NON-AQUEOUS ELECTROLYTE FOR A LITHIUM ION BATTERY AND LITHIUM ION BATTERY

Abstract

The present application belongs to the technical field of new energy, in particular to a non-aqueous electrolyte for a lithium ion battery and a lithium ion battery. The non-aqueous electrolyte for a lithium ion battery comprises a non-aqueous organic solvent, a lithium salt, and a spiro compound represented by Structural Formula 1. The compound represented by Structural Formula 1 has the characteristic of sulfonate additives to improve high-temperature storage performance of battery, and also has the characteristic of sulfate additives to improve high-temperature cycle performance of battery. A passivation film is deposited on the surface of positive electrode, and functional group X is further crosslinked to make the coated passivation film more compact and stable, which can effectively improve the electrochemical performance of the electrode, the storage performance and self-discharge performance of the battery.

##STR00001##

Claims

1. A non-aqueous electrolyte for a lithium ion battery, comprising a non-aqueous organic solvent, a lithium salt, and a spiro compound represented by Structural Formula 1, ##STR00008## wherein, X represents an oxygen atom, a carboxylate ester, a sulfite ester, a sulfate ester, a carbonate ester, a substituted or unsubstituted phosphate ester, and a substituted or unsubstituted borate ester; and R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are each independently selected from substituted or unsubstituted C1-C5 hydrocarbylene group.

2. The non-aqueous electrolyte for a lithium ion battery of claim 1, wherein at least one of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 is a substituted or unsubstituted C1-C5 alkylene group; a substituent of C1-C5 alkylene group comprises one or more of a halogen-substituted or unsubstituted C1-C20 alkyl group, a halogen-substituted or unsubstituted C2-C20 alkenyl group, a halogen-substituted or unsubstituted C2-C20 alkynyl group, a halogen-substituted or unsubstituted C3-C20 cycloalkenyl group, a halogen-substituted or unsubstituted C3-C20 heterocyclic group, a halogen-substituted or unsubstituted C6-C40 aryl group, a halogen-substituted or unsubstituted C2-C40 heteroaryl group or a polar functional group with at least one heteroatom.

3. The non-aqueous electrolyte for a lithium ion battery of claim 2, wherein the substituent of C1-C5 alkylene group is selected from one or more of halogen, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, alkylene, alkynyl, phenyl, trimethylsilyl, cyano, trifluoromethyl, tetrafluoroethyl, naphthyl, tetrafluorophenyl, pyrrolyl or pyridyl.

4. The non-aqueous electrolyte for a lithium ion battery of claim 1, wherein the spiro compound represented by Structural Formula 1 comprise at least one of Formulas 1 to 7, ##STR00009## wherein R.sub.5 and R.sub.6 are each independently selected from a hydrogen atom, halogen, hydrocarbon group, halogenated hydrocarbon group, oxygen-containing hydrocarbon group, silicon-containing hydrocarbon group, cyanide-containing hydrocarbon group or nitrogen-containing hydrocarbon group.

5. The non-aqueous electrolyte for a lithium ion battery of claim 4, wherein R.sub.5 and R.sub.6 are independently selected from hydrogen atom, fluorine atom, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, alkylene, alkynyl, phenyl, trimethylsilyl, cyano, trifluoromethyl, tetrafluoroethyl, naphthyl, tetrafluorophenyl, pyrrolyl or pyridyl.

6. The non-aqueous electrolyte for a lithium ion battery of claim 1, wherein a mass percentage of the compound represented by Structural Formula 1 in the non-aqueous electrolyte for a lithium ion battery is 0.05%-10%.

7. The non-aqueous electrolyte for a lithium ion battery of claim 1, wherein the non-aqueous electrolyte further comprises one or more of 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate and ethylene sulfate.

8. The non-aqueous electrolyte for a lithium ion battery of claim 1, wherein the lithium salt is selected from one or more of LiPF.sub.6, LiBF.sub.4, LiBOB, LiPO.sub.2F.sub.2, LiDFOB, LiSbF.sub.6, LiAsF.sub.6, LiN(SO.sub.2CF.sub.3).sub.2, LiN(SO.sub.2C.sub.2F.sub.5).sub.2, LiC(SO.sub.2CF.sub.3).sub.3 or LiN(SO.sub.2F).sub.2; and the non-aqueous organic solvent is a mixture of cyclic carbonate and chain carbonate, the cyclic carbonate is selected from one or more of ethylene carbonate, propylene carbonate or butylene carbonate, and the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate or methyl propyl carbonate.

