Electrolyte solution for lithium secondary battery and lithium secondary battery

Abstract

The invention belongs to the field of new energy, and relates to an electrolyte for a lithium secondary battery and the lithium secondary battery. The electrolyte comprises an organic silicon amine compound containing a phosphorus-nitrogen double bond as a component (A), a lithium salt as a component (B) and a non-aqueous solvent as a component (C), the structural formula of the organic silicon amine compound containing the phosphorus-nitrogen double bond as the component (A) is shown as a formula (I), in the formula (I), when R1 to R4 appear each time, R1 and R2 are in the form of a positive electrode, and R2 is in the form of a negative electrode. R < 5 >-R < 7 > independently represent a hydrogen atom, a monovalent organic group or a group of the following general formula (a): in formula (a), * represents a connection site with a Si atom of formula (I), R < 5 >-R < 7 > independently represent a saturated or unsaturated alkyl group, an aromatic group or a silane-containing group having an optionally substituted group each time R < 5 >-R < 7 > appear, and R < 5 >-R < 7 > independently represent a hydrogen atom, a monovalent organic group or a group having an optionally substituted group each time R < 5 >-R < 7 > appear; and each of R1-R4 includes one or more groups represented by formula (a). The electrolyte can improve the high-temperature performance, reduce the internal resistance of the battery and improve the cycle performance of the battery.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of new energy, and relates to an electrolyte for a lithium secondary battery and a lithium secondary battery. BACKGROUND

[0002] Lithium ion batteries have been widely used in 3C consumer electronics, unmanned aerial vehicle devices, electric vehicles and other fields due to their high energy density, long cycle life and no memory effect. With the continuous expansion of application fields, people have put forward higher requirements for the performance of lithium ion batteries, especially in improving the energy density and cycle life of the battery.

[0003] The electrolyte, as an important medium for ion transmission in lithium ion batteries, has a decisive influence on the performance of the battery. The electrolyte not only needs to provide an efficient ion transmission channel between the positive and negative electrodes, but also needs to maintain excellent chemical and electrochemical stability under extreme conditions such as high temperature, to ensure the long-term operation of the battery. However, lithium ion batteries often face problems such as accelerated decomposition of electrolyte, instability of electrode / electrolyte interface and other problems under high temperature environment, leading to rapid capacity decay and potential safety hazards. Specifically, under high temperature conditions, lithium salts such as lithium hexafluorophosphate (LiPF6) in the electrolyte are prone to decompose to generate hydrofluoric acid (HF), which corrodes the electrode material and destroys the interface film; at the same time, carbonate solvent molecules are prone to oxidative decomposition under high temperature, further exacerbating the increase of interface impedance and the degradation of battery performance.

[0004] Some documents disclose an electrolyte, which uses lithium bis(oxalato)borate (LiBOB) for propylene carbonate (PC) electrolyte, can form a stable SEI (solid electrolyte interface) film on the surface of the graphite negative electrode, so that the battery has good stability at 70℃. However, the SEI film formed by LiBOB is thick, and the interface impedance is large, which affects the rate performance.

[0005] Some documents disclose an electrolyte, which uses lithium hexafluorophosphate as a lithium salt, a nitrile compound with 2 or 3 cyano functional groups as a positive electrode protection additive, lithium difluorophosphate as a low impedance additive, and fluoroethylene carbonate as a negative electrode film forming additive. Through the comprehensive effect of the above components, and through the synergistic effect generated by optimizing the solvent system, the side reactions between the electrolyte and the electrode material under high voltage and the interface impedance of the battery can be reduced, thereby improving the low-temperature discharge performance of the lithium ion battery, while also having excellent high-voltage high-temperature storage and cycle performance. However, simply using lithium difluorophosphate as a low impedance additive has limited improvement effect on the dynamics and high temperature performance of the system, and the electrolyte formula has high requirements for the solvent system, and the adaptation range is narrow.

[0006] In addition, there are also reports that the cyclotriphosphazene with side groups of nitrogen-containing silane is applied to the electrolyte as an additive, but it is mainly to provide flame retardancy.

[0007] It can be seen that although the electrolyte with high temperature stability has been researched in the art, the research is not sufficient and there is still room for further research. SUMMARY

[0008] Problems to be solved by the invention

[0009] As described above, the electrolyte has a decisive effect on the performance of the battery, and there are problems of accelerated decomposition of the electrolyte and instability of the electrode / electrolyte interface under high temperature conditions.

