Asymmetric Energy Storage Devices Based on Surface-Driven Sodium-Ion Storage

Energy storage devices (ESDs) based on Na ions are potential sustainable power sources for large-scale applications. However, they suffer from an unsatisfactory electrochemical performance originating from the unfavorable intercalation of large and heavy Na ions. In this study, two different types of nanostructured carbons were fabricated from renewable bioresources by simple pyrolysis and used as an anode/cathode pair for surface-driven Na-ion storage. Hierarchically porous carbon nanowebs (HP-CNWs) composed of highly defective pseudographitic layers were prepared from bacterial cellulose and used as the anode for Na-ion storage. In contrast, the corresponding cathode consisted of functionalized microporous carbon nanosheets (FM-CNSs) fabricated from waste coffee grounds. The HP-CNWs and FM-CNSs exhibited pseudocapacitive Na-ion storage, achieving remarkably fast and stable energy storage for the anodic and cathodic potential ranges, respectively. Moreover, asymmetric ESDs based on HP-CNWs and FM-CNSs showed a high specific energy of ∼130.6 W h kg^-1 at ∼210 W kg^-1 and a high specific power of ∼15,260 W kg^-1 at 43.6 W h kg^-1 with a stable behavior over 3,000 cycles.