Dual Carbon Potassium-Ion Capacitors: Biomass-Derived Graphene-like Carbon Nanosheet Cathodes.

Potassium-ion storage devices are attracting tremendous attention for wide-ranging applications on account of their low cost, fast charge transport in electrolytes, and large working voltage. However, developing cost-effective, high-energy electrodes with excellent structural stability to ensure long-term cycling performance is a major challenge. In this contribution, we have derived two different forms of carbon materials from almond shells using different chemical treatments. For instance, hard carbon (HC) and graphene-like activated carbon (AC) nanosheets are developed by employing simple carbonization and chemical activation routes, respectively. The resultant hard carbon (AS-HC) and activated carbon (AS-AC) exhibit outstanding electrochemical performance as negative and positive electrodes in a potassium-ion battery (KIB), respectively, through their tailor-made surface properties. These promising benefits pave a way to construct a biomass-derived carbon potassium-ion capacitor (KIC) by employing AS-HC as the negative electrode and AS-AC as the positive electrode in a K-based electrolyte. The as-fabricated KIC delivers a reasonable specific energy of 105 Wh/kg and excellent cycling life with negligible capacitance fading over 10 000 cycles. This "waste-to-wealth" approach can promote the development of sustainable KICs at low cost and inspire their use for fast-rate K-based energy storage applications.