Patent Description:
Since commercialization of a lithium-ion battery, the lithium-ion battery has been widely used in the fields of digital, energy storage, power, military aerospace and communication equipment and etc., and due to its lightness, high specific energy, no memory effect and good cycle performance. With a widespread application of the lithium-ion battery, consumers have put forward higher requirements for an energy density, cycle life, high temperature performance, safety and other performances of the lithium-ion battery.

Most lithium-ion battery products have a problem that high temperature performance and low temperature performance cannot be taken into account together. Therefore, an additive is usually added into an electrolyte to improve the high and low temperature performances of the lithium-ion battery. However, when a general additive has a better high-temperature effect, its impedance is large, while a high-temperature effect of a low-impedance additive is not enough. Therefore, it is necessary to optimize a combination of additives to obtain excellent high and low temperature performances.

<CIT> discloses a lithium-ion battery and a non-aqueous electrolyte. An additive containing a single nitrile group can stabilize a surface of a positive electrode and inhibit a side reaction of transition metal ions in a high oxidation state and the electrolyte under high voltage. In addition, another sulfur-containing additive can form a solid electrolyte interphase (SEI) on a negative electrode, stabilize the negative electrode, and simultaneously protect the positive electrode. Through a synergy effect between the two additives, it can improve a cycle performance and high-temperature storage performance of the battery.

<CIT> discloses an electrolyte additive and use thereof in lithium-ion battery. The lithium-ion battery includes an electrolyte solution including an organic solvent, a lithium salt, and an electrolyte additive. The use of the electrolyte additive in a lithium-ion battery enables the lithium-ion battery to maintain a good cycle life, low-temperature discharge characteristics, and high-temperature storage characteristics.

<CIT> discloses a rechargeable lithium battery. The lithium battery cell includes a compound bonded with an electrode surface material and suppresses gas generation on a surface of a positive electrode. The battery cell has an effect of having a coordination bond of the compound with metal ions therein, and thus preventing a fine short circuit due to extraction of the metal ions on a surface of a negative electrode. The rechargeable lithium battery can replace a rechargeable lithium battery that includes <NUM>,<NUM>-propane sultone (PS) used as a conventional additive to improve thermal impact durability but having a problem of causing cancer.

<CIT> discloses a silicon-carbon negative electrode lithium-ion battery electrolyte and a lithium battery. The electrolyte includes a lithium salt, an organic solvent, a first additive that is used as a functional additive to form a thin SEI film, good toughness and low lithium-ion migration resistance. The electrolyte further adopts a second additive to improve a high-temperature cycle performance of the lithium-ion battery.

<CIT> discloses a lithium titanate secondary battery including a positive electrode, a negative electrode and a PC-based electrolyte. It utilizes a high potential reduction characteristic of lithium tetrafluorooxalate phosphate to reduce a formation of a film before the negative electrode is charged and prevent gas production of the batteries under high temperature, thereby extending a cycle life of the lithium batteries.

In order to overcome the shortcomings of the prior art, the present invention provides a non-aqueous electrolyte for a lithium-ion battery and a lithium-ion battery using the non-aqueous electrolyte. The non-aqueous electrolyte includes (a) a lithium salt, (b) a non-aqueous organic solvent, and (c) at least one compound represented by formula <NUM>; where the non-aqueous electrolyte further includes at least one of the following components (d) and (e): (d) a nitrile compound, and (e) ethylene sulfate. The impedance of the lithium-ion battery can be reduced through a synergy effect between them, and at the same time, the lithium-ion battery has a good high temperature storage performance, high temperature cycle performance, and low temperature charge and discharge performance.

The present invention is achieved through the following technical solution:
a non-aqueous electrolyte, the non-aqueous electrolyte including (a) a lithium salt, (b) a non-aqueous organic solvent, and (c) at least one compound represented by formula <NUM>; where the non-aqueous electrolyte further includes at least one of the following components (d) and (e):.

According to the present invention, R<NUM> and R<NUM> are the same or different, and are each independently selected from hydrogen, halogen, a halogen substituted or unsubstituted C<NUM>-C<NUM> alkyl group.

