High-performance sodium-ion batteries with a hard carbon anode: transition from the half-cell to full-cell perspective

Hard carbon is an appealing anode material for sodium-ion batteries (SIBs) due to renewable resources, low cost and high specific capacity. Practical full cells based on hard carbon with high energy density and long cyclability are expected to possess application interest for grid-scale energy storage. In this review, following this archetypal use scenario of SIBs, we aim at providing a quantitative full-cell metric for evaluating newly designed anodes or cathodes. Some significant problems in conventional half-cell and full-cell tests, including unfaithful prediction of capacity loss by coulombic efficiency in the full-cell and under-estimated capacity of hard carbon in the half-cell test, are discussed to better assess the actual capacity and cyclability of the hard carbon anode in sodium-matched full cells. Finally, we review rational design of hard carbon itself and the selection of electrolytes from such a full-cell perspective.