Growing Faceted Lithium Crystals to Enable Stable Solid-State Li Metal Batteries

Observing and controlling the nucleation and growth of lithium metal in solid-state lithium (Li) metal batteries are crucial for optimizing their performance. However, this has been challenging largely due to the instability of the Li/solid-state electrolyte (SSE) interface and the large stack pressure commonly employed which prevent assessment of the morphology of Li deposition. We report here our observation of faceted Li crystal growth in a solid-state battery. The interfacial instability of the sulfide electrolyte Li₆PS₅Cl with Li is overcome by modifying the interface with a bifunctional molecule, sodium 3-mercapto-1-propanesulfonate (3M1P). Surprisingly, the deposited Li is found to crystalize into a hexagonal close-packed structure that has only been previously known to be stable at low temperatures and high pressure. Moreover, the crystals are oriented with their (0001) facet parallel to the substrate, thus facilitating intimate contact and a homogeneous Li⁺ flux between Li/SSE. As a result, the pellet and laboratory pouch cells of Li/LPSC@3M1P/NCM811 successfully completed 500 and 100 cycles respectively under a modest stack pressure of 2 MPa. Our findings demonstrate the effectiveness of controlling Li crystal growth in enabling stable solid-state batteries.