'Li'BC: synthesis, electrochemical and solid-state NMR investigations

Abstract

'LI'BC was synthesized from the elements in a sealed niobium ampoule. It represents a totally intercalated heterographite with a structural relationship to graphite, the most commonly used anode material for lithium ion batteries. Since 'LI"BC could accommodate three times as much lithium as graphite, its electrochemical properties in the anode and the cathode voltage range were investigated. However, 'LI'BC did show poor performance both as an anode and as a cathode material. The unfavorable characteristics of 'LI'BC with respect to electrochemical de-lithiation and re-insertion can be rationalized on the basis of nuclear magnetic resonance results. 'ANTIPOT. 7 LI' and 'ANTIPOT. 6 LI' isotropic chemical shifts are consistent with complete ionization of the lithium species. Variable-temperature static 'ANTIPOT 7 LI' NMR lineshapes indicate that the mobility of the lithium ions is rather restricted, even at temperatures up to 500 K. The 'ANTIPOT. 11 B' and 'ANTIPOT. 13 C' NMR parameters are consistent with those measured in 'sp POT. 2'-hybridized boron/carbon networks and also support the ionic bonding model.