CN112838269A

CN112838269A - Electrolyte solution, electrochemical device and electronic apparatus including the same

Info

Publication number: CN112838269A
Application number: CN202110031482.7A
Authority: CN
Inventors: 张丽兰; 袁晓; 唐超; 张水蓉
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2021-01-11
Filing date: 2021-01-11
Publication date: 2021-05-25
Anticipated expiration: 2041-01-11
Also published as: CN112838269B

Abstract

The application relates to the technical field of energy storage, in particular to an electrolyte, an electrochemical device comprising the electrolyte and electronic equipment comprising the electrolyte. The electrolyte comprises a first compound shown in a formula I and/or a formula II;

wherein m and n are each independently an integer in the range of 0 to 10; in the formula I, R₁、R₂And R₃At least one of which is a fluorine atom or at least one substituent having fluorine; or in formula II, R₄And R₅Each independently selected from cyano, substituted or unsubstituted hydrocarbyl, wherein when substituted, the substituent is a fluorine atom or a cyano. The electrolyte provided by the application can improve the cycle performance of an electrochemical device and inhibit the cycle processThe impedance in (1) increases.

Description

Electrolyte solution, electrochemical device and electronic apparatus including the same

Technical Field

The application relates to the technical field of energy storage, in particular to an electrolyte, an electrochemical device comprising the electrolyte and electronic equipment, in particular to a lithium ion battery.

Background

With the development of science and technology and the continuous expansion of lithium ion batteries, people have higher and higher requirements on the performance of the lithium ion batteries. In order to meet the increasing energy density requirement of commercial lithium ion batteries, increasing the charge cut-off voltage is one of the most effective ways to increase the energy density of lithium ion batteries. The higher the voltage of the lithium ion battery is, the higher the energy density of the battery is, but simultaneously, along with the increase of the charge cut-off voltage, the instability of the anode or the cathode is enhanced, so that the battery core is easy to react with the electrolyte in the long circulation process, the accelerated attenuation of the battery performance is caused, the cycle life is obviously reduced, and the like. Especially under high temperature environment, the cell capacity attenuation is accelerated. At present, in the prior art, esters are replaced by more stable non-aqueous solvents such as sulfones and ionic liquids, so that the oxidation resistance of the electrolyte is expected to be improved, but the viscosity of the solvents is larger, so that the conductivity is smaller than that of the traditional carbonate electrolyte, the low-temperature and high-rate discharge performance of a battery cell is reduced, and the price of part of the solvents is higher, so that the application of the solvents is limited.

Accordingly, there is a need for an improved electrolyte that can suppress the reaction of an electrode with the electrolyte during a long cycle and improve the cycle performance, and an electrochemical device and an electronic apparatus using the same.

Disclosure of Invention

The present application seeks to solve at least one of the problems existing in the related art to at least some extent by providing an electrolyte and an electrochemical device and an electronic apparatus using the same. The electrolyte has the characteristics that the decomposition effect of the electrode on the electrolyte can be reduced, so that an electrochemical device containing the electrolyte has good cycle performance under a high-voltage condition, and the impedance increase in the cycle process can be inhibited.

According to a first aspect of the present application, there is provided an electrolyte comprising a first compound comprising a compound represented by formula i and/or formula ii;

in the formula I, R₁、R₂And R₃At least one of which is a fluorine atom or at least one substituent having fluorine; or in formula II, R₄And R₅Each independently selected from cyano, substituted or unsubstituted hydrocarbyl, wherein when substituted, the substituent is a fluorine atom or a cyano.

According to some embodiments of the application, in formula I, R₁Including hydrogen, halogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C2-C12 alkenyl, substituted or unsubstituted C2-C12 alkynyl, sulfonic acid group, silicon group, and substituted or unsubstituted C6-C12 aryl.

According to some embodiments of the application, the compound of formula I comprises at least one of the following compounds:

the compound shown in the formula II comprises at least one of the following compounds:

according to some embodiments of the present application, based on the mass of the electrolyte, the mass percentage of the first compound is a%, and a is in a range from 0.1 to 10.

According to some embodiments of the present application, the electrolyte further includes a second compound including at least one of a polynitrile compound, fluoroethylene carbonate, vinylene carbonate, lithium difluorooxalate borate, or lithium difluorophosphate.

According to some embodiments of the present application, the second compound comprises a polynitrile compound comprising at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, nonanenitrile, sebaconitrile, ethylene glycol (dipropionitrile) ether, fumarodinitrile (1, 4-dicyano-2-butene), 1,3,6 hexanetricarbonitrile, nonanetricarbonitrile, 1,3, 5-benzenetrinitrile, 2,4, 6-trifluorobenzene-1, 3, 5-trinitrile, 2-bromobenzene-1, 3, 5-trinitrile, 1,3, 5-cyclohexanetricarbonitrile, 1,2, 3-propanetricitrile, 1,3, 5-benzenetricyano group, or 1,2, 3-tris (2-cyanato) propane.

According to some embodiments of the present application, the polynitrile compound is b% by mass based on the mass of the electrolyte, and a/b is in a range of 0.1 to 10.

According to some embodiments of the present application, the second compound comprises fluoroethylene carbonate; based on the mass of the electrolyte, the mass percentage content of the fluoroethylene carbonate is c%, and the value range of b/c is 0.13-40.

According to a second aspect of the present application, there is provided an electrochemical device comprising: a positive electrode including a positive electrode current collector and a positive electrode active material layer that is provided on a surface of the positive electrode current collector and contains a positive electrode active material; a negative electrode including a negative electrode current collector and a negative electrode active material layer that is provided on a surface of the negative electrode current collector and contains a negative electrode active material; a separator provided between the positive electrode and the negative electrode; and the electrolyte solution.

According to some embodiments of the present application, the particle size distribution of the anode active material satisfies: d is more than or equal to 0.02_n10/D_v50≤1。

According to some embodiments of the present application, the negative active material includes a silicon-based material having a protective layer on at least a part of a surface thereof.

According to some embodiments of the present application, the protective layer satisfies at least one of conditions (a) - (c): (a) the protective layer comprises Me_xO_yWherein Me comprises at least one of Al, Si, Mn, V, Cr, Co or Zr, x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 3; (b) the protective layer comprises a carbon material; (c) the thickness of the protective layer is 0.5nm to 100 nm.

According to a third aspect of the present application, there is provided an electronic apparatus comprising the aforementioned electrochemical device.

