Problem and Simple Solutions of Layered Cathode Materials

Abstract

Layered cathode materials, including Ni-rich and Li-rich lithium transition metal oxides, are one class of the most promising cathode materials for high energy density Li-ion batteries because of their high capacity and low cost. However, the Ni-rich and Li-rich cathode materials face two same problems of (1) oxygen evolution at high potentials, and (2) significant amount of Li residues in the forms of Li2O, LiOH, and Li2CO3 on the particle surface. Most of known concerns with these two types of cathode materials can be attributed to these two problems, such as irreversible phase transition from hexagonal to cubic phase, intergranular cracking with repeated cycling, transition metal ion dissolution, as well as electrolyte degradation that consequently results in impedance increase and volumetric swelling of the batteries. Since these two problems are the intrinsic properties of the layered lithium transition metal oxides, there are no perfect solutions that can completely solve these two problems. What one can do is to minimize the negative effects caused by these two problems. By selecting Ni-rich LiNi0.80Mn0.10Co0.10O2 (NMC811) as an example, in this presentation we demonstrate two simple strategies: (1) removing Li residues in the cathode slurry-coating step, and (2) in-situ eliminating the released active oxygen in the battery. Both strategies are simple without need of changing the existing procedures, and show different degree improvements on the cycling stability and rate capability of the Li/NMC811 cells. Our presented strategies are believed to be applicable to all other Ni-rich and Li-rich layered cathode materials.