Enhanced electrochemical properties of the Cd-modified LiNi_(0.6)Co_(0.2)Mn_(0.2)O_2 cathode materials at high cut-off voltage

摘要

High voltage property applied in cells is one of the critical directions for high energy density lithium-ion battery. In this work, cadmium oxides are used as the modifying material on the LiNi0.6Co0.2Mn0.2O2 cathode materials by a facile chemical precipitation method followed by post-calcination. The cadmium oxides not only cover on the LiNi0.6Co0.2Mn0.2O2 particles surface homogenously, but also diffuse into the crystal lattice of the LiNi0.6Co0.2Mn0.2O2 with gradient distribution. The formed cadmium oxide and metal fluorides mixed-layer during cycling on the surface makes the interfacial stability significantly improved. Therefore, the side-reactions are suppressed effectively. The gradient doping of the cadmium in the crystal lattice enhances the structural stability of the LiNi0.6Co0.2Mn0.2O2 and facilitates the Li+ and electron transportation in the bulk material. Moreover, the residual lithium components (Li2CO3/LiOH) also decrease significantly. As a result, the obtained Cd-modified LiNi0.6Co0.2Mn0.2O2 cathodes rise 16.60 (100 cycles, 3.0-4.6 V) and 13.87 (200 cycles, 3.0-4.5 V) percentage points at 1 C rate, respectively. The initial capacity of cadmium-modified LiNi0.6Co0.2Mn0.2O2 is 160.8 mAh g(-1) at 8 C rate over 3.0-4.5 V. The proposed cadmium oxide modification may be also potentially applied in other active cathode materials, especially for the high voltage performance.