Additive for battery electrolyte, lithium ion battery electrolyte, lithium ion battery

Abstract

The application provides a battery electrolyte additive, which comprises at least a formula I shown in the following structure, wherein R1 and R2 are independently selected from one of fluorine atom-substituted or unsubstituted methyl, fluorine atom-substituted or unsubstituted benzyl, fluorine atom-substituted or unsubstituted benzoyl, fluorine atom-substituted or unsubstituted alkanoyl, fluorine atom-substituted or unsubstituted alkylsulfonyl, fluorine atom-substituted or unsubstituted trimethylsilyl and fluorine atom-substituted or unsubstituted trimethylsiloxy; R3-R5 are independently selected from substituted or unsubstituted alkyl with 1-10 carbon atoms, substituted or unsubstituted alkenyl with 2-10 carbon atoms and substituted or unsubstituted aryl with 6-10 carbon atoms. The application provides a battery electrolyte additive, which can consider high and low temperature performance and improve the overall output performance of a lithium ion battery.

Description

TECHNICAL FIELD

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

[0002] With the rapid development of pure electric vehicles and hybrid electric vehicles, the requirements for the energy density, cycle life and safety of lithium ion batteries are continuously improved, and the high-nickel ternary positive electrode system becomes an effective way. However, the high-nickel system still has some problems: on the one hand, the high-nickel ternary material will release [O] with high activity under high temperature and high pressure, the high activity [O] and the protons generated by the oxidation of the solvent generate H2O, and then react with LiPF6 to generate HF, which corrodes the electrode surface and accelerates the destruction of the metal ions and active hydrogen substances in the battery system, which easily causes the problems of battery swelling and thermal runaway. On the other hand, the traditional electrolyte system using LiPF6 / carbonate is used with the current high-nickel ternary material, and the carbonate solvent is more easily oxidized under high temperature conditions to generate gas byproducts and protons, which react with the high-nickel material interface to generate phase transition and cause material damage. SUMMARY

[0003] The purpose of the present application is to provide a battery electrolyte additive, which aims to solve the problem that the existing high lithium ion battery is oxidized and decomposed under high temperature conditions, resulting in the problem that the high temperature storage performance and the low temperature discharge performance of the battery cannot be considered.

[0004] Another purpose of the present application is to provide a lithium ion battery electrolyte containing the above-mentioned battery electrolyte additive.

[0005] Still another purpose of the present application is to provide a lithium ion battery containing the above-mentioned lithium ion battery electrolyte.

[0006] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0007] The present application provides a battery electrolyte additive, which at least comprises a formula I as shown below,

[0008]

[0009] In formula I, R1 and R2 are independently selected from one of a fluorine atom-substituted or unsubstituted methyl group, a fluorine atom-substituted or unsubstituted benzyl group, a fluorine atom-substituted or unsubstituted benzoyl group, a fluorine atom-substituted or unsubstituted alkanoyl group, a fluorine atom-substituted or unsubstituted alkylsulfonyl group, a fluorine atom-substituted or unsubstituted trimethylsilyl group, and a fluorine atom-substituted or unsubstituted trimethylsiloxy group.

[0010] R3, R4, R5 are independently selected from substituted or unsubstituted alkyl group with carbon number of 1-10, substituted or unsubstituted alkenyl group with carbon number of 2-10, substituted or unsubstituted aryl group with carbon number of 6-10.

[0011] Preferably, the compound of formula I is selected from the following structures:

[0012]

[0013]

[0014] The second aspect of the present application provides a lithium ion battery electrolyte, the lithium ion battery electrolyte comprises non-aqueous organic solvent, lithium salt and additive, wherein the additive is the additive for battery electrolyte of the present application.

[0015] Preferably, the total mass percentage of the compound of formula I is 0.05%-2% based on the total mass of the lithium ion battery electrolyte.

[0016] Preferably, the additive further comprises at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, ethylene sulfate, propylene sulfate.

[0017] Preferably, the total mass percentage of the additive is less than or equal to 15% based on the total mass of the lithium ion battery electrolyte.

[0018] Preferably, the total mass percentage of the non-aqueous organic solvent is 55%-75% based on the total mass of the lithium ion battery electrolyte.

[0019] The third aspect of the present application provides a lithium ion battery, the lithium ion battery comprises positive electrode, negative electrode, separator and electrolyte, characterized in that the electrolyte is the lithium ion battery electrolyte of the present application.

[0020] Preferably, the active material of the positive electrode is transition metal oxide.

[0021] Preferably, the active material of the negative electrode is graphite, Si-containing composite material or lithium titanate.

[0022] Preferably, the transition metal oxide is LiNi x Co y Mn z L (1-x-y-z)O2, wherein L is one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si and Fe, and x, y, z satisfy 0≤x<1, 0<y≤1, 0≤z<1, and 0<x+y+z≤1.

