| One of the large controversies regarding lithium cathodes concerns the arrangement of the local electronic environments in the host material and how these environments are affected by lithium intercalation. Electron energy-loss spectrometry was used to study charge compensation in lithiated transition-metal oxides (e.g., LiCoO2 and LiNi0.8Co0.2O 2) during electrochemical cycling. The oxygen K-edge and transition metal L2,3 white lines were used to probe the oxygen 2p and transition metal 3d states, respectively. These results show a large increase in state occupancy of the oxygen 2p band during lithiation, suggesting that much of the lithium 2s electron is accommodated by the anion. Ab initio calculations of the oxygen 2p partial density of states curves confirm the increase in unoccupied states that accompany lithium extraction. In contrast with the large changes observed in the oxygen K-edge, much smaller changes were observed in the transition metal L2,3 white lines. Surprisingly, for layered LiCoO 2 and Li(Ni, Co)O2, the transition metal valence changes little during the charge compensation accompanying lithiation.; Recent demand for alternatives to graphitic carbon for lithium anodes motivated an investigation into novel binary lithium alloys. The large volume expansions associated with lithium insertion is known to generate tremendous microstructural damage, making most alloys unsuitable for rechargeable lithium batteries. Electrodes of nanostructured lithium alloys were prepared in an attempt to mitigate the particle decrepitation that occurs during cycling and to shorten diffusion times for lithium. Anodes of silicon and germanium were prepared in thin film form as nanocrystalline particles (10 nm mean diameter) and as continuous amorphous thin films (60–250 nm thick). These nanostructured materials exhibited stable capacities up to six times larger than what is found in graphitic carbons, which are currently the industry standard. In addition, these electrodes do not suffer from particle decrepitation and therefore exhibit excellent cycle life. The reversibility of these electrodes is attributed to the nanoscale dimensions, which circumvent conventional mechanisms of mechanical deterioration. Nanostructured Li-Si and Li-Ge exhibit the highest reversible electrochemical capacities yet reported for an alloy electrode. |
