High-voltage performance of concentration-gradient Li[Ni 0.67Co 0.15Mn 0.18]O 2 cathode material for lithium-ion batteries

Abstract

A novel Li[Ni 0.67Co 0.15Mn 0.18]O 2 cathode material encapsulated completely within a concentration-gradient shell was successfully synthesized via co-precipitation. The Li[Ni 0.67Co 0.15Mn 0.18]O 2 has a core of Li[Ni 0.8Co 0.15Mn 0.05]O 2 that is rich in Ni, a concentration-gradient shell having decreasing Ni concentration and increasing Mn concentration toward the particle surface, and a stable outer-layer of Li[Ni 0.57Co 0.15Mn 0.28]O 2. The electrochemical and thermal properties of the material were investigated and compared to those of the core Li[Ni 0.8Co 0.15Mn 0.05]O 2 material alone. The discharge capacity of the concentration-gradient Li[Ni 0.67Co 0.15Mn 0.18]O 2 electrode increased with increasing upper cutoff voltage to 4.5 V, and cells with this cathode material delivered a very high capacity, 213 mAh/g, with excellent cycling stability even at 55 °C. The enhanced thermal and lithium intercalation stability of the Li[Ni 0.67Co 0.15Mn 0.18]O 2 was attributed to the gradual increase in tetravalent Mn concentration and decrease in Ni concentration in the concentration-gradient shell layer.