Vacancy-Assisted Construction of a Co ₃ O ₄ /TiO ₂ Heterostructure with PPy Coating for Sodium-Ion Battery Anodes

Co3O4 has emerged as a promising electrode material for sodium-ion batteries (NIBs) owing to its high initial specific capacity and natural abundance. However, its practical application is severely limited by rapid capacity degradation caused by drastic volume fluctuations during repeated cycling. In this work, TiO2 containing cation vacancies is employed as a structural matrix to anchor Co3O4 nanoparticles. The presence of cation vacancies facilitates the formation of a TiO2/Co3O4 heterostructure, which exhibits a markedly improved electrochemical performance compared with a simple mechanical mixture of the two components. This improvement is mainly attributed to the increased interfacial sodium storage sites and the alleviated volume deformation. Furthermore, conformal PPy coating is introduced to enhance charge-transfer kinetics and maintain structural integrity. As a result, the PPy-coated TiO2/Co3O4 composite (TCOP) delivers a reversible discharge capacity of 159.7 mAh g–1 at 50 mA g–1 after 100 cycles. Even at a high current density of 1 A g–1, TCOP retains a capacity of ∼100 mAh g–1 after 500 cycles.