Marriage of an Ether-Based Electrolyte with Hard Carbon Anodes Creates Superior Sodium-Ion Batteries with High Mass Loading

Inferior rate performance, insufficient cycle life, and low mass loading have restricted the practical application of hard carbon (HC) anodes in sodium-ion batteries (NIBs). Here, a compatible strategy is developed by matching HC anodes with an ether-based electrolyte. Systematical investigation reveals that good compatibility of the electrode–electrolyte systems forms thinner but a more sustainable solid-electrolyte interphase and delivers a higher ionic conductivity and Na+ ion diffusion coefficient than the commonly used ester-based electrolytes. Therefore, an excellent electrochemical performance is demonstrated with a long cycle life (∼196 mA h/g and 90% capacity retention after 2000 cycles at 1 A/g), a super rate capability (∼51% capacity retention at 10 A/g) at a mass loading of 1.5 mg/cm2, and a high initial Coulombic efficiency of 85.9%. More importantly, a high reversible areal capacity of 4.3 mA h/cm2 can be achieved at an ultrahigh mass loading of 17 mg/cm2, superior to all reported HC anodes. Our findings not only shed light on the design of high-performance battery systems but also promise a commercial transformation from the lab test to mass production of NIBs.