Fluorinated ionic liquids for multi-layer Li ion battery applications
Fluorinated ionic liquids have been prepared to be used as catholytes in lithium battery cells. Such ionic liquids are immiscible with polyethylene-oxide-based solid polymer electrolytes, which may be used as separators in such cells. Such catholytes can increase the lifetime and boost the performance of lithium battery cells.
1. An electrochemical cell, comprising: a negative electrode configured to absorb and release alkali metal ions; a positive electrode comprising a positive electrode active material, a binder, a fluorinated ionic liquid catholyte, a first salt comprising an alkali metal, and, optionally, electronically conducting carbon; a separator layer comprising a block copolymer electrolyte and a second salt comprising the alkali metal, the separator layer disposed between the negative electrode and the positive electrode and facilitates ionic communication therebetween; and wherein the fluorinated ionic liquid catholyte is immiscible with the block copolymer electrolyte; and wherein the fluorinated ionic liquid catholyte is
wherein X is TFSI; R is hydrogen; Rf is (CF2) a CF 3 , in which a is 7; and n is 2.
2. The electrochemical cell of claim 1 wherein a first block of the block copolymer electrolyte is ionically conductive and is a polyether.
3. The electrochemical cell of claim 2 wherein a second block of the block copolymer electrolyte is polystyrene.
4. The electrochemical cell of claim 1 wherein the alkali metal comprises lithium and the first salt and the second salt are each selected independently from the group consisting of LiTFSI, LiFSI, LiPF 6 , LiFAP, LiBF 4 , LiClO 4 , LiOTf, LiC(Tf) 3 , LiBOB, and LiDFOB.
5. The electrochemical cell of claim 4 wherein the first salt and the second salt are the same.
6. The electrochemical cell of claim 1 wherein the negative electrode is a lithium-containing metal foil, and the first salt and the second salt are both lithium salts.