Model Studies on Solid Electrolyte Interphase Formation on Graphite Electrodes in Ethylene Carbonate and Dimethyl Carbonate II: Graphite Powder Electrodes

Abstract

As part of a systematic study on the formation and composition of the solid electrolyte interphase (SEI) in lithium-ion batteries (LIBs), going stepwise from highly idealized electrodes such as highly oriented pyrolytic graphite and conditions such as ultrahigh vacuum conditions to more realistic materials and reaction conditions, we investigated the decomposition of simplified electrolytes (ethylene carbonate (EC) + 1 M LiPF 6 and dimethyl carbonate (DMC) + 1 M LiPF 6) at binder-free graphite powder model electrodes. The results obtained from cyclic voltammetry and ex situ X-ray photoelectron spectroscopy halfcell measurements-in particular on the effect of cycling rate, solvent and electrode-are explained in terms of a mechanistic model where electrolyte decomposition occurs at the SEI j electrode interface and where transport of solvent and salt species through the growing SEI plays an important role for explaining the observed change from preferential salt decomposition to solvent decomposition with increasing cycling rate.

Graphite Electrodes Immersed in Nonaqueous Li+ Electrolytes Studied with a Combined Ultrahigh Vacuum–Electrochemistry Approach

“…LiF is accepted as a notable inorganic component of the SEI resulting from LiPF 6 degradation by hydrolysis ,, and is in line with the observation of LiF on the HOPG electrode following OCP conditions (Figure S6), while comparable behavior has been reported for electrodes that were simply placed “in contact” with LiPF 6 -based electrolytes . Meanwhile, other F-compounds are evidenced in the F 1 s spectrum (Figure d) by the intense feature at higher energies centered at 689.1 eV attributed to Li x PF y or Li x PF y O z (from LiPF 6 degradation) that is corroborated by the pair of doublets in the P 2p spectrum (Figure f) centered at 139.8 and 137.7 eV, assigned to Li x PF y and Li x PF y O z , respectively. ,,, In terms of other potential components of the SEI, alkylcarbonates (i.e., ROCO 2 Li) and Li 2 CO 3 are absent owing to the negligible features at binding energies >286 eV in the C 1s spectrum, while Li 2 O not present because of the absence of shoulder features in the O 1s and Li 1s (<532 and <56 eV, respectively). ,, Therefore, the O 1s features are ascribed to the residual electrolyte (solvent) and products from LiPF 6 degradation. Our findings indicate that alkylcarbonate, Li 2 CO 3 , and Li 2 O formation occurs at more cathodic potentials (<1.75 V) when significant (bulk) SEI formation is met with the reductive decomposition of the EC and DMC solvents .…”

“…39 Meanwhile, other F-compounds are evidenced in the F 1 s spectrum (Figure 4d) by the intense feature at higher energies centered at 689.1 eV attributed to Li x PF y or Li x PF y O z (from LiPF 6 degradation) that is corroborated by the pair of doublets in the P 2p spectrum (Figure 4f) centered at 139.8 and 137.7 eV, assigned to Li x PF y and Li x PF y O z , respectively. 39,43,44,46 In terms of other potential components of the SEI, alkylcarbonates (i.e., ROCO 2 Li) and Li 2 CO 3 are absent owing to the negligible features at binding energies >286 eV in the C 1s spectrum, while Li 2 O not present because of the absence of shoulder features in the O 1s and Li 1s (<532 and <56 eV, respectively). 21,39,47 Therefore, the O 1s features are ascribed to the residual electrolyte (solvent) and products from LiPF 6 degradation.…”

Composition‐Dependent Long‐Term Stability of Mosaic Solid‐Electrolyte Interface for Long‐Life Lithium‐Ion Battery

“…To date, the structure and chemical composition of the SEI layer has been reported to be dependent on the salt, solvent, and additives present in the electrolyte, but under extreme battery operating conditions, including high voltage window, high C-rate, and high temperature (> 40 °C), the SEI suffers from inferior stability. [8][9][10] Therefore, more comprehensive research on this topic is required to improve the stability of the SEI layer.…”

Review on Action Mechanism and Characterization of Natural/Artificial Solid Electrolyte Interphase of Lithium Battery: Latest Progress and Future Directions

“…More importantly, using XPS characterization, one can clearly see the evolution of SEI film. For example, Nojabaee et al used XPS to fully track the chemical and electrochemical evolution of SEI under static current conditions − and according to the electrode materials studied, the SEI formed in contact with LiTDI/glyme-based electrolytes is mainly composed of inorganic material. It is composed of LiF and Li 3 N without Li 2 CO 3 .…”