[0023] The battery electrolyte additive provided by the application at least comprises a structure shown in Formula I. The structure shown in Formula I contains an amino silane structure (Si-N). On the one hand, the amino silane structure is a Lewis base, can hydrolyze or polymerize with HF and H2O containing active proton hydrogen in the electrolyte, achieve the purpose of removing H2O and inhibiting HF, and further improve the thermal stability of LiPF6 and the high-temperature performance of the battery. In addition, Si in the amino silane structure can react with F to reduce LiF on the electrode surface, reduce the interfacial impedance, and improve the low-temperature performance of the lithium ion battery. On the other hand, the N atom in the amino silane structure contains a lone pair of electrons, is easy to lose electrons and oxidize into a protective film at the positive electrode of the battery, inhibits the oxidative decomposition of the electrolyte at the positive electrode, and improves the high-temperature storage performance of the lithium ion battery. In addition, since the fluorine atom has the largest electronegativity, the Formula I provided by the application after fluorine substitution is conducive to the dispersion of the electron cloud, thereby improving the electron-accepting ability of the central atom, preferentially reducing the protective film at a high solvent reduction potential, and further improving the electrochemical stability and high-temperature resistance.

[0024] In particular, when R1 and R2 in Formula I are independently selected from a benzoyl group substituted or unsubstituted with a fluorine atom, an alkanoyl group substituted or unsubstituted with a fluorine atom, and an alkylsulfonyl group substituted or unsubstituted with a fluorine atom, the benzoyl group, the alkanoyl group, and the alkylsulfonyl group in the substituent form an amide after the Si-N bond is broken, which is conducive to reducing the occurrence of side reactions and improving the battery gas production problem. In addition, the C=O and O=S=O functional groups can be preferentially reduced on the negative electrode surface to protect the electrode from being eroded by the electrolyte.

[0025] In summary, the battery electrolyte additive provided by the application contains the structure shown in Formula I, can form a low-impedance protective film on the surface of the electrode (positive electrode and negative electrode), inhibit the side reactions of the electrode and the electrolyte, reduce the interfacial impedance, and take into account the high and low temperature performance (has good low-temperature discharge performance, good cycle performance and high-temperature storage performance), thereby improving the overall output performance of the lithium ion battery.

[0026] The lithium ion battery electrolyte provided by the application contains the battery electrolyte additive provided by the application, can form a low-impedance protective film on the surface of the electrode (positive electrode and negative electrode), inhibit the side reactions of the electrode and the electrolyte, reduce the interfacial impedance, take into account the high and low temperature performance (has good low-temperature discharge performance, good cycle performance and high-temperature storage performance), and improve the overall output performance of the lithium ion battery.

[0027] The lithium ion battery provided by the application can significantly improve the cycle performance and low-temperature discharge performance of the lithium ion battery and improve the overall output performance of the lithium ion battery due to containing the lithium ion battery electrolyte of the application. DETAILED DESCRIPTION

[0028] In order to make the technical problems to be solved by the application, the technical solutions and the beneficial effects more clearly understood, the application will be further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not used to limit the application.

[0029] In the description of the application, it should be understood that the terms "first", "second" are only used for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can explicitly or implicitly include one or more of the features. In the description of the application, the meaning of "a plurality of" is two or more, unless otherwise specifically limited.

[0030] The first aspect of the embodiment of the application provides a battery electrolyte additive, which at least comprises a formula I as shown below,

[0031]

[0032] In formula I, R1 and R2 are independently selected from one of a fluorine atom-substituted or unsubstituted methyl group, a fluorine atom-substituted or unsubstituted benzyl group, a fluorine atom-substituted or unsubstituted benzoyl group, a fluorine atom-substituted or unsubstituted alkanoyl group, a fluorine atom-substituted or unsubstituted alkylsulfonyl group, a fluorine atom-substituted or unsubstituted trimethylsilyl group, and a fluorine atom-substituted or unsubstituted trimethylsiloxy group.

[0033] R3, R4 and R5 are independently selected from a substituted or unsubstituted alkyl group with 1-10 carbon atoms, a substituted or unsubstituted alkenyl group with 2-10 carbon atoms, and a substituted or unsubstituted aryl group with 6-10 carbon atoms.

[0034] The additive for battery electrolyte provided by the embodiment of the present application at least comprises a structure shown in Formula I. The structure shown in Formula I contains an amino silane structure (Si-N). On one hand, the amino silane structure is a Lewis base, which can cause hydrolysis or polymerization reaction with HF and H2O containing active proton hydrogen in the electrolyte, so as to remove H2O and inhibit HF, thereby improving the thermal stability of LiPF6 and the high-temperature performance of the battery. On the other hand, the Si in the amino silane structure can react with F to reduce LiF on the electrode surface, reduce the interfacial impedance, and improve the low-temperature performance of the lithium ion battery. In addition, the N atom in the amino silane structure contains lone pair electrons, which is easy to be oxidized into a protective film on the positive electrode of the battery, inhibits the oxidative decomposition of the electrolyte on the positive electrode, and improves the high-temperature storage performance of the lithium ion battery.

