Three-dimensional carbon framework anode improves sodiation–desodiation properties in ionic liquid electrolyte

Ionic liquid (IL), characterized by wide potential window, high thermal stability, negligible volatility, and low flammability, is a promising electrolyte for sodium-ion batteries (NIBs). However, the typical NIB anodes, such as hard carbon, show unsatisfactory capacities and poor charge–discharge rate capability in IL electrolyte at room temperature. A three-dimensional carbon framework (3-D CF) constructed with graphene nanosheets and carbon nanospheres is developed to address this issue. With this unique nano-architecture, the interfacial charge transfer, IL electrolyte infiltration, and Na⁺ transport can be improved at room temperature. As a consequence, this electrode shows superior sodiation–desodiation properties, with a charge–discharge efficiency being stable over 250 cycles in N-propyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide IL electrolyte. We also confirm that the 3-D CF electrode exhibits higher Coulombic efficiency and better cycling stability in the IL electrolyte than those found in conventional organic carbonate electrolyte, especially at an elevated temperature, due to the different chemistry of the solid–electrolyte interphase. The total heat releases of the sodiated 3-D CF samples contacted with IL and carbonate electrolytes, measured with differential scanning calorimetry up to 300 °C, are 250 and 805 J g^–1, respectively. The combination of the 3-D CF electrode and IL electrolyte shows great potential for NIB applications.