Biodegradable Poly(l-Lactic Acid) Films with Excellent Cycle Stability and High Dielectric Energy Storage Performance

Abstract

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 (U rec ) with charge−discharge efficiency (η) of 90% was improved from ∼2.9 J/cm 3 for amorphous PLLA to ∼5.7 J/cm 3 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), U rec of 0.82 J/cm 3 with η of 95% is achieved in the crystallized PLLA film, which is much higher than that of BOPP (below 0.5 J/cm 3 ). 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 SiO2 Layers for High-Temperature Dielectric Energy Storage

“…When breakdown occurs, the polymer together with the gold electrode evaporates instantly at the breakdown point due to its appropriate element ratio, forming an insulation site and achieving self-healing (Section 15 of the Supporting Information). 44 Figure 6a,b shows the comparison of U e and η of PP-based dielectric materials with PPO-218 nm SiO 2 in our work at 200 and 300 MV/m, respectively, at high temperatures. One can see that PPO-based materials have overwhelming advantages in both energy density and efficiency.…”

“…This phenomenon was confirmed by the SEM around the self-healing point in Figure c,d. When breakdown occurs, the polymer together with the gold electrode evaporates instantly at the breakdown point due to its appropriate element ratio, forming an insulation site and achieving self-healing (Section 15 of the Supporting Information) …”

Recent advancements in bio-based dielectric and piezoelectric polymers and their biomedical applications

“…46 Several fundamental dielectric properties, including space charge buildup, permittivity, conductivity, dielectric strength, and Reproduced with permission. 49 Copyright 2022, American Chemical Society. (c) Schematic illustration of the orientation difference in stretched films and (d) energy density and charge efficiency of pristine and stretched films.…”

“…The crystallization of PLA plays a key role in ultimate dielectric properties. 48 Recently, Jia et al 49 demonstrated that the recoverable energy density ( U rec ) enhanced from approximately 2.9 J cm −3 for amorphous PLLA (amor-PLLA) to about 5.7 J cm −3 for crystallized α-PLLA with a charge–discharge efficiency of 90%. In addition to demonstrating this enhancement in crystallized form, they compared α-PLLA to commercial biaxially oriented polypropylene (BOPP)-based capacitors.…”

“…2 (a) Structure of PLA. (b) Comparison of energy density between amor-PLLA, a-PLLA, and some other commercial polymeric dielectrics.Reproduced with permission 49. Copyright 2022, American Chemical Society.…”