Potential hysteresis between charge and discharge reactions in Li1.2Ni0.13Mn0.54Co0.13O2 for lithium ion batteries

The mechanism responsible for the large potential hysteresis between charge and discharge reactions in Li1.2Ni0.13Mn0.54Co0.13O2 was investigated. The relationship between open circuit potential and the oxidation state of each transition metal during charge-discharge processes was evaluated. The results indicated that the electrochemical reaction in Li1.2Ni0.13Mn0.54Co0.13O2, which can be expressed as 0.5Li2MnO3−0.5LiNi0.33Mn0.33Co0.33O2, was composed of two kinds of reactions such as LiNi0.33Mn0.33Co0.33O2-like and Li2MnO3-like reactions. For the LiNi0.33Mn0.33Co0.33O2-like reaction, nickel and cobalt contributed to the redox reaction. The electrochemical reaction progressed within a potential range of 3.6-4.6 V, both during charge and discharge processes; thereby, there was little potential hysteresis between charge and discharge processes. For Li2MnO3-like reaction, manganese and oxygen contributed to the redox reaction. The reaction that occurred within a potential range of 3.6-4.6 V in a charge process mainly progressed within a potential range of 3.6-2.5 V during the discharge process, which indicated that there was large potential hysteresis between charge and discharge processes in the Li2MnO3-like reaction. Therefore, the large hysteresis of reaction potential between charge and discharge processes in the Li2MnO3-like reaction was mainly related to that in the 0.5Li2MnO3−0.5LiNi0.33Mn0.33Co0.33O2.