Additive composition, lithium ion battery electrolyte containing additive composition and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries. Specifically, the invention relates to the additive composition for the lithium ion battery electrolyte, the lithium ion battery electrolyte containing the additive composition and the preparation method of the lithium ion battery electrolyte. The invention also relates to a lithium ion battery containing the lithium ion battery electrolyte. The lithium ion battery electrolyte comprises a non-aqueous organic solvent, a lithium salt and the additive composition, and the additive composition comprises a combination of a halogen-containing sulfimide salt, alkenyl ether and an oxalic acid / borate additive, therefore, the problems of low storage performance, short long cycle life, high safety risk and the like of the conventional lithium ion battery electrolyte at high temperature are effectively solved, the cycle life of the battery can be remarkably prolonged, the capacity retention rate is high in a high-temperature environment, and meanwhile, the lithium ion battery electrolyte has excellent performance in the aspect of safety and is suitable for popularization and application. And part of possible problems of the traditional lithium ion battery electrolyte are effectively solved, and the lithium ion battery electrolyte has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries. Specifically, the present invention relates to an additive composition for lithium ion battery electrolyte, a lithium ion battery electrolyte comprising the additive composition, and a method for preparing the lithium ion battery electrolyte. In addition, the present invention also relates to a lithium ion battery comprising the lithium ion battery electrolyte. Background Art

[0002] With the rapid development of new energy vehicles, portable electronic devices and large-scale energy storage systems, the demand for lithium-ion batteries is increasing, and the performance requirements for lithium-ion batteries are also increasing.

[0003] As a key component of lithium-ion batteries, the performance of lithium-ion battery electrolyte directly affects the overall performance of the battery. However, current lithium-ion battery electrolytes are easily decomposed in high-temperature environments, their capacity decays severely during long-term cycles, and there are safety hazards when encountering abnormal situations such as short circuits and overcharging. These have limited the reliable application of lithium-ion batteries in a wider range of scenarios.

[0004] When traditional lithium-ion battery electrolytes are stored at high temperatures, the chemical stability between the solvent and the lithium salt is poor, which causes the internal resistance of the battery to rise sharply, and the battery capacity after storage is greatly reduced, seriously affecting the battery performance. In terms of long cycles, side reactions continue to occur at the interface between the electrode and the electrolyte during repeated charge and discharge, which destroys the electrode surface structure, hinders the normal insertion and removal of lithium ions, and causes the battery capacity to decline rapidly. In addition, in terms of safety, ordinary lithium-ion battery electrolytes are flammable and explosive. Once the internal thermal runaway of the battery occurs, it is very easy to cause a fire or even an explosion, threatening the safety of people and property.

[0005] Therefore, the development of new lithium-ion battery electrolytes with excellent comprehensive performance, especially high-temperature storage performance and high-temperature cycle performance, long cycle life and excellent safety performance has become a hot research direction. Summary of the invention

[0006] Purpose of the Invention

[0007] In view of the problems existing in the prior art described in the above background technology section, the purpose of the present invention is to provide an additive composition for lithium ion battery electrolyte, a lithium ion battery electrolyte containing the additive composition, and a method for preparing the lithium ion battery electrolyte. In addition, the purpose of the present invention is also to provide a lithium ion battery containing the lithium ion battery electrolyte.

[0008] Technical Solution

[0009] In order to achieve the above object, the present invention adopts the following technical solutions:

[0010] Scheme 1: An additive composition for lithium-ion battery electrolyte, wherein the additive composition comprises:

[0011] (1) A halosulfonyl imide salt additive of formula (I):

[0012]

[0013] in

[0014] R1 and R2 are independent of each other and are the same or different and represent substituted or unsubstituted C 1-10 Any of a haloalkyl group and a halogen group, and

[0015] M1 + It refers to alkali metal ions whose ionic radius is larger than that of lithium ions;

[0016] (2) Alkenyl ether additive of formula (II):

[0017] R3R4C=CH-O-R5(II)

[0018] in

[0019] R3 and R4 each independently represent hydrogen and substituted or unsubstituted C 1-10 Any of the alkyl groups;

[0020] R5 represents substituted or unsubstituted C 1-10 Alkyl group or C 2-10 alkenyl groups;

[0021] and

[0022] (3) Oxalic acid / borate additives, wherein the oxalic acid / borate additives include one or more of lithium tetrafluoroborate, lithium difluorooxalatoborate and lithium bisoxalatoborate.

[0023] Scheme 2: The additive composition according to Scheme 1 above, wherein the C 1-10 The haloalkyl group is a halomethyl group, more preferably a fluoromethyl group, most preferably a trifluoromethyl group.

[0024] Scheme 3: The additive composition according to Scheme 1 or 2 above, wherein the halogen is selected from fluorine, chlorine, bromine or iodine.

[0025] Scheme 4: The additive composition according to any one of Schemes 1 to 3 above, wherein the alkali metal element ion having an ion radius larger than that of lithium ions is selected from Na + , K + , Rb + or Cs + , preferably Rb + or Cs+ .

