Electrolyte solution and electrochemical device using the same

Abstract

The present application relates to an electrolytic solution and an electrochemical device using same. The electrolytic solution of the present application comprises a compound containing a —CN functional group and a compound containing a P—O bond. By introducing the compound containing a —CN functional group and the compound containing a P—O bond into the electrolytic solution, an active material can be better protected, thereby effectively improving floatation performance and nailing performance of a battery, and cycle impedance of the battery.

Claims

1. An electrolytic solution, comprising a compound containing a —CN functional group and a compound containing a P—O bond, wherein the compound containing a P—O bond comprises at least one selected from the group consisting of a compound represented by formula II-A and a compound represented by formula II-B: ##STR00024## wherein R.sub.21, R.sub.22, R.sub.23, R.sub.24, and R.sub.25 are each independently selected from R.sup.a, Si—(R″).sub.3, or R′—Si—(R″).sub.3; wherein R.sub.26 is selected from a C.sub.1-C.sub.12 alkyl group, a C.sub.2-C.sub.12 alkenyl group, a C.sub.6-C.sub.10 cyclic hydrocarbon group, or a C.sub.6-C.sub.26 aryl group; each of R.sup.a and R″ is independently selected from a C.sub.1-C.sub.12 alkyl group, a C.sub.2-C.sub.12 alkenyl group, a C.sub.6-C.sub.10 cyclic hydrocarbon group, or a C.sub.6-C.sub.26 aryl group; R′ is selected from a C.sub.1-C.sub.12 alkylene group or a C.sub.2-C.sub.12 alkenylene group; and R.sub.21, R.sub.22, R.sub.23, R.sub.24, R.sub.25, and R.sub.26 are each independently substituted or non-substituted, and when being substituted, a substituent is selected from a halogen, a C.sub.1-C.sub.6 alkyl group, a C.sub.2-C.sub.6 alkenyl group, or any combination thereof; wherein based on a total weight of the electrolytic solution, a weight percentage of the compound containing a —CN functional group is A %, and a weight percentage of the compound containing a P—O bond is B %, wherein 0.5≤A/B≤5; wherein the compound containing a —CN functional group comprises at least one selected from the group consisting of a compound represented by formula I-2 and a compound represented by formula I-10: ##STR00025## wherein the electrolytic solution further includes a dinitrile compound; wherein the dinitrile compound comprises at least one selected from the group consisting of butanedinitrile, hexanedinitrile, and ethyleneglycoldi(2-cyanoethyl)ether.

2. The electrolytic solution according to claim 1, wherein the compound containing a P—O bond comprises a compound represented by formula II-5: ##STR00026##

3. The electrolytic solution according to claim 1, wherein based on the total weight of the electrolytic solution, the weight percentage of the compound containing a —CN functional group is about 1 wt % to 3 wt %, and the weight percentage of the compound containing a P—O bond is about 0.1 wt % to 2 wt %.

4. The electrolytic solution according to claim 1, further comprising a cyclic carbonate, the cyclic carbonate comprising a compound represented by formula III-A: ##STR00027## wherein R.sub.31 is selected from a substituted or non-substituted C.sub.1-C.sub.12 alkylene group, or a substituted or non-substituted C.sub.2-C.sub.12 alkenylene group; and when being substituted, a substituent is selected from a halogen, a C.sub.1-C.sub.6 alkyl group, a C.sub.2-C.sub.6 alkenyl group or any combination thereof.

5. The electrolytic solution according to claim 1, further comprising a carbonate compound containing a silicon functional group, wherein the carbonate compound containing a silicon functional group comprises at least one of the following compounds: ##STR00028## based on the total weight of the electrolytic solution, the weight percentage of the carbonate compound containing a silicon functional group is about 0.01 wt % to about 50 wt %.

6. The electrolytic solution according to claim 1, wherein the compound containing a —CN functional group comprises a compound represented by formula I-2: ##STR00029##

7. The electrolytic solution according to claim 1, wherein the compound containing a —CN functional group comprises a compound represented by formula I-2: ##STR00030## wherein the dinitrile compound comprises butanedinitrile.

8. The electrolytic solution according to claim 1, further comprising a carboxylate, wherein the carboxylate comprises at least one of the following compounds: propylpropionate, trifluoroethylacetate or fluoroethylacetate; and wherein based on the total weight of the electrolytic solution, the content of the carboxylate is about 0.01 wt % to about 60 wt %.

