Polyanion-stabilized amorphous halide electrolytes with low lithium content for all-solid-state lithium batteries

Lithium halide solid electrolytes have garnered significant attention owing to their high ionic conductivity and positive electrode compatibility. However, achieving target ionic conductivity typically requires high lithium concentration (>4.3 wt%) within optimal structure, which raises costs and exacerbates air sensitivity. Here, we leverage anion clusters to synthesize a series of amorphous halide electrolytes xLi₂SO₄-ZrCl₄, with optimal ionic conductivities of 1.5 mS cm^-1 at 30 °C and a significantly reduced lithium content of 2.4 wt%, alongside good air stability. Through neutron/synchrotron X-ray experiments, first-principles calculations and machine learning-accelerated molecular dynamics simulations, we reveal a disordered backbone of [Zr_aCl_4a(SO₄)]^2- (1 ≤ a ≤ 4) that enables fast Li-ion diffusion via under-coordinated oxygen sites. All-solid-state lithium batteries employing these electrolytes and LiNi_0.8Co_0.1Mn_0.1O₂ positive electrode exhibit 81.1% capacity retention after 1400 cycles at 1 C (60 min) and 30 °C. Our findings reveal anion-cluster chemistry as an approach that transforms solid electrolyte design for advanced batteries, bridging materials science with practical energy storage innovation.