Insights into the thermochemical evolution of maleic anhydride-initiated esterified starch to construct hard carbon microspheres for lithium-ion batteries

Starch, as a typical polysaccharide with natural spherical morphology, is not only a preferred precursor for preparing carbon materials but also a model polymer for investigating thermochemical evolution mechanisms. However, starch usually suffers from severe foaming and low carbon yield during direct pyrolysis. Herein, we report a simple and eco-friendly dry strategy, by maleic anhydride initiating the esterification of starch, to design carbon microspheres against the starch foaming. Moreover, the influence of ester grafting on the pyrolytic behavior of starch is also focused. The formation of ester groups in precursor guarantees the structural stability of starch-based intermediate because it can promote the accumulation of unsaturated species and accelerate the water elimination during pyrolysis. Meanwhile, the esterification and dehydration reactions greatly deplete the primary hydroxyl groups in the starch molecules and thus the rapid levoglucosan release is inhibited, which well keeps the spherical morphology of starch and ensures the high carbon yield. In further exploration as anode materials for Lithium-ion batteries, the obtained carbon microspheres exhibit good cyclability and rate performance with a reversible capacity of 444 mAh g−1 at 50 mA g−1. This work provides theoretical fundamentals for the controllable thermal transformation of biomass towards wide applications.