Lithium-ion batteries are efficient electrochemical devices for storing electrical energy, produced for instance by intermittent sources (wind, solar). They are also attracting a growing interest due to their use in on-board automotive and portable applications. Nowadays, the improvement of energy density and safety aspects is a major issue. However, the development of this technology is limited by short -circuiting hazards and flammability of standard liquid electrolytes. The CEA-LITEN recently developed a new material based on free solvent lithium ion conducting polymer. High performances (safety, conductivity) were obtained when such electrolytes have a crystalline structure in the solid state. The thesis aims at understanding the microscopic properties of these promising materials and their impact on the functional properties, for the design of high performance batteries. A systematic study of the structure / transport relationship will be carried out by combining sophisticated experimental tools: cutting-edge scattering experiments on Large Scale Facilities, AFM, impedance spectroscopy and NMR. The impact of both chemical parameters and process will be evaluated to optimize the best electrolyte material. At the end, a prototype of a safer and efficient battery will be delivered. This basic research project t is therefore directly related to the technological development of new generation lithium-ion batteries and will benefit from the complementary expertise of the host laboratory CEA- INAC- SPrAM (multi- scale characterization of polymer electrolytes ) and his partner, CEA- LITEN (synthesis / test innovative materials).