Simulation of energy storage density and energy efficiency of polyetherimide composites by modulating charge injection characteristics

Polymer film capacitors are popular in many applications such as power systems, new energy vehicles and electromagnetic energy equipment. However, in the face of higher and higher working temperature and energy density requirements, energy storage characteristics of film capacitors needs to be improved. The charge injection characteristics between the electrode and the dielectric are a key factor affecting the energy storage characteristics of film capacitors. By depositing a high insulating inorganic layer on polymer surface, electrode-dielectric interface charge density can be controlled, and then the charge injection characteristics can be modulated to improve energy storage characteristics at high temperature. But the quantitative relationship between charge injection characteristics and energy storage performance needs further study. This paper proposed an energy storage and release model including charge injection characteristics, and simulated the impact of different interface charge density on energy storage of polyetherimide (PEI) composites at $150^{\circ}\mathrm{C}$. Simulation results match well with the experimental phenomena. Reducing electrode-dielectric interface charge density can effectively inhibit interface charge injection, reduce carrier mobility inside the dielectric and thus improve the energy storage density and efficiency. Under electric field of 511 $\mathrm{k}\mathrm{V}/\mathrm{m}\mathrm{m}$, with the interface charge density increasing from 0.1 $\mathrm{C}/\mathrm{m}^{3}$ to 15 $\mathrm{C}/\mathrm{m}^{3}$, the interface charge injection is obviously inhibited, the discharge energy density increasing from 1.86 $\mathrm{J}/\mathrm{m}^{3}$ to 3.62 $\mathrm{J}/\mathrm{m}^{3}$, and the charge-discharge efficiency increasing from 12.1% to 95.99%, which significantly improved high-temperature energy storage characteristics. This study provides theoretical guide for improving the high-temperature energy storage characteristics of dielectrics.