The effect of cooling process on the structure and charge/discharge capacities of Li-rich solid-solution layered...

The effect of cooling process after calcination at 900 °C in the preparation of cathode materials, on the crystal structure and charging/discharging capacities of Li₂MnO₃-LiNi_1/2Mn_1/2O₂-LiNi_1/3Mn_1/3Co_1/3O₂ Li-rich solid-solution layered oxide (LLO) cathode materials for the lithium ion battery was examined in twenty-one LLO samples having different compositions. This was achieved by applying two types of cooling processes: (i) quenching the calcinated LLO samples with liquid nitrogen (quenched cooling), and (ii) slow cooling of LLO samples in the furnace at a controlled decreasing rate of the temperature (slow cooling). The results of the comparison between discharging capacities observed with LLO samples prepared with two types of cooling processes indicated that the cooling process for LLO samples to exhibit high discharge capacity was not limited to either one. The process that can be more effective for LLO samples to exhibit the high discharge capacity depended on the composition of LLO samples. LLO samples containing Li₂MnO₃ of over 60% exhibited higher discharge capacity when samples were quenched with liquid nitrogen than those prepared with the slow cooling process. Among LLOs examined, the effect of quenching was maximum when the Li₂MnO₃ content was 60%. As the LLO composition deviated from the line of 60% Li₂MnO₃ in the Li[Li_0.20Mn_0.58Ni_0.18Co_0.04]O₂ sample compositions, the effect of quenching became smaller and the slow cooling process was superior to the quenching process. A connection was thus made between the structural difference of LLO samples prepared with the two types of cooling processes and the cathode performance was observed.