<p>Aromatic polymers possess superior thermal stability, rendering them promising candidates for high-temperature polymer capacitors. However, they suffer from severe intra-and inter-chain charge transport under high temperatures and fields, leading to deteriorated capacitive performances. While blending and crosslinking strategies have been attempted, inherent conjugated planar structures in the polymer backbone and interchain donor-acceptor stacking limit their effectiveness. Herein, a strict electron migration locking strategy is enabled by incorporating strong Lewis acid tris(pentafluorophenyl)borane into the Lewis-basic aromatic polyetherimide. The synergistic effects of the coordination between tris(pentafluorophenyl)borane and the carbonyl oxygen of polyetherimide, hydrogen bonding, and steric hindrance of tris(pentafluorophenyl)borane, induce short-range acceptor-acceptor and donor-donor ordered arrangements between molecular chains, and twisted molecular conformation. Consequently, the polyetherimide composite with 4% by weight tris(pentafluorophenyl)borane exhibits an ultra-high discharged energy density of 10.2 J cm⁻³ at 7300 kV cm⁻¹ and 150 °C, and 7.42 J cm⁻³ at 6300 kV cm⁻¹ and 200 °C with an efficiency higher than 90%, outperforming existing polymer composites.</p>