurrence of other parasitic reactions on the negative electrode surface, improving the cycle performance of the battery, and further forming fluorine-containing inorganic lithium salts in the CEI film, reducing the decomposition of electrolyte salts (such as lithium hexafluorophosphate, etc.) on the positive electrode, inhibiting the dissolution of transition metal ions from the positive electrode, inhibiting the side reactions at the positive electrode interface, and maintaining the good stability of the positive electrode structure and the electrolyte, thereby further improving the stability of the positive and negative electrode interfaces and improving the cycle performance and high and low temperature performance of the battery.

[0042] In some embodiments, the first additive can include at least one of the compounds shown in Formula A-1 to Formula A-8. The use of the compounds shown in Formula A-1 to Formula A-8 as the first additive in the electrolyte can effectively improve the cycle performance and high and low temperature performance of the battery. For example, the first additive can include at least one of the compounds shown in Formula A-1, Formula A-2, and Formula A-3, such as only the compound shown in Formula A-1. Among them, the CAS number of the compound shown in Formula A-1 is: 161589-07-7; the CAS number of the compound shown in Formula A-2 is: 380412-90-8; the CAS number of the compound shown in Formula A-3 is: 1445728-27-7; the CAS number of the compound shown in Formula A-4 is: 2892332-51-1; the CAS number of the compound shown in Formula A-5 is: 380412-89-5; the CAS number of the compound shown in Formula A-6 is: 660399-17-7; the CAS number of the compound shown in Formula A-7 is: 380412-91-9; and the CAS number of the compound shown in Formula A-8 is: 215953-23-4. The structural formulas of the compounds shown in Formula A-1 to Formula A-8 are shown as follows, respectively:

[0043] In some embodiments of the present application, the content of the first additive can be 0.1wt%-4wt% based on the total mass of the electrolyte, such as 0.1wt%, 0.3wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, etc. In the electrolyte, appropriately increasing the content of the first additive is conducive to improving the cycle stability of the battery at different ambient temperatures. By controlling the content of the first additive within the given range, it is not only conducive to improving the cycle performance and high-low temperature performance of the battery, but also conducive to avoiding the adverse effects on the performance of the electrolyte that may be caused by the use of the first additive exceeding its upper limit of solubility in the electrolyte, thereby further taking into account the improvement degree of the cycle performance and high-low temperature performance of the battery by the first additive. Further, the content of the first additive can be 0.5wt%-2wt% based on the total mass of the electrolyte, thereby being conducive to achieving a good improvement effect on the cycle performance and high-low temperature performance of the battery on the basis of a lower amount of the first additive.

[0044] In some embodiments of the present application, the content of the second additive can be 0.1wt%-5wt% based on the total mass of the electrolyte, such as 0.1wt%, 0.3wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, etc. Controlling the amount of the second additive to meet the given range can not only cooperate with the first additive to improve the stability of the positive and negative electrode interface, the stability of the electrolyte, the normal temperature cycle performance or the high temperature cycle performance of the battery, but also reduce the risk of problems such as an increase in interface impedance and a decrease in ion transport performance caused by a larger thickness of the negative electrode interface film due to a higher content of the second additive, thereby being conducive to achieving a good improvement effect on the cycle performance and high-low temperature performance of the battery.

[0045] In some embodiments of the present application, the content of the second additive can be 0.2wt% to 2wt% based on the total mass of the electrolyte, such as 0.2wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, etc. For example, the second additive can be methanedisulfonic acid methylene ester and / or the compound shown in Formula II, and the total content of the methanedisulfonic acid methylene ester and the compound shown in Formula II can be 0.2wt% to 2wt% based on the total mass of the electrolyte. In this way, not only is it beneficial to have a good improvement effect on the interface stability and high-temperature cycle performance of the negative electrode on the basis of a lower amount of the second additive, but it is also beneficial to further reduce the risk of an increase in the thickness of the SEI film and a decrease in the interface impedance and ion transport performance caused by an excessive amount of the second additive.

