Surface capacitive contributions: Towards high rate anode materials for sodium ion batteries

Due to the poor transportability of sodium ions, conventional sodium ion batteries (SIBs) cannot deliver sufficient capacity for high rate applications. Surface-induced capacitive processes (SCP) (e.g. capacitance and pseudocapacitance) could provide fast charge/discharge capacity in conjunction with the capacity provided by diffusion-controlled intercalation processes (DIP) to address this issue. For the first time, SCP was used to design a hierarchical layered graphene composite as an anode material for high rate SIBs. The contributions of the individual sodium storage processes were quantitatively evaluated, verifying the proposed mechanism. The resultant SCP-enhanced SIB delivers an outstanding rate capacity of 120 mAh/g at 10 A/g, which is among best of the state-of-the-art carbon-based SIBs. It also demonstrates exceptional cycling stability, retaining 83.5% capacity of 142 mAh/g at 0.5 A/g after 2500 cycles. (C) 2015 Published by Elsevier Ltd.