Minute-Scale Ultrafast Synthesis of Superionic Sodium Halide-Borate Electrolytes for Solid-State Batteries

Halides have emerged as promising solid electrolytes for solid-state batteries, owing to their good oxidative stability and favorable mechanical deformability. Nevertheless, the practical application of sodium chloride-based electrolytes has been severely hindered by sluggish Na+-ion transport and a strong reliance on prolonged mechanochemical processing, which substantially increases manufacturing cost. Here, we report a mixed-anion sodium halide-borate solid electrolyte, Na1+xTa(B4O7)xCl6–x, that effectively addresses these limitations. Partial substitution of Cl– by [B4O7]2– units creates mixed Ta–Cl–O coordination polyhedra that induce significant local structural distortion and promote rapid amorphization. As a result, a room-temperature ionic conductivity as high as 3.1 mS cm–1 is achieved within only 10 min of mechanochemical milling. Ab initio molecular dynamics simulations reveal that the incorporation of borate weakens Na+-ion coordination, activates coupled cation–anion dynamics, and enlarges Na+-ion transport bottleneck, which synergistically flattens the cation migration energy landscape for rapid Na+-ion diffusion. Benefiting from fast Na+-ion transport and favorable compatibility with cathode materials, Na1+xTa(B4O7)xCl6–x enables solid-state sodium batteries employing a NaCu0.12Ni0.22Fe0.33Mn0.33O2 cathode to sustain stable cycling for over 800 cycles with a capacity retention of 81.6%. These results establish Na1+xTa(B4O7)xCl6–x as a new class of halide-based superionic conductors and highlight mixed-anion engineering as an effective strategy for developing high-performance solid electrolytes.