Lanthanide doping induced electrochemical enhancement of Na₂Ti₃O₇ anodes for sodium-ion batteries

Na₂Ti₃O₇ is considered as a promising anode material for sodium ion batteries (SIBs) due to its excellent high-rate performance compared with hard carbons. However, the electrochemical performance of Na₂Ti₃O₇ is heavily limited by its low electrical conductivity. In this study, we synthesized a series of lanthanide (Ln = La, Ce, Nd, Sm, Gd, Er, and Yb) doped microsized Na₂Ti₃O₇ anode materials and systematically studied the electrochemical performance. Compared with pristine Na₂Ti₃O₇, all the doped samples show superior electrochemical performance. Especially, the Yb³⁺ doped sample not only delivers a high reversible capacity of 89.4 mA h g^-1 at 30C, but also maintains 71.6 mA h g^-1 at 5C after 1600 cycles, nearly twice that of pristine Na₂Ti₃O₇. It is found for the first time that the enhancement in doped samples is attributed to the introduction of lanthanides which induces lattice distortion and oxygen vacancies.