Cascade-Type Prelithiation Approach for Li-Ion Capacitors

Abstract

An industry-relevant method for pre-lithiation of lithium-ion capacitors to balance the first charge irreversibility is demonstrated, which addresses the prime bottleneck for their market integration. Based on a composite positive electrode that integrates pyrene monomers and an insoluble lithiated base, Li3PO4, a “cascade-type” process involving two consecutive irreversible reactions is proposed: i) oxidative electropolymerization of the pyrene moieties releases electrons and protons; ii) protons are captured by Li3PO4 and exchanged for a stoichiometric amount of Li+ into the electrolyte. (1H, 19F, and 31P) NMR spectroscopy, operando X-ray diffraction, and Raman spectroscopy support this mechanism. By decoupling the irreversible source of lithium ions from electrons, the cascade-type pre-lithiation allows the simultaneous enhancement of the capacity of the positive electrode, thanks to p-doping of the resulting polymer. Remarkably, the proton scavenging properties of Li3PO4 also boost the polymerization process, which enables a 16% increase in capacity without detrimental effect on power properties and cyclability. Full cells integrating a cheap carbon black based negative electrode, show much-improved capacity of 17 mAh g-1electrodes (44 F g-1electrodes, 3–4.4 V) and excellent stability over 2200 cycles at 1 A g-1. Thanks to its versatile chemistry and flexibility this approach in principle can be applied to any kind of ion-battery.