Electrochemical cells having ionic liquid-containing electrolytes
Electrolytes and electrochemical cells include a novel ionic liquid having a quaternary cation and a boron cluster anion. In some versions, the boron cluster anion will be a functionalized or unfunctionalized icosahedral boranyl or carboranyl anion. Electrochemical cells have an electrolyte including the ionic liquid. In some versions, the ionic liquid is used as a solvent to dissolve an ionic shuttle salt for transport of active material, with an optional co-solvent. Methods to synthesize the ionic liquid include contacting a boron cluster salt with a quaternary salt to form the ionic liquid by a metathesis reaction.
1. A lithium electrochemical cell, comprising:
an anode that contains a reduced form of an active material when at least partially charged;
a cathode; and
an electrolyte mediating ionic communication between the anode and the cathode, the electrolyte comprising:
a lithium salt; and
an ionic liquid having a formula:
A p Q,
wherein A is a quaternary cation comprising at least one of:
an ammonium cation having a structure:
and
a phosphonium cation having a structure:
wherein R 1 , R 2 , R 3 , and R 4 is each, independently, selected from a group consisting of:
C2-C12 alkyl; and
poly(ethylene glycol) methyl ether having from 1-20 ethylene glycol subunits, and
wherein Q is a boron cluster anion and p is one or two.
2. The lithium electrochemical cell as recited in claim 1 , wherein the boron cluster anion has a formula [B y H (y-z-i) R z X i ] 2− , [CB( y-1 )H (y-z-i) R z X i ] − , [C 2 B (y-2) H (y-t-j-1) R t X j ] − , [C 2 B (y-3) H (y-t-j) R t X j ] − , or [C 2 B (y-3) H (y-t-j-1) R t X j ] 2− , and wherein:
y is an integer within a range of 6 to 12;
(z+i) is an integer within a range of 0 to y;
(t+j) is an integer within a range of 0 to (y−1);
X is F, Cl, Br, I, or a combination thereof; and
R is a substituent comprising any of:
group (i): a linear, branched-chain, or cyclic C1-C18 alkyl, perfluoroalkyl, or partially fluorinated alkyl group;
group (ii): a C6-C14 aryl, perfluoroaryl, or partially fluorinated aryl group;
group (iii): a linear, branched-chain, or cyclic C1-C18 alkoxy, perfluoroalkoxy, or partially fluorinated alkoxy group;
group (iv): a C6-C14 aryloxy, perfluoroaryloxy, or partially fluorinated aryloxy group; and
group (v): a substituent that combines moieties defined by two or more of groups (i)-(iv).
3. The lithium electrochemical cell as recited in claim 2 , wherein the electrolyte comprises a shuttle salt to improve transport of the active material between the anode and the cathode, the shuttle salt having an oxidized form of the active material as a cation.
4. The lithium electrochemical cell as recited in claim 2 , wherein the boron cluster anion comprises an icosahedral, closo-boron cluster anion.
5. The lithium electrochemical cell as recited in claim 2 , wherein the boron cluster anion comprises at least one of closo-[B 12 H 12 ] 2− , closo-[CB 11 H 12 ] − , and closo-[C 2 B 10 H 11 ] − .
6. A sodium electrochemical cell, comprising:
an anode that contains a reduced form of an active material when at least partially charged;
a cathode; and
an electrolyte mediating ionic communication between the anode and the cathode, the electrolyte comprising:
a sodium salt; and
an ionic liquid having a formula:
A p Q,
wherein A is a quaternary cation comprising at least one of:
an ammonium cation having a structure:
and
a phosphonium cation having a structure:
wherein R 1 , R 2 , R 3 , and R 4 is each, independently, selected from a group consisting of:
C2-C12 alkyl; and
poly(ethylene glycol) methyl ether having from 1-20 ethylene glycol subunits, and
wherein Q is a boron cluster anion and p is one or two.
7. The sodium electrochemical cell as recited in claim 6 , wherein the boron cluster anion has a formula [B y H (y-z-i) R z X i ] 2− , [CB( y-1 )H (y-z-i) R z X i ] − , [C 2 B (y-2) H (y-t-j-1) R t X j ] − , [C 2 B (y-3) H (y-t-j) R t X j ] − , or [C 2 B (y-3) H (y-t-j-1) R t X j ] 2− , and wherein:
y is an integer within a range of 6 to 12;
(z+i) is an integer within a range of 0 to y;
(t+j) is an integer within a range of 0 to (y−1);
X is F, Cl, Br, I, or a combination thereof; and
R is a substituent comprising any of:
group (i): a linear, branched-chain, or cyclic C1-C18 alkyl, perfluoroalkyl, or partially fluorinated alkyl group;
group (ii): a C6-C14 aryl, perfluoroaryl, or partially fluorinated aryl group;
group (iii): a linear, branched-chain, or cyclic C1-C18 alkoxy, perfluoroalkoxy, or partially fluorinated alkoxy group;
group (iv): a C6-C14 aryloxy, perfluoroaryloxy, or partially fluorinated aryloxy group; and
group (v): a substituent that combines moieties defined by two or more of groups (i)-(iv).
8. The sodium electrochemical cell as recited in claim 6 , wherein the electrolyte comprises a shuttle salt to improve transport of the active material between the anode and the cathode, the shuttle salt having an oxidized form of the active material as a cation.