Improvement of the high-temperature, high-voltage cycling performance of LiNi0.5Co0.2Mn0.3O2 cathode with TiO2 coating

► TiO2 coating improves cycling stability of LiNi0.5Co0.2Mn0.3O2 at 328K and 4.4V. ► TiO2 coating can prevent the increase of charge-transfer resistance (Rct). ► LiF/MFx species deposited on the electrode lead to capacity deterioration. ► The deposition of LiF/MFx species can be suppressed by TiO2 coating. ► TiO2 coating reduces metal dissolution at a highly delithiated state. The high-temperature cycling stability at a high cutoff voltage of LiNi0.5Co0.2Mn0.3O2 was improved by TiO2 coating. The mechanism of enhancement was elucidated by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses. TiO2 coating formed a uniform layer on the surface of LiNi0.5Co0.2Mn0.3O2 particles without changing the crystal structure. Electrochemical tests indicated that TiO2 coating can improve the lithium ion intercalation stability at 328K and at a high cutoff voltage of 4.4V. The 1.0% TiO2-coated LiNi0.5Co0.2Mn0.3O2 discharged 149.2mAhg−1 after 100 cycles at 0.5C, and maintained 92.1% of the initial discharge capacity. By contrast, the bare sample discharged only 87.7mAhg−1 with 48.2% capacity retention. ICP-AES results proved that the TiO2 coating layer can reduce the dissolution of transition metal ions from LiNi0.5Co0.2Mn0.3O2. EIS and XPS confirmed that the improved cycling stability can be attributed to the suppression of the reaction between cathode and electrolyte in lithium-ion batteries.