The Importance of Fabricating Hard Carbon-Based Full Cells to Overcome Sodium Metal Anode Limitations in Evaluating High-Mass-Loading Cathodes

Developing advanced cathode materials is pivotal for successful commercialization of sodium-ion batteries (SIBs), but it requires reliable evaluation of electrochemical performance. However, the widely used sodium metal anode in academic research is not a “qualified counter electrode”, particularly under high-mass-loading and limited-Na conditions. Herein, the limitations of Na metal anode are discussed, and reliable high-mass-loading hard carbon (HC)-based full cells are proposed with a detailed guideline provided for qualified slurry preparation, electrode fabrication, and cell design. Three-electrode tests reveal Na metal’s severe potential fluctuations, which influences the evaluation of electrochemical performance for high-mass-loading NaNi1/3Fe1/3Mn1/3O2 cathodes. Encouragingly, HC-based pouch cells demonstrate good electrochemical performance, including lower polarization (∼0.07 Ω ohmic resistance), enhanced cycling stability (85% retention after 250 cycles), and rate performance (80% capacity maintained at 4 C), highlighting the exceptional reliability and suitability. This study offers a robust methodology for evaluating lab-developed cathode materials, bridging the gap between academia and industrial applications.