From Powder to Pouch Cell: Setting up a Sodium-Ion Battery Reference System Based on Na3V2(PO4)3/C and Hard Carbon

At the research level, novel active materials for batteries are synthesised on a small scale, fabricated into electrodes and electrochemically characterised using each group's established process due to the lack of standards. Recently, eminent researchers have criticised the implementation of e. g. low active material contents/electrode loadings, the use of research-type battery cell constructions, or the lack of statistically relevant data, resulting in overstated data and thus giving misleading predictions of the key performance indicators of new battery technologies. Here, we report on the establishment of a reference system for the development of sodium-ion batteries. Electrodes are fabricated under relevant conditions using 9.5 mg/cm2 self-synthesised Na3V2(PO4)3/C cathode active material and 3.6 mg/cm2 commercially available hard carbon anode active material. It is found that different types of battery cells are more or less suitable for half- and/or full-cell testing, resulting in ir/reproducible or underestimated active material capacities. Furthermore, the influence of electrode overhang, which is relevant for upscaling, is evaluated. The demonstrator cell (TRL 4-5) has been further characterised providing measured data on the power/energy density and thermal behaviour during rate testing up to 15 C and projections are made for its practical limits.