New and novel lithium imide electrolytes and copolymers: synthesis and characterization for lithium rechargeable batteries

Abstract

Several new and novel lithium imide salts were synthesized and characterized for their conductivities and electrochemical stabilities in nonaqueous solvent mixtures. Many copolymers and diblock copolymers using monomers such as polyethylene glycol methacrylate of different molecular weights and/or poly (lauryl methacrylate) were synthesized and characterized. Solid polymer electrolytes with promising lithium salts and copolymers were prepared with different Li/O ratios and varying ratios of copolymers and polyethylene oxide with inert additives. Their conductivities and electrochemical stabilities were measured. All lithium imide salts and copolymer based solid polymer electrolyte films are found to be stable from 0 to 4.5 V versus lithium. The solubilities and the conductivities of Lithium imide salts are found to depend on their structure. The physical properties of copolymers are known to depend on the type and the molecular weight of the monomer used and the polymerization process. The solid polymer electrolyte films containing a large fraction of the copolymers in the mixture with polyethylene oxide and lithium salts show much improved conductivity at room temperature. Both the solid polymer electrolyte films and the lithium imide salt solutions have been used in lithium cells to evaluate their performance. The performance data of cells with these electrolytes are discussed in terms of their structures and compositions.