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Yang et al. Energy Mater 2023;3:300029 https://dx.doi.org/10.20517/energymater.2023.10 Page 13 of 18

Figure 6. The formation mechanism of SEI and CEI films in LiDFOB-containing electrolyte by DFT calculation. (A) Reduction pathways
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+
of EC and Li -DFOB and corresponding decomposition products on the anode side. (B) The adsorption energy of decomposition
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products on Li (100) surface. (C) Oxidation pathways of EC and DFOB and corresponding decomposition products on the cathode side,
searched by DFT. (D) The adsorption energy of decomposition products on the LiNiO (104) surface.
2
respectively, which are both lower than that of -3.7 eV, -2.8 eV, and -1.73 eV for Li CO -Li (100), LEDC-Li
3
2
(100), and CH CH OLi-Li (100), suggesting a low bonding effect to Li, which can reduce the energy barrier
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3
associated with Li plating/stripping (as confirmed by the reduced nucleation overpotential in Figure 2A),
thereby effectively facilitating the homogeneous plating/stripping of Li and enhances the electrochemical
reversibility and cycling performance. For the NCM85 cathode, the EC molecules in the base electrolyte can
+
-
be easily oxidized, forming CH COOLi and H under the catalysis of O (formed from oxidation of the
3
lattice oxygen) [Supplementary Figure 10B]. Furthermore, the formed HF will corrode the NCM85 cathode
and further reduce the structural stability. With the introduction of the LiDFOB, the intermediates
generated by its preferential oxidative decomposition can capture the harmful O , H , and F , forming a BF ,
+
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3
BF OH, and BF OBF -rich CEI film. These CEI film components have high antioxidant stability [Figure 6C,
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2
2
Supplementary Figure 13] and electronic insulation [Supplementary Figure 12], which can effectively
suppress the decomposition of electrolytes and the subsequent attack of HF to the NCM85 crystal.
Moreover, the stronger adsorption energy of these B-containing compounds on the LiNiO surface
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(-1.21 eV, -1.27 eV, and -9.3 eV for BF , BF OH, and BF OBF respectively) compared to the -0.69 eV of
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2
2,
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CH COOLi-LiNiO (104), indicates the B elements can form a strong bonding with the lattice oxygen on the
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3
NCM surface [Figure 6D], thus significantly mitigating the loss of lattice oxygen and degradation of the
structural integrity of the cathode.
To further identify the composition and depth distribution of the SEI and CEI films, TOF-SIMS tests were
performed for the Li anode [Figure 7A and B] and NCM85 cathodes [Figure 7C and D] after 20 cycles in the
base and LiDFOB-containing electrolytes, respectively. The fragments of CH , LiO , and LiCO are mainly
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2
3
2
derived from the redox decomposition products of carbonate-based solvents in the electrolytes, such as
lithium alkyl esters and Li CO . The OH and LiF and NiF fragments are by-products of the
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-
-
2
2
2
3
decomposition of the electrolyte or the corrosion of the electrodes by HF, respectively. It can be noted from