Electrolyte and electrochemical device

1. An electrolyte, comprising an additive A and an additive B, wherein the additive A is selected from a group consisting of multi-cyano six-membered N-heterocyclic compounds represented by Formula I-1 and Formula I-3, and combinations thereof:

wherein R 1 , R 2 , R 3 and R 4 are each independently selected from a group consisting of hydrogen, halogen, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 1 -C 12 alkoxy, substituted or unsubstituted C 1 -C 12 amine group, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 2 -C 12 alkynyl, substituted or unsubstituted C 6 -C 26 aryl, or substituted or unsubstituted C 4 -C 12 heterocyclic group;

the substituent for the above groups, if present, is independently selected from a group consisting of halogen, cyano, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 1 -C 6 alkoxy, and combinations thereof;

x, y and z are each an integer independently selected from 0-8; and

m, n and k are each an integer independently selected from 0-2;

wherein the electrolyte comprises 0.001% to 10% by weight of the additive A;

wherein the additive B is at least one halogenated cyclic carbonate compound; and

wherein the electrolyte comprises 0.1% to 10% by weight of the additive B.

2. The electrolyte according to claim 1 , wherein

R 1 , R 2 , R 3 and R 4 are each independently selected from a group consisting of hydrogen, halogen, substituted or unsubstituted C 1 -C 3 linear or branched alkyl, substituted or unsubstituted C 5 -C 7 cycloalkyl, substituted or unsubstituted C 1 -C 3 alkoxy, substituted or unsubstituted C 1 -C 3 amine group, substituted or unsubstituted C 2 -C 3 alkenyl, substituted or unsubstituted C 2 -C 3 alkynyl, substituted or unsubstituted C 6 -C 8 aryl, or substituted or unsubstituted C 4 -C 7 heterocyclic group,

the substituent for the above groups, if present, is halogen.

3. The electrolyte according to claim 1 , wherein

in Formula I-1, R 1 and R 3 are identical; and

in Formula I-3, at least two of R 1 , R 2 and R 3 are identical.

4. The electrolyte according to claim 3 , wherein

in Formula I-1, R 1 , R 3 and R 4 are identical.

5. The electrolyte according to claim 3 , wherein

in Formula I-1, R 1 and R 3 are hydrogen; and

in Formula I-3, at least two of R 1 , R 2 and R 3 are hydrogen.

6. The electrolyte according to claim 5 , wherein

in Formula I-1, R 1 , R 3 and R 4 are hydrogen.

7. The electrolyte according to claim 1 , wherein the electrolyte comprises 0.01% to 6% by weight of the additive A.

8. The electrolyte according to claim 7 , wherein the electrolyte comprises 0.1% to 3.5%, by weight of the additive A.

9. The electrolyte according to claim 1 , wherein the multi-cyano six-membered N-heterocyclic compound represented by Formula I-1 (a-g) is selected from a group consisting of the following compounds and combinations thereof:

the multi-cyano six-membered N-heterocyclic compound represented by Formula I-3 (a-f) is selected from a group consisting of the following compounds and combinations thereof:

10. The electrolyte according to claim 1 , wherein the at least one halogenated cyclic carbonate compound is selected from a group consisting of compounds represented by Formula II, and combinations thereof;

wherein R 21 is selected from halogenated C 1 -C 6 alkylene, and halogenated C 2 -C 6 alkenylene.

11. The electrolyte according to claim 10 , wherein the electrolyte comprises 0.5% to 6% by weight of the additive B.

12. The electrolyte according to claim 11 , wherein the electrolyte comprises 1% to 3% by weight of the additive B.

13. The electrolyte according to claim 1 , wherein the electrolyte further comprises an additive C, and the additive C is selected from a group consisting of a sulfate compound, a sulfite compound, and combinations thereof,

wherein the electrolyte comprises 0.1% to 10% by weight of the additive C.

14. The electrolyte according to claim 13 , wherein the electrolyte comprises 0.5% to 6% by weight of the additive C.

15. The electrolyte according to claim 13 , wherein the sulfate compound is a cyclic sulfate compound, and the cyclic sulfate compound is selected from a group consisting of compounds represented by Formula III-1 and combinations thereof:

R 31 is selected from substituted or unsubstituted C 1 -C 6 alkylene, and substituted or unsubstituted C 2 -C 6 alkenylene, wherein the substituent for the above groups, if present, is selected from a group consisting of halogen, C 1 -C 3 alkyl, C 2 -C 4 alkenyl, and combinations thereof;

the sulfite compound is a cyclic sulfite compound, and the cyclic sulfite compound is selected from a group consisting of compounds represented by Formula III-2 and combinations thereof:

R 32 is substituted or unsubstituted C 1 -C 6 alkylene, or substituted or unsubstituted C 2 -C 6 alkenylene, wherein the substituent for the above groups, if present, is selected from a group consisting of halogen, C 1 -C 3 alkyl, C 2 -C 4 alkenyl, and combinations thereof.

16. An electrochemical device, comprising a positive electrode plate, a negative electrode plate, a separator positioned between the positive electrode plate and the negative electrode plate, and an electrolyte according to claim 1 .

17. The electrochemical device according to claim 16 , wherein the electrochemical device is a lithium-ion secondary battery, a lithium primary battery, or a lithium-ion capacitor.

18. The electrochemical device according to claim 16 , wherein the electrochemical device is a lithium-ion secondary battery, and the lithium-ion secondary battery has a charge cut-off voltage of 4.2V to 4.35V.

19. The electrolyte according to claim 1 , wherein in Formula I-1 and Formula I-3, m, n and k are each independently 1 or 2.