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

Co 3 O 4 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, TiO 2 containing cation vacancies is employed as a structural matrix to anchor Co 3 O 4 nanoparticles. The presence of cation vacancies facilitates the formation of a TiO 2 /Co 3 O 4 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 TiO 2 /Co 3 O 4 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.