Mechanochemical Synthesis of Pyrite Ni₁₋<i>_x</i>Fe<i>_x</i>S₂ Electrode for All-solid-state Sodium Battery (Supporting Information)

All-solid-state sodium secondary batteries are expected to be low-cost, next-generation batteries. NiS2 and FeS2 are potential candidates as positive electrode materials owing to their high theoretical capacities. However, it is difficult to achieve sufficient capacity with bulk FeS2. In this study, pyrite Ni1−xFexS2 (x = 0, 0.3, 0.5, 0.7, 0.9, and 1) electrodes are prepared by a mechanochemical process. The all-solid-state sodium cells with Ni1−xFexS2 show higher discharge–charge potentials than those with NiS2, and higher capacities than those with FeS2. In addition, Ni1−xFexS2 exhibits a higher rate performance than those of NiS2 and FeS2. The all-solid-state cells using Ni1−xFexS2 (x = 0.3, 0.5, and 0.7) are discharged and charged with a high capacity of approximately 390 mAh g−1, without significant capacity fading for at least 30 cycles. The solid-solution formation of NiS2 and FeS2 results in lower material cost, higher rate performance, higher discharge–charge potential than those of NiS2, and higher capacity than that of FeS2. Pyrite Ni1−xFexS2 is a promising positive electrode material for all-solid-state sodium secondary batteries.全固态钠二次电池有望成为低成本的下一代储能电池。二硫化镍（NiS₂）与二硫化亚铁（FeS₂）因具备极高的理论比容量，成为正极材料的潜在候选者。然而，块状二硫化亚铁难以实现足够的放电比容量。本研究通过机械化学法制备了黄铁矿型Ni₁₋ₓFeₓS₂（x=0、0.3、0.5、0.7、0.9及1）正极材料。搭载Ni₁₋ₓFeₓS₂的全固态钠电池，其充放电电位高于搭载二硫化镍的电池，且比容量高于搭载二硫化亚铁的电池。此外，Ni₁₋ₓFeₓS₂的倍率性能优于二硫化镍与二硫化亚铁。搭载Ni₁₋ₓFeₓS₂（x=0.3、0.5及0.7）的全固态钠电池可实现约390 mAh·g⁻¹的高比容量充放电，且至少30次循环内无明显容量衰减。二硫化镍与二硫化亚铁形成固溶体后，材料成本更低、倍率性能更优，充放电电位高于纯二硫化镍，且比容量高于纯二硫化亚铁。黄铁矿型Ni₁₋ₓFeₓS₂是一种极具应用前景的全固态钠二次电池正极材料。