[0010] In order to solve the above problems, the prior art mainly uses methods such as replacing lithium salt and using additives to improve the high temperature stability of the electrolyte. At present, the main lithium salts replacing the traditional lithium salt LiPF6 are lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiODFB), lithium bis(fluorosulfonyl)imide (LiFSI) and the like. Although they can improve the problem of easy generation of HF existing in the traditional lithium salt, thereby improving the high temperature performance, there are still certain problems, for example, the SEI film formed by LiBOB is relatively thick, the interface impedance is relatively large, and the decomposition problem of the carbonate solvent molecule cannot be solved only by replacing the lithium salt. When the additive is used, in order to effectively improve the high temperature performance, multiple additives often need to be compounded, and such compounding often has high requirements for the solvent system.

[0011] In view of the above problems, the present application provides an electrolyte for a lithium secondary battery, which introduces an organic silamine compound containing a phosphorus-nitrogen double bond having both a nitrogen-phosphorus double bond (P=N) and a silicon-nitrogen bond (Si-N) as an additive in a traditional electrolyte, so as to effectively improve the high temperature performance, reduce the internal resistance of the battery, improve the cycle performance of the battery, and significantly improve the electrochemical performance of the battery.

[0012] In addition, the present application also provides a lithium secondary battery comprising the electrolyte according to the present application.

[0013] Solution to the problem

[0014] The present application first provides an electrolyte for a lithium secondary battery, wherein the electrolyte comprises:

[0015] an organic silamine compound containing a phosphorus-nitrogen double bond as component (A), a lithium salt as component (B), and a non-aqueous solvent as component (C),

[0016] wherein the structural formula of the organic silamine compound containing a phosphorus-nitrogen double bond as component (A) is shown as formula (I):

[0017]

[0018] In formula (I),

[0019] Each occurrence of R1 to R4 independently represents a hydrogen atom, a monovalent organic group or a group of the following general formula (a):

[0020]

[0021] In formula (a), * represents the site of attachment to the Si atom of formula (I), and R5 to R7, when they appear each time, independently represent a saturated or unsaturated alkyl group, an aromatic group or a silane-containing group with optional substituents;

[0022] Furthermore, R1 to R4 include one or more groups of formula (a).

[0023] According to the electrolyte of the present invention, the monovalent organic group in formula (I) is selected from substituted or unsubstituted alkyl groups or aromatic groups.

[0024] According to the electrolyte of the present invention, the monovalent organic group in formula (I) is selected from substituted or unsubstituted C1-C6 alkyl groups.

[0025] According to the electrolyte of the present invention, R1 to R4 include two identical or different groups of formula (a).

[0026] According to the electrolyte of the present invention, each occurrence of R5 to R7 independently represents a C1 to C6 saturated or unsaturated alkyl group, a phenyl group, or an alkylene silane group with an optional substituent.

[0027] According to the electrolyte of the present invention, the organosilicon amine compound containing phosphorus and nitrogen double bonds as component (A) includes one or more compounds represented by the following formulas (I-1) to (I-9):

[0028]

[0029] According to the electrolyte of the present invention, the mass of the organosilicon amine compound containing phosphorus-nitrogen double bonds as component (A) accounts for 0.1% to 2% by mass of the total mass of the electrolyte.

[0030] According to the electrolyte of the present invention, the lithium salt as component (B) is selected from one or more salts formed by lithium ions and the following anions: PF6 - 、BF4 - 、P(C2FO4)2 - 、Cl - Br -, I - , ClO4 - , AsF6 - , SiF6 2- , AlCl4 - , B(C2O4)2 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , N(FSO2)2 - , C(CF2SO2)3 - , C2BF2O4 - ; and / or, the non-aqueous solvent as component (C) comprises one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, nitrile solvents and ketone solvents.

[0031] The electrolyte according to the present application, wherein the electrolyte further comprises other additives as component (D), the other additives comprising at least one of vinyl sulfate and lithium difluorophosphate.

[0032] The present application also provides a lithium secondary battery, wherein the lithium secondary battery comprises a positive electrode, a negative electrode, a separator and the electrolyte according to the present application, and the lithium secondary battery is a battery for energy storage system, a power battery or a battery for personal consumer electronics.

