Closed Nanopores Enhance the Stability of Nitrogen-doped Hard Carbon in Potassium Storage by Buffer Activity Structure

Abstract

Carbon materials are among the leading anodes for potassium-ion batteries (PIBs) due to their low cost, natural abundance, and promising performance. However, their performance is often constrained by sluggish ion intercalation, attributed to the relatively large ionic radius of potassium ions. A common approach to address this limitation involves engineering porous carbon materials to accommodate volume changes during the potassiation process. Nonetheless, the role of porosity remains contentious, as larger surface areas can also heighten the risk of solid electrolyte interphase (SEI) rupture during cycling, thereby increasing porosity and decreasing specific surface area, which become compelling challenges in carbon materials. Herein, the closed nanopore structure (diameter <2.0 nm) and low surface area form a buffer-activity structure that mitigates expansion during potassiation, acting to stabilize the solid electrolyte interphase (SEI) layer, enabling the synthesis of N-doped hard carbon nanosheets (NHC) with two types of microstructures via direct pyrolysis. Our findings regarding the closed nanopore structure formed during buffer activity have significantly enhanced the stably SEI layer by the buffer-structure, thereby achieving a remarkable 93% capacity retention following 1000 cycles at a current density of 1.0 A·g‒1. These results offer valuable insights into the impact of closed pore structures and electrolyte/solid interfaces on the electrochemical behavior of hard carbons, providing a strategic pathway for designing high-performance anode materials for next-generation PIBs.