Rice husk derived anodes for Li-ion batteries and beyond

Rice husk (RH), the outer covering of a rice kernel, is an abundant agricultural byproduct that can be source of anode materials for lithium-ion and new generation batteries. Actually, it is easy to imagine that organic constituents as lignin and cellulose can be suitably treated to obtain carbon. The carbon obtained by direct carbonization of RH at high temperature in inert atmosphere has a disordered structure, so it is suitable for either lithium and sodium intercalation. [1] Moreover, containing about 10-15% wt of hydrated SiO2, from RH silicon and its derivatives can be obtained. [2] In this work, two different C/SiO2 RH-based composites were directly obtained by carbonization of the RH in a tubular furnace under Ar atmosphere either up to 800°C or up to 1000°C. The samples have been characterized by X-Ray diffraction (XRD), BET surface analysis, X-ray photon absorption spectroscopy (XPS), scanning-electron microscopy and elemental differential analysis (SEM-EDX). Electrodes were prepared by depositing (Doctor Blade coating) on a dendritic Cu foil a slurry made by mixing the active material, carbon black and carbomethylcellulose (CMC) in a mass ratio of 90:5:5 in distilled water. The average electrode active mass loading was 2 mg/cm2. All the samples were characterized by cyclic voltammetry (CV) and galvanostatically cycled at different C rates (based on theoretical capacity of graphite) in Li-half cells, are tested in half-cell configuration vs. Li, both with conventional (LP30) and a non-conventional glyoxal based electrolyte, namely 1M LiTFSI Bis(trifluoromethansulfonyl)imide-lithium salt (LiTFSI) in tetraethoxyglyoxal/propylene carbonate (TEG/PC) 3:7 solvent. The glyoxal-based electrolytes have been selected because the formulation with LiTFSI salt has been proved to provide similar performances than standard LP30 while being more thermally stable (flash point 96°C). [3,4] Directly carbonized samples have also been similarly tested in Na-half cells, using 1M NaTFSI in TEG/PC (3:7) as electrolyte. Preliminary results show that the directly carbonized samples behave like hard-carbons, showing no clear redox peaks during CVs, good capacity retention at 1C cycling, and good long term capacity stability at 0.1 C. References [1] L. Wang, RSC Advances, 2014, 4, 64744. [2] Y. Shen, Renewable and Sustainable Energy Reviews, 2017, 80, 453–466. [3] L. Köps et al., Journal of The Electrochemical Society, 2021,168, 010513. [4] C. Leibing, Journal of The Electrochemical Society, 2021, 168, 090533.