[0033] Effects of the present application

[0034] By implementing the above technical solution, the present application can at least achieve the following technical effects:

[0035] 1) The present application introduces an organic silamine compound containing phosphorus-nitrogen double bond as shown in structural formula (I) as an additive into the non-aqueous electrolyte, the nitrogen-phosphorus double bond (P=N) in the molecule of the additive has high nucleophilicity, which can neutralize trace amounts of hydrofluoric acid (HF) in the electrolyte, thereby reducing the corrosion of HF to the electrode material and inhibiting the dissolution of positive transition metal ions. In addition, the nitrogen-phosphorus double bond has excellent thermal stability, which can maintain the stability of its structure under high temperature environment, effectively inhibiting the decomposition of the electrolyte under high temperature conditions, reducing the internal resistance and polarization of the battery. At the same time, the silicon-nitrogen bond (Si-N) in the structure of the additive can participate in the formation of a dense and uniform CEI (Cathode Electrolyte Interface, positive electrode electrolyte interface film) film on the surface of the positive electrode, the CEI film has excellent mechanical strength and electrochemical stability, which can effectively alleviate the occurrence of electrode / electrolyte interface side reactions and reduce the interface impedance, thereby improving the cycle performance of the lithium ion battery.

[0036] 2) In some preferred embodiments, at least one of vinylsulfate and lithium difluorophosphate is further used as an additional additive in the electrolyte, and the high-temperature stability of the electrolyte can be further improved by the synergistic cooperation of the organosilane compound containing a phosphorus-nitrogen double bond and the additional additive. DETAILED DESCRIPTION

[0037] Hereinafter, the content of the present application will be described in detail. The description of the technical features described below is based on representative embodiments, specific examples of the present application, but the present application is not limited to these embodiments, specific examples. Note that:

[0038] In the present specification, a numerical range indicated by "numerical value A to numerical value B" means a range including the end point numerical values A and B.

[0039] In the present specification, a numerical range indicated by "above" or "below" means a numerical range including the present number.

[0040] In the present specification, the meaning indicated by "may" includes both the meaning of performing a certain process and the meaning of not performing a certain process.

[0041] In the present specification, "optionally" or "optional" indicates the use or non-use of certain substances, components, execution steps, applied conditions, and the like.

[0042] In the present specification, "room temperature" or "ambient temperature" means an indoor environmental temperature of "23 ± 2°C".

[0043] In the present specification, the unit names used are international standard unit names, and if not specifically stated, "%" used means a weight or mass percentage content.

[0044] In the present specification, "substantially" or "essentially" means that the standard deviation from a theoretical model, theoretical data, or target data is within a numerical range of 2%, preferably 1%, and more preferably 0.8%.

[0045] In the present specification, the terms "comprising" and / or "including" mean that the features, steps, operations, devices, components, and / or combinations thereof are present.

[0046] In the present specification, "some specific / preferred embodiments", "other specific / preferred embodiments", "embodiments", and the like mean that the specific elements (for example, features, structures, properties, and / or characteristics) described in relation to the embodiments are included in at least one embodiment described herein, and can be present in other embodiments or can not be present in other embodiments. In addition, it should be understood that the elements can be combined in various embodiments in any suitable manner.

[0047] The present application mainly provides an electrolyte, which uses an organic silamine compound containing a phosphorus-nitrogen double bond as an additive, and can effectively improve the high-temperature stability of the electrolyte.

[0048] The present application is mainly obtained through the following insights:

[0049] The conventional electrolyte currently often has poor high-temperature stability, and the main factors causing these problems are as follows: on the one hand, the dissolution of transition metal ions, the conventional electrolyte currently uses LiPF6 as a lithium salt, but it has the disadvantage of thermodynamic instability and is easily decomposed to release strong Lewis acid phosphorus pentafluoride (PF5) at high temperatures, PF5 reacts with trace water in the electrolyte to generate HF, HF has a strong corrosion and damage effect on the interface film layer, leading to the dissolution of transition metal ions and poor high-temperature storage and high-temperature cycle performance of the battery; on the other hand, the carbonic acid ester solvent is often used as an organic solvent in the conventional electrolyte, which is easily oxidized and decomposed at high temperatures, further increasing the interface impedance and degrading the battery performance, resulting in loss of battery capacity and deterioration of cycle performance. In order to improve the high-temperature performance of the electrolyte, the methods of replacing the lithium salt and using the additive used in the prior art all have certain problems.

