The invention provides novel lithium salts of pentafluorophenylamide in particular lithium pentafluorophenyl(trifluoromethylsulfonyl)imide (Li-PFTFSI). Li-PFTFSI has improved thermal stability and ion mobility compared to known lithium salts. It is also electrochemically stable near the reduction potential of lithium and has a wide electrochemical window of over 4.0V. Furthermore Li-PFTFSI is resistant to hydrolysis. These characteristics make Li-PFTFSI desirable for use as electrolytes in lithium ion batteries.