9. An electrochemical device, comprising an electrolytic solution, wherein the electrolytic solution comprises a compound containing a —CN functional group and a compound containing a P—O bond, wherein the compound containing a P—O bond comprises at least one selected from the group consisting of a compound represented by formula II-A and a compound represented by formula II-B: ##STR00031## wherein R.sub.21, R.sub.22, R.sub.23, R.sub.24, and R.sub.25 are each independently selected from R.sup.a, Si—(R″).sub.3, or R′—Si—(R″).sub.3; wherein R.sub.26 is selected from a C.sub.1-C.sub.12 alkyl group, a C.sub.2-C.sub.12 alkenyl group, a C.sub.6-C.sub.10 cyclic hydrocarbon group, or a C.sub.6-C.sub.26 aryl group; each of R.sup.a and R″ is independently selected from a C.sub.1-C.sub.12 alkyl group, a C.sub.2-C.sub.12 alkenyl group, a C.sub.6-C.sub.10 cyclic hydrocarbon group, or a C.sub.6-C.sub.26 aryl group; R′ is selected from a C.sub.1-C.sub.12 alkylene group or a C.sub.2-C.sub.12 alkenylene group; and R.sub.21, R.sub.22, R.sub.23, R.sub.24, R.sub.25, and R.sub.26 are each independently substituted or non-substituted, and when being substituted, a substituent is selected from a halogen, a C.sub.1-C.sub.6 alkyl group, a C.sub.2-C.sub.6 alkenyl group, or any combination thereof; wherein based on a total weight of the electrolytic solution, a weight percentage of the compound containing a —CN functional group is A %, and a weight percentage of the compound containing a P—O bond is B %, wherein 0.5≤A/B≤5; wherein the compound containing a —CN functional group comprises at least one selected from the group consisting of a compound represented by formula I-2 and a compound represented by formula I-10: ##STR00032## wherein the electrolytic solution further includes a dinitrile compound; wherein the dinitrile compound comprises at least one selected from the group consisting of butanedinitrile, hexanedinitrile, and ethyleneglycoldi(2-cyanoethyl)ether.

10. The electrochemical device according to claim 9, wherein the electrolytic solution further comprises a cyclic carbonate, the cyclic carbonate comprising a compound represented by formula III-A: ##STR00033## wherein R.sub.31 is selected from a substituted or non-substituted C.sub.1-C.sub.12 alkylene group, or a substituted or non-substituted C.sub.2-C.sub.12 alkenylene group; and when being substituted, a substituent is selected from a halogen, a C.sub.1-C.sub.6 alkyl group, a C.sub.2-C.sub.6 alkenyl group or any combination thereof.

11. The electrochemical device according to claim 9, wherein the compound containing a —CN functional group comprises a compound represented by formula I-2: ##STR00034##

12. The electrochemical device according to claim 11, further comprising a carbonate compound containing a silicon functional group, wherein the carbonate compound containing a silicon functional group comprises at least one of the following compounds: ##STR00035##

13. The electrochemical device according to claim 9, wherein the compound containing a P—O bond comprises a compound represented by formula II-5: ##STR00036##

14. The electrochemical device according to claim 9, wherein the compound containing a —CN functional group comprises a compound represented by formula I-2: ##STR00037## wherein the dinitrile compound comprises butanedinitrile.

15. The electrochemical device according to claim 9, wherein based on the total weight of the electrolytic solution, the weight percentage of the compound containing a —CN functional group is 1 wt % to 3 wt %, and the weight percentage of the compound containing a P—O bond is 0.1 wt % to 2 wt %.

16. The electrochemical device according to claim 9, further comprising a carboxylate, wherein the carboxylate comprises at least one of the following compounds: propylpropionate, trifluoroethylacetate or fluoroethylacetate; wherein based on the total weight of the electrolytic solution, the content of the carboxylate is about 0.01 wt % to about 60 wt %.

17. An electronic device, comprising an electrochemical device comprising an electrolytic solution, wherein the electrolytic solution comprises a compound containing a —CN functional group and a compound containing a P—O bond, wherein the compound containing a P—O bond comprises at least one selected from the group consisting of a compound represented by formula II-A and a compound represented by formula II-B: ##STR00038## wherein R.sub.21, R.sub.22, R.sub.23, R.sub.24, and R.sub.25 are each independently selected from R.sup.a, Si—(R″).sub.3, or R′—Si—(R″).sub.3; wherein R.sub.26 is selected from a C.sub.1-C.sub.12 alkyl group, a C.sub.2-C.sub.12 alkenyl group, a C.sub.6-C.sub.10 cyclic hydrocarbon group, or a C.sub.6-C.sub.26 aryl group; each of R.sup.a and R″ is independently selected from a C.sub.1-C.sub.12 alkyl group, a C.sub.2-C.sub.12 alkenyl group, a C.sub.6-C.sub.10 cyclic hydrocarbon group, or a C.sub.6-C.sub.26 aryl group; R′ is selected from a C.sub.1-C.sub.12 alkylene group or a C.sub.2-C.sub.12 alkenylene group; and R.sub.21, R.sub.22, R.sub.23, R.sub.24, R.sub.25, and R.sub.26 are each independently substituted or non-substituted, and when being substituted, a substituent is selected from a halogen, a C.sub.1-C.sub.6 alkyl group, a C.sub.2-C.sub.6 alkenyl group, or any combination thereof; wherein based on a total weight of the electrolytic solution, a weight percentage of the compound containing a —CN functional group is A %, and a weight percentage of the compound containing a P—O bond is B %, wherein 0.5≤A/B≤5; wherein the compound containing a —CN functional group comprises at least one selected from the group consisting of a compound represented by formula I-2 and a compound represented by formula I-10: ##STR00039## wherein the electrolytic solution further includes a dinitrile compound; wherein the dinitrile compound comprises at least one selected from the group consisting of butanedinitrile, hexanedinitrile, and ethyleneglycoldi(2-cyanoethyl)ether.