9. A lithium ion battery, comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte for a lithium ion battery of claim 1.

10. The lithium ion battery of claim 9, wherein the positive electrode comprises a positive electrode active material, the positive electrode active material comprises one or more of LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2O.sub.4, LiCo.sub.1-yM.sub.yO.sub.2, LiNi.sub.1-yM.sub.yO.sub.2, LiMn.sub.2-yM.sub.yO.sub.4, LiCo.sub.xM.sub.(1-x)O.sub.2 or LiNi.sub.xCo.sub.yMn.sub.zM.sub.1-x-y-zO.sub.2; wherein M is selected from one or more of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe, and 0x1, 0y1, 0z1, x+y+z1.

11. The non-aqueous electrolyte for a lithium ion battery of claim 1, wherein the spiro compound represented by Structural Formula 1 has an asymmetric structure.

12. The non-aqueous electrolyte for a lithium ion battery of claim 1, wherein the compound represented by Structural Formula 1 is: ##STR00010## ##STR00011##

13. A lithium ion battery, comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte for a lithium ion battery of claim 2.

14. A lithium ion battery, comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte for a lithium ion battery of claim 3.

15. A lithium ion battery, comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte for a lithium ion battery of claim 4.

16. A lithium ion battery, comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte for a lithium ion battery of claim 5.

17. A lithium ion battery, comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte for a lithium ion battery of claim 6.

18. A lithium ion battery, comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte for a lithium ion battery of claim 7.

19. A lithium ion battery, comprising a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte for a lithium ion battery of claim 8.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] In order to make the beneficial effects, technical solutions and technical problems solved by the present application clearer, the present application will be further illustrated in detail with reference to the drawings and embodiments. It should be understood that the specific embodiments described here are merely for illustrating the present application, not for limiting the present application.

[0022] The non-aqueous electrolyte for a lithium ion battery provided by an embodiment of the present application includes a non-aqueous organic solvent, a lithium salt, and a spiro compound represented by Structural Formula 1,

##STR00004##

[0023] wherein, X represents an oxygen atom, a carboxylate ester, a sulfite ester, a sulfate ester, a carbonate ester, a substituted or unsubstituted phosphate ester, and a substituted or unsubstituted borate ester; and

[0024] R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are each independently selected from substituted or unsubstituted C1-C5 hydrocarbylene group.

[0025] The non-aqueous electrolyte for a lithium ion battery provided by the present application includes the compound represented by Structural Formula 1 as an additive, and this asymmetric spirocyclic compound has the characteristic of sulfonate additives to improve high-temperature storage performance of battery, and also has the characteristic of sulfate additives to improve high-temperature cycle performance of battery.

[0026] The mechanism is that in the first charging process, the sulfonate structure in Structural Formula 1 can take precedence over solvent molecules in the reduction and decomposition reaction at positive electrode, and the reaction product forms a passivation film on the surface of the positive electrode. The passivation film can inhibit further decomposition of solvent molecules in the electrolyte. The strong coordination between atom O of sulfonate structure and Li+ leads to the disconnection of the five-membered ring of 1,3-PS (1,3-propane sultone) of Structural Formula 1, and Li+ obtains an electron to form an anionic free radical. Because anionic free radicals are very active and highly reactive, lithium sulfonate is further generated, and a passive film is deposited on the surface of the positive electrode. In the first charging process, the sulfate structure of Structural Formula 1 can improve the composition of SEI film, slow down the exothermic decomposition of SEI film at high temperature, and improve the high-temperature cycle performance of the battery cooperatively.

[0027] The functional group X may be selected from oxygen atoms, carboxylate group, sulfite group, sulfate group, carbonate group, substituted or unsubstituted phosphate group, and substituted or unsubstituted borate group. These groups all have crosslinking activity, and further cross-link with solvent molecules in the electrolyte, which makes the passive film coated on the surface of the positive electrode more compact and stable, and can effectively improve the electrochemical performance of the electrode, the storage performance and self-discharge performance of the battery.

