Abstract
Garnet-type solid-state Li metal batteries (SSLMBs) are viewed as hopeful next-generation batteries due to their high energy density and safety. However, the major obstacle to the development of garnet-type SSLMBs is the lithiophobicity of Li(6.75)La(3)Zr(1.75)Ta(0.25)O(12) (LLZTO), resulting in a large interfacial impedance. Herein, a LiI/ZnLi(x) mixed ion/electron conductive buffer layer is constructed at the interface by an in situ reaction of molten Li metal with ZnI(2) film. This mixed buffer layer ensures close contact between the Li metal and garnet, significantly reducing interfacial impedance. As a result, the Li symmetrical cell with the LiI/ZnLi(x) buffer layer shows an interface impedance of 10.3 Ω cm(2), much lower than that of the cell with bare LLZTO (1173.4 Ω cm(2)). The critical current density (CCD) is up to 2.3 mA cm(-2), and the symmetric cells present a long cycle life of 2000 h at 0.1 mA cm(-2) and 800 h at 1.0 mA cm(-2). In addition, the full cells assembled with the LiFePO(4) cathode show a capacity of 143.9 mA h g(-1) after 200 cycles at 0.5C with a low-capacity decay of 0.021% per cycle. This work reveals a simple, feasible, and practical interface modification strategy for solid-state Li metal batteries.