Shear Mixing Suppresses Density-Driven Electrolyte−Binder Segregation in MgO-Based Separator Powders for Lithium Thermal Batteries

Abstract In lithium thermal batteries, electrolyte−binder (EB) separator powders comprise a molten salt electrolyte that provides ionic conduction after activation and porous MgO that immobilizes the molten salt, maintains electrode separation, and suppresses leakage. EB powders are typically prepared by conventional three-dimensional (3D) mixing before fusion, cooling, sieving, and palletization. However, bulk density mismatch between MgO and electrolyte powders can drive segregation, generating MgO-rich/electrolyte-lean and MgO-lean/electrolyte-rich domains that promote transport heterogeneity, salt leakage, and inconsistent discharge. Moreover, practical methods for quantifying EB homogeneity remain lacking. Here, we develop a potentiometric EDTA titration method to quantify EB homogeneity through MgO content dispersion. For 3D-mixed LiCl−KCl/MgO, LiCl−LiBr−KBr/MgO, and LiF−LiCl−LiBr/MgO powders, the MgO content standard deviation (SD) was 0.75%, 1.75%, and 9.25%, respectively, correlating with increasing bulk density mismatch. An internal-agitator shear-mixing strategy was then developed for the most inhomogeneous LiF−LiCl−LiBr/MgO EB, reducing the MgO content standard deviation from 9.25% to 0.6%, the leakage rate standard deviation from 2.18% to 0.50%, and pulse-derived area-specific resistance from 2.18 to 1.43 Ω. This work not only establishes a quantitative evaluation method for EB mixing homogeneity but also provides an effective processing strategy to improve powder mixing uniformity, offering important guidance for the manufacturing and quality control of EB separators in lithium thermal batteries.