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 LiNi0.8Co0.16Al0.04O2 cathode material during storage at 90 degrees C was completely blocked by a lithium-reactive Co-3(PO4)(2) nanoparticle coating. As opposed to conventional coating methods, in which the coating material did not react with LiOH and Li2CO3 impurities dissolved from the cathode, the Co-3(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 degrees 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 degrees C after 7 days showed that the bare sample was transformed into the spinel phase with a Fd3m space group, whereas the Co-3(PO4)(2)-coated sample remained as a layered hexagonal phase with an R (3) over barm space group. (c) 2007 The Electrochemical Society.