[0028] In one embodiment, the spiro compound represented by Structural Formula 1 has an asymmetric structure, and the asymmetric structure represented by Structural Formula 1 includes a five-membered ring structure similar to 1,3-PS and a multi-membered ring structure of cyclic lactone, which can improve the high-temperature cycle performance of battery cooperatively.

[0029] In one embodiment, at least one of R.sub.1, R.sub.2, R.sub.3 and R.sub.4 is a substituted or unsubstituted C1-C5 alkylene group; a substituent of C1-C5 alkylene group includes one or more of a halogen-substituted or unsubstituted C1-C20 alkyl group, a halogen-substituted or unsubstituted C2-C20 alkenyl group, a halogen-substituted or unsubstituted C2-C20 alkynyl group, a halogen-substituted or unsubstituted C3-C20 cycloalkenyl group, a halogen-substituted or unsubstituted C3-C20 heterocyclic group, a halogen-substituted or unsubstituted C6-C40 aryl group, a halogen-substituted or unsubstituted C2-C40 heteroaryl group or a polar functional group with at least one heteroatom.

[0030] It should be noted that when R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently select from alkylene group, it is preferable that the number of carbon atoms be controlled to 5 or less (including 5). When the number of carbon atoms is controlled below 5, the high-temperature performance can be guaranteed as well. However, when the number of carbon atoms in the alkyl group is more than 6, the more carbon atoms there are, the more the relative density of the alkyl group will gradually increase, which will adversely affect the high-temperature performance and inflation inhibition of battery.

[0031] According to the present application, when the number of carbon atoms is less than 5 or more than 6, the effects of improving the SEI film and improving the high-temperature cycle performance of battery can be achieved. Preferably, the number of carbon atoms of alkylene groups each independently selected by R.sub.1, R.sub.2, R.sub.3 and R.sub.4 is controlled to be less than 5.

[0032] In one embodiment, the substituent of C1-C5 alkylene group includes one or more of halogen, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, alkylene, alkynyl, phenyl, trimethylsilyl, cyano, trifluoromethyl, tetrafluoroethyl, naphthyl, tetrafluorophenyl, pyrrolyl or pyridyl.

[0033] In one embodiment, the spiro compound represented by Structural Formula 1 include at least one of Formulas 1 to 7,

##STR00005##

[0034] wherein R.sub.5 and R6 are each independently selected from a hydrogen atom, halogen, hydrocarbon group, halogenated hydrocarbon group, oxygen-containing hydrocarbon group, silicon-containing hydrocarbon group, cyanide-containing hydrocarbon group or nitrogen-containing hydrocarbon group.

[0035] In one embodiment, R.sub.5 and R6 are independently selected from hydrogen atom, fluorine atom, methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, alkylene, alkynyl, phenyl, trimethylsilyl, cyano, trifluoromethyl, tetrafluoroethyl, naphthyl, tetrafluorophenyl, pyrrolyl or pyridyl.

[0036] In one embodiment, the compound represented by Structural Formula 1 may be:

##STR00006## ##STR00007##

[0037] It should be noted that the above compounds are part of the claimed subject matter of the present application, but not limited to this, and should not be considered as limitations to the present application.

[0038] The addition amount of the compound represented by Structural Formula 1 in the present application is not intended to limit the present application. However, controlling the content of the compound represented by Structural Formula 1 in non-aqueous electrolyte has a favorable influence on further optimization of high-temperature performance.

[0039] In one embodiment, based on the total mass of the non-aqueous electrolyte for a lithium ion battery being 100%, a mass percentage of the compound represented by Structural Formula 1 in the non-aqueous electrolyte for a lithium ion battery is 0.05%-10%. Specifically, the mass percentage of the compound represented by Structural Formula 1 may be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5% and 10%.

