Metal-organic frameworks (MOFs) are materials composed of metallic centers linked to organic ligands. The possibility of controlling their structure and their pore size makes them very promising candidates for certain applications such as gas storage, sensors, or energy storage.[1] Regarding the latter application, MOFs are particularly interesting due to the greater theoretical specific capacities that they can provide in comparison to graphite or traditional inorganic materials used in commercial lithium-ion batteries (LIBs). Energy density is directly proportional to specific capacity, so MOFs could help to achieve the goal of electrification of energy. Nevertheless, most of the published studies for this application use MOFs as precursors for obtaining structured derivatives such as metal oxides or carbon-based structures containing metals. Even though really good performances can be obtained by this strategy [2][3], the techniques used for this typically involve heating the samples at really high temperatures, which would cause an significant impact not only in the environment but also in the manufacturing cost of a battery. Using pristine MOFs as electrodes in LIBs would avoid this step. But, before considering these materials as potential candidates for replacing graphite, it is necessary to study the mechanism of Li⁺ (de)insertion in their structure.

Here, we present our study about the mechanism of Li⁺ (de)insertion in a pristine MOF based on pyrazine used as an anode in LIBs. Electrodes were fabricated by mixing in an agate mortar the active materials with a carbon additive and a binder (polyvinylidene fluoride) in a proportion 80:15:5 in weight using N-Methyl-2-pyrrolidone as the solvent. The slurry obtained was then deposited on a copper foil using doctor-blade technique and dried in vacuum conditions. The copper foil with the active materials was then compressed and electrodes were cut from it and assembled in half-cells using lithium as both counter and reference electrode. Half-cells were characterized by different techniques to understand the reaction that occurs when lithium-ions are (de)inserted from the electrodes such as cyclic voltammetry and EIS measurements. In addition, the electrodes before and after cycling were measured by XRD, XPS and SEM. Also, the rate capability and cyclability were tested doing charge-discharge cycles. These measurements show that MOFs can provide great specific capacities even when used pristine.