Toward a high-voltage fast-charging pouch cell with TiO₂ cathode coating and enhanced battery safety

Nickel-rich layered lithium transition metal oxides, LiNi_xCo_yMn_1-x-yO₂, are key cathode materials for high-energy lithium-ion batteries owing to their high specific capacity. However, the commercial deployment of nickel-rich oxides has been hampered by their poor thermostability and insufficient cycle life. Here full batteries with uncoated and TiO₂-coated LiNi_0.5Co_0.2Mn_0.3O₂ cathodes and graphite anodes are compared in terms of electrochemical performance and safety behavior. The battery using a TiO₂-coated LiNi_0.5Co_0.2Mn_0.3O₂ cathode exhibited better cyclic performance at high cutoff voltage. Electrochemical impedance spectroscopy analysis indicated that the TiO₂-coated LiNi_0.5Co_0.2Mn_0.3O₂ cathode gave the battery a more stable charge transfer resistance. Transmission electron microscopy demonstrated that TiO₂ coating reduced accumulation of the cathode electrolyte interface layer on the particle surface. Time-of-flight secondary ion mass spectrometry demonstrated that TiO₂ coating markedly enhanced the interface stability of the cathode particle and protected the particle from serious etching by the electrolyte. Accelerating rate calorimetry revealed that the trigger temperature of thermal runaway for the battery using TiO₂-coated LiNi_0.5Co_0.2Mn_0.3O₂ as cathode material was 257 °C, which was higher than that of the battery with the uncoated LiNi_0.5Co_0.2Mn_0.3O₂ cathode (251 °C). In situ X-ray diffraction during heating demonstrated that this enhanced safety can be attributed to the suppressed phase evolution of the coated cathode material.