[0040] Within the above range, the compound represented by Structural Formula 1 may obviously improve the high-temperature storage performance and high-temperature cycle performance of battery, and the battery will not swell as well. When the mass percentage of the compound represented by Structural Formula 1 is less than 0.05%, the content of the compound represented by Structural Formula 1 in the electrolyte is too low to form a complete passivation film on the surface of the positive electrode, thus it is unlikely to visibly improve high-temperature performance of the non-aqueous electrolyte, and the internal resistance of battery would not be significantly reduced. However, when the mass percentage of the compound represented by Structural Formula 1 exceeds 10.0%, an excessively thick passivation film would likely to be formed on the surface of the positive electrode, which increases the internal resistance of battery, and the battery capacity retention rate is obviously deteriorated.

[0041] In an embodiment, additives in the non-aqueous electrolyte further include 1,3-propane sultone (1,3-PS), 1,4-butane sultone (BS), 1,3-propylene sultone (PST), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC) and ethylene sulfate (DTD). These additives may be used in combination with the compound represented by Structural Formula 1 to form a more stable SEI film on the surface of graphite negative electrode, thus significantly improving the cycle performance of lithium-ion batteries, and obtaining more excellent effects compared with those adding compound represented by Structural Formula 1 alone.

[0042] Based on the total mass of the non-aqueous electrolyte for a lithium ion battery being 100%, the mass percent of the additive in the non-aqueous electrolyte for a lithium ion battery is 0.05-10%. Preferably, the mass percentage of addictive in the non-aqueous electrolyte for a lithium ion battery is 0.2-5%, and more preferably, the mass percentage of addictive in the non-aqueous electrolyte for a lithium ion battery is 0.5-2%. Specifically, the mass percentage of the additive may be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5% and 10%.

[0043] In one embodiment, the non-aqueous organic solvent is a mixture of cyclic carbonate and chain carbonate. The cyclic carbonate includes one or more of ethylene carbonate, propylene carbonate and butylene carbonate. The chain carbonate includes one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate.

[0044] There is no specific limitation on lithium salt in the solution of the present application, and various existing substances may be used.

[0045] In an embodiment, the lithium salt is selected from one or more of one or more of LiPF.sub.6, LiBF.sub.4, LiBOB, LiPO.sub.2F.sub.2, LiDFOB, LiSbF.sub.6, LiAsF.sub.6, LiN(SO.sub.2CF.sub.3).sub.2, LiN(SO.sub.2C.sub.2F.sub.5).sub.2, LiC(SO.sub.2CF.sub.3).sub.3 or LiN(SO.sub.2F).sub.2. Preferably, the lithium salt is LiPF.sub.6 or a mixture of LiPF.sub.6 with other lithium salts.

[0046] Based on the total mass of the non-aqueous electrolyte for a lithium ion battery being 100%, the mass percentage of the lithium salt in the non-aqueous electrolyte for a lithium ion battery is 0.1-15%

[0047] Another embodiment of the present application discloses a lithium ion battery, which includes a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is the non-aqueous electrolyte for a lithium ion battery described above.

[0048] As in the prior art, non-aqueous organic solvent and lithium salt are both contained in the non-aqueous electrolyte for a lithium ion batteries. For the solution of the present application, there are no special limitations on the types or contents of the solvent and lithium salt, and various existing substances may be used.

[0049] In an embodiment, the positive electrode includes a positive electrode active material, the positive electrode active material includes one or more of LiCoO.sub.2, LiNiO.sub.2, LiMn.sub.2O.sub.4, LiCo.sub.1-yM.sub.yO.sub.2, Ni.sub.1-yM.sub.yO.sub.2, LiMn.sub.2-yM.sub.yO.sub.4, LiCo.sub.xM.sub.(1-x)O.sub.2 or LiNi.sub.xCo.sub.yMn.sub.zM.sub.1-x-y-zO.sub.2; wherein M is selected from one or more of Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Cu, V or Fe, and 0x1, 0y1, 0z1, x+y+z1.

[0050] The positive electrode further includes a positive electrode current collector for extracting current, and the positive electrode active material covers the positive electrode current collector.

[0051] The negative electrode includes a negative electrode active material, and the negative electrode active material includes a graphite, a conductive agent, SBR (styrene butadiene rubber), CMC (sodium carboxymethyl cellulose) and NMP (N-methylpyrrolidone).

[0052] The negative electrode further includes a negative electrode current collector for extracting current, and the negative electrode active material covers the negative electrode current collector.

