Composite of activated carbon derived from coconut shell with sulfur as a high-performance cathode for β"-alumina-based sodium solid-state batteries

Abstract

A novel activated carbon/sulfur (AC/S) composite cathode was synthesized from coconut shell charcoal through a thermal treatment method, with a sulfur-to-activated carbon (S/AC) mass ratio of 5:1. The AC/S composite displayed broad diffraction peaks at 2 theta = 23.03 degrees and 2 theta = 43.45 degrees, indicating an amorphous carbon structure. Morphology analysis revealed a dense, pore-free structure with particle sizes ranging from 50 to 200 nm. Meanwhile, TEM analysis revealed sulfur encapsulation within a carbon matrix, with encapsulated particle sizes ranging from 10 to 20 nm. FTIR analysis confirmed C-S bonding with characteristic vibrations at 1189.17 cm(-)1, supported by Raman peak at 996.08 cm(-)1 and XPS signals at 164.03 eV and 165.21 eV. The composite exhibited a high electronic conductivity of 1.11 x 10<^> (- 1) S cm-1. Electrochemical performance tests of the AC/S composite as a cathode in an all-solid-state sodium battery (AC/S | PTFE-beta"-Al2O3 | Na) demonstrated promising initial charge and discharge capacities of 553.01 mAh/g and 331.9 mAh/g, respectively. Cycle stability tests further showed a Coulombic efficiency of 74% and capacity retention of 22.33% over 150 cycles, highlighting the composite's potential for sustainable, high-capacity sodium storage applications.