Ultrahigh Rate and Long-Life Sodium-Ion Batteries Enabled by Engineered Surface and Near-Surface Reactions.

To achieve the high-power sodium-ion batteries, the solid-state ion diffusion in the electrode materials is a highly concerned issue and needs to be solved. In this study, a simple and effective strategy is reported to weaken and degrade this process by engineering the intensified surface and near-surface reactions, which is realized by making use of a sandwich-type nanoarchitecture composed of graphene as electron channels and few-layered MoS2 with expanded interlayer spacing. The unique 2D sheet-shaped hierarchical structure is capable of shortening the ion diffusion length, while the few-layered MoS2 with expanded interlayer spacing has more accessible surface area and the decreased ion diffusion resistance, evidenced by the smaller energy barriers revealed by the density functional theory calculations. Benefiting from the shortened ion diffusion distance and enhanced electron transfer capability, a high ratio of surface or near-surface reactions is dominated at a high discharge/charge rate. As such, the composites exhibit the high capacities of 152 and 93 mA h g-1 at 30 and 50 A g-1 , respectively. Moreover, a high reversible capacity of 684 mA h g-1 and an excellent cycling stability up to 4500 cycles can be delivered. The outstanding performance is attributed to the engineered structure with increased contribution of surface or near-surface reactions.