The technical scheme of the application has at least the following beneficial effects:

the electrolyte provided by the application comprises the compound shown as the formula I and/or the formula II, the decomposition effect of the electrode on the electrolyte can be effectively passivated, and a protective film can be formed on the surface of the electrode, so that an electrochemical device containing the electrolyte has good cycle performance under a high-voltage condition, the increase of impedance in the cycle process of the electrochemical device can be inhibited, and the cycle performance can be improved.

Detailed Description

Additional aspects and advantages of embodiments of the present application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the present application. Embodiments of the present application will be described in detail below. The embodiments of the present application should not be construed as limiting the present application.

The following terms used herein have the meanings indicated below, unless explicitly indicated otherwise.

In the detailed description and claims, a list of items linked by the term "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if item A, B is listed, the phrase "at least one of A, B" means only a; only B; or A and B. In another example, if item A, B, C is listed, the phrase "at least one of A, B, C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

In the description of the present application, unless otherwise expressly specified or limited, the terms "first," "second," "formula I," "formula II," "formula I-1," "formula II-1," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or relationship to each other. The term "and/or"/"as used herein is merely an associative relationship that describes the associated object, meaning that three relationships may exist, e.g., a and/or B, may mean: a exists alone, A and B exist simultaneously, and B exists alone.

Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity, and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited. Further, "about" as used herein is used to describe and illustrate minor variations.

Herein, unless otherwise specified, the functional groups of all compounds may be substituted or unsubstituted.

In the present text, the expression concerning the number of carbon atoms (also referred to as carbon number), i.e., the number following the capital letter "C", such as "C1-C12", "C6-C12", etc., the numbers 1, 6, 12 following "C" represent the number of carbons in a specific functional group. That is, the functional groups may include 1 to 12 carbon atoms and 6 to 12 carbon atoms, respectively.

As used herein, the term "alkyl" contemplates alkyl groups having 1 to 12 carbon atoms, which may be chain alkyl groups, as well as cycloalkyl groups. "alkyl" is also contemplated to be a branched or cyclic hydrocarbon structure having 2 to 10 carbon atoms. For example, the alkyl group may be an alkyl group of 1 to 12 carbon atoms, an alkyl group of 1 to 10 carbon atoms, an alkyl group of 1 to 5 carbon atoms, an alkyl group of 5 to 12 carbon atoms. When an alkyl group having a particular carbon number is specified, all geometric isomers having that carbon number are intended to be encompassed; thus, for example, "butyl" is meant to include n-butyl, sec-butyl, isobutyl, tert-butyl, and cyclobutyl; "propyl" includes n-propyl, isopropyl and cyclopropyl. Examples of alkyl groups include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, cyclopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, cyclobutyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, methylcyclopentyl, ethylcyclopentyl, n-hexyl, isohexyl, cyclohexyl, n-heptyl, octyl, cyclopropyl, cyclobutyl, norbornyl, and the like. In addition, the alkyl group may be optionally substituted.

As used herein, the term "alkoxy" refers to an L-O-group, wherein L is alkyl. The alkoxy group herein may be an alkoxy group of 1 to 12 carbon atoms, and may also be an alkoxy group of 1 to 10 carbon atoms, an alkoxy group of 1 to 5 carbon atoms, an alkoxy group of 5 to 12 carbon atoms, or an alkoxy group of 5 to 10 carbon atoms.

As used herein, the term "alkenyl" refers to a monovalent unsaturated hydrocarbon group that can be straight-chain or branched and has at least one and typically 1,2, or 3 carbon-carbon double bonds. Unless otherwise defined, the alkenyl group typically contains 2 to 12 carbon atoms, and may be, for example, an alkenyl group of 2 to 10 carbon atoms, an alkenyl group of 2 to 8 carbon atoms, an alkenyl group of 2 to 6 carbon atoms, or an alkenyl group of 6 to 12 carbon atoms. Representative alkenyl groups include, by way of example, ethenyl, n-propenyl, isopropenyl, n-but-2-enyl, but-3-enyl, n-hex-3-enyl, and the like. In addition, the alkenyl group may be optionally substituted.

As used herein, the term "alkynyl" refers to a monovalent unsaturated hydrocarbon group that can be straight-chain or branched and has at least one, and typically 1,2, or 3 carbon-carbon triple bonds. Unless otherwise defined, the alkynyl group typically contains 2 to 12 carbon atoms, and may be, for example, an alkynyl group of 2 to 10 carbon atoms, an alkynyl group of 2 to 8 carbon atoms, an alkynyl group of 2 to 6 carbon atoms, or an alkynyl group of 6 to 10 carbon atoms. Representative alkynyl groups include, for example, ethynyl, prop-2-ynyl (n-propynyl), n-but-2-ynyl, n-hex-3-ynyl, and the like. In addition, the alkynyl group may be optionally substituted.

As used herein, the term "aryl" encompasses monocyclic and polycyclic ring systems. Polycyclic rings can have two or more rings in which two carbons are common to two adjoining rings (the rings are "fused"), wherein at least one of the rings is aromatic, e.g., the other rings can be cycloalkyls, cycloalkenyls, aryls, heterocyclics, and/or heteroaryls. For example, the aryl group can be an aryl group containing 6 to 12 carbon atoms or 6 to 10 carbon atoms. Representative aryl groups include, for example, phenyl, methylphenyl, propylphenyl, isopropylphenyl, benzyl, and naphthalen-1-yl, naphthalen-2-yl, and the like. In addition, the aryl group may be optionally substituted.

As used herein, the term "hydrocarbyl" encompasses alkanes, alkenes, and alkynes.

As used herein, the term "sulfonic acid group" encompasses organic group-containing-HSO₃Of (4) is an organic substance.

As used herein, the term "silicon-based" encompasses organic containing the group-Si.

As used herein, the term "cyano" encompasses organic species containing an organic group-CN.

As used herein, the term "halogen" encompasses fluorine (F), chlorine (Cl), bromine (Br), iodine (I). Preferably, the halogen is selected from F.

As used herein, the term "substituted or unsubstituted" means that the specified group is unsubstituted or substituted with one or more substituents. When the substituent is substituted, the substituent may be selected from halogen.

