High performance spherical hard carbon anodes for Na-ion batteries derived from starch-rich longan kernel

Hard carbons are so far the most promising anode materials of sodium ion batteries, and fabricating hard carbons with various biomasses have been the research focus of many studies. In this work, instead of edible starch, longan kernel that is rich of starch is used as the precursor of hard carbon anodes. Taking advantage of the spherical morphology of starch in longan kernel, spherical hard carbons with low specific surface area and high closed micropore volume are prepared by optimizing the low-temperature pre-oxidation crosslinking conditions. In Na-ion half cells, the optimized hard carbon anode exhibits a high reversible capacity of 385 mAh g- 1 at 20 mA g- 1 and excellent rate capability (256 mAh g- 1 at 2000 mA g- 1), which are higher than those of most edible starch-derived hard carbon anodes reported previously. Moreover, when the prepared hard carbon anode is paired with Na3V2(PO4)3 cathode, the assembled Na-ion full cells preserve 83 % of its starting capacity after 500 cycles at 200 m A g- 1, demonstrating a high prospect for practical applications.