Aromatic fluoronitrile electrolyte material, electrolyte and battery

Abstract

The invention relates to the technical field of electrolyte, in particular to an aromatic fluoronitrile electrolyte material, electrolyte and a battery. The aromatic fluoronitrile electrolyte material comprises aromatic hydrocarbon and substituted ether-containing groups, fluorine-containing groups and nitrile-containing groups, and the rest groups are selected from at least one of hydrogen groups, alkyl groups and alkenyl groups. The electrolyte material with high voltage resistance, high ionic conductivity and good long cycle performance is obtained through the combined action of the aromatic hydrocarbon structure fragment, the nitrile structure fragment, the fluorine structure fragment and the ether structure fragment, the variety of high voltage resistant fluoronitrile electrolytes is expanded, and the electrical performance of the fluoronitrile electrolytes is further improved. Meanwhile, the battery designed based on the electrolyte has higher safety performance and allows higher charging voltage, in addition, the fast charging capacity of the battery can be effectively improved by improving the ionic conductivity and reducing the interface resistance, and the cycle performance of the battery can be effectively improved by stable SEI film impedance.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes, and in particular to an aromatic fluoronitrile electrolyte material, an electrolyte and a battery. Background Art

[0002] How to further improve the energy density, fast charging and long cycle performance of lithium batteries is the current research focus. The charging voltage of positive electrode materials with high energy density (such as ternary, lithium nickel manganese oxide, etc.) is generally high, and when traditional carbonate electrolytes are charged to above 4.3V, the electrolyte is prone to oxidative decomposition, which consumes electrolyte, increases interfacial resistance and battery gas production, and limits the capacity of positive electrode materials and the fast charging and cycling capabilities of batteries. In addition, ester electrolytes have defects such as difficulty in forming a stable interface film at the interface between the positive and negative electrodes, which further inhibits the fast charging and cycling performance of the battery. Therefore, it is very necessary to develop a type of electrolyte that is resistant to high voltage, has high ionic conductivity, and is easy to form an excellent interface film.

[0003] Studies have found that aliphatic or aromatic nitrile electrolytes have the advantages of high voltage resistance, non-flammability, high flash point, wide liquid range, low gas production, and high ionic conductivity, and are expected to become an ideal choice for battery systems with higher charging cut-off voltages. With in-depth research, it was found that nitrile electrolytes are difficult to form excellent SEI films with electrode materials, are difficult to be compatible with negative electrode materials, and cannot guarantee long battery cycles, which limits the application of nitrile electrolytes.

[0004] For this reason, people have made a lot of modifications to nitrile electrolytes. For example, the patent document with publication number CN116632358A discloses an electrolyte containing aromatic hydrocarbon nitrile compounds, including electrolyte lithium salt, organic solvent and additives; wherein the organic solvent is at least selected from aromatic hydrocarbon nitrile compounds, the additives include fluoroethylene carbonate and lithium difluorooxalatoborate, and the additives account for 1 to 20 wt% of the total amount of electrolyte lithium salt and organic solvent; the structural formula of the aromatic hydrocarbon nitrile compound includes aromatic hydrocarbon, nitrile group, and R1, R2, R3, R4, R5 are selected from at least one of hydrogen, hydrocarbon group, halogen-containing hydrocarbon group and halogen. Another example is a type of partially fluorinated nitrile electrolyte material disclosed in the patent document with publication number CN117903001A, whose structural formula is Rf-O-CH2CH2CN, wherein the -Rf group is selected from partially fluorinated C1-C10 alkyl groups; the -Rf group is selected from -CH2CH2F, -CH2CHF2, -CH2CH2CH2F, -CH2CF2CHFCF2.

[0005] These existing technologies solve the problem that nitriles are not compatible with negative electrode materials by replacing hydrogen atoms on aliphatic or aromatic nitriles with fluorine, and utilizing the property that fluoride can form an excellent SEI film. However, fluorination may reduce the solvation capacity of the solvent, making the transmission of ions in the solvent difficult, weakening the interaction between ions and solvent molecules, thereby reducing the migration rate of ions and ionic conductivity, affecting the electrical properties of the electrolyte. In addition, the ability to improve the performance of nitrile electrolytes by fluorine substitution alone is limited. Summary of the invention

[0006] The present invention aims to solve the above problems and provide an aromatic fluoronitrile electrolyte material, electrolyte and battery which have good compatibility with the negative electrode, good solvation ability and good performance in long-term cycle performance and ion conductivity.