[0026] Scheme 5: The additive composition according to any one of Schemes 1 to 4 above, wherein the substituted C 1-10 Alkyl group or C 2-10 Alkenyl groups are 1-10 Alkoxy group or C 2-10 Alkenyloxy group substituted.

[0027] Scheme 6: An additive composition according to any one of Schemes 1 to 5 above, wherein the halosulfonyl imide salt-containing additive of formula (I) comprises one or more compounds of the following formula (I-1), formula (I-2) and formula (I-3):

[0028]

[0029] Scheme 7: The additive composition according to any one of Schemes 1 to 6 above, wherein the alkenyl ether additive of formula (II) comprises one or more compounds of the following formula (II-1) and formula (II-2):

[0030] CH3CH=CH-O-CH=CHCH3 (II-1)

[0031] CH2=CH-O-CH2CH2-O-CH=CH2 (II-2).

[0032] Scheme 8: A lithium-ion battery electrolyte comprising a non-aqueous organic solvent, a lithium salt, and the additive composition according to any one of Schemes 1 to 7 above, and optionally other additives.

[0033] Solution 9: The lithium-ion battery electrolyte according to Solution 8 above, wherein the non-aqueous organic solvent comprises a carbonate solvent.

[0034] Option 10: A lithium-ion battery electrolyte according to any one of the above options 8 to 9, wherein the non-aqueous organic solvent comprises one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC) and diethyl carbonate (DEC).

[0035] Option 11: A lithium ion battery electrolyte according to any one of the above options 8 to 10, wherein the non-aqueous organic solvent comprises about 25 to about 40 wt% of ethylene carbonate (EC), about 30 to about 45 wt% of dimethyl carbonate (DMC) and about 30 to about 45 wt% of ethyl methyl carbonate (EMC), based on the total weight of the non-aqueous organic solvent.

[0036] Scheme 12: A lithium-ion battery electrolyte according to any one of schemes 8 to 11 above, wherein the lithium salt comprises one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0037] Solution 13: The lithium ion battery electrolyte according to any one of the above solutions 8 to 12, wherein the other additives include one or more of the following additives:

[0038] Cyclic carbonate additives;

[0039] a cyclic sultone additive and / or a cyclic sulfate additive; and

[0040] An additional lithium salt additive other than the lithium salt and the oxalic acid / borate additive.

[0041] Option 14: A lithium-ion battery electrolyte according to Option 13 above, wherein the cyclic carbonate additive comprises vinylene carbonate (VC), fluoroethylene carbonate (FEC) and / or vinyl ethylene carbonate (VEC).

[0042] Option 15: According to the lithium ion battery electrolyte described in the above Option 13, the cyclic sultone additive and / or the cyclic sulfate additive comprises 1,3-propane sultone (PS), 1,3-propylene sultone (PST) and / or dithiothreitol (DTD).

[0043] Option 16: The lithium-ion battery electrolyte according to Option 13 above, wherein the additional lithium salt additive comprises lithium difluorophosphate (LiPO2F2) and / or lithium difluorobis(oxalate)phosphate (LiODFP).

[0044] Scheme 17: A lithium-ion battery electrolyte according to any one of schemes 8 to 16 above, wherein in the electrolyte, the concentration of the lithium salt is in the range of about 13.5 to about 16.5 weight %.

[0045] Scheme 18: A lithium-ion battery electrolyte according to any one of schemes 8 to 17 above, wherein in the electrolyte, the concentration of the halogen sulfonyl imide salt additive of formula (I) is in the range of about 0.2 to about 5 weight %.

[0046] Scheme 19: A lithium ion battery electrolyte according to any one of schemes 8 to 18 above, wherein in the electrolyte, the concentration of the alkenyl ether additive of formula (II) is in the range of about 0.1 to about 3 weight %.

[0047] Scheme 20: A lithium-ion battery electrolyte according to any one of schemes 8 to 19 above, wherein in the electrolyte, the concentration of the oxalic acid / borate additive is in the range of about 1 to about 2 weight %.

[0048] Option 21: A lithium-ion battery electrolyte according to any one of options 8 to 20 above, wherein in the electrolyte, the concentration of the other additives is below about 4.5 wt %.

[0049] Scheme 22: A method for preparing a lithium-ion battery electrolyte according to any one of Schemes 8 to 21 above, wherein the method comprises fully dissolving the lithium salt in the non-aqueous organic solvent, and then adding the halogenated sulfonyl imide salt additive of formula (I), the alkenyl ether additive of formula (II) and the oxalic acid / borate additive and the optional other additives to the resulting solution to completely dissolve them, thereby obtaining the lithium-ion battery electrolyte.

[0050] Scheme 23: A lithium-ion battery comprising a lithium-ion battery electrolyte according to any one of Schemes 8 to 21 above or a lithium-ion battery electrolyte prepared according to the preparation method described in Scheme 22 above.

