Understanding the electrode/electrolyte interfaces is an essential issue when describing a lithium ion battery. This work reports the application of electrochemical impedance and infrared spectroscopies on the study of interfacial properties of two novel kinds of lithium reservoirs: an electrodeposited Li film onto magnesium foil and an electroformed Li–Al alloy onto aluminium foil. LiFePO4-based lithium ion cells with both electrodes showed high values of energy densities. However, LiAl(Al) failed in guaranteeing capacity retention due to irreversible crumbling. Nevertheless, optimization of its practical cycling life can be envisaged. We observed that the impedance of a LiFePO4-battery built with LiAl(Al) in 1M LiPF6 (EC/DMC) solution, is quite smaller than for a Li(Mg)-based system by virtue of an attenuated formation of surface films on the former. It was also evidenced that electrolyte degradation products migrate from the negative electrode towards the positive one. This phenomenon proceeds in a major extent for LiAl(Al) but results in the formation of a thinner and more conductive film onto the positive electrode than when Li(Mg) acts as negative electrode. The major interfacial drawback of LiAl(Al) is the lack of its passivation since a corrosion process is still observed after 10 cycles.