Surface functionalized porous spherical hard carbon material derived from taro starch for high performance sodium storage

Hard carbon materials synthesized from biomass precursors exhibit the excellent characteristics of high capacity, cost-effectiveness and wide-ranging availability. In this study, the aniline-functionalized hard carbon material (HC-P-F) with porous spherical morphology was prepared successfully by enzymatic hydrolysis combing with “burying” heat treatment and diazotization reaction using taro starch as carbon source. The HC-P-F possesses porous morphology, which can shorten the ion transport path, thereby increasing the ion transport rate, and also providing more active sites for Na⁺ storage. At the same time, the aniline radical grafting on the surface of the hard carbon materials helps to improve the battery life and cycle stability. The porous spherical structure and surface functionalization produce a good synergistic effect, increasing the specific surface area, enhancing the stability of the cycle, improving the electrical conductivity and promoting the rapid insertion and removal of ions of the hard carbon material. The results show that the HC-P-F maintains a high reversible specific capacity of 260.19 mAh g^-1 after 300 cycles at 0.5 A g^-1. And it displays excellent rate performance with an average reversible specific capacity of 358.5, 338.39, 308.32, 276.86, 231.61 and 120.46 mAh g^-1 at 0.1, 0.2, 0.5, 1, 2 and 5 A g^-1, respectively. Furthermore, the HC-P-F exhibits lower impedance, significant capacitive behavior dominated by pseudocapacitance contribution and faster sodium ion interface dynamics comparing with other hard carbon materials. In addition, when assembled into full cell with commercial sodium vanadate (NVP), it demonstrates exceptional cycling stability with a high energy density of 184.06 Wh kg^-1 after 300 cycles at 0.5 A g^-1. This successful preparation of the aniline-functionalized hard carbon materials provides another solution for improving the electrochemical properties of the anode electrode materials, which would promote the application research of starch-based hard carbon anode materials in sodium ion batteries (SIBs).