  Graphite intercalation compounds (GICs) have a variety of functions due to
their rich material variations, and thus,innovative methods for their synthesis
are desired for practical applications. We have discovered that Na has a
catalytic property that dramatically accelerates the formation of GICs. We
demonstrate that LiC6n (n = 1, 2), KC8, KC12n (n = 2, 3, 4), and NaCx are
synthesized simply by mixing alkali metals and graphite powder with Na at room
temperature (~25 {\deg}C), and AEC6 (AE = Ca, Sr, Ba) are synthesized by
heating Na-added reagents at 250 {\deg}C only for a few hours. The NaCx, formed
by the mixing of C and Na, is understood to act as a reaction intermediate for
a catalyst, thereby accelerating the formation of GICs by lowering the
activation energy of intercalation. The Na-catalyzed method, which enables the
rapid and mass synthesis of homogeneous GIC samples in a significantly simpler
manner than conventional methods, is anticipated to stimulate research and
development for GIC applications.
