Simplified Lithium-Ion Capacitors with Irreversible Lithiated Materials in the Positive Electrode

Abstract

The lithium-ion capacitor (LIC) is a high energy hybrid system which combines an electrical double-layer (EDL) positive electrode made from nanoporous carbon with a negative intercalation electrode made from graphite or hard carbon [1,2]. The electrolyte is a lithium salt (LiPF6) which is generally dissolved in ethylene carbonate:dimethyl carbonate (EC:DMC) mixture. The most common concept of LIC uses an auxiliary metallic lithium electrode for graphite pre-lithiation [1,2]. Since this additional lithium electrode complicates the cell construction and might be the cause of thermal runaway during LIC operation, alternative strategies have been considered. Pre-lithiation has been proposed directly from the electrolyte [3], but it leads to a decrease of electrolyte concentration and conductivity, which might have a negative impact on the LIC power. A better strategy to lithiate the negative electrode consists in irreversible lithium de-intercalation from lithium metal oxide (Li2MoO3, Li5FeO6, Li0.65Ni1.35O2) incorporated together with activated carbon in the positive electrode [4,5]. However, for some of these oxides, the extraction potential of lithium ions exceeds 4.5 V vs. ref. Li/Li+, which causes detrimental electrochemical oxidation of the electrolyte. The first objective of this presentation is to design new materials from which high amounts of lithium can be irreversibly de-intercalated at potential lower than 4.2 V vs. Li/Li+. For example, we demonstrated that lithium can be irreversibly extracted at 3.3 V vs. Li/Li+ with a capacity of ca. 350 mAh/g during galvanostatic oxidation of the renewable organic derivative C6H3CN(OLi)2; the LIC cell based on the use of this material demonstrates an excellent cycle life in the potential range from 2.2 ~ 4.0 V. The second objective is to investigate materials with the lowest residual mass after the delithiation step. We will show that this can be achieved by selecting materials which liberate neutral gases simultaneously to lithium deintercalation. Hence, after this step, the positive electrode contains only activated carbon, leading the system to display much higher energy density. [1] N. Ando, S. Takasi, H. Taguchi, Y. Hato, Organic electrolyte capacitor, EP1400996A1 (2002) [2] T. Aida, K. Yamada and M. Morita, Electrochem. Solid-State Lett. 9 (2006) A534. [3] V. Khomenko, E. Raymundo-Piñero, F. Béguin, J. Power Sources 177 (2008) 643. [4] M.-S. Park, Y.-G. Lim, J.-H. Kim, Y.-J. Kim, J. Cho and J.-S. Kim, Adv. Energy Mater. 1 (2011) 1002. [5] P. Jeżowski, K. Fic, O. Crosnier, T. Brousse, F. Béguin, Electrochim. Acta (2016) http://dx.doi.org/10.1016/j.electacta.2015.12.034.