Controllable Synthesis of Anatase TiO₂ Nanosheets Grown on Amorphous TiO₂/C Frameworks for Ultrafast Pseudocapacitive Sodium Storage

Abstract

Pseudocapacitance has been confirmed to significantly improve the rate capability and cycling durability of electrode materials. However, rational design and controllable synthesis of intercalation pseudocapacitive materials for sodium-ion batteries (SIBs) still remain greatly challenging. Herein, a core-shell TiO₂-based anode composed of S-, Co-, and N-doped amorphous TiO₂/C framework cores and ultrathin anatase TiO₂ nanosheet shells (SCN-TC@UT) was synthesized using Ti-based metal-organic frameworks (Ti-MOFs) as self-sacrificing templates coupled with a solvothermal sulfidation process. Thanks to heteroatom doping, integration of carbon species, and 2D nanosheet coating, the kinetic properties of SCN-TC@UT have been significantly improved. As a consequence, the anode achieves ultrahigh capacitive contributions up to 90.9 and 96.3% of the total capacity at scan rates of 5 and 10 mV s^-1 and delivers unprecedented capacities of 211, 201, and 100 mA h g^-1 at 1, 5, and 30 C (1 C=335 mA g^-1) for over 800, 2000, and 18,000 cycles, respectively. Even at an ultrahigh rate of 50 C, the anode can still deliver a capacity of 108 mA h g^-1. This work demonstrates the most efficient TiO₂-based anode ever reported for SIBs and holds great potential in directing the development of amorphous materials for intercalation pseudocapacitance.