Description

EXAMPLES

(1) Hereinafter, this application will be specifically described by way of examples and comparative examples; however, this application is not limited to these examples as long as they do not deviate from the subject of this application.

(2) 1. Preparation of a Lithium Ion Battery

(3) 1) Preparation of an electrolytic solution: In an argon atmosphere glove box with a water content less than 10 ppm, ethylene carbonate (EC), diethyl carbonate (DEC), and propylene carbonate (PC) were evenly mixed according to a weight ratio of about 3:4:3, and then a sufficiently dried lithium salt LiPF.sub.6 was dissolved in the solvent to obtain a basic electrolytic solution, where the concentration of LiPF.sub.6 in the basic electrolytic solution was about 1 mol/L. Substances with different contents shown in the following tables were added to the basic electrolytic solution to obtain electrolytic solutions in different examples and comparative examples. The contents of all the substances in the electrolytic solution described below were calculated based on the total weight of the electrolytic solution.

(4) 2) Preparation of a cathode: The cathode active material lithium cobalt oxide (LiCoO.sub.2), the conductive agent acetylene black, and the binder polydifluoroethylene (PVDF) were fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent according to a weight ratio of about 96:2:2, to form a uniform cathode slurry. The slurry was coated on a current collector Al foil of the cathode, dried, and cold-pressed to obtain a positive pole piece.

(5) 3) Preparation of an anode: The anode active material graphite, the conductive agent acetylene black, the binder styrene butadiene rubber (SBR), and the thickener sodium carboxymethylcellulose (CMC) were fully stirred and mixed in an appropriate amount of deionized water solvent according to a weight ratio of about 95:2:2:1, to form a uniform anode slurry. The slurry was coated on a current collector Cu foil of the anode, dried, and cold-pressed to obtain a negative pole piece.

(6) 4) Separator: A porous PE polymer film was used as a separator.

(7) 5) Preparation of a lithium ion battery: The cathode, the separator, and the anode were stacked in sequence, so that the separator was located between the cathode and the anode to act as the insulation, then wound and placed in packaging foil, with a liquid injection port remained. The electrolytic solution was poured into the liquid injection port, and a lithium ion battery was produced after processes such as vacuum packaging, standing, formation, and shaping.

(8) The compounds containing a —CN functional group used in the examples are shown as follows:

(9) ##STR00021##

(10) The compounds containing a P—O bond used in the examples are shown as follows:

(11) ##STR00022##

(12) The specific cyclic carbonate used in the examples was fluoroethylene carbonate (FEC) or vinylethylene carbonate (VEC).

(13) The silicon-containing carbonate used in the examples is shown as follows:

(14) ##STR00023##

(15) The specific carboxylate used in the examples was propylpropionate (PP) or trifluoroethylacetate (TFEA).

(16) The specific lithium salt additive used in the examples was lithium tetrafluorophosphateoxalate (LiPF.sub.4C.sub.2O.sub.2).

(17) The specific cesium salt additive used in the examples was cesium hexafluorophosphate (CsPF.sub.6).

(18) A. The electrolytic solutions and lithium ion batteries in Examples 1-18 and Comparative Examples 1-4 were prepared according to the foregoing preparation method, wherein the contents of substances in the electrolytic solutions are shown in Table 1.

(19) TABLE-US-00001 TABLE 1 Compound containing a Compound —CN functional containing a P—O group (wt %) bond (wt %) No. I-1 I-2 I-7 II-1 II-5 11-9 Example 1 — 0.1 — — 1 — Example 2 — 0.3 — — 1 — Example 3 — 0.5 — — 1 — Example 4 — 1 — — 1 — Example 5 — 1.5 — — 1 — Example 6 — 2 — — 1 — Example 7 — 5 — — 1 — Example 8 — 10 — — 1 — Example 9 — 2 — — 0.1 — Example 10 — 2 — — 0.5 — Example 11 — 2 — — 0.6 — Example 12 — 2 — — 1.5 — Example 13 — 2 — — 2 — Example 14 — 2 — — 4 — Example 15 — — 2   0.6   Example 16 —   2     0.6 Example 17 2       0.6   Example 18 2 — — 0.6 — — Comparative — — — — — — Example 1 Comparative — 15 — — 0.6 — Example 2 Comparative — — — — 0.6 — Example 3 Comparative — 15 — — 7 — Example 4 ″—″ represents substance not present.