[ electrolyte ]

In some embodiments, an electrolyte is provided that includes a first compound comprising a compound of formula i and/or formula ii;

wherein m and n are each independently an integer in the range of 0 to 10;

The electrolyte is used as an important component of an electrochemical device such as a lithium ion battery, has a great influence on the performances of the lithium ion battery such as high voltage, high temperature and the like, and the reaction activity of the electrolyte and the surfaces of a positive electrode and a negative electrode is further intensified at high temperature under a high voltage system, so that the problems of decomposition and cyclic gas generation of the electrolyte under the conditions of high temperature/high voltage need to be solved. Although some additives in the electrolyte in some existing high-voltage systems can solve the problem of electrolyte decomposition, the anode and cathode protective films generated by the existing additives can cause the battery performance to be influenced due to overlarge impedance. The existing conventional additives cannot well inhibit impedance increase in the battery cycle process, and influence the relevant electrochemical performance of the lithium ion battery. Therefore, there is a need for further research or development of an electrolyte having good safety performance that can effectively achieve both of the cycle performance in a high voltage system and the resistance increase during the cycle.

In view of this, the compound shown in formula i and/or formula ii is added to the electrolyte, and the compound shown in formula i and formula ii is a compound containing cyano, wherein the cyano has a strong coordination ability, and can be combined with active sites (such as some high-valence metal ions, e.g. nickel/cobalt/manganese, etc.) on the surface of the electrode to mask the active ions on the surface of the positive electrode, thereby reducing the decomposition effect of the electrode on the electrolyte and improving the cycle performance. Furthermore, when the compounds shown in the formulas I and II are halogen substituted (such as fluorine atom) substituted nitriles, a LiF protective layer can be formed on the negative electrode, the negative electrode SEI can be continuously repaired, and the damage of cyano groups to the negative electrode SEI is reduced, so that the cycle performance can be better improved.

Therefore, the electrolyte can inhibit the reaction of the electrode and the electrolyte in the long circulation process by introducing the compound shown in the formula I or the formula II, reduce the circulating gas generation, improve the circulation performance of the electrochemical device under high voltage, inhibit the impedance increase in the circulation process, reduce the impedance of the anode and the cathode in the circulation process and ensure the safety performance of the battery. For an electrochemical device containing the electrolyte, the stability of a positive electrode interface and a negative electrode interface can be effectively improved, the oxidation-reduction reaction of the electrolyte on the interface is reduced, and the compound shown in the formula I or the formula II is low in consumption rate and can continuously protect the interface.

In some embodiments, in formula I, m and n are each independently an integer in the range of 0 to 10, e.g., m is 0, 1,2,3, 4, 5, 6, 7, 8, 9, or 10 and n is 0, 1,2,3, 4, 5, 6, 7, 8, 9, or 10. Preferably, in some embodiments, at least one of m and n is other than 0, e.g., m is an integer ranging from 0 to 10 and n is an integer ranging from 1 to 10; alternatively, m is an integer ranging from 1 to 10, and n is an integer ranging from 0 to 10. Preferably, in some embodiments, m is an integer in the range of 1 to 10 and n is an integer in the range of 1 to 10. More preferably, in some embodiments, m is an integer in the range of 1 to 5 and n is an integer in the range of 1 to 5.

In some embodiments, in formula I above, R₁、R₂、R₃Each independently comprises at least one of hydrogen, halogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C1-C12 alkoxy; when substituted, the substituent is halogen. Preferably, in some embodiments, R₁、R₂、R₃Each independently comprises at least one of hydrogen, halogen, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C1-C8 alkoxy. Preferably, in some embodiments, the halogen is selected from F or Cl. More preferably, in some embodiments, the halogen is selected from F.

In some embodiments, in formula I, R₂And R₃At least one of which is fluorine or at least one substituent having fluorine, R₁Including hydrogen, halogen, substituted or unsubstituted C1-C12 alkyl.

In some embodiments, the number of fluorine atoms contained in the compound of formula I is 1 to 6. Preferably, in some embodiments, the number of fluorine atoms contained in the compound of formula I is 1 to 3.

In some embodiments, specific examples of compounds of formula I include:

in some embodimentsIn the above formula II, R₄And R₅Each independently comprises at least one of halogen, substituted or unsubstituted C1-C12 alkyl, substituted or unsubstituted C1-C12 alkoxy, and R₄And R₅At least one of which contains a cyano group; when substituted, the substituent is halogen. Preferably, in some embodiments, R₄And R₅Each independently comprises at least one of halogen, substituted or unsubstituted C1-C8 alkyl, substituted or unsubstituted C1-C8 alkoxy. Preferably, in some embodiments, the halogen is selected from F or Cl. More preferably, in some embodiments, the halogen is selected from F.

In some embodiments, the number of fluorine atoms contained in the compound of formula ii is 1 to 6. Preferably, in some embodiments, the compound of formula ii contains from 1 to 3 fluorine atoms.

In some embodiments, specific examples of compounds of formula ii include:

in some embodiments, the mass percentage of the first compound is a% based on the mass of the electrolyte, and a is in a range from 0.1 to 10. Namely, the mass percentage of the compound represented by the formula I and/or the formula II is 0.1 to 10%. Preferably, in some embodiments, a is in a range of 0.5 to 7. Illustratively, the lower limit of a may be 0.1, 0.2, 0.5, 1,2,3, the upper limit of a may be 10, 9, 8, 7, 6, and the range of the mass percentage content of the first compound may be composed of any value of the upper limit or the lower limit.

When the content of the compound represented by the formula I and/or the compound represented by the formula II is within the above range, the improvement effect on the performance of the electrochemical device is more obvious, the cycle performance can be better improved, and the impedance of the positive electrode and the negative electrode in the cycle process can be reduced. When the content of the compound shown in the formula I and/or the formula II is less than 0.1%, the formed protective film does not sufficiently protect the surface of the pole piece, and the performance improvement effect on the electrochemical device is small; when the content of the compound represented by formula I and/or formula ii is more than 10%, the cycle performance is lowered, and the conductivity of the electrolyte is greatly affected, affecting the dynamic performance of the electrolyte.

