The use of the TAP additives altered the EEI compositions markedly. We performed x-ray photoelectron spectroscopy (XPS) on the graphite and NCM electrodes after 4021 cycles and compared the EEI structure of the samples from the baseline cell after 956 cycles. At the graphite anode, the TAP-containing electrolyte-derived SEI contains high concentrations of C, O, and P elements, compared to the control sample of the baseline cell (Fig. 6 and fig. S5). In addition, a higher content of C─C species in the entire C-containing species was also found in the TAP-containing electrolyte-derived SEI, suggesting the decomposition of the TAP at the anode (fig. S5). Meanwhile, the composition of the cathode CEI was also changed. With the TAP additive, the SEI layer has more C, P, and F and less Li and O, compared to the baseline SEI (Fig. 6 and fig. S5). High contents of LiF and P-containing species (O─P═O, LixPyOFz, and LixPyFz) (9) were found in the cathode CEI layer, owing to the use of the TAP additive (Fig. 6). A detailed peak interpretation is as follows: peaks at 284.6, 286.1, 288.8, and 290.1 eV in the C 1s spectrum are attributed to C─C, C─O, O─C═O, and poly(O─C═O) (10), respectively; peaks at 684.6 eV in the F 1s spectrum are attributed to LiF; peaks at 686.9 eV in the F 1s spectrum and 136.7 eV in the P 2p spectrum are attributed to O─P═O and LixPyOFz; and peaks at 686.3 eV in the F 1s spectrum and 134.5 eV in the P 2p spectrum are attributed to LixPyFz. In comparing O 1s spectrum of the aged baseline (956 cycles) and SEB-3 electrodes (4021 cycles), the peak at 529.2 eV for SEB-3 cathode is effectively eliminated in comparison to that for the baseline cathode (Fig. 6). This indicates that less lattice oxygen of NCM622 is detected for SEB-3 cathode attendant to a relatively thicker CEI layer. This is consistent with the thicker CEI layer detected by Xia et al. (2) on the coated NMC442 surface in the presence of TAP additive. Thus, the XPS result confirms that the TAP additive leads to a thick CEI layer and, in consequence, slower crack evolution, less gas generation, and longer cycle life.