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Page 12 of 14 Kühn et al. Energy Mater 2023;3:300020 https://dx.doi.org/10.20517/energymater.2023.07

CONCLUSION
The two different ICCAs (GB and DR) were found to have a substantial impact on the coin cell
performance of the LMB, originating from the altered interphase compositions of the SEI and CEI covering
the lithium metal anode and NMC811 cathode, respectively. Furthermore, the effect of the ICCA itself was
differently pronounced depending on the film-forming electrolyte additives VC or FEC. However, both
additive-containing electrolytes were shown to form performance-enhancing chemical CEI compositions
with a DR ICCA. Stripping/Plating experiments and operando EIS analysis also revealed that the ICCA has a
considerable impact on overvoltage vs. time profiles and R values for Li||Li symmetric cells containing BE
SEI
and AE-VC. Differences in stripping/plating homogeneity were observed by post-mortem optical analysis
(incl. SEM imaging) for different ICCAs and electrolytes, while post-mortem XPS analysis revealed different
atomic SEI compositions for all three considered electrolyte formulations. In the case of NMC811||Li full
cell setups, the DR ICCA resulted in a reduced capacity fade and delayed rollover effect, ultimately leading
to an increased lifetime (EOL: 80% SOH) for both AE-VC and AE-FEC of up to 50%. This enhancement is
the result of a modified CEI composition, containing more linear carbonates in the case of AE-VC × DR
and the formation of carboxylates for AE-FEC × DR, which was revealed by post-mortem ATR-FTIR
analysis. Based on the FTIR analysis, a new oxidative decomposition mechanism for FEC in the presence of
oxygen was proposed and supported by quantum chemical calculations, revealing lithium formate as the
newly formed CEI component. In particular, the formation of new chemical components and overall
impacted electrolyte interphase compositions of anode (SEI) and cathode (CEI) demonstrates the previously
underestimated impact of the ICCA as a highly influential factor for the comparability of research results as
well as the transfer of research knowledge to industrial application for future LMBs.

DECLARATIONS
Authors’ contributions
Methodology, investigation, formal analysis, writing (original draft): Kühn SP
Investigation, formal analysis: Weiling M, Diddens D
Formal analysis, writing (review & editing): Baghernejad M
Writing (review & editing), supervision: Winter M
Conceptualization, supervision, writing (review & editing): Cekic-Laskovic I

Availability of data and materials
Data will be made available on request.

Financial support and sponsorship
The authors are grateful for the financial support provided within the LILLINT project (13XP0225B) funded
by the German Federal Ministry of Education and Research (BMBF).

Conflicts of interest
All authors declared that there are no conflicts of interest.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.