Highly stable and encapsulation-microstructural cathode derived by self-pressurization behavior in Na-halides-based all-solid-state batteries

The emerging halide solid electrolytes (SEs) possess superior (electro)chemical oxidation stabilities compared to sulfide SEs , but the understanding on their good compatibility toward oxide active materials needs to be further studied. Here, we develop a type of Zr-doped Na 3 YbCl 6 chloride SEs. The optimized composition gains a high ionic conductivity and broad electrochemical oxidation window. The in situ and ex situ analyses verify that the chloride as ionic additive in the cathode is highly compatible with NaCrO 2 . Importantly, it is revealed that the volume change in the cathode can act a position effect on the microstructure evolution . It promotes to form a special core-shell-like structure with homogeneous chloride encapsulating NaCrO 2 grains. Such a soft intimate contact promotes a uniform ion transport and mitigate (electro)chemo-mechanical stresses. The prerequisites generating this specific microstructure are proposed. The main capacity loss of the assembled all-solid-state Na batteries (ASSNBs) only occurs in the initial dozens of cycles, induced by the irreversible O3→O'3 phase transition in NaCrO 2 . The chloride additives with a soft feature and high oxidation-stability allow a high-quality interface in the oxide cathode and an excellent cycling stability of the ASSNBs.