Among various energies, electric energy is one that we cannot live without for a moment in this automated and computerized society. There are electric energy devices to allow people to store and use electric energy as needed. It is important to understand characteristics of electric energy devices for efficiently using these devices. This thesis is performed to predict characteristics of electric energy devices as a lithium ion battery, an absorbent glass mat (AGM) battery and an ultracapacitor.
Chapter 1 described the fundamentals and application field for a lithium ion battery, an AGM battery and an ultracapacitor as typical electrical energy storage device.
In chapter 2, this thesis reported a modeling methodology to predict the effects on the discharge behavior of the cathode composition of a lithium iron phosphate (LFP) battery cell comprising a LFP cathode, a lithium metal anode, and an organic electrolyte. A one-dimensional model based on a finite element method is presented to calculate the cell voltage change of a LFP battery cell during galvanostatic discharge. To test the validity of the modeling approach, the modeling results for the variations of the cell voltage of the LFP battery as a function of time are compared with the experimental measurements during galvanostatic discharge at various discharge rates of 0.1C, 0.5C, 1.0C, and 2.0C for three different compositions of the LFP cathode. The discharge curves obtained from the model are in good agreement with the experimental measurements. On the basis of the validated modeling approach, the effects of the cathode composition on the discharge behavior of a LFP battery cell are estimated.
In chapter 3, for optimal design and operation of vehicle electrical systems, we conducted modeling to predict the AGM battery cycle life and performance. The AGM battery model was formulated considering various phenomena occurring inside an AGM battery, including electrochemical reaction, transfer of ions, and porosity of electrode. In addition, to predict AGM battery cycle life, we considered the additional factors of corrosion of electrode plate and loss of active materials as a function of charge?discharge cycles. Using electrochemical modeling of the AGM battery, we incorporated nonlinearity of AGM battery aging, which was impossible with electrical equivalent circuit modeling. The model was validated by comparison of results of the modeling and actual experimental data. Using the development modeling, SOH and SOF were calculated.
In chapter 4, this thesis reported a modeling methodology to predict the electrical and thermal behaviors of a 2.7 V/650 F ultracapacitor (UC) cell from LS Mtron Ltd. (Anyang, Korea). The UC cell is subject to the charge/discharge cycling with constant-current between 1.35 V and 2.7 V. The charge/discharge current values examined are 50, 100, 150, and 200 A. A three resistor-capacitor (RC) parallel branch model is employed to calculate the electrical behavior of the UC. The modeling results for the variations of the UC cell voltage as a function of time for various charge/discharge currents are in good agreement with the experimental measurements. A three-dimensional thermal model is presented to predict the thermal behavior of the UC. Both of the irreversible and reversible heat generations inside the UC cell are considered. The validation of the three-dimensional thermal model is provided through the comparison of the modeling results with the experimental infrared (IR) image at various charge/discharge currents. A zero-dimensional thermal model is proposed to reduce the significant computational burden required for the three-dimensional thermal model.