[0007] The technical solution of the present invention to solve the problem is: first , providing an aromatic fluoronitrile electrolyte material selected from compounds with the following general structural formula:

[0008]

[0009] Among them, at least one of R1, R2, R3, R4, R5, and R6 is selected from ether-containing groups, at least one is selected from fluorine-containing groups, at least one is selected from nitrile-containing groups, and the rest are selected from at least one of hydrogen groups, alkyl groups, and alkenyl groups.

[0010] In this application, the performance of the electrolyte is improved by aromatic hydrocarbons and substituted ether-containing groups, fluorine-containing groups, and nitrile-containing groups:

[0011] Aromatic hydrocarbon structural fragments can improve the ionic conductivity of the electrolyte by improving the solvation structure of the electrolyte and reducing the viscosity of the electrolyte; the nitrile structural fragments provided by the nitrile group effectively improve the electrolyte's resistance to high voltage, high temperature, low gas production, and high ionic conductivity; the fluorine-based structural fragments provided by the fluorine-containing group can form an excellent interface film and reduce interface resistance. The ether-based structural fragments provided by the ether-containing group can improve the dissociation degree of the electrolyte salt and the compatibility of the electrolyte and the negative electrode. Specifically, it is speculated that: the introduction of ether-based structural fragments on aromatic hydrocarbons with fluorine-based structural fragments and nitrile-based structural fragments makes the molecule more polar; in terms of compatibility with negative electrode materials, its highly electronegative oxygen atoms may be able to interact with the surface of the negative electrode material through dipole-dipole interactions, or react with the active sites on the surface of the negative electrode material to form chemical bonds, further increasing the interaction and compatibility between the material and the negative electrode material; in terms of the dissociation degree of the electrolyte salt, or the dissociation In terms of electron conductivity, due to its strong polarity, it may be easier to form a solvation shell with the ions in the electrolyte, which helps to reduce interactions and collisions between ions, reduce the migration resistance of ions, and improve the solubility and mobility of ions; the oxygen atoms may also form intramolecular or intermolecular hydrogen bonds or other interaction forces with fluorine atoms, which helps to stabilize the microstructure of the electrolyte, reduce the disordered movement of ions and energy loss, thereby improving the migration efficiency and conductivity of ions; in addition, it may also affect the viscosity of the electrolyte, which helps to reduce the resistance during ion migration and make it more suitable for ion migration.

[0012] The selection of ether-containing groups, fluorine-containing groups, and nitrile-containing groups is not limited, as long as they can provide ether-based structural segments, fluorine-based structural segments, and nitrile-based structural segments.

[0013] As a preferred embodiment of the present invention, the fluorine-containing group is selected from fluorine (-F), fluorine-containing alkyl (-C x H y F z ), fluorinated alkenyl (-C x H y F z ), fluorinated alkoxy (-OC x H y F z ), fluorinated olefinic oxide (-OC x H y F z )

[0014] The nitrile-containing group is selected from nitrile (-CN), alkyl nitrile (-C x H y CN), alkenyl nitrile (-C x H y CN), alkoxy nitrile (-OC x H yCN), olefin oxynitrile (-OC x H y CN);

[0015] The ether-containing group is selected from alkoxy (-OC x H y ), alkenyloxy (-OC x H y ), fluorinated alkoxy (-OC x H y F z ), fluorinated olefinic oxide (-OC x H y F z ), alkoxy nitrile (-OC x H y CN), olefin oxynitrile (-OC x H y CN).

[0016] It is understood that the ether-containing group, the fluorine-containing group, and the nitrile-containing group are not necessarily three different groups. For example, the fluorine-containing alkoxy group and the fluorine-containing alkenyloxy group (-OC x H y F z ), both contain ether-based structural segments and fluorine-based structural segments, and belong to both fluorine-containing groups and ether-containing groups. When one of R1, R2, R3, R4, R5, and R6 is a fluorine-containing alkoxy group or a fluorine-containing alkenyloxy group, it can be considered that at this time it satisfies the condition of "at least one is selected from a fluorine-containing group and at least one is selected from an ether-containing group". Similarly, alkoxy nitrile and alkenyloxy nitrile (-OC x H y CN), both contain ether group structural fragments and nitrile group structural fragments, and belong to both ether-containing groups and nitrile-containing groups. When one of R1, R2, R3, R4, R5, and R6 is selected from alkoxy nitrile or alkenyloxy nitrile, it can be considered that at this time it satisfies the condition of "at least one is selected from ether-containing groups, and at least one is selected from nitrile-containing groups".