[0053] In some embodiments, there is a separator between the battery positive electrode and battery negative electrode, and the separator is a conventional diaphragm in the field of lithium ion batteries, which will not be described in detail here.

[0054] The present application will be further illustrated with embodiments.

EMBODIMENT 1

[0055] This embodiment is used to illustrate the non-aqueous electrolyte for a lithium ion battery, lithium ion battery and its preparation method, which are disclosed in the present application. The preparation process includes the following steps.

[0056] 1) Preparation of Non-Aqueous Electrolyte

[0057] Ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) were mixed according to the mass ratio of EC:DEC: EMC=1:1:1, and then lithium hexafluorophosphate (LiPF6) was added until the molar concentration was 1 mol/L. Based on the total mass of the non-aqueous electrolyte being 100%, 1.0% of Compound 1 was added.

[0058] 2) Preparation of Positive Electrode Plate

[0059] According to the mass ratio of 93:4:3, the positive electrode active material LiNi.sub.0.5Co.sub.0.2Mn.sub.0.3O.sub.2, conductive carbon black Super-P and binder polyvinylidene fluoride (PVDF) were mixed, and then they were dispersed in N-methyl-2-pyrrolidone (NMP), and uniformly mixed to obtain a positive electrode slurry for lithium ion batteries. Both sides of the aluminum foil of the positive electrode current collector were evenly coated with the positive electrode slurry. After vacuum dried, calendered and trimmed, it was cut into pieces and divided into strips. And the aluminum lead-out wire was welded by an ultrasonic welder to obtain a positive electrode plate with a thickness of 120-150 m.

[0060] 3) Preparation of Negative Electrode Plate

[0061] According to the mass ratio of 94:1:2.5:2.5, the negative electrode active material of artificial graphite, conductive carbon black Super-P, binder styrene-butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) were mixed, and then they were dispersed in deionized water to obtain negative electrode slurry. Both sides of the copper foil were evenly coated with the slurry. After vacuum dried, calendered and trimmed, it was cut into pieces and divided into strips. And the nickel lead-out wire was welded by an ultrasonic welder to obtain a negative electrode plate with a thickness of 120-150 m.

[0062] 4) Preparation of Battery Core

[0063] A three-layered lithium battery separator with a thickness of 20 m was placed between the prepared positive electrode and negative electrode, and the sandwich structure consisting of the positive electrode, negative electrode and separator was wound, then the wound body was pressed flat and put into an aluminum foil packaging bag, then baked in vacuum at 75 C. for 48 hours to obtain a battery core to be injected with liquid.

[0064] 5) Liquid Injection and Formation of Battery Core

[0065] In a glove box with the dew point controlled below 40 C., the prepared electrolyte was injected into the dried battery core, vacuum-packaged, and left stand for 24 hours. Then, the first charge was normalized according to the following steps: charged for 180 min at 0.05 C constant current, then charged to 3.95V at 0.2 C constant current, vacuum sealed for a second time, then further charged to 4.2V at 0.2 C constant current, and after standing at room temperature for 24 hours, discharged to 3.95 V at 0.2 C constant current.

EMBODIMENTS 2-15

[0066] The battery was prepared according to the preparation process described in Embodiment 1, except that that the types and contents of the compound additives added in the non-aqueous electrolyte during the preparation step were different. See Table 1 for details.

COMPARATIVE EXAMPLE 1

[0067] A battery was prepared as described in Embodiment 1, except that:

[0068] 1.0% of Compound 1 was not added in the non-aqueous electrolyte during the preparation step.

COMPARATIVE EXAMPLES 2-7

[0069] The battery was prepared according to the preparation process described in Embodiment 1, except that that the types and contents of the compound additives added in the non-aqueous electrolyte during the preparation step were different. See Table 1 for details.

