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

Abstract

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 µm 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.