Natural Pigment from Madder Plant as an Eco-Friendly Cathode Material for Aqueous Li and Na-Ion Batteries

Abstract

Modifying commercial Li-ion batteries to become more environmentally friendly is of a growing concern. This paper provides an examination of a potential replacement for commercial cathode material using a naturally occurring purpurin in aqueous solutions of lithium and sodium salts. The purpurin is extracted from the Madder plant (Rubia tinctorum) and characterized through XRPD, FTIR, and SEM methods. The intercalation and de-intercalation capacities obtained for the purpurin as a cathode material in the aqueous solution of LiNO3 are approximately 40 mAh g-1. Compared to the capacity of ∼35 mAh g-1 obtained for commercially used transition metal oxides in an aqueous solution of Li salt, results presented make the purpurin a promising material for the "green"development of Li-ion batteries. Although the initial purpurin capacity in NaNO3 solution is almost doubled (∼73 mA h g-1) compared to that of Li-salt, it is unstable and fades during cycling. The possible explanation of the electrochemical behavior of purpurin as the cathode material in aqueous solutions of Li and Na salts is discussed in detail.