Improvement of the Cyclability and Coulombic Efficiency of Li-Ion Batteries Using Li[Ni0.8Co0.15Al0.05]O2 Cathode Containing an Aqueous Binder with Pressurized CO2 Gas Treatment

Abstract

Li-ion batteries using the Li[Ni0.8Co0.15Al0.05]O2 (NCA) electrode containing an aqueous binder have been fabricated by a pressurized CO2 gas treatment (PCT). With the PCT, the pH of the NCA slurry containing an aqueous binder significantly decreased from 12.2 to 8.3 in 3 minutes. The cyclability and coulombic efficiency were greatly improved and the retention rate of the discharge capacity at the 50th cycle with respect to that at the 1st cycle achieved 82%. A Li2CO3 layer may be formed on the NCA electrode surfaces during the PCT, and the corrosion reaction on the Al foil collector was significantly suppressed. The Li2CO3 layer is electronically insulating and prevents decomposition of the electrolyte during the cycling, resulting in a decreased film resistance (Rf) between the 25th and 50th cycles. On the other hand, without the PCT, the discharge capacity drastically decreased during the cycling. The aqueous binder may be degraded, the corrosion reaction on the Al foil collector occurred, and Al compound layers were formed on an Al foil collector. However, these layers didn't protect the NCA particle surfaces. Therefore, the electrolyte was decomposed during the cycling. These results caused an increase in the charge transfer resistance and Rf.