**5. Conclusions**

In this paper we have investigated tributyl acetylcitrate as a novel and ecofriendly electrolyte-solvent for lithium-ion cells. Compared to conventional solvents, the flash point and the boiling point are almost 200 K higher than that of EMC or DEC. The melting point is more than 100 K lower than that of EC. In combination with LiPF6 and other solvents (TBAC:EC:EMC:DEC, 60:15:5:20 wt), TBAC shows good electrochemical stability between −4 V and 3 V vs. stainless steel. In graphite/NCM cells the coulombic efficiency is above

*ηcoul* = 99%. After 100 cycles the remaining capacity is still above 90%. Therefore, TBAC when compared to other solvents is a promising alternative to improve the intrinsic thermal stability of lithium-ion cells.

**Author Contributions:** Conceptualization, M.S. and K.P.B.; methodology, M.S. L.K., and K.P.B.; investigation, M.S. and L.K.; writing—original draft preparation, M.S.; writing—review and editing, L.K. and K.P.B.; visualization, M.S. and L.K.; supervision, K.P.B.; project administration, M.S.; funding acquisition, K.P.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the Bundesministerium fuer Bildung und Forschung within the BCT—Battery Cell Technology project (03XP0109H).

**Institutional Review Board Statement:** Not Applicable.

**Informed Consent Statement:** Not Applicable.

**Data Availability Statement:** Not Applicable.

**Acknowledgments:** The authors thank Münster Electrochemical Energy Technology for providing the NCM622 electrode material and Varta AG for providing the graphite electrode material.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
