Olivine LiCoPO4 phase grown LiCoO2 cathode material for high density Li batteries

Olivine LiCoPO4 phase grown LiCoO2 cathode material was prepared by mixing precipitated Co3(PO4)2 nanoparticles and LiCoO2 powders in distilled water, followed by drying and annealing at 120 °C and 700 °C, respectively, for 5 h. As opposed to ZrO2 or AlPO4 coatings that showed a clearly distinguishable coating layer from the bulk materials, Co3(PO4)2 nanoparticles were completely diffused into the surface of the LiCoO2 and reacted with lithium of LiCoO2. An olivine LiCoPO4 phase was grown on the surface of the bulk LiCoO2, with a thickness of ∼7 nm. The electrochemical properties of the LiCoPO4 phase, grown in LiCoO2, had excellent cycle life performance and higher working voltages at a 1C rate than the bare sample. More importantly, Li-ion cells, containing olivine LiCoPO4, grown in LiCoO2, 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 LiCoPO4, grown in LiCoO2 at 4.4 V, did not exhibit thermal runaway with a cell surface temperature of ∼80 °C. However, the cell containing bare LiCoO2 showed a burnt-off cell pouch with a temperature above 500 °C.