Electrolyte for a lithium secondary battery including an ionic liquid containing an ether functional group and a lithium secondary battery including the same
Disclosed is an electrolyte for a secondary battery that includes an ionic liquid containing an ether functional group, thereby providing effects of lowering the viscosity and improving lithium ion conductivity even when a molecular weight is increased.
1 . An electrolyte for a lithium secondary battery, the electrolyte comprising:
an ionic liquid comprising a cation and an anion; and
a metal salt,
wherein the cation and the anion each comprises an ether group, and
wherein the ionic liquid comprises up to 7 ether groups.
2 . The electrolyte of claim 1 , wherein the cation comprises pyrrolidinium, piperidinium, morpholinium, ammonium, phosphonium, or combinations thereof.
3 . The electrolyte of claim 1 , wherein the cation comprises:
or
combinations thereof,
wherein R 1 , R 2 , R 3 , and R 4 each comprise a substituted or unsubstituted C1-C12 alkyl group, and
wherein at least one of R 1 , R 2 , R 3 , and R 4 comprises an aliphatic compound comprising the ether group.
4 . The electrolyte of claim 1 , wherein the cation comprises:
or combinations thereof.
5 . The electrolyte of claim 1 , wherein the anion comprises the ether group represented by:
wherein n is an integer in a range of 1 to 3.
6 . The electrolyte of claim 1 , wherein the anion comprises phosphite, phosphate, sulfide, or combinations thereof.
7 . The electrolyte of claim 1 , wherein the anion comprises:
or combinations thereof.
8 . The electrolyte of claim 1 , wherein the metal salt comprises a salt having a structure of A + B − ,
wherein A + comprises at least one alkali metal cation, and
wherein B − comprises BF 4 − , B(CN) 4 − , CH 3 BF 3 − , C 2 H 5 BF 3 − , CF 3 BF 3 − , C 2 F 5 BF 3 − , n-C 3 H 7 BF 3 − , n-C 4 F 9 BF 3 − , PF 6 − , CF 3 CO 2 − , CF 3 SO 3 − , N(SO 2 F) 2 − , N(SO 2 CF 3 ) 2 − , N(SO 2 C 2 F 5 ) 2 − , N(COCF 3 ) (SO 2 CF 3 ) − , N(CN) 2 − , C(CN) 3 − , SCN − , SeCN − , CuCl 2 − , AlCl 4 − , F(HF) 2.3 − , BOB − , ODFB − , or combinations thereof.
9 . The electrolyte of claim 1 , wherein a molar ratio of the ionic liquid to the metal salt is in a range of 0.1:1 to 1:1.
10 . The electrolyte of claim 1 , wherein a lowest unoccupied molecular orbital (LUMO) energy of the electrolyte is higher than a lowest unoccupied molecular orbital (LUMO) energy level of lithium.
11 . The electrolyte of claim 1 , wherein the electrolyte is a liquid state in a range of 15° C. to 25° C. when the electrolyte has a molecular weight of 350 g/mol or less.
12 . A lithium secondary battery comprising:
a cathode;
an anode comprising a lithium metal; and
a separator interposed between the cathode and the anode,
wherein the lithium secondary battery is impregnated with an electrolyte comprising:
an ionic liquid comprising a cation and an anion; and
a metal salt,
wherein at least one of the cation and the anion each comprises an ether group, and
wherein the ionic liquid comprises up to 7 ether groups.
13 . The lithium secondary battery of claim 12 , wherein the cation of the electrolyte comprises pyrrolidinium, piperidinium, morpholinium, ammonium, phosphonium, or combinations thereof.
14 . The lithium secondary battery of claim 12 , wherein the cation of the electrolyte comprises:
or
combinations thereof,
wherein R 1 , R 2 , R 3 , and R 4 each comprise a substituted or unsubstituted C1-C12 alkyl group, and
wherein at least one of R 1 , R 2 , R 3 , and R 4 comprises an aliphatic compound comprising the ether group.
15 . The lithium secondary battery of claim 12 , wherein the cation of the electrolyte comprises:
or combinations thereof.
16 . The lithium secondary battery of claim 12 , wherein the anion of the electrolyte comprises the ether group represented by:
wherein n is an integer in a range of 1 to 3.
17 . The lithium secondary battery of claim 12 , wherein the anion of the electrolyte comprises phosphite, phosphate, sulfide, or combinations thereof.
18 . The lithium secondary battery of claim 12 , wherein the anion of the electrolyte comprises:
or combinations thereof.
19 . The lithium secondary battery of claim 12 , wherein the metal salt of the electrolyte comprises a salt having a structure of A + B − ,
wherein A + comprises at least one alkali metal cation, and
wherein B − comprises BF 4 − , B(CN) 4 − , CH 3 BF 3 − , C 2 H 5 BF 3 − , CF 3 BF 3 − , C 2 F 5 BF 3 − , n-C 3 H 7 BF 3 − , n-C 4 F 9 BF 3 − , PF 6 − , CF 3 CO 2 − , CF 3 SO 3 − , N(SO 2 F) 2 − , N(SO 2 CF 3 ) 2 − , N(SO 2 C 2 F 5 ) 2 − , N(COCF 3 )(SO 2 CF 3 ) − , N(CN) 2 − , C(CN) 3 − , SCN − , SeCN − , CuCl 2 − , AlCl 4 − , F(HF) 2.3 − , BOB − , ODFB − , or combinations thereof.