High performance Li-ion capacitor (LIC) laminate cells have been fabricated with activated carbon positive electrodes (PEs) and hard carbon/lithium stripes negative electrodes (NEs). The lithium stripes on the surface of NEs enable a novel pre-lithiation approach for the LIC cells. The LIC laminate cells can achieve a maximum specific power of 6 kW kg−1 and a maximum power density of 12 kW L−1. The specific energy and energy density of the LIC laminate cells are 14 Wh kg−1 and 28 Wh L−1 respectively, which is about 3 times of the traditional electric double layer capacitors (EDLCs). The DC life of such LIC cell has passed 2000 h testing while held at maximum operation voltage 3.8 V and 65°C. Extended cycle performance under 50 C rate of the LIC laminate cell has been tested: such LIC can remain 89% of the original discharge capacitance after 100,000 cycles without obvious changes in ESR value. When the LIC cell is charging and discharging under 125 C rate, the cycle life is still more than 50,000 cycles.
Earlier research determined that lithium-ion capacitor (LIC) cycle life degradation can be accelerated by elevated temperature. LIC cycle life degradation can be described by an Arrhenius equation. This study performed cycle life testing at a constant temperature but varied cycle current. The results were described by an Arrhenius equation relying upon the number of cycles and a constant, which was determined by cycle current. Using mathematical derivations and experimental results, the researchers quantified the effects of activation energy and temperature upon this constant. Because cell temperature is nearly constant during cycles, it was deduced that elevated cycle current decreases activation energy. This lower activation energy then accelerates degradation. Thus this research demonstrates that cycle current ages LICs through its effects on their activation energies.
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