Lithium rhenium(VII) oxide as a novel material for graphite pre-lithiation in high performance lithiumion capacitors

The electrochemical reversibility of lithium extraction from lithium rhenium oxide (Li5ReO6, LReO) has been studied using standard 1 mol L-1 LiPF6 in EC/DMC electrolyte. An irreversible capacity of 410 mA h g(-1) was observed below 4.3 V vs. Li/Li+ (close to the total theoretical capacity of 423 mA h g(-1)). Owing to this huge irreversible capacity, LReO could be included as a sacrificial material in the positive activated carbon electrode of a lithium-ion capacitor (LIC) to be used for pre-lithiating the graphite negative electrode. After the pre-lithiation step, the hybrid lithium-ion capacitor constituted of Li doped graphite and activated carbon as negative and positive electrodes, respectively, was cycled at current densities from 0.25 A g(-1) to 0.65 A g(-1). The LIC system demonstrated excellent capacitance stability up to 5000 cycles in the voltage range 2.2-4.1 V. The energy and power densities calculated per total mass of both electrodes reached 40 W h kg(-1) and 0.5 kW kg(-1), respectively. Hence, by using LReO, the prelithiation of graphite can be considerably simplified in comparison to traditional LIC systems, while enabling safer operating conditions owing to the absence of metallic lithium.