The design of polymeric semiconductors exhibiting high electrical conductivity (σ) and thermoelectric power factor (PF) will be vital for flexible large‐area electronics. In this work, four polymers based on diketopyrrolopyrrole (DPP), 2,3‐dihydrothieno[3,4‐b][1,4]dioxine (EDOT), thieno[3,2‐b]thiophene (TT), and 3, 3′‐bis (2‐(2‐(2‐methoxyethoxy) ethoxy) ethoxy)‐2, 2′‐bithiophene (MEET) are investigated as side‐chains, with the MEET polymers newly synthesized for this study. These polymers are systematically doped with tetrafluorotetracyanoquinodimethane ( F4TCNQ), CF3SO3H, and the synthesized dopant Cp(CN)3‐(COOMe)3, differing in geometry and electron affinity. The DPP‐EDOT‐based polymer containing MEET as side‐chains exhibits the highest conductivity (σ) ≈700 S cm−1 in this series with the acidic dopant (CF3SO3H). This polymer also shows the lowest oxidation potential by cyclic voltammetry (CV), the strongest intermolecular interactions evidenced by differential scanning calorimetry (DSC), and has the most oxygen‐based functionality for possible hydrogen bonding and ionic screening. Other polymers exhibit high σ ≈300–500 S cm−1 and power factor up to 300 µW m−1K−2. The mechanism of conductivity is predominantly electronic, as validated by time‐dependent conductance studies and transient thermo voltage monitoring over time, including for those doped with the acid. These materials maintain significant thermal stability and air stability over ≈6 weeks. Density functional theory calculations reveal molecular geometries and inform about frontier energy levels. Raman spectroscopy, in conjunction with scanning electron microscopy (SEM‐EDS) and x‐ray diffraction, provides insight into the solid‐state microstructure and degree of phase separation of the doped polymer films. Infrared spectroscopy enables this study to further quantify the degree of charge transfer from polymer to dopant.
Achieving the targeted control of layered oxide properties calls for more fundamental studies to mechanistically probe their evolution during their synthesis. Herein, dopant distribution, phase propagation, and local chemical changes as well as their interplay in multielement‐doped LiNiO2materials are investigated using spectroscopic, imaging, and scattering techniques. It is shown that dopants undergo dynamic redistribution in the Ni(OH)2host lattice at the early stage of calcination (below 300 °C). Such redistribution behavior exhibits strong dopant‐dependent characteristics, allowing for targeted surface and bulk doping control. The Ni oxidation process exhibits depth‐dependent characteristics and the most rapid Ni oxidation takes place between 300 and 700 °C. Using Ni oxidation state as the proxy for the phase transformation, the buildup of heterogenous phase propagation in the early stage of calcination is shown, especially along the radial direction of secondary particles. The radial heterogenous phase distribution gradually decreases upon completing the calcination. However, a high degree of mosaic‐like heterogeneity may still be present in the final product, departing from the perfect layered oxide. The present study offers fundamental insights into manipulating multiscale materials properties during calcination for obtaining stable, high‐energy layered oxide cathodes.
more » « less- NSF-PAR ID:
- 10447381
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Energy Materials
- Volume:
- 11
- Issue:
- 1
- ISSN:
- 1614-6832
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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