Nanoporous carbons from hydrothermally treated biomass as anode materials for lithium ion batteries

Biomass is transformed to carbon nanoparticles with surface-end groups called ‘hydrochar’ (HC) by an efficient and green hydrothermal carbonization (HTC) method. Three different approaches are used to introduce porosity to the HC: sole heat treatment, traditional potassium hydroxide (KOH) activation, and environmentally benign magnesium oxide (MgO) templating. All the resulting microporous materials are tested as Li-ion intercalation hosts in lithium cells by using an 1 M LiPF6 in EC/DMC electrolyte solution. They all show stable reversible capacities at elevated current rates (1C), closely comparable to the maximum theoretical capacity of graphite. Among all the materials studied, the HC-MA with a surface area of 150 m2 g1 and obtained by MgO templating of the hydrochar shows the best cycling performance in lithium cell at room temperature (307 mAh g1 at cycle 100 at 1C). The HC-600 with the highest degree of aromaticity/order, lowest content of oxygen functional groups and surface area of 250 m2 g1, obtained by heating the hydrochar at 600 C under inert atmosphere, shows the best power and overall performance with its ability to sustain high discharge/charge rates (1C, 2C, 5C, 10C, 20C). These electrochemical performances attained with materials of reasonable specific surface areas – obtained by green, low cost and practical strategies – can address the space limitations in Li-ion battery applications by improving volumetric energy densities.