Effects of aluminum substitution in nickel-rich layered LiNixAl1−xO2 (x = 0.92, 0.95) positive electrode materials for Li-ion batteries on high-rate cycle performance

Abstract

Co-free Ni-rich (Ni ≥ 80 at%) layered positive electrode materials have been attracting attention for lithium-ion batteries with high energy density and low cost. In this study, LiNi_xAl_1−xO₂ (x = 0.92, 0.95), in which Ni and Al are atomically mixed, was synthesized. LiNiO₂, LiNi_0.95Co_0.05O₂ and LiNi_0.95Co_0.03Al_0.02O₂ with similar particle morphologies were also synthesized to clarify the effects of Al and Co substitution in Ni-rich layered electrode materials. After 500 cycles in full cells under conditions of 45 °C, 2C, and 2.5–4.2 V, LiNi_0.95Al_0.05O₂ and LiNi_0.95Co_0.05O₂ showed a similar capacity retention (54.1%, 56.5%), whereas LiNi_0.92Al_0.08O₂ showed excellent capacity retention (75%). The increase of charge transfer resistance with cycling was remarkably suppressed in LiNi_xAl_1−xO₂, compared to LiNiO₂ and LiNi_0.95Co_0.05O₂, owing to nano-scale Al-rich layers on the surface of LiNi_xAl_1−xO₂ suppressing the side reactions with the electrolytes and thus the surface degradation. Furthermore, though the Co substitution has some effects of preventing particle cracking, the least particle cracking was observed in LiNi_0.92Al_0.08O₂, suggesting that the surface degradation and the bulk degradation were suppressed with the Al substitution to produce the excellent cycle performance. This indicates that LiNi_xAl_1−xO₂ synthesized under optimum conditions is a promising Co-free Ni-rich electrode material.