[0035] In summary, the additive for battery electrolyte provided by the embodiment of the present application contains the structure shown in Formula I, which can form a low-impedance protective film on the surface of the electrode (positive electrode and negative electrode), inhibit the side reaction of the electrode and the electrolyte, reduce the interfacial impedance, and balance the high-temperature and low-temperature performance (good low-temperature discharge performance, good cycle performance and high-temperature storage performance), thereby improving the overall output performance of the lithium ion battery.

[0036] In the embodiment of the present application, the additive is mainly used to improve the film forming performance of the battery during the first charge and discharge. Due to the structure of Formula I provided by the embodiment of the present application, which has the above-mentioned amino silane structure characteristics, the above-mentioned technical effects can be achieved.

[0037] Specifically, in the structure of Formula I, R1 and R2 are important structural functional groups, which have obvious influence on the electrochemical performance of the battery. In some embodiments, R1 or R2 is selected from one of methyl, benzyl, benzoyl, alkanoyl, alkylsulfonyl, trimethylsilyl and trimethylsiloxy. In some embodiments, R1 or R2 is selected from one of fluorine atom-substituted methyl, fluorine atom-substituted benzyl, fluorine atom-substituted benzoyl, fluorine atom-substituted alkanoyl, fluorine atom-substituted alkylsulfonyl, fluorine atom-substituted trimethylsilyl and fluorine atom-substituted trimethylsiloxy. At this time, since the fluorine atom has the largest electronegativity, the Formula I after fluorine substitution is beneficial to the dispersion of the electron cloud, thereby improving the electron-capturing ability of the central atom, and the protective film can be preferentially reduced at a higher solvent reduction potential, thereby improving the electrochemical stability and high-temperature resistance. Of course, it should be understood that the present application does not require that R1 and R2 are both unsubstituted groups, nor that R1 and R2 are both fluorine atom-substituted groups.

[0038] In this case, it is particularly preferred that R1and R2in formula I are independently selected from a group consisting of a benzoyl group substituted or unsubstituted by fluorine atoms, an alkanoyl group substituted or unsubstituted by fluorine atoms, and an alkylsulfonyl group substituted or unsubstituted by fluorine atoms. When R1and R2in formula I are independently selected from a group consisting of a benzoyl group substituted or unsubstituted by fluorine atoms, an alkanoyl group substituted or unsubstituted by fluorine atoms, and an alkylsulfonyl group substituted or unsubstituted by fluorine atoms, the benzoyl group, the alkanoyl group, and the alkylsulfonyl group in the substituents form amides after the Si-N bond is broken, which is advantageous for reducing the occurrence of side reactions and improving the gas production problem of the battery. In addition, the C=O and O=S=O functional groups can be preferentially reduced on the surface of the negative electrode, protecting the electrode from corrosion by the electrolyte.

[0039] In formula I, R3, R4, and R5 are all connected to the silicon atom and are independently selected from a group consisting of an alkyl group having 1 to 10 carbon atoms substituted or unsubstituted, an alkenyl group having 2 to 10 carbon atoms substituted or unsubstituted, and an aryl group having 6 to 10 carbon atoms substituted or unsubstituted. In formula I, the R3 to R5 groups have a suitable carbon chain length, a suitable molecular structure size, good compatibility with non-aqueous organic solvents, and good reactivity with the positive and negative electrodes, which is advantageous for forming a low-impedance SEI film on the positive and negative electrodes, improving the low-temperature characteristics and power characteristics of the lithium ion battery, inhibiting the oxidative decomposition of the electrolyte on the positive electrode, and improving the high-temperature storage performance of the lithium ion battery. If the number of carbon atoms in the R3 to R5 groups is too high, not only the solubility is reduced, but also the spatial steric hindrance is too large, which can block some reaction sites, increase the reaction difficulty, reduce the reaction activity, and ultimately affect the formation of the electrode surface protection film (SEI).

[0040] In some embodiments, when R3, R4, and R5 are substituted alkyl groups, alkenyl groups, or aryl groups, the substituting atom is a fluorine atom. Since the fluorine atom has the largest electronegativity, formula I after fluorine substitution is advantageous for the dispersion of the electron cloud, thereby improving the electron-capturing ability of the central atom, preferentially reducing the formation of a protection film at a higher solvent reduction potential, and further improving the electrochemical stability and high-temperature resistance.

[0041] Specifically, the formula I is selected from the following compounds:

[0042]

[0043]

[0044] The compound of formula I is preferably used as an additive for the electrolyte of a lithium ion battery, which has excellent effects on improving the cycle performance, high-temperature storage performance, and low-temperature discharge performance of the lithium ion battery.

