Leeet al. reported that the addition of PAA significantly decreased the viscosity of the LiFePO4 and CMC slurry, leading to an increased solid concentration and improved discharge capacity in terms of volumetric density.
Hanet al.investigated the impact of the degree of neutralization of poly(acrylic acid) on electrode performance for Si–graphite composite electrodes. Excellent capacity retentionfor a 100 cycle test with a high reversible capacity of approxi-mately 1000 mAh/g is achieved with 80% neutralized(PAH0.2Na0.8) PAA as a binder for Si-based composite electrodes. It was found that 80% neutralized PAA provides a moderately porous structure inside the composite electrode with 10 wt% binder content because of its unique rheological properties during the drying process after the slurry is coated onto the current collector. The self-formed porous structure arising from the partially neutralized PAA is beneficial for buffering the volume expansion caused by lithiation of Si.
Dahnet al. reported that a lithium polyacrylate (Li-PAA)binder performed even better than the CMC binder.
According to the authors, 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 analyzed 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, the authors 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, LiCoO2and sulphur.
Article type： perspectiveSubmitted: 05 Jun 2014Accepted: 17 Jun 2014First published:25 Jun 2014