NMR determination of trace water in lithium salts for battery electrolytes

The Karl Fischer titration is the standard method for the determination of the water content in many materials. However, in particular cases, unwanted side reactions occur which leads to unacceptably large errors. We present here an nuclear magnetron resonance (NMR)-based method for the determination of trace impurities of water in a salt recently developed for lithium ion cells, i.e., lithium bis[1,2-oxalato(2-)-O,O']borate (LiBOB). The method, which may be applied to many lithium salts used in batteries, is able to determine traces of water in the salt down to similar to 6 ppm. Errors depend strongly on the salt studied. Deviations from expected values obtained by standard addition were 28% for LiBOB, 4% for LiPF6, and 6% for LiClO4 . Using the error propagation law, we estimated an overall error of about 10%. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1859693] All rights reserved.