According to the present invention, R<NUM> and R<NUM> are the same or different, and are each independently selected from hydrogen, fluorine, a methyl group, an ethyl group or a propyl group.

According to the present invention, the compound represented by formula <NUM> is selected from at least one of the following compounds A1 to A5:
<CHM>
<CHM>.

According to the present invention, the nitrile compound is selected from at least one of <NUM>,<NUM>,<NUM>-hexane tricarbonitrile, <NUM>,<NUM>,<NUM>-propane tricarbonitrile and <NUM>-methoxypropionitrile, a selection of the nitrile compound can make the non-aqueous electrolyte of the present invention have a better high-temperature storage performance and a better high-temperature cycle performance.

According to the present invention, a content of the compound represented by formula <NUM> is <NUM>-<NUM> wt% of a total mass of the non-aqueous electrolyte, for example, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt% or <NUM> wt%.

According to the present invention, a content of the nitrile compound is <NUM>-<NUM> wt% of the total mass of the non-aqueous electrolyte, preferably <NUM>-<NUM> wt%, for example, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt% or <NUM> wt%.

According to the present invention, a content of the ethylene sulfate is <NUM>-2wt% of the total mass of the non-aqueous electrolyte, preferably <NUM>-2wt%, for example, <NUM>. 1wt%, <NUM>. 2wt%, <NUM>. 5wt%, <NUM>. 0wt%, <NUM>. 5wt% or 2wt%.

According to the present invention, the lithium salt is selected from one or more of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorooxalate borate, lithium bisfluorosulfonimide, lithium bistrifluoromethanesulfonimide, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide and lithium bis(trifluoromethylsulfonyl)imide.

According to the present invention, a content of the lithium salt is <NUM>-<NUM> wt% of the total mass of the non-aqueous electrolyte, for example, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt%, <NUM> wt% or <NUM> wt%.

According to the present invention, the non-aqueous organic solvent is selected from carbonate and/or carboxylate.

Exemplarily, the carbonate is selected from one or more of the following fluorinated or unsubstituted solvents: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

Exemplarily, the carboxylate is selected from one or more of the following fluorinated or unsubstituted solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isoamyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, and ethyl n-butyrate.

The present invention also provides a method for preparing the above-mentioned non-aqueous electrolyte. The method includes the following steps:.

Exemplarily, the method includes the following steps:
mixing (b) a non-aqueous organic solvent, (c) at least one compound represented by formula <NUM>, (d) a nitrile compound including at least one of <NUM>,<NUM>,<NUM>-hexane tricarbonitrile, <NUM>,<NUM>,<NUM>-propane tricarbonitrile, and <NUM>-methoxypropionitrile evenly, and detecting moisture, and after the moisture is detected to be qualified, then freezing at a low temperature about -<NUM> for <NUM>-<NUM> hours, and then adding (a) a lithium salt quickly, and after the moisture and free acid are detected to be qualified, obtaining the prepared non-aqueous electrolyte.

Exemplarily, the method includes the following steps:
mixing (b) a non-aqueous organic solvent, (c) at least one compound represented by formula <NUM>, and (e) ethylene sulfate evenly; and detecting moisture, and after the moisture is detected to be qualified, then freezing at a low temperature about -<NUM> for <NUM>-<NUM> hours, and then adding (a) a lithium salt quickly, and after the moisture and free acid are detected to be qualified, obtaining the prepared non-aqueous electrolyte.

Exemplarily, the method includes the following steps:
mixing (b) a non-aqueous organic solvent, (c) at least one compound represented by formula <NUM>, (d) a nitrile compound including at least one of <NUM>,<NUM>,<NUM>-hexane tricarbonitrile, <NUM>,<NUM>,<NUM>-propane tricarbonitrile, and <NUM>-methoxypropionitrile, and (e) ethylene sulfate evenly; and detecting moisture, and after the moisture is detected to be qualified, then freezing at a low temperature about -<NUM> for <NUM>-<NUM> hours, and then adding (a) a lithium salt quickly, and after the moisture and free acid are detected to be qualified, obtaining the prepared non-aqueous electrolyte.

The present invention also provides a lithium-ion battery, the lithium-ion battery includes the above-mentioned non-aqueous electrolyte.

