“Range of Potentials Impedance Spectroscopy”: A Tool for Understanding the Positive Effect of LATP in Solid-State Lithium Batteries Based on Polymeric Electrolyte

Composite solid electrolytes with ceramic particles dispersed in polymeric matrices are promising for all-solid-state batteries, based on active metal anodes. However, a systematic analysis of the beneficial features that ceramic particles in polymeric electrolytes can provide, was never done so far. In this study, we offered electrochemical methods based on previous experience with liquid electrolytes to distinguish between the resistance of interfacial surface films and the resistance of charge transfer processes. In all-solid-state batteries, charge transfer and ion migration through surface films may have similar time constants, which makes electrochemical analyses of these systems a great challenge. We report herein on developing a method termed: "Range of Potentials Impedance Spectroscopy" (RPIS). The underlying concept of this method is that changes in cells potentials during their operation should accelerate the kinetics of charge transfer processes but should affect only moderately migration of ions through interfacial surface films. Consequently, it may be possible to evaluate separately resistances that reflect charge transfer and ionic migration processes. Here, we present the method using a specific case as a prototype: 30% weight of Li1.3Al0.3Ti1.7(PO4)3 (LTAP) was embedded in PEO20:LiTFSI matrices. (denoted as LATP30 electrolyte). LATP30-based Li||LiFePO4 batteries show superior performance: after ~150 cycles, cells retained 84% of their original capacity in comparison to the same batteries, LATP free, that showed only 51% capacity retention after 150 cycles. At 5C, these cells with the composite polymeric electrolyte demonstrated 43% higher discharge capacity than their counterparts. In symmetric cells and all-solid-state batteries, LATP30 lowers the impedance of the electrode-electrolyte interfaces, conferring stability during cycling. By applying RPIS, we could identify the electrochemical barrier that the presence of LATP helps to lower. We discovered that LATP reduces both surface film and charge transfer resistances, enabling batteries to withstand prolonged cycling and high C-rates. These results have significant implications for further studies that should focus significantly on interfacial impedances as major barriers, rather than on bulk electrolyte resistance as a key factor. Reference: Ortal Breuer et al J. Electrochem. Soc. 2023, 170, 090509