| 1. |
- Adnan, Mohammed Mostafa, et al.
(författare)
-
The Structure, Morphology, and Complex Permittivity of Epoxy Nanodielectrics with In Situ Synthesized Surface-Functionalized SiO2
- 2021
-
Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 13:9
-
Tidskriftsartikel (refereegranskat)abstract
- Epoxy nanocomposites have demonstrated promising properties for high-voltage insulation applications. An in situ approach to the synthesis of epoxy-SiO2 nanocomposites was employed, where surface-functionalized SiO2 (up to 5 wt.%) is synthesized directly in the epoxy. The dispersion of SiO2 was found to be affected by both the pH and the coupling agent used in the synthesis. Hierarchical clusters of SiO2 (10–60 nm) formed with free-space lengths of 53–105 nm (increasing with pH or SiO2 content), exhibiting both mass and surface-fractal structures. Reducing the amount of coupling agent resulted in an increase in the cluster size (~110 nm) and the free-space length (205 nm). At room temperature, nanocomposites prepared at pH 7 exhibited up to a 4% increase in the real relative permittivity with increasing SiO2 content, whereas those prepared at pH 11 showed up to a 5% decrease with increasing SiO2 content. Above the glass transition, all the materials exhibited low-frequency dispersion effect resulting in electrode polarization, which was amplified in the nanocomposites. Improvements in the dielectric properties were found to be not only dependent on the state of dispersion, but also the structure and morphology of the inorganic nanoparticles.
|
|
| 2. |
- Pollen, Harald Norrud, et al.
(författare)
-
Interphase Engineering of LiNi0.88Mn0.06Co0.06O2 Cathodes Using Octadecyl Phosphonic Acid Coupling Agents
- 2023
-
Ingår i: ACS Applied Energy Materials. - : American Chemical Society (ACS). - 2574-0962. ; 6:23, s. 12032-12042
-
Tidskriftsartikel (refereegranskat)abstract
- Ni-rich layered oxides are proven high-energy cathode materials for Li-ion batteries, but their characteristic short cycle life remains a challenge for implementation on a wider scale. The surface reactivity of Ni-rich layered oxides is the driving force for several capacity fading mechanisms, and a common strategy to combat these issues is to apply a protective surface coating. In this work, LiNi0.88Mn0.06Co0.06O2 (NMC) is surface-modified using octadecyl phosphonic acid (OPA) as a coupling agent through a wet-chemical process. Post-treatments of the coated NMC material at 350 and 450 degrees C in an O-2 atmosphere are also evaluated. Physical characterization confirms the presence of a surface coating and confirms that the surface modification processing has a negligible effect on the bulk material structure. The bare NMC material shows an initial discharge capacity of 199 mAh/g in NMC||LTO cells. The coated NMC material shows a slightly lower initial discharge capacity of 188 mAh/g, but the capacity retention after 210 cycles improves from 86 to 95%. The coated NMC material shows higher discharge capacities than the bare NMC material beyond cycle 75. Postmortem characterizations indicate that the surface reactivity is reduced by the OPA coating as less fluorinated byproducts are formed. The high-temperature post-treatments of the coated NMC material change the surface chemistry but do not improve the electrochemical performance.
|
|
