Work

Impact of lithium composition on the thermoelectric properties of the layered cobalt oxide system Li x CoO 2

Year: 2011

Type: article

Abstract: Thermoelectric properties of the layered cobalt oxide system Li${}_{x}$CoO${}_{2}$ were investigated in a wide range of Li compositions, 0.98 \ensuremath{\geqslant} $x$ \ensuremath{\geqslant} 0.35. Single-phase bulk samples of Li${}_{x}$CoO${}_{2}$ were successfully obtained through electrochemical deintercalation of Li from the pristine LiCoO${}_{2}$ phase. While Li${}_{x}$CoO${}_{2}$ with $x$ \ensuremath{\geqslant} 0.94 is semiconductive, the highly Li-deficient phase (0.75 \ensuremath{\geqslant} $x$ \ensuremath{\geqslant} 0.35) exhibits metallic conductivity. The magnitude of the Seebeck coefficient at 293 K (${S}_{293\mathrm{K}}$) significantly depends on the Li content ($x$). The ${S}_{293\mathrm{K}}$ value is as large as $+$70 up to $+$100 \ensuremath{\mu}V/K for $x$ \ensuremath{\geqslant} 0.94, and it rapidly decreases from $+$90 \ensuremath{\mu}V/K to $+$10 \ensuremath{\mu}V/K as $x$ is lowered within a Li composition range of 0.75 \ensuremath{\geqslant} $x$ \ensuremath{\geqslant} 0.50. This behavior is in sharp contrast to the results of $x$ \ensuremath{\leqslant} 0.40 for which the ${S}_{293\mathrm{K}}$ value is small and independent of $x$ (+10 \ensuremath{\mu}V/K), indicating that a discontinuous change in the thermoelectric characteristics takes place at $x$ $=$ 0.40--0.50. The unusually large Seebeck coefficient and metallic conductivity are found to coexist in a narrow range of Li composition at about $x$ $=$ 0.75. The coexistence, which leads to an enhanced thermoelectric power factor, may be attributed to unusual electronic structure of the two-dimensional CoO${}_{2}$ block.

Source: Physical Review B

DOI: 10.1103/physrevb.83.195128