In Situ Diffuse Reflectance Infrared Fourier-Transform Spectroscopy Investigation of Fluoroethylene Carbonate and Lithium Difluorophosphate Dual Additives in SEI Formation over Cu Anode

Abstract

The synergetic effect of fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO2F2) dual additives on the cycling stability of lithium metal batteries has been previously reported. This study applies in situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) to examine the impact of these two additives on SEI species formation over Cu anode using a base electrolyte of LiPF6 in ethylene carbonate (EC) and diethyl carbonate (DEC). The results indicate that all electrolyte components and additives can be electrochemically reduced over the Cu anode following a potential sequence of LiPO2F2 > FEC > EC > DEC. The results illustrate that LiPF6 likely interacts with the Cu anode upon contact, resulting in Li x PF y , which can lead to a reduction peak at ∼1.44 V in CV. With the base electrolyte, reduced species from Li x PF y lead to the formation of alkyl phosphorus fluorides (RPF), which can be suppressed by the presence of FEC and/or LiPO2F2. Similar to previous reports, FEC reduction in the 1st lithiation cycle leads to the continuous formation of poly(FEC), while EC is electrochemically reduced to (CH2OCO2Li)2 and Li2CO3 and DEC is reduced to CH3CH2OCO2Li and Li2CO3. With only the LiPO2F2 additive, the redox of LiPO2F2 can be found in CV with Li x PO y as the possible reduced product. In addition, Li2CO3 formation from EC and DEC reduction was relatively suppressed by the presence of LiPO2F2. The simultaneous presence of the FEC additive can suppress the redox of LiPO2F2 and partly the decomposition of LiPF6 likely via the preferential adsorption of FEC on Cu. Similar DRIFTS observations are found over the Li anode. The electrolyte with dual additives demonstrates a possible advantage from poly(FEC) and Li x PO y species formation, suppressing the reduction of Li x PF y , EC, and DEC though not completely.

High Response and Selectivity of the SnO2 Nanobox Gas Sensor for Ethyl Methyl Carbonate Leakage Detection in a Lithium-Ion battery

“…It showed a decreasing trend in the adsorption capacity due to the continuous passage of EMC occupying the adsorption site of the CO 2 , rather than no CO 2 being generated during the reaction. The band at 3777 cm –1 , which is accompanied by a weak shoulder at 3648 cm –1 , was due to the ν(OH) mode of different types of isolated hydroxyl groups . We attribute the occurrence of hydroxyl vibrational peaks to two reasons.…”

“…The band at 3777 cm −1 , which is accompanied by a weak shoulder at 3648 cm −1 , was due to the ν(OH) mode of different types of isolated hydroxyl groups. 55 We attribute the occurrence of hydroxyl vibrational peaks to two reasons. One is because water was produced in eq 3 and the exposure SnO 2 crystal to water vapor causes hydroxylation as a result of dissociative chemisorption of molecular water to satisfy the coordination of the surface Sn 4+ sites.…”

Material–electrolyte interfacial interaction enabling the formation of an inorganic-rich solid electrolyte interphase for fast-charging Si-based lithium-ion batteries

“…S3a, ESI †). [33][34][35] The corresponding FTIR signal of the SiO x @P electrode consistently exceeded that of the bare SiO x electrode with the potential decrease from OCV to 1.4 V (Fig. S3b, ESI †).…”

Understanding the formation chemistry of native solid electrolyte interphase over lithium anode and its implications using a LiTFSI/TME-TTE electrolyte and polysulfide additive

“…SEI formation on an anode surface is mostly expected owing to the electrochemical reduction of electrolyte components, and the electrolyte components govern the formed SEI species. 8–10 In addition, SEI can lead to uneven Li deposition and dissolution during cycling and aggravate lithium dendrite growth. 5,11,12 To address the challenges associated with the use of Li metal anodes, various strategies have been suggested.…”