SBR binder (for Negative Electrode) and ACM binder (for positive electrode)

Abstract

An electrode binder for lithium-ion (Li-Ion) secondary batteries is used either to bind active material layers or between active material layers and collectors. The binder in general is preferably electrochemically inert. Although the binder is not essential for the battery, it has an important role in the facilitation of producing batteries and in their properties. Therefore, the binder is said to be one of the major elements of the battery. Table 7.1 shows a number of excellent binders developed to date. Binders properties include - besides the actual binding - flexibility when used for electrodes, insolubility in the electrolyte, compactness, chemical and electrochemical stability, and easy application to electrode paints. The binder should be able to satisfy all of these properties simultaneously. This is a difficult task, and only two binders that comply with all these requisites have been found: polyvinylidene fluoride (PVDF) and styrene-butadiene copolymer (SBR). Initially PVDF was the main binder employed for negative electrodes 1 but now the use of SBR has become more popular.2 SBR is now used in almost 70% of all batteries. Compared to PVDF, SBR provides better battery properties. For example: more flexible electrode; higher binding ability with a small amount; larger battery capacity; and higher cyclability. SBR also is suitable for graphite with a larger relative surface area and it is operation-environment friendly because SBR uses aqueous solvent. Due to these advantages, Korea and China recently have begun switching from PVDF to SBR. A binder for positive electrodes demand more rigorous qualities than those for negative electrodes. For example, the binder has to be oxidation-resistant in the unstable oxidation atmosphere that occurs in charging batteries. SBR is suitable for negative electrodes used in a reduction atmosphere; however, it is not suitable for positive electrodes with double bonds, which are prone to be oxidized. These requirements (Table presented) have caused delays in its development. Nowadays, PVDF is still used for positive electrodes, although more recently, the highly flexible acrylate-type copolymer (ACM) has started to be used in prismatic batteries.3 This report introduces BM-400B and BM-500B, which Zeon Corporation has developed as SBR binder for negative electrodes and ACM binder for positive electrodes, respectively. SBR and ACM binders are very different from PVDF binder in their usage. Once accustomed to the use of PVDF, it becomes difficult to make electrode paint when switching from PVDF to SBR or ACM. Therefore, this report also describes in detail how to use SBR and ACM binders. © 2009 Springer Science+Business Media, LLC.