LAUSR

All‐solid‐state sodium batteries (ASSSBs) have attracted extensive attention for the high abundancy of sodium resources, enhanced safety, and superior energy density. As a critical component of ASSSBs, halide solid‐state electrolytes (SSEs) have been widely studied in recent years, but still suffer from low ion conductivity and poor interfacial contact with the cathode due to their high crystallinity. Here, a completely amorphized Na1.33Ta0.67Zr0.33Cl6 (NTZC) SSEs is reported, with a remarkable ionic conductivity of 3.4 mS cm−1 at 25 °C and exceptional viscoelasticity. Zr‐doping induces complete amorphization via twisting the [TaCl6]– octahedra. The distortion of the [TaCl6]– octahedra not only enlarges Na+ migration channels but also reduces the Cl− blocking effects on Na+ transport, while Zr‐doping also expands the lattice volume due to its larger ionic radius compared to Ta5+. ASSSBs with the Na0.95Ni0.33Fe0.33Mn0.33O2 cathode achieve 77.45% retention after 450 cycles at 0.5 C under high mass loading (20.85 mg cm−2). This work provides a feasible way for the design and preparation of sodium halide solid electrolytes in the future.