[0051] Scheme 24: Use of a combination of an alkenyl ether additive of formula (II), formula (II-1) or formula (II-2) as defined in the above Scheme 1 or 7, a halogenated sulfonyl imide salt additive of formula (I), formula (I-1), formula (I-2) or formula (I-3) as defined in the above Scheme 1 or 6, and an oxalic acid / borate additive as defined in the above Scheme 1 as an additive for lithium-ion battery electrolyte.

[0052] Technical Effects

[0053] The lithium-ion battery electrolyte containing the additive composition of the present invention effectively solves the problems of poor storage performance, insufficient long cycle life and high safety risks of lithium-ion battery electrolyte in the prior art at high temperatures, and can significantly improve the cycle life of the battery, has a high capacity retention rate under high temperature environment, and performs well in terms of safety, effectively solving some problems existing in traditional electrolytes, and has broad application prospects.

[0054] Specifically, the lithium ion battery electrolyte comprising the additive composition of the present invention has the following significant advantages:

[0055] (1) Strong cycle stability: The protective film formed on the electrode surface by the halosulfonyl imine salt additive effectively inhibits the side reactions between the electrode and the electrolyte, such as effectively inhibiting the corrosion of the electrode and the decomposition of the electrolyte, thereby extending the cycle life of the battery and improving the high temperature performance of the battery;

[0056] (2) Excellent high-temperature performance: Alkenyl ether additives can stabilize the chemical structure of the electrolyte, reduce the decomposition of the electrolyte, improve the interfacial compatibility between the electrode and the electrolyte, and enhance the transmission efficiency of lithium ions at the interface, so that the battery can still maintain stable performance under high temperature conditions, thereby improving the battery's charge and discharge performance;

[0057] (3) High energy density: Oxalic acid / borate additives have good flame retardant properties, which can improve the safety of the battery and help stabilize the electrochemical window of the electrolyte. Their addition improves the ion conductivity of the electrolyte and increases the power density and energy density of the battery.

[0058] (4) High safety performance: The electrolyte of the present invention is not easy to decompose under high temperature and high pressure conditions, reducing safety hazards;

[0059] (5) Excellent overall performance: By optimizing the types and contents of various additives, the electrolyte can exhibit excellent performance under different working conditions. For example, under high temperature conditions, the protective film can prevent excessive decomposition of the electrolyte, reduce gas generation, and maintain stable pressure inside the battery. During rapid charging and discharging, the improvement of interface compatibility is conducive to the rapid insertion and extraction of lithium ions, thereby improving the power performance of the battery. DETAILED DESCRIPTION

[0060] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without paying creative work belong to the scope of protection of the present invention. The process parameters of the following embodiments that do not specify specific conditions are usually based on normal conditions.

[0061] The endpoints and any values ​​of the range disclosed in the context of the present invention are not limited to the precise range or value, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. The term "about" used in the context of the present invention means that the modified numeral can fluctuate within the range of ±20%, ±15%, ±10%, ±5% or ±2% of the numeral. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in the context of the present invention.

[0062] According to a first aspect of the present invention, the present invention provides a lithium ion battery electrolyte, which comprises a non-aqueous organic solvent, a lithium salt and an additive. The following is a detailed description of each component of the lithium ion battery electrolyte of the first aspect of the present invention.

[0063] Non-aqueous organic solvents:

[0064] Solvents have an important impact on the electrochemical performance, life and safety of lithium-ion batteries. In the lithium-ion battery of the present invention, the non-aqueous organic solvent used may include a non-aqueous organic solvent system commonly used in the art. For example, in some preferred embodiments of the present invention, the non-aqueous organic solvent may include a carbonate solvent.

[0065] In some exemplary embodiments, the non-aqueous organic solvent may include one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC), and diethyl carbonate (DEC).

[0066] In some exemplary embodiments, the non-aqueous organic solvent may, for example, specifically contain about 25 to about 40 wt % (e.g., about 30 wt % or about 35 wt %) of EC, 30 to 45 wt % (e.g., about 35 wt % or about 40 wt %) of DMC, and 30 to 45 wt % (e.g., about 35 wt % or about 40 wt %) of EMC, based on the total weight of the non-aqueous organic solvent.

[0067] Lithium salts:

[0068] Lithium salt is the main source of lithium ions in the electrolyte of lithium ion batteries, and is also the main body of lithium ion transmission during the charging and discharging process of lithium ion batteries. In the lithium ion battery of the present invention, the lithium salt used can be an inorganic lithium salt and / or an organic lithium salt commonly used in the art, including but not limited to one or more of lithium perchlorate, lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethyl)sulfonylimide. However, in some particularly preferred embodiments of the present invention, the lithium salt used is LiPF6.

[0069] In some exemplary embodiments of the present invention, the concentration of the lithium salt in the lithium ion battery electrolyte may be set to be in the range of about 13.5 to about 16.5 wt %, for example, about 14 wt %, about 14.5 wt %, about 15 wt %, about 15.5 wt % or about 16 wt %.

