Dual sulfur-doped sites boost potassium storage in carbon nanosheets derived from low-cost sulfonate

Abstract

• Dual S-doped carbon sheets are obtained by one-step low-cost pyrolysis. • C-S bonds and ultrafine sulfate are tailored on enlarged d-spacing carbon sheets. • High-capacity, long-life and high-rate K-ion battery is obtained. • Ex-situ XPS and capacity-contribution analysis reveal storage mechanism. As a new energy storage system, K-ion batteries (KIBs) have the advantages of low price and competitive high energy density. However, due to the large radius of K + , in the process of intercalation/deintercalation, the traditional carbon anode materials usually display insufficient cycle life and poor rate performance in KIBs. In this work, inexpensive and widely-sourced sodium p-toluenesulfonate (CH 3 C 6 H 4 SO 3 Na) is used as raw material to synthesize dual sulfur-doped carbon nanosheets (DS-CN) by a simple one-step carbonization method. The nanosheets possess an enlarged interlayer distance (4.25 Å) which allows large K + to intercalate. C-S bonds and the embedded ultrafine sulfate provide active sites to enhance capacity and accelerate kinetics. Moreover, a high S/O ratio would reduce the irreversible reactions caused by oxygen functional groups. The high reversible specific capacity (331.9 mA h g −1 at 50 mA g −1 ), good rate performance (165.3 mA h g −1 at 1000 mA g −1 ) and long cycle stability (0.011% capacity decay per cycle) are attributed to the multiple synergistic effects of enlarged layer spacing, reaction between C-S bonds and K + , as well as more active -C-SO 2 - bonds, as confirmed by ex-situ XPS and electrochemical analysis. Our work shows a feasible and effective way to develop low-cost, high-performance carbon anode materials for KIBs.