Impacts of Lithium Salts on the Thermal and Mechanical Characteristics in the Lithiated PEO/LAGP Composite Electrolytes

Jeremy Lee,Hong Huang,Michael Rottmayer

doi:10.3390/jcs6010012

Jeremy Lee, Hong Huang + Show 1 more

Open Access

https://doi.org/10.3390/jcs6010012

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Abstract

Lithium batteries utilizing solid-state electrolytes have the potential to alleviate their safety hazard, reduce packaging volume, and enable flexible design. Polymer/ceramic composite electrolytes (CPE) are more attractive because the combination is capable of remedying and/or transcending individual constituent’ properties. Recently, we fabricated a series of free-standing composite electrolyte membranes consisting of Li1.4Al0.4Ge1.6(PO4)3 (LAGP), polyethylene oxide (PEO), and lithium salts. In this study, we characterized thermal and mechanical properties of the CPEs with two representative lithium salts, i.e., lithium boron fluoride (LiBF4) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). We found that the type of lithium salt can prevail the LAGP ceramic loadings on altering the key properties. It is observed that LiTFSI, compared with LiBF4, causes more significant reduction in terms of the crystallinity of PEO, melting transition, and mechanical strengths. The differences in these aspects can be ascribed to the interactions between the polymer matrix and anions in lithium salt.

Highlights

Advanced lithium-ion batteries and lithium batteries based on the lithium–sulfur and lithium–oxygen chemistries have been the main foci to meet the ever-increased demands for higher energy density and safety
We have investigated the impacts of LAGP loading on the electrical, thermal, and mechanical characteristics in the polyethylene oxide (PEO)/LAGP/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) composite system [29]
In order to understand if the observed phenomena reflect a general trend in the presence of LAGP and to explore an alternative lithium salt candidate which has better thermal stability and mechanical strength, we have investigated the PEO/LAGP/LiBF4 system

Summary

Introduction

Advanced lithium-ion batteries and lithium batteries based on the lithium–. We are not aware systematic studies focusing on the impacts of lithium salts on thermal and mechanical properties in a same polymer/ceramic electrolyte setting. LiTFSI is presently one of the most favorable lithium salts owing to its sufficient ionic conductivity, good thermal stability (up to 300 ◦ C), and its remarkable tolerance to hydrolysis [21,25]. In order to understand if the observed phenomena reflect a general trend in the presence of LAGP and to explore an alternative lithium salt candidate which has better thermal stability and mechanical strength, we have investigated the PEO/LAGP/LiBF4 system. Since the polymer matrix and ceramic filler ratio are fixed, the systematic studies render us to exclusively determine the impacts of type of lithium salt on the thermal and mechanical properties. The discussion emphasizes on the aspects of melting transition and mechanical reinforcement differences resulting from the two lithium salts

Experimental

Thermal and Mechanical Characterizations

Results and Discussion

Conclusions