Single-salt Electrolyte Research Articles

Li2CO3/LiF-Rich Solid Electrolyte Interface Stabilized Lithium Metal Anodes for Durable Li-CO2 Batteries

Lithium carbon dioxide (Li-CO2) batteries are considered a promising next-generation energy storage device due to their high theoretical energy density and potential carbon neutralization. Despite numerous iterative advancements in cathode catalysts for Li-CO2 batteries, the cycling stability still to be hindered by the growth of lithium dendrites during cycling, primarily due to uneven deposition and the side reaction of sufficient CO2 with the Li metal anode. In this work, bisalt electrolyte (BE) consisting of LiPF6 and LiTFSI is used as a localized anode surface stabilizer to achieve durable Li-CO2 batteries. The introduction of PF6− promotes the decomposition and reduction of TFSI−, leading to the formation of LiF-rich inorganic SEI (Li2CO3/LiF-rich) with enhanced Li+ affinity and good electronic insulating properties. This effectively inhibits lithium dendrite formation while also insulating CO2 and electrolytes from contacting the lithium anode. Consequently, the Li symmetric battery incorporating the novel BE exhibits a long cycling life of 912 hours (∼3.8 times of the cell with a single-salt electrolyte (SE)). The BE based Li-CO2 battery achieves an ultra-long cyclelife of 2720 hours (∼2.6 times of SE battery) and outstanding rate capability. In addition, the assembled belt-shaped Li-CO2 batteries could stably power a digital watch for 1267 hours.

A Study on the Reaction Mechanism of a Model Organic Cathode in Magnesium-Ion Batteries

The need for abundant, sustainable, and cost-effective energy storage technologies has been generating increased interests in batteries that rely on the use of earth abundant elements such as multivalent batteries. Those that utilize metallic anodes (Mg, Ca, Al) and organic cathodes are attractive as they can offer a path forward toward a competitive gravimetric energy density and in some cases fast charge capabilities. In particular, reports of a variety of Mg metal anode–organic cathodes batteries with good performances compel further research efforts of these systems and understanding of processes that govern their performances. However, studies of organic cathodes in competent, Cl– free Mg electrolytes remain limited, and the mechanisms that govern the cycling of these batteries are unclear. Herein, we assess the Mg battery performance using a typical benzoquinone type organic molecule in a competent Cl– free, single salt electrolyte and investigate the mechanisms at play. Combining the findings from battery and analytical studies reveal reversible structural transformations driven by a new precedence of a unique dissolution/precipitation mechanism. The implications of this mechanism on the performance of the battery are evaluated and discussed. The findings unveiled shed light onto potential challenges and opportunities with these systems and help guide future advancements.

Measurements of mean activity coefficients and solubility prediction in ternary system KBr-K2SO4-H2O at 308.15 K and 288.15 K

In this work, the mean activity coefficients of KBr in KBr-H2O binary system and KBr-K2SO4-H2O ternary system were determined at 308.15 K and 288.15 K by the cell potential method. The potassium ion selective electrode and bromide ion selective electrode are used to measure the cell potential value of single salt electrolyte solution,and the standard potential value E0 and electrode response slope k of the binary system are obtained. The experimental results showed that ion selective electrodes of used in this work had a good Nernst response. The mean activity coefficients KBr in KBr-K2SO4-H2O system are also determined, the total ionic strength in the mixed solution ranging from (0.0100 to 1.0000) mol·kg−1, and ionic strength fractions yb of K2SO4 with yb=(0.8, 0.6, 0.4, 0.2 and 0.0). Using mean activity coefficients obtained in this work and Pitzer model, the Pitzer mixed ion interaction parameters θBr,SO4 and ψK,Br,SO4are fitted respectively. Furthermore, those osmotic coefficient Φ, water activity aw, excess Gibbs free energy GE were also calculated by Pitzer’s equations. The solubilities of salts in the KBr-K2SO4-H2O system at 308.15 K and 288.15 K are predicted by using Pitzer equations and ion interaction parameters fitted in this work, and phase diagrams of the ternary system are also plotted according to the calculated solubilities. The results show that the ion interaction parameters of Pitzer equations by fitting the activity coefficients can be used for calculation thermodynamic parameters and prediction of phase equilibria.

