Structural, electrochemical and Li-ion transport properties of Zr-modified LiNi_0.8Co_0.1Mn_0.1O₂ positive electrode materials for Li-ion batteries

We modify a nickel-rich layered LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) positive electrode material by substituting the transition metals with Zr to mitigate its structural instability and capacity degradation. We show that Zr, over a concentration range of 0.5–5.0 at.%, can simultaneously reside on and expand the lattice of NCM811 and form Li-rich lithium zirconates on their surfaces. In particular, Li(Ni_0.8Co_0.1Mn_0.1)_0.99Zr_0.01O₂ (1% Zr-NCM811) exhibits the best rate capability among all the compositions in this study. It shows higher cycling durability than the raw NCM811 at both low and high current density lithiation and de-lithiation. According to X-ray photoelectron spectroscopy and cyclic voltammetry measurements, the 1% Zr-NCM811 sample is more chemically/electrochemically stable than the raw. In addition to comparing the diffusivities in the coin-cell measurements, we demonstrate that Zr modification can facilitate Li-ion diffusion in the NCM811 balk material by direct-current polarization measurements. The superior performance of Zr-NCM811 results from the lattice expansion induced by Zr doping and the presence of ion-conducting lithium zirconates partially coated on the surface of Zr-NCM811 particles.