Use of Rutherford Backscattering Spectrometry for studying the passivationof materials of rechargeable batteries: application to petroleum coke in LiCF3SO3/carbonates mixture electrolyte

The evolution of the passivating layer (during the first reduction/reoxidat ion cycle, in function of the number of reduction/reoxidation cycles and wi th the storage of the electrode in the electrolyte) formed at the surface o f a lithiated carbon electrode in LiCF3SO3/carbonates mixture electrolyte h as been followed by using 1 MeV He-4(+) induced Rutherford Backscattering S pectrometry (RBS). Two RES simulation codes " RUMP" and "PERM ", whose appr oaches are different, have been applied to the treatment of the RES data an d have allowed to obtain informations about the structure (thickness and at omic elemental composition) of the passivating layer. These two codes provi de similar results. The passivating layer has a thickness in the range 20-3 0 nm. Its structure appears to be complex with the presence of two differen t sublayers respectively composed of the reduction products of the salt in the inner sublayer (with the main presence of fluorine and sulphur indicati ng the possible existence of LiF and Li2S) and reduction products of the so lvents in the outer sublayer (with a high concentration in oxygen indicatin g the presence of Li2CO3 and RCO3Li where R is an alkyl radical).