LiBC – Synthesis, Electrochemical and Solid-state NMR Investigations

Abstract

LiBC 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 LiBC could accommodate three times as much lithium as graphite, its electrochemical properties in the anode and the cathode voltage range were investigated. However, LiBC did show poor performance both as an anode and as a cathode material. The unfavorable characteristics of LiBC with respect to electrochemical de-lithiation and re-insertion can be rationalized on the basis of nuclear magnetic resonance results. 7Li and 6Li isotropic chemical shifts are consistent with complete ionization of the lithium species. Variable-temperature static 7Li NMR lineshapes indicate that the mobility of the lithium ions is rather restricted, even at temperatures up to 500 K. The 11B and 13C NMR parameters are consistent with those measured in sp2-hybridized boron/carbon networks and also support the ionic bonding model.