Facial-shape controlled precursors for lithium cobalt oxides and the electrochemical performances in lithium ion battery

Two types of lithium cobalt oxides (LiCoO sub(2)) as cathode materials for lithium ion batteries are synthesized from two cobalt sources of different facial-shapes (octahedral and truncated-octahedral Co sub(3)O sub(4)) and Li sub(2)CO sub(3) using solid state synthesis. From X-ray diffraction and scanning electron microscopy measurements, the reaction mechanism of the formation of LiCoO sub(2) is investigated. It is revealed that LiCoO sub(2) from octahedral Co sub(3)O sub(4) with only {111} surfaces grows in one direction whereas the crystal orientation of LiCoO sub(2) from truncated-octahedral Co sub(3)O sub(4) with {111} and {100} surfaces is not unique and the spinel intermediates of Li sub(x)Co sub(2)O sub(4) are formed during synthesis. They show largely unequal rate and cycling performances for lithium ion battery, even though their outer appearances are nearly identical. Almost single-crystalline LiCoO sub(2) from octahedral precursors shows much better electrochemical performances than LiCoO sub(2) from truncated-octahedral precursors as a lithium ion battery cathode. By studying crystal orientation, it is shown that the poor electrochemical performances of LiCoO sub(2) from truncated-octahedral Co sub(3)O sub(4) are originated by crystal-mismatch between crystallites.