(20) The performance of the lithium ion batteries in Examples 1-18 and Comparative Examples 1-4 was tested according to the following test methods.

(21) 1. Floatation Performance Test:

(22) The battery was discharged to 3.0 V at 0.5 C at a temperature of 25° C., and then charged to 4.4 at 0.5 C. The battery was charged to 0.05 C at the constant voltage of 4.4 V. The thickness of the battery at this time was recorded. The thickness of the battery at this time was used as a reference, which was marked as a.sub.1. Then, the battery was placed into an oven at 45° C. and allowed to stand for 50 days at the constant voltage of 4.4 V. A change in the thickness was monitored and marked as b.sub.1. A formula for calculating the floatation thickness swelling rate is as follows: thickness percentage=(b.sub.1/a.sub.1−1)*10000. The thickness of the battery was measured by using a PPG soft pack battery thickness gauge, and the measurement was carried out at a pressure of 300 g. Test results after 50 days are shown in Table 2.

(23) TABLE-US-00002 TABLE 2 45° C.-4.4 V 45° C.-4.4 V 50 days 50 D floatation floatation thickness thickness No. swelling rate No. swelling rate Example 1 8.54% Example 12  6.25% Example 2 7.80% Example 13  6.27% Example 3 7.00% Example 14  6.30% Example 4 6.60% Example 15  6.23% Example 5 6.30% Example 16  6.22% Example 6 6.20% Example 17  6.21% Example 7 6.21% Example 18  6.22% Example 8 6.20% Comparative Example 1 20.50% Example 9 6.21% Comparative Example 2  9.30% Example 10 6.22% Comparative Example 3 18.10% Example 11 6.23% Comparative Example 4 11.20%

(24) It can be seen from the test results of Examples 1-14, Comparative Example 1, and Comparative Example 3 that, the addition of the compound containing a —CN functional group and the compound containing a P—O bond can improve the floatation performance of the battery, because, on one hand, the combination of them can protect the surface of the active material better, and on the other hand, the stability of the electrolytic solution can improve, thereby reducing side reactions.

(25) 2. Nailing Test:

(26) The battery was charged to 4.4 V at a constant current of 0.5 C at a temperature of 25° C. and then charged at the constant voltage of 4.4 V until the current reached 0.05 C; the voltage was kept in a full-state at the voltage of 4.4 V. The temperature was 25±5° C., the diameter of the nail was 4 mm, a nailing speed was 30 mm/s, and the nail was retained for 300 s. The battery passed the test if it did not burn or explode. The results of the nailing test are shown in Table 3.

(27) TABLE-US-00003 TABLE 3 No. 4.4 V-Nail Example 1 3/5pass Example 2 4/5pass Example 3 4/5pass Example 4 5/5pass Example 5 5/5pass Example 6 5/5pass Example 7 5/5pass Example 8 5/5pass Example 9 5/5pass Example 10 5/5pass Example 11 5/5pass Example 12 5/5pass Example 13 5/5pass Example 14 5/5pass Example 15 5/5pass Example 16 5/5pass Example 17 5/5pass Example 18 5/5pass Comparative Example 1 0/5pass Comparative Example 2 2/5pass Comparative Example 3 1/5pass Comparative Example 4 2/5pass

(28) It can be seen from the test results of Examples 1-14, Comparative Example 1, and Comparative Example 3 that, the addition of the compound containing a —CN functional group and the compound containing a P—O bond can enhance the protection of the active material, thereby improving the safety performance of the battery.

(29) 3. Cycle Impedance Test

(30) The battery was charged to 4.4 V at 0.7 C at a temperature of 25° C. and then charged to 0.05 C at the constant voltage of 4.4 V. An impedance value of the battery in this state was monitored and recorded by using a battery impedance testing instrument. Then, the battery was discharged to 3.0 V at a constant current of 1.0 C. The foregoing steps were repeated. Impedance values of the battery during cycles were recorded at frequency of every 10 cycles. Table 4 shows the impedance test results after the 800.sup.th cycle.

(31) TABLE-US-00004 TABLE 4 800-cycles No. impedance/milliohm Example 1 37.7 Example 2 37.2 Example 3 37.1 Example 4 37 Example 5 36.9 Example 6 36.5 Example 7 36.7 Example 8 36.8 Example 9 37.1 Example 10 36.3 Example 11 36.2 Example 12 36.6 Example 13 36.6 Example 14 36.5 Example 15 36.3 Example 16 36.2 Example 17 36.2 Example 18 36.3 Comparative Example 1 55.4 Comparative Example 2 50.2 Comparative Example 3 43.5 Comparative Example 4 53.2

(32) It can be seen from the test results of Examples 1-14, Comparative Example 1, and Comparative Example 3 that, the addition of the compound containing a —CN functional group and the compound containing a P—O bond can enhance the protection for the active material and reduce side reactions, thereby improving the cycle impedance performance of the battery.

