sp2 configuration coupled vacancy rich carbon enables excellent low potential potassium storage

Abstract

Building abundant sp² hybridized carbon and vacancies in hard carbon is highly approved in respect of boosting its low potential (below 1.0 V) charging capacity, but it remains a challenge based on current synthesis strategies. Herein, the hard carbon with high sp² carbon and vacancy content is constructed by combining amidation reactions between esterified starch/N-containing fragments and temperature regulation. It is demonstrated that the introduced N-atoms can promote the formation of sp² domains via replacing O-atoms, which tend to cause excessive cross-linking between precursor molecules. Besides, the N-atoms bonded to carbon-atoms are gradually removed as the pyrolysis proceeds, helping to emerge vacancies, while a higher carbonization temperature can induce partial vacancies to heal. As a result, the optimized electrode delivers an excellent low potential charging capacity (214.5 mAh g⁻¹), based on “vacancy-adsorption/intercalation” mechanism, accounting for a high energy density (159.6 Wh kg⁻¹). Benefiting from the beneficial effect of vacancies and sp² domains on ion/electron migration, a superior rate capability is also gained (258.7 mAh g⁻¹ at 2 A g⁻¹). Moreover, rich vacancies synergize enlarged interlayer spacing to enable an ultra-long cycling stability over 4000 cycles (218.2 mAh g⁻¹).