Combined contributions from multidimensional micropores and mesopores of hierarchical porous carbons for extraordinary Li-ion storage applications

Abstract

Hierarchical porous carbons (HPCs) with optimized ultrafine micropores (<1 nm), large micropores (1–2 nm), small mesopores (2–5 nm) and large mesopores (>5 nm) are synthesized for a state-of-the-art Li-ion storage capacity. The HPCs are synthesized by direct carbonization of zinc citrate, while joint templating and activation effects of ZnO result in this hierarchical porous architecture and large specific area. The HPC obtained at 1200 °C (HPC-1200) displays the largest specific area (2245 m2 g−1) and pore volume (3.45 cm3 g−1) combined with an average pore size of 3.63 nm. This unique porous structure results in the highest specific capacity of 1850 mA h g−1 (Li5C6) at 0.1 A g−1, and superior rate performance and cycling stability. More significantly, mechanisms for this maximal capacity are investigated. It is found that mesopores are more effective to increase capacity, while micropores buffer Li-intercalation stress. Energy storage of HPC is surface-controlled with enhanced capacity achieved at enlarged surface area. In addition, the HPC-1200 exhibits excellent performance for assembly of full batteries with noticeable specific energy of 271.4 W h kg−1 achieved at 195.5 W kg−1, and the full battery is workable for energy-delivery when the specific power increases to 19 kW kg−1.