Composite lithium with high ionic conducting Li3Bi alloy enabled high-performance garnet-type solid-state lithium batteries

Solid-state lithium metal batteries (SSLMBs) are regarded as an important development direction due to their high energy density and safety. Nevertheless, the application of SSLMBs is hampered by the poor interfacial contact with large resistance and dendrite issue, as well as volume variation of metallic lithium anode. Here, a high-performance Li-BiF3 composite lithium having successive ion-conducting phase was constructed via the conversion reaction between commercial BiF3 powders and molten lithium, which shows reduced surface tension of lithium and improved wettability toward Li6.4La3Zr1.4Ta0.6O12 electrolytes. The as-formed Li3Bi in the anode with high ionic diffusion coefficient can quickly transport lithium from the bulk to the solid-state interface to compensate for the lithium depletion during stripping, thus ensuring tight interface contact, inhibiting the generation of gaps, and homogenizing current and Li+ flux. The Li-BiF3/LLZTO/Li-BiF3 symmetric cells present small interfacial resistance (7.4 Ω cm2), large critical current density (1.1 mA cm−2) and superior cyclic stability of 850 h under 0.3 mA cm−2 at 25 °C. In addition, full cells assembled together with LiFePO4 and LiNi0.8Co0.1Mn0.1O2 cathodes demonstrate exceptional cyclic performance with 92.9% and 86.5% capacity maintenance upon 100 cycles under 0.5 C.