[0046] In some embodiments of the present application, the second additive can include methanedisulfonic acid methylene ester and / or the compound shown in Formula II, thereby having a good improvement effect on the cycle performance and high-low temperature performance of the battery.

[0047] In some embodiments of the present application, the electrolyte can further include at least one of vinylene carbonate, fluoroethylene carbonate, and vinyl ethylene carbonate. On the basis of the use of the first additive and the second additive, the use of at least one of vinylene carbonate, fluoroethylene carbonate, and vinyl ethylene carbonate in combination can cause ring-opening reaction, form organic polymers in combination with lithium bisalicylate borate, and at the same time provide some inorganic salts such as Li2CO3 and LiF, so that the SEI film is more flexible. In this way, an organic polymer can be further formed on the surface of the negative electrode tab, the composition of the SEI film is optimized, the SEI film is more flexible, the damage to the SEI film caused by the volume change of the electrode material during the cycle process is reduced, the interface stability of the negative electrode tab can be further improved, and the cycle performance of the battery at room temperature can be further improved.

[0048] In some embodiments of the present application, the total content of vinylene carbonate, fluoroethylene carbonate and vinyl ethylene carbonate can be no more than 4wt%, such as 0.2wt% to 2wt%, etc., based on the total mass of the electrolyte. Further, the total content of the first additive and vinylene carbonate, fluoroethylene carbonate and vinyl ethylene carbonate can be no more than 4wt%, such as 0.3wt%, 0.5wt%, 0.8wt%, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, etc., based on the total mass of the electrolyte. Thus, not only is it beneficial to have a good improvement effect on the interface stability and room temperature cycle performance of the negative electrode on the basis of a lower total additive amount, but it is also beneficial to further reduce the risk of an increase in the thickness of the SEI film and a decrease in the interface impedance and ion transport performance that may be caused by an excessive amount of carbonate-based additives.

[0049] In some embodiments of the present application, the electrolyte can further include at least one of tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, and triallyl phosphate. Where the first additive and the second additive are used in combination, the at least one of tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, and triallyl phosphate not only reacts with water to reduce the formation of HF and its destruction of the cross-section film, thereby maintaining the stability of the interface film, but also is beneficial to further improve the stability of the electrolyte, avoid the influence of trace water in the electrolyte on the electrolyte, inhibit the decomposition of the electrolyte during storage, transportation and use, and thus improve the cycle performance, thereby being beneficial to further consuming water and the like that can exist in the electrolyte, and further improving the stability of the electrolyte. In some embodiments, the total content of the second additive and the at least one of tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, and triallyl phosphate can be 0.1wt% to 5wt%, such as no more than 4wt%, or 0.2wt% to 2wt%, etc., based on the total mass of the electrolyte. Thus, it is beneficial to further reduce the risk of a decrease in the improvement effect of the electrolyte on the cycle performance and high and low temperature performance of the battery that can be caused by an excessive amount of additives.

[0050] In some embodiments of the present application, the electrolyte can further comprise at least one of an anhydride additive and a nitrile additive. The use of the anhydride additive in combination with the first additive and the second additive can further assist the formation of a film on the surface of the positive electrode tab and optimize the composition of the CEI film. The use of the nitrile additive in combination with the first additive and the second additive can provide functional groups to complex the dissolved transition metal, reduce the deposition of the dissolved transition metal ions on the negative electrode, and poison the SEI film, thereby further improving the interface stability of the positive electrode and maintaining the overall stability of the battery. It should be noted that in the present application, the specific types of the anhydride additive and the nitrile additive are not particularly limited and can be selected as needed by those skilled in the art, for example, the anhydride additive can include but is not limited to at least one of succinic anhydride, maleic anhydride, citraconic anhydride, butyric anhydride, and heptafluorobutyric anhydride; the nitrile additive can include but is not limited to at least one of butanedinitrile, hexanedinitrile, 1,3,6-hexanetricarbonitrile, fumaronitrile, 1,2-bis(cyanoethoxy)ethane, and 1,2,3-tris(2-cyanoethoxy)propane. In some embodiments, the total content of the second additive, the anhydride additive, and the nitrile additive can be 0.1wt% to 5wt%, such as not more than 4wt%, or 0.2wt% to 2wt%, etc., based on the total mass of the electrolyte. This is advantageous for further reducing the risk of excessive use of additives that may reduce the improvement effect of the electrolyte on the cycle performance and high and low temperature performance of the battery.