(33) B. The electrolytic solutions and lithium ion batteries in Examples 19-27 were prepared according to the foregoing preparation method, wherein the contents of the substances in the electrolytic solutions are shown in Table 5.

(34) TABLE-US-00005 TABLE 5 Compound containing a P—O Compound bond of a containing a —CN phosphorous Cyclic functional group functional group carbonate (wt %) (wt %) (wt %) No. I-2 II-5 FEC VEC Example 11 2 0.6 — — Example 19 2 0.6 0.1 — Example 20 2 0.6 2 — Example 21 2 0.6 4 — Example 22 2 0.6 6 — Example 23 2 0.6 8 — Example 24 2 0.6 10 — Example 25 2 0.6 15 — Example 26 2 0.6 — 4 Example 27 2 0.6 — 6 ″—″ represents substance not present.

(35) A 4.4V floatation performance test and a 3.0V storage test were performed on the batteries in Example 11 and Examples 19-27, wherein the process of the 3.0V storage test is as follows:

(36) 4. 3.0V Storage Test:

(37) The battery was discharged to 3.0 V at 0.5 C, and after a 5-minute rest, the battery was continued to be discharged to 3.0 V at a current of 0.2 C. The thickness of the battery was measured at this time, and recorded as a reference thickness, marked as a.sub.2. Then, the battery was placed into an oven at 60° C. and allowed to stand for 15 days at a voltage of 3 V at a constant temperature. The battery was taken out after 15 days, and the thickness of the battery was measured within 1 h after the battery was taken out. The thickness of the battery at this time was marked as b.sub.2. A formula for calculating the thickness swelling rate is as follows: thickness percentage=(b.sub.2/a.sub.2−1)*100%. The thickness of the battery was measured by using a PPG soft pack battery thickness gauge, and the measurement was carried out under a pressure of 300 g. The test results after 15 days are shown in Table 6.

(38) TABLE-US-00006 TABLE 6 45° C.-4.4 V 50 days 60° C.-3.0 V 15 floatation thickness days thickness No. swelling rate swelling rate Example 11 6.23% 7.70% Example 19 6.20% 6.00% Example 20 6.18% 5.90% Example 21 6.20% 5.80% Example 22 6.18% 5.71% Example 23 6.19% 5.71% Example 24 6.20% 5.72% Example 25 7.21% 5.74% Example 26 6.17% 5.75% Example 27 6.50% 5.65%

(39) It can be seen from the test results of Example 11 and Examples 19-27 that, the storage performance of the battery at 3.0 V was significantly improved after the cyclic carbonate was added to the electrolytic solution, due to the excellent film-forming effect of the cyclic carboxylate on the anode.

(40) C. The electrolytic solutions and lithium ion batteries in Examples 28-42 were prepared according to the foregoing preparation method, wherein the contents of the substances in the electrolytic solutions are shown in Table 7.

(41) TABLE-US-00007 TABLE 7 Compound Silicon- containing a Compound containing —CN containing a Cyclic chain functional P—O bond carbonate carbonate group (wt %) (wt %) (wt %) (wt %) No. I-2 II-5 FEC IV-1 IV-2 Comparative — — — — — Example 1 Example 11 2 0.6 — — — Example 22 2 0.6 6 — — Example 28 2 0.6 — 1 — Example 29 2 0.6 — 5 — Example 30 2 0.6 — 7 — Example 31 2 0.6 — 10 — Example 32 2 0.6 — 15 — Example 33 2 0.6 — 20 — Example 34 2 0.6 — 50 — Example 35 2 0.6 — — 5 Example 36 2 0.6 — — 7 Example 37 2 0.6 6 1 — Example 38 2 0.6 6 5 — Example 39 2 0.6 6 7 — Example 40 2 0.6 6 10 — Example 41 2 0.6 6 20 — Example 42 2 0.6 6 50 — ″—″ represents substance not present.

(42) A 4.4V floatation performance test, a 3.0V storage test, and a 3 C/7V overcharge test were performed on the lithium ion batteries in Examples 11 and 22 and Examples 28-42, wherein the process of the 3 C/7V overcharge test was as follows:

(43) 5. 3 C/7V Overcharge Test:

(44) The battery was discharged to 3.0 V at 0.5 C, and after a 5-minute rest, the battery was charged to 7 V at a current of 3 C. The battery was charged for 1 h at the constant voltage of 7 V. The battery passed the test if it does not burn or explode. The results of the overcharge test are shown in Table 8.

