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@PHDTHESIS{Daniel:1037190,
      author       = {Daniel, Davis Thomas and Granwehr, Josef and Pich, Andrij},
      title        = {{E}lectron paramagnetic resonance spectroscopic
                      investigations of organic radical polymer batteries},
      school       = {RWTH Aachen},
      type         = {Dissertation},
      publisher    = {RWTH Aachen University},
      reportid     = {FZJ-2025-00535},
      pages        = {pages 1 Online-Ressource : Illustrationen},
      year         = {2024},
      note         = {Dissertation, RWTH Aachen, 2024},
      abstract     = {Organic radical polymer batteries (ORBs) represent a viable
                      pathway to a more sustainable energy storage technology
                      compared to conventional Li-ion batteries which utilise
                      metal oxides as cathodes. ORBs feature rapid charging
                      capabilities, long cycle life and can be constructed from
                      non–toxic raw materials. Furthermore, the use of polymers
                      extend the scope of their application to fields which
                      conventional batteries fail to cater to. For further
                      materials and cell development towards competitive energy
                      and power densities, a deeper understanding of redox
                      processes in an ORB is essential. Presently, realisation of
                      high energy densities in ORB is challenged by the need to
                      use large amount of conductive additives to the cathode
                      composite for ensuring sufficient electronic conductivity.
                      Optimisation of cathode composition necessitates the
                      formulation of specific methods and investigative protocols,
                      tailored to ORBs, which can aid in their practical
                      implementation and transition to the next generation of
                      all–organic batteries. In this thesis, a Li-ORB, which
                      consists of lithium as the anode and a poly(2,2,6,6-
                      tetramethyl-1-piperidinyloxy methacrylate) (PTMA)–carbon
                      black (CB) composite as the cathode is investigated. The
                      main technique which is applied is electron paramagnetic
                      resonance (EPR) spectroscopy, which detects unpaired
                      electrons and is therefore particularly amenable to the
                      study of redox processes. Furthermore, EPR results are
                      complemented with nuclear magnetic resonance spectroscopic,
                      electrochemical and theoretical methods. First, individual
                      components of the ORB such as the active material and the
                      conductive additive are studied using routine EPR techniques
                      such as continuous wave (CW) EPR. Then, the interactions
                      between these components such as active
                      material–electrolyte interactions and active
                      material–carbon black contact, are investigated using
                      advanced pulsed EPR techniques. Finally, in operando EPR is
                      used to probe the whole PTMA–ORB cell system.
                      Investigation into the interaction between the active
                      material, TEMPO ((2,2,6,6- tetramethylpiperidin-1-yl)oxyl)
                      methacrylate (PTMA monomer) and the electrolyte revealed
                      that the microenvironment of the radical species differs
                      depending on the solvent used for the electrolyte. In case
                      of linear carbonates, Li nuclei preferentially bind to the
                      radical species while in case of cyclic carbonates, a
                      significantly smaller fraction of lithium bound radical
                      species is found. The findings indicate that ionic transport
                      in ORBs may be crucially influenced by the redox unit and
                      the composition of solvent system used for preparing the
                      electrolyte. In this aspect, EPR hyperfine spectroscopic
                      techniques provide very localised information about Li–ion
                      solvation and its interaction with the redox unit. Two
                      relevant electron spin processes, electron spin exchange and
                      electron spin relaxation are exploited to bridge
                      electrochemical performance with EPR observables. T1 was
                      found to be a good indicator of the electronic contact
                      quality between CB and the active material. A method based
                      on the combination of Laplace inversion and T1 relaxation
                      was used to monitor the contact quality and its dependence
                      on the ratio of CB to active material in the composite
                      samples. Within the same composite sample, different
                      fractions of radicals with varying contact quality with the
                      CB were identified. A hypothesis for the origin of different
                      relaxation modes was devised. It suggests that the electrode
                      composition may locally affect the quality of electronic
                      contact between the active material and CB. The method was
                      also applied to unravel a possible pathway for isolated
                      redox units to participate in the main electron transport
                      mechanism in ORBs i.e. electron hopping. While the isolated
                      redox units were found to have high affinity for carbon
                      black, loss in contact with the conductive additive due to
                      dissolution into the electrolyte was shown by
                      Laplace–inverted pulsed EPR relaxation. CW EPR indicated
                      that the cross–linked PTMA polymers adopt conformations
                      which lead to an increase in radical–radical contacts. In
                      operando EPR further revealed that such conformational
                      changes may be influenced by rate of charging and
                      discharging. At high charge rates, regions of the cathode
                      film were rendered electrochemically inactive which could be
                      made active again at slower charging rates. Electrochemical
                      capacity showed correlation with the radical concentration
                      and, EPR linewidth allowed for a quantification of state of
                      charge dependent electron hopping (or spin exchange) rates.
                      Transient changes in the radical density also caused a
                      variation in the observed g values, indicating that g values
                      can be used as a parameter to validate theoretical
                      simulations of the organic cathode at different states of
                      charge. Density functional theory (DFT) was used to
                      calculate g tensors for radical polymers, which served as
                      training data for a machine learning (ML) based approach to
                      predict g values. The ML based approach was found to be a
                      viable alternative to computationally–demanding DFT
                      calculations, thereby offering a more scalable method to
                      predict g–values for systems with a larger size and
                      complexity.},
      keywords     = {DFT (Other) / EPR (Other) / NMR (Other) / batteries (Other)
                      / electrolyte degradation (Other) / machine learning (Other)
                      / organic radical poylmer batteries (Other) / polymers
                      (Other) / sustainable energy storage (Other)},
      cin          = {IET-1},
      ddc          = {540},
      cid          = {I:(DE-Juel1)IET-1-20110218},
      pnm          = {1223 - Batteries in Application (POF4-122) / DFG project
                      G:(GEPRIS)422726248 - SPP 2248: Polymer-basierte Batterien
                      (422726248) / HITEC - Helmholtz Interdisciplinary Doctoral
                      Training in Energy and Climate Research (HITEC)
                      (HITEC-20170406)},
      pid          = {G:(DE-HGF)POF4-1223 / G:(GEPRIS)422726248 /
                      G:(DE-Juel1)HITEC-20170406},
      typ          = {PUB:(DE-HGF)11},
      doi          = {10.18154/RWTH-2024-05180},
      url          = {https://juser.fz-juelich.de/record/1037190},
}