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

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 in situ 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 in situ/ex situ characterizations, DFT calculations, and various electrochemical tests. This work provides insight into developing energy materials and power devices based on multiple lithiation mechanisms.