Electrochemical cells with ionic liquid electrolyte

A battery pack comprising a plurality of cells, wherein each cell comprises:

• an ionic liquid of formula (I):
• Q+E−(I)
• wherein
• Q+ is a cation selected from the group consisting of dialkylammonium, trialkylammonium, tetraalkylammonium, dialkylphosphonium, trialkylphosphonium, tetraalkylphosphonium, trialkylsulfonium, (Rf)4N+ and an N-alkyl or N-hydrogen cation of a 5- or 6-membered heterocycloalkyl or heteroaryl ring having from 1-3 heteroatoms as ring members selected from N, O or S, wherein the heterocycloalkyl or heteroaryl ring is optionally substituted with from 1-5 optionally substituted alkyls;
• E−is an anion selected from the group consisting of R1—X−R2(R3)m, NC—S−, BF4−, PF6−, RaSO3−, RaP−F3, RaCO2−, I−, ClO4−, (FSO2)2N—, AsF6−, SO4− and bis[oxalate(2-)O,O′]borate, wherein
• m is 0 or 1;
• X is N when m is 0;
• X is C when m is 1;
• R1, R2 and R3 are each independently an electron-withdrawing group selected from the group consisting of halogen, —CN, —SO2Rb, —SO2-La-SO2N−Li+SO2Rb, —P(O)(ORb)2, —P(O)(Rb)2, —CO2Rb, —C(O)Rb and —H;
• with the proviso that R1 and R2 are other than hydrogen when m=0, and no more than one of R1, R2 and R3 is hydrogen when m=1;
• each Ra is independently C1-8perfluoroalkyl;
• each Rb is independently selected from the group consisting of C1-8alkyl, C1-8haloalkyl, C1-8 perfluoroalkyl, perfluorophenyl, aryl, optionally substituted barbituric acid and optionally substituted thiobarbituric acid;
• each Rf is independently alkyl or alkoxyalkyl;
• and
• wherein at least one carbon-carbon bond of the alkyl or perfluoroalkyl are optionally substituted with a member selected from —O— or —S— to form an ether or a thioether linkage and the aryl is optionally substituted with from 1-5 members selected from the group consisting of halogen, C1-4haloalkyl, C1-4perfluoroalkyl, —CN, —SO2Rc, —P(O)(ORc)2, —P(O)(Rc)2, —CO2Rc and —C(O)Rc, wherein Rc is independently C1-8 alkyl, C1-8 perfluoroalkyl or perfluorophenyl and La is C1-4perfluoroalkylene;
• and
• a positive electrode comprising a positive electrode active material and a free-standing carbon sheet current collector in electronically conductive contact with the positive electrode material, wherein the carbon sheet current collector has a purity of greater than 95% and an in-plane electronic conductivity of at least 1000 S/cm.

A lithium-ion electrochemical cell comprising:

• a positive electrode comprising a positive electrode active material and a free-standing carbon sheet current collector in electronically conductive contact with the positive electrode material, wherein the carbon sheet current collector has a purity of greater than 95% and an in-plane electronic conductivity of at least 1000 S/cm;
• a negative electrode comprising a negative electrode active material and a current collector in electronically conductive contact with the negative electrode material;
• at least one positive electrode tab having a first attachment end and a second attachment end, wherein the first attachment end of said at least one positive electrode tab is connected to said positive electrode carbon sheet current collector;
• at least one negative electrode tab having a first attachment end and a second attachment end, wherein said first attachment end of said at least one negative electrode tab is connected to said negative electrode current collector;
• an ion permeable separator;
• and
• an electrolyte solution in ionically conductive contact with said negative electrode and positive electrode, wherein the electrolyte solution comprises a lithium compound and a solvent selected from an ionic liquid of formula (I) or a mixture of an organic solvent and an ionic liquid of formula (I):
• Q+E− (I)
• wherein
• Q+ is a cation selected from the group consisting of dialkylammonium, trialkylammonium, tetraalkylammonium, dialkylphosphonium, trialkylphosphonium, tetraalkylphosphonium, trialkylsulfonium, (Rf)4N+ and an N-alkyl or N-hydrogen cation of a 5- or 6-membered heterocycloalkyl or heteroaryl ring having from 1-3 heteroatoms as ring members selected from N, O or S, wherein the heterocycloalkyl or heteroaryl ring is optionally substituted with from 1-5 optionally substituted alkyls;
• E− is an anion selected from the group consisting of R1—X−R2(R3)m, NC—S−, BF4−, PF6−, RaSO3−, RaP−F3, RaCO2−, I−, ClO4−, (FSO2)2N—, AsF6−, SO4− and bis[oxalate(2-)-O,O′]borate, wherein
• m is 0 or 1;
• X is N when m is 0;
• X is C when m is 1;
• R1, R2 and R3 are each independently an electron-withdrawing group selected from the group consisting of halogen, —CN, —SO2Rb, —SO2-La-SO2N−Li+SO2Rb, —P(O)(ORb)2, —P(O)(Rb)2, —CO2Rb, —C(O)Rb and —H;
• with the proviso that R1 and R2 are other than hydrogen when m=0, and no more than one of R1, R2 and R3 is hydrogen when m=1;
• each Ra is independently C1-8perfluoroalkyl;
• each Rb is independently selected from the group consisting of C1-8alkyl, C1-8haloalkyl, C1-8 perfluoroalkyl, perfluorophenyl, aryl, optionally substituted barbituric acid and optionally substituted thiobarbituric acid;
• each Rf is independently alkyl or alkoxyalkyl;
• and
• wherein at least one carbon-carbon bond of the alkyl or perfluoroalkyl are optionally substituted with a member selected from —O— or —S— to form an ether or a thioether linkage and the aryl is optionally substituted with from 1-5 members selected from the group consisting of halogen, C1-4haloalkyl, C1-4perfluoroalkyl, —CN, —SO2Rc, —P(O)(ORc)2, —P(O)(ORc)2, —P(O)(Rc)2, —CO2Rc and —C(O)Rc, wherein Rc is independently C1-8 alkyl, C1-8 perfluoroalkyl or perfluorophenyl and La is C1-4perfluoroalkylene.