Carbon Nanosphere-Encapsulated LiNi0.8Co0.15Al0.05O2 Cathode By Solvent-Free Mechanofusion Process for High Stable 18650 Lithium-Ion Batteries

Abstract

LiNi0.8Co0.15Al0.05O2 namely NCA is one of the most promising Nickel-rich cathode materials since Panasonic and Tesla have been utilizing it in the electric vehicles (EVs) due to its high energy density (up to ~250 Wh kg-1). However, the unsolved problems of using NCA still hinder its electrochemical performance including (i) the severe capacity fading during cycling owing to side reactions of Ni4+ and carbonate-based electrolyte, (ii) low thermal stability, (iii) poor ionic conductivity, and (iv) microcracks at grain boundaries after long testing. Herein, NCA particles were mechanically encapsulated with nanosized-carbon black spheres (20-50 nm) as the core-shell structure (NCA@C) via a solvent-free mechanofusion process. In order to access the highest utilization of NCA@C, it was prepared as the cathode for cylindrical 18650 batteries coupled with commercial graphite anode. The embedded carbon nanospheres on the NCA surface can act as the buffer layers protecting the direct contact with electrolyte inhibiting the microcrack generation improving the long-term stability. The cell electrochemical performances were investigated using CCCV charge-CV discharge at 0.1C and followed by a long-term stability at 1.0C. The ex situ FE-SEM and EDX mapping after the charge-discharge and cycling were further evaluated in order to study the comparative structural changes of NCA cathode with and without carbon protective shell. The novel core-shell of Ni-rich material produced by the scalable dry-synthesized process can be one of the alternative cathode materials providing high energy and stability for 18650 batteries which are beneficial for future EV applications.