A family of dual-anion-based sodium superionic conductors for all-solid-state sodium-ion batteries
Xiaoting Lin, Shumin Zhang, Menghao Yang, Biwei Xiao, Yang Zhao, Jing Luo, Jiamin Fu, Changhong Wang, Xiaona Li, W.S. Li, Feipeng Yang, Hui Duan, Jianwen Liang, Bolin Fu, Hamidreza Abdolvand, Jinghua Guo, Graham King, Xueliang Sun
Abstract
The sodium (Na) superionic conductor is a key component that could revolutionize the energy density and safety of conventional Na-ion batteries. However, existing Na superionic conductors are primarily based on a single-anion framework, each presenting inherent advantages and disadvantages. Here we introduce a family of amorphous Na-ion conductors (Na2O2–MCly, M = Hf, Zr and Ta) based on the dual-anion framework of oxychloride. Benefiting from a dual-anion chemistry and with the resulting distinctive structures, Na2O2–MCly electrolytes exhibit room-temperature ionic conductivities up to 2.0 mS cm−1, wide electrochemical stability windows and desirable mechanical properties. All-solid-state Na-ion batteries incorporating amorphous Na2O2–HfCl4 electrolyte and a Na0.85Mn0.5Ni0.4Fe0.1O2 cathode exhibit a superior rate capability and long-term cycle stability, with 78% capacity retention after 700 cycles under 0.2 C (1C = 120 mA g−1) at room temperature. The discoveries in this work could trigger a new wave of enthusiasm for exploring new superionic conductors beyond those based on a single-anion framework. All-solid-state sodium-ion batteries are promising candidates for grid-scale energy storage, but they require superior solid-state electrolytes (SSEs). Here sodium-ion SSEs based on dual-anion frameworks of oxychloride are studied and found to show high ionic conductivity and electrochemical oxidative stability with mechanical softness.