[0051] In some embodiments of the present application, the first additive has a low oxidation potential and is easily oxidized to form a CEI film on the surface of the positive electrode, and is also preferentially reduced compared to vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, triallyl phosphate, an anhydride additive, and a nitrile additive. For example, taking the compound of formula A-1 as an example, Figure 1 shows the dQ / dV curve of the battery during the formation stage, and shows the reduction potential of the compound of formula A-1 (about 2.45V) and the reduction potential of vinylene carbonate (VC) (about 2.65V), indicating that the compound of formula A-1 is reduced more easily than the second additive VC; Figure 2 shows the current density as a function of voltage curve obtained by intrinsic LSV test of the compound of formula A-1, from which it can be seen that the oxidation potential of the compound of formula A-1 is about 4.3V, indicating that it is easily oxidized on the surface of the positive electrode to form a CEI film.

[0052] In some embodiments of the present application, the total content of the second additive, vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, triallyl phosphate, anhydride additive and nitrile additive can be no more than 5wt% based on the total mass of the electrolyte. This is advantageous for further reducing the risk of overuse of additives which can reduce the improvement effect of the electrolyte on the cycle performance and high and low temperature performance of the battery.

[0053] In some embodiments of the present application, the lithium salt can include at least one of LiPF6, LiAsF6, LiClO4, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2and LiPF4C2O4.

[0054] In some embodiments of the present application, the content of the lithium salt can be 8wt% to 20wt%, for example, can be 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, etc. based on the total mass of the electrolyte. This is advantageous for further improving the performance of the battery.

[0055] In some embodiments of the present application, the organic solvent in the electrolyte can include a cyclic organic solvent and / or a chain organic solvent, the cyclic organic solvent can include at least one of vinyl carbonate, propylene carbonate, γ-butyrolactone, sulfolane, fluoroethylene carbonate; the chain organic solvent can include at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-difluoroethyl acetate.

[0056] In some embodiments of the present application, the content of the organic solvent can be 71wt% to 91.3wt%, for example, can be 71wt%, 75wt%, 80wt%, 85wt%, 90wt%, 91.3wt%, etc. based on the total mass of the electrolyte. This is advantageous for further improving the performance of the battery.

[0057] In some embodiments of the present application, the electrolyte is suitable for a wide range of applications, such as lithium ion batteries with relatively low working voltage such as lithium iron phosphate system, and also suitable for lithium ion batteries with relatively high working voltage such as nickel cobalt manganese system. For systems with low or high working voltage, it is advantageous to widen the temperature range of lithium ion batteries, improve the cycle performance and high and low temperature performance of the battery, for example, to improve the low temperature discharge performance of the battery and the cycle stability at different environmental temperatures.

[0058] In some embodiments of the present application, the electrolyte can optionally further comprise a small amount of other conventional additives or auxiliary agents capable of improving certain properties of the battery, which can be selected by those skilled in the art according to actual needs, and will not be described here.

[0059] The second aspect of the present application provides a battery comprising the electrolyte of the first aspect of the present application. It should be noted that the features and effects described for the electrolyte of the first aspect of the present application are also applicable to the battery of the second aspect of the present application, which will not be described here. In general, the battery has good cycle performance, high and low temperature performance, and a long service life. In addition, it should be noted that the type of the battery is not particularly limited, and those skilled in the art can flexibly select according to actual needs, for example, it can be a secondary battery.

