High energy density and superior charge/discharge efficiency polymer dielectrics enabled by rationally designed dipolar polarization

Although many dielectric polymers exhibit high energy storage density (U) with enhanced dipolar polarization at room temperature, the substantially increased electric conduction loss at high applied electric fields and high temperatures remains a great challenge. Here, we report a strategy that high contents of medium-polar ester group and end-group (St) modification are introduced into a biodegradable polymer polylactic acid (PLA) to synergistically reduce the loss and enhance U and charge-discharge efficiency (η). The resultant St-modified PLA polymer (PLA-St) exhibits an U of 6.5 J/cm with an ultra-high η (95.4%), far outperforming the best reported dielectric polymers. It is worth noting that the modified molecular structures can generate deep trap centers and restrict the local dipole motions in the polymer, which are responsible for the reduction of conduction loss and improvements in high-temperature capacitive performance. In addition, the PLA-St polymer shows intrinsically excellent self-healing ability and cyclic stability surviving over 500 000 charge-discharge cycles. This work offers an efficient route to next-generation eco-friendly dielectric polymers with high energy density, low loss, and long-term stability.