[0045] More preferably, the compound of formula I is selected from the group consisting of compounds in which R1 and R2 are independently selected from the group consisting of fluorine atom-substituted or unsubstituted benzoyl, fluorine atom-substituted or unsubstituted alkanoyl, and fluorine atom-substituted or unsubstituted alkylsulfonyl.

[0046]

[0047] The compound of formula I as an additive for lithium ion battery electrolyte has excellent effects on improving the cycle performance, high-temperature storage performance and low-temperature discharge performance of the lithium ion battery, because R1 and R2 are independently selected from the group consisting of fluorine atom-substituted or unsubstituted benzoyl, fluorine atom-substituted or unsubstituted alkanoyl, and fluorine atom-substituted or unsubstituted alkylsulfonyl.

[0048] Correspondingly, the second aspect of the embodiment of the present application provides a lithium ion battery electrolyte, which comprises a non-aqueous organic solvent, a lithium salt and an additive, wherein the additive is the additive for battery electrolyte described above. Specifically, the additive for battery electrolyte comprises at least a compound of formula I as shown below,

[0049]

[0050] In formula I, R1 and R2 are independently selected from one of fluorine atom-substituted or unsubstituted methyl, fluorine atom-substituted or unsubstituted benzyl, fluorine atom-substituted or unsubstituted benzoyl, fluorine atom-substituted or unsubstituted alkanoyl, fluorine atom-substituted or unsubstituted alkylsulfonyl, fluorine atom-substituted or unsubstituted trimethylsilyl, and fluorine atom-substituted or unsubstituted trimethylsiloxy.

[0051] R3, R4 and R5 are independently selected from substituted or unsubstituted alkyl with carbon number of 1-10, substituted or unsubstituted alkenyl with carbon number of 2-10, and substituted or unsubstituted aryl with carbon number of 6-10.

[0052] The lithium ion battery electrolyte provided by the embodiment of the present application contains the additive for battery electrolyte of formula I. The structure of formula I contains an aminosilane structure (Si-N). On the one hand, the aminosilane structure is a Lewis base, which can hydrolyze or polymerize with HF and H2O containing active proton hydrogen in the electrolyte, so as to remove H2O and inhibit HF, thereby improving the thermal stability of LiPF6 and the high-temperature performance of the battery. In addition, Si in the aminosilane structure can react with F to reduce LiF on the electrode surface, reduce the interfacial impedance and improve the low-temperature performance of the lithium ion battery. On the other hand, the N atom in the aminosilane structure contains lone pair electrons, which is easy to lose electrons and oxidize into a protective film on the positive electrode, thereby inhibiting the oxidative decomposition of the electrolyte on the positive electrode and improving the high-temperature storage performance of the lithium ion battery.

[0053] In summary, the additive containing the structure shown in Formula I provided by the embodiment of the application can form a low-impedance protective film on the surface of the electrode (positive electrode and negative electrode), inhibit the side reaction of the electrode and the electrolyte, reduce the interface impedance, take into account the high and low temperature performance (has good low-temperature discharge performance, and good cycle performance and high-temperature storage performance), and improve the overall output performance of the lithium ion battery.

[0054] The components of the lithium ion battery electrolyte are described in detail as follows.

[0055] Non-aqueous organic solvent

[0056] Water has certain influence on the formation of SEI of the lithium ion battery and the performance of the battery, which is specifically manifested in that the battery capacity becomes small, the discharge time becomes short, the internal resistance increases, the cycle capacity attenuates, the battery expands, etc. The non-aqueous organic solvent is used as the solvent component of the electrolyte in the embodiment of the application.

[0057] Preferably, the non-aqueous organic solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, γ-butyrolactone, γ-valerolactone, δ-valerolactone and ε-caprolactone. The addition of the preferred non-aqueous organic solvent can improve the comprehensive performance of the lithium ion secondary battery.

[0058] Further preferably, the sum of the mass percentage contents of the non-aqueous organic solvents is 55% to 75% based on 100% of the total mass of the electrolyte.

[0059] Lithium salt

[0060] In the embodiment of the application, the lithium salt can be selected from the lithium salts commonly used in lithium ion batteries, including but not limited to one or more of lithium hexafluorophosphate, lithium perchlorate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium bis(fluoro)oxalato borate, lithium bis(trifluoromethylsulfonyl)imide and lithium bis(fluoro)sulfonimide. Further, the amount of the lithium salt accounts for 10% to 18% of the mass percentage in the lithium ion secondary battery electrolyte.

[0061] Additive

[0062] In the embodiment of the application, the additive is mainly used to improve the film forming performance during the first charge and discharge.

[0063] In the embodiment of the application, the additive is mainly used to improve the film forming performance of the battery during the first charge and discharge. Due to the structure of Formula I provided by the embodiment of the application, which has the above-mentioned amino silane structure characteristics, the above-mentioned technical effects can be achieved.