[0070] additive:

[0071] Generally speaking, the electrolyte of lithium-ion batteries is mainly composed of solvents and lithium salts. However, this simple formula usually cannot fully meet the use requirements of lithium-ion batteries in complex environments. Therefore, on the basis of the electrolyte formula composed of high-purity solvents and solutes, a small amount (for example, usually less than about 10% by weight) of other non-energy storage materials is also needed to improve certain properties of lithium-ion batteries in a targeted manner. Such a small amount of substances is also called additives.

[0072] In the lithium ion battery electrolyte of the first aspect of the present invention, the additive comprises an additive composition and optionally other additives, wherein the additive composition comprises a halosulfonyl imide salt additive, an alkenyl ether additive and an oxalic acid / borate additive.

[0073] The present invention optimizes the types and contents of each additive substance, so that the lithium ion battery electrolyte of the present invention can show excellent performance under different working conditions. In the present invention, the "alkenyl ether additive", "halogen-containing sulfonyl imide salt additive" and "oxalic acid / borate additive" are used together as an additive composition for the lithium battery electrolyte, which plays a synergistic role, thereby further improving the cycle life of the lithium ion battery electrolyte. For example, under high temperature environment, the protective film formed by the additive substance can prevent excessive decomposition of the electrolyte, reduce gas generation, and maintain the pressure inside the battery stable; and in the process of rapid charge and discharge, the improvement of the interface compatibility caused by the additive substance is conducive to the rapid insertion and removal of lithium ions, thereby improving the power performance of the battery.

[0074] Halogen sulfonyl imide salt additives:

[0075] The halogen-containing sulfonyl imine salt additive is preferably a fluorine-containing sulfonyl imine salt additive, which can form a stable protective film on the electrode surface of the lithium ion battery, effectively inhibiting the corrosion of the electrode and the decomposition of the electrolyte, thereby improving the cycle life and high temperature performance of the battery.

[0076] The halide-containing sulfonyl imide salt has the following formula (I):

[0077]

[0078] in

[0079] R1 and R2 are the same as or different from each other and represent substituted or unsubstituted C 1-10 any one of a haloalkyl group and a halogen group,

[0080] M1 + It refers to alkali metal ions whose ionic radius is larger than that of lithium ions, such as Na + , K + , Rb + or Cs +, preferably Rb + or Cs + ,and

[0081] The negative sign in the circle under the symbol N representing the nitrogen element in the molecular formula indicates that the nitrogen element nominally has a negative charge, which is the same as that represented by M1. + This means that the nominal positive charge of the alkali metal ions forms a charge balance.

[0082] In the context of the present invention, C 1-10 A haloalkyl group refers to an alkyl group containing 1 to 10 (e.g., 2, 3, 4, 5, 6, 7, 8, or 9) carbon atoms, and at least one or more hydrogen atoms in the alkyl group are replaced by a halogen atom. The halogen atom is preferably selected from fluorine, chlorine, bromine or iodine, particularly preferably fluorine. In some preferred embodiments, the C 1-10 The haloalkyl group may be a mono- or poly-halogenated methyl group, preferably a mono- or poly-fluorinated methyl group, more preferably a trifluoromethyl group.

[0083] Halogen radicals in the context of the present invention denote radicals formed from elements of the seventh main group of the periodic table of chemical elements (halogen), said halogen being preferably selected from fluorine, chlorine, bromine or iodine, particularly preferably fluorine.

[0084] The expression "substituted or unsubstituted" in the context of the present invention means that the group modified by the expression may be unsubstituted or substituted, i.e. one or more hydrogen atoms in the group may be replaced by one or more C 1-10 Alkyl, C 2-10 Alkenyl, C 2-10 Alkynyl, phenyl, silanyl, biphenyl, cyclic sulfate, halide, nitro and cyano groups are substituted.

[0085] In some preferred embodiments, the halosulfonyl imide salt additive of formula (I) may include one or more compounds of the following formula (I-1), formula (I-2) and formula (I-3):

[0086]

[0087] In some particularly preferred embodiments, the halosulfonyl imide salt additive of formula (I) comprises a compound having the molecular formula (I-1) above. Studies have shown that the compound of formula (I-1) has relatively small side effects in lithium-ion battery electrolytes, and the electrolyte containing it has relatively better performance.

[0088] On the other hand, in some preferred embodiments, the concentration of the halogen-containing sulfonyl imide salt additive of formula (I) can be set to be in the range of about 0.2 to about 5 weight %, for example, about 1 weight %, about 2 weight %, about 3 weight % or about 4 weight %. Here, the concentration of the halogen-containing sulfonyl imide salt additive of formula (I) should not be too large or too small, for example, it should not exceed about 5 weight %, because too much halogen-containing sulfonyl imide salt additive is easy to form a thicker protective film on the electrode surface during the cycle, which increases the resistance and ion transmission distance of the battery, which is not conducive to the rate performance and later cycle life of the battery; it should not be less than about 0.2 weight %, because the halogen-containing sulfonyl imide salt additive with too low content is not easy to form an effective protective film on the electrode surface, and a part of the solvent will be consumed during the cycle, which is not conducive to extending the cycle life of the battery.

