We propose a novel method to determine the thermodynamic factor of binary salts dissolved in aprotic solvents as a function of salt concentration. The method is based on cyclic voltammetry experiments conducted in a three-electrode cell with the ferrocene/ferrocenium redox couple being used as an internal standard. The main advantage of this experimental setup is the direct electrochemical determination of the thermodynamic factor from a single type of experiment without the necessity of additional assumptions on other transport parameters. The theoretical derivation of the used relationship between peak/half-wave potentials and the thermodynamic factor as well as non-ideal effects which distort the experimental results, such as uncompensated resistances or concentration overpotentials are discussed in detail. Different strategies are suggested to avoid these non-ideal effects using the peak separation of the cyclic voltammograms as an inherent quality measure for the experimental data. Applicability of the experimental procedure is demonstrated for LiClO 4 in EC:DEC (1:1, w:w) in the range from 5 mM to 2 M and repeated for typical LiPF 6 containing electrolytes. At the end, the obtained results are compared to thermodynamic factors of similar electrolyte solutions published in literature.

To bridge the gap between current lithium-ion battery technology and alternative cell chemistries such as, e.g., sodium-ion batteries, the majority of the research in this field focuses on the improvement of the cell’s energy density by the development of new active materials for reversible storage of sodium ions. On the other hand, the power density, which is determined by the ionic transport and thermodynamic parameters in the electrolyte, namely the conductivity, the thermodynamic factor, the transference number, and the diffusion coefficient, is attracting little attention. In this contribution, we determine these electrolyte properties for 0.1 M to 2 M LiPF6 and NaPF6 in a mixture of ethylene carbonate and diethyl carbonate (EC:DEC (1:1 v:v)) and use them in 1D simulations to show their impact on the theoretical discharge rate performance of the lithium and sodium cell chemistry. We show that the increased cation size of sodium and its corresponding weaker solvent interactions are beneficial for high power applications and that the improved ionic transport properties would allow for a substantial increase of either the (dis)charge currents or the electrode areal loading, compared to the well-established lithium system.

Microscale silicon particles in lithium-ion battery anodes undergo large volume changes during (de)lithiation, resulting in particle pulverization and surface area increase concomitant with a continuous growth of the solid-electrolyte-interphase. One approach to overcome these phenomena is to operate the silicon anode under capacity-limited conditions (i.e., with partial capacity utilization). Since crystalline silicon is irreversibly transformed into amorphous phases upon lithiation, the purpose of the partial capacity utilization is to maintain a crystalline phase and thus prevent particle disintegration. Here, we investigate the amorphization process of micro-sized silicon particles in a silicon-rich anode (70 wt% silicon) over extended charge/discharge cycling in half-cells with a lithium reference electrode, varying the lower cutoff potential of the Si electrode. While the capacity of Si electrodes after formation remain constant for lithiation cutoffs of ≥170 mV vs Li+/Li, their capacity continuously increases over cycling for cutoffs of <170 mV vs Li+/Li, implying an ongoing amorphization of the crystalline phase. To quantify the ratio of the amorphous phase fraction over cycling, we employed an in-situ XRD method, utilizing the copper reflex of the current collector as internal standard. This allowed to determine the extent of amorphization over the course of cycling depending on the lithiation potentials.

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A meaningful benchmarking of battery active materials with inherently different properties requires knowledge of both their intrinsic electrochemical properties as well as of the differences in the resulting porous electrode structures for equal, practically relevant areal capacities. Here we compare graphite and microsilicon anodes with practical areal capacities of 2.8 mAh cm−2 for lithium-ion batteries with regard to their temperature-dependent kinetic charge-transfer resistances (R ct) and their ion transport resistances through the electrolyte phase within the pores of the electrodes (R ion), measured via impedance spectroscopy. We deconvolute the kinetic resistance from the impedance spectra by individually measuring the temperature-dependent pore resistance between −5 and +45 °C, showing that the charge-transfer resistance dominates at low temperatures, while at high temperatures the pore resistance dominates for both electrode types due to the significantly higher activation energy of R ct. An analysis of the potential profile of the electrodes at different lithiation rates shows how the thinner silicon electrode is significantly less affected by R ion-induced transport losses compared to a thicker graphite electrode, resulting in lower overpotentials when fast-charging at high temperatures, despite similar kinetic resistances. Overall the silicon electrodes could be charged up to two times faster than graphite before reaching 0 V vs Li+/Li.