Lithium ion batteries for electrical energy storage require a relatively long cycle life of more than several thousand cycles as compared to those of other applications. As the nickel content in a NCM cathode material increase, the performances at a high C-rate and low temperature improve. However, long-term performance metrics such as the cycle life of NCM2 with high nickel contentsare inferior to those of NCM3. In addition, as the nickel contents increase, the cell temperature becomes much higher during the discharge process and more severe degradation of the cell occurs. Because the lifecycle characteristics are more important than the energy density with regard to the use of these batteries in electrical energy storage systems, cathode materials with high nickel contents should be avoided.
The performances of NCM2 and NCM3 in relation to the frequency regulation, peak shaving, and degree of renewable integration were compared under actual operation conditions. Initially, we tested cells using NCM2 and NCM3 cathodes with regard to frequency regulations given the pattern developed by the USDOE and Pacific Northwest National Laboratory and the pattern generated using an algorithm based on a domestic power system frequency and the SoC of the batteries.
Secondly, the peak shaving operation capabilities of energy storage systems refer to the efficient use of an electrical power system. This operation accounts for the highest level of demand among the application fields related to electrical energy storage in that it can support the efficient use of the power grid and lead to successfularbitrage in the electricity market and the deferral of the building of facilities for power generation, transmission and distribution. Therefore, it can contribute to the reduction of greenhouse gases. Using an algorithm for peak shaving, the effects of the reduction of the maximum daily load could be confirmed. The C-rates during the charge and discharge processesduring the peak shaving operation could be derived; they were found to be comparable to those of the patterns developed by the USDOE and PNNL.
Finally, we tested cells using NCM2 and NCM3 cathodes for use as a means of stabilization of a renewable energy source, particularly a wind turbine with a ramp rate of less than 10%/min. In this thesis, many other possible options were not tested; however, it can be concluded that the long-term stability during ESS operation for integration with a wind turbine can be expected with slight temperature increases and high energy efficiency levels while operating under each application condition tested here.