Effect of testing temperature on the electrochemical properties of Li(Ni0.6Mn0.2Co0.2)O2 and its Ti3C2(OH)2 modification as cathode materials for lithium-ion batteries

The effects of testing temperature on the electrochemical properties of Li(Ni_0.6Mn_0.2Co_0.2)O₂ are investigated in detail. When the testing temperature is 40 °C, the Li(Ni_0.6Mn_0.2Co_0.2)O₂ cathode material possesses the highest initial discharge capacity of 162.4 mAh·g⁻¹ at 0.5C rate, but their cycling stability decreases markedly. When the test temperature rises up to 60 °C, the side reaction between electrolyte and cathode material becomes serious, and the Li(Ni_0.6Mn_0.2Co_0.2)O₂ cannot work. When the testing temperature decreases, the electrochemical impedances like R_ct values increase, and then the discharge capacity at 0 °C, −10 °C and −20 °C is only 80%, 53% and 23% of that at 25 °C. Based on the electrochemical impedance spectra at different temperatures, four kinds of equivalent circuit models are classified. The cycle and rate performance of Li(Ni_0.6Mn_0.2Co_0.2)O₂ cathode material could be improved obviously through Ti₃C₂(OH)₂ modification in an extreme environment, and especially in sub-zero environment.