Constructing High Energy and Power Densities Li-Ion Capacitors Using Li Thin Film for Pre-Lithiation

Abstract

Lithium-ion capacitor (LIC) contains negative electrodes (NEs), positive electrodes (PEs), separator and lithium source for pre-lithiation of NEs. Activated carbon was used as the active materials of PEs, and hard carbon will be chosen as NEs. As we know, the specific capacity of NE is ∼372 mAh/g. The most concerned work for our cells now is the pre-lithiation method. With published data from Cao's group before, pre-lithiation with 99.9% purity Li strips can manufacture cells more efficient and safer than using stabilized lithium metal powder (SLMP). However, even this method may take up to 18 h for electrode to finish the pre-lithiation process. In this paper, five pre-lithiation methods for LICs were evaluated in this work, and strip cells were used as control samples and further provided the base for the whole comparison. This research brought up a new method of using 15∼20 um Li ultra-thin film for pre-lithiation. During tests, both sandwich LIC cells and 200F LICs were fabricated to demonstrate this new method. As supplementary evidence, DC life and cycle life tests were conducted after initial tests. Thus, 200F LICs using 20 μm Li film for pre-lithiation can achieve higher capacitance (246 F) and lower ESR (19 mOhm) than Li strip cells. Higher energy and power densities (26.9 Wh/L and 18.3 kW/L) have also been achieved. Moreover, sandwich cells with 15∼20 μm Li thin film has passed 100,000 charge-discharge cycle tests, and their capacitance and ESR can be maintain stable after 1500 h constantly charging at 3.8 V under 65°C.