According to the present invention, the lithium-ion battery further includes a positive electrode sheet containing a positive electrode active material, a negative electrode sheet containing a negative electrode active material, and a lithium-ion diaphragm.

According to the present invention, the positive electrode active material is selected from one or more of layered lithium transition metal composite oxide, a lithium manganate, and a lithium cobalt oxide mixed ternary material; a chemical formula of the layered lithium transition metal composite oxide is Li<NUM>+xNiyCozM(<NUM>-y-z)Q<NUM>, where - <NUM>≤x≤<NUM>, <NUM>≤y≤<NUM>, <NUM>≤z≤<NUM>, and <NUM>≤y+z≤<NUM>; where M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo and Zr; and Q is one or more of O, F, P and S.

According to the present invention, the negative active material is selected from one or more of a carbon material, a silicon-based material, a tin-based material or their corresponding alloy materials.

According to the present invention, an operating voltage range of the lithium-ion battery is <NUM>. 25V and more.

According to the present invention, after cycling for <NUM> cycles under a chargedischarge system of being charged at <NUM>. 3C and being discharged at <NUM>. 5C, at <NUM>, a thickness change rate of the lithium-ion battery is less than or equal to <NUM>% (for example, less than or equal to <NUM>%); and a capacity retention rate is greater than or equal to <NUM>% (for example, greater than or equal to <NUM>%).

According to the present invention, after cycling for <NUM> cycles under a chargedischarge system of being charged to <NUM>. 2V at 1C, then charged to <NUM>. 4V at <NUM>. 7C, then charged at a constant voltage of <NUM>. 4V until a cut-off current of <NUM>. 05C, and then discharged to 3V at <NUM>. 5C, at <NUM>, a thickness change rate of the lithium-ion battery is less than or equal to <NUM>%; and a capacity retention rate is greater than or equal to <NUM>% (for example, greater than or equal to <NUM>%).

According to the present invention, after cycling for <NUM> cycles under a chargedischarge system of being charged to <NUM>. 4V at a constant current of <NUM>. 7C, charged at a constant voltage of <NUM>. 4V until a cut-off current of <NUM>. 05C, and then discharged at <NUM>. 5C, at <NUM>, a thickness change rate of the lithium-ion battery is less than or equal to <NUM>%; and a capacity retention rate is greater than or equal to <NUM>% (for example, greater than or equal to <NUM>%).

According to the present invention, a thickness change rate of the lithium-ion battery is less than or equal to <NUM>% (for example, less than or equal to <NUM>%) after the lithium-ion battery is charged to <NUM>. 4V at <NUM>. 7C, then charged at a constant voltage of <NUM>. 4V until a cut-off current is <NUM>. 05C, then discharged to <NUM>. 0V at a constant current of <NUM>. 5C, then charged to <NUM>. 4V at <NUM>. 7C, and then charged at a constant voltage of <NUM>. 4V until a cut-off current is <NUM>. 05C, at <NUM>, and is set aside for <NUM> days.

The term "halogen" refers to F, Cl, Br and I.

The term "C<NUM>-C<NUM> alkyl group" should be understood to preferably represent a linear or branched saturated monovalent hydrocarbon group having <NUM> to <NUM> carbon atoms, preferably a C<NUM>-C<NUM> alkyl group. "C<NUM>-C<NUM> alkyl group" should be understood to preferably represent a linear or branched saturated monovalent hydrocarbon group having <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> carbon atoms. The alkyl group is, for example, methyl, ethyl, propyl, butyl, pentyl, hexyl, isopropyl, isobutyl, sec-butyl, tert-butyl, isoamyl, <NUM>-methylbutyl, <NUM>-methylbutyl, <NUM>-ethylpropyl, <NUM>,<NUM>-dimethylpropyl, neopentyl, <NUM>,<NUM>-dimethylpropyl, <NUM>-methylpentyl, <NUM>-methylpentyl, <NUM>-methylpentyl, <NUM>-methylpentyl, <NUM>-ethylbutyl, <NUM>-ethylbutyl, <NUM>,<NUM>-dimethylbutyl, <NUM>,<NUM>-dimethylbutyl, <NUM>,<NUM>-dimethylbutyl, <NUM>,<NUM>-dimethylbutyl, <NUM>,<NUM>-dimethylbutyl, <NUM>,<NUM>-dimethylbutyl, etc., or their isomers. In particular, the group is, for example, methyl, ethyl, propyl, butyl, isopropyl, isobutyl, sec-butyl, tert-butyl, more particularly, the group has <NUM>, <NUM> or <NUM> carbon atoms ("C<NUM>-<NUM> alkyl group"), for example, methyl, ethyl, n-propyl or isopropyl.

