Impact of Microcrack Generation and Surface Degradation on a Nickel-Rich Layered LiNi0.9Co0.05Mn0.05O2 Cathode for Lithium-Ion Batteries

In this work, to address the growing demand for energy density, the Ni-rich layered Ni0.90Co0.05Mn0.05O2 cathode has been synthesized and its electrochemical performance in lithium-ion cells has been benchmarked against a lower-Ni content LiNi0.6Co0.2Mn0.2O2 cathode. LiNi0.90Co0.05Mn0.05O2 delivers a high discharge capacity of 227 mA h g-1 compared to a capacity of 189 mA h g-1 for LiNi0.6Co0.2Mn0.2O2 when cycled up to a lower cutoff voltage of 4.3 V, making it an appealing candidate for electric vehicles. With an increase in the charge cutoff voltage to 4.5 V, LiNi0.90Co0.05Mn0.05O2 displays a capacity of 238 mA h g-1 compared to a capacity of 208 mA h g-1 for LiNi0.6Co0.2Mn0.2O2. Although LiNi0.90Co0.05Mn0.05O2 suffers during cycling from the usual rapid capacity fade in a manner similar to that of LiNiO2, 87 and 81% of the initial capacity could still be retained after 100 cycles even after cycling to higher cutoff voltages of 4.3 and 4.5 V, respectively. A comparison of LiNi0.90Co0.05Mn0.05O2 and LiNi0.6Co0.2Mn0.2O2 reveals that the capacity fade of LiNi0.90Co0.05Mn0.05O2 originates largely from the anisotropic volume change and subsequent microcrack propagation in the bulk and NiO-like rock salt impurity phase formation on the particle surface, which are exacerbated at 4.5 V. Lastly, future work with appropriate doping and surface modification could improve further the performance of LiNi0.90Co0.05Mn0.05O2.