Rechargeable lithium ion batteries help to enable sustainable energy systems by storing electricity generated by intermittent renewable resources such as wind and solar energy, or by powering zero-emission electric vehicles charged by electricity from renewable resources. A key challenge to improve performance and to reduce cost of lithium batteries is to increase charge capacity. Solid-state lithium batteries that use the element sulfur as the cathode have a theoretical storage capacity that is nearly three times higher than conventional lithium ion batteries, but suffer from low conductivity of the solid electrolyte needed stabilize the battery. To improve the conductivity of the electrolyte, this project will develop new solid electrolyte materials composed of ceramic conductor materials mixed with polyimine materials. The key innovations are that the ceramic materials will be engineered for high lithium ion conduction, and the polyimines will improve the mechanical stability of ceramic conductor material during repeated charging and discharging cycles. Furthermore, to facilitate technology transfer to the private sector, the solid electrolyte fabrication steps will be designed to enable scalable manufacture in the future. The educational activities associated with this project include active participation of undergraduates in research, particularly from under-represented groups in engineering, with recruitment coordinated through a variety of programs at the University of Colorado, Boulder.
The overall goal of the research is to develop solid-state hybrid electrolytes for lithium-sulfur batteries composed of binary inorganic lithium sulfide and phosphorous sulfide based ceramic conductors, and malleable self-healing polyimines that serve as the binder material. The proposed solid-state hybrid electrolytes are anticipated to have significantly improved mechanical properties, lithium ionic conductivity, and cycling stability. Highly-conductive, thin film electrolytes free of pinholes and defects will be fabricated and integrated into the electrochemical cell. The effects of polymer structure and surface chemistry at the polyimine polymer/ceramic conductor interface on battery performance will be studied. The research plan has four objectives. The first objective is to develop ion-conducting, malleable, self-healing polyimine polymers to serve as the matrix of solid-state hybrid electrolyte. The second objective is to identify conductive ceramic materials with good surface adhesion to the matrix polymers. The third objective is to develop a reliable process for fabrication of ion-conducting thin continuous hybrid membranes, and the fourth objective is to study the structure-property relationships of the solid-state lithium-sulfur batteries containing the new hybrid electrolytes.
