2, Nantes University, Nantes, , France
Internal hybridization of a battery-type electrode with an electrical double-layer (EDL) electrode appears as a key for opening a path to more versatile devices which can at the same time deliver high power and high energy, while being able to display a long term cycle life. The best example is the lithium-ion capacitor (LIC) which implements an EDL positive electrode made from porous carbon and a LIB faradaic negative electrode made from graphite or hard carbon, while using a lithium salt (LiPF6) generally dissolved in ethylene carbonate:dimethyl carbonate (EC:DMC) mixture . Since lithium must be intercalated in the graphite/carbon negative electrode, the first concept of LIC included an auxiliary metallic lithium electrode which was used for pre-lithiation, hence complicating the cell design and being potentially the cause of safety issues as thermal runaway. Therefore, pre-lithiation has been proposed directly from the electrolyte , but it leads to a decrease of ionic concentration and conductivity, which might have a negative impact on the LIC power.
A novel strategy to lithiate the negative electrode consists in an irreversible lithium de-intercalation from a sacrificial lithiated material incorporated together with activated carbon in the positive electrode . Using lithiated oxides with low band gaps, such as Li5ReO6, enables extracting lithium ions at a potential around 4.2 V vs. ref. Li/Li+ and to avoid detrimental electrochemical oxidation of the electrolyte . Very promising performance was obtained with renewable organic lithium salts from which lithium is irreversibly extracted, with a capacity of ca. 350 mAh/g, at potential as low as. 3.3 V vs. Li/Li+; the resulting LIC cells demonstrate an excellent cycle life in the potential range from 2.2 ~ 4.0 V .
This presentation will briefly introduce the various strategies which have been successfully used by our group with a special focus on the structural/microstructural changes occurring after the first pre-lithiation step and on the performance of LICs in terms of energy and power densities as well as cycle life. New perspectives, using materials leaving a reduced dead-mass after pre-lithiation, will be also detailed.
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