[0017] Although the selection of ether-containing groups, fluorine-containing groups, and nitrile-containing groups is not limited, further optimization in the selection can further improve the electrical properties of the electrolyte material.

[0018] In the fluorine-containing group, the fluorine group may be on the aromatic ring or on the alkyl group or alkoxy group outside the aromatic ring. In some Implementation In order to further reduce the adverse effects of the fluorine group on solvation, the fluorine group is preferably set on the alkyl or alkoxy group outside the aromatic ring. As a preferred embodiment of the present invention, the fluorine-containing group is selected from at least one of a fluorine-containing alkyl group, a fluorine-containing alkenyl group, a fluorine-containing alkoxy group, and a fluorine-containing alkenyloxy group.

[0019] Also in some embodiments In order to further improve the cycle performance, as a preferred embodiment of the present invention, at least one of R1, R2, R3, R4, R5, and R6 is selected from alkoxy nitrile, alkenyloxy nitrile (-OC x H y That is to say, by selecting a group containing both an ether structural fragment and a nitrile structural fragment, and by combining the ether structural fragment with the nitrile structural fragment, the effect of the ether group on promoting the compatibility of the nitrile group with the negative electrode material can be further improved.

[0020] In this embodiment, at least one of R1, R2, R3, R4, R5, and R6 is selected from a fluorine-containing group. In this case, the fluorine-containing group may be a group containing only a fluorine-based structural segment, or a group containing a fluorine-based structural segment and an ether-based structural segment, preferably a group containing a fluorine-based structural segment and an ether-based structural segment. Specifically, at least one of R1, R2, R3, R4, R5, and R6 is selected from a fluorine-containing alkoxy group, a fluorine-containing alkenyloxy group (-OC x H y F z )

[0021] The alkoxy nitrile or alkenyloxy nitrile (-OC x H y CN), and the position of the fluorine-containing group is not limited, and the alkoxy nitrile or alkenyloxy nitrile (-OC x H y CN) can be the ortho, meta, or para position of the fluorine-containing group. As a preferred embodiment of the present invention, the alkoxy nitrile or alkenyloxy nitrile (-OC x H y CN) is the ortho or para position of the fluorine-containing group.

[0022] In this embodiment, for example, the aromatic fluoronitrile electrolyte material can be selected from at least one of 2 / 3 / 4-(fluoromethyl)phenoxyacetonitrile, 2 / 3 / 4-(difluoromethyl)phenoxyacetonitrile, 2 / 3 / 4-(trifluoromethyl)phenoxyacetonitrile; 2 / 3 / 4-(2-fluoroethoxy)phenoxyacetonitrile, 2 / 3 / 4-(2,2-difluoroethoxy)phenoxyacetonitrile, and 2 / 3 / 4-(2,2,2-trifluoroethoxy)phenoxyacetonitrile. Wherein, "2 / 3 / 4" means that the group in the brackets can be the ortho, meta, or para position of the oxyacetonitrile.

[0023] In some other embodiments In order to further improve the cycle performance and ion conductivity, as a preferred embodiment of the present invention, at least one of R1, R2, R3, R4, R5, and R6 is selected from fluorine-containing alkoxy, fluorine-containing alkenyloxy (-OC x H y F z) In other words, a group containing both a fluorine-based structural segment and an ether-based structural segment is selected, and by combining the ether-based structural segment with the fluorine-based structural segment, the polarity of the group is adjusted, the solvation ability of the fluorine-containing group is improved, and the compatibility of the fluorine-based group with the negative electrode material is further promoted.

[0024] In this embodiment, at least one of R1, R2, R3, R4, R5, and R6 is selected from a nitrile-containing group. In this case, the nitrile-containing group can be a group containing only a nitrile structural fragment, or a group containing a nitrile structural fragment and an ether structural fragment, preferably a group containing a nitrile structural fragment and an ether structural fragment. Specifically: at least one of R1, R2, R3, R4, R5, and R6 is selected from an alkoxynitrile, an alkeneoxynitrile (-OC x H y CN).

