Tailoring superficial morphology, defect and functional group of commercial carbon cloth for a flexible, stable and high-capacity anode in sodium ion battery

Abstract Developing a flexible hard carbon-based anode is very important for the flexible sodium ion battery. Here, a porous carbon cloth with lots of defects and C=O functional groups is prepared by combining the thermal etching with oxidation-exfoliation method. The partial graphitization and N and S codoping improve the conductivity and electrochemical properties. Multi-step modifications stabilize the defects, which is proved by in situ Raman and leads to the enhanced initial coulombic efficiency. Benefiting from the increased interlayer distance, C=O functional group, pore and defect, the Na+ adsorption (sloping region in discharging curve) plays an important role in Na+ storage process specially at high current density. In comparison with other hard carbon materials (0.40 V), the low midpoint voltages in sloping region of carbon cloth-derived electrodes (0.11 V) promote the energy density of full cell. The optimized electrode based on the total weight of electrode exhibits a high discharging capacity (0.983 mAh cm−2 at 0.2 mA cm−2 or 98.3 mAh g−1 at 20 mA g−1) and a long-term cycling performance (91.6% capacity retention after 1000 cycles at 0.6 mA cm−2). The high reversible capacity of coin-type full cell (≈0.515 mAh cm−2 at 0.2 mA cm−2) and the outstanding flexibility of pouch cell further reveal its potential.