Co-Intercalation Batteries (CoIBs): Role of TiS_2 as Electrode for Storing Solvated Na Ions

摘要

The co-intercalation of solvent molecules along with Na+ into the crystallattice of electrode materials is an undesired process in sodium batteries.An exception is the intercalation of ether solvated alkali ions into graphite, afast and highly reversible process. Here, reversible co-intercalation is shownto also be possible for other layered materials, namely titanium disulfide.Operando X-ray diffraction and dilatometry are used to demonstrate differentstorage mechanisms for different electrolyte solvents. Diglyme is found toco-intercalate into the TiS2 leading to a change in the voltage profile and anincrease in the interlayer spacing (≈150%). This behavior is different comparedto other solvents, which expand much less during Na storage (24% fortetrahydrofuran [THF] and for a carbonate mixture). For all solvents, specificcapacities (2nd cycle) exceed 250 mAh g?1 whereas THF exhibited the beststability after 100 cycles. The solvent co-intercalation is rationalized by densityfunctional theory and linked to the stability of the solvation shells, whichis largest for diglyme. Finally, the TiS2 electrode with diglyme electrolyte ispaired with a graphite electrode to realize the first proof-of-concept solventco-intercalation battery, that is, a battery with two electrodes that both rely onreversible co-intercalation of solvent molecules.