Role of site–specific doping in stabilizing high–nickel cathodes for high-performance lithium- ion -batteries

Abstract

The growing demand for high-capacity and energy-dense lithium-ion batteries has driven the increase of nickel content in commercially available cathodes. However, during deep charging (delithiation), these Ni-rich cathodes experience a detrimental phase transformation and a sudden, significant decrease in lattice volume. This lattice collapse is considered the primary culprit behind the limitations in the cathode's electrochemical performance. Notably, the exact cause-and-effect relationship between the phase change and the collapse remains unclear. In the present study, the effect of the site of substitution on the performance of the LiNiO₂ cathode has been investigated by adopting tungsten as a dopant. To gain deeper insights into this connection within Ni-rich LiNiO₂, the contraction of the c-axis and the change in the a-axis during the delithiation have been investigated using ab initio density functional theory. Findings reveal that the free energy difference between the suspected phases in Ni-rich LiNiO2 is minimal at room temperature, facilitating the transition from the H2 to the H3 phase. This transition appears to be driven by the movement (gliding) of the NiO₂ layer towards the adjacent Li layer. The findings of the present study indicate that among two different configurations due to different sites of substitution, the WLNO-2 configuration suppresses H2 –H3 phase conversion to a greater extent by hindering the gliding of the NiO₂ layer toward the Li layer. Furthermore, a reduction in the collapse of the c-axis lattice during deep de-lithiation for the WLNO-2 configuration has been observed. This reduced collapse is primarily attributed to the altered charge distribution within oxygen atoms and the weakened screening effect from lithium ions.