The term "C<NUM>-<NUM> alkenyl group" should be understood to preferably represent a linear or branched monovalent hydrocarbon group which contains one or more double bonds and has <NUM>, <NUM>, <NUM> or <NUM> carbon atoms, especially, <NUM> or <NUM> carbon atoms ("C<NUM>-<NUM> alkenyl group"). It should be understood that in the case where the alkenyl group contains more than one double bonds, the double bonds may be separated from each other or conjugated. The alkenyl group is, for example, vinyl, allyl, (E)-<NUM>-methylvinyl, (Z)-<NUM>-methylvinyl, (E)-but-<NUM>-enyl, (Z)-but-<NUM>-enyl, (E)-but-<NUM>-enyl, (Z)-but-<NUM>-enyl, pent-<NUM>-enyl, (E)-pent-<NUM>-enyl, (Z)-pent-<NUM>-enyl, (E)-pent-<NUM>-enyl, (Z)-pent-<NUM>-enyl, (E)-pent-<NUM>-enyl, (Z)-pent-<NUM>-enyl, hex-<NUM>-enyl, (E)-hex-<NUM>-enyl, (Z)-hex-<NUM>-enyl, (E)-hex-<NUM>-enyl, (Z)-hex-<NUM>-enyl, (E)-hex-<NUM>-enyl, (Z)-hex-<NUM>-enyl, (E)-hex-<NUM>-enyl, (Z)-hex-<NUM>-enyl, isopropenyl, <NUM>-methylprop-<NUM>-enyl, <NUM>-methylprop-<NUM>-enyl, <NUM>-methylprop-<NUM>-enyl, (E)-<NUM>-methylprop-<NUM>-enyl, (Z)-<NUM>-methylprop-<NUM>-enyl, <NUM>-methylbut-<NUM>-enyl, <NUM>-methylbut-<NUM>-enyl, <NUM>-methylbut-<NUM>-enyl, <NUM>-methylbut-<NUM>-enyl, (E)-<NUM>-methylbut-<NUM>-enyl, (Z)-<NUM>-methylbut-<NUM>-enyl, (E)-<NUM>-methylbut-<NUM>-enyl, (Z)-<NUM>-methylbut-<NUM>-enyl, (E)-<NUM>-methylbut-<NUM>-enyl, (Z)-<NUM>-methylbut-<NUM>-enyl, (E)-<NUM>-methylbut-<NUM>-enyl, (Z)-<NUM>-methylbut-<NUM>-enyl, (E)-<NUM>-methylbut-<NUM>-enyl, (Z)-<NUM>-methylbut-<NUM>-enyl, <NUM>,<NUM>-dimethylprop-<NUM>-enyl, <NUM>-ethylprop-<NUM>-enyl, <NUM>-propylvinyl, or <NUM>-isopropyl vinyl.

The term "C<NUM>-C<NUM> alkynyl group" should be understood to represent a linear or branched monovalent hydrocarbon group which contains one or more triple bonds and has <NUM> to <NUM> carbon atoms, especially, <NUM> or <NUM> carbon atoms ("C<NUM>-C<NUM> alkynyl group"). The alkynyl group is, for example, ethynyl, prop-<NUM>-ynyl, prop-<NUM>-ynyl, but-<NUM>-ynyl, but-<NUM>-ynyl, but-<NUM>-ynyl, pent-<NUM>-ynyl, pent-<NUM>-ynyl, pent-<NUM>-ynyl, pent-<NUM>-ynyl, hex-<NUM>-ynyl, hex-<NUM>-ynyl, hex-<NUM>-ynyl, hex-<NUM>-ynyl, hex-<NUM>-ynyl, <NUM>-methylprop-<NUM>-ynyl, <NUM>-methylbut-<NUM>-ynyl, <NUM>-methylbut-<NUM>-ynyl, <NUM>-methylbut-<NUM>-ynyl, <NUM>-methylbut-<NUM>-ynyl, <NUM>-ethylprop-<NUM>-ynyl. In particular, the alkynyl group is ethynyl, prop-<NUM>-ynyl or prop-<NUM>-ynyl.

