Olivine LiCoPO 4 phase grown LiCoO 2 cathode material for high density Li batteries

Abstract

Olivine LiCoPO 4 phase grown LiCoO 2 cathode material was prepared by mixing precipitated Co 3(PO 4) 2 nanoparticles and LiCoO 2 powders in distilled water, followed by drying and annealing at 120 °C and 700 °C, respectively, for 5 h. As opposed to ZrO 2 or AlPO 4 coatings that showed a clearly distinguishable coating layer from the bulk materials, Co 3(PO 4) 2 nanoparticles were completely diffused into the surface of the LiCoO 2 and reacted with lithium of LiCoO 2. An olivine LiCoPO 4 phase was grown on the surface of the bulk LiCoO 2, with a thickness of ∼7 nm. The electrochemical properties of the LiCoPO 4 phase, grown in LiCoO 2, had excellent cycle life performance and higher working voltages at a 1C rate than the bare sample. More importantly, Li-ion cells, containing olivine LiCoPO 4, grown in LiCoO 2, showed only 10% swelling at 4.4 V, whereas those containing bare sample showed a 200% increase during storage at 90 °C for 5 h. In addition, nail penetration test results of the cell containing olivine LiCoPO 4, grown in LiCoO 2 at 4.4 V, did not exhibit thermal runaway with a cell surface temperature of ∼80 °C. However, the cell containing bare LiCoO 2 showed a burnt-off cell pouch with a temperature above 500 °C.