Enhancing the Thermal Stability of NASICON Solid Electrolyte Pellets against Metallic Lithium by Defect Modification

All-solid-state batteries (ASSBs) are expected to address the battery safety issues fundamentally by replacing the flammable electrolyte with solid electrolytes (SEs). However, recent studies report that the thermal runaway happened for NASICON-type SEs when they contact with Li metal at high temperature and indicate that the ASSBs may not be totally safe. Here, the thermal stability of a NASICON-type Li1.4Al0.4Ti1.6(PO4)(3) (LATP) SE pellet against metallic lithium is quantified in a quasi-practical situation. Accelerated thermal runaway of the LATP pellet compared to LATP powder is observed when they contact with lithium. Combining electrochemical impedance spectroscopy and X-ray computed tomography analysis, lithium penetration into the pellet at high temperature has been observed. The penetrated lithium without surface impurities and the high reactivity of LATP at defect sites (atomic structural defects, cracks, voids, etc.) lead to higher interfacial reactivity and earlier thermal runaway. By adding LiPO2F2 to modify those defect sites of the LATP pellet and impede the lithium/SE interfacial reactions, the thermal runaway can be remarkably delayed. This work elucidates the thermal runaway behaviors of Li/LATP pellets in a quasi-practical environment, provides new information about safety issues of ASSBs, and inspires future investigations into this urgent-needed area.

Automated summary

Recent studies have shown that thermal runaway can occur when NASICON-type SEs come in contact with lithium metal at high temperatures, indicating potential safety concerns for all-solid-state batteries. Experimental observations also suggest that the thermal runaway of LATP pellets in contact with lithium metal can be accelerated, highlighting the importance of understanding and addressing safety issues in ASSBs. Adding LiPO2F2 to modify defect sites in LATP pellets has been shown to significantly delay thermal runaway, suggesting potential strategies for improving the safety of all-solid-state batteries.