Low-cost water caltrop shell-derived hard carbons with high initial coulombic efficiency for sodium-ion battery anodes

Hard carbon possesses excellent properties of sodium storage, but high cost and low initial coulombic efficiency significantly affect the anode in large-scale application of sodium-ion batteries (SIBs). Here, we first report the waste water caltrop shell-derived hard carbons prepared by facile pyrolysis and subsequent an acid treatment. With the dense structure, low specific surface area and large interlayer spacing, the water caltrop shell carbonized at 1300 degrees C exhibits superior electrochemical performance, including the desirable reversible specific capacity, high initial coulombic efficiency, and excellent cycle stability. The electrode delivers the reversible specific capacity of 394.0 mAh g(-1), the plateau capacity as high as 285.2 mAh g(-1) with an initial coulombic efficiency up to 84.31% at the current density of 0.1C, and the reversible specific capacity of 313.9 mAh g(-1) only degraded by similar to 8% after 200 cycles even at 0.4C. This work provides a promising biowaste-derived anode for the future high-energy SIBs. (C) 2018 Elsevier B.V. All rights reserved.