Surface double coating of a LiNiaCobAl1−a−bO2 (a > 0.85) cathode with TiOx and Li2CO3 to apply a water-based hybrid polymer binder to Li-ion batteries

Abstract

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 LiNi_aCo_bAl_1−a−bO₂ (a > 0.85, NCA) cathode with a high voltage and high capacity was coated doubly with water-insoluble titanium oxide (TiO_x) and Li₂CO₃ layers to protect the NCA surface from the damage caused by contacting with water during its production process. The TiO_x layer was at first coated on the NCA particle surface with a tumbling fluidized-bed granulating/coating machine for producing TiO_x-coated NCA. However, the TiO_x layer could not coat the NCA surface completely. In the next place, the coating of the TiO_x-uncoated NCA surface with Li₂CO₃ layer was conducted by bubbling CO₂ gas in the TiO_x-coated NCA aqueous slurry on the grounds that Li₂CO₃ is formed through the reaction between CO₃²⁻ ions and residual LiOH on the TiO_x-uncoated NCA surface, resulting in the doubly coated NCA particles (TiO_x/Li₂CO₃-coated NCA particles). The Li₂CO₃ coating is considered to take place on the TiO_x layer as well as the TiO_x-uncoated NCA surface. The results demonstrate that the double coating of the NCA surface with TiO_x and Li₂CO₃ allows for a high water-resistance of the NCA surface and consequently the TiO_x/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.