Synthesizing Microporous Carbon from Soybean and Use It to Develop Cathode Material for High Performance Lithium-Selenium Batteries

Selenium is considered as a promising cathode material for lithium-ion batteries due to its high electrical conductivity (10 −3 S m −1 ) and volumetric capacity (3253 mA h cm −3 ). Though, feasibility of high-performance lithium-selenium (Li-Se) batteries depends on designing a cost-effective substrate for Se with desired porous structure. In this study, porous carbon was synthesized from soybean in a two-step carbonization/activation process and used as Se host to develop cathode for lithium-selenium (Li-Se) batteries. The activated carbon/selenium (C/Se) composites were prepared using a melt diffusion process at 260 ℃ inside an argon-filled autoclave. The cathode material consisted of C/Se composite, carbon black, and sodium alginate with a mass ratio of 8:1:1. The effect of activation temperature (500, 600, and 700 ℃) on the porous structure of activated carbon was investigated. It was revealed that both specific surface area and pore volume increased with activation temperature. Moreover, the carbon activated at 500 ℃ (C500) possessed mainly mesopores while the pore structure in the other carbon samples was microporous. The quality of Se impregnation in C/Se composites and their distinct electrochemical performance were correlated to the porous structure of the activated carbon. Using the carbon obtained at 600 ℃ (C600), the Li-Se coin cell exhibited a superior discharge capacity (664 mAh g-1 at 0.1C current density), rate capability, and long cycling stability at higher current densities. It was believed that the microporous feature of C600 along with high surface area and pore volume could favor effective confinement of Se, electrolyte wetting of the cathode, lithium-ion diffusion, and charge transfer, which resulted in better electrochemical performance. This work suggests the sustainable development of microporous carbon with a unique structure suitable for cathode material in Li-Se batteries.