(45) TABLE-US-00008 TABLE 8 45° C.-4.4 V 60° C.-3.0 V 50 days floatation 15 days 3 C./7 V thickness swelling thickness overcharge No. rate swelling rate test Comparative Example 1 20.5% 15.6% 0/5pass Example 11  6.23%  7.70% 1/5pass Example 22  6.18%  5.71% 1/5pass Example 28  6.18%  7.71% 4/5pass Example 29  6.19%  7.73% 5/5pass Example 30  6.20%  7.80% 5/5pass Example 31  6.19%  7.91% 5/5pass Example 32  6.18%  8.10% 5/5pass Example 33  6.20%  8.30% 5/5pass Example 34  6.19%  8.90% 5/5pass Example 35  6.18%  7.75% 5/5pass Example 36  6.19%  7.80% 5/5pass Example 37  6.18%  5.72% 4/5pass Example 38  6.19%  5.74% 5/5pass Example 39  6.20%  5.80% 5/5pass Example 40  6.18%  5.90% 5/5pass Example 41  6.19%  6.00% 5/5pass Example 42  6.20%  6.50% 5/5pass

(46) It can be seen from the test results of Example 11, Example 22, Examples 28-42 and Comparative Example 1 that, the addition of the silicon-containing chain carbonate to the electrolytic solution can significantly improve the overcharge safety performance of the battery.

(47) D. The electrolytic solutions and lithium ion batteries in Examples 43-56 were prepared according to the foregoing preparation method, wherein the contents of the substances in the electrolytic solutions are shown in Table 9.

(48) TABLE-US-00009 TABLE 9 Compound Silicon- containing a Compound containing —CN containing a Cyclic chain functional P—O bond carbonate carbonate Carboxylate group (wt %) (wt %) (wt %) (wt %) (wt %) No. I-2 II-5 FEC IV-1 PP TFEA Example 11 2 0.6 — — — — Example 22 2 0.6 6 — — — Example 38 2 0.6 6 5 — — Example 43 2 0.6 — — 5 — Example 44 2 0.6 — — 10 — Example 45 2 0.6 — — 15 — Example 46 2 0.6 — — 20 — Example 47 2 0.6 — — 30 — Example 48 2 0.6 — — 60 — Example 49 2 0.6 — — — 15 Example 50 2 0.6 — — — 20 Example 51 2 0.6 6 — 15 — Example 52 2 0.6 6 — 20 — Example 53 2 0.6 6 5 10 — Example 54 2 0.6 6 5 20 — Example 55 2 0.6 6 5 30 — Example 56 2 0.6 6 5 60 —

(49) A 4.4V floatation performance test, a 3.0V storage test, a 3 C/7V overcharge test, and a discharge rate test were performed on the lithium ion batteries in Examples 11, 22, and 38 and Examples 43-56, wherein the process of the discharge rate test is as follows:

(50) 6. Discharge Rate Test:

(51) The battery was charged to 4.4 V at 0.2 C at a temperature of 25° C., and then charged to 0.05 C at the constant voltage of 4.4 V. The battery was discharged to 3.0 V at a current of 0.5 C. The discharged capacity was recorded and marked as a.sub.3. Then, the battery was charged to 4.4 V at 0.2 C, and charged to 0.05 C at the constant voltage of 4.4 V. The battery was discharged to 3.0 V with a current of 2 C, and the discharged capacity was recorded and marked as b.sub.3. The percentage of the capacity discharged with 2 C was calculated based on the capacity discharged with 0.5 C. A calculation formula was as follows: 2 C discharge capacity=b.sub.3/a.sub.3*100%. Test results are shown in Table 10.

(52) TABLE-US-00010 TABLE 10 45° C.-4.4 V 60° C.-3.0 V 50 days 15 days floatation thickness 3 C./7 V 2 C. thickness swelling overcharge discharge No. swelling rate rate test capacity Example 11 6.23% 7.70% 1/5pass 80.1% Example 22 6.18% 5.71% 1/5pass 80.1% Example 38 6.19% 5.74% 5/5pass 75.4% Example 43 6.18% 7.71% 1/5pass 83.2% Example 44 6.19% 7.69% 1/5pass 85.4% Example 45 6.19% 7.71% 1/5pass 87.2% Example 46 6.20% 7.69% 1/5pass 88.1% Example 47 6.20% 7.70% 1/5pass 88.2% Example 48 6.20% 7.69% 1/5pass 88.5% Example 49 6.19% 7.71% 1/5pass 87.2% Example 50 6.18% 7.69% 1/5pass 88.2% Example 51 6.18% 5.80% 1/5pass 83.2% Example 52 6.19% 6.60% 1/5pass 88.1% Example 53 6.18% 5.75% 5/5pass 84.0% Example 54 6.19% 6.50% 4/5pass 85.1% Example 55 6.20% 7.70% 4/5pass 86.6% Example 56 6.20% 9.00% 3/5pass 87.5%

(53) It can be seen from the test results of Example 11, Example 22, Example 38, and Examples 43-56 that, the addition of the carboxylate to the electrolytic solution can significantly improve the 2 C discharge capacity of the battery.

