Gradient SEI layer induced by liquid alloy electrolyte additive for high rate lithium metal battery

Current energy storage device has fallen short behind from the fast growing requirement for (hybrid) electric vehicles and portable devices including mobile phones, which drives the lithium metal anode to be a research hot topic. However, the large volume change of lithium metal anode induces instable solid electrolyte interface (SEI) layer, which prevents its further development. A stable SEI layer required flexible surface to accommodate the large volume variation and inorganic core with low Li+ partial molar volume for dendrite suppression. Herein, we achieved a gradient SEI which is composed of flexible surface-rich polycarbonate moieties and low Li+ partial molar volume inorganic LiF-rich core by applying liquid alloy GaSnIn as electrolyte additive. Initially, the calculation verified that liquid alloy GaSnIn as electrolyte additive would facilitate the initial decomposition of LiPF6, and lead to the formation of the gradient SEI layer. In the Li||Li half‐cell test, we successfully achieved dense deposition of Li metal and in this way, the cycling performance with liquid alloy GaSnIn as electrolyte additive is greatly improved especially at high rate (10 mA cm−2). Voltage polarization was greatly reduced and Coulombic efficiency was effectively improved due to the gradient SEI layer achieved in the interface of Li anode and electrolyte. In the Li||LFP cell, high average coulombic efficiency (99.06%) at long cycle life (>2500 cycles) is achieved for the liquid alloy GaSnIn‐protected Li metal anode at high areal capacity (3 mAh/cm2). These results deepen our understanding on liquid alloy as a promising electrolyte additive for efficient dendrite suppressing, enabling the practical lithium metal batteries (LMBs).