Pyrolysed coffee grounds as a conductive host agent for sulfur composite electrodes in Li–S batteries

Abstract

Biomass is an abundant and valuable carbon source that can be utilised in many applications such as gas separation and energy storage. Resolving methods to process biomass cheaply and efficiently into useful carbons for such applications remains a significant area of research. Herein carbons prepared via facile pyrolysis (or thermal transformation) of waste coffee grounds at 900 °C have been used as an electrode material for lithium–sulfur (Li–S) cells, resulting in specific capacities of ~340 mAh g−1 at 0.1 C after 100 cycles and coulombic efficiencies of >98% at 1 C even after 100 cycles. Cells using these pyrolysed coffee grounds in the electrode mixture are observed to exhibit a significant improvement in cyclability compared to a standard Li–S cell configuration utilising only carbon black as the electrode carbon source. This markedly improved cell cyclability is correlated to ex situ X-ray Absorption Near-Edge Structure (XANES) spectroscopic data, which provides useful insight into the evolution of sulfur, carbon and fluorinated species on the electrode surface over multiple electrochemical cycles.

Keywords

• Sustainable materials
• X-ray absorption near-edge structure
• Interface chemistry
• Electrochemical performance