Finding Suitable Discharge Potential and Effect of Succinic Anhydride as Electrolyte Additive on MoS₂/Carbon Composites for Efficient and Stable Sodium Ion Battery Anode

A series of MoS₂/C composites are synthesized for sodium-ion battery anode by changing sulfur sources using a facile hydrothermal and ball milling strategy. The carbon modification increases the conductivity and minimizes volume expansion of the material. The intercalation potential is found out for MoS₂/C composites by several electrochemical and ex situ X-ray diffraction measurements. The MoS₂-NS/C, MoS₂-Tu/C, and MoS₂-S/C electrodes deliver ≈312, 304, and 293 mAh g^-1 reversible capacities at 50 mA g^-1 current densities between 0.3 and 2.5 V. The different reversible capacities of MoS₂/C composites could be due to the different surface areas or morphologies of the composites. The effect of succinic anhydride (SA) as electrolyte additive in cyclic stabilities, which shows an increment of (≈60-≈76%) capacity retention with SA addition, is demonstrated. The ex situ X-ray photoelectron spectroscopy and transmission electron microscopy analysis reveal that more Na₂CO₃-rich solid-electrolyte interphase (SEI) is formed in the presence of SA. The SA-derived SEI also prevents the NaPF₆ degradation, thereby increases the cyclic performance. Furthermore, the full cells assembled with MoS₂/C (anode) and Na₃V₂(PO₄)₃ (cathode) show ≈280 mAh g^-1 specific capacity at 0.05 A g^-1 based on active mass of anode. The improved Na⁺ storage performance is attributed to the fast Na⁺ intercalation, improved conductivity, and stable SEI formation during charge/discharge.