Lithium-ion batteries (LIBs) have become ubiquitous in modern technology, powering our devices and vehicles. Part of the design of robust and high-performance battery chemistries focuses on electrolytes, exerting direct influence on various aspects crucial for resulting performance and safety. These aspects encompass broad electrochemical stability and formation of effective solid-electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) during the initial cycles and is governed by the decomposition of electrolyte components[1].
To enhance the properties of SEI and CEI, a prevalent and cost-effective strategy involves incorporating functional electrolyte additives in the baseline electrolyte formulation. These additives can sacrificially interact at the corresponding electrodes, forming protective layers (SEI and CEI) that address challenges such as electrode failure, particularly in silicon-rich anodes.
Recent research, including our own, has shown that phosphorus-based functional additives play a critical role in maintaining electrode|electrolyte interfaces,[2] enhancing safety characteristics such as flame-retardant capability [3], and ultimately advancing the overall cell performance [2,4].
This study highlights the advancements and potential of two specific functional additives: 2-phenoxy-1,3,2-dioxaphospholane (PhEPi) as a novel film-forming additive [5] and 2,2,4,4,6-pentafluoro-6-(2,2,2-trifluoroethoxy)-1,3,5,2λ5,4λ5,6λ5-triazatriphosphinine (CF3PFFPN) as a novel flame-retardant additive synthesized by our group. We demonstrated that incorporating PhEPi and CF3PFPN at optimized concentrations in the baseline electrolyte (1 M LiPF6 in EC: EMC 3:7 + 8% VC) significantly enhances the performance of the resulting NMC811||Si-graphite (20% Si) cell chemistry.

Furthermore, we explored the synergistic effect of LiPF6 on the performance of aforementioned functional additives by replacing LiPF6 with analogue salts. To gain a better understanding of each additive’s role in individual SEI and CEI, we conducted a systematic investigation, including post mortem spectroscopic analysis of the corresponding interphases. This deeper insight into the synergistic effect of PhEPi, CF3PFPN, and LiPF6 in the NMC811||Si-graphite cell chemistry is crucial for further advancements of LIB technologies.
In conclusion, research into novel electrolyte additives and their synergistic effects is pivotal for advancing LIB performance. By understanding the intricate interplay between additives, electrolytes, and electrodes, we can pave the way for safer, more effective, long-lasting lithium-ion batteries, and accelerate the transition to a sustainable energy future.

References:
[1] C. Wölke, B. A. Sadeghi, G. G. Eshetu, E. Figgemeier, M. Winter, I. Cekic-Laskovic, Adv. Mater. Interfaces 2022, 9, 2101898, DOI 10.1002/admi.202101898.
[2] N. Von Aspern, D. Diddens, T. Kobayashi, M. Börner, O. Stubbmann-Kazakova, V. Kozel, G. V. Röschenthaler, J. Smiatek, M. Winter, I. Cekic-Laskovic, ACS Appl. Mater. Interfaces 2019, 11, 16605–16618, DOI 10.1021/acsami.9b03359.
[3] T. Dagger, B. R. Rad, F. M. Schappacher, M. Winter, Energy Technol. 2018, 6, 2011–2022, DOI 10.1002/ente.201800132.
[4] C. Wölke, D. Diddens, B. Heidrich, M. Winter, I. Cekic-Laskovic, ChemElectroChem 2021, 8, 972–982, 10.1002/celc.202100107.
[5] B. A. Sadeghi, C. Wölke, F. Pfeiffer, M. Baghernejad, M. Winter, I. Cekic-Laskovic, J. Power Sources 2023, 557, 232570, DOI 10.1016/j.jpowsour.2022.232570