Mn3O4 nanoparticles in situ embedded in TiO2 for High-Performance Na-ion capacitor: Balance between 3D ordered hierarchically porous structure and heterostructured interfaces

Sodium-ion hybrid capacitors (SICs) are recognized as a promising new energy storage devices. The design of anodes with high rates to balance the fast desorption/adsorption process in cathode is a key way to construct desirable SICs. Herein, Mn3O4 nanoparticles are in situ embedded in TiO2 to form Mn3O4@TiO2 nanocomposite as anode for SICs. The prepared Mn3O4@TiO2 nanocomposite shows hierarchically porous structure with macropores and mesopores. The Mn3O4 content in the composites can be adjusted to achieve the balance between the hierarchically porous structure and heterostructured Mn3O4/TiO2 interfaces. The optimized Mn3O4@TiO2 with ∼30 wt% Mn3O4 achieves this balance, delivering a large discharge capacity of 247.8 mAh g−1 at 1 A g−1 after 1000 cycles in SIBs. The assembled SICs by using Mn3O4@TiO2-2 as anode and commercial activated carbon as cathode can achieve a high energy and power densities of 106.5 Wh kg−1 and 10140.5 W kg−1, respectively, and an extended cycle life of 92.8 % retention after 5000 cycles. The good Na-ion storage performance mainly arises from the macropores that can provide rapid mass transfer channels, the mesopores that can offer high specific surface areas and highly dispersed Mn3O4 nanoparticles and abundant Mn3O4/TiO2 interfaces that can afford a lot of active sites.