[0064] Specifically, in the structure of formula I, R1 and R2 are important structural functional groups, which have obvious influence on the electrochemical performance of the battery. In some embodiments, R1 or R2 is selected from one of methyl, benzyl, benzoyl, alkanoyl, alkylsulfonyl, trimethylsilyl and trimethylsilyloxy. In some embodiments, R1 or R2 is selected from one of fluorine atom-substituted methyl, fluorine atom-substituted benzyl, fluorine atom-substituted benzoyl, fluorine atom-substituted alkanoyl, fluorine atom-substituted alkylsulfonyl, fluorine atom-substituted trimethylsilyl and fluorine atom-substituted trimethylsilyloxy. At this time, since the fluorine atom has the largest electronegativity, the formula I after fluorine substitution is beneficial to the dispersion of the electron cloud, thereby improving the electron-accepting ability of the central atom, and the priority reduction to form a protective film at a higher solvent reduction potential, thereby improving the electrochemical stability and high-temperature resistance. Of course, it should be understood that the embodiments of the present application do not require R1 and R2 to be unsubstituted groups at the same time, nor do they require R1 and R2 to be fluorine atom-substituted groups at the same time.

[0065] On this basis, it is particularly preferred that R1 and R2 in formula I are independently selected from fluorine atom-substituted or unsubstituted benzoyl, fluorine atom-substituted or unsubstituted alkanoyl, and fluorine atom-substituted or unsubstituted alkylsulfonyl. When R1 and R2 in formula I are independently selected from fluorine atom-substituted or unsubstituted benzoyl, fluorine atom-substituted or unsubstituted alkanoyl, and fluorine atom-substituted or unsubstituted alkylsulfonyl, the benzoyl, alkanoyl and alkylsulfonyl substances in the substituent group form amides after Si-N bond breaking, which is beneficial to reducing the occurrence of side reactions and improving the battery gas production problem. In addition, the C=O and O=S=O functional groups can be preferentially reduced on the negative electrode surface to protect the electrode from corrosion by the electrolyte.

[0066] In the structure of formula I, R3, R4 and R5 are all connected to the silicon atom and are independently selected from substituted or unsubstituted alkyl with 1-10 carbon atoms, substituted or unsubstituted alkenyl with 2-10 carbon atoms, and substituted or unsubstituted aryl with 6-10 carbon atoms. The formula I structure of the above R3-R5 groups has a suitable carbon chain length, a suitable molecular structure size, good compatibility with non-aqueous organic solvents, and good reactivity with positive and negative electrodes, which is beneficial to the formation of a low-impedance SEI film on the positive and negative electrodes, improves the low-temperature characteristics and power characteristics of the lithium ion battery, inhibits the oxidative decomposition of the electrolyte on the positive electrode, and improves the high-temperature storage performance of the lithium ion battery. If the number of carbon atoms in the R3-R5 groups is too high, not only the solubility is reduced, but also due to the excessive steric hindrance, some reaction sites are blocked, the reaction difficulty is increased, the reaction activity is reduced, and finally the formation of the electrode surface protective film (SEI) is affected.

[0067] In some embodiments, when R3, R4, R5 are substituted alkyl, alkenyl or aryl, the substituting atom is fluorine atom. In some embodiments, when R3, R4, R5 are substituted alkyl, alkenyl or aryl, the substituting atom is fluorine atom. Since fluorine atom has the largest electronegativity, the compound of formula I after fluorine substitution is beneficial to the dispersion of electron cloud, thereby improving the electron-accepting ability of the central atom, and the compound of formula I can be preferentially reduced to form a protective film at a higher solvent reduction potential, thereby improving the electrochemical stability and high-temperature resistance. Specifically preferably, the compound of formula I is selected from the following compounds:

[0068]

[0069] The compound of formula I as the additive of the electrolyte of the lithium ion battery has excellent effects in improving the cycle performance, high-temperature storage performance and low-temperature discharge performance of the lithium ion battery.

[0070] More preferably, the compound of formula I is selected from the following compounds in which R1, R2 are independently selected from fluorine atom-substituted or unsubstituted benzoyl, fluorine atom-substituted or unsubstituted alkanoyl, fluorine atom-substituted or unsubstituted alkylsulfonyl:

[0071]

[0072]

[0073] The compound of formula I as the additive of the electrolyte of the lithium ion battery has excellent effects in improving the cycle performance, high-temperature storage performance and low-temperature discharge performance of the lithium ion battery.

