Self-healing gallium phosphide embedded in a hybrid matrix for high-performance Li-ion batteries

Abstract Self-healing materials have recently received considerable attention for improving the Li storage in anodes with high theoretical capacity that suffer from the mechanical instability triggered by the large volume change that occurs during electrochemical reactions. Ga has recently been explored for self-healing liquid metal electrodes in Li-ion batteries because it can be melted near room temperature. Previous reports have demonstrated the ultra-long cycling stability of these Ga-based electrodes owing to their self-healing properties. Unfortunately, despite these efforts, the performance of these Ga-based self-healing electrodes have not been fully satisfactory, particularly in terms of capacity. More importantly, the self-healing mechanism of liquid Ga has not been clearly investigated. Here, we synthesized GaP as a novel self-healing anode with an ultra-high capacity and stability. Self-healing in this Ga-based alloy occurred via the liquid-solid-liquid transition of Ga during lithiation/delithiation. In addition, by confining the liquid Ga in an appropriate binder (poly(acrylic acid)) through strong hydrogen bonding, stable cyclic behavior of the GaP was achieved. Furthermore, the TiO2-C hybrid matrix promoted the mechanical integrity and electrical conductivity of the GaP (GaP@TiO2-C). Consequently, the GaP@TiO2-C electrode showed superb cyclic performance (1012.0 mAh g−1 at 0.5 A g−1 after 500 cycles) and great rate capability. Various post-mortem analyses, including X-ray diffraction, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy, revealed the in-depth electrochemical reaction and self-healing mechanism of the GaP electrode. This study provides insight into the development of self-healing electrodes with high capacities and long cycling stabilities.