[0025] Likewise, the fluorinated alkoxy or fluorinated alkenyloxy (—OC x H y F z ), and the position of the nitrile-containing group is not limited, and the fluorine-containing alkoxy or fluorine-containing alkenyloxy (-OC x H y F z ) can be the ortho, meta, or para position of the nitrile-containing group. As a preferred embodiment of the present invention, the fluorine-containing alkoxy or fluorine-containing alkenyloxy (-OC x H y F z ) is the ortho or para position of the nitrile-containing group.

[0026] In this embodiment, for example, the aromatic fluoronitrile electrolyte material can be selected from at least one of 2 / 3 / 4-(2-fluoroethoxy)benzonitrile, 2 / 3 / 4-(2,2-difluoroethoxy)benzonitrile, 2 / 3 / 4-(2,2,2-trifluoroethoxy)benzonitrile; 2 / 3 / 4-(2-fluoroethoxy)phenoxyacetonitrile, 2 / 3 / 4-(2,2-difluoroethoxy)phenoxyacetonitrile, 2 / 3 / 4-(2,2,2-trifluoroethoxy)phenoxyacetonitrile; 2,3 / 2,4 / 2,5 / 2,6 / 3,5-di-(2,2,2-trifluoroethoxy)benzonitrile. Wherein, "2 / 3 / 4" means that the group in the brackets can be the ortho, meta or para position of benzonitrile or phenoxyacetonitrile. “2,3 / 2,4 / 2,5 / 2,6 / 3,5-bis-(2,2,2-trifluoroethoxy)benzonitrile” means that when benzonitrile is at the 1st position on benzene, the two 2,2,2-trifluoroethoxy groups can be at the 2nd and 3rd positions, or at the 2nd and 4th positions, or at the 2nd and 5th positions, or at the 2nd and 6th positions, or at the 3rd and 5th positions, respectively.

[0027] In some embodimentsIn order to further improve the cycle performance, based on the role of fluoride in forming an excellent SEI film and the problem of unfavorable solvation of fluorination solved by ether-based structural fragments, as a preferred embodiment of the present invention, the fluorine-containing group includes at least two fluorine substituents, and the cycle performance is improved by increasing the number of fluorine substituents. For example, the material can be selected from at least one of 2 / 3 / 4-(difluoromethyl)phenoxyacetonitrile, 2 / 3 / 4-(trifluoromethyl)phenoxyacetonitrile, 2 / 3 / 4-(2,2-difluoroethoxy)benzonitrile, 2 / 3 / 4-(2,2,2-trifluoroethoxy)benzonitrile, 2 / 3 / 4-(2,2-difluoroethoxy)phenoxyacetonitrile, 2 / 3 / 4-(2,2,2-trifluoroethoxy)phenoxyacetonitrile, and 2,3 / 2,4 / 2,5 / 2,6 / 3,5-di-(2,2,2-trifluoroethoxy)benzonitrile.

[0028] Further preferably, the fluorine-containing group is perfluorinated. For example, the material can be selected from 2 / 3 / 4-(trifluoromethyl)phenoxyacetonitrile, 2 / 3 / 4-(2,2,2-trifluoroethoxy)benzonitrile, 2 / 3 / 4-(2,2,2-trifluoroethoxy)phenoxyacetonitrile, 2,3 /

[0029] At least one of 2,4 / 2,5 / 2,6 / 3,5-bis-(2,2,2-trifluoroethoxy)benzonitrile.

[0030] Secondly Another object of the present invention is to provide an electrolyte comprising an electrolyte salt and a solvent, wherein the solvent comprises any one of the above-mentioned aromatic fluoronitrile electrolyte materials.

[0031] The solvent may also include other commonly used additives, such as at least one of cyclic carbonate compounds, cyclic sulfate compounds, sulfonate compounds, phosphate compounds, borate compounds, nitrile compounds and ion additives. No additives may be used. As a preferred embodiment of the present invention, the solvent is composed of any of the above aromatic fluoronitrile electrolyte materials.

[0032] The choice of electrolyte salt is not limited, for example, lithium salt, sodium salt, potassium salt, etc. can be selected. As a preferred embodiment of the present invention, the electrolyte salt is a lithium salt. Further preferably, the electrolyte salt is selected from at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluoroborate and lithium difluorophosphate.

[0033] The amount of the electrolyte salt and the aromatic fluoronitrile electrolyte material is not limited. As a preferred embodiment of the present invention, the amount ratio of the electrolyte salt to the aromatic fluoronitrile electrolyte material is 0.1 to 3 mol / L. For example, it can be 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2 mol / L, 2.2 mol / L, 2.5 mol / L, 2.8 mol / L, 3 mol / L.

