Crosslinked Single-Ion-Conductor Polymer Electrolytes

Liquid based electrolytes used in conventional Li-ion batteries are made of a mixture of Li salt and flammable alkyl carbonate solvents. In addition, their transference number (t +) is low, typically 0.3, which limits the battery power performance because of the formation of strong gradient of concentration during operation.[1] To increase both safety of energy density a solution is to develop a Li metal based battery comprising a single-ion-conductor solid polymer electrolyte.[2] Poly(ethylene oxide) (PEO) doped with a Li salt is the fundamental solid polymer electrolyte due to its high ionic conductivity (> 10-4 S/cm) above its melting temperature (> 60°C), and, chemical and electrochemical stability towards Li metal. However, its t + is low, about 0.15.[3] A strategy is then to develop a single-ion-conductor polymer electrolyte comprising PEO to ensure Li metal stability and battery operation at room temperature.[4] In this study, we report on the facile synthesis and the physico-chemical and electrochemical characterizations of series of crosslinked single-ion electrolytes based on a PEO matrix. These materials are shown to be single-ion-conductors with interesting Li dendrite resistance. In addition, for these electrolytes a thorough study by impedance spectroscopy using symmetrical cells with either Li reversible electrodes or stainless steel blocking electrodes reveals a complex electrolyte resistance response composed of two contributions as encountered in materials with bulk and grains boundaries (Figure 1). We thus proposed a methodology to extract the grain and grain boundary contributions, which is essential to correctly determine in turn the electrolyte transport properties (transference number, diffusion coefficient). Furthermore, a discussion on the origin of this phenomena is proposed. References [1] K. Xu, Chem. Rev., 104 (2004) 4303. [2] R. Bouchet et al., Nat. Mater., 487 (2012) 1 [3] K. Pozyczka et al., Electrochim. Acta., 227 (2017) 127 [4] L. Long et al., J. Mater. Chem. A, 4 (2016) 10038 Figure 1