Hierarchical microporous nitrogen self-doped carbon derived from biomass as a multifunctional material for beyond lithium-ion batteries

Abstract

Agro-industrial residues are emerging as abundant, low-cost, carbon-rich and renewable feedstocks for the development of sustainable energy storage materials. In this study, pistachio shells were valorised as carbon sources for functional electrodes in lithium–sulfur (Li–S) and lithium–oxygen (Li–O2) batteries. Two carbon matrices were prepared: a non-activated carbon (PSC), and a KOH-activated carbon (PSAC). Both of these materials have inherent nitrogen functionalities, acting as self-doped heteroatoms that can improve conductivity, enhance polysulfide confinement, and facilitate redox kinetics without additional treatments. The carbon samples were loaded with 80 wt% sulfur, and were first evaluated in Li–S coin cells. PSAC exhibited outstanding electrochemical performance, with a high specific capacity of 955 mAh·g−1 at a rate of 1C, with near-ideal coulombic efficiency (∼100%) and excellent long-term stability. KOH activation generates a hierarchical microporous network that enables efficient sulfur impregnation and strong polysulfide immobilisation, resulting in superior electrochemical performance. In the context of these results, the PSAC-based electrodes were scaled to Li–S pouch cell configurations, and were also tested in Li–O2 systems, with broad electrochemical applicability. The effectiveness of PSAC when used in both Li–S and Li–O2 batteries underscores its potential as a multifunctional cathode material. Overall, this study highlights the use of pistachio shells as a sustainable and scalable precursor for high-performance carbon electrodes, thereby bridging the fields of biomass waste management and the development of next-generation rechargeable batteries.