Lithium-ion capacitors (LICs) were investigated for high power, moderate energy density applications for operation in extreme environments with prolonged cycle life performance. The LICs were prepared as three-layer pouch cells with an asymmetric configuration employing Faradaic pre-lithiated hard carbon anodes and non-Faradaic anion adsorption−desorption activated carbon (AC) cathodes. The studies were conducted in order to develop and improve the LIC cell design, the cell formation procedure, the stability of the electrolytes and additives, and the long-term capacity retention under high stress conditions. The LIC cells have been evaluated using critical performance tests under the following conditions: long-term cycling stability at room temperature (2.2-3.8 V), high temperature holds at 3.8 V, and high upper cut-off potential conditions (2.2 V to 3.8-5.0 V). The rate performance of different electrolytes and additives were measured after the LIC cell formation by charging at a 1C rate and discharging at a 1C, 2C, 4C, 6C, 10C, and again 1C rate from 2.2 V to 3.8 V. The performance of the energy storage devices were evaluated in terms of the specific discharge capacity, operational voltage/temperature window, coulombic efficiency, and cycling stability under different conditions using various electrolytes and additives. The presence of electrolyte additives were found to be essential to the improved performance of the LIC cells at room temperature, at high temperature, and at higher cut-off potentials.