[0050] Through long-term research by the inventors, it is found that using an organic silamine compound containing a phosphorus-nitrogen double bond as shown in structural formula (I) as an additive can effectively inhibit the side reaction at the electrode / electrolyte interface, alleviate the dissolution of transition metal, and significantly improve the electrochemical performance of the lithium ion battery at high temperatures.

[0051] <First aspect>

[0052] The first aspect of the present application provides an electrolyte for a lithium secondary battery, and the electrolyte of the present application includes an organic silamine compound containing a phosphorus-nitrogen double bond as component (A), a lithium salt as component (B), and a non-aqueous solvent as component (C).

[0053] In addition, without limitation, as long as the implementation of the technical effects of the present application is not hindered, various functional additive components can also be used in the non-aqueous electrolyte.

[0054] (Component (A))

[0055] The structural formula of the organic silamine compound containing a phosphorus-nitrogen double bond as component (A) of the present application is shown as formula (I):

[0056]

[0057] In formula (I),

[0058] R1-R4, each occurrence, independently represents a hydrogen atom, a monovalent organic group, or a group of the following general formula (a):

[0059]

[0060] In formula (a), * indicates a bonding site to the Si atom of formula (I), and R5to R7independently of one another on each occurrence represent a saturated or unsaturated alkyl group, an aromatic group, or a silyl group, each of which can have an optional substituent.

[0061] As the saturated or unsaturated alkyl group, a C1to C6alkyl group, alkenyl group, or alkynyl group, which can be linear or have one or more branches, such as a methyl group, ethyl group, propyl group, isopropyl group, ethenyl group, 2-propynyl group, and the like, can be used, and as a preference, a methyl group, ethyl group, or 2-propynyl group can be used.

[0062] As the aromatic group, a carbocyclic aromatic group or heterocyclic aromatic group can be used, and in some specific embodiments, a carbocyclic aromatic group is preferred, and for example, a phenyl group can be used.

[0063] As the silyl group, as a preference, an alkylidene silyl group, such as an alkylidene trimethylsilyl group (TMS), alkylidene triethylsilyl group (TES), alkylidene tert-butyldimethylsilyl group (TBS), alkylidene triisopropylsilyl group (TIPS), and the like, can be used, and as a preference, an alkylidene trimethylsilyl group or the like can be used. As the alkylidene group, a preference can be given to a methylene group, ethylene group, and the like.

[0064] As the substituent that can be used for the above-mentioned groups, a halogen atom can be used, and as the halogen atom, a preference can be given to a fluorine atom.

[0065] As the monovalent organic group in formula (I), in principle, there is no particular limitation, and in some specific embodiments, it can be selected from a substituted or unsubstituted alkyl group or aromatic group. Among these, as the alkyl group, a C1to C6alkyl group, which can be linear or have one or more branches, such as a methyl group, ethyl group, propyl group, isopropyl group, and the like, can be used, and as a preference, a methyl group or ethyl group can be used; and as the aromatic group, a carbocyclic aromatic group or heterocyclic aromatic group can be used, and in some specific embodiments, a carbocyclic aromatic group is preferred, and for example, a phenyl group can be used. As the substituent that can be used for the alkyl group or aromatic group, there is no particular limitation, and a halogen atom can be used, and as the halogen atom, a preference can be given to a fluorine atom.

[0066] Further, R1to R4include one or more groups of formula (a), and for example, one or two groups of formula (a) can be included, and when two groups of formula (a) are included, the two groups of formula (a) can be the same or different.

[0067] In some preferred embodiments, the phosphorus-nitrogen double bond-containing organosilane amine compound as component (A) includes one or more of the compounds represented by the following formulae (I-1) to (I-9):

[0068]

[0069]

[0070] (component (B))

[0071] As for the kind of the lithium salt as component (B) according to the present application, the present application is not particularly limited, and it can be a lithium salt commonly used in the art. In some specific embodiments, the lithium salt can be selected from one or more of the salts formed by lithium ion and the following anions: PF6 - , BF4 - , P(C2FO4)2 - , CI - , Br - , I - , CIO4 - , AsF6 - , SiF6 2- , AICI4 - , B(C2O4)2 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , N(FSO2)2 - , C(CF2SO2)3 - , C2BF2O4 - , and the like.

[0072] In some specific embodiments, the lithium salt can be lithium hexafluorophosphate (LiPF6).

