A self-regulated gradient interphase for dendrite-free solid-state Li batteries

Abstract

Solid-state Li metal batteries (SSLMBs) have emerged as an important energy storage technology that offers the possibility of both high energy density and safety by combining a Li metal anode (LMA), a high-capacity cathode and a nonflammable solid-state electrolyte (SSE). However, the major challenges of poor LMA/SSE interface wetting and the easy growth of Li dendrites in SSEs remain unsolved. Here, we have addressed these challenges by using a functional gradient Li anode (FGLA), which is formed through a self-regulated reaction between molten Li and AlF₃. A composition gradient of Li–LiAl–LiF is spontaneously formed from the reaction of molten Li with AlF₃ due to the large difference in interfacial energy between Li/LiAl and Li/LiF, where the LiAl reduces the interface resistance and LiF suppresses Li dendrites. The FGLA not only dramatically reduces the resistance at the FGLA/Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZTO) garnet SSE interface to ∼1 Ω cm⁻², but also largely increases the critical current density (CCD) to over 3.0 mA cm⁻² at room temperature. Moreover, the full cells paired with LiNi_0.5Co_0.2Mn_0.3O₂, sulfur and thick LiFePO₄ cathodes (∼2.8 mA h cm⁻²) also show excellent cycling performances. The FGLA design provides a great opportunity for safe and high-energy SSLMBs.