Electrochemical Performance and Elevated Temperature Properties of the TiO₂-Coated Li[Ni_0.8Co_0.1Mn_0.1]O₂ Cathode Material for High-Safety Li-Ion Batteries

Nowadays, the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode material has attracted great research interest due to its high energy density and less usage of costly raw materials. However, the high nickel content of NCM811 brings about an extremely unstable interface between the electrode and electrolyte and therefore inferior cyclic stability. Herein, we have proposed a straightforward method to deliver 1, 2, and 4 wt % of TiO2 nanoparticles (NPs) on the surface of the NCM811 cathode material and to improve its properties at room and high temperatures. Based on scanning electron microscopy and transmission electron microscopy observations, the coating thickness varies from 10 to 35 nm and the 2 wt % TiO2-coated cathode is provided with uniformly distributed NPs that could result in an improved structural stability and electrochemical performance. In detail, at 25 and 55 °C and 1 C, the 2 wt % TiO2-coated cathode shows capacity retentions of 90.0 and 80.5% after 100 cycles, higher than those of pristine and coated cathodes. Under a high current rate of 10 C at 25 and 55 °C, the discharge capacities of the 2 wt % TiO2-coated cathode were 135.9 and 141.4 mA h g–1, which are significantly higher than those of the pristine cathode material (128.3 and 89.1 mA h g–1). Results of the dissolution test at 55 °C reflect the effectiveness of the TiO2 coating in maintaining the structural integrity of the cathode material and protecting it from HF attack and deleterious side reactions. Also, the differential scanning calorimetry result proves the enhanced safety after surface modification; the TiO2 coating shifts the exothermic peak of the electrode from 231.1 to 242.9 °C. Therefore, surface modification with TiO2 NPs can be proposed as a practical and cost-effective method for the commercial application of the high energy density NCM811 cathode at room and high temperatures.