Novel synthesis of Li1.2Mn0.4Co0.4O2 with an excellent electrochemical performance from −10.4 to 45.4 °C

Abstract

Lithium-ion batteries continue to dominate the market and transportation applications of portable electronics, while these applications are still very difficult at low or elevated temperatures. In this work, the cathode material Li_1.2Mn_0.4Co_0.4O₂ was initially synthesized via an oxalate-precursor method. During sample preparation, lithium ions were co-precipitated with transition metal ions to form a uniform distribution of reactants at the molecular level. As a consequence, the current preparation method gave rise to a uniform cation distribution inside the target materials with no need of the additional process of mixing with lithium salt, which is however always required when using conventional co-precipitation methods. Due to the uniform cation distribution inside the material, the Li_1.2Mn_0.4Co_0.4O₂ cathode thus prepared was found to exhibit an excellent electrochemical performance. At room temperature, the initial discharge capacity and capacity retention ratio after 20 cycles were 284 mA h g⁻¹ and 82.75%, respectively, which are superior to 246 mA h g⁻¹ and 79.27%, the best results ever reported for the counterparts. Further, the low and elevated-temperature electrochemical performance for this cathode was also explored. It was found that the maximal discharge capacity measured at a current density of 20 mA g⁻¹ between 2.0 and 4.6 V was maintained as high as 296 and 200 mA h g⁻¹, at 45.4 and −10.4 °C, respectively. The change in the state of health (SOH) in the temperature range −10.4 to 45.4 °C was investigated by EIS. It was demonstrated that the %SOH operation window for Li_1.2Mn_0.4Co_0.4O₂/Li cells was somewhat broad, which indicated a potential application at low/elevated temperatures. The synthetic route described in this work is new, and may help to prepare more advanced cathode materials essential for a broad class of applications.