Layered germanium phosphide (GeP), a recently developed two-dimensional material, promises highly attractive theoretical capacity for use as a lithium-ion battery anode. Here, we comprehensively investigate its electrochemical performance and the modification mechanism. GeP flakes demonstrate large initial discharge/charge capacity and high initial Coulombic efficiency. However, the cycling performance is disappointing in the potential window of 0.001-3 V in which capacity retention is only ∼18% after 100 cycles. In situ transmission electron microscopy reveals that the poor cycling behavior results in the unexpected large volume change induced by complex reaction processes in cycles. Serious cracking and fracture appear clearly on the electrode surface after cycling. Narrowing the working voltage window to 0.001-0.85 V, cycling stability will be greatly enhanced, with 75% capacity retaining after 100 cycles and ∼50% left after 350 cycles due to the absence of the dealloying of Li3P in the narrowed working voltage window. Additionally, the electric contact among the electrode components has been enhanced by the alleviation of the electrode volume change in the narrowed working voltage window. Our work provides one effective method to give a deep understanding of the high-energy-density electrode failure and helps to narrow the huge gap between the microstructure and the performance of the electrode.
Keywords: electrode failure; germanium phosphide; in situ TEM; lithium-ion batteries; narrowing voltage window.