Boron doped Ni-rich LiNi_0.85Co_0.10Mn_0.05O₂ cathode materials studied by structural analysis, solid state NMR, computational modeling, and electrochemical performance

This work is part of ongoing and systematic investigations by our groups on the synthesis, electrochemical behavior, structural investigations, and computational modeling of the Ni-rich materials Li[Ni_xCo_yMn_z]O₂ (x+y+z=1; x≥0.8) for advanced lithium-ion batteries. This study focuses on the LiNi_0.85Co_0.10Mn_0.05O₂ (NCM85) material and its improvement upon doping with B³⁺ cations. The data demonstrate the substantial improvement of the doped electrodes in terms of cycling performance, lower voltage hysteresis and reduced self-discharge upon high temperature storage. The electronic structure of the undoped and B-doped material was modelled using density functional theory (DFT), which identified interstitial positions as the preferential location of the dopant. DFT models were also used to shed light on the influence of boron on surface segregation, surface stability, and oxygen binding energy in NCM85 material. Experimental evidence supports the suggestion that the boron segregates at the surface, effectively reducing the surface energy and increasing the oxygen binding energy, and possibly, as a result, inhibiting oxygen release. Additionally, the presence of borate species near the surface can reduce the nucleophilicity of surface oxygens. Cycling of the Li-cells did not cause noticeable changes in the microstructure of the B-doped materials, whereas significant microstructural changes, like a propagating network of cracks, was observed across all grains in the cycled undoped NCM85 cathodes. Analysis by high-resolution microscopy and ⁶Li and ¹¹B solid-state nuclear magnetic resonance (ss NMR) allowed for the correlation of capacity fade and degradation of the different NCM85 materials with their structural characteristics.