[0089] In addition, M1 + The ionic radius of the alkali metal ion represented should be larger than that of the lithium ion, and the alkali metal elements with larger ionic radius (such as Rb + or Cs + ) is preferred because the reduction chemical potential of this type of metal ion is similar to that of Li + Since the metal lithium ions of this type are aggregated and adsorbed on the surface of the negative electrode and will not be reduced, when charge accumulation (local polarization) occurs locally at the negative electrode during high-rate charging, more metal ions of at least one of these types will be attracted to form an electrostatic layer, thereby inhibiting the Li + Reduction here slows down or even completely eliminates the growth of lithium dendrites and can significantly improve the morphology of lithium deposits and the cyclability of lithium deposition-stripping.

[0090] Alkenyl ether additives:

[0091] The alkenyl ether additive can improve the interfacial compatibility between the electrode and the electrolyte of the lithium ion battery, enhance the transmission efficiency of lithium ions at the interface, and thus improve the charge and discharge performance of the battery.

[0092] The alkenyl ether has the following formula (II):

[0093] R3R4C=CH-O-R5(II)

[0094] in

[0095] R3 and R4 each independently represent hydrogen and substituted or unsubstituted C 1-10 any of the alkyl groups; and

[0096] R5 represents substituted or unsubstituted C 1-10 Alkyl group or C 2-10 Alkenyl group, wherein the substituted C 1-10 Alkyl group or C 2-10The alkenyl group may preferably be replaced by one or more C 1-10 Alkoxy group or C 2-10 Alkenyloxy group substitution.

[0097] In the context of the present invention, C 1-10 Alkyl refers to an alkyl group containing 1 to 10 (e.g., 2, 3, 4, 5, 6, 7, 8 or 9) carbon atoms. 1-10 The alkyl group may be methyl, ethyl, n-propyl, isopropyl or the like.

[0098] In the context of the present invention, C 2-10 Alkenyl denotes an alkenyl group comprising 2 to 10 (eg 3, 4, 5, 6, 7, 8 or 9) carbon atoms.

[0099] In the context of the present invention, C 1-10 Alkoxy denotes an alkoxy group comprising 1 to 10 (eg 2, 3, 4, 5, 6, 7, 8 or 9) carbon atoms.

[0100] In the context of the present invention, C 2-10 Alkenyloxy denotes an alkenyloxy group comprising 2 to 10 (eg 3, 4, 5, 6, 7, 8 or 9) carbon atoms.

[0101] In some particularly preferred embodiments, the alkenyl ether additive of formula (II) may include one or more compounds of the following formula (II-1) and formula (II-2):

[0102] CH3CH=CH-O-CH=CHCH3 (II-1)

[0103] CH2=CH-O-CH2CH2-O-CH=CH2 (II-2).

[0104] On the other hand, in some preferred embodiments, the concentration of the alkenyl ether additive of formula (II) in the electrolyte can be set to be in the range of about 0.1 to about 3 weight %, for example, about 0.5 weight %, about 1 weight %, about 1.5 weight %, about 2 weight % or about 2.5 weight %. Here, the concentration of the alkenyl ether additive of formula (II) should not be too large or too small, for example, it should not exceed about 3 weight %, because the alkenyl ether additive of formula (II) with too much content tends to form a thicker protective film on the electrode surface during the cycle, increasing the resistance and ion transmission distance of the battery, which is not conducive to the rate performance, storage performance and later cycle life of the battery; it should not be less than about 0.1 weight %, because the alkenyl ether additive of formula (II) with too low content cannot form an effective passivation film on the electrode surface, and the effect of inhibiting the oxidation or reduction decomposition of the electrolyte components on the positive and negative electrode surfaces is reduced, so that it cannot ensure the reduction of the high temperature gas production of the battery, which is not conducive to improving the high temperature performance of the lithium battery.

[0105] Oxalate / Borate Additives:

[0106] The oxalic acid / borate additive has good flame retardant properties, can improve the safety of lithium-ion batteries, and also helps to stabilize the electrochemical window of the electrolyte.

[0107] The oxalic acid / borate additive contained in the lithium ion battery electrolyte of the present invention is preferably an oxalic acid / lithium borate additive, including but not limited to one or more of lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiODFB) and lithium bis(oxalatoborate) (C4BLiO8).

[0108] In addition, in some preferred embodiments, the concentration of the oxalic acid / borate additive can be set to be in the range of about 1 to about 2 weight %, for example, about 1.2 weight %, about 1.5 weight % or about 1.7 weight %. Here, the concentration of the oxalic acid / borate additive can improve the ion conductivity and safety performance of the battery without reducing the electrical performance and cycle life performance of the battery only when it is in a relatively appropriate range. For example, the concentration of the oxalic acid / borate additive should not exceed about 2 weight %, otherwise the content of the oxalic acid / borate additive is too high, although it may relatively improve the ion conductivity and safety performance of the battery, it will also reduce the proportion of other solutes, which is not conducive to the improvement of the electrical performance and cycle life performance of the battery; it should not be less than about 1 weight %, otherwise the content of the oxalic acid / borate additive is too low, it cannot be guaranteed that it can play a good flame retardant performance, and it cannot be guaranteed that the safety performance of the battery can be improved.

