An innovative strategy of introducing space charge traps to dielectric materials is developed by copolymerization of MMA with conjugated VK, which enables superior energy storage performance (Ue = 15.7 J cm−3 @ 750 MV m−1, η = 88%).
Polymer-based
dielectrics with high energy density and low dielectric
loss are urgently needed in microelectronic equipment and high-power
density electric energy storage devices. In an effort to overcome
the disadvantage of the high energy loss of poly(vinylidene fluoride)
(PVDF)-based ferroelectric fluoropolymers, herein, a series of poly(vinylidene
fluoride-co-trifluoroethylene-co-chlorotrifluoroethylene)-g-poly(vinyl alcohol)
[P(VTrCT)-g-PVA] were fabricated using the reversible
addition–fragmentation chain transfer polymerization procedure.
The PVA side chain shows great compatibility with the PVDF main chain
and the hydrogen bond could be constructed among the hydroxyl and
ester groups, which is responsible for the suppressed ferroelectric
loss and enhanced breakdown strength and thus improved energy density
and charge–discharge efficiency observed in the P(VTrCT)-g-PVAs. The graft copolymer containing 23 mol % PVA shows
the maximum discharge energy density of 13.6 J/cm3 at 500
MV/m. The work demonstrates that the hydrogen bond constructed based
on the hydroxyl group may offer a strategy to tune the ferroelectric
and energy storage performance of PVDF-based fluoropolymers.
As the core unit of energy storage equipment, high voltage pulse capacitor plays an indispensable role in the field of electric power system and electromagnetic energy related equipment. The mostly utilized polymer materials are metallized polymer thin films, which are represented by biaxially oriented polypropylene (BOPP) films, possessing the advantages including low cost, high breakdown strength, excellent processing ability, and self-healing performance. However, the low dielectric constant (εr < 3) of traditional BOPP films makes it impossible to meet the demand for increased high energy density. Controlled/living radical polymerization (CRP) and related techniques have become a powerful approach to tailor the chemical and physical properties of materials and have given rise to great advances in tuning the properties of polymer dielectrics. Although organic-inorganic composite dielectrics have received much attention in previous studies, all-organic polymer dielectrics have been proven to be the most promising choice because of its light weight and easy large-scale continuous processing. In this short review, we begin with some basic theory of polymer dielectrics and some theoretical considerations for the rational design of dielectric polymers with high performance. In the guidance of these theoretical considerations, we review recent progress toward all-organic polymer dielectrics based on two major approaches, one is to control the polymer chain structure, containing microscopic main-chain and side-chain structures, by the method of CRP and the other is macroscopic structure design of all-organic polymer dielectric films. And various chemistry and compositions are discussed within each approach.
The degradation mechanism of ZnO varistor under impulse current stress has been studied in this paper. It is found that the impulse degradation like DC degradation is also arised from the variation of double Schottky barriers at grainboundary which has been investigated by Thermally Stimulated Current (TSC). It is concluded that the differing change of Schottky barriers is due to the high concentration carriers injecting to the grainboundary layer and accumulating of trapping effects in the layer which result in the torture of space charge field, hence, the change of Fermi levels.
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