Physicochemical activation of soap-nut seeds-derived hard carbon as a sustainable anode for lithium-ion batteries

Abstract

Research studies on biomass-derived hard carbon are gaining notable scientific interest due to its potential application as a sustainable anode for Li-ion batteries (LIBs). The current study presents the development of hard carbon from soap-nut seed biomass, with the optimization of its pyrolysis temperature, followed by chemical activation using KOH- and ZnCl₂-activated reagents. The physicochemical behaviour of the developed materials is studied by utilizing XRD, HRTEM, BET, and XPS techniques. CV and galvanostatic charge–discharge curves are examined to assess the potential of the material for the application as a sustainable anode in LIBs. The electrochemical performance of the developed materials obtained at various pyrolysis temperatures (600, 700, 800 and 900 °C) and chemically activated with KOH and ZnCl₂ is explained with respect to their interplanar spacing, I_D/I_G ratio, and specific pore area. Among the different pyrolysis temperatures, the hard carbon pyrolyzed at 700 °C exhibits the maximum reversible specific discharge capacity of 391 mA h g⁻¹ at a current density of 100 mA g⁻¹. The present study also demonstrates that the electrochemical performance of the hard carbon deteriorates after chemical activation with ZnCl₂, whereas chemical activation with KOH enhances its performance. The chemically-activated hard carbon using KOH exhibits a reversible specific discharge capacity of 454 mA h g⁻¹ at 100 mA g⁻¹ and delivers a better cycling stability (500 cycles) of 83 mA h g⁻¹ at 300 mA g⁻¹.