In Situ Investigation of the Electrochemical Reduction of Carbonate Electrolyte Solutions at Graphite Electrodes

Abstract

The reductive decomposition of carbonate electrolyte solutions containing lithium ions was studied by differential electrochemical mass spectrometry (DEMS) and subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS). The influence of the composition of the negative electrode on its electrochemical behavior was investigated by varying the graphite/binder ratio and using nongraphitic materials. The effect of different electrolyte salts was studied in a 1:1 ethylene carbonate (EC)/dimethyl carbonate (DMC) mixture. In addition, EC/DMC-based electrolyte solutions containing different amounts of water were used to investigate the influence of H20 on the performance of graphite electrodes. Ethylene and hydrogen were the volatile decomposition products monitored by DBMS. Ethylene evolution is restricted to a potential region between about 0.8 and 0.3 V vs Li/Lit and occurs only during the first cycle.Hydrogen begins to evolve at about 1.3 V vs Li/Lit in the first cycle and the amount of gas decreases with increasing cycle number. The experimental results are discussed in terms of proposed reaction mechanisms.

Analysis of Vinylene Carbonate (VC) as Additive in Graphite/LiNi0.5Mn1.5O4Cells

“…For cells with 0, 0.09, and 0.17 wt% VC, the impedance decreases after the formation cycle, reaching a constant value of ∼5 cm 2 after 20 cycles. In contrast, the LNMO cathode interfacial impedance starts out with a significantly higher value after the first formation cycle (∼22 cm 2 ) for the cells with 0.52 wt% VC and increases with cycle number to ∼30 cm 2 . We believe that the most likely explanation for the LNMO cathode impedance decrease for low VC concentrations is related to the different temperatures during the first formation cycle (25 • C) and the subsequent extended charge/discharge cycling (40…”

“…Interfacial resistance of graphite anodes after formation at 25 • C in graphite/LNMO cells (this study) compared to graphite anodes in graphite/LFP cells from our earlier study. 13 The VC concentration is recalculated in units of mg VC /m 2 Graphite to assess for the slightly different areal loadings (namely ∼2.6 mAh/cm 2 geo in the graphite/LNMO cells and ∼2.2 mAh/cm 2 geo in the graphite/LFP cells, based on 340 mAh/g graphite ). The error bars represent the standard deviation between two measurements.…”

“…A typical value for the liquid diffusion is in the order of 10 −6 cm 2 /s (J. Landesfeind et al 40 ). In our lab test cells, two glass fiber separators have been used (x ≈ 2 · 200 μm, τ ≈1), yielding a diffusion time on the order of: t = (400 μm) 2 …”

“…Starting from a potential of ∼0.8 V vs. Li/Li + , EC is reduced electrochemically into ethylene gas and lithium ethylene dicarbonate (LEDC), which is a key component of the SEI. 2,3 Vinylene carbonate (VC) is one of the most effective additives to modify the SEI on graphite anodes, as it is reduced at potentials more positive than 1.0 V vs. Li/Li + and hence suppresses the reduction of EC. 4,5 Aurbach et al have used VC as electrolyte additive in an EC/DMC (dimethyl carbonate) based electrolyte and that time reported a reduction of the irreversible capacity in the first cycles and an improved cycling stability at elevated temperatures for graphite anodes.…”

Three-Dimensional Visualization of Gas Evolution and Channel Formation inside a Lithium-Ion Battery

“…13 Actually, significant evolution of gaseous products such as CO 2 , CO, O 2 , H 2 , CH 4 , C 2 H 4 , C 2 H 6 , C 3 H 6 and C 3 H 8 from the decomposition of carbonate solvents and lithium during battery operation has been detected by various characterization techniques. [14][15][16][17][18][19][20][21] In addition, utilizing isotope analysis, Onuk et al have unambiguously identified the origin of gases evolving in LIBs. 22 Furthermore, by adopting in situ transmission electron microscopy (TEM) 23 and neutron radiography (NR), 9,11 the generation of gaseous bubbles channels formed by the gas have recently been visualized.…”