Boosting sodium storage properties of titanium dioxide by a multiscale design based on MOF-derived strategy

Cost-effective sodium-ion batteries (SIBs) are the most promising candidate for grid-scale energy storage. However, the lack of suitable high-performance anode materials has hindered their large-scale applications. In this study, we report a multiscale design to optimize a TiO2-based anode from atomic, microstructural, and macrostructural levels. A key point in our design is the use of Co-doped amine-functionalized Ti-MOFs as multifunctional precursors, which not only achieves Co, N double-doping, and encapsulation of ultrafine TiO2 nanoparticles in mesoporous C frameworks, but also endows the precursors with positive surface charges, driving them to combine with graphene nanosheets into a 3D macroporous network architecture by self-assembly. The well-designed anode delivered high reversible capacities of 174 mA h g(-1) at 6 C for over 5000 cycles, 121 mA h g(-1) at 15 C for over 10,000 cycles, and 100mA h g(-1) at 30 C for over 3000 cycles, demonstrating the most efficient TiO2-based anode ever reported for SIBs. The unprecedented sodium storage performance is attributed to the multiscale integration yielding a high content of oxygen vacancies, 3D continuous conductive networks, and open diffusion channels, promoting both electron conduction and Na+ diffusion not only inside and around the TiO2 nanoparticles but also through overall electrode. The unique multiscale design based on MOF-derived strategy holds great potential in generalizable synthesis of versatile electrode materials for advanced battery systems.