[0073] (component (C))

[0074] As for the kind of the nonaqueous solvent as component (C) according to the present application, the present application is not particularly limited, as long as it is a nonaqueous solvent commonly used for nonaqueous electrolyte.

[0075] In some specific embodiments, the non-aqueous solvent can be selected from one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, nitrile solvents, and ketone solvents. Specifically, the cyclic carbonate solvents can be selected from ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC), etc.; the linear carbonate solvents can be selected from diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC), methyl trifluoroethyl carbonate (FEMC), di(2,2,2-trifluoroethyl) carbonate (DFDEC), etc.; the ester solvents can be selected from methyl formate (MA), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), and propyl butyrate (PB), etc.; the ether solvents can be selected from dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, ethylene glycol dimethyl ether (DME), ethylene glycol diethyl ether (DEE), dioxane (DX), dioxolane (DOL), etc.; for the nitrile solvents, acetonitrile can be listed; the ketone solvents can be selected from polymethylvinyl ketone, etc. These non-aqueous solvents can be used alone or in the form of a mixture of two or more.

[0076] In some preferred embodiments, the non-aqueous solvent can be selected from one or two of ethylene carbonate (EC), ethyl methyl carbonate (EMC), etc. in any ratio.

[0077] (Other additives)

[0078] For other additives, there is no particular restriction in principle, for example, a film-forming agent can be included to facilitate film formation.

[0079] For such additives, ethylene vinyl carbonate (VC), lithium difluorophosphate (LiPO2F2), fluoroethylene carbonate (FEC), boron-containing additives, sulfur-containing additives, or oxalate-containing additives, etc. can be listed.

[0080] The boron-containing additive can be selected from lithium tetrafluoroborate (LiBF4), trimethylsilyl borate (TMSB), etc.; the sulfur-containing additive can be selected from 1,3-propane sultone (1,3-PS), 1,4-butane sultone (1,4-BS), 2,4-butane sultone (2,4-BS), 1,3-propene sultone (PST), ethylene sulfate (DTD), methane disulfonate methylene (MMDS), ethylene sulfite (ES), etc.; the oxalate-containing additive can be selected from lithium difluoro oxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium tetrafluoro oxalate phosphate (LiTFOP), lithium difluoro bisoxalate phosphate (LiDFOP), etc. These additives can be used alone or in the form of a mixture of two or more.

[0081] In some preferred embodiments, at least one of lithium difluorophosphate and ethylene sulfate is used as the other additive of component (D).

[0082] (Composition of the electrolyte)

[0083] In the present application, the content of component (A) is not particularly limited in principle, and it has been found that even a small amount of component (A) added to the electrolyte can significantly improve the high-temperature performance. In addition, there is no significant limitation on the upper limit of component (A), which depends on the cost and the solubility of different structures of component (A), as well as the marginal effect of high-temperature performance improvement.

[0084] In some preferred embodiments, the mass of component (A) can account for 0.1 mass% to 2 mass% of the total mass of the electrolyte, for example, it can be 0.2 mass%, 0.5 mass%, 0.8 mass%, 1 mass%, 1.2 mass%, 1.5 mass%, 1.8 mass%, etc., from the perspective of better improving the high-temperature cycle performance.

[0085] The content of the lithium salt of component (B) is not particularly limited in principle. In some specific embodiments, the lithium salt of component (B) accounts for 5 mass% to 20 mass% of the total mass of the electrolyte, for example, it can be 8 mass%, 10 mass%, 12 mass%, 15 mass%, 18 mass%, etc.

[0086] The content of the other additive of component (D) is not particularly limited in principle, which is related to the solubility of different substances. In some specific embodiments, the mass of the other additive of component (D) accounts for 0.2 mass% to 3 mass% of the total mass of the electrolyte, for example, it can be 0.5 mass%, 0.8 mass%, 1 mass%, 1.5 mass%, 2 mass%, 2.5 mass%, etc.

[0087] <Second aspect>

[0088] The second aspect of the present application provides a lithium secondary battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte according to the first aspect of the present application.

[0089] The lithium secondary battery according to the present application is a battery for energy storage system, power battery or personal consumer electronics.

[0090] (Positive electrode)

[0091] For the positive electrode, it comprises a current collector and a positive active material layer. For the current collector of the positive electrode, there is no particular restriction in principle, for example, it can be copper or aluminum, preferably aluminum.

[0092] For the positive active material layer, it can comprise a positive active material, a binder and optionally a conductive agent, an auxiliary agent, etc.