TABLE-US-00001 TABLE 1 Additive represented Embodiment/Comparative by Structural Formula Other additives Example 1 and its content and content Embodiment 1 Compound 1: 1.0% Embodiment 2 Compound 2: 1.0% Embodiment 3 Compound 3: 1.0% Embodiment 4 Compound 4: 1.0% Embodiment 5 Compound 5: 1.0% Embodiment 6 Compound 6: 1.0% Embodiment 7 Compound 7: 1.0% Embodiment 8 Compound 8: 1.0% Embodiment 9 Compound 5: 0.1% Embodiment 10 Compound 5: 2% Embodiment 11 Compound 5: 3% Embodiment 12 Compound 5: 5% Embodiment 13 Compound 5: 1.0% FEC: 1.0% Embodiment 14 Compound 5: 1.0% VEC: 1.0% Embodiment 15 Compound 5: 1.0% VC: 1.0% Comparative Example 1 Comparative Example 2 FEC: 1.0% Comparative Example 3 VEC: 1.0% Comparative Example 4 VC: 1.0% Comparative Example 5 1,3PS: 1.0% Comparative Example 6 1,3PTS: 1.0% Comparative Example 7 DTD: 1.0%

[0070] Performance Test

[0071] In order to verify the performance of the electrode of lithium ion battery of the present application, the lithium ion batteries prepared in the above Embodiments 1-15 and Comparative Examples 1-7 were tested. The specific test method is as follows.

[0072] 1) High-Temperature Cycle Performance Test

[0073] At 45 C., the formed battery was charged to 4.2V (LiNi.sub.0.5Co.sub.0.2Mn.sub.0.3O.sub.2/artificial graphite battery) at 1 C constant current and constant voltage, then charged at constant voltage until the current dropped to 0.02 C, and then discharged at 1 C constant current to 3.0V. After N cycles of charge/discharge, capacity retention rate after the 500th cycle was calculated to evaluate its high-temperature cycle performance.

[0074] The calculation formula of the 500th cycle capacity retention rate at 45 C., 1 C is as follows:

The 500th cycle capacity retention rate(%)=the 500th cycle discharge capacity/the 1st cycle discharge capacity*100% .

[0075] 2) High-Temperature Storage Performance Test

[0076] The formed lithium-ion battery was charged to 4.2V (LiNi.sub.0.5Co.sub.0.2Mn.sub.0.3O.sub.2/artificial graphite battery) at 1 C constant current/constant voltage at room temperature, and the initial discharge capacity and initial battery thickness of battery were measured. After being stored at 60 C. for 30 days, the battery was discharged to 3V at 1 C, and the retention capacity, recovery capacity and battery thickness after storage were measured.

[0077] The calculation formula is as follows:

Battery capacity retention rate(%)=Retention capacity/Initial capacity*100%;

Battery capacity recovery rate(%)=Recovery capacity/Initial capacity*100%;

Thickness expansion rate(%)=(Battery thickness after storageInitial battery thickness)/Initial battery thickness*100%.

[0078] The performance test results of Embodiments 1-15 and Comparative Examples 1-7 are shown in Table 2.

TABLE-US-00002 TABLE 2 The 500th cycle capacity After 30 days of storage at 60 C. retention Capacity Capacity Thickness Embodiment/Comparative rate (%) at retention recovery expansion Example 45 C./1 C rate rate rate Embodiment 1 73.9% 84.6% 89.9% 9.8% Embodiment 2 82.7% 85.7% 90.0% 7.6% Embodiment 3 83.0% 86.0% 90.4% 7.2% Embodiment 4 83.8% 84.8% 91.7% 8.5% Embodiment 5 83.3% 84.1% 91.9% 7.6% Embodiment 6 75.5% 86.2% 89.1% 7.8% Embodiment 7 74.8% 85.0% 91.3% 8.5% Embodiment 8 75.6% 84.6% 90.2% 6.8% Embodiment 9 82.4% 89.1% 90.8% 10.10% Embodiment 10 84.4% 90.5% 92.1% 8.6% Embodiment 11 83.5% 89.3% 91.0% 9.8% Embodiment 12 82.0% 88.8% 89.7% 10.1% Embodiment 13 85.5% 92.2% 95.1% 7.8% Embodiment 14 84.8% 92.0% 94.3% 8.5% Embodiment 15 85.0% 91.9% 95.1% 8.4% Comparative Example 1 70.2% 69.6% 70.8% 19.2% Comparative Example 2 80.0% 79.2% 82.1% 29% Comparative Example 3 82.8% 79.6% 83.3% 12.6% Comparative Example 4 83.5% 78.7% 83.5% 26.1% Comparative Example 5 71.1% 81.4% 88.5% 8.1% Comparative Example 6 70.5% 82.5% 89.9% 7.5% Comparative Example 7 75.4% 81.7% 88.1% 9.5%

