Small things make a big difference: binder effects on the performance of Li and Na batteries.

Li and Na batteries are very important as energy storage devices for electric vehicles and smart grids. It is well known that, when an electrode is analysed in detail, each of the components (the active material, the conductive carbon, the current collector and the binder) makes a portion of contribution to the battery performance in terms of specific capacity, rate capability, cycle life, etc. However, there has not yet been a review on the binder, though there are already many review papers on the active materials. Binders make up only a small part of the electrode composition, but in some cases, they play an important role in affecting the cycling stability and rate capability for Li-ion and Na-ion batteries. Poly(vinylidene difluoride) (PVDF) has been the mainstream binder, but there have been discoveries that aqueous binders can sometimes make a battery perform better, not to mention they are cheaper, greener, and easier to use for electrode fabrication. In this review, we focus on several kinds of promising electrode materials, to show how their battery performance can be affected significantly by binder materials: anode materials such as Si, Sn and transitional metal oxides; cathode materials such as LiFePO4, LiNi1/3Co1/3Mn1/3O2, LiCoO2 and sulphur.