Fundamental mechanism revealed for lithium deficiencies engineering in a new spherical Li-Rich Mn-based layered Li1.23Mn0.46Ni0.246Co0.046Al0.015O2 cathode

Here, a new spherical Li1.23Mn0.46Ni0.246Co0.046Al0.015O2 (0.6Li2MnO3•0.4LiNi0.8Co0.15Al0.05O2, LMNCA) cathode with low cobalt content is rationally designed and prepared. The lithium deficiencies engineering with different lithium (from 75% to 103% of theoretically stoichiometric ratio lithium) is conducted in LMNCA to enhance its electrochemical performance. For the first time, it is found that the Li-rich phase of Li2MnO3 decreases while the distorted spinel phase with low electrochemical kinetics is in-situ formed and increases with the gradual increase of the lithium deficiencies. However, the content of layered LiMO2 with the space group R3—m does not change. Proper amount of Lithium deficiencies and phase composition with appropriate phase ratios can make the LMNCA exhibit excellent electrochemical cycling stability, which shows the first cycle discharge specific capacity of 233 mAh g−1 with an initial Coulombic efficiency of 81% at C/10, and decays to 195 mAh g−1 over 200 cycles with the capacity retention of 90.6% under C/5 charge and C/3 discharge. However, excessive lithium deficiencies and phase composition with unbalanced phase ratios reduce the electrochemical performance of the LMNCA. The relationship between the lithium deficiencies, the crystalline component, and the electrochemical performance of the novel LMNCA is fundamental disclosed, which would shed light on the designing and synthesis of advanced Li-rich Mn-based layered oxide cathode with low or free cobalt content .