[0034] The preparation method of the electrolyte is not limited. As a preferred embodiment of the present invention, the preparation of the electrolyte comprises the following steps:

[0035] S1. Mixing the aromatic fluoronitrile electrolyte material and the electrolyte salt in proportion;

[0036] S2. Stir the mixture to fully dissolve the electrolyte salt.

[0037] at last Another object of the present invention is to provide a battery comprising any one of the electrolytes described above. The components of other battery structures are not limited.

[0038] Beneficial effects of the present invention:

[0039] 1. The present application provides an aromatic fluoronitrile electrolyte material and an electrolyte, wherein the nitrile-based structural fragments effectively improve the electrolyte's performance of high voltage resistance, high temperature resistance, low gas production, and high ionic conductivity; the aromatic hydrocarbon structural fragments can improve the electrolyte's ionic conductivity by improving the electrolyte's solvation structure and reducing the electrolyte's viscosity; the fluorine-based structural fragments can form an excellent interface film and reduce the interface resistance; the ether-based structural fragments can improve the dissociation degree of the lithium salt and the compatibility of the electrolyte with the lithium negative electrode; thereby obtaining an electrolyte material with high voltage resistance, high ionic conductivity, and good long cycle performance, which not only expands the types of high-voltage resistant fluoronitrile electrolytes, but also further improves the electrical properties of fluoronitrile electrolytes.

[0040] 2. The present application provides a battery. The battery designed based on the above-mentioned electrolyte has higher safety performance and allows a higher charging voltage. In addition, the increased ionic conductivity and reduced interface resistance can effectively improve the fast charging capability of the battery, and the stable SEI film impedance can effectively improve the cycle performance of the battery. DETAILED DESCRIPTION

[0041] The following are specific embodiments of the present invention, and further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0042] Example 1

[0043] Aromatic fluoronitrile electrolyte material , select 2-fluoro-4-methoxybenzeneacetonitrile (C9H8FNO), specifically: it includes -CH2CN at position 1, -F at position 2, and -OCH3 at position 4.

[0044] An electrolyte , which is composed of lithium bis(fluorosulfonyl)imide as an electrolyte salt and the above-mentioned aromatic fluoronitrile electrolyte material as a solvent. The electrolyte is prepared by the following steps: in a glove box filled with high-purity argon, lithium bis(fluorosulfonyl)imide and aromatic fluoronitrile electrolyte material are mixed at a dosage ratio of 1 mol / L, stirred evenly, and the lithium salt is fully dissolved to obtain an electrolyte.

[0045] A battery , prepared by the following steps: 0.93g LiNi0.8Co0.1Mn0.1O2 powder, 0.04g conductive agent carbon black, 0.03g binder PVDF were added to an agate mortar, and then an appropriate NMP solvent was added and ground evenly; then the slurry was evenly coated on the surface of aluminum foil (i.e., positive electrode current collector), and vacuum dried at 60℃ for 12h, and the dried electrode sheet was cut into a 12mm diameter disc, and the positive electrode was obtained after compaction. With the lithium sheet as the counter electrode and the electrolyte obtained above as the electrolyte, a button cell (NCM / LE / Li) composed of graphite and lithium sheets was assembled.

[0046] Example 2

[0047] This embodiment is basically the same as the embodiment 1, and the only difference is that the aromatic fluoronitrile electrolyte material is 2-(fluoromethyl)phenoxyacetonitrile (C9H8FNO), specifically, it includes aromatic hydrocarbons, ortho-CH2F and -OCH2CN.

[0048] Example 3

[0049] This embodiment is basically the same as the embodiment 1, and the only difference is that the aromatic fluoronitrile electrolyte material is 2-(2-fluoroethoxy)benzonitrile (C9H8FNO), specifically, it includes aromatic hydrocarbons, ortho-OCH2CH2F and -CN.

[0050] Example 4

[0051] This embodiment is basically the same as the embodiment 1, and the only difference is that the aromatic fluoronitrile electrolyte material is 2-(fluoromethoxy)phenylacetonitrile (C9H8FNO), specifically, it includes aromatic hydrocarbons, ortho-OCH2F and -CH2CN.

[0052] Example 5

[0053] This embodiment is basically the same as the embodiment 1, and the only difference is that the aromatic fluoronitrile electrolyte material is 2-(difluoromethyl)phenoxyacetonitrile (C9H7F2NO), specifically, it includes aromatic hydrocarbons, ortho-CHF2 and -OCH2CN.

