Effects of Polyelectrolyte Surface Coating on the Energy Storage Performance in Supercapacitors

Abstract

Polymer electrode materials are critical components to achieve the excellent energy storage performance (ESP) of supercapacitors, while the underlying microscopic mechanism by which the polymer structure on the electrode surface affects the energy storage remains unclear. Herein, we explore the effects of a polyelectrolyte (PE) coating on the ESP of supercapacitors by using the polymer density functional theory. The ESP is determined by the adsorption of free ions at the electrode surface, which is jointly affected by the interactions from both the charged surface and the anchored PE chains. Once the PE chains carry like charges as the electrode, the energy density can be significantly promoted by two orders of magnitude. However, if the PE chains carry opposite charges to the electrode, the energy density can be suppressed. The effect of PE coating on the capacitance is similar to that on the energy density if the surface voltage is fixed during the operation, and otherwise, if the surface charge density is fixed, the effect on the capacitance is opposite to that on the energy density. This work provides a microscopic understanding of the complex polyelectrolyte coating’s effects on the ESP in supercapacitors.

Interfacial Microstructure of Neutral and Charged Polymer Brushes: A Density Functional Theory Study

“…[30][31][32][33][34][35][36][37] However, the significant deviations in the interfacial density distributions between PDFT and simulations are found in the literature. 38 The accurate and reliable predictions of PDFT leave much to be desired in the relevant thermodynamic and structural properties (e.g., the capacitance of supercapacitors).…”

“…38,49 However, there are remarkable deviations between PDFT and MC simulation, such as overestimated interfacial densities and mismatched brush heights. Here, corresponding to the four cases reported by Borówko et al, the PDFT and MD simulation are implemented to study the microstructure of neutral PBs.…”

Phase Behavior of Ion-Containing Polymers in Polar Solvents: Predictions from a Liquid-State Theory with Local Short-Range Interactions

“…Such an LS theory has also been applied to study the phase behaviors of concentration-asymmetric mixtures of polycation and polyanion solutions and has also revealed a wealth of interesting and complex phase separations scenarios [57]. Classical density functional theories (cDFT) for charged polymers have also been developed based on a similar framework and have found wide applications in many polyelectrolyte systems [58][59][60][61][62][63][64][65]. A complete theoretical understanding of the solution phase behaviors of charged polymers, however, remains challenging, not only because of the multi-component nature of the system (which, in the simplest case of a salt-free solution of fully charged polymers, consists of solvent, counterions, and charged polymers), but also because of the delicate interplay among various factors, including the translational entropy of each component, excluded volume interactions, chain connectivity, and more importantly the long-range electrostatic interactions.…”

“…Increasing the length of the neutral side chains shrinks the phase-separated region, while increasing the acid-to-ether ratio expands the phase-separated region. A combination of PC-SAFT and cDFT for charged polymers has found applications in studies of the thermodynamic responsive properties of a grafted polyanion layer on a planar surface [63] and effects of polyelectrolyte surface coating on the energy storage performance in supercapacitors [64].…”

Phase Behavior of Ion-Containing Polymers in Polar Solvents: Predictions from a Liquid-State Theory with Local Short-Range Interactions

“…Such an LS theory has been applied to study the phase behaviors of concentration-asymmetric mixtures of polycation and polyanion solutions, and has revealed a wealth of interesting and complex phase separation scenarios [ 57 ]. Classical density functional theories (cDFT) for charged polymers have been developed based on a similar framework, and have found wide application in many polyelectrolyte systems [ 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 ]. A complete theoretical understanding of the solution phase behaviors of charged polymers, however, remains challenging, both because of the multi-component nature of the system (which, in the simplest case of a salt-free solution of fully charged polymers, consists of solvent, counterions, and charged polymers) and because of the delicate interplay among various factors, including the translational entropy of each component, excluded volume interactions, chain connectivity, and more importantly, the long-range electrostatic interactions.…”