Self-supporting Fe7S8 microsphere/N-doped carbonized silk textile for high-performance sodium-ion batteries†

High-performance sodium-ion batteries (SIBs) represent an optimal energy solution for flexible wearable devices, with the design and development of advanced anodes being crucial in determining their overall performance. A major challenge for flexible electrodes is achieving both high energy density and long-term cycle stability. To address these issues, a Fe₇S₈ microsphere/N-doped carbonized silk textile as a self-supporting anode for SIBs is developed. Fe₇S₈ microspheres are anchored onto a three-dimensional carbon network derived from silk fabric via electrostatic adsorption followed by calcination. The as-prepared flexible self-supporting Fe₇S₈ microsphere/N-doped carbonized silk textile demonstrates exceptional mechanical durability, maintaining structural integrity and stable resistance after 2000 bending cycles. Electrochemical performance shows a notable areal capacity of 1.42 mA h cm⁻² at 0.3 mA cm⁻², along with impressive cycling stability. After 600 cycles at 5 mA cm⁻², it maintains 0.39 mA h cm⁻², with a modest capacity loss of 21% at high current density. It also demonstrates excellent rate performance, achieving reversible capacities of 1.67, 1.32, 1.12, 0.87, 0.71 and 0.37 mA h cm⁻² at current densities of 0.1, 0.3, 0.5, 1, 2 and 5 mA cm⁻², respectively. The microsphere structure of Fe₇S₈ ensures extensive contact with the electrolyte, enhancing ion accessibility and structural stability. The carbonized silk textile provides higher flexibility, which helps alleviate strain during deformation. Simultaneously, the N-doped carbon network derived from silk fabric offers additional Na⁺ adsorption sites, and facilitates efficient electron and ion transport. Moreover, the excellent mechanical flexibility of the electrode offers promising prospects for its potential application in flexible wearable electronic devices.