Porous biochar purification method from coconut shell by alkali roasting followed by leaching and its application as a lithium primary battery

Abstract

Abstract The electrochemical performance of coconut shells biochar can be improved as a Lithium primary battery by increasing its purity. Biochar was synthesized by pyrolysis under N2 atmospheric conditions at a temperature of 500°C for 5 hours. The methods to purify biochar were the alkaline roasting method to reduce silica content and the leaching method at room temperature using 10% w/w H2SO4 to reduce metal oxide content. The used alkaline substance was 45% w/w NaOH solution under process temperature, which varied between 200-350°C with increasing the pressure. Energy-dispersive X-ray results show that biochar’s carbon purity increased from 90.18% w/w to 97.41% w/w at the alkaline roasting temperature of 300°C. The surface area of biochar is also increased from 782,112 m2/gram to 1218,646 m2/gram at the same temperature. Electro Impedance Spectroscopy test shows charge transfer and semi-infinite diffusion, which can be explained by the diffusion of Li+ ions from LiClO4 solution to purified biochar at the cathode. The charge transfer resistance value in purified biochar is less than in biochar that has not been purified. The discharge performance test shows that lithium primary batteries’ capacity increases along with biochar purity. The highest capacity of biochar is 126.21 mAh/gram at 300°C.