Tunable ionic conductivity in halide electrolytes through cation ion exchange and channel engineering

Halide solid electrolytes hold great promise for all-solid-state batteries, yet their ionic conductivity requires further optimization. This study demonstrates a powerful strategy for tuning ionic transport in Li2ZrCl6 through cation ion exchange and precise channel engineering. Using first-principles calculations, we show that replacing Li+ with Na+ in the Li2 − 2xNa2xZrCl6 system induces controlled lattice expansion, which directly engineers the size and geometry of ion migration channels. This enables remarkable tunability: Li+ conductivity is enhanced by two orders of magnitude, reaching 2.1 mS/cm for x = 0.75, while the migration barrier plummets from 0.298 to 0.044 eV. Crucially, the conductivity is anisotropic and dependent on the exchange pattern; a-axis-aligned Na+ creates channels (∼1.87 Å) optimal for Li+ mobility, whereas c-axis alignment yields channels (∼1.81 Å) that favor Na+ diffusion. This work establishes cation ion exchange as a fundamental lever for channel engineering, providing a direct pathway to design high-performance, tunable solid electrolytes.