Boosting the interfacial superionic conduction of halide solid electrolytes for all-solid-state batteries

Designing highly conductive and (electro)chemical stable inorganic solid electrolytes using cost-effective materials is crucial for developing all-solid-state batteries. Here, we report halide nanocomposite solid electrolytes (HNSEs) ZrO₂(-ACl)-A₂ZrCl₆ (A = Li or Na) that demonstrate improved ionic conductivities at 30 °C, from 0.40 to 1.3 mS cm⁻¹ and from 0.011 to 0.11 mS cm⁻¹ for Li⁺ and Na⁺, respectively, compared to A₂ZrCl₆, and improved compatibility with sulfide solid electrolytes. The mechanochemical method employing Li₂O for the HNSEs synthesis enables the formation of nanostructured networks that promote interfacial superionic conduction. Via density functional theory calculations combined with synchrotron X-ray and ⁶Li nuclear magnetic resonance measurements and analyses, we demonstrate that interfacial oxygen-substituted compounds are responsible for the boosted interfacial conduction mechanism. Compared to state-of-the-art Li₂ZrCl₆, the fluorinated ZrO₂-2Li₂ZrCl₅F HNSE shows improved high-voltage stability and interfacial compatibility with Li₆PS₅Cl and layered lithium transition metal oxide-based positive electrodes without detrimentally affecting Li⁺ conductivity. We also report the assembly and testing of a Li-In||LiNi0.88Co0.11Mn0.01O₂ all-solid-state lab-scale cell operating at 30 °C and 70 MPa and capable of delivering a specific discharge of 115 mAh g⁻¹ after almost 2000 cycles at 400 mA g⁻¹.