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 Na3YbCl6 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 NaCrO2. 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 NaCrO2 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 NaCrO2. 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.