Impact of Microcrack Generation and Surface Degradation on a Nickel-Rich Layered Li[Ni0.9Co0.05Mn0.05]O2 Cathode for Lithium-Ion Batteries

In this work, to address the growing demand for energy density, the Ni-rich layered [Ni_0.90Co_0.05Mn_0.05]O₂ cathode has been synthesized and its electrochemical performance in lithium-ion cells has been benchmarked against a lower-Ni content Li[Ni_0.6Co_0.2Mn_0.2]O₂ cathode. Li[Ni_0.90Co_0.05Mn_0.05]O₂ delivers a high discharge capacity of 227 mA h g^-1 compared to a capacity of 189 mA h g^-1 for Li[Ni_0.6Co_0.2Mn_0.2]O₂ 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, Li[Ni_0.90Co_0.05Mn_0.05]O₂ displays a capacity of 238 mA h g^-1 compared to a capacity of 208 mA h g^-1 for Li[Ni_0.6Co_0.2Mn_0.2]O₂. Although Li[Ni_0.90Co_0.05Mn_0.05]O₂ 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 Li[Ni_0.90Co_0.05Mn_0.05]O₂ and Li[Ni_0.6Co_0.2Mn_0.2]O₂ reveals that the capacity fade of Li[Ni_0.90Co_0.05Mn_0.05]O₂ 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 Li[Ni_0.90Co_0.05Mn_0.05]O₂.