SSEs) because of their nonflammability and mechanical strength to block dendritic Li growth. [5,6] Among the many SSEs studied, [7][8][9][10][11][12][13][14] the cubic garnet phase SSEs [15][16][17][18][19][20][21] are more attractive because of their excellent chemical stability, [22,23] high ionic conductivities, [15,16,[24][25][26] and wide electrochemical potential window. [27][28][29] One of the major challenges for the application of the garnet-based solid-state Li metal batteries is the poor interfacial contact between garnet SSEs and electrode materials. [24,30,31] Direct contact between Li metal foil and garnet pellets normally results in poor contact and large interfacial resistance. By adding a polymer interface [32,33] or applying pressure, [34,35] the Li and garnet interface can be improved marginally, but still has high resistance. The poor wettability of molten Li against garnet substrates also makes it unfeasible to directly coat Li metal on garnet SSEs. In the previous work, [36][37][38][39][40] the wettability of garnet pellets against molten Li was significantly improved by coating a modification layer on the garnet surface, and the interfacial resistance was decreased from more than 1000 Ω cm 2 to as low as 1-20 Ω cm 2 . [36,37] However, for large-scale practical applications, this additional surface modification step under high vacuum is time-consuming and an additional cost. Therefore, a lower cost and more effective method is still strongly desired to solve the interfacial problem between Li metal anode and garnet SSEs for practical solid-state Li metal batteries.Fundamentally, the poor wetting between molten Li metal and garnet pellets is due to the large difference in surface energy. Our previous strategy introduces new interfaces that have better wettability against molten Li, but another strategy is to tune the surface energy of molten Li itself to match with the garnet SSEs. This wetting issue between liquid metals and ceramic substrates has been extensively studied for multiple applications, such as metal-ceramic joining by brazing and fabricating metal matrix composites. [41][42][43] To improve the wettability between liquid metals and ceramic substrates, alloying elements were normally added to tune the surface energy of the liquid metals and significantly decrease the contact angle on ceramic substrates. [41,43,44] Recently, with the rise in solid-state Li metal batteries, the metal-ceramic contact has become a critical challenge toward the development of high energy density and safe energy storage devices.The high theoretical specific capacity of lithium (Li) metal and the nonflammability of solid-state electrolytes (SSEs) make the solid-state Li metal battery a promising option to develop safe batteries with high energy density. To make the switch from liquid to solid-state electrolyte, the high interfacial resistance resulting from the poor solid-solid contacts between Li metal and SSEs needs to be addressed. Herein, a one-step soldering technique to quickly coat molten Li onto ...