Promising porous Cu2ZnSnS4 electrode composition synthesized by acetate route-based sol-gel process for lithium battery application

Abstract

This study aims to identify an optimum electrode composition ratio of Cu2ZnSnS4 (CZTS)/Super P® active carbon and evaluate the effects on electrochemical properties of CZTS/Super P® electrode in a lithium battery. Hence, the CZTS at a molar ratio of 2:1:1:4 was synthesized using the acetate route sol-gel process which was subsequently annealed at 550 °C using argon gas. The copper-rich CZTS stannite structure was confirmed by X-ray diffractometer (XRD) (2θ = 28.5°, 47.2° and 56.2°), Raman shift (at 283 and 333 cm-1) and energy dispersive spectroscopy (EDX) (CZTS-86 = Cu2.6Zn1.2Sn1.5S4 & CZTS-90 = Cu2.2Zn1.2Sn1.2S4) analyses. The CZTS powder produced was then mixed with the polyvinylidene fluoride (PVdF) solution, and Super P® to form a homogenous slurry. The slurry was then used to coat a copper substrate before drying in a vacuum oven. Next, the coin cell fabrication process was performed using the prepared CZTS electrode, lithium metal and LiPF6 as an electrolyte. The battery performance analysis upon optimization indicated that the CZTS-86 electrode with open-circuit voltage (OCV) at 1.96 V exhibited a discharge capacity of ~571.4 mAh/g. The desired discharge capacity was obtained due to a sufficient pore size of 0.9089 m2/g, which provided a favorable condition for charge carrier transport in electrolyte-electrode interfaces. The formation of solid electrolyte interfaces was assumed to have improved electrical characteristics by narrowing the gap created by the high porosities on the electrode surface. This effect can be observed through the reduction of Rct with an increasing amount of Super P®. Moreover, the Rct of the CZTS-86 electrode became consistant after aging compared to other compositions. The improvement of relaxation time (τ) of charge carrier demonstrated a more consistent pattern for Li+ Warburg diffusion coefficient. The electrochemical performances were ascribed to the synergetic effects of different components that make the CZTS electrode a promising electrode material for lithium rechargeable batteries.