Lithium-reactive Co-3(PO4)(2) nanoparticle coating on high-capacity LiNi0.8Co0.16Al0.04O2 cathode material for lithium rechargeable batteries

Abstract

Metal ion dissolution from high-capacity LiNi0.8 Co0.16 Al0.04 O2 cathode material during storage at 90°C was completely blocked by a lithium-reactive Co3 (PO4) 2 nanoparticle coating. As opposed to conventional coating methods, in which the coating material did not react with LiOH and Li2 CO3 impurities dissolved from the cathode, the Co3 (PO4) 2 coating material reacted with such impurities during annealing to form an olivine LiCoPO4 phase on the bulk surface. Electrochemical properties of the optimized sample, annealed at 700°C for 5 h, demonstrated a 30% enhancement of the cycle life, compared to a bare sample without a loss in the first discharge capacity. Storage tests of the 4.3 V charged electrode at 90°C after 7 days showed that the bare sample was transformed into the spinel phase with a Fd3m space group, whereas the Co3 (PO4) 2 -coated sample remained as a layered hexagonal phase with an R 3- m space group.