Polyethylene oxide-Li6.5La3Zr1.5Ta0.5O12 hybrid electrolytes: Lithium salt concentration and biopolymer blending

Wirtz, Maike; Linhorst, Max; Veelken, Philipp; Tempel, Hermann; Kungl, Hans; Moerschbacher, Bruno M.; Eichel, Rüdiger-A

Abstract

Hybrid electrolytes are developed to meet the requirements of safety, performance, and manufacturing for electrolytes suitable for Li-ion batteries with Li-anodes. Recent challenges—in addition to these key properties—emphasize the importance of sustainability. While compromising between these three objectives, the currently available materials are still well below the targeted goals. Three important issues for the design of hybrid electrolytes are (i) the role of the morphology and surface state of the ceramic particles in the polymer matrix, (ii) the dependence of salt concentration and ionic conductivity and, (iii) the effects of substituting part of the polyethylene oxide (PEO), with biopolymers. Electrolyte films were prepared from PEO, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), Li6.5La3Zr1.5Ta0.5O12 (LLZO:Ta), and biopolymers with varying contents of these components by a solution casting method. The films were analyzed with respect to structural and microstructural characteristics by DSC, Raman spectroscopy, and SEM. Ionic conductivity was evaluated by electrochemical impedance spectroscopy. Most interesting, when comparing films with LLZO:Ta versus without, the content of LiTFSI required for the maximum conductivity in the respective systems is different: a higher LiTFSI concentration is required for the former type. Overall, addition of LLZO:Ta as well as partial substitution of PEO by chitosan mesylate or cellulose acetate decrease the ionic conductivity. Thus—at least in the present approaches—a loss in performance is the drawback from attempts to enhance the safety by LLZO:Ta additions and sustainability by biopolymer blending of hybrid electrolytes.