Versatile Composite Binder with Fast Lithium-Ion Transport for LiCoO2 Cathodes.

The low ionic conductivity of LiCoO2 limits the rate performance of the overall electrode. Here, a polymeric composite binder composed of poly(vinylidene fluoride) (PVDF) and poly(ethylene oxide) (PEO) is reported to efficiently improve the ion transport in the LiCoO2 electrode. This is where the lithium-ion transport channel constructed by oxygen atoms of PEO can afford the electrode a lithium-ion transport number (tLi+) as high as 0.70 with the optimized composite binder in a mass ratio of 1:1 (O5F5), significantly higher than that of traditional PVDF (0.44). As a result, the O5F5 binder endows the LiCoO2 electrode with an impressive capacity of 90 mAh g-1 even at 15 C, which is twice as high as the PVDF electrode. In addition, the initial Coulombic efficiency of the LiCoO2 electrode with the O5F5 binder is close to 100% and the capacity retention is 91% after 100 cycles at 1 C. This study overcomes the problem of slow ion conductivity of the LiCoO2 electrode, providing an easy method for developing high-rate cathode binders.