Superionic Conductor Enabled Composite Lithium with High Ionic Conductivity and Interfacial Wettability for Solid‐State Lithium Batteries

Abstract The urgent demand for high energy and safety batteries has generated the rapid development of Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) type solid‐state lithium metal batteries. However, severe dendritic lithium growth, which is caused by poor interfacial contact of the Li/LLZTO interface and loss of electrical contact during cycles due to low intrinsic Li + diffusion coefficient of lithium, greatly hampers its practical application. Here, from the point of view of reducing surface tension and improving ion diffusion of lithium, a composite lithium anode (CLA) with high wettability and ion diffusion coefficient is prepared by adding GaP into molten lithium, thus strengthening the CLA/LLZTO interface even in cycling. As envisioned, compared to pure lithium, CLA presents lower surface tension, larger adhesion work, and higher ion diffusion coefficient, ensuring close contact of the CLA/LLZTO interface. Therefore, the assembled symmetric cells exhibit a low area specific resistance of 4.5 Ω cm 2 , a large critical current density of 2.5 mA cm −2 , and ultra‐long lifespan of 5700 h at 0.3 mA cm −2 at 25 °C. Meanwhile, full cells coupled with LiFePO 4 cathode show a high‐capacity retention of 97.32% after 490 cycles at 1C. This work provides a new solution to the interfacial challenges of solid‐state lithium‐metal batteries.