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Sustainable electrical energy storage devices are an effective solution for the fossil fuel-based electrical power systems and aid in abating the environmental pollution. In this study, we design a sustainable and green approach for producing hard carbon from the biomass feedstock of waste mango peels through a simple carbonization route at low and high temperatures, namely, 600 °C (C600) and 1000 °C (C1000), respectively. The resultant hard carbon is used as an anode for lithium-ion batteries. The sample prepared at higher temperature exhibits a higher reversible cyclic capacity and rate capability than the sample prepared at low temperature. The C1000 sample delivers a reversible discharge capacity of 801 mA h g–1 at 100 mA g–1 and sustains a discharge capacity of 628 mA h g–1 over 200 cycles. The hard carbon electrode cell has a high capacitive charge and stable plateau capacity, indicating that the performance of the C1000 cell is good. Moreover, the higher specific surface area and hierarchical porous structure provide more Li-ion active sites, faster diffusion kinetics, and higher electronic conductivity during the charge/discharge process. The hard carbon derived from mango peels is a potential candidate for use in advanced large-scale energy storage applications. Specifically, this work presents a sustainable approach to achieve eco-friendly and cost-effective waste biomass management for energy applications.

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A series of Na3−xV2(PO4−xFx)3 (x = 0, 0.1, 0.15 and 0.3) polyanion cathode materials are synthesized via a sol-gel method. The optimal doping concentration of F in Na3V2(PO4)3 is 0.15 mol %. By neutron powder diffraction data, the chemical composition of as-synthesized material is Na2.85V2(PO3.95F0.05)3. The half-cell of Na2.85V2(PO3.95F0.05)3 cathode exhibits a stable discharge capacity of 103 mAh g−1 and 93% of capacity retention over 250 cycles without decay at 0.1 A g−1, which is higher than that of bare Na3V2(PO4)3 (98 mAh g−1). The high rate capability of Na2.85V2(PO3.95F0.05)3 is also dramatically enhanced via increase the conductivity of host material by F-doping. Moreover, the symmetrical Na-ion full-cell is fabricated using Na2.85V2(PO3.95F0.05)3 as cathode and anode materials. It is achieved that the good reversibility and superior cycling stability about 98% of capacity retention with ~100% of coulombic efficiency at 1.0 A g−1 throughout 1000 cycles. These results demonstrate that the optimal amount of Na2.85V2(PO3.95F0.05)3 is a distinctive potential candidate for excellent long-term cyclic stability with high rate low-cost energy storage applications.