[0060] In some embodiments of the present application, the battery can further comprise: a positive active material and a negative active material, the positive active material can include but is not limited to at least one of LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x MxPO4, Li2Mn 1-x O4, wherein M can include at least one selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, F, 0≤a≤0.2, 0≤x<1; and / or the negative active material can include but is not limited to at least one of graphite, silicon-carbon composite material, silicon material, lithium metal, lithium titanate.

[0061] Generally, the battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly to prevent short circuiting of the positive and negative electrodes, while allowing ions to pass through.

[0062] In some embodiments of the present application, the positive electrode tab can include a positive current collector and a positive active material layer disposed on the surface of the positive current collector, the positive active material layer including a positive active material, a conductive agent, and a binder, the positive current collector can include a metal foil or a composite positive current collector, for example, the metal foil can be an aluminum foil, the composite positive current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer, for example, the composite negative current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, etc.) on a polymer material base material (such as a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. base material). The positive active material can include the above-mentioned positive active material or the positive active material commonly used in the art. The conductive agent and the binder can be conventional materials in the art.

[0063] In some embodiments of the present application, the negative electrode tab can include a negative current collector and a negative active material layer disposed on the surface of the negative current collector, the negative active material layer including a negative active material, a conductive agent, and a binder, wherein the negative current collector can be a metal foil or a composite current collector, for example, the metal foil can be a copper foil, the composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base material, for example, the composite current collector can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, etc.) on a polymer material base material (such as a polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc. base material). The negative active material can include the above-mentioned negative active material or the negative active material commonly used in the art. The conductive agent and the binder can be conventional materials in the art.

[0064] In some embodiments of the present application, the separator film can use a separator film commonly known in the art that can be used in a battery and is stable to the electrolyte used, such as its material can include but is not limited to at least one of polyolefin, aromatic polyamide, polytetrafluoroethylene, polyether sulfone, such as it can be a polyethylene separator, a polypropylene separator, a PE ceramic coated separator, etc., which can be flexibly selected as needed.

[0065] In some embodiments of the present application, the battery of the second aspect of the present application can be used in an electrical device. It should be noted that the specific type of the electrical device is not particularly limited, and those skilled in the art can flexibly select according to actual needs, for example, it can include but is not limited to electronic devices, vehicles, etc.

[0066] The embodiments of the present application are described in detail below, it should be noted that the embodiments described below are exemplary, only for explaining the present application, and can not be understood as limiting the present application. In addition, if not specifically stated, all reagents used in the following examples are commercially available or can be synthesized according to the methods described herein or known to those skilled in the art, and the reaction conditions not listed are also readily available to those skilled in the art.

[0067] Example 1

[0068] 1. Preparation of positive electrode sheet

[0069] The positive electrode material LiFePO4, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) were dispersed in the solvent N-methyl pyrrolidone (NMP) at a mass ratio of 96:2:2 to obtain a positive electrode active material layer slurry; the positive electrode active material layer slurry was uniformly coated on the double-sided surface of the positive electrode current collector aluminum foil, with a surface density of 40 mg / cm 2 After drying, rolling, baking, slitting and spot welding of the tab, the positive electrode sheet was obtained, and the total thickness of the positive electrode sheet was 190 μm.

[0070] 2. Preparation of negative electrode sheet

[0071] The negative electrode active material graphite, the conductive agent conductive carbon black (super-p) and the binder styrene-butadiene rubber (SBR) were dispersed in deionized water at a mass ratio of 96:2:2, and stirred uniformly to obtain a negative electrode active material layer slurry; the negative electrode active material layer slurry was uniformly coated on the double-sided surface of the negative electrode current collector copper foil, with a surface density of 18 mg / cm 2 After drying, rolling, baking, slitting and spot welding of the tab, the negative electrode sheet was obtained, and the total thickness of the negative electrode sheet was 123 μm.

