Structures of Orthoborate Anions and Physical Properties of Their Lithium Salt Non-aqueous Solutions

We compare the physical properties and solution conductivities of three new lithium orthoborate salts with those of the well known slat lithium bis(trifluoromethanesulfony)imide LiTFSI. The three new lithium salts are lithium bis(perfluoropinacolato)borate (LiBPFPB), lithium bis(oxalato)borate (LiBOB) and lithium bis(malonato)borate (LiBMB). Computational models of the three orthoborate anions show that the borate oxygens in BPFPB anion are the least exposed. The oxygens are electronically identical in BPFPB, but not in the other anions. The three new lithium salts show conductivities that closely approach those of LiTFSI but show surprising and solvent-dependent orderings. The conductivity is nearly independent of the salt content in the salt concentration range of 0.5 ~ 1M, which is advantageous for their applications. Self-diffusivity measurements for Li, F and H are presented and are consistent with the very high ionic dissociation levels proposed for these salts on the basis of other evidence. Lithium ion * Electrochemical Society Student Member. # Present address: Institute of Polymer Science, University of Akron, Akron, OH 44325, USA. ** Electrochemical Society Active Member. Email: [email protected] PDF created with FinePrint pdfFactory trial version http://www.fineprint.com 2 transport number at room temperature for LiBPFPB in non-aqueous solutions exceeds 0.5 and for LiBMB is about 0.4.