Impedance measurements on lithium-ion battery consisting of Li[Li1/3Ti5/3]O4 and LiCo1/2Ni1/2O2

A 2-V lithium-ion battery consisting of Li[Li1/3Ti5/3]O4 (zero-strain insertion material) and LiCo1/2Ni1/2O2 was constructed, and accelerated cycle tests were performed for 50,000 cycles in order to examine whether or not high-rate charge and discharge were possible for the lithium-ion battery. Mode of accelerated cycle tests consisted of quick charge at 2.5 V and discharge at 1.7 V, respectively, for 25.6 s, which corresponded to about 10% change in capacity determined for the fresh cell. Maximum charge and discharge currents were, respectively, 3.4 and 4.2 A g−1 based on LiCo1/2Ni1/2O2 weight. Capacity failure was not observed even after 50,000 cycles; specifically 90% of initial capacity was observed when the cell was cycled at 0.17 mA cm−2 in voltages of 1.0–2.7 V. However, power fade was observed during the accelerated cycle tests for both input and output. Impedance spectra as a function of depth-of-discharge (DOD) were measured before and after the cycle tests. After the 50,000 cycle tests, internal resistance observed at 0.1 Hz increased twice, while that at 1 kHz increased about 10% for 50% of DOD. From these results, an application of impedance measurements to basic researches on lithium insertion materials for high-power and long-life lithium-ion batteries was discussed.