[0109] Optional other additives:

[0110] In some other preferred embodiments of the present invention, the lithium ion battery electrolyte of the above aspect of the present invention may further contain other additives, including but not limited to one or more of the following additives:

[0111] Cyclic carbonate additives such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), and vinylethylene carbonate (VEC);

[0112] Cyclic sultone additives and / or cyclic sulfate additives, such as 1,3-propane sultone (PS), 1,3-propylene sultone (PST), and dithiothreitol sulfate (DTD); and

[0113] Additional lithium salt additives other than the lithium salt and oxalate / borate additives, such as lithium difluorophosphate (LiPO2F2) and lithium difluorobisoxalatephosphate (LiODFP).

[0114] Here, the other additives may be added to the lithium ion battery electrolyte of the present invention as needed, and the total concentration thereof in the electrolyte is preferably no more than about 4.5 wt %, such as in the range of about 3.5 wt % to about 4.5 wt %, such as about 3.8 wt % or about 4.1 wt %. And in a specific exemplary embodiment, the other additives may specifically include about 0.8 wt % of LiPO2F2, about 0.5 wt % of FEC, about 1 wt % of DTD, about 0.5 wt % of VC, and about 1 wt % of PS.

[0115] In an exemplary embodiment of the present invention, the total concentration of the additive composition and the optional other additives does not exceed about 10 wt %.

[0116] According to a second aspect of the present invention, the present invention provides a method for preparing the lithium ion battery electrolyte according to the present invention described above.

[0117] The preparation method of the present invention comprises fully dissolving the lithium salt in the non-aqueous organic solvent, and then adding the halogenated sulfonyl imide salt additive of formula (I), the alkenyl additive of formula (II), the oxalic acid / borate additive and other optional additives to the resulting solution, so that the additives are completely dissolved, thereby obtaining the lithium ion battery electrolyte.

[0118] According to a third aspect of the present invention, the present invention provides a lithium ion battery comprising the lithium ion battery electrolyte according to the first aspect of the present invention or the lithium ion battery electrolyte prepared according to the preparation method described in the second aspect of the present invention.

[0119] According to the fourth aspect of the present invention, the present invention provides a combination of an alkenyl ether additive conforming to formula (II), formula (II-1) or formula (II-2) as described in the first aspect above, a halogenated sulfonyl imide salt additive conforming to formula (I), formula (I-1), formula (I-2) or formula (I-3) and an oxalic acid / borate additive as described in the first aspect above as a lithium ion battery electrolyte additive, in particular for improving the high temperature storage performance and high temperature cycle performance of lithium ion batteries.

[0120] The present invention is further described in detail below with reference to specific embodiments and comparative examples.

[0121] The chemical raw materials used in the following examples and comparative examples are all commercially available analytical grade products.

[0122] Example and Comparative Example: General Preparation Method of Lithium Ion Battery Electrolyte

[0123] The lithium salt is fully dissolved in a composite non-aqueous organic solvent with the types and amounts of component materials as shown in Table 1 below, and then the halogenated sulfonyl imide salt additive, the alkenyl additive, the oxalic acid / borate additive and other additives are added to the formed solution, wherein the other additives include about 0.8 wt % of LiPO2F2, about 0.5 wt % of FEC, about 1 wt % of DTD, about 0.5 wt % of VC and about 1 wt % of PS, thereby preparing a lithium ion battery electrolyte having lithium salts and additives at concentrations specified in Table 1.

[0124] Table 1:

[0125]

[0126] Table 1 (continued):

[0127]

[0128] Table 1 (continued)

[0129]

[0130] The lithium battery electrolytes obtained from Examples 1 to 8 of the present invention and Comparative Examples 1 to 4 are used to assemble lithium ion batteries, and the specific process is as follows:

[0131] The positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2O2 (LNCM), conductive carbon black SP, carbon nanotubes CNT, and binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in an N-methylpyrrolidone solvent system in a mass ratio of about 96.2:2:0.5:1.3, and then coated on aluminum foil, dried, and cold pressed to obtain a positive electrode sheet with a compaction density of about 3.45 g / cm 3 .

[0132] The negative electrode active material graphite, conductive carbon black SP, binder styrene butadiene rubber (SBR), and thickener carbon methyl cellulose sodium (CMC) were fully stirred and mixed in a deionized water solvent system according to a mass ratio of about 95.6:1.6:1.6:1.2, and then coated on a copper foil, dried, and cold pressed to obtain a negative electrode sheet with a compaction density of about 1.57 g / cm 3 .

[0133] A polyethylene (PE) with a thickness of about 7 μm is used as a base film, and a nano-aluminum oxide coating (about 2 μm) and a PVDF glue (about 2 μm) are coated on the base film to obtain a separator.

