Comprehensive analysis of boron-induced modification in LiNi0.8Mn0.1Co0.1O2 positive electrode material for lithium-ion batteries

Ni-rich layered oxides (Ni-rich NMCs) are attractive cathodes for LIBs demonstrating remarkable specific capacity. Still, their commercial deployment is hindered by insufficient cycle life. To address this issue, both doping with boron and coating with boron-containing species are known to work effectively, however, the exact nature of stability improvement along with the precise effect of boron on the crystal structure and morphology of Ni-rich NMCs are not comprehensively understood. Herein, we scrutinized B-modified LiNi0.8Mn0.1Co0.1O2 (NMC811) with a combination of bulk and local experimental techniques supported with DFT calculations, both of which exclude insertion of boron into the crystal lattice of NMC811 and indicate that it is present as Li3BO3. We have visualized ∼2 nm Li3BO3 coating at the surface of NMC811 primary particles using electron-energy loss spectroscopy. This coating induces plate-shaped morphology of the primary particles instead of suggested earlier rod- and needle-like shapes and provides enhancement of capacity retention mainly due to improved reversibility of the H2→H3 phase transition upon charge/discharge. This study covers a plethora of boron modification aspects that have remained unclear or controversial so far, eliminating common misconceptions and contributing to understanding of boron impact on the electrochemical properties of Ni-rich NMCs.