Regulating Electrostatic Phenomena by Cationic Polymer Binder: Toward Scalable High-Areal-Capacity Li Battery Electrodes

The promising potential of forthcoming smart electronics, electric vehicles, and grid-scale energy storage systems has spurred the unremitting pursuit of high-energy-density Li batteries. Accordingly, in addition to the ever-continuing search for advanced electrode active materials, designing high-areal-capacity (C/A) electrodes has garnered attention as a facile and scalable approach to achieve this goal. High-C/A electrodes increase the energy density of a cell without requiring the synthesis of new electrode active materials.<br/><br/>To achieve high-C/A electrodes (= areal-mass-loading (M/A) × specific capacity of electrode active materials (C_sp)), the M/A should be maximized while stably maintaining the C_sp. However, owing to the use of thick electrodes (physical issue) and non-uniform charge transfer throughout the electrodes (electrochemical issue), conventional electrodes cannot achieve this requirement. Particularly, the drying of processing solvents, such as N-methyl pyrrolidone (NMP) and water, during the fabrication of thick electrodes often induces crack formation and delamination from metallic current collectors, thus limiting the increase in the M/A values. Additionally, with an increase in the electrode thickness, charge transfer in electrode active materials tends to demonstrate uneven and sluggish reaction kinetics in the through-thickness direction of the electrodes, resulting in the loss of the Csp values.<br/><br/>Herein, we present a cationic semi-interpenetrating polymer network (c-IPN) binder strategy, with a focus on the regulation of electrostatic phenomena in electrodes. Compared to conventional neutral linear binders, the c-IPN suppresses solvent-drying-induced crack evolution of electrodes and improves dispersion state of electrode components owing to its surface charge-driven electrostatic repulsion and mechanical toughness. The c-IPN immobilizes anions of electrolytes inside the electrodes via electrostatic attraction, thereby facilitating Li⁺ conduction and forming stable cathode–electrolyte interphases. Consequently, the c-IPN enables high-C/A (20 mAh cm^–2) cathodes with decent cyclability using commercial slurry-cast electrode fabrication, while fully utilizing the theoretical C_sp of LiNi_0.8Co_0.1Mn_0.1O₂. Further, coupling of the c-IPN cathodes with Li-metal anodes yields double-stacked pouch-type cells with high-energy-density (376 Wh kg_cell⁻¹/1043 Wh L_cell^–1), demonstrating practical viability of the c-IPN binder for scalable high-C/A electrodes.