Microscale Core-shell structured Li[(Ni0.8Co0.1Mn0.1)0.8(Ni0.5Mn0.5)0.2]O2 as positive electrode material for lithium batteries

Abstract

LiCoO2 is the most common storage material for the lithium battery system. However, due to the poor thermal characteristics of LiCoO2 in the charged state, battery explosions have occurred. The high capacity of Ni-rich LiNi1?xMxO2(M=Co, Mn) makes it an attractive alternative material. However, a violent exothermic reaction of Li1-δNi1-xMxO2 electrodes accompanied by oxygen release from the host structure has hindered their commercial use in lithium battery systems. Recently, the use of LiNi0.5Mn0.5O2 has been introduced by Ohzuku et al. Unlike LiNiO2, with an average Ni oxidation state of +3, the formal charges of Ni and Mn in LiNi0.5Mn0.5O2 are +2 and +4, respectively. In this case, the average oxidation state of Mn is tetravalent and electrochemically inactive. Due to this improved structural stability, the onset of exothermal temperature by Li1-δNi0.5Mn0.5O2 is usually as high as 280°C, and heat generation at that temperature is reduced compared with Ni-rich Li1-δNi1-xMxO2(M=metals). Even with the advantages of the LiNi0.5Mn0.5O2 compound, its poor rate capability must be improved for it to be used as a Li+ intercalation material in lithium-ion batteries. Therefore, it was expected that the two materials described above could have a synergetic effect, i.e., a higher capacity for LiNi0.8Co0.1Mn0.1O2 and good thermal stability for LiNi0.5Mn0.5O2. In order to achieve this, a spherical core-shell structure was developed with LiNi0.8Co0.1Mn0.1O2 as the core and LiNi0.5Mn0.5O2 as the shell. In this paper, we report a significant improvement in the electrochemical and safety properties of electrodes for lithium batteries through the use of the microscale core-shell structure Li[(Ni0.8Co0.1Mn0.1)1-x(Ni0.5Mn0.5)x]O2 synthesized via coprecipitation.