The beneficial effects of the present invention:
The present invention provides a non-aqueous electrolyte for a lithium-ion battery and a lithium-ion battery using the non-aqueous electrolyte. The non-aqueous electrolyte used in the present invention includes (a) a lithium salt, (b) a non-aqueous organic solvent, and (c) at least one compound represented by formula <NUM>; where the non-aqueous electrolyte further includes at least one of the following components (d) and (e): (d) a nitrile compound including at least one of <NUM>,<NUM>,<NUM>-hexane tricarbonitrile, <NUM>,<NUM>,<NUM>-propane tricarbonitrile and <NUM>-methoxypropionitrile, and (e) ethylene sulfate. Where at least one compound (c) represented by formula <NUM> has a relatively lower reaction potential, and can preferentially form a dense and reduced impedance film on a surface of the positive and negative electrode sheets, and at the same time a nitrile compound (d) including at least one of <NUM>,<NUM>,<NUM>-hexane tricarbonitrile, <NUM>,<NUM>,<NUM>-propane tricarbonitrile, and <NUM>-methoxypropionitrile can further protect the positive electrode sheet and improve the toughness of the film through a complexation effect at a position of the film formed by the compound represented by formula <NUM>. And the ethylene sulfate (e) can further make up for a denseness of the positive electrode surface film, and can also form a low-impedance SEI (solid electrolyte interphase) film on the negative electrode. Through the synergistic effect between them, the present invention protects the positive electrode and at the same time, also has a certain protective effect on the negative electrode, and the impedance of film is low. The battery has an excellent high temperature storage performance, high temperature cycle performance and low temperature charge and discharge performance.

Hereinafter, the present invention will be further described in detail in conjunction with specific embodiments. It should be understood that the following embodiments are only to exemplarily illustrate and explain the present invention, and should not be construed as limiting protection scope of the present invention. All technical solution implemented based on the foregoing contents of the present invention are covered within the scope intended to be protected by the present invention.

The experimental methods used in the following examples are conventional methods unless otherwise specially stated; the reagents and materials used in the following examples can be obtained from commercial sources unless otherwise specially stated.

4V lithium cobalt oxide (LCO) as a positive active material, polyvinylidene fluoride (PVDF) as a binder, and acetylene black as a conductive agent are mixed in a weight ratio of <NUM>:<NUM>:<NUM>, and N-methylpyrrolidone (NMP) is added, stirring under an action of a vacuum mixer until a mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is uniformly coated on an aluminum foil with a thickness of <NUM>; after the above-mentioned well-coated aluminum foil is baked in an oven with five different temperature gradients, then it is dried in an oven at <NUM> for <NUM> hours, and then is rolled and slit, to obtain a desired positive electrode sheet.

Graphite as a negative active material, sodium carboxymethyl cellulose (CMC-Na) as a thickener, styrene butadiene rubber as a binder, acetylene black as a conductive agent are mixed in a weight ratio of <NUM>:<NUM>:<NUM>:<NUM>, and a deionized water is added. A negative electrode slurry is obtained under an action of a vacuum mixer; the negative electrode slurry is evenly coated on a copper foil with a thickness of <NUM>; the copper foil is dried at room temperature and then is transferred to an oven to dry at <NUM> for <NUM> hours, and then is cold pressed and slit, to obtain the negative electrode sheet.

In a glove box filled with argon gas and with qualified water and oxygen contents, ethylene carbonate, propylene carbonate, diethyl carbonate, n-propyl propionate, and fluoroethylene carbonate are mixed evenly in a mass ratio of <NUM>:<NUM>:<NUM>:<NUM>:<NUM> (solvents and additives need to be normalized together), then <NUM> wt% of fully dried lithium hexafluorophosphate (LiPF<NUM>) is quickly add to it, and is dissolved in the organic solvents, stirring well, and after passing moisture and free acid tests, an electrolyte of Comparative Example <NUM> is obtained.

