The design of new materials that provide high energy densities and long cycle life together with being economic and environmental benign is crucial for the energy storage. Therefore, the soft chemistry used to prepare the original frameworks, new structures is in perfect appropriateness with such a target. Our research is focused on the synthesis by soft chemistry of new “metastable” frameworks with large tunnels or layered structures at low temperature. We will discuss on our strategies to generate original framework showing ionic conductivity. The first approach is based on topotactic reactions starting from existing ionic conductors with a compact anionic framework [1]. In this case, we will show that the lithium/sodium insertion leads to new rock salt type structure. The second approach is related to polyanionic frameworks [2]. In order to favor reactivity, we are using protonic materials containing transition elements with adequate redox potential (Fe, Mn). We will show for example that lithium or sodium insertion into the jarosite hydroxysulfate phase NaFe₃(SO₄)₂(OH)₆ leads to an amorphous phase Na₃Fe₃(SO₄)₂(OH)₆ which exhibits a reversible electrochemical sodium intercalation/deintercalation through a solid solution-like process, leading back to the jarosite NaFe₃(SO₄)₂(OH)₆, at  2.72V and a capacity of 100 mAh/g at C/20. This unique topotactic reaction between an amorphous and a well crystallized phase is interpreted on the basis of the formation of an inorganic polymer and will be discuss in the presentation.

1. V. Pralong, V. Gopal, V. Caignaert, et al., Chem. Mat. Com., 2012, 24, 12; V. Pralong, Progress in Solid State Chem., 2009, 37, 4, 262-277; V. Gopal, V. Pralong, et al., Electrochem. Com., 40, 100-102, 2014; V. Pralong et al., Inorg. Chem., 53, 522, 2014
2. M. A. Reddy, V. Pralong, V. Caignaert, et al., Electrochem. Com., 2009, 11 1807; V. Pralong, V. Caignaert, B. Raveau, J. Mater. Chem., 2011, 21, 12188; M. Gnanavel et al., Chem Mater., 26, 4521, 2014