[0093] For the positive active material, there is also no particular restriction in principle, which can include:

[0094] Layered transition metal oxides mainly include LiMO2(M=Co, Ni, Mn) positive electrode materials, lithium-rich manganese-based positive electrode materials xLi[Li 1 / 3 Mn 2 / 3 ]O2·(1-x)LiMO2(M=Ni, Co, Mn), nickel-cobalt-manganese oxide Li[Ni 1-x-y Co x Mn y ]O2(NCM) and nickel-cobalt-aluminum oxide Li[Ni 1-x-y Co x Al y ]O2(NCA) ternary positive electrode materials;

[0095] Olivine structure compounds such as LiMPO4(M=Fe, Co, Ni, V, Mn);

[0096] Spinel structure compounds such as LiM2O4(M=Mn, Ni).

[0097] From the perspective of high capacity, the preferred ternary layered transition metal oxide positive electrode material has a higher specific capacity, which can better meet the demand for high energy density

[0098] Further, for the positive active material, especially for NCM and NCA, the key to improving the discharge capacity of the ternary positive electrode material lies in increasing the proportion of nickel content, therefore, in the further preferred embodiments of the present application, the positive active material can include ternary positive electrode materials with medium nickel (mainly 5 series such as NCM523), medium-high nickel (mainly 6 series such as NCM613, NCM622) and high nickel (mainly 8 series such as NCM811) content.

[0099] Further, for other components in the positive electrode active material layer, there is no particular restriction in principle, and for example, an adhesive, a conductive agent, and an auxiliary agent, which are generally used in the art, can be used. For such an adhesive, for example, a fluorine-containing polyolefin, an acrylate-based adhesive, a cellulose-based adhesive can be used; for a usable conductive agent, for example, a carbon nanotube, a conductive metal particle, and the like can be used; and for a usable auxiliary agent, for example, a thickening agent, a dispersing aid, and the like can be used.

[0100] (Negative electrode)

[0101] For the negative electrode, a current collector and a negative electrode active material layer are included. For the current collector of the negative electrode, there is no particular restriction in principle, and for example, copper or aluminum, preferably copper, can be used.

[0102] For the negative electrode active material layer, it can include a negative electrode active material, an adhesive, and an optional auxiliary agent, and the like.

[0103] For the negative electrode active material, a carbon-based material or a silicon-based material can be used.

[0104] From the perspective of improving the high capacity of the battery, it includes a Si element. There is no particular restriction on the source of such a Si element, and for example, a silicon element, a silicon element, an oxide of silicon, or a silicon alloy can be used.

[0105] From the perspective of balancing capacity and good dimensional stability, the negative electrode active material further includes a C element. There is no particular restriction on the source of such a C element, and for example, a carbon material or graphite can be used.

[0106] In some preferred embodiments of the present application, the negative electrode active material includes a C element and a Si element, that is, the preferred negative electrode active material includes a silicon-carbon composite material.

[0107] Further, for other components in the negative electrode active material layer, such as an adhesive, other auxiliary agents, and the like, they can be selected from conventional components in the art.

[0108] For the content of the Si element in the negative electrode active material layer, the higher the content of the silicon element in the negative electrode active material layer, the higher the energy density of the battery, but at the same time, it also faces huge volume expansion, so it is necessary to reasonably control the content of the silicon element. In some preferred embodiments, the content of Si in the negative electrode active material layer can generally be 5 to 30 mass%, more preferably 10 to 25 mass%, and examples that can be cited include 8 mass%, 12 mass%, 14 mass%, 16 mass%, 18 mass%, 20 mass%, 22 mass%, 28 mass%, and the like.

[0109] (Separator)

[0110] In some embodiments of the present application, the lithium ion battery further uses a separator.

[0111] For the separator, it can include a porous membrane and optionally also include a modification layer formed on one or both main surfaces of the porous membrane.

[0112] For the porous membrane layer, there is no particular restriction in principle, for example, it can be an olefin (polypropylene PP, polyethylene PE), a polyamide, etc., and such a porous membrane layer can be composed of one or more organic resin layers.

[0113] For the modification layer, there is no particular restriction in principle, for example, it can include organic heat-resistant particles, inorganic particles, a conductive agent, a lithium supplement agent, a binder, etc.