[0074] On the basis of the above embodiments, further preferably, the total mass percentage of the compounds of formula I is 0.05% to 2% based on 100% of the total mass of the electrolyte. If the mass percentage of the compound of formula I is less than 0.05%, a stable protective film cannot be formed on the electrode surface, and the improvement effects of “inhibiting the side reaction of the electrode and the electrolyte, reducing the interfacial impedance, and comprehensively improving the output performance of the battery” cannot be achieved, and in addition, the low-temperature discharge performance of the high-nickel and silicon-carbon system cannot be improved. If the mass percentage of the compound of formula I is more than 2%, the protective film formed on the electrode surface is too thick, the battery polarization is increased, and the battery performance is deteriorated.

[0075] In the embodiment of the present application, the lithium ion battery performance can be optimized by adding other additives to the compound shown in formula I. Preferably, the additives further include at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sulfone, ethylene sulfate, and propylene sulfate. The other additives can improve the electron-accepting ability of the central atom by means of the electron-withdrawing effect of unsaturated bonds or halogen atoms or S-containing functional groups, can be reduced at a higher solvent reduction potential, and the reduction product is adsorbed on the "catalytically active point" on the surface of the negative electrode such as graphite, thereby assisting the formation of SEI film and improving the cycle stability of the battery.

[0076] Further preferably, the sum of the mass percentages of the additives is less than or equal to 15% based on 100% of the total mass of the electrolyte, so as to ensure the content of non-aqueous organic solvents and lithium salt in the electrolyte, and further ensure the performance thereof. On this basis, the mass percentage of any one of the preferred additives (fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sulfone, ethylene sulfate, and propylene sulfate) alone accounts for 0.1% to 10% of the total mass of the electrolyte.

[0077] In addition, the embodiment of the present application provides a lithium ion battery, which comprises a positive electrode, a negative electrode, a separator, and an electrolyte, and the electrolyte is the lithium ion battery electrolyte according to the present application.

[0078] The lithium ion secondary battery provided by the embodiment of the present application can significantly improve the cycle performance and low-temperature discharge performance of the lithium ion battery, and improve the overall output performance of the lithium ion battery due to the presence of the lithium ion secondary battery electrolyte according to the present application.

[0079] In the embodiment of the present application, the composition of the electrolyte, the selection, content, and preferred type of each component, and the selection basis thereof are as described above, and will not be described herein again in order to save space.

[0080] The positive electrode comprises a positive electrode active material, and the positive electrode active material commonly used in lithium ion batteries can be used in the embodiment of the present application. Preferably, the active material of the positive electrode is a transition metal oxide.

[0081] Specifically preferably, the transition metal oxide is LiNi x Co y Mn z L (1-x-y-z) O2, wherein L is one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, and Fe, the values of x, y, and z satisfy: 0≤x<1, 0<y≤1, 0≤z<1, and 0<x+y+z≤1.

[0082] The negative electrode comprises a negative electrode active material, and the negative electrode active material commonly used in lithium ion batteries can be used in the embodiments of the present application. Preferably, the active material of the negative electrode is graphite, a Si-containing composite material, or lithium titanate.

[0083] The selection of the separator includes, but is not limited to, a single-layer polyethylene (PE), a single-layer polypropylene (PP), a double-layer PP / PE, a three-layer PP / PE / PP, or a ceramic separator.

[0084] The following will be described in conjunction with specific embodiments.

[0085] In each embodiment, the Chinese interpretation of the English abbreviations is as follows:

[0086] EC: ethylene carbonate

[0087] EMC: ethyl methyl carbonate

[0088] DMC: dimethyl carbonate

[0089] LiPF6: lithium hexafluorophosphate

[0090] FEC: fluoroethylene carbonate

[0091] DTD: ethylene sulfate

[0092] PS: 1,3-propane sulfone lactone

[0093] PST: 1,3-propylene sulfone lactone

[0094] In each embodiment, the structure of the additive used and its corresponding letter number are shown in Table 1.

[0095] Table 1

[0096]

[0097]

[0098]

[0099] Embodiment 1

[0100] A lithium ion secondary battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode active material is a lithium nickel cobalt manganese oxide (NCM811) material; the negative electrode active material is a silicon-carbon composite material (Si / C), and the preparation method of the lithium ion secondary battery comprises the following steps:

[0101] Mixing positive active material NCM811, conductive carbon black and binder polyvinylidene fluoride in a certain mass ratio, dispersing in N-methyl-2-pyrrolidone to obtain positive electrode slurry, uniformly coating the positive electrode slurry on both sides of the aluminum foil, drying, calendering and vacuum drying, and welding the aluminum lead wire with an ultrasonic welding machine to obtain a positive electrode plate (positive electrode sheet), the thickness of the electrode plate is between 100-115 μm;

[0102] Mixing silicon-carbon composite material, conductive carbon black, binder styrene-butadiene rubber and carboxymethyl cellulose in a certain mass ratio, dispersing in deionized water to obtain negative electrode slurry, coating the negative electrode slurry on both sides of the copper foil, drying, calendering and vacuum drying, and welding the nickel lead wire with an ultrasonic welding machine to obtain a negative electrode plate (negative electrode sheet), the thickness of the electrode plate is between 115-135 μm;

[0103] Mixing ethylene carbonate (EC), methyl ethyl carbonate (EMC) and dimethyl carbonate (DMC) in a mass ratio of 2:1:7, then adding 12.5% lithium hexafluorophosphate based on the total mass of the electrolyte, and adding 1% P1 based on the total mass of the electrolyte to prepare the electrolyte.