[0054] Example 6

[0055] This embodiment is basically the same as the embodiment 1, and the only difference is that the aromatic fluoronitrile electrolyte material is 2-(trifluoromethyl)phenoxyacetonitrile (C9H6F3NO), specifically, it includes aromatic hydrocarbons, ortho-CF3 and -OCH2CN.

[0056] Example 7

[0057] This embodiment is basically the same as the embodiment 1, and the only difference is that the aromatic fluoronitrile electrolyte material is 2-fluorophenoxypropionitrile (i.e., 3-(2-fluorophenoxy)propionitrile, C9H8FNO), specifically, including aromatic hydrocarbons, ortho-F and -OCH2CH2CN.

[0058] Example 8

[0059] This embodiment is basically the same as the embodiment 1, the only difference being that the aromatic fluoronitrile electrolyte material is 2-fluoro-4,5-dimethoxyphenylacetonitrile (C 10 H 10 FNO2), specifically: including aromatic hydrocarbons, -CH2CN at position 1, -F at position 2, and -OCH3 at positions 4 and 5.

[0060] Example 9

[0061] This embodiment is basically the same as the embodiment 1, the only difference being that the aromatic fluoronitrile electrolyte material is 2-(2-fluoroethoxy)phenoxyacetonitrile (C 10 H 10 FNO2), specifically: including aromatic hydrocarbons, ortho-OCH2CH2F and -OCH2CN.

[0062] Example 10

[0063] This embodiment is basically the same as the embodiment 2, and the only difference is that the aromatic fluoronitrile electrolyte material is 3-(fluoromethyl)phenoxyacetonitrile (C9H8FNO), specifically, it includes aromatic hydrocarbons, meta-position -CH2F and -OCH2CN.

[0064] Embodiment 11

[0065] This embodiment is basically the same as the embodiment 2, and the only difference is that the aromatic fluoronitrile electrolyte material is 4-(fluoromethyl)phenoxyacetonitrile (C9H8FNO), specifically, it includes aromatic hydrocarbons, para-CH2F and -OCH2CN.

[0066] Example 12

[0067] This embodiment is basically the same as the embodiment 1, and the only difference is that the aromatic fluoronitrile electrolyte material is 2-fluoro-4-methoxybenzonitrile (C8H6FNO), specifically, it includes -CN at position 1, -F at position 2, and -OCH3 at position 4.

[0068] Comparative Example 1

[0069] This comparative example is basically the same as Example 1, the only difference being that commercial esters are used as electrolyte materials.

[0070] Comparative Example 2

[0071] This comparative example is basically the same as Example 1, and the only difference is that the electrolyte material is benzyl cyanide, which has no fluorine-containing group and ether-containing group.

[0072] Comparative Example 3

[0073] This comparative example is basically the same as Example 1, except that the electrolyte material is 2-fluorobenzeneacetonitrile, which has no ether-containing group.

[0074] Comparative Example 4

[0075] This comparative example is basically the same as Example 1, and the only difference is that the electrolyte material is p-methoxyphenylacetonitrile, which has no fluorine-containing group.

[0076] Comparative Example 5

[0077] This comparative example is substantially the same as Example 1, except that the electrolyte material is a mixture of 2-fluorobenzeneacetonitrile and tetrahydrofuran in a mass ratio of 3:7.

[0078] The electrolytes or batteries obtained in the examples and comparative examples were tested for performance

[0079] Electrolyte ion conductivity: Use an ion conductivity tester to measure the ion conductivity of the electrolyte;

[0080] High-voltage resistance of electrolyte: Assemble button cells composed of lithium sheets and steel sheets (SS / LE / Li), and determine the electrochemical stability window of the electrolyte, i.e. the high-voltage resistance of the electrolyte, through LSV;

[0081] Rate performance and cycle performance of the battery: 0.93g LiNi0.8Co0.1Mn0.1O2 powder, 0.04g conductive agent carbon black, and 0.03g binder PVDF were added to an agate mortar, and then an appropriate NMP solvent was added and ground evenly; then the slurry was evenly coated on the surface of the aluminum foil (i.e., the positive electrode current collector), and vacuum dried at 60℃ for 12h, and the dried electrode sheet was cut into a 12mm diameter disc, and the positive electrode was obtained after compaction. With the lithium sheet as the counter electrode and the above solution as the electrolyte, a button cell (NCM / LE / Li) composed of graphite and lithium sheets was assembled, and the rate performance and cycle performance of the battery were determined by testing.