[0072] 3. Composition of electrolyte

[0073] In a dry environment with less than 5 ppm of moisture, lithium hexafluorophosphate (LiPF6), a first additive represented by formula A-1, and a second additive vinylene carbonate (VC) were added to an organic solvent and stirred uniformly to mix uniformly. After mixing uniformly, the electrolyte was obtained. The organic solvent included vinyl carbonate (EC), propylene carbonate (PC) and methyl ethyl carbonate (EMC) at a mass ratio of 32:4:49.5. Based on the total mass of the electrolyte, the lithium salt content in the electrolyte was 12.5 wt%, the organic solvent content was 85.5 wt%, the content of the first additive represented by formula A-1 was 2 wt%, and the content of VC was 1 wt%.

[0074] 4. Separating membrane

[0075] A 16 μm polypropylene porous membrane was used as the separating membrane.

[0076] 5. Preparation of lithium ion battery

[0077] The prepared positive electrode sheet, negative electrode sheet and separator film are stacked in order, the separator film is placed between the positive electrode sheet and the negative electrode sheet, and after winding and flattening, the product is placed in an aluminum foil packaging bag. The product is vacuum baked at 75°C for 48h to obtain a battery cell. The above electrolyte is injected into the battery cell in a glove box, and the preparation of the lithium ion battery is completed after packaging, formation, aging and capacity distribution.

[0078] Examples 2-33 and Comparative Examples 1-9

[0079] The differences between Examples 2-33 and Comparative Examples 1-9 and Example 1 are shown in Table 1 and Table 2.

[0080] In Examples 30-33 and Comparative Examples 4-9, the organic solvent is composed of ethylene carbonate (EC), methyl ethyl carbonate (EMC) and diethyl carbonate (DEC) in a mass ratio of 26:44:17. In addition, the CAS numbers of the second additive and other additives involved in Examples 1-33 and Comparative Examples 1-9 are as follows: vinylene carbonate: 872-36-6; fluoroethylene carbonate: 114435-02-8; vinyl ethylene carbonate: 4427-96-7; 1,3-propane sultone: 1120-71-4; 1,3-propene sultone: 21806-61-1; ethylene sulfate: 1072-53-3; methanedimethanolate: 99591-74-9; tris(trimethylsilyl)borate: 4325-85-3; tris(trimethylsilyl)phosphate: 10497-05-9; triallyl phosphate: 1623-19-4; succinic anhydride: 108-30-5; adiponitrile: 111-69-3; 2520352-94-5.

[0081] Performance test:

[0082] The redox potential, normal temperature and high temperature cycle performance and low temperature discharge performance of the lithium ion battery obtained from Examples 1-33 and Comparative Examples 1-9 were characterized, and the test method is shown below, and the characterization results are shown in Table 1.

[0083] Redox potential test

[0084] The battery after injection was formed with a current of 0.01C, the formation curve was collected, the capacity difference corresponding to different voltages in the charging process was observed, and the dQ / dV-V curve of the battery in the formation process was obtained, i.e. the curve of the capacity change rate (dQ / dV) per voltage interval during formation with voltage change. The dQ / dV-V curve of the example and the comparative example is combined to obtain the reduction potential of the additive.

[0085] Linear sweep voltammetry (LSV) test was performed: EC, PC, EMC were configured into organic solvent according to the mass ratio of 32:4:60, and the organic solvent was configured into electrolyte according to the additive mass ratio of 4wt%, to characterize the intrinsic oxidation potential of the additive. The prepared electrolyte was added into a three-electrode electrolytic cell, the working electrode was a platinum electrode, and the counter electrode and reference electrode were lithium sheets. LSV test was performed on an electrochemical workstation, the voltage test started from open circuit voltage, the scan rate was 0.5mV / s, and the curve of current density versus voltage was obtained, from which the oxidation potential of the additive was obtained.

