Insights into the Microstructural Engineering of Cobalt-Free, High-Nickel Cathodes Based on Surface Energy for Lithium-Ion Batteries

In order to reduce cost and increase energy density, it is critical to eliminate cobalt and increase nickel content in practical LiNi1-x-yMnxCoyO2 (NMC) and LiNi1-x-yCoxAlyO2 (NCA) cathodes. However, the implementation of cobalt-free, high-nickel layered oxide cathodes in lithium-ion batteries (LIBs) is hindered by the inherent issue of high surface reactivity with the electrolyte and microcrack formation during cycling. Herein, the origin of key parameters for microstructural engineering in cobalt-free LiNiO2 (LNO) is comprehensively investigated with two representative dopants, B and Al. A notable difference in the segregation energy between B and Al results in different morphologies of LNO particles. The low solubility of B into the host structure leads to a surface-confined distribution of B, inhibiting the growth of primary particles, whereas the highly soluble Al facilitates primary particle growth. Recognition of this key parameter can help improve the cycle life of cobalt-free LIBs via microstructural engineering by increasing the aspect ratio inside the cathode particle. It is demonstrated that boron-doping in LNO (B-LNO) is the most effective dopant strategy for microstructural engineering of the primary particles. The B-LNO exhibits an excellent capacity retention of 81% in full cells after 300 cycles compared to both LNO and Al-doped LNO (Al-LNO).