SPP 2248 - Subproject: Insight into doping mechanisms of polymer electrolyte / redox-active organic radical polymer lamellar composites

Basic data for this project

Description

Organic radical batteries are particularly promising because of their high power density. From a fundamental perspective, favorable charge-transfer kinetics and fast charge-transport must be simultaneously enabled. Additionally, charge storage necessitates aliovalent doping to ensure charge neutrality. The underlying mechanisms on an atomic scale, however, are not well understood. This is particularly the case for „dry" gel-type or „solid" polymer multi-layered electrolytes, which are currently the materials-of-choice because of their high electrochemical stability.In a systematic approach, a family of multilayer polymer systems will be prepared and investigated with respect to PolyTEMPO, an established redox polymer system for liquid electrolytes. The model systems are comprised of a lithium metal anode, a highly lithium ion conducting polymer electrolyte layer and mixed conducting polymer composites, including electron conductor, redox polymer and a highly anion conducting polymer. The preparation part covers manufacturing and processing of the polymer materials into lamellar composites, as well as comprehensive electrochemical characterization.Details of the radical transfer mechanisms and occurring ion speciation will be elucidated based on c.w. and pulsed EPR methods, comparing and determining spectral features of pristine and cycled materials (post-mortem), including application of PELDOR/DEER to elucidate the distances and likely distributions of the radical species formed upon cell operation, despite challenging high local radical concentrations. Where feasible, ENDOR / HYSCORE will be invoked to further characterize the radical species with the materials. In-operando EPR will be performed on selected samples to monitor the evolution of the radical species based on their fingerprint signal, allowing insight into molecular details of the charge-transfer processes. Additional insights into mechanistic details of the electronic and ionic charge-transport will be provided by computational modelling of relevant processes from elementary electron transfer to ion transport across the interfaces within the layered composite. Ab initio methods will be utilized to characterize electronic properties of the redox-active polymers, whereas long-range ion transport and doping mechanisms of the organic cathode will be unraveled based on classical molecular dynamics simulations. In summary, apart from a deeper fundamental understanding, all these efforts will serve as guideline for an identification of promising redox-active materials and design of interfaces within the multilayer structures, in this way fostering future development of high performance solid organic electrolytes.