Failure analysis of the Ge-substituted Li6PS5I with bare LiNi0.8Co0.1Mn0.1O2 and performance improvement via Li2ZrO3 coating

Inorganic sulfide solid electrolytes with high ionic conductivity and low interfacial resistance attract extensive research attention. Here, we successfully synthesize Li6.7P0.3Ge0.7S5I argyrodite electrolyte with ultrahigh Li-ion conductivity (13.1 mS cm(-1) at room temperature) and low activation energy (0.19 eV). All-solid-state lithium batteries based on the prepared electrolyte and pristine LiNi0.8Co0.1Mn0.1O2 cathode show fast capacity degradation due to the side reaction between the active materials and Li6.7P0.3Ge0.7S5I electrolytes. XRD and TEM results confirm the existence of MnO2 and Ni3S2 at the interface between the pristine cathode and solid electrolyte, leading to high resistance and poor electrochemical performances. SEM results indicate that the large volume changes during cycling also contribute to the deteriorating battery performance. A thin layer of the Li2ZrO3 coating layer is then applied onto the surface of cathode materials, which delivers superior capacity properties and cyclability at ambient temperature. The coated electrode also delivers a high area capacity of 5.1 mA h cm(-2) with an ultrahigh area loading of 26.8 mg cm(-2) at 0.5C at ambient temperature when combined with the Li6.7P0.3Ge0.7S5I electrolytes. Moreover, the assembled battery offers an initial discharge capacity of 107.8 mA h g(-1) at 0.1C at -20 degrees C and maintains a capacity retention of 62% after 200 cycles.

Automated summary

Inorganic sulfide solid electrolytes with high ionic conductivity and low interfacial resistance have been successfully synthesized in this study. However, when applied in all-solid-state lithium batteries, fast capacity degradation is observed due to side reactions between the active materials and the electrolyte. The formation of high resistance interfaces between the cathode and solid electrolyte, as well as the large volume changes during cycling, also contribute to the poor battery performance. By applying a thin layer of Li2ZrO3 coating onto the cathode materials, the battery performance and cyclability can be significantly improved.