Interface-Driven Pseudocapacitance Endowing Sandwiched CoSe 2 /N-Doped Carbon/TiO 2 Microcubes with Ultra-Stable Sodium Storage and Long-Term Cycling Stability.

Cobalt diselenide (CoSe 2 ) has drawn great concern as an anode material for sodium-ion batteries due to its considerable theoretical capacity. Nevertheless, the poor cycling stability and rate performance still impede its practical implantation. Here, CoSe 2 /nitrogen-doped carbon-skeleton hybrid microcubes with a TiO 2 layer (denoted as TNC-CoSe 2 ) are favorably prepared via a facile template-engaged strategy, in which a TiO 2 -coated Prussian blue analogue of Co 3 [Co(CN) 6 ] 2 is used as a new precursor accompanied with a selenization procedure. Such structures can concurrently boost ion and electron diffusion kinetics and inhibit the structural degradation during cycling through the close contact between the TiO 2 layer and NC-CoSe 2 . Besides, this hybrid structure promotes the superior Na-ion intercalation pseudocapacitance due to the well-designed interfaces. The as-prepared TNC-CoSe 2 microcubes exhibit a superior cycling capability (511 mA h g -1 at 0.2 A g -1 after 200 cycles) and long cycling life (456 mA h g -1 at 6.4 A g -1 for 6000 cycles with a retention of 92.7%). Coupled with a sodium vanadium fluorophosphate (Na 3 V 2 (PO 4 ) 2 F 3 )@C cathode, this assembled full cell displays a specific capacity of 281 mA h g -1 at 0.2 A g -1 for 100 cycles. This work can be potentially used to improve other metal selenide-based anodes for rechargeable batteries.