Utilization of The Indonesian's Spent Tea Leaves as Promising Porous Hard Carbon Precursors for Anode Materials in Sodium Ion Batteries

Sodium ion battery (SIB) has become one of the alternative battery system to replace lithium ion battery in the future. The abundant resource and low price of sodium are the main reasons for the development of SIB. However, the absence of suitable anode materials for SIB is the main problem for the commercial application of SIB. Graphite, the well known anode material in LIB, can not be used in SIB due to the larger size of sodium ions. In this present work, spent tea leaves were used as porous carbon precursors for anode materials in SIB. Porous hard carbons were prepared by three simple processes such as the direct carbonization, the hydrothermal carbonization and combination of hydrothermal and pyrolysis carbonization. When utilized as anodes in SIB, the best carbon electrodes performed a first discharge capacity as high as 363 mAh g(-1) and maintained a stable cycle profiles with high discharge capacity of 179 mAh g(-1) after 100 cycles at a current density of 100 mA g(-1). These excellent performances were attributed to synergistic effects of the large interlayer spacing, unique morphology and high degree of disordered carbon which can provide more active sites for sodium storage and diffusion. Based on the renewable and abundant advantage as well as simple preparation process, porous hard carbon materials originated from spent tea leaves may become promising anode materials for SIB.