Failure mechanisms of layered LiNixCoyMn1-x-yO2 cathodes for Li-ion batteries

Abstract

As the promising cathode material, Ni-containing layered Li NCM oxide has several advantages; low-cost, high capacity, etc. but hard to commercialize because of its poor cycle performance. About this, many researchers studied the failure mechanisms and regard the surface part problems as the failure mechanism of layered LI NCM oxide. However, apart from surface part problem, there are other failure mechanisms affect to the poor cycle performance of Li NCM. Among them, we focus and suggest new kinds of failure mechanism; Ni disordering as bulk part problem. To identify, at first, the half cell test shows that the poor cycle performance of Li NCM in several factors, and the degree of Ni disordering during cycling is analyzed using Rietveld refinement method. As results, when the Ni disordering is increased during cycling, the capacity of Li NCM is decreased more and more, and this indicates that Ni disordering can affect the cycle performance of Li NCM during cycling, so it is demonstrated that the Ni disordering is one of the failure mechanism of poor cycle performance of layered LI NCM. Moreover, we suggest new type solution to improve; Mg doping at Li layer of Li NCM. Several analyses, such as TEM, refinement data show the Mg is successfully doped into Li layer, and the half cell test shows its better cycle performance than bare Li NCM (1C, 30℃). Also, through refinement analysis of cycled Mg-doped Li NCM electrode, we observe that the Ni disordering is also inhibited somewhat, comparing the bare Li NCM results.