Lithium rhenium(vii) oxide as a novel material for graphite pre-lithiation in high performance lithium-ion capacitors

Abstract

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.