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.

一种新型的苯乙烯丙烯酸橡胶（SAR）与羧甲基纤维素钠的复合物被开发为适用于高电压下运行的LiCoO2复合电极的水性粘合剂。通过丁二烯丙烯酸酯或2-乙基己基丙烯酸酯单体与苯乙烯的共聚合反应，合成了四种基于SAR的新型乳胶粘合剂，其中使用了不同交联程度的共聚物。采用低交联度SAR粘合剂制备的复合电极展现出更高的可拉伸性和柔性。利用电子显微镜和X射线光电子能谱进行的表面分析表明，当使用传统的聚偏氟乙烯粘合剂时，循环后的LiCoO2电极表面覆盖了大约10纳米厚的分解产物。采用低交联度SAR粘合剂的电极在初次循环中形成了稳定的钝化表面，并成功抑制了进一步的电解液分解。这种钝化作用提升了LiCoO2电极在4.5 V电压下的循环稳定性，即达到87.1%的容量保持率，即便经过100次循环，并在45°C时抑制了自放电性能。