Chemomechanical Failure Mechanism Study in NASICON-Type Li1.3Al0.3Ti1.7(PO4)3 Solid-State Lithium Batteries

NASICON-type solid electrolytes such as Li1.3Al0.3Ti1.7(PO4)3 (LATP) have the following advantages: they are of low cost and environmentally friendly and they exhibit air stability and high ionic conductivity. However, the unstable Li/LATP interface usually leads to fast degradation of batteries. The knowledge of the inherent failure mechanism of the interface, especially the interfacial reaction products, dynamic electron/ion transport processes, and subsequent chemomechanical effects at the nanoscale level will provide an important scientific basis to develop strategies toward mitigation failure of batteries. Herein, we conduct a series of studies on the interface between LATP and lithium metal by using solid-state NMR along with X-ray diffraction and in situ transmission electron microscopy. A lithiated-phase Li3Al0.3Ti1.7(PO4)3 is first confirmed with at least 3 orders of magnitude of higher electronic conductivity enhanced at the Li/electrolyte interface, which is the chief culprit for continuous growth of the interphase. The high electronic conductivity can also induce direct deposition of lithium dendrites inside the electrolyte. Moreover, the sizeable volumetric expansion was observed in the lithiated LATP, which eventually breaks up the bulk electrolyte and induces high resistance. Finally, we elucidated the chemomechanical degradation mechanism of the Li/LATP interface, which has important implications to the interfacial problems in numerous electrolytes which are unstable with lithium.