Effect of Substituted Styrene‐Butadiene Rubber Binders on the Stability of 4.5 V‐Charged LiCoO 2 Electrode

The combination of synthetically modified styrene‐butadiene rubber (SBR) and sodium carboxymethyl cellulose (CMC) was studied as an aqueous binder for LiCoO 2 composite electrodes under high‐voltage operation. Methyl methacrylate (MMA) and 2‐vinylpyridine (VP) substituted SBR copolymers were synthesized and examined as functional polymer binders. The electrolyte‐solvent uptake of the binder‐polymer film was increased by the introduction of the MMA units, but the solubility of the polymer in the solvent remained negligibly low. Hard‐X‐ray photoelectron spectroscopy revealed the formation of a relatively thick passivation layer on the LiCoO 2 surface with MMA‐substituted SBR and CMC binder, which suppressed the self‐discharge of 4.5 V‐charged LiCoO 2 . The capacity retention during battery cycling experiments was similar for the LiCoO 2 electrodes with MMA‐modified and unmodified SBR binders. While the effect of VP‐substitution was not significant, incorporation of the MMA unit enhanced the stability of the charged LiCoO 2 electrode and provided improved self‐discharge performance.