Electrochemical reaction mechanisms under various charge-discharge operating conditions for Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 in a lithium-ion battery

Abstract The potential in each state of charge (SOC) during charging of Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 is higher than that during discharging. In other words, the potential hysteresis occurs between charging and discharging. Furthermore, the potential in each SOC changes according to the charge-discharge operating conditions, indicating that the charge-discharge reaction mechanism is also affected. To clarify the effect of charge-discharge operating conditions on the electrochemical reaction, Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 was charged and discharged under various charge-discharge operating ranges, and open-circuit potential (OCP), crystal structure, and oxidation states of the transition metals were evaluated by electrochemical measurement, X-ray diffraction (XRD), and X-ray absorption fine structure (XAFS). These results indicate that OCP, lattice parameters, and oxidation states of the transition metals of Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 in each SOC are not constant. The XRD results indicate that two phases, namely, LiNi 0.33 Mn 0.33 Co 0.33 O 2 -like and Li 2 MnO 3 -like, exist in Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 . For the LiNi 0.33 Mn 0.33 Co 0.33 O 2 -like phase, the relationship between OCP, lattice parameters, and oxidation states of the transition metals in each SOC is not affected by the charge-discharge operating conditions, indicating that extraction and insertion of lithium ions for the LiNi 0.33 Mn 0.33 Co 0.33 O 2 -like phase progresses at almost the same potential. Although the extraction and insertion of lithium ions for the Li 2 MnO 3 -like phase progresses at almost the same potential in the low-SOC region, the OCP and lattice parameter in each SOC in the high-SOC region are not constant. Therefore, the extraction of lithium ions from the Li 2 MnO 3 -like phase in the high-SOC region causes the potential hysteresis of Li 1.2 Ni 0.13 Mn 0.54 Co 0.13 O 2 .