  We present a comparative ab initio computational study of sodium and lithium
storage in amorphous (glassy) carbon (a-C) vs. graphite. Amorphous structures
are obtained by fitting stochastically generated structures to a reference
radial distribution function. Li insertion is thermodynamically favored in both
graphite and a-C. While sodium insertion is thermodynamically unfavored in
graphite, a-C possesses multiple insertion sites with binding energies stronger
than Na cohesive energy, making it usable as anode material for Na-ion
batteries.