In some embodiments, the electrolyte of the present application may further include a second compound, that is, in some embodiments, the electrolyte includes a first compound and a second compound, wherein the first compound includes a compound represented by formula I and/or formula ii as described above, and the second compound may include at least one of a polynitrile compound, fluoroethylene carbonate, vinylene carbonate, lithium difluoroborate, or lithium difluorophosphate. For example, the second compound may be a polynitrile compound, may be fluoroethylene carbonate, may be vinylene carbonate, may be lithium difluorooxalato borate, may be lithium difluorophosphate, may be a polynitrile compound and fluoroethylene carbonate, may be a polynitrile compound and vinylene carbonate, may be fluoroethylene carbonate and vinylene carbonate, and the like, which are not listed herein. By using the compound represented by the above formula I and/or formula ii in combination with one or more of a polynitrile compound, fluoroethylene carbonate, vinylene carbonate, lithium difluorooxalato borate, or lithium difluorophosphate, the protection of the active material can be enhanced, and the cycle performance can be further improved.

In some embodiments, the second compound comprises a polynitrile compound comprising at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, nonadinitrile, sebaconitrile, ethylene glycol (dipropionitrile) ether, fumaronitrile (1, 4-dicyano-2-butene), 1,3,6 hexanetrinitrile, nonanetrinitrile, 1,3, 5-benzenetrinitrile, 2,4, 6-trifluorobenzene-1, 3, 5-trinitrile, 2-bromobenzene-1, 3, 5-trinitrile, 1,3, 5-cyclohexanetrinitrile, 1,2, 3-propanetricitrile, 1,3, 5-benzenetricyano, 1,2, 3-tris (2-cyanato) propane.

The compound shown in the formula I and/or the formula II and the polynitrile compound can form a film on a positive electrode and a negative electrode more easily under the combined action, and an excellent nitrile protective film can be further formed on the surface of the active material, so that the cycle performance can be further improved, and the storage performance can be considered.

Further, as examples of the polynitrile compound, the following compounds may be further selected but not limited thereto: methyl succinonitrile, 2-dimethyl succinonitrile, 2,3, 3-trimethyl succinonitrile, 2-methylglutaronitrile, 2, 3-dimethyl glutaronitrile, 2, 4-dimethyl glutaronitrile and the like.

In some embodiments, the polynitrile compound is b% by mass and a/b ranges from 0.1 to 10 based on the mass of the electrolyte. Illustratively, the lower limit of a/b can be 0.1, 0.2, 0.5, 1,2,3, the upper limit of a/b can be 10, 9, 8, 7, 6, and the range of a/b can be any value of the upper limit or the lower limit.

In this electrolyte, a polynitrile compound is further added in addition to the compound represented by the above formula I and/or formula ii, and the ratio of the amount of the added polynitrile compound to the amount of the compound represented by the formula I and/or formula ii needs to be within an appropriate range. When the value range of a/b is 0.1-10, a complete and effective organic film can be formed on the surface of the electrode, the stability of the electrolyte is enhanced, and the cycle performance of the electrochemical device is improved. When the value of a/b is less than 0.1 or more than 10, the cycle performance may be deteriorated because the cyano group may effectively stabilize the interface, but an excessive amount of the cyano group may be easily reduced at the negative active site and may generate an unstable SEI layer, and in addition, when the compounds represented by formula I and/or formula ii in the electrolyte are insufficient to repair the SEI, the cycle may be decreased.

In some embodiments, the second compound comprises fluoroethylene carbonate. For example, in some embodiments, the electrolyte includes a compound of formula I and/or formula II, as described above, and fluoroethylene carbonate. Alternatively, in some embodiments, the electrolyte comprises a compound of formula I and/or formula II, as described above, and a polynitrile compound and fluoroethylene carbonate, as described above.

In some embodiments, the fluoroethylene carbonate is present in an amount of c% by mass, and b/c ranges from 0.13 to 40, based on the mass of the electrolyte. Illustratively, the lower limit of b/c may be 0.13, 0.16, 0.2, 0.5, 0.8, 1,2, 5, 10, the upper limit of b/c may be 40, 35, 30, 25, 20, and the range of a/b may be any value of the upper limit or the lower limit.

In this electrolyte, a polynitrile compound and fluoroethylene carbonate are further added in addition to the compound represented by the above formula I and/or formula II, and the ratio of the amount of the polynitrile compound to the amount of fluoroethylene carbonate added needs to be within an appropriate range. When the value range of b/c is 0.13-40, a complete and effective organic film can be formed on the surface of the electrode, the stability of the electrolyte is enhanced, and the cycle performance of the electrochemical device is improved. And when the value of b/c is less than 0.13 or more than 40, the cycle performance is deteriorated, and although fluoroethylene carbonate has better repair to SEI and can effectively improve the cycle performance, the fluoroethylene carbonate is easy to generate HF under high temperature condition to etch the positive electrode interface and cause capacity attenuation, so that the value of b/c needs to be controlled within the range in practical application.

In some embodiments, the electrolyte includes a non-aqueous solvent, which may be a commonly used non-aqueous solvent known in the art to be suitable for electrochemical devices, such as a commonly used non-aqueous organic solvent. In the electrolyte of the embodiment of the present application, the kind of the nonaqueous solvent is not particularly limited, and may be selected according to actual requirements.

In some embodiments, the non-aqueous solvent may include at least one of any kind of carbonate, carboxylate. The carbonate ester may include chain carbonate and cyclic carbonate ester. The non-aqueous solvent may also include halogenated compounds of carbonates.

In some embodiments, the non-aqueous solvent comprises at least one of dimethyl carbonate and halogenated derivatives thereof, diethyl carbonate (DEC) and halogenated derivatives thereof, dipropyl carbonate and halogenated derivatives thereof, ethyl methyl carbonate and halogenated derivatives thereof, Ethylene Carbonate (EC), Propylene Carbonate (PC) and halogenated derivatives thereof, butylene carbonate and halogenated derivatives thereof, γ -butyrolactone and halogenated derivatives thereof, pentylene carbonate and halogenated derivatives thereof, ethyl butyrate, methyl butyrate, Propyl Propionate (PP), ethyl propionate, methyl propionate, ethyl acetate, methyl acetate.

In some embodiments, the non-aqueous solvent comprises at least one of diethyl carbonate (DEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Propyl Propionate (PP), ethyl propionate.

In some embodiments, the electrolyte comprises an electrolyte salt. The electrolyte salt is well known to those skilled in the art and can be used for an electrochemical device. For different electrochemical devices, suitable electrolyte salts may be selected. For example, for a lithium ion battery, a lithium salt is generally used as the electrolyte salt. The lithium salt may be a lithium salt known in the art that may be used in a lithium ion battery.

