  Within the t-J model, the heat transport of electron-doped cobaltates is
studied based on the fermion-spin theory. It is shown that the temperature
dependent thermal conductivity is characterized by the low temperature peak
located at a finite temperature. The thermal conductivity increases
monotonously with increasing temperature at low temperatures T $<$ 0.1$J$, and
then decreases with increasing temperature for higher temperatures T $>$
0.1$J$, in qualitative agreement with experimental result observed from
Na$_{x}$CoO$_{2}$ .
