Generation of Cathode Passivation Films via Oxidation of Lithium Bis(oxalato) Borate on High Voltage Spinel (LiNi 0.5

The reactions of lithium ion battery electrolyte (LiPF6 in ethylene carbonate/ethyl methyl, EC/EMC, 3:7 v/v) with and without added lithium bis(oxalato) borate (LiBOB) on the surface of high voltage LiNi 0.5Mn1.5O4 cathodes has been investigated via a combination of electrochemical measurements, in situ gas analysis, and ex situ surface analysis. The oxidation of LiBOB on the cathode results in the generation of CO2 and a cathode passivation film containing borate oxalates. The cathode passivation film inhibits oxidation of the bulk electrolyte at high potential (\u3e4.8 V vs Li/Li+). © 2014 American Chemical Society

Role of Solution Structure in Solid Electrolyte Interphase Formation on Graphite with LiPF 6

An investigation of the interrelationship of cycling performance, solution structure, and electrode surface film structure has been conducted for electrolytes composed of different concentrations of LiPF6 in propylene carbonate (PC) with a binder-free (BF) graphite electrode. Varying the concentration of LiPF6 changes the solution structure, altering the predominant mechanism of electrolyte reduction at the electrode interface. The change in mechanism results in a change in the structure of the solid electrolyte interface (SEI) and the reversible cycling of the cell. At low concentrations of LiPF6 in PC (1.2 M), electrochemical cycling and cyclic voltammetry (CV) of BF graphite electrodes reveal continuous electrolyte reduction and no lithiation/delithiation of the graphite. The solution structure is dominated by solvent-separated ion pairs (Li+(PC) 4//PF6-), and the primary reduction product of the electrolyte is lithium propylene dicarbonate (LPDC). At high concentrations of LiPF6 in PC (3.0-3.5 M), electrochemical cycling and CV reveal reversible lithiation/delithiation of the graphite electrode. The solution structure is dominated by contact ion pairs (Li+(PC) 3PF6-), and the primary reduction product of the electrolyte is LiF. © 2013 American Chemical Society