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

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; 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.