Surface double coating of a LiNi_aCo_bAl_{1-a-bO2 (a > 0.85) cathode with TiOx and Li2CO3 to apply a water-based hybrid polymer binder to Li-ion batteries}

Recently a water-based polymer binder has been getting much attention because it simplifies the production process of lithium ion batteries (LIBs) and reduce their cost. The surface of LiNiaCobAl1-a-bO2 (a > 0.85, NCA) cathode with a high voltage and high capacity was coated doubly with water-insoluble titanium oxide (TiOx) and Li2CO3 layers to protect the NCA surface from the damage caused by contacting with water during its production process. The TiOx layer was at first coated on the NCA particle surface with a tumbling fluidized-bed granulating/coating machine for producing TiOx-coated NCA. However, the TiOx layer could not coat the NCA surface completely. In the next place, the coating of the TiOx-uncoated NCA surface with Li2CO3 layer was conducted by bubbling CO2 gas in the TiOx-coated NCA aqueous slurry on the grounds that Li2CO3 is formed through the reaction between CO32- ions and residual LiOH on the TiOx-uncoated NCA surface, resulting in the doubly coated NCA particles (TiOx/Li2CO3-coated NCA particles). The Li2CO3 coating is considered to take place on the TiOx layer as well as the TiOx-uncoated NCA surface. The results demonstrate that the double coating of the NCA surface with TiOx and Li2CO3 allows for a high water-resistance of the NCA surface and consequently the TiOx/Li2CO3-coated NCA particle cathode prepared with a water-based binder possesses the same charge/discharge performance as that obtained with a "water-uncontacted" NCA particle cathode prepared using the conventional organic solvent-based polyvinylidene difluoride binder.