First time proposed conversion or displacement reaction in Pb as anode in Li-ion batteries

Full text: Li-ion batteries lead the technology used in portable electronics devices. The appeal of Li-electrochemistry lies in its low redox potential (E_Li + _/Li = -3.04V), its low molecular weight, which is beneficial for its diffusion and the high energy efficiency that can release and store. Up to now, the systems mostly employed are those based on Li-ion, as LiCoO₂ , LiMn₂O₄ and LiFePO₄. Nevertheless, the searching for new systems keep on. A 3D system, Prussian Blue Analogues (PBA), have been attracting battery researcher´s attention during the last two decades because of the large and tunable channels its structure has. Prussian Blue (PB), KFe₂ (CN)_6∙xH₂O, is a metal-organic compound with cubic structure, presenting Fe in two different oxidation states, Fe(II) and Fe(III), that are connected by linear C≡N groups all along the network. In this arrangement, alkali atoms are alternately occupying the centres of the small cubes created by these Fe(II)-C≡N-Fe(III) units, which supposes half of the total occupation, and allow the insertion and also the de-insertion of cations. When the Fe(II) is substituted by another transition metal M(II) in the structure, a PBA is obtained. Through the PBA's electrochemistry history, these family of compounds have been widely studied as cathode both in Na and Li batteries, either in aqueous or organic media, enabling fast and rapid insertion of monovalent-cations such as Li⁺ , Na⁺ , NH4⁺ and divalent-cations as Mg²⁺, Ca²⁺. Nevertheless, its exploitation as anode is beginning now. Only, two groups have reported the use of Co-based PBA as anode for Li-ion batteries. In this poster, we present the electrochemical performance of purely Fe-based PB when cycled vs lithium as anode in organic media and the mechanism proposed for the large capacities it displays. For the first time, a possible conversion mechanism is reported for this kind of systems, based on ex-situ IR, XRD and TEM experiments of the cycled electrodes. (author)