Insights into Electrochemical Reactions in High Voltage Electrode Materials for Li Ion Batteries

High voltage batteries are commercially attractive because they lead to high energy densities. LiCoPO4 is one such promising electrode material owing to its high theoretical energy density and low cost. Despite the promising upside, LiCoPO4 has failed to penetrate the market due to fading of storage capacity that arises during electrochemical cycling. To address this problem, ion substitution of Co by other metals (such as Fe, Mn, Cr) has been utilized to improve electrochemical performance without sacrificing energy density. The mechanism behind the drastic electrochemical improvements is revealed through a spectroscopic study on how ion substitution affects the electronic structure at both the surface and bulk of the electrode. The bulk crystallographic changes that take place in LiCoPO4 and ion substituted derivatives during electrochemical cycling are also discussed based on operando x-ray diffraction data. Dual graphite batteries are also explored as high voltage, environmentally friendly, alternatives to conventional Li ion batteries. The electronic and structural changes that take place within a graphite electrode during anion intercalation are discussed. Spectroscopic techniques sensitive to the electrode bulk and surface show intercalation coincides with a lowering of the Fermi level and the generation of new unoccupied states in the graphite electronic structure.