[0104] Using single-sided coating of Al2O3 to prepare the ceramic separator.

[0105] Placing the prepared positive electrode sheet, separator and negative electrode sheet on an automatic winding machine to wind to obtain a bare cell; placing the bare cell in a cylindrical steel shell, welding the negative electrode tab and the cap tab, injecting the electrolyte prepared above into the dried cell, sealing, standing, pre-charging, aging and distributing to complete the preparation of the lithium ion secondary battery (18650).

[0106] Examples 2-27

[0107] Examples 2-23, except that the components in the electrolyte are different, the rest of the positive electrode, negative electrode, separator and preparation of lithium ion secondary battery are the same as Example 1, the selection of the compound represented by structural formula I and its content in each example are shown in Table 2.

[0108] Examples 24-27, in order to further improve the comprehensive output performance of the battery, on the basis of the above Examples 1-23, a film-forming additive is added, the selection of each component and its content are shown in Table 3.

[0109] Comparative Examples 1-5

[0110] In Comparative Examples 1 to 5, except that the nonaqueous organic solvent and the type and content of the additive in the electrolyte solution (based on the total mass of the electrolyte solution) were different from those of Example 1, the positive electrode, the negative electrode, the separator, and the lithium ion secondary battery were prepared in the same manner as in Example 1. The type and content of the nonaqueous organic solvent and the additive in Comparative Example 1 are shown in Table 2, and the type and content of the nonaqueous organic solvent and the additive in Comparative Examples 2 to 4 are shown in Table 3.

[0111] The lithium ion secondary batteries prepared in Examples 1 to 27 and Comparative Examples 1 to 5 were subjected to performance tests, and the test methods were as follows.

[0112] 1) Cycle performance test: After the battery was subjected to capacity equalization at 25 ± 2°C / 45°C ± 2°C, the battery was charged at 0.5C constant current and constant voltage to 4.2V (cut-off current: 0.01C), and then discharged at 1C constant current to 2.75V. After N cycles of charging / discharging, the capacity retention rate at the Nth cycle was calculated using the following formula:

[0113] Nth cycle capacity retention rate (%) = (Nth cycle discharge capacity / 1st cycle discharge capacity) x 100%;

[0114] 2) High-temperature storage performance: After the battery was subjected to capacity equalization at room temperature, the battery was charged at 0.5C constant current and constant voltage to 4.2V (cut-off current: 0.01C), and the initial discharge capacity of the battery was measured. After storage at 60°C for 7 days, the retention capacity and the recovery capacity of the battery were measured by discharging at 0.5C to 2.75V. The calculation formulae were as follows:

[0115] Battery capacity retention rate (%) = retention capacity / initial capacity x 100%;

[0116] Battery capacity recovery rate (%) = recovery capacity / initial capacity x 100%.

[0117] 3) Low-temperature discharge: The battery was charged at 0.5C constant current and constant voltage to 4.2V at room temperature, left to stand for 5 min, and discharged at 0.2C to 2.75V, and the initial capacity of the battery was measured. The battery was left to stand for 5 min, and then charged at 0.5C constant current and constant voltage to 4.2V (cut-off current: 0.01C). The battery was left to stand in a low-temperature chamber at -20°C for 6 h, and discharged at 0.2C to 2.75V under the same conditions, and the discharge capacity at low temperature was measured.

[0118] Low-temperature discharge retention rate (%) = low-temperature discharge capacity / initial capacity x 100%.

[0119] The test results are shown in Tables 2 and 3 below.

[0120] Table 2

[0121]

[0122]

[0123]

[0124]

[0125]

[0126] Comparative analysis was made on the battery system NCM811 matched with silicon-carbon composite materials of Examples 1-23 and Comparative Example 1. As shown in Table 2, the lithium ion batteries of Examples 1 to 23 using the technical solutions of the application have good cycle performance, high-temperature storage performance and low-temperature discharge performance; while the lithium ion batteries using the electrolyte of Comparative Example 1 have poor output performance, low high-temperature and cycle performance, and cannot balance the high-temperature and cycle performance.

[0127] Specifically, compared with Comparative Example 1, Examples 1 to 23 containing the compound of structural formula I have significantly better low-temperature discharge performance, high-temperature cycle, room-temperature cycle and high-temperature storage performance. This shows that the presence of P1, P2, P3, P4, P5, P6, P7, P8, P9, P10, P11, P12, P13 and P14 can effectively improve the comprehensive output performance of the battery.