[0082] The test results are shown in Table 1 below.

[0083] Table 1.

[0084]

[0085] As shown in Table 1, it can be seen from the comparative examples and comparative example 1 that the aromatic fluoronitrile electrolyte material of the present application has good performance in ionic conductivity, initial decomposition voltage, rate performance and capacity retention after 500 cycles (i.e., long-term cycle performance).

[0086] By comparing Example 1 with Comparative Examples 2 to 5, it can be seen that in the present application, the aromatic nitrile and the fluorine-based structural fragments and ether-based structural fragments substituted thereon work synergistically to achieve improvements in ionic conductivity and long-term cycle performance. Specifically:

[0087] In terms of ionic conductivity, Comparative Example 2 uses benzyl cyanide, and Comparative Example 3 uses 2-fluorobenzene acetonitrile, and only adds a fluorine-based structural fragment compared to Comparative Example 2, resulting in a decrease in ionic conductivity; Comparative Example 4 uses p-methoxybenzene acetonitrile, and only adds an ether-based structural fragment compared to Comparative Example 2. Although the ionic conductivity is improved to a certain extent, the improvement rate is lower than the improvement rate of Example 1 having both a fluorine-based structural fragment and an ether-based structural fragment; this may be because the ether-based structural fragment and the fluorine-based structural fragment work together to help stabilize the microstructure of the electrolyte, reduce the disordered movement of ions and energy loss, and thus further improve the ionic conductivity.

[0088] In terms of long-term cycle performance, Comparative Example 2 uses benzyl cyanide, Comparative Example 3 uses 2-fluorobenzene acetonitrile, and only adds a fluorine-based structural fragment compared to Comparative Example 2; Comparative Example 4 uses p-methoxybenzene acetonitrile, and only adds an ether-based structural fragment compared to Comparative Example 2. Although Comparative Examples 3 and 4 can improve the long-term cycle performance of the battery to a certain extent, the improvement rate is less than that of Example 1, indicating that the ether-based structural fragment and the fluorine-based structural fragment can further synergistically improve the long-term cycle performance of the battery.

[0089] In Comparative Example 5, although it contains aromatic nitrile, fluorine-based structural fragments and ether-based structural fragments, since the ether-based structural fragment is not on the aromatic nitrile, its improvements in ionic conductivity and long-term cycle performance are not as good as those in Example 1. This may be because the ether-based structural fragment in Comparative Example 5 has no way to adjust the polarity of the aromatic fluorine nitrile.

[0090] In addition, it can be seen from the comparison in the embodiments that by further optimizing the groups on the electrolyte material, a technical solution for ion conductivity and long-term cycle performance can be obtained. Specifically:

[0091] The molecular formulas of Examples 1, 2, 3, and 4 are consistent, but Example 1 uses 2-fluoro-4-methoxyphenylacetonitrile, and the nitrile structural fragment, the fluorine structural fragment, and the ether structural fragment are distributed in three groups respectively. While Example 2 uses 2-(fluoromethyl)phenoxyacetonitrile, the ether structural fragment and the nitrile structural fragment are in one group, and Example 2 is further improved in terms of ionic conductivity and long-term cycle performance compared to Example 1, which may be because the ether structural fragment is bound to the nitrile structural fragment, which can further improve the ether group's compatibility with the negative electrode material. The ether structural fragment and the fluorine structural fragment are in one group, and Examples 3 and 4 are also further improved in terms of ionic conductivity and long-term cycle performance compared to Example 1, which may be because the ether structural fragment is bound to the fluorine structural fragment, which can further adjust the polarity of the group, improve the solvation ability of the fluorine-containing group, and further promote the compatibility of the fluorine-containing group with the negative electrode material. At the same time, Examples 3 and 4 compared and found that the position of the methyl group in the ether-containing group, the fluorine-containing group, and the nitrile-containing group has little effect on the electrical properties.

[0092] On this basis, we continue to compare Examples 8 and 9. Example 8 uses 2-fluoro-4,5-dimethoxybenzeneacetonitrile and adds a methoxy group compared to Example 1, which can slightly improve the ionic conductivity and long-term cycle performance, but the improvement rate is not large. Example 9 has the same molecular formula as Example 8, but in Example 9, the ether structural fragment and the nitrile structural fragment are in one group, and the ether structural fragment and the fluorine structural fragment are in one group, as mentioned above, which can significantly improve the ionic conductivity and long-term cycle performance.

