Halide Heterogeneous Structure Boosting Ionic Diffusion and High_Voltage Stability of Sodium Superionic Conductors

Abstract

Abstract The development of solid_state sodium_ion batteries (SSSBs) heavily hinges on the development of an superionic Na + conductor (SSC) that features high conductivity, (electro)chemical stability, and deformability. The construction of heterogeneous structures offers a promising approach to comprehensively enhancing these properties in a way that differs from traditional structural optimization. Here, this work exploits the structural variance between high_ and low_coordination halide frameworks to develop a new class of halide heterogeneous structure electrolytes (HSEs). The halide HSEs incorporating a UCl 3 _type high_coordination framework and amorphous low_coordination phase achieves the highest Na + conductivity (2.7 mS cm _1 at room temperature, RT) among halide SSCs so far. By discerning the individual contribution of the crystalline bulk, amorphous region, and interface, this work unravels the synergistic ion conduction within halide HSEs and provides a comprehensive explanation of the amorphization effect. More importantly, the excellent deformability, high_voltage stability, and expandability of HSEs enable effective SSSB integration. Using a cold_pressed cathode electrode composite of uncoated Na 0.85 Mn 0.5 Ni 0.4 Fe 0.1 O 2 and HSEs, the SSSBs present stable cycle performance with a capacity retention of 91.0% after 100 cycles at 0.2 C.