[0134] The multi-electrode positive and negative electrode sheets prepared by the above method are wound together with the diaphragm, and the positive and negative electrode ears of the wound core are overlapped respectively by setting the distance between the electrodes; finally, the core is welded with the pole and packaged. The resulting assembly is vacuum-baked at about 80°C for about 48 hours to obtain a battery cell to be injected with liquid. In a glove box with a dew point controlled at about -40°C or below, the electrolyte prepared above is injected into the battery cells of each embodiment respectively, vacuum-packaged, and left to stand for about 24 hours, and then conventional formation and capacity division are carried out according to the following steps: charging at a constant current of about 0.05C for about 180 minutes, charging at a constant current of about 0.2C to about 3.75V, and vacuum sealing for the second time; then further charging at a constant current of about 0.2C to about 4.25V, leaving it at room temperature for about 24 hours, and discharging at a constant current of about 0.2C to about 2.75V; finally charging at a constant current of about 1C to about 4.25V and leaving it for standby use to obtain a finished lithium-ion battery.

[0135] The obtained lithium-ion batteries were subjected to performance tests, including cycle life test, discharge performance test, high temperature storage test and safety test, etc. The specific test steps are as follows.

[0136] The prepared lithium-ion battery was charged to about 4.25V at a current of about 1C at a temperature of about 45°C, and the voltage was kept constant to about 0.05C current, and then discharged to about 2.75V at about 1C, and the discharge capacity was recorded. After the first cycle of discharge, the cycle test was performed until the battery discharge capacity was about 80% of the first cycle capacity, and the number of cycles when the battery reached about 80% SOH (battery health state) after the cycle was completed was recorded.

[0137] The prepared lithium-ion battery was placed in an oven at a constant temperature of about 45°C, and charged at a constant current of about 1C to about 4.25V, then the constant voltage charging current was reduced to about 0.05C, and then discharged at a constant current of about 1C to about 2.75V, and this cycle was repeated for 500 cycles. The discharge capacity of each week was recorded, and the capacity retention rate of the high temperature cycle was calculated as the "500 cycles @45°C discharge capacity retention rate" according to the following formula:

[0138] n-week capacity retention rate = discharge capacity in the nth week / discharge capacity in the first week×100%.

[0139] At a temperature of about 25°C, the lithium-ion battery was charged at a constant current of about 1C to about 4.25V, and then charged at a constant voltage to a current of about 0.05C. The thickness of the lithium-ion battery before storage was tested and recorded as D0. The fully charged battery was then placed in an oven at about 60°C for about 30 days, and the thickness after storage was tested and recorded as D1. The thickness expansion rate of the lithium-ion battery before storage was calculated according to the following formula:

[0140] Thickness expansion ratio after storage at 60°C / 30 days (%) = (D1-D0) / D0×100%.

[0141] The prepared lithium-ion battery was placed in an oven at a constant temperature of about 25°C, charged at a constant current of about 1.5C to about 4.25V, then the constant voltage charging current was reduced to about 0.05C, and then discharged at a constant current of about 3C to about 2.75V, and this cycle was repeated for about 500 times. Finally, when the battery was fully charged at about 100% SOC, it was disassembled in a glove box with a dew point controlled at below about -40°C to observe whether there was lithium deposition on the negative electrode sheet.

[0142] The above test results are shown in Table 2 below.

[0143] Table 2

[0144]

[0145] It can be seen from the performance data results in Table 2 above that the lithium ion battery electrolytes of Examples 1 to 8 of the present invention are not easily oxidized and reduced on the surfaces of the positive and negative electrodes under high temperature conditions, thereby reducing the high-temperature gas production of the lithium ion battery and improving the high-temperature storage performance, high-temperature cycle performance and safety performance of the lithium ion battery.

[0146] Specifically, it can be seen from the test results of Examples 1 to 8 of the present invention and Comparative Example 1 that the number of cycles of the lithium ion battery prepared by the electrolyte of Examples 1 to 8 of the present invention reaching 80% SOH at a temperature of about 45°C reaches about 1446 to about 1698 cycles, the thickness expansion rate after storage at a high temperature of about 60°C for 30 days is in the range of about 5.2 to about 9.6%, and there is no lithium precipitation in the negative electrode after 500 cycles of 1.5C / 3C at 25°C, while the number of cycles of Comparative Example 1 reaching 80% SOH at a temperature of about 45°C is only 821 cycles, the thickness expansion rate after storage at a high temperature of about 60°C for 30 days reaches about 38.9%, and serious lithium precipitation occurs in the negative electrode after 500 cycles of 1.5C / 3C at 25°C. These results show that the high temperature storage performance, high temperature cycle performance and safety performance of the lithium ion battery can be significantly improved by adding halosulfonyl imide salts, alkenyl ethers and oxalic acid / borate additives.

