Quantitive unravelling for the governing role of diffusion energy barrier on the self-discharge of supercapacitors

Self-discharge is unneglectable for fast electrochemical devices. The suppression of self-discharge using existing strategies based on known extrinsic mechanisms (charge redistribution, faradaic reaction and ohmic leakage) is far from satisfactory (endowing supercapacitors being similar to batteries). Herein, we propose the previously unnoticed diffusion process, which is dependent on the intrinsic bulk property of the active materials, can play deterministic role on self-discharge. The quantitive unravelling of such process is based on a conjugatedly configured supercapacitor constructed by pairs of pre-lithiated poly(benzodifurandione) (PBFDO), forming a LiyPBFDO vs. Lix-yPBFDO configuration. The functioning process involves the transfer of a single type of charge carrier and similar reaction environment at both the cathode and anode side. This configuration, along with the continuously tunable polymerization degree (therefore its property), provides an ideal platform to quantify the governing role of energy barrier in self-discharge process. A shift of control step is theoretically predicted and then experimentally observed when the diffusion barrier is in the range of 0.59 +/- 0.05 eV. The quantitive unravelling of the governing role for diffusion barrier is expected to provide general guidance for suppressing self-discharge of supercapacitors.