[0114] For the porosity of the separator, it can generally be 20 to 60 vol%, preferably 30 to 46 vol%, and for the thickness of the separator, it can generally be 30 μm or less.

[0115] Examples

[0116] Embodiments of the present application will be described in detail below with reference to Examples, but those skilled in the art will understand that the following Examples are for illustration only and should not be construed as limiting the scope of the present application. In the Examples, specific conditions not mentioned are performed under conventional conditions or under conditions recommended by the manufacturer. In the Examples, reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially.

[0117] Example 1

[0118] Positive electrode sheet: A positive electrode active material Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, a conductive agent (Super P), and a binder polyvinylidene fluoride (PVDF) were uniformly mixed with an appropriate amount of N-methyl-2-pyrrolidone (NMP) in a mass ratio of 96:2:2 to prepare a positive electrode slurry. Thereafter, the prepared positive electrode slurry was coated on an aluminum foil, and a positive electrode sheet was obtained by baking, rolling, and die cutting.

[0119] Negative electrode sheet: Graphite, a conductive agent (Super P), a thickening agent CMC, and a binder SBR were added to an appropriate amount of deionized water and stirred well in a mass ratio of 95:2:1:2 to prepare a negative electrode slurry. Thereafter, the prepared negative electrode slurry was coated on a copper foil, and a negative electrode sheet was obtained by baking, rolling, and die cutting.

[0120] Electrolyte: The electrolyte was prepared in an argon-filled glove box at room temperature, the water content in the glove box was less than 0.1 ppm, ethylene carbonate (EC) and methyl ethyl carbonate (EMC) were mixed according to the mass ratio (EC: EMC = 30:70), then 12.5% of lithium hexafluorophosphate (LiPF6) by mass of the total mass of the electrolyte was gradually added to the mixed solvent, and the mixture was continuously stirred. In the above mixed solution, 1% of the compound represented by formula (I-1) by mass of the total mass of the electrolyte was added to obtain the final electrolyte.

[0121] Preparation of lithium ion battery: The prepared negative electrode sheet, separator and positive electrode sheet were stacked in order, then the tab welding was performed and the aluminum plastic film was used for packaging to obtain a soft package dry cell, and finally the electrolyte prepared above was injected into the cell, and the standing, formation and capacity distribution operations were performed to complete the preparation of the lithium ion battery.

[0122] Examples 2-13

[0123] According to the preparation method described in Example 1, the lithium ion batteries of Examples 2-13 were prepared using the battery parameters of Examples 2-13 in Table 1.

[0124] Comparative Examples 1-2

[0125] According to the preparation method described in Example 1, the lithium ion batteries of Comparative Examples 1-2 were prepared using the battery parameters of Comparative Examples 1-2 in Table 1.

[0126] Electrical performance test method:

[0127] 1. High temperature cycle performance test: At 45±2℃, the above lithium ion battery was charged at 1C constant current to 4.4V, then charged at constant voltage to 0.05C, and then discharged at 1C constant current to 2.5V after 30min standing. The initial discharge capacity of the first cycle of the battery was obtained and recorded as C0, and then the above charging and discharging cycle was repeated, and the capacity after the 500th discharge was recorded as C500. 500 , then the capacity retention rate (%) after 500 cycles at high temperature = C500 / C0x 100%. 500

[0128] ​2. High temperature cycle DCR (Direct Current Resistance) growth rate test: at 25±2℃, the above lithium ion battery is charged at 1C constant current to 4.4V, then charged at constant voltage to current of 0.05C, then discharged at 1C for 30min (adjust to 50% SOC), then discharged at 2C constant current pulse for 10s, record the voltage V0 before 10s pulse discharge and the voltage V1 after 10s pulse discharge. DCR1 = (pulse discharge voltage V0 - pulse discharge voltage V1) / discharge current. Then after the battery is cycled at 45℃ for 500 cycles, when the battery is completely cooled to 25±2℃, the DCR of the 500th cycle is tested again according to the above discharge process 500 , then the high temperature cycle DCR growth rate (%) of 500 cycles = (DCR 500 - DCR1) / DCR1 * 100%.

[0129] The lithium ion batteries prepared by the examples and comparative examples are subjected to high temperature cycle performance test and high temperature cycle DCR growth rate test, and the test results are shown in Table 1.

