Chemical-enzymatic fractionation to unlock the potential of biomass-derived carbon materials for sodium ion batteries

Plant biomass, the most abundant and sustainable carbon source, offers a rich chemical space to design hard carbons for sodium ion batteries. However, the compositional complexity of biomass has for a long time compromised the predictability of the structural and electrochemical properties of carbon. Using the chemical-enzymatic fractionation technique, we successively remove non-lignocellulosic components, hemicellulose and cellulose to create a suite of precursors for carbonization, in order to understand the roles of each biomass component in battery performance. Brewer's spent grain, an agricultural waste, is used as a representative biomass platform. The resulting hard carbon, with non-lignocellulosic components removed prior to carbonization, exhibits a dramatically reduced surface area and an increased specific capacity. Simultaneously removing non-lignocellulosic components and hemicellulose results in more sp 2 carbon, expanded (002) interlayer spacing, and a remarkably improved specific capacity by four fold. Further removing cellulose, with only lignin remaining, significantly reduces the sp 2 carbon and undermines the cycling stability of the derived carbon. Our finding reveals that the electrochemical properties of the biomass-derived hard carbons in sodium ion batteries may be positively correlated with cellulose and lignin but negatively impacted by non-lignocellulosic components and hemicellulose. Guided by this knowledge, we further fractionated two additional biomasses, i.e. grape pomace and walnut shells, for improving the carbon performance. After removing non-lignocellulosic components and hemicellulose, the resulting hard carbon delivers a reversible capacity of 296 mA h g −1 at 50 mA g −1 and retains 86.4% capacity after 200 cycles. Therefore, our results lay the foundation for unlocking the potential of biomass-derived carbon materials by precise fractionation of biomass components. Plant biomass, the most abundant and sustainable carbon source, offers a rich chemical space to design hard carbons for sodium ion batteries.