<NUM> thick polyethylene is selected as the diaphragm (provided by Asahi Kasei).

The positive electrode sheet, the diaphragm, and the negative electrode sheet, as prepared above, are laid in order, to ensure that the diaphragm is located between the positive and negative electrode sheets and plays a role of isolation, and then a bare battery core without liquid injection is got by winding; the bare battery core is placed in an outer packaging foil, the electrolyte prepared above is injected into a dried bare battery core, going through processes of vacuum packaging, standing, forming, shaping, and sorting etc., to obtain a required lithium-ion battery.

Before a test, a thickness D<NUM> of a fully charged battery core is tested. The battery is placed in an environment of <NUM>±<NUM> and left to stand for <NUM> hours. When the battery core body reaches <NUM>±<NUM>, the battery is charged to <NUM>. 4V at <NUM>. 3C, then is charged at a constant voltage of <NUM>. 4V until a cut-off current is <NUM>. 05C, then is discharged to 3V at <NUM>. 5C, and an initial capacity Q<NUM> is recorded. When a required number of cycles is reached or a capacity attenuation rate is less than <NUM>% or the thickness exceeds the thickness required by the test, the previous discharge capacity is used as the battery's capacity Q<NUM>, and a capacity retention rate (%) is calculated, then the battery is fully charged, and the battery core is taken out, then left at room temperature for <NUM> hours, and the thickness D<NUM> at full charge is tested, and a thickness change rate (%) is calculated. Recorded results are shown in Table <NUM>. Where calculation formulas used are as follows: <MAT>.

Before the test, the thickness D<NUM> of the fully charged battery core is tested. The battery is placed in an environment of <NUM>±<NUM> and left to stand for <NUM> hours. When the battery core body reaches <NUM>±<NUM>, the battery is charged to <NUM>. 4V at 1C, then is charged to <NUM>. 4V at <NUM>. 7C, then is charged at a constant voltage of <NUM>. 4V until a cut-off current is <NUM>. 05C, then is discharged to 3V at <NUM>. 5C, and an initial capacity Q<NUM> is recorded. When the required number of cycles is reached or the capacity attenuation rate is less than <NUM>% or the thickness exceeds the thickness required by the test, the previous discharge capacity is used as the battery's capacity Q<NUM>, and the capacity retention rate (%) is calculated, then the battery is fully charged, and the battery core is taken out, then left at room temperature for <NUM> hours, and the thickness D<NUM> at full charge is tested, and the thickness change rate (%) is calculated, Recorded results are shown in Table <NUM>. Where the calculation formulas used are as follows: <MAT>.

Before the test, the thickness D<NUM> of the fully charged battery core is tested. The battery is placed in an environment of <NUM>±<NUM> and left to stand for <NUM> hours. When the battery core body reaches <NUM>±<NUM>, the battery is charged to <NUM>. 4V at a constant current of <NUM>. 7C, then is charged at a constant voltage of <NUM>. 4V until a cut-off current is <NUM>. 05C, then is discharged at <NUM>. 5C, and an initial capacity Q<NUM> is recorded. The cycle is repeated. When required number of cycles is reached or the capacity attenuation rate is less than <NUM>% or the thickness exceeds the thickness required by the test, the previous discharge capacity is used as the battery's capacity Q<NUM>, and then the capacity retention rate (%) is calculated, then the battery is fully charged, and the battery core is taken out, then left at room temperature for <NUM> hours, and the thickness D<NUM> at full charge is tested, and the thickness change rate (%) is calculated. Recorded results are shown in Table <NUM>. Where the calculation formulas used are as follows: <MAT>.

At <NUM>, the thickness D<NUM> of the fully charged battery core is tested, the sorted battery is charged to <NUM>. 4V at <NUM>. 7C, then is charged at a constant voltage of <NUM>. 4V until a cut-off current is <NUM>. 05C, then is discharged to <NUM>. 0V at a constant current of <NUM>. 5C, then is charged to <NUM>. 4V at <NUM>. 7C, then is charged at a constant voltage of <NUM>. 4V until a cut-off current is <NUM>. 05C, and it is placed in an environment at <NUM> for <NUM> days. The thickness D<NUM> at full charge is tested, and the thickness change rate (%) is calculated. Recorded results are shown in Table <NUM>. Where the calculation formula used is as follows: <MAT>.

