Defect-Rich Soft Carbon Porous Nanosheets for Fast and High-Capacity Sodium-Ion Storage

Soft carbon has attracted tremendous attention as an anode in rocking-chair batteries owing to its exceptional properties including low-cost, tunable interlayer distance, and favorable electronic conductivity. However, it fails to exhibit decent performance for sodium-ion storage owing to difficulties in the formation of sodium intercalation compounds. Here, microporous soft carbon nanosheets are developed via a microwave induced exfoliation strategy from a conventional soft carbon compound obtained by pyrolysis of 3,4,9,10-perylene tetracarboxylic dianhydride. The micropores and defects at the edges synergistically leads to enhanced kinetics and extra sodium-ion storage sites, which contribute to the capacity increase from 134 to 232 mAh g(-1) and a superior rate capability of 103 mAh g(-1) at 1000 mA g(-1) for sodium-ion storage. In addition, the capacitance-dominated sodium-ion storage mechanism is identified through the kinetics analysis. The in situ X-ray diffraction analyses are used to reveal that sodium ions intercalate into graphitic layers for the first time. Furthermore, the as-prepared nanosheets can also function as an outstanding anode for potassium-ion storage (reversible capacity of 291 mAh g(-1)) and dual-ion full cell (cell-level capacity of 61 mAh g(-1) and average working voltage of 4.2 V). These properties represent the potential of soft carbon for achieving high-energy, high-rate, and low-cost energy storage systems.