Layer-by-Layer Assembly with Lithiophilic and Electrophobic Interlayer for Dendrite-Free Lithium-Metal Solid-state Batteries

All-solid-state batteries (ASSBs) are an advanced safety system pursued by the battery industry to avoid the combustion problem of current liquid organic electrolytes through the exploitation of non-flammable inorganic solid electrolytes.^1,2 Moreover, ASSBs can potentially achieve high volumetric energy density by allowing the use of a lithium-metal anode, which exhibits the highest theoretical capacity (3860 mAh g⁻¹) and lowest redox potential (0 V versus Li/Li⁺).^3,4 However, the formation of lithium dendrites throughout the inorganic solid electrolyte leads to short circuits at low current densities, hindering their practical application. The underlying origin of the short circuits is considered to be the non-uniform lithium-ion flux induced by poor contacts at the interface and non-negligible electron leakage from the electrode to the solid electrolyte.^5,6 In this respect, <u>it is of paramount importance to build a robust interface between the lithium metal and solid electrolyte to optimize wettability for the uniform lithium-ion flux and to minimize the leakage of electrons.</u><br/>Herein, we report that a layer-by-layer strategy using a lithiophilic and electrophobic multi-layer simultaneously improves the lithium wettability and suppresses the electron leakage. The lithiophilic layer exhibited homogeneous lithium-ion conduction with low interfacial resistance at 13.4 Ω cm² at room temperature, and the electrophobic layer maintained significantly low electron conductivity of 10⁻⁹ S cm⁻¹ even at high temperature or high electric field. Our multi-layer delivered a high critical current density (CCD) of 3.1 mA cm⁻² at 60 °C in a symmetric cell. In a full cell with a commercial LiFePO₄ cathode, it exhibited improved performance with long durability (&gt; 1550 cycles) and stable coulombic efficiency (99.96%) at a high current density (2C, ~1.0 mA cm⁻²), which is the highest performance reported to date. Our findings indicate that the use of combined lithiophilic and electrophobic layers is a viable strategy to address the major problems of all-solid-state lithium-metal batteries, which is expected to expedite the commercialization of all-solid-state batteries.<br/>1. Manthiram, A., Yu, X. & Wang, S. <i>Nat. Rev. Mater.</i> <b>2</b>, 16103, (2017).<br/>2. Janek, J. & Zeier, W. G. <i>Nat. Energy</i> <b>1</b>, 16141, (2016).<br/>3. Liu, Y.<i> et al.</i> <i>Nat. Energy</i> <b>2</b>, 17083, (2017).<br/>4. Albertus, P., Babinec, S., Litzelman, S. & Newman. <i>Nat. Energy</i> <b>3</b>, 16-21, (2018).<br/>5. Swamy, T.<i> et al.</i> <i>J. Electrochem. Soc.</i> <b>165</b>, A3648-A3655, (2018).<br/>6. Han, F.<i> et al.</i> <i>Nat. Energy</i> <b>4</b>, 187-196, (2019).