In some embodiments, the lithium salt comprises one or more of an inorganic lithium salt and an organic lithium salt. Preferably, according to some embodiments of the present application, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF)₆) Lithium tetrafluoroborate (LiBF)₄) Lithium hexafluoroarsenate, lithium perchlorate, lithium difluorophosphate (LiPO)₂F₂) And lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (oxalato) borate (LiBOB), and lithium bis (oxalato) borate (LiODFB).

According to some embodiments of the present application, the lithium salt is selected from lithium hexafluorophosphate (LiPF)₆)。

The content of the electrolyte salt is not particularly limited as long as the effect of the present application is not impaired. In some embodiments, the molar concentration of the electrolyte salt is about 0.5M to about 2.5M, based on the total volume of the electrolyte. Preferably, according to some embodiments of the present application, the electrolyte salt has a molarity of about 1M to about 1.5M. When the concentration of the electrolyte salt is within the above range, the content of lithium as charged particles in the electrolyte solution can be made more appropriate, the viscosity of the electrolyte solution can be made more appropriate, and the electrolyte solution can have good conductivity.

The electrolyte of the present application can be prepared by any known method. In some embodiments, the electrolytes of the present application can be prepared by mixing the components.

[ electrochemical device ]

The electrochemical device of the present application includes any device in which electrochemical reactions occur, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery including, but not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

In some embodiments, the electrochemical device of the present application comprises a positive electrode, a negative electrode, a separator, and an electrolyte as described herein.

Positive electrode

In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on a surface of the positive electrode current collector and including a positive electrode active material. Wherein the positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions.

In some embodiments, the positive active material includes at least one of a sulfide, a phosphate compound, and a lithium transition metal complex oxide, but is not limited thereto, and various conventionally known materials capable of intercalating and deintercalating active ions, which can be used as a positive active material for an electrochemical device, which are well known in the art, may be used as the positive active material for the electrochemical device.

In some embodiments, the lithium transition metal composite oxide contains lithium and at least one element including cobalt, manganese, and nickel. The specific kind of the positive electrode active material is not particularly limited and may be selected as desired. Illustratively, in some embodiments, the positive electrode active material comprises at least one of: lithium cobaltate (LiCoO)₂) Lithium nickel manganese cobalt ternary material and lithium manganate (LiMn)₂O₄) Lithium nickel manganese oxide (LiNi)_0.5Mn_1.5O₄) Lithium iron phosphate (LiFePO)₄)。

In some embodiments, the positive current collector is a metal, for example including, but not limited to, aluminum foil.

In some embodiments, the positive active material layer further comprises a binder. The binder may improve the binding of the positive electrode active material particles to each other, and may improve the binding of the positive electrode active material to the positive electrode current collector. In some embodiments, the binder includes, but is not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy, nylon, and the like.

In some embodiments, the positive electrode active material layer further includes a conductive material, thereby imparting conductivity to the electrode. The conductive material may include any conductive material as long as it does not cause a chemical change. Non-limiting examples of the conductive material include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

In some embodiments, the structure of the positive electrode is a positive electrode sheet structure that can be used in electrochemical devices as is known in the art.

In some embodiments, the method of preparing the positive electrode is a method of preparing a positive electrode that can be used in an electrochemical device, which is well known in the art.

Negative electrode

In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on a surface of the negative electrode current collector and including a negative electrode active material. The specific kind of the negative electrode active material is not particularly limited and may be selected as desired.

In some embodiments, the negative current collector is a metal, such as, but not limited to, copper foil.

In some embodiments, the negative active material includes at least one of a carbonaceous material, a silicon-carbon material, an alloy material, and a lithium-containing metal composite oxide material, but is not limited thereto, and various conventionally known materials capable of electrochemically intercalating and deintercalating active ions, which are known in the art and can be used as a negative active material for an electrochemical device, may be used as the negative active material.

In some embodiments, the particle size distribution of the anode active material satisfies: d is more than or equal to 0.02_n10/D_v50Less than or equal to 1. In some embodiments, the particle size distribution of the anode active material satisfies: d is more than or equal to 0.1_n10/D_v50Less than or equal to 0.8. Wherein D is_n10Represents that the number of particles smaller than the particle diameter is 10%; d_v50Indicating that the volume ratio of particles smaller than the particle diameter was 50%. When the particle size of the negative active material particles is too small, although the expansion of lithium intercalation is smaller than that of large particles, the surface active sites are more numerous than large particles, the activity is stronger, and the capacity fading due to the reaction with the electrolyte during the cycle is more likely, and when the particles of the negative active material are too large, the reaction with the electrolyte is less, but the volume expansion is larger than that of small particles. Therefore, the size of the anode active material particles needs to be moderate. By making the particle diameter distribution of the negative electrode active material satisfy D of 0.02. ltoreq_n10/D_v50Less than or equal to 1, can ensure the electrochemical performance of the electrochemical device, and particularly has better cycle performance.

In some embodiments, the negative active material comprises a silicon-based material having a protective layer on at least a portion of a surface thereof. The surface of the silicon-based material is covered with the protective layer, so that the cycle performance of the electrochemical device can be improved, and the impedance increase in the cycle process can be inhibited.

In some embodiments, the protective layer comprises a carbon material.

In some embodiments, the protective layer comprises Me_xO_yWherein Me comprises at least one of Al, Si, Mn, V, Cr, Co or Zr, x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 3.

In some embodiments, the protective layer has a thickness of 0.5nm to 100 nm. In some embodiments, the protective layer has a thickness of 1nm to 50 nm. By making the thickness of the protective layer in the range of 0.5nm to 100nm, both the cycle performance and the impedance of the electrochemical device can be further improved.

In some embodiments, the negative active material layer further comprises a binder, and optionally comprises a conductive material. The binder improves the binding of the negative active material particles to each other and the binding of the negative active material to the current collector. In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

In some embodiments, the conductive material includes, but is not limited to: a carbon-based material, a metal-based material, a conductive polymer, or a mixture thereof. In some embodiments, the carbon-based material comprises natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material comprises metal powder, metal fibers, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

In some embodiments, the structure of the negative electrode is a negative electrode tab structure known in the art that can be used in electrochemical devices.

In some embodiments, the method of preparing the negative electrode is a method of preparing a negative electrode that can be used in an electrochemical device, which is well known in the art. Illustratively, the negative electrode may be obtained by: the active material, the conductive material, and the binder are mixed in a solvent to prepare an active material composition, and the active material composition is coated on a current collector. In some embodiments, the solvent may include water, and the like, but is not limited thereto.