(54) E. The electrolytic solutions and lithium on batteries in Examples 57-79 were prepared according to the foregoing preparation method, wherein the contents of the substances in the electrolytic solutions are shown in Table 11.

(55) TABLE-US-00011 TABLE 11 Compound Silicon- containing a Compound containing —CN containing a Cyclic chain Lithium salt Cesium salt functional P—O bond carbonate carbonate Carboxylate additive additive group (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) No. I-2 II-5 FEC IV-1 PP LiPF.sub.4C.sub.2O.sub.2 CsPF.sub.6 Example 11 2 0.6 — — — — — Example 22 2 0.6 6 — — — — Example 38 2 0.6 6 5 — — — Example 46 2 0.6 — — 20 — — Example 52 2 0.6 6 5 20 — — Example 57 2 0.6 — — — 0.1 — Example 58 2 0.6 — — — 0.3 — Example 59 2 0.6 — — — 0.5 — Example 60 2 0.6 — — — 1 — Example 61 2 0.6 — — — 2 — Example 62 2 0.6 — — — 5 — Example 63 2 0.6 — — — 10 — Example 64 2 0.6 — — — — 0.1 Example 65 2 0.6 — — — — 0.3 Example 66 2 0.6 — — — — 0.5 Example 67 2 0.6 — — — — 1 Example 68 2 0.6 6 — — 0.1 — Example 69 2 0.6 6 — — 0.3 — Example 70 2 0.6 6 — — 0.5 — Example 71 2 0.6 6 5 — 0.1 — Example 72 2 0.6 6 5 — 0.3 — Example 73 2 0.6 6 5 — 0.5 — Example 74 2 0.6 — — 20 0.1 — Example 75 2 0.6 — — 20 0.3 — Example 76 2 0.6 — — 20 0.5 — Example 77 2 0.6 6 5 20 0.1 — Example 78 2 0.6 6 5 20 0.3 — Example 79 2 0.6 6 5 20 0.5 — ″—″ represents substance not present.

(56) A 4.4V floatation performance test, a 3.0V storage test, a 3 C/7V overcharge test, a discharge rate test, and a 25° C. capacity retention rate test were performed on the lithium ion batteries in Examples 11, 22, 38, 46, 52, and 57-79, wherein the process of the 25° C. capacity retention rate test is as follows:

(57) 7. 25° C. Cycle Test:

(58) The battery was charged to 4.4 V at 0.7 C at a temperature of 25° C., and then charged to 0.05 C at the constant voltage of 4.4 V. The battery was discharged to 3.0 V at a current of 1 C. The discharged capacity was recorded. The process of charging at 0.7 C and discharging at 1 C was cycled 800 times. The battery capacity discharged in each cycle was recorded. By using the battery capacity discharged in the first cycle as a reference, a percentage of the battery capacity discharged at 1 C in each cycle to the battery capacity discharged in the first cycle was calculated. The test results are shown in Table 12.

(59) TABLE-US-00012 TABLE 12 25° C.- 45° C.-4.4 V 800- 50 days 60° C.-3.0 V cycles floatation 15 days 3 C./7 V 2 C. capacity thickness thickness overcharge discharge retention No. swelling rate swelling rate test capacity rate Example 11 6.23% 7.70% 1/5pass 80.1% 83.2% Example 22 6.18% 5.71% 1/5pass 80.1% 84.2% Example 38 6.19% 5.74% 5/5pass 75.4% 83.8% Example 46 6.20% 7.71% 1/5pass 88.1% 82.1% Example 52 6.19% 6.50% 4/5pass 88.1% 83.7% Example 57 6.19% 7.65% 1/5pass 80.2% 85.4% Example 58 6.20% 7.60% 1/5pass 80.3% 87.4% Example 59 6.19% 7.51% 1/5pass 80.3% 87.8% Example 60 6.20% 7.40% 1/5pass 80.1% 87.5% Example 61 6.18% 7.31% 1/5pass 80.3% 87.4% Example 62 6.19% 7.32% 1/5pass 80.2% 87.4% Example 63 6.18% 7.41% 1/5pass 80.2% 87.3% Example 64 6.19% 7.64% 1/5pass 80.1% 85.4% Example 65 6.20% 7.55% 1/5pass 80.2% 87.4% Example 66 6.19% 7.48% 1/5pass 80.1% 87.8% Example 67 6.20% 7.35% 1/5pass 80.3% 87.5% Example 68 6.19% 5.61% 1/5pass 80.1% 85.4% Example 69 6.18% 5.55% 1/5pass 80.2% 88.4% Example 70 6.19% 5.51% 1/5pass 80.3% 89.0% Example 71 6.19% 5.71% 5/5pass 75.5% 83.1% Example 72 6.18% 5.65% 5/5pass 75.6% 85.4% Example 73 6.19% 5.60% 5/5pass 75.7% 86.0% Example 74 6.20% 7.65% 1/5pass 88.2% 84.1% Example 75 6.20% 7.60% 1/5pass 88.3% 86.2% Example 76 6.20% 7.55% 1/5pass 88.4% 86.9% Example 77 6.19% 6.40% 4/5pass 88.2% 84.5% Example 78 6.19% 6.35% 4/5pass 88.3% 87.3% Example 79 6.20%  6.3% 4/5pass 88.4% 87.6%

