2 research outputs found
Biodegradable Poly(l‑Lactic Acid) Films with Excellent Cycle Stability and High Dielectric Energy Storage Performance
Polymer-based film capacitors play
key roles in numerous applications,
such as converter/inverter systems in hybrid electric vehicles (HEVs),
smart grids, and pulsed power sources. However, nearly all actively
studied dielectric polymers are nondegradable. In this work, we prepare
flexible biodegradable poly(l-lactic acid) (PLLA) films via
a simple solvent casting method and achieve enhanced dielectric performances
by polymer crystallization. The recoverable energy density (Urec) with charge–discharge efficiency
(η) of 90% was improved from ∼2.9 J/cm3 for
amorphous PLLA to ∼5.7 J/cm3 for the crystallized
PLLA film at room temperature. Under 200 MV/m at 85 °C (the operation
conditions of commercial biaxially oriented polypropylene-based capacitors
in HEVs), Urec of 0.82 J/cm3 with η of 95% is achieved in the crystallized PLLA film, which
is much higher than that of BOPP (below 0.5 J/cm3). In
particular, the remarkable cyclic stability of the crystallized PLLA
film is demonstrated by charge–discharge tests for 20 000
cycles at both room temperature and 85 °C under 200 MV/m. Moreover,
the low C/(H+O) atom ratio helps metalized PLLA films exhibit a valuable
self-healing ability after breakdown. With excellent recoverable energy
density, high efficiency, good cyclic reliability, low-cost preparation
method, self-healing ability, and eco-friendliness, the crystallized
biodegradable PLLA film provides an eco-friendly and high-performance
candidate to develop high-energy-storage capacitors
Polyphenylene Oxide Film Sandwiched between SiO<sub>2</sub> Layers for High-Temperature Dielectric Energy Storage
The commercial capacitor using dielectric
biaxially oriented polypropylene
(BOPP) can work effectively only at low temperatures (less than 105
°C). Polyphenylene oxide (PPO), with better heat resistance and
a higher dielectric constant, is promising for capacitors operating
at elevated temperatures, but its charge–discharge efficiency
(η) degrades greatly under high fields at 125 °C. Here,
SiO2 layers are magnetron sputtered on both sides of the
PPO film, forming a composite material of SiO2/PPO/SiO2. Due to the wide bandgap and high Young’s modulus
of SiO2, the breakdown strength (Eb) of this composite material reaches 552 MV/m at 125 °C
(PPO: 534 MV/m), and the discharged energy density (Ue) under Eb improves to 3.5
J/cm3 (PPO: 2.5 J/cm3), with a significantly
enhanced η of 89% (PPO: 70%). Furthermore, SiO2/PPO/SiO2 can discharge a Ue of 0.45 J/cm3 with an η of 97% at 125 °C under 200 MV/m (working
condition in hybrid electric vehicles) for 20,000 cycles, and this
value is higher than the energy density (∼0.39 J/cm3 under 200 MV/m) of BOPP at room temperature. Interestingly, the
metalized SiO2/PPO/SiO2 film exhibits valuable
self-healing behavior. These results make PPO-based dielectrics promising
for high-temperature capacitor applications