Isolation film

In some embodiments, a separator is provided between the positive and negative electrodes to prevent short circuits. The material and shape of the separator are not particularly limited, and may be any of the techniques disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance or the like formed of a material stable to the electrolyte of the present application.

In some embodiments, the barrier film comprises a substrate layer. In some embodiments, the substrate layer is a nonwoven fabric, a film, or a composite film having a porous structure. In some embodiments, the material of the substrate layer comprises at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. In some embodiments, the material of the substrate layer includes a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film.

In some embodiments, a surface treatment layer is disposed on at least one surface of the substrate layer. In some embodiments, the surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic. In some embodiments, the polymer layer comprises a polymer, and the material of the polymer comprises at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly (vinylidene fluoride-hexafluoropropylene).

In some embodiments, the inorganic layer comprises inorganic particles and a binder. In some embodiments, the inorganic particles comprise one or a combination of alumina, silica, magnesia, titania, hafnia, tin oxide, ceria, nickel oxide, zinc oxide, calcium oxide, zirconia, yttria, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. In some embodiments, the binder comprises one or a combination of polyvinylidene fluoride, copolymers of vinylidene fluoride-hexafluoropropylene, polyamides, polyacrylonitriles, polyacrylates, polyacrylic acids, polyacrylates, polyvinylpyrrolidone, polyvinyl ethers, polymethyl methacrylates, polytetrafluoroethylene, and polyhexafluoropropylene.

The thickness of the separator is arbitrary. In some embodiments, the thickness of the separator is greater than 1 μm, greater than 5 μm, or greater than 8 μm. In some embodiments, the thickness of the isolation film is less than 50 μm, less than 40 μm, or less than 30 μm. In some embodiments, the thickness of the barrier film is within a range consisting of any two of the above values. When the thickness of the separator is within the above range, the insulating property and mechanical strength can be ensured, and the rate characteristics and energy density of the electrochemical device can be ensured.

[ electronic apparatus ]

In some embodiments, the present application provides an electronic device comprising the aforementioned electrochemical device.

The use of the electrochemical device of the present application is not particularly limited, and it can be used for any electronic apparatus known in the art. In some embodiments, the electrochemical device of the present application can be used in, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, cellular phones, portable facsimile machines, portable copiers, portable printers, headphones, video recorders, liquid crystal televisions, portable cleaners, portable CDs, mini-discs, transceivers, electronic organizers, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large batteries, lithium ion capacitors, and the like. In addition, the electrochemical device of the present application is applicable to an energy storage power station, a marine vehicle, and an air vehicle, in addition to the above-exemplified electronic devices. The air transport carrier device comprises an air transport carrier device in the atmosphere and an air transport carrier device outside the atmosphere.

While the present application is illustrated below in further detail by way of example with reference to specific examples, those skilled in the art will appreciate that the fabrication methods described herein are merely examples and that any other suitable fabrication methods are within the scope of the present application.

In the following examples and comparative examples, reagents, materials and instruments used therefor were commercially available or synthetically available, unless otherwise specified.

The following describes performance evaluation according to examples and comparative examples of lithium ion batteries of the present application.

The lithium ion batteries in the examples and comparative examples were prepared as follows.

Preparation of lithium ion battery

1. Preparation of the electrolyte

Ethylene Carbonate (EC), Propylene Carbonate (PC) diethyl carbonate (DEC) were mixed in a dry (e.g. water content < 10ppm) argon atmosphere glove box according to 3: 1: 6, and then fully drying lithium salt lithium hexafluorophosphate (LiPF)₆) The lithium salt, having a concentration of 1M (1mol/L), was dissolved in the above non-aqueous solvent, and then a certain mass percentage of the first compound or the first compound and the second compound (as shown in tables 1 to 3 below) was added to investigate the effect of each compound on the performance of the lithium ion battery.

2. Preparation of the Positive electrode

The positive electrode material lithium cobaltate (LiCoO)₂) The adhesive polyvinylidene fluoride (PVDF), the conductive agent Super-P are mixed according to the mass ratio of 96: 2: 2 is dissolved in N-methyl pyrrolidone (NMP) solvent, and is fully stirred and mixed to form uniform anode slurry. The anode material is coated on an anode current collector aluminum foil with the thickness of 12 microns, dried for 1 hour at 120 ℃, and then compacted and cut to obtain the anode.

3. Preparation of the negative electrode

Mixing negative active material powder (a mixture of 15% of silicon and 85% of graphite), sodium carboxymethyl cellulose thickener (CMC) and styrene butadiene rubber serving as a binder according to a mass ratio of 85: 2: 13 are dissolved in water and are fully mixed and stirred to obtain the cathode slurry. And uniformly coating the negative electrode slurry on a copper foil of a negative electrode current collector with the thickness of 12 microns, baking for 1h at 120 ℃, and then compacting and slitting to obtain the negative electrode.

4. Preparation of the separator

A 12 micron polypropylene film was used as the separator.

5. Preparation of lithium ion battery

Stacking the obtained positive electrode, the isolating film and the negative electrode in sequence to enable the isolating film to be positioned between the positive electrode and the negative electrode to play an isolating role, and then winding to obtain a square bare cell; placing the bare cell in an outer packaging aluminum foil, baking at 80 ℃ to remove water to obtain a dry cell core, injecting the prepared electrolyte into the dried cell, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.

The measurement methods of the respective performance parameters of the examples and comparative examples are as follows.

Second, testing method

1. High temperature cycle performance testing of lithium ion batteries

And (3) placing the lithium ion battery in a constant temperature box at 45 ℃, and standing for 30 minutes to keep the temperature of the lithium ion battery constant. Charging the lithium ion battery reaching the constant temperature to 4.45V at a constant current of 1C at 45 ℃, charging the lithium ion battery to 0.025C at a constant voltage of 4.45V, standing for 30 minutes, and then discharging the lithium ion battery to 3.0V at a constant current of 1C; this is one charge-discharge cycle. Thus, the capacity retention rate after 500 cycles of the battery was calculated.

The capacity retention after cycling of the lithium ion battery was calculated by the following formula:

capacity retention (%) after N cycles of the lithium ion battery is equal to discharge capacity/first discharge capacity of N-th cycle × 100%

2. Lithium ion battery anode and cathode impedance increase test

(1) Pressure regulation: and adjusting the voltage of the three-electrode soft package cell to 50% SOC, and charging to 3.95V at 1C.

