Carbon-coated TiO2 anode with solid electrolyte interphase engineered by Ca(ClO4)2 as electrolyte additive towards superior sodium storage

Sodium-ion batteries (SIBs) have attracted much attention for their high energy densities and low cost. However, the unstable solid-liquid interphase seriously restricts the development and application of SIBs. Herein, Ca(ClO4)2 as a new-type electrolyte additive is developed to engineer the solid-liquid interphase of carbon-coated anodes. In the electrolyte with an appropriate concentration of Ca(ClO4)2, Ca2+ can insert into the carbon coating and form a passivation layer during the first cycle, reducing the irreversible sodium-ion capture in the carbon coating and the electrolyte decomposition at the solid-liquid interface. Thus, the carbon-coated anode with a thin and stable solid electrolyte interphase (SEI) layer formed realizes the superior sodium storage performance with enhanced sodium-ion diffusion kinetics. Specifically, after adding 0.015 M Ca(ClO4)2 into the electrolyte, the reversible capacity of carbon-coated TiO2 anode could be greatly improved from 271.2 mAh g−1 to 335.1 mAh g−1 at 50 mA g−1, with the initial coulombic efficiency increasing from 41.2 % to 48.7 %. This study provides an alternative strategy to optimizing the SEI layer of carbon-coated TiO2 anode for superior sodium storage property, which also can be applied to other carbon-coated anodes for SIBs. [Display omitted] •Ca(ClO4)2 is developed to optimize the SEI layer of carbon-coated TiO2 anode.•Ca2+ can be inserted into the carbon coating with a passivation layer formed.•Ca(ClO4)2 suppresses electrolyte decomposition and irreversible Na+ capture.•A thin and stable SEI layer realizes a superior sodium storage performance.