Ozonation of Dielectric Fosters Self-Healing Efficiency in Metalized-Film Capacitors: Quantum-Chemical Simulation

Metalized-film capacitors (MFCs) employ polymer organic dielectrics like polypropylene (PP) and polyimide (PI), in which self-healing is seen as a key advantage. However, the performance of self-healing depends on specific chemical mechanisms involved. The formation of semiconductive carbonaceous soot represents a critical failure risk. This study investigates how oxygen atom impregnation through ozonation of the dielectric material tunes the composition and electrical conductivity of breakdown products in the PP and PI systems with aluminum-zinc electrodes. We revealed, at the atomistic level, that oxygen atoms tend to remove a fraction of carbon atoms from the semiconductive soot by oxidizing carbon into carbon monoxide in both polymers. In PP, oxygen fraction linearly increases gas mass fraction, thereby reducing soot fraction. In PI, the gas/soot ratio effect of oxygen content is less drastic, still clearly positive. The PP soot conductivity decreases uniformly as larger fractions of oxygen atoms are added. In turn, the PI conductivity drops to ~1500 S/m quickly. The PI soot exhibits narrower band gaps compared to that of PP. The oxygen fraction non-monotonically tailors band gaps, which generally increase. To summarize, ozonation enhances MFC reliability by increasing gas species fraction and reducing soot conductivity. We hereby provide numerical molecular-level insights to rationalize self-healing performance enhancement through polymer ozonation.

💡 Research Summary

This paper investigates how intentional oxygen incorporation—via ozonation—affects the self‑healing performance of metalized‑film capacitors (MFCs) that employ polypropylene (PP) and polyimide (PI) as dielectric films. The authors model the dielectric breakdown event at the atomistic level, including a realistic representation of the aluminum‑zinc alloy electrode (3 Zn + 1 Al atoms) and varying the number of oxygen atoms (0–10) introduced into the polymer matrix.

The simulation protocol begins by heating the system to 5000 K, mimicking the extreme temperatures (5000–7000 K) reached during an electrical breakdown. A kinetic‑energy injection method supplies random momentum to overcome activation barriers, after which the system is gradually cooled to 300 K using a Berendsen thermostat. Molecular dynamics is performed with the semi‑empirical PM7 method, and the resulting low‑energy structures are refined with plane‑wave density‑functional theory (PBE‑D3) in Quantum ESPRESSO. Conductivity is evaluated via the Kubo‑Greenwood formalism (KGEC), and band gaps are extracted from the electronic density of states.

Key findings are as follows:

1. Oxygen‑driven gas formation: Added oxygen atoms preferentially oxidize carbon fragments to CO (and to a lesser extent CO₂), thereby increasing the mass fraction of gaseous products at the expense of solid carbonaceous soot. In PP the gas‑to‑soot ratio rises almost linearly with oxygen content; in PI the increase is less steep but still positive.

2. Soot conductivity suppression: For PP, soot conductivity decreases gradually as oxygen content grows, reflecting a progressive disruption of the carbon network. PI soot initially exhibits higher conductivity than PP soot, but once four or more oxygen atoms are present the conductivity drops sharply to ~1500 S m⁻¹, indicating that PI’s aromatic backbone is more susceptible to oxidative fragmentation.

3. Band‑gap modulation: PI soot possesses a narrower band gap than PP soot, consistent with its more delocalized π‑system. Oxygen incorporation generally widens the band gap in a non‑monotonic fashion, suggesting that oxygen creates localized states that both open the gap and introduce disorder.

4. Implications for self‑healing: The combined effect of higher gas yield and lower soot conductivity reduces the probability that residual carbon bridges the electrodes after a breakdown. Consequently, the self‑healing process—where the vaporized metal electrode isolates the fault—becomes more reliable.

The authors acknowledge limitations: the simulated clusters are small compared with real capacitor volumes, the breakdown is modeled as a single event rather than multiple cycling, and experimental validation is absent. Nevertheless, the work provides the first quantitative atomistic evidence that controlled ozonation can tailor the composition and electronic properties of breakdown products, offering a rational route to improve MFC reliability.

Future directions suggested include systematic experimental studies of ozonated PP and PI films (e.g., dielectric strength, breakdown statistics, gas chromatography of breakdown products), exploration of other polymer systems, and optimization of ozone exposure parameters (dose, duration, temperature) to balance dielectric performance with self‑healing efficiency.