A Novel Cathode Material with a Concentration-Gradient for High-Energy and Safe Lithium-Ion Batteries

Abstract

A high-energy functional cathode material with an average composition of Li[Ni(0.72)Co(0.18)Mn(0.10)]O(2), mainly comprising a core material Li[Ni(0.8)Co(0.2)]O(2) encapsulated completely within a stable manganese-rich concentration-gradient shell is successfully synthesized by a co-precipitation process. The Li[Ni(0.72)Co(0.18)Mn(0.10)]O(2) with a concentration-gradient shell has a shell thickness of about 1 mu m and an outer shell composition rich in manganese, Li[Ni(0.55)Co(0.15)Mn(0.30)]O(2). The core material can deliver a very high capacity of over 200 mA h g(-1), while the manganese-rich concentration-gradient shell improves the cycling and thermal stability of the material. These improvements are caused by a gradual and continuous increase of the stable tetravalent Mn in the concentration-gradient shell layer. The electrochemical and thermal properties of this cathode material are found to be far superior to those of the core Li[Ni(0.8)Co(0.2)]O(2) material alone. Electron microscopy also reveals that the original crystal structure of this material remains intact after cycling.