Electrolyte and electrochemical device

1. An electrolyte comprising an additive A and an additive B, wherein the additive A is selected from one or more of the compounds of Formula I-1, Formula I-3;

in which Formula I-1, Formula I-3: R 1 , R 2 , R 3 , R 4 are each independently selected from a hydrogen atom, a halogen atom, a substituted or unsubstituted C 1 -C 12 alkyl group, a substituted or unsubstituted C 1 -C 12 alkoxy group, a substituted or unsubstituted C 1 -C 12 amino group, a substituted or unsubstituted C 2 -C 12 alkenyl group, a substituted or unsubstituted C 2 -C 12 alkynyl group, a substituted or unsubstituted C 6 -C 26 aryl group, and a substituted or unsubstituted C 2 -C 12 heterocyclic group, wherein the substituent is selected from one or more of a halogen atom, cyano, a C 1 -C 6 alkyl group, a C 2 -C 6 alkenyl group, and a C 1 -C 6 alkoxy group; x, y, and z are each independently selected from an integer of 0 to 8; m, n, and k are each independently selected from an integer of 0 to 2; and wherein the additive B is selected from a lithium sulfonimide salt represented by formula II, in which formula II, R F is one of C p1 F 2p1+1 and F(CF 2 CF 2 O) q1 CF 2 CF 2 , R f is one of C p2 F 2p2+1 and F(CF 2 CF 2 O) q2 CF 2 CF 2 , p1 and p2 are each independently selected from an integer of 0 to 8; and q1 and q2 are each independently selected from an integer of 1 to 6,

wherein the additive A is present in an amount of 0.001% to 10% by mass in the electrolyte; the additive B is present in an amount of 0.1% to 10% by mass in the electrolyte; and the electrolyte has a conductivity of 4 mS/cm to 12 mS/cm at 25° C.

2. The electrolyte according to claim 1 , wherein the additive A is present in an amount of 0.01% to 6% by mass in the electrolyte and wherein the additive B is present in an amount of 0.5% to 6% by mass in the electrolyte.

3. The electrolyte according to claim 2 , wherein the additive A is present in an amount of 0.1% to 3.5% by mass in the electrolyte.

4. The electrolyte according to claim 2 , wherein the additive B is present in an amount of 1% to 4% by mass in the electrolyte.

5. The electrolyte of claim 1 wherein the additive A is selected from one or more of the following compounds:

6. The electrolyte according to claim 1 , wherein the additive B is selected from one or more of the following compounds:

7. The electrolyte according to claim 1 , wherein the electrolyte further comprises an additive C and the additive C is selected from one or more of a cyclic carbonate compound containing a carbon-carbon unsaturated bond and a halogen-substituted cyclic carbonate compound.

8. The electrolyte according to claim 7 , wherein the cyclic carbonate compound containing a carbon-carbon unsaturated bond is selected from one or more of the compounds represented by Formula III-I, in which Formula III-1, R 20 is selected from a C 1 -C 6 alkylene group with an alkenyl group or an alkynyl group in its branched chain and a substituted or unsubstituted C 2 -C 6 linear alkenylene group, wherein the substituent is selected from one or more of a halogen atom, a C 1 -C 6 alkyl group and a C 2 -C 6 alkenyl group; and

wherein the halogen-substituted cyclic carbonate compound is selected from one or more of the compounds represented by Formula III-2 in which Formula III-2, R 21 is selected from one or more of a halogen-substituted C 1 -C 6 alkylene group and a halogen-substituted C 2 -C 6 alkenylene group

9. The electrolyte according to claim 7 , wherein the additive C is present in an amount of 0.1% to 10% by mass in the electrolyte.

10. The electrolyte according to claim 7 , wherein the additive C is present in an amount of 0.5% to 6% by mass in the electrolyte.

11. The electrolyte according to claim 7 , wherein the additive C is present in an amount of 1% to 3% by mass in the electrolyte.

12. The electrolyte according to claim 1 , wherein the organic solvent comprises a mixture of a cyclic carbonate, a chain carbonate, and a carboxylic acid ester;

the cyclic carbonate is selected from one or more of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, and 2,3-butylene glycol carbonate; and

the chain carbonate is selected from one or more of ethyl methyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, methyl butyl carbonate, ethyl propyl carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, and dibutyl carbonate; and

the carboxylic acid ester is selected from one or more of methyl pivalate, ethyl pivalate, propyl pivalate, butyl pivalate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl acetate, ethyl acetate, propyl acetate and butyl acetate.

13. The electrolyte according to claim 12 , wherein based on the total mass of the organic solvent,

the cyclic carbonate is present in an amount of 15% to 55% by mass;

the chain carbonate is present in an amount of 15% to 74% by mass; and

the carboxylic acid ester is present in an amount of 0.1% to 70% by mass.

14. The electrolyte according to claim 13 , wherein based on the total mass of the organic solvent, the cyclic carbonate is present in an amount of 25% to 50% by mass.

15. The electrolyte according to claim 13 , wherein based on the total mass of the organic solvent, the chain carbonate is present in an amount of 25% to 70% by mass.

16. The electrolyte according to claim 13 , wherein based on the total mass of the organic solvent, the carboxylic acid ester is present in an amount of 5% to 50% by mass.

17. An electrochemical device comprising a positive electrode plate, a negative electrode plate, a separator disposed between the positive electrode plate and the negative electrode plate, and an electrolyte, wherein the electrolyte is the electrolyte according to claim 1 .