Electrochemical Properties of Polyaniline-Coated Li-Rich Nickel Manganese Oxide and Role of Polyaniline Coating Layer

Abstract

Polyaniline is coated on Li[Li0.2Ni0.2Mn0.6]O2 synthesized via co-precipitation. X-ray diffraction patterns exhibit that the polyaniline coating does not affect structural change of the Li[Li0.2Ni0.2Mn0.6]O2, and the resulting transmission electron microscopic images show the presence of coating layers on the surface of Li[Li0.2Ni0.2Mn0.6]O2. Electrochemical tests using coin type cells confirm that the surface modification by polyaniline is effective in maintaining capacity and retention upon cycling. The conducting coating character also assists improvement in rate capability. The polyaniline layer forms F-doped polyaniline during cycling, as is proved by time-of-flight secondary ion mass spectroscopy. Therefore, the presence of the polyaniline layers plays a role in lowering HF levels via scavenging F− from HF in the electrolyte, and this F–doped polyaniline layer also assists in protecting the Li[Li0.2Ni0.2Mn0.6]O2 from HF attack upon cycling, resulting in improved electrochemical properties.