Exploring processability limitations of commercial hard carbon for negative electrodes of Na-ion batteries

Optimizing electrode manufacturing processes for sodium-ion batteries (SIBs) is crucial for enhancing their performance and commercial viability. This study systematically investigates the influence of critical electrode fabrication parameters, including solid content, mass loading, and calendering, on commercial hard carbon (HC) electrode properties. Slurries prepared with 35 % and 40 % solid content (SC) demonstrated distinct rheological behaviours, directly affecting electrode mechanical stability and processability. The slurry with SC-35 % provided a better balance between manageable viscosity and robust mechanical stability upon drying, whereas SC-40 % slurry exhibited higher viscosity, particle agglomeration, and poorer electrode mechanical integrity. Calendering was studied at compression degrees of 10 %, 20 %, and 30 %, revealing limited effectiveness in reducing porosity due to the intrinsic mechanical properties of HC, whereas, higher compression degrees led to structural damage. Electrochemical studies conducted in half-cells (HC vs. Na) and full-cells (HC vs. Na₃V₂(PO₄)₃) clearly indicated better electrochemical performance at moderate calendering degrees (10–20 %), effectively balancing mechanical integrity and electrical conductivity. This comprehensive study results in a useful experimental database in academic literature, underscoring the importance of precise control over slurry formulation and calendering parameters to achieve structurally robust electrodes, thus significantly enhancing the practical performance of SIBs.