Exploring the application of carbon xerogels as anodes for sodium-ion batteries

Carbon xerogels (CXs) with the same chemical composition and BET surface area but different pore sizes (10-200 nm), which had been easily produced in large amounts via a cost-effective microwave-based process, are investigated as anodes for sodium-ion batteries (SIBs). The role of textural properties of CXs in the process of sodium ions storage was evaluated. The most suitable anode for SIBs was CX-100 with a pore size of 100 nm, the largest micropore volume and the lowest external surface area (S-ext), which gives an idea of the most accessible surface of the material, along with relatively high open porosity. Larger pore sizes facilitate electrolyte penetration, thus improving Na+ ions diffusion inside the electrode, while microporosity is crucial in increasing electrode capacity since Na+ ions storage on CXs is mainly due to absorption on the surface and in structural defects (i.e., micmporosity). Moreover, lowering S-ext leads to a decrease in the Na+ ions used in the formation of the SEI layer and irreversibly absorbed during initial cycles, therefore improving electrode performance. In summary, an optimal combination of textural properties, including pore structure and S-ext, should be considered in order to effectively design CXs for SIBs.