Reversible Sodium Storage of CoTe2 Anode via Lanthanum Doping

Cobalt telluride (CoTe2) is considered an advanced anode material for sodium-ion batteries (SIBs) because of its high theoretical capacity and high conductivity. Nevertheless, the ionic radius of the Co2+ ion (0.74 Å) is smaller than that of the Na+ ion, meaning the integrity of CoTe2 electrodes can be easily damaged when Na+ ions diffuse into CoTe2 and convert to large Na2Te. Herein, we propose a doping strategy by introducing an unreactive element but with a large radius to enhance the overall performance. Lanthanum (La) can be doped into the CoTe2 structure to counteract the size effect of Na2Te since La has a large radius. On the other hand, La with abundant electrons in CoTe2 can also facilitate the charge transfer during charge/discharge. As a result, La-doped CoTe2 (La-CoTe2) can deliver a maximum capacity of 345 mAh g−1 at 0.05 A g−1 and has a decent rate performance. After 2000 cycles at 2 A g−1, a capacity of 88 mAh g−1 remained, which is a notable improvement compared to undoped CoTe2. These results demonstrate the potential of rare earth elements in preparing advanced SIB electrode materials.