[0147] It can be seen from the test results of Comparative Example 2 that, compared with the performance test results of Examples 1 to 8 of the present invention and Comparative Example 1, when halogen-containing sulfonyl imide salts and oxalic acid / borate additives are added to the electrolyte without adding alkenyl ether additives, the high temperature cycle of the battery is slightly improved, indicating that the addition of halogen-containing sulfonyl imide salts and oxalic acid / borate additives is beneficial to improving the high temperature cycle performance of the battery.

[0148] From the test results of Comparative Examples 3 and 4, it can be seen that when alkenyl ether and oxalic acid / borate additives are added to the electrolyte without adding the halogenated sulfonyl imide salt additive, the high-temperature cycle performance of the battery is improved, the high-temperature storage gas production is reduced, and only slight lithium precipitation is observed during 500-cycle disassembly, indicating that the addition of alkenyl ether additives and oxalic acid / borate additives is beneficial to improving the high-temperature performance and safety performance of the battery.

[0149] Therefore, adding halogen sulfonyl imide salt, alkenyl ether and oxalic acid / borate additives to the lithium ion battery electrolyte of the present invention can improve the high temperature storage performance, high temperature cycle performance and safety performance of the lithium ion battery.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions claimed to be protected by the present invention.

Claims

1. An additive composition for lithium ion battery electrolyte, characterized in that: The additive composition comprises: The halogen sulfonyl imide salt additive of formula (I): in R1 and R2 are independent of each other and are the same or different and represent substituted or unsubstituted C 1-10 Any of a haloalkyl group and a halogen group, and M1 + It refers to alkali metal ions whose ionic radius is larger than that of lithium ions; Alkenyl ether additive of formula (II): R3R4C=CH-O-R5(II) in R3 and R4 each independently represent hydrogen and substituted or unsubstituted C 1-10 Any of the alkyl groups; R5 represents substituted or unsubstituted C 1-10 Alkyl group or C 2-10 alkenyl groups; and The oxalic acid / borate additive comprises one or more of lithium tetrafluoroborate, lithium difluorooxalatoborate and lithium bisoxalatoborate.

2. The additive composition according to claim 1, characterized in that The C 1-10 The haloalkyl group is a halomethyl group, a fluoromethyl group, or a trifluoromethyl group; and / or The halogen is selected from fluorine, chlorine, bromine or iodine; and / or The M1 + Indicates Na + , K + , Rb + or Cs + ; and / or The substituted C 1-10 Alkyl group or C 2-10 Alkenyl groups are 1-10 Alkoxy group or C 2-10 Alkenyloxy group substituted.

3. The additive composition according to claim 1 or 2, characterized in that The halosulfonyl imide salt additive of formula (I) comprises one or more compounds of the following formula (I-1), formula (I-2) and formula (I-3): and / or The alkenyl ether additive of formula (II) comprises one or more compounds of the following formula (II-1) and formula (II-2): CH3CH=CH-O-CH=CHCH3(II-1) CH2=CH-O-CH2CH2-O-CH=CH2(II-2).

4. A lithium ion battery electrolyte comprising a non-aqueous organic solvent, a lithium salt and the additive composition according to any one of claims 1 to 3 and optionally other additives.

5. The lithium ion battery electrolyte according to claim 4, characterized in that: The non-aqueous organic solvent comprises a carbonate solvent, or The non-aqueous organic solvent comprises one or more of ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate and diethyl carbonate, or The nonaqueous organic solvent includes 25 to 40 wt % of ethylene carbonate, 30 to 45 wt % of dimethyl carbonate, and 30 to 45 wt % of ethyl methyl carbonate, based on the total weight of the nonaqueous organic solvent.

6. The lithium ion battery electrolyte according to claim 4, characterized in that: The lithium salt comprises one or more of lithium perchlorate, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

7. The lithium ion battery electrolyte according to claim 4, characterized in that: The other additives include one or more of the following additives: Cyclic carbonate additives; a cyclic sultone additive and / or a cyclic sulfate additive; and An additional lithium salt additive other than the lithium salt and the oxalic acid / borate additive.

8. The lithium ion battery electrolyte according to any one of claims 4 to 7, characterized in that: In the electrolyte, The concentration of the lithium salt is in the range of 13.5 to 16.5 wt %; and / or The concentration of the halosulfonyl imide salt additive of formula (I) is in the range of 0.2 to 5 wt %; and / or The concentration of the alkenyl ether additive of formula (II) is in the range of 0.1 to 3 wt %; and / or The concentration of the oxalic acid / borate additive is in the range of 1 to 2 wt %; and / or The concentration of the other additives is below 4.5 wt %.

9. A method for preparing a lithium ion battery electrolyte according to any one of claims 4 to 8, characterized in that: The method comprises fully dissolving the lithium salt in the non-aqueous organic solvent, and then adding the halogenated sulfonyl imide salt additive of formula (I), the alkenyl ether additive of formula (II), the oxalic acid / borate additive and the optional other additives to the resulting solution to completely dissolve them, thereby obtaining the lithium ion battery electrolyte.

10. A lithium ion battery comprising the lithium ion battery electrolyte according to any one of claims 4 to 8 or the lithium ion battery electrolyte prepared by the preparation method according to claim 9.

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