(60) It can be seen from the test results of Example 11, Example 22, Example 38, Example 46, Example 52, and Examples 57-79 that, after the lithium salt additive and the cesium salt additive were added to the electrolytic solution, the cycle capacity retention rate of the battery can be significantly improved. The reason may be that the combination of the lithium salt and the cesium salt with the compound containing a —CN functional group and the compound containing a P—O bond enhances the protection effect of the electrolytic solution to the active material of the battery.

(61) F. The electrolytic solutions and lithium ion batteries in Examples 80-84 were prepared according to the foregoing preparation method, wherein the contents of the substances in the electrolytic solutions are shown in Table 13.

(62) TABLE-US-00013 TABLE 13 Compound containing a Compound —CN containing functional a P—O Additive group bond Butane- 1,3- Diethoxy- Trimethyl Fluoro- No. I-2 II-5 dinitrile dioxolan methane phosphate benzene Example 11 2 0.6 — — — — — Example 80 2 0.6 3 — — — — Example 81 2 0.6 — 1 — — — Example 82 2 0.6 — — 3 — — Example 83 2 0.6 — — — 4 — Example 84 2 0.6 — — — — 6 ″—″ represents substance not present.

(63) A 4.4V floatation performance test, a hot box test, and a 3 C/6V overcharge test were performed on the lithium ion batteries in Examples 11 and 80-84, wherein the processes of the hot box test and 3 C/6V overcharge test were as follows:

(64) 8. Hot Box Test:

(65) The battery was charged to 4.4 V at 0.7 C at a temperature of 25° C. and then charged to 0.05 C at the constant voltage of 4.4 V. Next, the battery was placed into a test chamber, and the test chamber was heated at a rate of (5±2) ° C./min. When the temperature in the box reached 150° C.±2° C., the temperature was maintained for 60 min. The battery passed the test if it did not burn or explode. 9. Overcharge Test:

(66) The battery was charged to 6 V at 3 C at a temperature of 25° C. and then charged at the constant voltage of 6 V. Temperature changes of the battery were detected during the test. The test was terminated upon occurrence of one of the following two situations:

(67) a) a continuous charging time of the battery reached 7 h; and

(68) b) the temperature of the battery lowered to a value that was 20% less than a peak value.

(69) The battery passed the test if it did not burn or explode.

(70) The results of the hot box test and the overcharge test are shown in Table 14:

(71) TABLE-US-00014 TABLE 14 45° C.-4.4 V 50 days 3 C./6 V floatation thickness Hot overcharge No. swelling rate box test test Example 11 6.23% 4/5pass 3/5pass Example 80 5.80% 5/5pass 4/5pass Example 81 6.10% 4/5pass 5/5pass Example 82 6.20% 4/5pass 5/5pass Example 83 6.21% 5/5pass 5/5pass Example 84 6.21% 3/5pass 4/5pass

(72) It can be seen from the test results of Example 11 and Examples 80-84 that the additive in combination with the compound containing a —CN functional group and the compound containing a P—O bond can improve the safety performance of the battery to some extent.

(73) Described above are merely some embodiments of the present invention, and are not intended to limit the present invention in any form. Although the present invention is disclosed above with exemplary embodiments, the present invention is not limited thereto. Changes or modifications made by any person skilled in the art according to the technical content disclosed above and without departing from the scope of the technical solutions of the present invention are all equivalent to equivalent embodiments, and all fall within the scope of the technical solutions.

(74) References throughout the specification to “embodiments”, “partial embodiments”, “one embodiment”, “another example”, “example”, “specific example” or “partial examples” mean that at least one embodiment or example of the application includes specific features, structures, materials or characteristics described in the embodiments or examples. Thus, the descriptions appear throughout the specification, such as “in some embodiments”, “in an embodiment”, “in one embodiment”, “in another example”, “in an example”, “in a particular example” or “for example”, are not necessarily the same embodiment or example in the application. Furthermore, the particular features, structures, materials or characteristics herein may be combined in any suitable manner in one or more embodiments or examples.

(75) While the illustrative embodiments have been shown and described, it will be understood by a person skilled in the art that the embodiments are not to be construed as limiting the this application, and modifications, substitutions and changes can be made to the embodiments without departing from the spirit, principle, and scope of the this application.