Hard Carbon Anode with a Sodium Carborane Electrolyte for Fast-Charging All-Solid-State Sodium-Ion Batteries

Compared with conventional lithium-ion batteries, all-solid-state sodium-ion batteries (AS3IBs) have the potential to achieve fast charging. This is due to the fast diffusion of sodium ions in the solid phase. Unfortunately, AS3IBs have often been limited by poor contact area and incompatibility between the active material and the solid electrolyte. Herein, we demonstrate a fast-charging AS3IB utilizing a hard carbon anode and a sodium carborane solid electrolyte, Na(CB9H10)0.7(CB11H12)0.3. The highly deformable nature of Na(CB9H10)0.7(CB11H12)0.3 enabled an intimate and stable contact with the hard carbon through forming a thin oxide interphase, which resulted in a small interfacial resistance (0.68 Ω cm2 at 0.1 V vs Na+/Na) for the hard carbon anode (active mass loading, 5.8 mg cm–2). A battery cell that paired the hard carbon anode with a Na0.7Mn0.5Ni0.2Co0.3O2 cathode exhibited an excellent fast-charging capability, storing an areal capacity of over 1 mA h cm–2 in about 5 min.