Enabling a compatible Li/garnet interface via a multifunctional additive of sulfur

Abstract

Ceramic-based solid-state batteries with lithium metal anode show great potential to realize a battery revolution because of their features of nonflammability and high energy density. Among the inorganic electrolytes, garnet-type Li₇La₃Zr₂O₁₂ attracts much attention as a promising alternative owing to its advantages of high ionic conductivity, wide electrochemical voltage window, and excellent thermal stability. However, the critical issue of the insufficient lithium–electrolyte interface contact significantly hinders its practical application. Herein, an intimate physical connection between the Li anode and garnet is achieved by improving the wettability of molten Li with multifunctional sulfur (S) addition. The generated Li₂S with high ionic conductivity could also provide an extended interface area for charge transfer, enabling a reduced local current density and thus favoring the rate performance. Because of the tightly increased contact area and the homogenized interface electric-field distribution, the fabricated symmetric cells with an optimal Li–Li₂S anode (LS10: 10 wt% S addition) show a significantly decreased interfacial resistance (12.4 Ω cm²) and a stable Li plating/stripping performance for over 900 h at 0.2 mA cm⁻². The constructed LS10|Li_6.4La₃Zr_1.4Ta_0.6O₁₂|LiFePO₄ full cell delivers a high reversible specific capacity of 154.7 mA h g⁻¹ at 0.1C and stable cycling with a capacity fading rate of ∼0.033% per cycle.