Rational Screening of Siloxane Molecules as Electrolyte Additive for High-Temperature Sodium Ion Batteries.

Sodium-ion batteries hold great promise for large-scale energy storage, but face significant challenges at extreme temperatures. Especially at high temperatures, side reactions and electrode dissolution are exacerbated by repeated cycling. It is therefore essential to optimize the electrolyte formulation. Here, a series of siloxane molecules are screened to boost the high-temperature performance of anode materials in SIBs. Octamethyltrisiloxane (MDM), as a result of this screening prefers to interact with anions, resulting in reduced P-F bonding and the formation of a NaF-rich solid electrolyte interphase. This association also raises the oxidation potential and improves the Na-ion transfer. Additionally, MDM inhibits the hydrolysis of PF6-, reducing the deleterious species in the electrolyte. Therefore, commercial Sn microparticles show a reversible capacity of 752 mAh g-1 at 60 oC after 750 cycles at 2 A g-1, much better than the case without MDM. This result exceeds the reported data at high temperatures. MDM as an electrolyte additive also improves the high-temperature performance of Bi and hard carbon. These results provide useful guidance for the rational selection of electrolyte additives for high-temperature sodium-ion batteries.