Development of block copolymer electrolytes for lithium metal batteries

Solvent-free electrolytes are being considered as the keystone element for the development of safer lithium-ion batteries. In this field, solid polymer electrolytes have emerged as a promising alternative to flammable liquid electrolytes. Some polymers such as poly(ethylene oxide) (PEO) promote the solvation of lithium salts and the conduction of lithium ions in its amorphous phase. However, satisfying conductivities are only reached above the melting point of the PEO crystallites (> 65°C) rendering PEO unpractical. Most of the current approaches have significantly improved the ionic conductivity, but at the expense of a severe worsening of the mechanical properties. Consequently, a major problem associated with polymer electrolytes in Li-batteries is its inability to combine simultaneously high ionic conductivity and high mechanical strength at room temperature. Herein, by means of block copolymer engineering, we design a mechanically clamped liquid-PEO electrolyte that combines the high ionic conductivity of a low molecular mass PEO and the dimensional integrity of a solid-like material. This unique combination results from the phase separation into microdomains. Only a minor fraction of structuring block confined inside microdomains maintains the mechanical integrity of the electrolyte while clamped liquid-PEO matrix ensures the ion conduction. In this thesis, the macromolecular architecture has been optimized to reach attractive ionic conductivities at room temperature without compromising the mechanical properties. Competitive performances are attained when integrating the developed materials into functional lithium metal battery prototypes. Moreover, the electrolyte integration has been attempted to thin-film and interdigitated microbatteries highlighting the provided potential. To achieve the goals of this project, polymer synthesis, physical characterization, electrolyte formulation, and battery prototyping were carried out.