[0086] Normal temperature cycle performance test:

[0087] The battery was charged at 25℃ with a charge rate of 1C to the upper limit cutoff voltage (for example, the upper limit cutoff voltage of Example 1 was 3.65V), then charged at constant voltage to the cutoff current of 0.05C, and then discharged at a discharge rate of 1C to the lower limit cutoff voltage (for example, the lower limit cutoff voltage of Example 1 was 2V), and the discharge capacity at this time was recorded as A1. Repeat the charge and discharge for 1000 cycles, test and record the cycle discharge capacity of the 1000th cycle as A2, and calculate the capacity retention rate η1 at 25℃ for 1000 cycles according to the following formula: capacity retention rate η1 = A2 / A1 × 100%.

[0088] High temperature cycle performance test:

[0089] The battery was charged at a high temperature of 45℃ with a charge rate of 1C to the upper limit cutoff voltage, then charged at constant voltage to the cutoff current of 0.05C, and then discharged at a discharge rate of 1C to the lower limit cutoff voltage, and the discharge capacity at this time was recorded as A3. Repeat the charge and discharge for 1000 cycles, test and record the cycle discharge capacity of the 1000th cycle as A4, and calculate the capacity retention rate η2 at 45℃ for 1000 cycles according to the following formula: capacity retention rate η2 = A4 / A3 × 100%.

[0090] Low temperature discharge performance test:

[0091] The battery was charged at 25℃ with a charge rate of 1C to the upper limit cutoff voltage, then charged at constant voltage to the cutoff current of 0.05C, and then discharged at a discharge rate of 1C to the lower limit cutoff voltage, and the discharge capacity at this time was recorded as B1. The battery was charged at 25℃ with a charge rate of 1C to the upper limit cutoff voltage, then charged at constant voltage to the cutoff current of 0.05C, and then transferred to a low temperature of-20℃ for 240min, and then discharged at a constant current of 0.5C, and the discharge capacity was recorded as B2. The capacity retention rate η3 at-20℃ was calculated according to the following formula: capacity retention rate η3 = B2 / B1 × 100%.

[0092] Table 1 Electrolyte compositions of Examples 1-33 and Comparative Examples 1-9

[0093] Table 2 Partial differences and test results of Examples 1-33 and Comparative Examples 1-9

[0094] Results and conclusions:

[0095] As can be seen from Examples 1-33 and Comparative Examples 1-9 and Tables 1-2, the simultaneous introduction of the first additive and the second additive into the electrolyte can improve the room temperature and high temperature cycle stability of the battery and the discharge performance of the battery under low temperature conditions. As can be seen from Examples 5-14 and Comparative Examples 1-3, with the increase of the content of the first additive in the electrolyte, the overall improvement effect on the room temperature and high temperature cycle stability of the battery and the discharge performance of the battery under low temperature conditions is first increased and then decreased, and with the increase of the content of the second additive in the electrolyte, the overall improvement effect on the room temperature and high temperature cycle stability of the battery and the discharge performance of the battery under low temperature conditions is also first increased and then decreased, and the content of the first additive in the electrolyte is controlled to be 0.3-2wt%, which can achieve a better overall improvement effect; the content of the second additive in the electrolyte is controlled to be 0.2-2wt%, which can also achieve a better overall improvement effect; and further, the total content of the additives in the electrolyte can be controlled to be less than 4wt%. Further, as can be seen from Examples 5, 7, 8, 11 and Comparative Examples 1-3, the combination of the first additive and the second additive is conducive to reducing the overall amount of the first additive and the second additive on the basis of achieving a better improvement effect; and further, as can be seen from Examples 1-33 and Comparative Examples 1-9, the electrolyte compositions of the above examples are not only suitable for battery systems with low working voltage such as lithium iron phosphate, but also suitable for battery systems with high working voltage such as nickel-cobalt-manganese system and lithium cobaltate system.

[0096] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0097] Although the embodiments of the present application have been shown and described above, it is understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and that changes, modifications, substitutions and variations can be made by those skilled in the art without departing from the scope of the present application.

