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Page 8 of 18 Yang et al. Energy Mater 2023;3:300029 https://dx.doi.org/10.20517/energymater.2023.10

indicating the effective suppression of electrolyte decomposition by the SEI film derived from LiDFOB. The
F 1s spectra provide valuable information regarding the SEI on the Li anode. In the case of the Li anode
cycled in the base electrolyte, the observed peaks at 684.42 eV and 686.65 eV can be attributed to the
presence of LiF and LiP F /LiP F O , resulting from the decomposition of LiPF . It is well known that the
x y
z
6
x y
decomposition of LiPF to LiF often leads to the generation of PF . While LiF has been extensively studied
6
5
[72]
for its beneficial effects , its advantages may be overshadowed by the strong reactivity of PF with the
5
electrolyte due to its Lewis acid property. Furthermore, Supplementary Figure 3 demonstrates a significantly
higher energy barrier for breaking the B-F bond during the reduction decomposition of LiDFOB compared
to its ring-opening reaction. This finding suggests that the ring-opening reaction is the predominant
pathway for the decomposition of LiDFOB, thereby confirming that a major portion of the LiF originates
from the decomposition of LiPF . The peaks of LiP F and LiP F O can also be observed in P 2p spectra. The
x y
x y
z
6
peak areas of the two compounds, along with LiF, as represented in Supplementary Figure 2, indicate that
the intensity of these compounds is greater in the case of Li anode cycled in the base electrolyte as compared
to the LiDFOB-containing electrolyte. This provides further confirmation that the SEI film formed by
LiDFOB is stable and robust enough to suppress severe electrolyte decomposition. Notably, the weak peak
signal observed in the position range from 198 eV to 184 eV for the Li anode cycled in the base electrolyte
can be attributed to the overlap between B 1s and P 2s XPS peak positions. Specifically, the peak signal in
the base electrolyte primarily corresponds to the P 2s spectra of Li PF O (192.1 eV) and Li PF (194.5 eV)
x
y
z
y
x
species as detected in P 2p spectra. The electrode cycled in the LiDFOB-containing electrolyte displays
additional peaks associated with B-F (193.1 eV) and B-O (191.1 eV) in P 2s/B 1s spectra, B-O eV in O 1s,
and B-O-C (290.3 eV) in C 1s spectra [52,73] . These results suggest that the reduction decomposition products
of LiDFOB participate in the SEI formation process.
Protection of microstructure for Ni-rich cathode
To evaluate the compatibility of LiDFOB with Ni-rich cathodes, various concentrations of the LiDFOB
additive were added to the base electrolyte and evaluated in Li||NCM85 batteries with the cut-off voltages of
4.3 V. As shown in Supplementary Figure 4, Li||NCM85 batteries show improved capacity retention with
the addition of LiDFOB additive, from 85.5% (utilizing the base electrolyte) to 91.9 % (with 1 wt% LiDFOB-
added electrolyte), 100% (with 2 wt% LiDFOB-added electrolyte), and 88.4% (with 3 wt% LiDFOB-added
electrolyte). These results suggest that 2 wt% is the optimized content of LiDFOB for Li||NCM85 batteries. It
can be noted from Figure 3A that the Li||NCM85 battery cycled in the 2 wt% LiDFOB-containing electrolyte
demonstrates a notable initial CE of 85.7% and an average CE of 99.9% throughout the 6th cycle to the 200th
cycle, surpassing those observed in the base electrolyte. These findings suggest that the CEI film derived
from LiDFOB effectively mitigates interfacial parasitic reactions. Consequently, the capacity retention of the
battery after 250 cycles is substantially higher at 90.9% compared to the base electrolyte at 64.6% [Figure 3B,
vs. the discharge capacity at the 3rd cycle]. Accordingly, by comparing the GITT curves of the battery after
the first and 150 cycles, the corresponding overpotentials, and Li diffusion coefficients (D ), the battery
+
Li+
cycled in the base electrolyte exhibits a significantly increased overpotential, accompanied by a rapidly
reduced D [Figure 3C and Supplementary Figure 5]. This may be related to the increasing electrode
Li+
polarization due to the continuous accumulation of electrolyte parastic reaction products and the structural
[64]
degradation of the NCM85 cathode . In contrast, the NCM85 electrodes maintained a lower overpotential
and a higher D during cycling with the addition of LiDFOB, which is attributed to the stable NCM85
Li+
i n t e r f a c i a l s t r u c t u r e i n t h e p r e s e n c e o f t h e L i D F O B - d e r i v e d C E I f i l m
[Figure 3D and Supplementary Figure 5]. Moreover, we further investigated the effect of LiDFOB on the
stability of the NCM85 interfacial structure by increasing the charge cut-off voltage to 4.6 V. As shown in
Figure 3E, the introduction of LiDFOB into the base electrolyte can achieve a remarkable enhancement in
the electrochemical performance of NCM85 with capacity retention as high as 74% after 300 cycles. This
comprehensive performance is comparable to the high-voltage Ni-rich cathodes that have been reported