Pitch-derived N-doped porous carbon nanosheets with expanded interlayer distance as high-performance sodium-ion battery anodes

Soft carbons with high conductivity have potential advantages as high-performance sodium-ion battery anodes, however, they suffer from small interlayer distance and low hereoatom content. In this work, porous carbon nanosheets (PCNS1000) with tunable microstructure, pore structure and chemical composition were prepared from coal tar pitch through a two-step process involving NaCl template method and NH3 treatment. PCNS1000 possesses an expanded interlayer distance of 3.82 Å, mesopore structure with average pore size of 5.7 nm, and a high nitrogen content of 4.17 wt%. Moreover, PCNS1000 retains soft carbon feature to a certain extent and consequent relative high conductivity. Benefiting from its appropriate structure and chemical composition, PCNS1000 exhibits a high reversible capacity of 270 mAh g−1 at 100 mA g−1 in sodium-ion half cells and excellent rate capability of 124 mAh g−1 at large current of 10 A g−1. After an ultralong charge-discharge cycling of 10,000 times, a high capacity retention of 86% was achieved, indicating its excellent electrochemical stability. The full cell assembled by Na3V2(PO4)3 cathode and PCNS1000 anode delivers a high capacity of 265 mAh g−1 at 100 mA g−1, with a good cycling ability of 89% capacity retention after 100 cycles at 1.0 A g−1.