[0130] Table 1 Composition and performance test results of examples, reference examples and comparative examples

[0131]

[0132] As can be seen from Table 1, by comparing the experimental results of Examples 1-8 with Comparative Example 1, it can be seen that the introduction of component (A) containing phosphorus-nitrogen double bond organic silane compound represented by formula (I) in the electrolyte can effectively improve the high temperature cycle life and cycle DCR growth rate of the lithium ion battery.

[0133] In addition, as can be seen from Example 2, even if a small amount of component (A) is added, it can also improve the high temperature performance of the battery.

[0134] As can be seen from the experimental results of Comparative Examples 1-8 and Examples 9-13, the introduction of component (D) other additives (DTD and / or LiPO2F2) can further improve the high temperature cycle performance of the battery, and at the same time alleviate the DCR growth.

[0135] In addition, a reference example is also set, and the battery parameter composition is shown in Table 1. In the reference example, the content of LiPO2F2 is increased to 1.5%, but under this system, LiPO2F2 cannot be completely dissolved (the solubility is about 0.8% or less).

[0136] It should be noted that although the technical solutions of the present application are introduced by specific examples, those skilled in the art can understand that the present application should not be limited thereto.

[0137] Having described various embodiments of the application, it is to be understood that the above description is meant not to limit and not to encompass all of the possible embodiments covered by the claims. Many modifications and variations of this application can be apparent to those of ordinary skill in the art without departing from the spirit and scope of the described embodiments. It is intended that the scope of the application should only be limited by the appended claims.

Claims

1. An electrolyte for a lithium secondary battery, characterized in that The electrolyte comprises: As component (A), an organosilicon amine compound containing a phosphorus-nitrogen double bond, as component (B), a lithium salt, and as component (C), a non-aqueous solvent, The structural formula of the organosilicon amine compound containing phosphorus and nitrogen double bonds as component (A) is shown in formula (I): In formula (I), Each occurrence of R1 to R4 independently represents a hydrogen atom, a monovalent organic group or a group of the following general formula (a): In formula (a), * represents the site of attachment to the Si atom of formula (I), and R5 to R7, when they appear each time, independently represent a saturated or unsaturated alkyl group, an aromatic group or a silane-containing group with optional substituents; Furthermore, R1 to R4 include one or more groups of formula (a).

2. The electrolyte according to claim 1, characterized in that The monovalent organic group in formula (I) is selected from substituted or unsubstituted alkyl groups or aromatic groups.

3. The electrolyte according to claim 1 or 2, characterized in that The monovalent organic group in formula (I) is selected from substituted or unsubstituted C1-C6 alkyl groups.

4. The electrolyte according to any one of claims 1 to 3, characterized in that R1 to R4 include two identical or different groups of formula (a).

5. The electrolyte according to any one of claims 1 to 4, characterized in that Each occurrence of R5 to R7 independently represents a C1 to C6 saturated or unsaturated alkyl group, a phenyl group, or an alkylenesilane group, which may have an optional substituent.

6. The electrolyte according to any one of claims 1 to 5, characterized in that The organosilicon amine compound containing phosphorus and nitrogen double bonds as component (A) includes one or more compounds represented by the following formulas (I-1) to (I-9):

7. The electrolyte according to any one of claims 1 to 6, characterized in that The mass of the organosilicon amine compound containing phosphorus and nitrogen double bonds as component (A) accounts for 0.1% to 2% by mass of the total mass of the electrolyte.

8. The electrolyte according to any one of claims 1 to 7, characterized in that The lithium salt as component (B) is selected from one or more salts formed by lithium ions and the following anions: PF6 - 、BF4 - 、P(C2FO4)2 - 、Cl - Br - , I - 、ClO4 - 、AsF6 - 、SiF6 2- 、AlCl4 - 、B(C2O4)2 - 、CH3CO2 - CF3SO3 - 、N(CF3SO2)2 - 、N(FSO2)2 - 、C(CF2SO2)3 - 、C2BF2O4 - ; and / or, the non-aqueous solvent as component (C) includes one or more of cyclic carbonate solvents, linear carbonate solvents, ether solvents, ester solvents, nitrile solvents and ketone solvents.

9. The electrolyte according to any one of claims 1 to 8, characterized in that The electrolyte further includes other additives as component (D), and the other additives include at least one of vinyl sulfate and lithium difluorophosphate.

10. A lithium secondary battery, characterized in that: The lithium secondary battery comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1 to 9, wherein the lithium secondary battery is an energy storage system battery, a power battery or a battery for personal consumer electronics.

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