Concentration Effects on the Entropy of Electrochemical Lithium Deposition: Implications for Li⁺ Solvation

Abstract

The solvation behavior of Li(+) in ethylene carbonate and dimethylcarbonate upon dilution has been investigated by electrochemical microcalorimetry. We measured the heat effects at a Li electrode upon electrochemical Li deposition and dissolution from Li(+) solutions of varying concentration. The exchanged heat is correlated to the entropy of lithium deposition and therefore reveals information about the solvation of Li(+). Lithium deposition from electrolytes with lower concentrations showed less entropy gain than deposition from electrolytes with higher concentrations. This can be fully explained by the entropy of dilution of the Li(+) ions. From our data we further concluded that the inner coordination shell of the Li(+) ions does not significantly change between 0.01 and 1 M Li(+) concentration. The results also suggest that contact ion pairs, which are probably present in the electrolyte, show a similar solvation behavior as regular lithium ions.

Evaluating the Free Energies of Solvation and Electronic Structures of Lithium‐Ion Battery Electrolytes

“…quantum calculations and molecular dynamics (MD) simulations] and experimental studies (e.g. photoelectron, FTIR, Raman, NMR, and neutron scattering spectroscopy in addition to electrospray ionization mass spectrometry) have been performed to consider the interactions of Li + ions with pure and mixed carbonate‐based electrolytes, the solvation structure, dynamics of the Li + ions in carbonate solvents, and determination of the coordination number around the Li + ions in pure and mixed carbonate‐based electrolytes have not been clearly resolved. For example, many existing studies in the Li‐ion battery field have demonstrated that Li + ions can be solvated primarily due to their interaction with the carbonyl oxygen atoms, although the exact nature of these interactions remains a subject of debate.…”

“…It is our understanding that such properties would have a bearing on the charging–discharging mechanism of non‐aqueous liquid electrolytes, and hence, we aim to obtain fundamental insight into the structure and dynamics of Li + ‐ion solvation in such electrolytes. In addition, the nature of the interactions of the Li + ions with carbonate solvents remains largely unknown, and thus, we investigate that by the above analyses, including NBO, QTAIM, LMO‐EDA, and NCI plots, and it is our understanding that the results of such analyses would add appropriately to the growing body of literature in the field of LIBs …”

Review—The Thermistor-Electrode as a Temperature Sensor to Obtain Thermodynamic Data of Electrochemical Systems

“…42 The effect of these electrolytes on the temperature increase at the working electrode was determined by measuring the temperature difference between the anode and cathode, the cathode and solution, and the anode and solution. It was shown that the effect of the electrolytes can be adequately explained either by the concept of ionic heat of transport 14 which is related to the migration of ions in the electrolyte or by the irreversible thermodynamics of nonisothermal cells. More importantly, the thermodynamic data obtained by Holmes and Joncich 20,42 were comparable with those obtained by other authors, 35 who used thermocouples in their experimental setup, as thermocouples had been conventionally preferred for thermometric works until then.…”

“…Thermodynamic parameters of electrochemical systems can be determined by measuring the electrochemical Peltier heat (EPH), which is the heat associated with electron transfer at the electrode/ electrolyte interface. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Consequently, data derived from the measurement of the EPH such as the molar EPH and the entropy changes of a variety of faradic electrochemical reactions have been published by several authors who have employed different experimental configurations, among them, the most used historically is the calorimeter. [1][2][3][4][5][6][7][10][11][12][13][14][15][16][17] This has confirmed the thermodynamic data obtained through conventional electrochemical techniques, such as cyclic voltammetry and electrolysis.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] Consequently, data derived from the measurement of the EPH such as the molar EPH and the entropy changes of a variety of faradic electrochemical reactions have been published by several authors who have employed different experimental configurations, among them, the most used historically is the calorimeter. [1][2][3][4][5][6][7][10][11][12][13][14][15][16][17] This has confirmed the thermodynamic data obtained through conventional electrochemical techniques, such as cyclic voltammetry and electrolysis. 18 Nevertheless, despite the valuable contribution of calorimetric measurements, their implementation in laboratories is not yet as extended.…”