Enabling Fast Mass Transport in Anode by a Smartly Built‐in LiC₆ Phase for High‐Performance Solid‐State Lithium Metal Batteries

The practical use of solid‐state lithium metal batteries is hindered by the rapid growth of lithium dendrites through the solid electrolyte, leading to a short lifespan, and poor performance at high rates. The mass transport in anode bulk is proposed as a critical reason related to the chemo‐mechanical failure of the interface and growth of lithium dendrites. In this study, a lithium‐composite anode with a smartly integrated LiC 6 phase is developed using a thermodynamic reaction between molten Li and thermally expanded graphite. The gravity segregation effect creates a gradient dispersion of LiC 6 in Li, resulting in improved bulk Li diffusion kinetics (70 times higher than that of a pure Li anode). This composite electrode exhibits low interfacial resistance (≈2.3 Ω cm 2 ) and an ultra‐high critical current density of 2.4 mA cm −2 in all‐solid‐state symmetric cells at room temperature. During repeated Li stripping/plating cycles, the enhanced bulk Li diffusion kinetics maintain the close interfacial contact, leading to excellent long‐term cycling stability for over 4000 h with a high cumulative areal capacity. These findings provide valuable insights that promoted mass transport in lithium metal anode is of great benefit to high‐performance solid‐state lithium metal batteries.