Exploring Phenolphthalein Polyarylethers as High‐Performance Alternative Binders for High‐Voltage Cathodes in Lithium‐Ion Batteries

Abstract Polyvinylidene fluoride (PVDF) has unique electrochemical oxidation resistance and is the only binder for high‐voltage cathode materials in the battery industry for a long time. However, PVDF still has some drawbacks, such as environmental limitations on fluorine, strict requirements for environmental humidity, weak adhesion, and poor lithium ion conductivity. Herein, the long‐standing issues associated with high‐voltage lithium cobalt oxide (LiCoO 2 ; LCO) are successfully addressed by incorporating phenolphthalein polyetherketone (PEK‐C) and phenolphthalein polyethersulfone (PES‐C) as binder materials. These binders have unexpected electrochemical oxidation resistance and robustness adhesion, ensure uniform coverage on the surface of LCO, and establish an effective and fast ion‐conductive CEI/binder composite layer. By leveraging these favorable characteristics, electrodes based on polyarylether binders demonstrate significantly better cycling and rate performance than their counterparts using traditional PVDF binders. The fast ion‐conductive CEI/binder composite layer effectively mitigates adverse reactions at the cathode–electrolyte interface. As anticipated, batteries utilizing phenolphthalein polyarylether binders exhibit capacity retention rates of 88.92% and 80.4% after 200 and 500 cycles at 4.5 and 4.6 V, respectively. The application of binders, such as polyarylether binders, offers a straightforward and inspiring approach for designing high‐energy‐density battery materials.