Modulation of Ionic Current Limitations by Doping Graphite Anodes

Abstract

Density functional theory calculations were performed to study the impact of carbon site doping on akali metal intercalation behavior into graphite compounds. Substitutional boron doping was shown to effectively increase the intercalation potential of graphite versus both lithium and sodium metal anodes. The reduced graphite Fermi level of boron doped graphite was shifted away from the π* antibonding domain toward the more stable π bonds, hence lowering the reduction potential and improving the formation energy for the intercalated graphite. It was further discussed how such methods could be used to improve the intrinsic rate capability of graphite anodes in lithium ion batteries and also enable the use of graphite anodes in sodium ion batteries. We derive an expression representing the transition between thermodynamically favorable intercalation and kinetically favorable metal plating in terms of the applied current. For currents below this transition level, plating should be minimal. This transition point is shown to grow with intercalation voltage, hence higher current capability in acceptor doped systems.