Achieving high capacity and rate capability in layered lithium transition metal oxide cathodes for lithium-ion batteries

In this study, we target to find a new composition for a layered mixed metal oxide, which has a high structural stability and a good electrochemical performance. Our strategy is to alter the transition metal composition focusing on the relative amounts of redox active Ni and Co to the inactive Mn, based on highly-stabilized LiNi_1/3Co_1/3Mn_1/3O₂. X-ray absorption near-edge structure and X-ray diffraction analyses show that the degree of cation disorder decreases on increasing the ratio of Ni and Co to Mn, by the presence of Ni³⁺, suggesting that slightly higher Ni and Co contents lead to improved structural stability. Electrochemical studies demonstrate that LiNi_0.4Co_0.4Mn_0.2O₂ cathodes exhibit considerable improvements in both the reversible capacity and the rate capabilities at a voltage range of 2.5–4.6 V. In situ XRD measurements reveal that LiNi_0.4Co_0.4Mn_0.2O₂ maintains a single-phase and undergoes lesser structural variations compared to controlled compositions during a delithiation process up to 4.6 V, while achieving a high reversible capacity over 200 mAh g⁻¹. As a result, LiNi_0.4Co_0.4Mn_0.2O₂ experiences fewer structural degradations during electrochemical cycling, which explains the excellent long-term cycling performance.