Effective regulation towards electrochemical stability of superionic solid electrolyte via facile dual-halogen strategy

Several halide electrolytes have come back into the spotlight with their high ionic conductivity, soft texture and compatibility with high-voltage electrodes. However, the instability with lithium metal has hindered their application in all-solid-state lithium-metal batteries (ASSLMBs). Thereby, it is urgent to find an efficient way to tackle this issue. Herein, we have simultaneously enhanced the kinetic stability towards lithium metal and intrinsic stability towards high-voltage cathodes for Li2ZrCl6 electrolytes via effective dual-halogen strategy while the ionic conductivity of electrolyte is not sacrificed due to the effects of morphology modification. Specially, the symmetric Li/Li2ZrCl5.2F0.8/Li cell can cycle stably for over 2000 h (0.1 mA cm-2, 0.5 mA h cm-2) and the modified electrolyte Li2ZrCl5.2F0.8 also shows higher oxidative stability than the original Li2ZrCl6. The in-situ formed fluoride interphase (LiF, ZrFx) can account for the excellent kinetic stability at Li/Li2ZrCl5.2F0.8 interface while the improved oxidative stability can be attributed to the higher electronegativity of F element. Finally, the Li2ZrCl5.2F0.8 is also proved appliable in the Li/Li2ZrCl5.2F0.8/LiNi0.8Co0.1Mn0.1O2 battery in the form of stable and satisfied discharge capacity (∼106.9 mAh g-1, the 20th - 65th cycle) due to the achievement of kinetic stability at Li/Li2ZrCl5.2F0.8 interface in the initial stage (the first ∼ 19 cycles). The clever dual-halogen strategy proposed in this work can effectively enhance the electrochemical stability of electrolytes and foster the application of cost-effective Li2ZrCl6 halides in ASSLMBs.