Catalytic graphitisation of Vigna Mungo (L) Hepper biomass: A renewable graphite source for high-performance energy storage applications

In this study, we explore the potential of Vigna Mungo (L) Hepper (black gram skin, BGS), an agricultural byproduct, for synthesising high-quality graphite through a catalytic graphitisation process. Using a nickel-catalysed method, we successfully transformed BGS-derived carbon into highly ordered graphite at 1300 °C (BG-1300), with further surface area enhancement achieved via KOH activation (BG-1300-KOH) including X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM), confirmed the formation of highly ordered graphite with a high degree of graphitisation (62.9 %) and crystallite size (9.69 nm). Electrochemical evaluations demonstrated the potential of BGS-derived graphite as an anode material for lithium-ion batteries (LIBs) and lithium-ion hybrid capacitors (Li-HCs). The BG-1300-KOH sample exhibited a reversible discharge capacity of 610 mAh g −1 , outperforming commercial graphite (410 mAh g −1 ) and pristine BG-1300 (380 mAh g −1 ). The extent of Na-ion intercalation indicates the degree of disorder in carbon. In this study, as the carbonization temperature increases, the intercalation capacity progressively decreased, reflecting a transition towards more ordered, graphitic carbon. Furthermore, a Li-HC device fabricated with BG-1300-KOH as the anode and nitrogen-phosphorous-doped hard carbon (BGAC-NP) as the cathode achieved a maximum energy density of 175 Wh kg −1 and a power density of 25,000 W kg −1 , surpassing many reported carbon-based Li-HC devices. This study highlights the feasibility of converting agricultural waste into high-performance graphite, offering a sustainable pathway for energy storage applications while addressing environmental concerns associated with biomass disposal. • Black Gram Skin, a novel biomass, is used to prepare graphite via catalytic method • Ordered graphite was made at 1300 °C with Ni; the KOH treatment improved porosity • XRD, Raman, TEM, XPS, and 13 C NMR revealed dominant sp 2 carbon in 1300 °C graphite • BG-1300-KOH graphite capacity surpassed commercial graphite's 610 vs. 410 mAh.g −1 • Li-HC using BG-1300-KOH achieved 53 Wh kg −1 at 1 A/g, outperforming Li₄Ti₅O₁₂//AC