[0093] In Examples 2, 5, and 6, when the number of fluorine substitutions increases to two, the long-term cycle performance is significantly improved; when it increases to three, the long-term cycle performance is further improved slightly. In addition, it is unexpectedly found that as the number of fluorine drives increases, the ionic conductivity is also improved. This may be because more fluorine groups can form more stable microstructures with the ether structure fragments to reduce the disordered movement of ions.

[0094] The molecular formula of Example 7 is consistent with that of Example 2, but the fluorine group in Example 7 is directly connected to the aromatic hydrocarbon, while the fluorine group in Example 2 is connected to the methyl group. The ionic conductivity and long-term cycle performance in Example 2 are relatively high, indicating that the fluorine group indirectly connected to the aromatic hydrocarbon can reduce the adverse effects of fluorination on solvation.

[0095] In Examples 2, 10, and 11, the fluoromethyl group is at the ortho, meta, and para positions of the oxyacetonitrile, respectively, but there is little change in the ionic conductivity and long-term cycle performance, indicating that the position of the group has little effect on its electrical properties, but the electrical properties of the ortho and para positions are slightly better than those of the meta position.

[0096] Compared with Example 1, Example 12 has one less methyl group, but the ionic conductivity and long-term cycle performance have little change, indicating that the number of methyl groups has little effect on its electrical properties. Compared with Comparative Examples 2 and 3, it can be shown that the changes in ionic conductivity and long-term cycle performance of Comparative Examples 2 and 3 compared with Example 1 are mainly caused by fluorine and ether groups, and have nothing to do with the reduction of methyl groups.

[0097] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. An aromatic fluoronitrile electrolyte material, characterized in that: Selected from compounds with the following general structural formula: Among them, at least one of R1, R2, R3, R4, R5, and R6 is selected from ether-containing groups, at least one is selected from fluorine-containing groups, at least one is selected from nitrile-containing groups, and the rest are selected from at least one of hydrogen groups, alkyl groups, and alkenyl groups.

2. The aromatic fluoronitrile electrolyte material according to claim 1, characterized in that: The fluorine-containing group is selected from at least one of a fluorine group, a fluorine-containing alkyl group, a fluorine-containing alkenyl group, a fluorine-containing alkoxy group, and a fluorine-containing alkenyloxy group; The nitrile-containing group is selected from at least one of a nitrile group, an alkyl nitrile, an alkenyl nitrile, an alkoxy nitrile, and an alkenyloxy nitrile; The ether-containing group is selected from at least one of an alkoxy group, an alkenyloxy group, a fluorine-containing alkoxy group, a fluorine-containing alkenyloxy group, an alkoxy nitrile and an alkenyloxy nitrile.

3. The aromatic fluoronitrile electrolyte material according to claim 2, characterized in that: At least one of R1, R2, R3, R4, R5 and R6 is selected from alkoxy nitrile and alkenyloxy nitrile.

4. The aromatic fluoronitrile electrolyte material according to claim 3, characterized in that: The alkoxy nitrile or alkenyloxy nitrile is at the ortho or para position of the fluorine-containing group.

5. An aromatic fluoronitrile electrolyte material according to claim 2 or 3, characterized in that: At least one of R1, R2, R3, R4, R5 and R6 is selected from the group consisting of fluorine-containing alkoxy groups and fluorine-containing alkenyloxy groups.

6. The aromatic fluoronitrile electrolyte material according to claim 2, characterized in that: The fluorine-containing group is selected from at least one of a fluorine-containing alkyl group, a fluorine-containing alkenyl group, a fluorine-containing alkoxy group, and a fluorine-containing alkenyloxy group.

7. The aromatic fluoronitrile electrolyte material according to claim 1, characterized in that: The fluorine-containing group includes at least two fluorine substituents.

8. An electrolyte solution comprising an electrolyte salt and a solvent, characterized in that: The solvent comprises the aromatic fluoronitrile electrolyte material as claimed in any one of claims 1 to 7.

9. An electrolyte according to claim 8, characterized in that: The usage ratio of the electrolyte salt to the aromatic fluoronitrile electrolyte material is 0.1 to 3 mol / L.

10. A battery, characterized in that: Comprising the electrolyte as described in any one of claims 8 to 9.

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