Li-ion battery negative electrodes based on the FexZn1−x alloy system

• First report of sputtered amorphous Fe–Zn alloys
• Discovery of a new Zn-rich Fe–Zn phase
• Mössbauer parameters sputtered Fe–Zn alloys
• First report of electrochemistry of the Fe–Zn alloy series

Thin-film Fe–Zn libraries were investigated as negative electrode materials for Li-ion batteries using combinatorial and high-throughput techniques. X-ray diffraction, Mössbauer effect spectroscopy and electron microprobe were used to characterize the library structure. A new Fe–Zn phase with an unknown structure was observed in the ζ (FeZn13) region on the phase diagram. The electrochemistry of FexZn1−x (0.01 < x < 0.45) was studied at 30 °C. The cycle life and coulombic efficiency improved as Fe concentration in electrodes increased to x = 0.12. However, the capacity decreased as the iron content increased and the FexZn1−x alloys became completely inactive when the Fe content was above 12 at.%. Ex-situ X-ray diffraction and Mössbauer measurements were used to explain the structural changes that occur during cycling. This is the first report of sputtered amorphous Fe–Zn alloys in the literature.