Recently, high energy density lithium ion batteries (LIBs) play an important role in the field of portable and electronic devices and electrical vehicles. Although conventional layered LiCoO2 cathode material has good electrical properties, the capacity of current LiCoO2 is around 160 mAhg-1 with lithium utilization in the structure less than 50%. Moreover, their cost and safety requirement are still problems for the adoption of lithium ion technology for these large-battery application. In this reasons, during the past two decades, several cathode materials have been emerged as an alternative layered structure compounds, such as olivine phosphates (LiMPO4; M = Fe, Co, Ni, and Mn) and spinel oxides (LiM2O4; M = Mn, Ni and Co), however these still have a relatively low capacity. To overcome this problem, Over-lithiated Layered Oxide (OLO) materials have been considered one of the promising cathode materials for the next generation of cathode materials. Among them, 0.5Li2MnO3·0.5LiNi0.5Mn0.5O2 which is known as high capability (250 mAhg-1) has excellent electrochemical performance and stability at higher cut-off voltage beyond 4.8 V. However, its severe capacity fading during high current rates is generally related to the unstable structure and the side reaction with electrolytes cause problems while cathode carries out beyond 4.8 in a range of high voltage. Herein, we reports Li2ZrO3 -coated Li1.2Ni0.2Mn0.8O2 for high performance cathode material in lithium ion batteries. The concept is both to decrease the interface resistance by crystallization of the surface layer and cover the particles with Li2ZrO3that would suppress the particles against side reactions with the electrolyte. In addition, it can circumvent the loss of transition-metal ions of oxygen, without changing the electronic and ionic conductivities. In this study, X-ray diffraction, Field Emission Scanning Electron Microscopy, Transmission Electron Microscopy, Electrochemical Impedance Spectroscopy and various Charge-discharge measurements were also performed to further investigate the effect of surface-coating layer.
Experimental
To make samples, OLO was made by adding Zirconium isopropoxide was added in the mixed powder and then mixed by hand. After pelletizing, it was put in Alumina crucible and calcinated in 900 °C for 10 hours (heating rate is 5 °C/min). After calcination, powder was filtered using D.I water to remove the residue of LiOH. Resulting powder was dried at 60oC (overnight). Electrode slurry has been made of 92% of cathode materials, 4% of Denka black, 4% of PVdF. The slurry was casted on the Al foil for current collector and assembled with 2032 coin cell.
Result and discussion
Surface modification of cathode electrodes with lithium zirconia oxide gives rise to the better rate properties than pristine OLO.