Claims

1. An electrolyte, characterized by, Comprising: a lithium salt, an organic solvent, a first additive as shown in Formula I, and a second additive including at least one of 1,3-propane sultone, 1,3-propene sultone, ethylene sulfate, methanedisulfonic acid methylene ester, a compound as shown in Formula II, In formula I, R1, R2, R3, R4, R5, R6, R7, R8 are independently selected from any one of hydrogen, halogen, alkyl and halogenated alkyl.

2. The electrolyte according to claim 1, characterized in that, said alkyl is C 1-8 alkyl, said haloalkyl is C 1-8 haloalkyl.

3. The electrolyte according to claim 1 or 2, characterized in that, The first additive includes at least one of compounds represented by Formula A-1 to Formula A-8:

4. The electrolyte according to any one of claims 1 to 3, characterized in that The content of the first additive is 0.1wt%-4wt% based on the total mass of the electrolyte; and / or, the content of the second additive is 0.1wt%-5wt% based on the total mass of the electrolyte.

5. The electrolyte according to any one of claims 1 to 4, characterized in that, At least one of the following conditions is satisfied: The content of the first additive is 0.5wt%-2wt% based on the total mass of the electrolyte; The content of the second additive is 0.2wt%-2wt% based on the total mass of the electrolyte; The second additive comprises methanedisulfonic acid methylene ester and / or a compound shown in formula II.

6. The electrolyte according to any one of claims 1 to 5, characterized in that, At least one of the following conditions is satisfied: The electrolyte further comprises at least one of vinylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate; The electrolyte further comprises at least one of tris(trimethylsilyl)borate, tris(trimethylsilyl)phosphate, triallyl phosphate; The electrolyte further comprises at least one of anhydride type additive and nitrile type additive.

7. The electrolyte according to claim 6, characterized in that The total content of the second additive, the vinylene carbonate, the fluoroethylene carbonate, the vinyl ethylene carbonate, the tris(trimethylsilyl)borate, the tris(trimethylsilyl)phosphate, the triallyl phosphate, the anhydride type additive and the nitrile type additive is not more than 5wt% based on the total mass of the electrolyte; and / or, The total content of the first additive, the vinylene carbonate, the fluoroethylene carbonate, the vinyl ethylene carbonate is not more than 4wt%.

8. The electrolyte according to any one of claims 1 to 7, characterized in that, At least one of the following conditions is satisfied: The lithium salt comprises at least one of LiPF6, LiAsF6, LiClO4, LiBF4, LiB(C2O4)2, LiBF2C2O4, LiN(SO2F)2, LiN(SO2CF3)2, LiPO2F2, LiPF2(C2O4)2 and LiPF4C2O4; The content of the lithium salt is 8wt%-20wt% based on the total mass of the electrolyte; The organic solvent comprises a cyclic organic solvent and / or a chain organic solvent, the cyclic organic solvent comprises at least one of vinyl carbonate, propylene carbonate, γ-butyrolactone, sulfolane, fluoroethylene carbonate; the chain organic solvent comprises at least one of dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl acetate, propyl propionate, ethyl propionate, propyl acetate, methyl propionate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 2,2-difluoroethyl acetate; The content of the organic solvent is 71wt%-91.3wt% based on the total mass of the electrolyte.

9. A battery, characterized by The electrolyte of any one of claims 1-8.

10. The battery of claim 9, wherein, Further comprising: a positive electrode active material including at least one of LiCoO2, LiMn2O4, LiMnO2, Li2MnO4, LiFePO4, Li 1+a Mn 1-x M x O2, LiCo 1-x M x O2, LiFe 1-x M x PO4, Li2Mn 1-x O4, wherein M includes at least one selected from Ni, Co, Mn, Al, Cr, Mg, Zr, Mo, V, Ti, B, F, 0≤a≤0.2, 0≤x<1; and / or a negative electrode active material including at least one of graphite, silicon-carbon composite material, silicon material, lithium metal, lithium titanate.

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