Cu₄SnS₄-Rich Nanomaterials for Thin-Film Lithium Batteries with Enhanced Conversion Reaction

Abstract

Through a simple gelation-solvothermal method with graphene oxide as the additive, a Cu₄SnS₄-rich composite of nanoparticles and nanotubes is synthesized and applied for thin and flexible Li-metal batteries. Unlike the Cu₂SnS₃-rich electrode, the Cu₄SnS₄-rich electrode cycles stably with an enhanced conversion capacity of ∼416 mAh g^-1 (∼52% of total capacity) after 200 cycles. The lithiation/delithiation mechanisms of Cu-Sn-S electrodes and the voltage ranges of conversion and alloying reactions are informed by <i>in situ</i> X-ray diffraction tests. The conversion process of three Cu-Sn-S compounds is compared by density functional theory (DFT) calculations based on three algorithms, elucidating the enhanced conversion stability and superior diffusion kinetics of Cu₄SnS₄ electrodes. The reaction pathway of Cu-Sn-S electrodes and the root cause for the unstable capacity are revealed by <i>in situ</i>/<i>ex situ</i> characterizations, DFT calculations, and various electrochemical tests. This work provides insight into developing energy materials and power devices based on multiple lithiation mechanisms.