Origin of superb electrical insulating capability of cellulose-liquid biphasic dielectrics by interfacial charge behaviors

The cellulose-liquid biphasic dielectric composite serves as the irreplaceable main electrical insulating structure in the power industry, owing to its peculiar high dielectric breakdown strength compared to that of monophasic cellulose paper or insulating liquid. Although this advanced electrical characteristic is utilized worldwide, its physical-chemical nature remains unclear, which greatly restricts the design and improvement of next generation electrical insulating composites. Herein, the interfacial charge behaviors in cellulose-liquid composites are investigated, and the results indicate that the majority of charge carriers in insulating liquid are electrostatically adsorbed at the nano-scale interface, forming interfacial charge traps, leading to 17.66 times increased deep trap density, which suppress further charge migration under high voltages, and consequently lead to the ∼400% improved dielectric breakdown strength compared to that of cellulose paper and insulating liquid. By controlling the interfacial trap characteristics with insulating liquids of strong electron withdrawing ability, the resistivity and breakdown strength of cellulose-liquid composites are further improved.