Peat-derived hard carbon electrodes with superior capacity for sodium-ion batteries

Herein we demonstrate how peat, abundant and cheap biomass, can be successfully used as a precursor to synthesize peat-derived hard carbons (PDCs), applicable as electrode materials for sodium-ion batteries (SIB). The PDCs were obtained by pre-pyrolysing peat at 300-800 °C, removing impurities with base-acid solution treatment and thereafter post-pyrolysing the materials at temperatures (T) from 1000 to 1500 °C. By modification of pre- and post-pyrolysis temperatures we obtained hard carbons with low surface areas, optimal carbonization degree and high electrochemical Na⁺ storage capacity in SIB half-cells. The best results were obtained when pre-pyrolysing peat at 450 °C, washing out the impurities with KOH and HCl solutions and then post-pyrolysing the obtained carbon-rich material at 1400 °C. All hard carbons were electrochemically characterized in half-cells (vs. Na/Na⁺) and capacities as high as 350 mA h g^-1 at 1.5 V and 250 mA h g^-1 in the plateau region (E < 0.2 V) were achieved at charging current density of 25 mA g^-1 with an initial coulombic efficiency of 80%.