Laplace inverted pulsed EPR relaxation to study contact between active material and carbon black in Li–organic battery cathodes

Daniel, Davis Thomas; Szczuka, Conrad; Jakes, Peter; Eichel, Rüdiger‐A.; Granwehr, Josef

doi:10.1039/d3cp00378g

Cited by 5 publications

(5 citation statements)

References 78 publications

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“…In the case of PTMA in an ORB, the disagreement between g iso calc of PTMA-1 and g iso exp for a state of low radical density of the ORB may stem from interactions between PTMA and other battery constituents, which are more effective when intramolecular radical–radical interactions are negligible. It is known that conductive additives used in organic cathodes affect experimental EPR parameters and battery performance . However, the current complexity of the simulated system does not account for such interactions.…”

Section: Resultsmentioning

confidence: 99%

“…It is known that conductive additives used in organic cathodes affect experimental EPR parameters and battery performance. 87 However, the current complexity of the simulated system does not account for such interactions. Another reason could be long-range radical–radical interactions which are not captured in the DFT calculations with individual polymer chains but are expected to be present even at low and intermediate radical densities as the polymer prefers to maximize radical–radical interactions.…”

Section: Resultsmentioning

confidence: 99%

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Machine Learning Isotropic g Values of Radical Polymers

Daniel,

Mitra,

Eichel

et al. 2024

J. Chem. Theory Comput.

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Methods for electronic structure computations, such as density functional theory (DFT), are routinely used for the calculation of spectroscopic parameters to establish and validate structure−parameter correlations. DFT calculations, however, are computationally expensive for large systems such as polymers. This work explores the machine learning (ML) of isotropic g values, g iso , obtained from electron paramagnetic resonance (EPR) experiments of an organic radical polymer. An ML model based on regression trees is trained on DFT-calculated g values of poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA) polymer structures extracted from different time frames of a molecular dynamics trajectory. The DFT-derived g values, g iso calc , for different radical densities of PTMA, are compared against experimentally derived g values obtained from in operando EPR measurements of a PTMA-based organic radical battery. The MLpredicted g iso values, g iso pred , were compared with g iso calc to evaluate the performance of the model. Mean deviations of g iso pred from g iso calc were found to be on the order of 0.0001. Furthermore, a performance evaluation on test structures from a separate MD trajectory indicated that the model is sensitive to the radical density and efficiently learns to predict g iso values even for radical densities that were not part of the training data set. Since our trained model can reproduce the changes in g iso along the MD trajectory and is sensitive to the extent of equilibration of the polymer structure, it is a promising alternative to computationally more expensive DFT methods, particularly for large systems that cannot be easily represented by a smaller model system.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Machine Learning Isotropic g Values of Radical Polymers

Daniel,

Mitra,

Eichel

et al. 2024

J. Chem. Theory Comput.

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“…The two samples showed almost identical relaxation characteristics, with a dominant relaxation mode at T 1 ≈ 4 µs and no slowly relaxing contributions. We recently reported such a pronounced relaxation enhancement for nitroxide radicals in direct contact with carbon black 35 . It suggests a good and direct contact of all the isolated radicals with CB, i.e.…”

Section: Pulsed Eprmentioning

confidence: 93%

“…Laplace inversion of T 1 relaxation data was done using an exponential kernel without non-negativity constraint, with pre-processing of data and parametrization as described elsewhere. 35,44 The inversion was performed using home-written scripts that were run on Octave v. 6.4. 45 were used to simulate the PTMA electrode in the presence of LP57.…”

Section: Epr Spectroscopy Sample Preparationmentioning

confidence: 99%

“…Electron paramagnetic resonance (EPR) spectroscopy, a technique which detects unpaired electron spins, is well suited for investigating battery materials [30][31][32][33] . In ORB research, continuous wave (CW) EPR is routinely used for radical quantification 8,34 , while pulsed EPR can be used to probe specific interactions between the ORB components 35 . Furthermore, in operando and in situ EPR techniques have also been applied to ORB systems [36][37][38] .…”

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confidence: 99%

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Multimodal investigation of electronic transport in PTMA and its impact on organic radical battery performance

Daniel

Oevermann

Mitra

et al. 2023

Sci Rep

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Organic radical batteries (ORBs) represent a viable pathway to a more sustainable energy storage technology compared to conventional Li-ion batteries. For further materials and cell development towards competitive energy and power densities, a deeper understanding of electron transport and conductivity in organic radical polymer cathodes is required. Such electron transport is characterised by electron hopping processes, which depend on the presence of closely spaced hopping sites. Using a combination of electrochemical, electron paramagnetic resonance (EPR) spectroscopic, and theoretical molecular dynamics as well as density functional theory modelling techniques, we explored how compositional characteristics of cross-linked poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA) polymers govern electron hopping and rationalise their impact on ORB performance. Electrochemistry and EPR spectroscopy not only show a correlation between capacity and the total number of radicals in an ORB using a PTMA cathode, but also indicates that the state-of-health degrades about twice as fast if the amount of radical is reduced by 15%. The presence of up to 3% free monomer radicals did not improve fast charging capabilities. Pulsed EPR indicated that these radicals readily dissolve into the electrolyte but a direct effect on battery degradation could not be shown. However, a qualitative impact cannot be excluded either. The work further illustrates that nitroxide units have a high affinity to the carbon black conductive additive, indicating the possibility of its participation in electron hopping. At the same time, the polymers attempt to adopt a compact conformation to increase radical–radical contact. Hence, a kinetic competition exists, which might gradually be altered towards a thermodynamically more stable configuration by repeated cycling, yet further investigations are required for its characterisation.

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Curvature‐Induced Electron Spin Catalysis with Carbon Spheres

Qiao,

Cao,

Wang

et al. 2024

Angewandte Chemie

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Here, we report curvature‐induced electron spin catalysis by using solid carbon spheres as catalysts, which were synthesized using positive curvature molecular hexabromocyclopentadiene as a precursor molecule, following a radical coupling mechanism. The curvature spin of carbon is regarded as an overlapping state of σ‐ and π‐radical, which is identified by the inverse Laplace transform of pulse‐electron paramagnetic resonance. The growth mechanism of carbon spheres abiding by Kroto's model, is supported by the density functional theory study of thermodynamics and kinetics calculations. The solid carbon spheres present excellent catalytic behaviour of oxidation coupling of amines to form corresponding imines with the conversion of >99 %, selectivity of 98.7 %, and yield of 97.7 %, which is attributed to the predominantly curvature‐induced electron spin catalysis of carbon, supported by the calculation of oxygen adsorption energy. This work proposes a view of curvature‐induced spin catalysis of carbon, which opens up a research direction for curvature‐induced electron spin catalysis.

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Laplace inverted pulsed EPR relaxation to study contact between active material and carbon black in Li–organic battery cathodes

Abstract: The addition of conductive additives during electrode fabrication is standard practice to mitigate a low intrinsic electronic conductivity of most cathode materials used in Li-ion batteries. To ensure an optimal...

Cited by 5 publications

References 78 publications

Machine Learning Isotropic g Values of Radical Polymers

Machine Learning Isotropic g Values of Radical Polymers

Multimodal investigation of electronic transport in PTMA and its impact on organic radical battery performance

Curvature‐Induced Electron Spin Catalysis with Carbon Spheres

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