Reduced Graphene Oxide-Wrapped Nickel-Rich Cathode Materials for Lithium Ion Batteries

The encapsulation of Ni-rich cathode materials (LiNi_0.6Co_0.2Mn_0.2O₂) for lithium ion batteries in reduced graphene oxide (rGO) sheets is introduced to improve electrochemical performances. Using (3-aminopropyl)triethoxysilane, the active materials are completely wrapped with several rGO layers of ∼2 nm thickness. By virtue of the great electrical conductivity of graphene, the rGO-coated cathode materials exhibit much enhanced electrochemical performances of cycling property and rate capability. In addition, it is shown that the structural degradation of the active materials, which is from the rhombohedral layered structure (R3̅m) to the spinel (Fd3̅m) or rock-salt phase (Fm3̅m), is significantly reduced as well as delayed due to the protection of the active materials in the rGO layers from direct contact with electrolytes and the consequent suppression of side reactions.