Examples <NUM>-<NUM> and Comparative Examples <NUM>-<NUM>.

The preparation processes of Examples <NUM>-<NUM> and Comparative Examples <NUM>-<NUM> are the same as the preparation process of Comparative Example <NUM>. The only difference lies in the components and contents of the electrolytes. The specifically added components and contents thereof are shown in Table <NUM>. The test results are listed in Table <NUM>.

It can be seen from above Table <NUM> that the batteries prepared in the examples of the present application have achieved a better electrical performance. The specific analysis is as follows:
Through comparisons of Comparative Example <NUM> and Comparative Examples <NUM>-<NUM>, it can be found that on the basis of a blank electrolyte, the compound represented by formula <NUM>, the nitrile compound and the ethylene sulfate can all improve the high-temperature cycle performance and high-temperature storage performance of the battery, but all of them will degrade low-temperature cycle performance.

Through comparisons of Comparative Examples <NUM>-<NUM> and Examples <NUM>-<NUM>, a combination of the compound represented by formula <NUM> and the nitrile compound including at least one of <NUM>,<NUM>,<NUM>-hexane tricarbonitrile, <NUM>,<NUM>,<NUM>-propane tricarbonitrile, and <NUM>-methoxypropionitrile, or a combination of the compound represented by formula <NUM> and the ethylene sulfate, can improve the high temperature cycle performance and high temperature storage performance of the battery, and take into account the low temperature cycle performance.

Through Comparative Example <NUM> and Examples <NUM>-<NUM>, <NUM>, it can be found that compared with succinonitrile, the nitrile compounds, i.e., <NUM>,<NUM>,<NUM>-hexane tricarbonitrile, <NUM>,<NUM>,<NUM>-propane tricarbonitrile and <NUM>-methoxypropionitrile in the present invention have a better high-temperature cycle performance and high-temperature storage performance.

Through comparisons of Examples <NUM> and <NUM>, Examples <NUM> and <NUM>, Examples <NUM> and <NUM>, Examples <NUM> and <NUM>, and Examples <NUM> and <NUM>, it can be found that a combination of the compound represented by formula <NUM>, the nitrile compound including at least one of <NUM>,<NUM>,<NUM>-hexane tricarbonitrile, <NUM>,<NUM>,<NUM>-propane tricarbonitrile, and <NUM>-methoxypropionitrile, and the ethylene sulfate can further improve the high-temperature cycle performance and high-temperature storage of the battery.

Through comparisons of Examples <NUM> and <NUM>, Examples <NUM> and <NUM>, it can be found that a combination of multiple compounds represented by formula <NUM> or a combination of multiple nitrile compounds including at least one of <NUM>,<NUM>,<NUM>-hexane tricarbonitrile, <NUM>,<NUM>,<NUM>-propane tricarbonitrile, and <NUM>-methoxypropionitrile can further improve the high-temperature cycle performance and high-temperature storage performance of the battery.

Claim 1:
A non-aqueous electrolyte, comprising: (a) a lithium salt, (b) a non-aqueous organic solvent, and (c) at least one compound represented by formula <NUM>; wherein the non-aqueous electrolyte further comprises at least one of the following components (d) and (e):
(d) a nitrile compound including at least one of <NUM>,<NUM>,<NUM>-hexane tricarbonitrile, <NUM>,<NUM>,<NUM>-propane tricarbonitrile, and <NUM>-methoxypropionitrile, and
(e) ethylene sulfate;
<CHM>
wherein R<NUM> and R<NUM> are the same or different, and are each independently selected from hydrogen, halogen, a halogen-substituted or unsubstituted C<NUM>-C<NUM> alkyl group, a halogen-substituted or unsubstituted C<NUM>-C<NUM> alkenyl group, or a halogen-substituted or unsubstituted C<NUM>-C<NUM> alkynyl group.