The development of polymer electrolytes with high ionic conductivity, high lithium transference number, and high electrochemical stability is one of the main aims in the field of lithium battery research. In this work, we describe the synthesis and the characterization of new electrolyte systems, composed of three-dimensional hybrid inorganic−organic networks doped with LiClO 4 . The preparation route comprises only three steps, namely a sol−gel reaction, salt dissolution, and an epoxide polymerization reaction. The lithium concentration, and thus the lithium transference number, was modulated by adding lithium hydroxide in the sol−gel step. In this way, seven electrolytes with varying salt concentrations were prepared. The hybrid electrolytes are characterized by good ionic conductivities (up to 8·10 −5 S/cm at room temperature) and high thermo-mechanical and electrochemical stabilities. Stability tests versus lithium metal via galvanostatic polarization showed that this material is superior with respect to reference poly(ethylene oxide) based electrolytes. W ith the demand for higher energy densities, coupled with the need of increased safety, the electrolyte is considered to be the key component for the development of improved lithium batteries. 1 In particular, much effort is currently spent on the development of solid polymer electrolytes (SPEs) which provide higher thermal stability with respect to standard liquid electrolytes. They also offer better resistance to dendrite formation, thus paving the way for the use of lithium metal anodes and to high energy density batteries such as Li/air and Li/S batteries. 2 The most studied class of polymer electrolytes consists of complexes of poly(ethylene oxide) (PEO) with various lithium salts, as described by Wright and Armand already in the 1970s. 3 These materials are of great interest because of their low cost and toxicity, but the conductivity at room temperature is restricted to ca. 10 −6 S/cm only, which is too low for practical purposes. 4 One of the causes of the low conductivity is the semicrystalline morphology of PEO: ionic conduction occurs predominantly in the amorphous domains, with the crystalline domains playing an impeding role by increasing the tortuosity of the conduction pathways. 5,6 Other drawbacks are the decrease of the mechanical and electrochemical stability at high temperatures 2 and the low Li + transport number. 7 This point is particularly critical for electrolyte application, and it has been variously addressed, either by varying the lithium salt 8 or by developing single-ion conduction electrolytes. 2,9−11 In the field of the binary polyether based electrolytes, one of the easiest and most rewarding research strategies consists of the preparation of composites, in which inorganic particles are dispersed in the PEO matrix. These systems usually benefit from improved mechanical properties and from an increased ionic conductivity. 12,13 The latter effect is attributed to the hindering of the crystallization process or to Lewis acid−ba...
