Boron Doped Defected Graphene: A Promising Anode Material for Li-Ion Battery

Li ion batteries (LIB) are most promising energy storage devices for today’s technologies due to their size, portability, and superior performance. In the search of an anode material having specific capacity far beyond that of the existing commercially used graphite (372 mAh g⁻¹ ), graphene emerges as a strong candidate for anode materials in Li ion battery due to its high surface area, high electrical conductivity, robust mechanical integrity and high capacity of about 540 mAh g⁻¹. The success of graphene as an anode material depends strongly on the diffusion kinetics of Li, through and across the graphene sheet. Here, we study the Li diffusion through and across the graphene sheet using first principle calculations. We found that for pristine graphene, across diffusion barrier is several orders less than the through diffusion barrier. In order to reduce the energy barrier more, we investigated Li diffusion through and across the graphene with most commonly observed defects. The barriers reduce significantly by the presence of defects, with di-vacancy having lowest barrier of 1.34 eV for through diffusion and Stone Wales having 0.13 eV for across diffusion. We explore doping as another alternative to manipulate Li diffusion rate. We studied the effect of both boron and nitrogen doping by calculating the energy barrier through the defected doped graphene sheets. The height of the barrier depends sensitively on the concentration and type of dopants. While, nitrogen doping in defected graphene leads to strong binding, boron doped defected graphene show consistently low barriers. Boron doping in mono-vacancy and di-vacancy graphene leads to better anode materials for across and through diffusion, respectively. 

Reference

1. D. Das, S. Kim, K-R. Lee, and A. K. Singh, Li diffusion through the doped and defected graphene, PCCP 15, 15128 (2013)
2. R. P. Hardikar, D. Das, S. S. Han, K-R. Lee, and A. K. Singh, Boron doped defected graphene as promising anode materials for Li-ion batteries, submitted