[0128] In Examples 1 to 23, when the same compound of structural formula I is used as an additive, the lithium ion batteries obtained have better electrochemical performance (both high-temperature and cycle performance are improved) when the mass percentage of the additive is between 0.05% and 2%.

[0129] Table 3

[0130]

[0131]

[0132] In Examples 24 to 27 in Table 3, in order to further improve the comprehensive output performance of the battery, a film-forming additive, i.e. fluorinated carbonate, 1,3-propane sulfolactone, 1,3-propylene sulfonolactone or ethylene sulfate, is added on the basis of Examples 1 to 23.

[0133] As shown in Table 3, Examples 24 to 27 containing the compound of structural formula I shown in the technical solutions of the application also have good cycle performance, high-temperature storage and low-temperature discharge performance; while the batteries using the electrolytes of Comparative Examples 2 to 5 have poor partial output performance and cannot balance the high-temperature and cycle performance.

[0134] As shown in Table 2 and Table 3, in the compound of structural formula I, when R1 and R2 are independently selected from a fluorine atom-substituted or unsubstituted benzoyl group, a fluorine atom-substituted or unsubstituted alkanoyl group, and a fluorine atom-substituted or unsubstituted alkylsulfonyl group, the high and low temperature performance and cycle performance of the lithium ion battery are obtained.

[0135] As shown in Table 2 and Table 3, in the embodiment of the present application, on the basis of adding the compound of structural formula I to the electrolyte of the lithium ion battery, further adding a film-forming additive: fluorocarbon carbonate, 1,3-propane sulfolane, 1,3-propylene sulfonic acid lactone, and vinyl sulfate, the electrochemical performance of the lithium ion battery can be further optimized.

[0136] In summary, through comparison of the examples and the comparative examples, it is found that, by adding the compound shown in structural formula I, the positive and negative electrodes form a protective film, so that the lithium ion secondary battery containing the non-aqueous electrolyte has good battery output performance. The technical scheme is applied to a high-nickel positive electrode combined with a silicon-carbon composite negative electrode system, and has obvious improvement effect.

[0137] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An additive for battery electrolytes, characterized in that, The additive comprises at least Formula I with the structure shown below. Formula I In Formula I, R1 and R2 are independently selected from one of the following: fluorine-substituted methyl, fluorine-substituted benzyl, fluorine-substituted benzoyl, fluorine-substituted alkanoyl, fluorine-substituted alkylsulfonyl, fluorine-substituted trimethylsilyl, and fluorine-substituted trimethylsiloxy. R3, R4, and R5 are independently selected from alkyl groups with 1 to 10 substituted carbon atoms, alkenyl groups with 2 to 10 substituted carbon atoms, and aryl groups with 6 to 10 substituted carbon atoms. When R3, R4, and R5 are substituted alkyl, alkenyl, or aryl groups, the substituted atom is a fluorine atom.

2. A lithium-ion battery electrolyte, characterized in that, The lithium-ion battery electrolyte includes a non-aqueous organic solvent, a lithium salt, and an additive, wherein the additive is the battery electrolyte additive described in claim 1.

3. The lithium-ion battery electrolyte as described in claim 2, characterized in that, With the total mass of the lithium-ion battery electrolyte being 100%, the sum of the mass percentages of Formula I is 0.05% to 2%.

4. The lithium-ion battery electrolyte as described in claim 2, characterized in that, The additives also include at least one of the following: fluoroethylene carbonate, vinylene carbonate, 1,3-propane sulfonyl lactone, 1,4-butane sulfonyl lactone, 1,3-propene sulfonate lactone, ethylene sulfate, and propylene sulfate.

5. The lithium-ion battery electrolyte according to any one of claims 2 to 4, characterized in that, Based on the total mass of the lithium-ion battery electrolyte being 100%, the sum of the mass percentages of the additives is less than or equal to 15%.

6. The lithium-ion battery electrolyte according to any one of claims 2 to 4, characterized in that, Based on the total mass of the lithium-ion battery electrolyte being 100%, the total mass percentage of the non-aqueous organic solvents is 55% to 75%.

7. A lithium-ion battery, said lithium-ion battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is the lithium-ion battery electrolyte as described in any one of claims 2 to 6.

8. The lithium-ion battery as described in claim 7, characterized in that, The active material of the positive electrode is a transition metal oxide; and / or The active material of the negative electrode is graphite, a Si-containing composite material, or lithium titanate.

9. The lithium-ion battery as described in claim 8, characterized in that, The transition metal oxide is LiNi. x Co y Mn z L (1-x-y-z) O2, where L is one of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si and Fe, and the values ​​of x, y and z satisfy: 0≤x<1, 0<y≤1, 0≤z<1, and 0<x+y+z ≤1.

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