(2) And (3) lithium plating of copper wires: carrying out lithium plating test on the three-electrode soft-package battery cell; connecting the anode of the test wire to the anode tab of the three-electrode cell, connecting the cathode of the test wire to the copper wire of the three-electrode cell, and charging for 2 hours at a current of 0.02 mA; and then connecting the anode of the test wire to the cathode lug of the three-electrode cell, connecting the cathode of the test wire to the copper wire of the three-electrode cell, charging for 2 hours at the same current of 0.02mA, and finishing lithium plating.

(3) Testing the impedance of the positive electrode: and (3) connecting the positive electrode lug of the battery cell and the three-electrode copper wire by using an electrochemical workstation at the temperature of 25 ℃, adjusting the frequency to 5mHz to 5000000Hz, setting the disturbance voltage to 5mV, and testing the positive electrode alternating current impedance.

(4) Testing the impedance of the negative electrode: and (3) connecting a negative electrode lug of the battery cell and the three-electrode copper wire by using an electrochemical workstation at the temperature of 25 ℃, adjusting the frequency to 5mHz to 5000000Hz, setting the disturbance voltage to 5mV, and testing the alternating-current impedance of the negative electrode.

(5) Pre-cycle and post-cycle impedance testing: using the above method, the positive and negative impedances before cycling and after cycling at 45 ℃ for 500cls were tested.

The positive impedance increase rate and the negative impedance increase rate were calculated by the following formulas:

positive impedance growth rate (positive impedance after cycle-positive impedance before cycle)/positive impedance before cycle × 100%;

the negative impedance increase rate is (negative impedance after cycle-negative impedance before cycle)/negative impedance before cycle × 100%.

Third, test results

Table 1 shows the kinds and contents of the first compounds used in the electrolytes in examples 1 to 33 and comparative example 1. Meanwhile, table 1 lists the test results of cycle performance, positive electrode resistance increase rate, and negative electrode resistance increase rate of the lithium ion batteries of examples 1 to 33 and comparative example 1.

Wherein the content of each first compound is a mass percentage calculated based on the mass of the electrolytic solution (the same applies below). The negative active materials in comparative example 1 and examples 1 to 33 were a mixture of silicon and graphite, silicon: 25:75 carbon, no coating layer is arranged on the surface layer of the silicon-based material, and the particle size distribution of the negative electrode active material meets the following requirements: 0 < D_n10/D_v50≤1.5。

TABLE 1

Wherein "-" means not added.

As can be seen from the data analysis in table 1, when the compounds represented by the formulas I and ii are applied to a lithium ion battery, the high-temperature cycle performance of the lithium ion battery can be effectively improved, and the positive electrode impedance increase rate and the negative electrode impedance increase rate of the lithium ion battery can be reduced.

Specifically, from the results of comparing examples 1 to 33 and comparative example 1, it is understood that the introduction of the compounds of formulae I and ii improves the high-temperature cycle performance and reduces the positive electrode resistance increase rate and the negative electrode resistance increase rate. The reason is that the cyano group has strong coordination ability and can be combined with active sites (for example, some high-valence metal ions such as nickel/cobalt/manganese and the like) on the surface of the electrode to mask the active ions on the surface of the positive electrode and reduce the decomposition effect of the electrode on the electrolyte. In addition, the nitrile substituted by fluorine can form a LiF protective layer on the negative electrode, so that the negative electrode SEI can be continuously repaired, and the damage of the cyano group to the negative electrode SEI is reduced.

As can be seen from the results of comparing examples 1 to 7 with comparative example 1, the addition of different amounts of the first compound to the electrolyte may affect the cycle performance and the resistance increase rates of the positive and negative electrodes of the lithium ion battery. Wherein the content of the first compound in example 2 exceeds 10%, the cycle performance is more reduced than that of the first compound added at a low content. The first compound can effectively improve the stability of the positive and negative electrode interfaces, reduce the oxidation reduction of the electrolyte at the interfaces, and can continuously protect the interfaces due to the low consumption rate of the first compound; the cycling performance is improved with the increase of the content in a certain range, but when the content exceeds 10%, the cycling performance is reduced compared with the low content, because when the addition amount is too large, the conductivity of the electrolyte is greatly influenced, and therefore, the dosage of the first compound needs to be controlled within 10%, such as between 0.5% and 10%, and further between 0.5% and 7%. In examples 8 to 33, different types of compounds of formula I and compounds of formula II were added, and different combinations of compounds of formula I and compounds of formula II also gave significant improvements in circulation and impedance, so that compounds I and compounds of formula II could be used not only alone but also in combination.

Table 2 shows the kinds and contents of the first compound and the second compound used in the electrolytic solutions in example 5, example 34 to example 46, and comparative example 2 to comparative example 3. Meanwhile, table 2 lists the test results of the cycle performance, the positive electrode resistance increase rate, and the negative electrode resistance increase rate of the lithium ion batteries in example 5, example 34 to example 46, and comparative example 2 to comparative example 3. The anode active materials in comparative examples 2 to 3 and examples 34 to 46 were the same as example 5.

TABLE 2

Wherein "-" means not added.

As can be seen from the data analysis in table 2, the compounds represented by the above formulae I and ii, in combination with the polynitrile compound and fluoroethylene carbonate, form an interfacial composite interfacial film, which can improve high temperature cycle performance and also can achieve storage performance.

Specifically, in examples 34 to 38, a polynitrile compound additive is additionally added in addition to the first compound. Among them, in examples 35 to 38, the value of a/b is in the range of 0.1 to 10, so that when the nitrile additive is added, the cycle is more preferable than comparative example 2, and it is known from example 34 that when a/b is 15, the rate of increase of the positive electrode resistance becomes larger than comparative example 2 although the cycle is somewhat improved, and thus the value of a/b is optimally 0.1 to 10. This is because, although cyano groups may effectively stabilize the interface, an excessive amount of cyano groups may be easily reduced at the negative active site, and an unstable SEI layer may be generated, and when the first compound in the electrolyte is insufficient to repair the SEI, the cycle may be decreased, so that it is necessary to control the value of a/b in the range of 0.1 to 10 to obtain a better cycle performance, and also to maintain the positive electrode impedance increase rate and the negative electrode impedance increase rate lower than those of comparative example 2.

