  Within the charge-spin separation fermion-spin theory, we have shown that the
mechanism of superconductivity in the electron doped cobaltate
Na$_{x}$CoO$_{2}\cdot y$H$_{2}$O is ascribed to its kinetic energy. The dressed
fermions interact occurring directly through the kinetic energy by exchanging
magnetic excitations. This interaction leads to a net attractive force between
dressed fermions, then the electron Cooper pairs originating from the dressed
fermion pairing state are due to the charge-spin recombination, and their
condensation reveals the superconducting ground state. The superconducting
transition temperature is identical to the dressed fermion pair transition
temperature, and is suppressed to a lower temperature due to the strong
magnetic frustration. The optimal superconducting transition temperature occurs
in the electron doping concentration $\delta\approx 0.29$, and then decreases
for both underdoped and overdoped regimes, in qualitative agreement with the
experimental results.
