The impact of various demineralization steps of Cocoa Pod Husk on the performance of hard carbons for sodium batteries

Abstract

Hard carbons are the most promising anode materials for Na-ion batteries (NIBs) because of its high storage capacity and good cycling stability. Among the candidates of carbon precursor for hard carbon, a biomass waste is the most appropriate sources of hard carbon because of its low cost, availability, and environmental friendliness. In fact, the biomass waste itself is not a pure chemical, it contains different composition of lignocellulosic materials with a wide variety of inorganic, leaving the complex behavior of each biomass precursor for the formation of microporous structure of hard carbon. Therefore, biomass preparation methods are a critical step to achieve high performance anode material for NIBs. Herein, high-temperature calcination was used to synthesize hard carbon from cocoa pods husk (CPH). CPH itself contains of 12 wt% inorganic, dominating by potassium (K) and calcium (Ca) ion. Different biomass preparation methods were investigated under two different calcination temperatures (1100 and 1300 °C). The demineralization of biomass before calcination (Pre-demin), without any demineralization (No-demin) and the demineralization step after calcination (Post-demin) were investigated to the hard carbon performance as an anode for NIBs. The hard carbon carbonized at 1300 °C with the Pre-demin step delivered total capacity about 310 mAh/g at 50 mA/g. The long-term stability test until 1000 cycle showed that hard carbon synthesized at 1300 °C with the Pre-demin step resulted in highest capacity and stability performance as compared to the other preparation methods. On the other hand, in the hard carbon synthesized at 1100 °C, the Post-water demin resulted in comparable capacity and performance as that of pre-demin.