Quaternary Cu₂TSiS₄ (T = Fe, Mn) Anodes for Li-Ion Batteries

Developing high-capacity and fast-charging anode materials is critical for achieving high-performance Li-ion batteries (LIBs). Herein, polycrystalline quaternary transition metal silicon sulfides, Cu₂TSiS₄ (T = Fe, Mn), were synthesized using a solid-state method and investigated as anode materials in LIBs. Cu₂FeSiS₄ retains a reversible capacity of 670 mAh g^-1 at 200 mA g^-1 for 400 cycles, while Cu₂MnSiS₄ suffers from a fast capacity loss in the initial 50 cycles. More importantly, Cu₂FeSiS₄ can maintain a reversible capacity of 379 mAh g^-1 after 700 cycles at a high current density of 2 A g^-1, demonstrating high cyclic stability and fast-charging capacity. To further understand the structure degradation and phase transformation, we investigated the postcycling electrodes using multiple techniques, including the scanning electron microscope with energy-dispersive X-ray spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy techniques. The results indicated that Cu₂FeSiS₄ undergoes reversible phase transitions with Li₂S as a major product component. To further assess the performance for practical applications, Cu₂FeSiS₄ was coupled with LiFePO₄ to make LiFePO₄||Cu₂FeSiS₄ full cells, which delivered superior electrochemical performance. These results demonstrate great promise for using quaternary transition metal silicon sulfides as anodes to achieve low-cost and sustainable LIBs.