In examples 39 to 46, the fluoroethylene carbonate with different contents is further added on the basis of the addition of the first compound and the polynitrile compound, so that the high-temperature cycle performance of the lithium ion battery can be effectively improved, and the positive electrode impedance increase rate and the negative electrode impedance increase rate of the lithium ion battery can be reduced. In examples 39 and 43, b/c was not in the range of 0.13 to 40, and the cycle performance was not significantly improved. The reason is that fluoroethylene carbonate has better repair effect on SEI and can effectively improve the cycle performance, but the additive is easy to generate HF under high temperature, and etches the positive electrode interface to cause capacity attenuation, so in practical application, the value of b/c needs to be controlled within the range of 0.13-40 to obtain better cycle performance.

Table 3 shows the relevant performance parameters of the negative active materials in example 40, example 47 to example 58, and the test results of the cycle performance, the positive resistance increase rate, and the negative resistance increase rate of the lithium ion battery.

The negative electrode active material in example 47 was a silicon-based material, the negative electrode active materials in examples 48 to 58 were a mixture of silicon and graphite, and the surface layer of the silicon material was coated with a carbon layer. The electrolytes of examples 47 to 58 contained 4% of the compound of formula I-13, 2% of 1,2, 3-tris (2-cyanato) propane, and 15% of fluoroethylene carbonate.

TABLE 3

As can be seen from the data analysis in table 3, the negative electrode active material in example 47 is a silicon-carbon composite particle without a coating layer, and compared with the negative electrode active material in examples 48 to 58 in which the surface of the silicon material has a carbon layer, the cycle decay of example 47 is serious, and the impedance increase is significant due to severe positive and negative side reactions.

In example 48, the silicon surface was coated with a carbon layer about 0.2nm thick, and the cycling performance was improved compared to the material without the carbon layer, i.e., example 47, but the normal cycling requirements were not met; when the thickness of the coated carbon layer is further increased, as shown in examples 50 to 58, the cycle performance and the impedance are further improved when the thickness of the coated carbon layer is between 0.5nm and 100 nm. In example 49, the silicon surface was coated with a carbon layer about 120nm thick, and it can be seen that when the coated carbon layer thickness exceeded 100nm, the capacity retention rate did not increase but decreased; this is because when the coated carbon layer is too thin, expansion of the particle diameter of the anode active material cannot be effectively suppressed, and thus the cycle is poor; when the coated carbon layer is too thick, the lithium deintercalation rate becomes slow, which also causes cycle decay, so in practical application, the cycle performance of the battery can be ensured by controlling the thickness of the coated carbon layer within the range of 0.5nm to 100 nm.

According to examples 52 to 58 and 50 (example 50, D)_n10/D_v50Ratio of (D) does not include 0.02) and example 51 (D in example 51)_n10/D_v50Comparison of the ratios excluding 1) shows that the particle diameter D of the negative electrode active material was adjusted in examples 50 and 51_n10/D_v50Range of (1), D_n10And D_v50All represent the particle size of the particles, D_n10Represents that the number of particles smaller than the particle diameter is 10%, D_v50Indicating that the volume ratio of particles smaller than the particle diameter was 50%. When the particle size of the negative active material is too small, although the expansion of lithium intercalation is smaller than that of the large particles, the surface active sites are more numerous than the large particles, the activity is stronger, and the capacity fading due to the reaction with the electrolyte during the cycle is more likely, and when the particles are too large, the reaction with the electrolyte is less, but the volume expansion is larger than that of the small particles. Therefore, the particle size of the anode active material needs to be moderate, so that the anode can be ensured to have smaller expansion in the circulation process, and meanwhile, the reaction with the electrolyte in the long circulation process is less; in examples 50 and 51, D_n10/D_v50When the ratio of (D) is less than 0.02 and more than 1, the cycle performance is not good, so that it is necessary to use D_n10/D_v50The ratio of (a) to (b) is controlled within a range of 0.02 to 1, so that the cycle performance of the battery can be ensured.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. An electrolyte, characterized in that the electrolyte comprises a first compound represented by formula I and/or formula II;

wherein m and n are each independently an integer in the range of 0 to 10;

2. The electrolyte of claim 1, wherein the compound of formula I comprises at least one of the following compounds:

3. the electrolyte according to claim 1 or 2, wherein the mass percentage of the first compound is a% based on the mass of the electrolyte, and the value of a is in a range from 0.1 to 10.

4. The electrolyte of claim 3, further comprising a second compound comprising at least one of a polynitrile compound, fluoroethylene carbonate, vinylene carbonate, lithium difluorooxalate borate, or lithium difluorophosphate.

5. The electrolyte of claim 4, wherein the polynitrile compound comprises at least one of succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, nonanenitrile, decanenitrile, ethylene glycol (dipropionitrile) ether, 1, 4-dicyano-2-butene, 1,3,6 hexanetricarbonitrile, nonanetricarbonitrile, 1,3, 5-benzenetrinitrile, 2,4, 6-trifluorobenzene-1, 3, 5-trinitrile, 2-bromobenzene-1, 3, 5-trinitrile, 1,3, 5-cyclohexanetricarbonitrile, 1,2, 3-propanetricitrile, 1,3, 5-benzenetricyano group, or 1,2, 3-tris (2-cyanato) propane.

6. The electrolyte of claim 4, wherein the polynitrile compound is present in an amount of b% by mass and a/b is in a range of 0.1 to 10% by mass, based on the mass of the electrolyte.

7. The electrolyte of claim 4, wherein the fluoroethylene carbonate is present in an amount of c% by mass and b/c ranges from 0.13 to 40% by mass, based on the mass of the electrolyte.

8. An electrochemical device, comprising:

a positive electrode including a positive electrode active material layer including a positive electrode active material;

an anode including an anode active material layer including an anode active material;

a separator provided between the positive electrode and the negative electrode;

and, an electrolyte as claimed in any one of claims 1 to 7;

the particle size distribution of the negative electrode active material satisfies: d is more than or equal to 0.02_n10/D_v50≤1。

9. The electrochemical device according to claim 8, wherein the negative electrode active material comprises a silicon-based material having a protective layer on at least a part of a surface thereof, and the protective layer satisfies at least one of conditions (a) to (c):

(a) the protective layer comprises Me_xO_yWherein Me comprises at least one of Al, Si, Mn, V, Cr, Co or Zr, x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 3;

(b) the protective layer comprises a carbon material;

(c) the thickness of the protective layer is 0.5nm to 100 nm.

10. An electronic device characterized by comprising the electrochemical device according to any one of claims 8 to 9.