Intercalation pseudocapacitance in a NASICON-structured Na2CrTi(PO4)3@carbon nanocomposite: towards high-rate and long-lifespan sodium-ion-based energy storage

Sodium-based energy storage devices hold great promise as an alternative to the existing lithium-ion battery owing to their abundant resources with potentially low cost, while the sluggish kinetic properties and unsatisfactory cycle stability are two major issues limiting their practical application. Herein, we propose the dominating pseudocapacitive contribution in the new NASICON-type Na2CrTi(PO4)3@C material, which delivers a high reversible capacity over 220 mA h g−1 at 0.1C rate, superior rate performance with a specific capacity of 110 mA h g−1 at 20C and an ultralong cycling stability over 20 000 cycles. A strongly enhanced pseudocapacitive contribution is observed by quantitatively analysing CV profiles at various sweep rates, well explaining the origin of the superior rate capability. Structural evolution is also comprehensively investigated by in situ X-ray diffraction technology, suggestive of a solid-solution transition during Na+ reversible insertion/extraction. Moreover, a sodium-based battery–supercapacitor hybrid device is constructed, demonstrating high energy and power densities as well as a long lifespan. The findings obtained in this study not only provide a practicable route to realize superior performance for Na+ storage, but also offer a versatile anode for promising sodium-based energy storage devices.