The rapid proliferation of 800 V high-voltage electric vehicles (EVs) has imposed stringent demands on insulation systems to endure the synergistic effects of thermo-electro-mechanical coupling (TEMC). However, the aging mechanisms of high thermal conductivity composites, which are pivotal for efficient heat dissipation in these advanced EV systems, remain inadequately understood. This study addresses this critical knowledge gap by systematically investigating the electrical aging behavior of h-BNNTs/epoxy composites (10 wt.% h-BNNTs) under TEMC conditions using a state-of-the-art, self-developed multi-field coupling test system. This innovative system integrates precise control of temperature gradients (Δ T = 55 °C/mm), electric fields (15 kV/mm), and mechanical vibration (10–2000 Hz, 5 g) to accurately replicate real-world operating environments.A comprehensive suite of cross-scale characterization techniques, including dielectric spectroscopy, pulsed electro-acoustic (PEA) space charge measurement, synchrotron X-ray micro-computed tomography (μCT), and atomic force microscopy–infrared (AFM–IR) spectroscopy, was employed to unravel the complex degradation dynamics. After 1500 h of aging under TEMC stress, the dielectric constant (ε′) increased by 28.9% from an initial value of 3.8 to 4.9, while the loss tangent (tanδ) experienced a three-fold increase. Concurrently, the Weibull breakdown strength plummeted from 28.7 to 19.4 kV/mm. The space charge injection depth reached 18 μm, and the interfacial microvoid density escalated to 4.3 × 10 4 /mm 3 , leading to a 57.6% rise in thermal resistance. Gray relational analysis identified interfacial debonding (with a weight of 0.45) and filler relaxation (0.38) as the primary drivers of insulation aging. Furthermore, a robust quantitative model was established, revealing a strong negative correlation ( r = −0.91) between space charge injection depth and breakdown strength. Based on this model, a design criterion of charge depth <15 μm was proposed, which has the potential to reduce the breakdown risk by 60%. This research provides invaluable mechanistic insights into TEMC-induced aging mechanisms and offers practical, evidence-based guidelines for the optimization of insulation systems in 800 V EVs, thereby contributing to the enhanced reliability and longevity of next-generation EV powertrain components.
Song et al. (Sun,) studied this question.