Application of modified styrene-butadiene-rubber-based latex binder to high-voltage operating LiCoO2 composite electrodes for lithium-ion batteries

Styrene-butadiene rubber (SBR) is modified either by changing the degree of cross linkage, or by the partial substitution of acrylonitrile for styrene. Four types of SBR-based latex binders (SBRx), which are used as a mixture with sodium carboxymethyl cellulose, are compared with conventional poly(vinylidene fluoride) (PVdF) binder by applying them to LiCoO2 composite electrodes in high-voltage operations up to 4.5 V vs. Li. The results demonstrate not only better electrode performance of SBRx compared with PVdF binder, but also some differences among SBRx binders. Further, they demonstrate good correlation between electrode performance and electrode analysis data by electrochemical impedance spectroscopy and hard X-ray photoelectron spectroscopy, suggesting better coverage with uniformity and stability on LiCoO2 particles composed of SBRx-based binder and deposition products of decomposed electrolyte than that by PVdF binder. The results reveal a clear dependency on the degree of cross linkage, and SBRlow modified by the low degree of cross linkage shows the best cyclability and rate capability. SBRCN, which is modified by acrylonitrile, shows a high solvent uptake and remarkable electrode performance in terms of rate capability and self-discharge suppression.