A low-cost, lithium-rich zirconium-based oxyhalide solid electrolyte featuring an efficient ion transport structure

Abstract

Emerging halide solid electrolytes have garnered significant attention in the development of high-performance all-solid-state lithium batteries (ASSLBs) due to their exceptional high-voltage oxidation stability and compressibility. Recently reported low-cost Li₂ZrCl₆ demonstrates considerable potential for application. However, its ionic conductivity remains relatively low at room temperature. Here, we employ a strategy of lithium enrichment and induce a phase transition in its crystal structure by incorporating Li₂O into Li₂ZrCl₆ through high-energy ball milling. The substitution of O²⁻ for Cl⁻ sites results in the synthesis of an electrolyte that retains the same structure as Li₃ScCl₆, rather than adopting a trigonal phase. The monoclinic structure of Li₆ZrCl₆O₂ facilitates faster ionic transport. At 25 °C, the conductivity of lithium ions is measured at 6.69 × 10⁻⁴ S cm⁻¹. The experimental results and density functional theory (DFT) calculations indicate that the incorporation of Li₂O enhances the concentration of lithium elements, transforms the crystal structure, and optimizes the surface structure. These changes effectively improve the conductivity of lithium ions in the solid electrolyte. In addition, the prepared solid electrolyte Li₆ZrCl₆O₂ is assembled with the Li₆PS₅Cl (LPSCl) isolation layer, the Li(Ni_0.8Co_0.1Mn_0.1)O₂ (sc-NCM811) positive electrode, and the Li–In alloy to form an ASSLB. The initial coulombic efficiency of the ASSLB is as high as 84.85%, with an initial discharge specific capacity of 204.58 mAh g⁻¹. Additionally, it demonstrates good long-term cycle stability, with a capacity retention rate of 93.5% after 100 cycles at 0.5C.