Quantitative Neutralization of Polyacrylic Acid Binders for Lithium-Ion Pouch Cells with a Coulombic Efficiency Exceeding 99.9%

Abstract

The binder plays a critical role in lithium-ion batteries by promoting the cohesion of active material particles and ensuring their stable adhesion to the current collector. Poly(acrylic acid) (PAA), a water-soluble polymer, has garnered considerable interest as a binder in numerous applications, particularly in energy storage systems, such as batteries and supercapacitors. However, the self-association of the carboxyl (−COOH) functional groups in PAA results in the formation of both intramolecular and intermolecular hydrogen bonds, which significantly compromises the adhesive’s binding strength to the current collector surface. Herein, we introduce a quantitatively neutralized poly(acrylic acid) (QN-PAA) binder designed to optimize interfacial adhesion strength and mechanical integrity. This binder promotes an in situ reaction between −COOH groups in PAA and copper oxide (CuO) layers on the surface of a copper foil current collector under thermally regulated conditions. The reaction forms durable ionic cross-linked networks (−COO^–···Cu²⁺···^–OOC−) that stabilize the active material–current collector interface while enhancing electrochemical compatibility. As a result, electrodes fabricated with 3 wt % QN-PAA-bonded graphite on a copper-current collector exhibit exceptional durability, sustaining over 30,000 consecutive bending cycles without structural disintegration or active material delamination. Notably, lithium-ion pouch cells (1 Ah) assembled with the QN-PAA binder exhibited a capacity retention rate of about 100% and Coulombic efficiency exceeding 99.9% over 100 cycles.