[0079] As can be seen from the data of Embodiments 1-12 in Table 2, compared with Comparative Examples 1-7, the lithium batteries prepared in Embodiments 1-12 have better high-temperature cycle performance and high-temperature storage performance after adding the compound represented by Structural Formula 1. And according to the data of thickness expansion rate, the gas generation is less after adding the compound represented by Structural Formula 1, thus improving the high-temperature performance of battery, preventing the battery from bulging after being stored at high temperature, and improving the charge-discharge performance and cycle times of battery.

[0080] According to the data of Embodiment 5 and Embodiments 9-12 in Table 2, compared with the lithium-ion batteries prepared by adding 1%, 2% or 3% of Compound 5, the high-temperature performance of lithium-ion batteries prepared by adding 0.1% or 5% of Compound 5 in the non-aqueous electrolyte is slightly deteriorated, indicating that too little or too much addition would lead to deterioration of high-temperature performance of lithium-ion battery.

[0081] According to the data of Embodiments 13-15 in Table 2, when the compound represented by Structural Formula 1 and FEC (or VEC, VC) are both added to the non-aqueous electrolyte, FEC can cooperate with the compound represented by Structural Formula 1 to form a more stable SEI film on the surface of the graphite negative electrode, which makes the lithium-ion batteries have good high-temperature performance and high-temperature storage performance, thus significantly improving the cycle performance of the lithium-ion batteries.

[0082] In Comparative Example 1, no additives are added. By comparing the experimental data, it can be seen that the compactness and stability of SEI film would be affected without any additives, which would affect the charge-discharge performance and cycle performance of lithium-ion batteries, and the high-temperature cycle performance and high-temperature storage performance are not good, the batteries would produce more gas.

[0083] Comparing and analyzing the experimental data of Comparative Examples 24, it can be seen that the lithium-ion batteries of Comparative Examples 24 have good high-temperature cycle performance, but their high-temperature storage performance is poor, and the gas produced by the batteries is serious, and the batteries swell seriously. Fluoroethylene carbonate (FEC) was added in Comparative Example 2, vinyl ethylene carbonate (VEC) was added in Comparative Example 3, and vinylene carbonate (VC) was added in Comparative Example 4. As additives, these substances could take precedence over solvent molecules to undergo reductive decomposition reaction on the negative electrode surface to generate polyalkoxylithium carbonate compounds, and a passive film was formed on the negative electrode surface to prevent the electrolyte from further decomposing on the electrode surface, thus improving the cycle performance of battery. However, after adding FEC, VEC or VC, the battery is likely to generate gas during high temperature storage, which leads to serious swelling of battery.

[0084] Comparing and analyzing the experimental data of Comparative Examples 5-7, it can be seen that the lithium-ion batteries in Comparative Examples 5-7 have good high-temperature storage performance, less gas generation and less battery swelling, however their high-temperature cycle performance is poor. This is because when 1,3-propane sultone (1,3-PS) added in Comparative Example 5, 1,3-propylene sultone (PST) added in Comparative Example 6, and ethylene sulfate (DTD) added in Comparative Example 7; as additives, they could suppress the decrease of initial capacity of battery, and increase initial discharge capacity. The battery expansion after high-temperature storage may be reduced, and the charge-discharge performance and cycle times of battery may be improved. However, the stability of the SEI film formed on the graphite negative electrode interface is poor. With the increase of cycle times, the resistance of the electrode interface would gradually increase, and the phenomenon of electronic polarization of battery would become more and more serious, which leads to the rapid decrease of reversible capacity of electrode and the degradation of high-temperature cycle performance of battery.

[0085] Through the comparison among the embodiments and comparative examples, it is concluded that the high-temperature cycle performance and high-temperature storage performance of battery are excellent when the compound represented by Structural Formula 1 is added to the electrolyte, or when the compound represented by Structural Formula 1 and other additives are added at the same time.

[0086] The above descriptions are only preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present application shall be included in the protection scope of the present application.