Publication

Abstract :

Extending the charge cutoff voltage of LiCoO₂ (LCO) beyond 4.2 V is considered as a key parameter to obtain higher energy densities. Following gaps have been identified based on a thorough literature survey especially for higher cutoff voltage of nanoscale engineered LCO cathodes, (i) different metal oxides and metal fluoride surface coatings have been mostly done independently by different groups, (ii) room temperature performance was the focus with limited investigations at high temperature, (iii) nonexistence of low temperature cycling studies and (iv) no reports on high rate capability of LCO beyond 4.5 V (especially at 4.8 V) needs to be investigated. Herein, we report the effect of nanoscale engineering of LCO along with the role of coating chemistry and thickness to study its electrochemical performance at higher voltages and at wide operating temperatures. Surface coating was implemented with different metal oxides and a metal fluoride with tunable thickness. At 4.5 V, 5 wt% Al₂O₃ coated LiCoO₂ (LCO@Al₂O₃-5) delivered a reversible capacity of 169 mAh g⁻¹ at 100 mA g⁻¹ and 151 mAh g⁻¹ at high rate of 10 C (2 A g⁻¹) and 72% retention at the end of 500 cycles. At 55 °C, it exhibited better stability over 500 cycles at 5 C and even at −12.5 °C it maintained 72% of its initial capacity after 100 cycles at 200 mA g⁻¹. At 4.8 V cut-off, LCO@Al₂O₃-5 rendered reversible capacity of 213 mAh g⁻¹ at 100 mA g⁻¹, a high value compared to literatures reported for LCO. Also noted that it delivered a capacity of 126 mAh g⁻¹ at a current density of 1 A g⁻¹, whereas bare could only exhibit 66 mAh g⁻¹ under same testing conditions. Enhanced performance of LCO@Al₂O₃-5 can be ascribed to the lower charge transfer resistance derived from the stable solid solution formation on the interface. Ex situ XRD and ex situ Raman analysis at different stages of charge/discharge cycles correlates the enhanced performance of LCO@Al₂O₃-5 with its structural stability and minimal structural degradation.