Clean and renewable energy is the primary choice to solve the problem of global energy demand and green capacity. Supercapacitors are the key energy storage devices for stable energy transport on new energy extraction, but their energy density is generally low. It is an important breakthrough direction to further improve the energy density and application scope of supercapacitors. Polyelectrolyte (PE) coating on the electrode surface (PE@ECs) can greatly improve the energy storage performance (ESP) of supercapacitors. However, it remains unclear the underlying relationship between PE@ECs and ESP of supercapacitors.

Herein, to better understand the internal mechanism, we have performed polymer density functional theory (pDFT) to investigate the energy density and capacitance of supercapacitors with PE@ECs. Moreover, the salinity energy extraction is explored by capacitive mixing (CapMix). This work provides a theoretical basis for the design and regulatory mechanism of high-performance supercapacitors.