  Measurements of electrical resistivity ($\rho$), DC magnetization ($M$) and
specific heat ($C$) have been performed on layered oxide Li$_x$CoO$_2$
(0.25$\leq$$x$$\leq$0.99) using single crystal specimens. The $\rho$ versus
temperature ($T$) curve for $x$=0.90 and 0.99 is found to be insulating but a
metallic behavior is observed for 0.25$\leq$$x$$\leq$0.71. At $T_{\rm
S}$$\sim$155 K, a sharp anomaly is observed in the $\rho$$-$$T$, $M$$-$$T$ and
$C$$/$$T$$-$$T$ curves for $x$=0.66 with thermal hysteresis, indicating the
first-order charactor of the transition. The transition at $T_{\rm S}$$\sim$155
K is observed for the wide range of $x$=0.46$-$0.71. It is found that the
$M$$-$$T$ curve measured after rapid cool becomes different from that after
slow cool below $T_{\rm F}$, which is $\sim$130 K for $x$=0.46$-$0.71. $T_{\rm
F}$ is found to agree with the temperature at which the motional narrowing in
the $^7$Li NMR line width is observed, indicating that the Li ions stop
diffusing and order at the regular site below $T_{\rm F}$. The ordering of Li
ions below $T_{\rm F}$$\sim$130 K is likely to be triggered and stabilized by
the charge ordering in CoO$_2$ layers below $T_{\rm S}$.
