Copper-doped sodium titanate with a hierarchical micro/nano structure as an anode material for Na-ion batteries

Na2Ti3O7 has attracted attention as an alternative to hard carbon anode for Na-ion batteries due to suitable sodiation potential and, hence, no serious safety issues at high current densities. However, unfavorable electronic transport properties of Na2Ti3O7 need to be addressed to make it applicable for practice. Herein, a hydrothermal method was adopted to fabricate Na2Ti3O7 having a hierarchical micro/nano architecture and to dope it with copper through one stage. As compared to the non-doped Na2Ti3O7, the copper-containing product shows increased electronic conductivity (2.5 times higher) due to a smaller band gap (reduced by ∼1 eV). Because of Cu-doping, the Na2Ti3O7 crystal structure has evolved, and its unit cell volume has increased by about 9.5 %. Doping with Cu enhances the electrochemical performance of Na2Ti3O7 in Na-ion batteries, which demonstrates higher rate capability (2.0–2.5 times more capacity at high current densities) and remarkable cycleability (85 % capacity retention over 300 cycles at 2C). The calculations show that Cu-doped Na2Ti3O7 is characterized by improved Na+ ion diffusion and increased contribution of the pseudocapacitive current during the sodiation–desodiation process. The research discloses the aspects of copper-doping strategy that enable to unfold the capability of Na2Ti3O7 for energy storage applications.