Effects of Oxygen Pressurization on Li⁺/Ni²⁺ Cation Mixing and the Oxygen Vacancies of LiNi_0.8Co_0.15Al_0.05O₂ Cathode Materials

Abstract

Ni-rich cathode materials are a low-cost and high-energy density solution for high-power lithium-ion batteries. However, Li+/Ni2+ cation mixing and oxygen vacancies are inevitably formed during the high-temperature calcination process, resulting in a poor crystal structure that adversely affects the electrochemical performance. In this work, the LiNi0.8Co0.15Al0.05O2 cathode material with a regular crystal structure was prepared through oxygen pressurization during lithiation–calcination, which effectively solved the problems caused by the high calcination temperature, such as oxygen loss and a reduction of Ni3+. The co-effect of oxygen pressure and calcination temperature on the properties of Ni-rich materials was systematically explored. Oxygen pressurization increased the redox conversion temperature, thus promoting the oxidation of Ni2+ and reducing Li+/Ni2+ cation mixing. Moreover, due to the strong oxidizing environment provided by the elevated calcination temperature and oxygen pressurization, the LiNi0.8Co0.15Al0.05O2 material synthesized under 0.4 MPa oxygen pressure and a calcination temperature of 775 °C exhibited few oxygen vacancies, which in turn suppressed the formation of microcracks during the electrochemical cycling. An additional feature of the LiNi0.8Co0.15Al0.05O2 material was the small specific surface area of the particles, which reduced both the contact area with the electrolyte and side reactions. As a result, the LiNi0.8Co0.15Al0.05O2 material exhibited remarkable electrochemical performance, with an initial discharge capacity of 191.6 mA h·g–1 at 0.1 C and a capacity retention of 94.5% at 0.2 C after 100 cycles.