The ecological transition has spurred the development of energy storage, and today Lithium-ion batteries (LIBs) dominate advanced electronics and EVs due to high energy density and long life. However, lithium's scarcity and price volatility hinder meeting growing demand. Sodium-ion batteries (SIBs) are emerging as a promising alternative, especially for large-scale storage and hybrid vehicles, owing to sodium's abundance and low cost. SIBs currently have lower energy density than LIBs due to sodium's atomic properties and standard potential. Efforts are focused on improving SIB performance, particularly electrode materials. Finding suitable negative electrode materials for SIBs with high capacity, stability, and appropriate voltage is a major challenge, as graphite, ideal for LIBs, doesn't work well with sodium ions in conventional electrolytes. Hard carbon has gained attention as a promising SIB intercalation material with notable charge storage capacity, influenced by its structure and surface properties.[1] HC presents, however, a limited volumetric capacity.  

On the other hand, alloys-type materials, forming stable alloys with sodium, have been heavily studied. [2-4] They often involve multiple electron exchange, leading to high gravimetric and volumetric specific capacities (with 670 mAh/cm³ for Sb) for high-energy SIBs. Sb exhibits a complex but highly reversible electrochemical alloying reaction with Na, resulting in good cyclability despite very large volume expansion, which can actually be partially absorbed by a suitable electrode formulation.[5] This volume expansion during cycling causes nevertheless unstable SEI formation, electrolyte consumption, and poor coulombic efficiency.

SIBs technology is maturing, with companies like Faradion, Novasis, HiNa, and Tiamat emerging, mostly using hard carbon anodes. Tiamat, a French pioneer, uses polyanionic cathodes Na₃V₂(PO₄)₂F₃ (100-120 Wh/kg) in its first generation and lamellar oxides (140 Wh/kg, aiming for 180 Wh/kg) in its second. While positive electrode progress is significant, negative electrodes still rely on hard carbon with limited capacity. A recent study demonstrated promising performance for Sb-based negative electrodes in SIBs.[6]

To boost the volumetric capacities of its negative electrodes, Tiamat company decided to launch a study on Sb-carbon composites. The presented study focuses on antimony (Sb) alloy based negative electrodes, aiming to improve gravimetric and volumetric capacity, playing with electrode formulations parameters. Carbon/Sb composites were prepared either by Sb incorporation in hard carbon or by mechano-synthesis of Sb/carbon. Full cells of the as-prepared composites were tested against Tiamat's cathode (NVPF) in full SIBs.

Thanks to many optimizations of Sb (with theoretical capacity of 660 mAh/g) based electrode formulation, higher gravimetric and volumetric capacities than HC were obtained. These latter depend strongly on the electrode preparation (carbon/Sb ratio and mixtures, conductive additives, electrolytes…). In conclusion, the use of antimony in the composition of negative electrodes material in SIBs offers significant advantages in terms of gravimetric and especially volumetric capacity.