Facile Construction of Nanofilms from a Dip-Coating Process to Enable High-Performance Solid-State Batteries

The use of solid-state electrolytes (SSEs) instead of those liquid ones has found promising potential to achieve both high energy density and high safety for their applications in the next-generation energy storage devices. Unfortunately, SSEs also bring forth challenges related to solid-to-solid contact, making the stability of the electrode/electrolyte interface a formidable concern. Herein, using a garnet-type Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZT) electrolyte as an example, we demonstrated a facile treatment based on the dip-coating technique, which is highly efficient in modifying the LLZT/Li interface by forming a MgO interlayer. Using polyvinyl pyrrolidone (PVP) as a coordination polymer, uniform and crack-free nanofilms are fabricated on the LLZT pellet with good control of the morphological parameters. We found that the MgO interlayer was highly effective to reduce the interfacial resistance to 6 Ω cm² as compared to 1652 Ω cm² of the unmodified interface. The assembled Li symmetrical cell was able to achieve a high critical current density of 1.2 mA cm^-2 at room temperature, and it has a long cycling capability for over 4000 h. Using the commercialized materials of LiFePO₄ and LiNi_0.83Co_0.07Mn_0.1O₂ as the cathode materials, the full cells based on the LLZT@MgO electrolyte showed excellent cyclability and high rate performance at 25 °C. Our study shows the feasibility of precise and controllable surface modification based on a simple liquid phase method and highlights the essential importance of interface control for the future application of high-performance solid-state batteries.