Application of Modified Styrene-Acrylic-Rubber-based Latex Binder to LiCoO₂ Composite Electrodes for Lithium-ion Batteries (Supporting Information)

A new combination of styrene acrylic rubber (SAR) and sodium carboxymethylcellulose was developed as a water-borne binder for LiCoO₂ composite electrodes operating at high voltages. Four novel SAR-based latex binders were synthesized with butyl acrylate or 2-ethylhexyl acrylate monomer and styrene via copolymerization with low and high crosslinking degrees. Composite electrodes prepared using lower-crosslinking-degree SAR binders became more stretchable and flexible. Surface analysis using electron microscopy and X-ray photoelectron spectroscopy revealed that the cycled LiCoO₂ electrode was covered with approximately 10-nanometer-thick decomposition products when a conventional poly(vinylidene fluoride) binder was used. The electrodes with SAR-based binders with low cross-linkage formed a stable passivation surface during the initial cycle, and further continuous electrolyte decomposition was successfully suppressed. This passivation improved the cycle stability of LiCoO₂ electrode up to 4.5 V, i.e., 87.1 % capacity retention, even after 100 cycles and suppressed self-discharge performance at 45 °C.