Dilute dual-salt electrolyte for successful passivation of in-situ deposited Li anode and permit effective cycling of high voltage anode free batteries

An investigation of the cycling stability of anode-free batteries (AFBs) using dilute dual-salt electrolytes is conducted in a mixture of ether and carbonate solvents. Using the AFB configuration, various compositions of the dual-salt electrolyte were optimized and it was found that 0.9M-LiTFSI+0.3M-LiDFOB in FEC/TTE (2:3, v/v) is the best. An in-depth investigation of the electrochemical performance of AFB was conducted in this optimized dual-salt composition in comparison to 1.2 M LiTFSI in the same solvent ratio. Accordingly, the performance of Cu||NMC cell in the dual-salt electrolyte surpassed that of the single-salt. The relative better performance of the AFB in the dual-salt electrolyte is attributed to the co-existence of dual-ion (TFSI−&DFOB−) in the electrolyte, which enhanced conductivity and introduces entirely new interphases via preferential decomposition mechanisms. The newly formed interface is stable, ionically conductive, and able to intercept parasitic side reactions between the electrolyte solvent and the deposited Li by blocking electron and solvent flow towards the deposit. As a result of the unique interfacial chemistry brought by this dual-salt system, this electrolyte supports a unique CE (98.6%) and capacity retention (63%) in 4.5V Cu||NMC cell and exhibited >27% improvement over the single salt electrolyte after 50 cycles.

Volumetric properties for the ternary system (CaCl2-SrCl2-H2O) and binary sub-systems at temperatures from 278.15 K to 323.15 K

Densities the ternary system (CaCl2-SrCl2-H2O) and its binary sub-systems (CaCl2-H2O and SrCl2-H2O) were elaborately measured with an Anton Paar Digital vibrating-tube densimeter at temperature intervals of 5 K from 278.15 K to 323.15 K. The coefficient of thermal expansion (α) and apparent mole volume (φV) for the binary systems were obtained based on the experimental density results. Apparent mole volumes of CaCl2 and SrCl2 varied smoothly with solute molality and could be fitted using an extended RRM equation. Based on the PK method, the density for the ternary system was predicted by the density of the two binary sub-systems, and there is a good consistency between the results of predicted and experimental. On the basis of volumetric property data for the binary and ternary systems, the Pitzer single-salt parameters (βMX(0)V, βMX(1)V and CMXV, MX = CaCl2 and SrCl2) and mixing ion-interaction parameters θCa,SrV , ψCa,Sr,ClV) were parameterized according to Pitzer ion-interaction theory of single salt electrolyte and mixture electrolytes, respectively. Volumetric property was analysed using the Pitzer model and the predicted values were comparable with experimental values. The simulation results indicate that the Pitzer model parameters can reliably represent the properties of the systems. The temperature-dependence equations and the temperature correlation coefficients for those parameters were also obtained. The volume properties of three systems can be quantitatively obtained according to the electrolyte parameterization model within the experimental temperature range.

High-performance Zn-graphite battery based on LiPF6 single-salt electrolyte with high working voltage and long cycling life

A Zn-graphite battery with high working voltage and long cycling life was fabricated based on LiPF 6 single-salt electrolyte. The working mechanism and electrochemical performance were investigated. • A high-voltage ZGB based on LiPF 6 single-salt in EMC/TMS electrolyte was constructed. • Zn 2+ was found to be dissolved in the electrolyte during resting and discharging. • The ZGB achieved long-term cyclability and high energy density over 1.0–3.1 V. Zinc-ion batteries (ZIBs) are promising alternative energy storage devices to lithium-ion batteries owing to the merits of large abundance, high theoretical capacity, and environmental friendliness. However, critical challenges including low working voltage (below 2 V), low energy density as well as dendrites formation during long cycling caused by aqueous ZIB systems still hinder their practical applications. Herein, a high-voltage Zn-graphite battery (ZGB) based on a non-zinc ion single-salt electrolyte (2.5 M LiPF 6 in carbonate solvent) is developed. Moreover, we surprisingly found that Zn 2+ is dissolved in the LiPF 6 single-salt electrolyte during resting and discharging processes, thus enabling reversible Zn plating/stripping mechanism on the Zn foil anode in the ZGB over the voltage window of 1.0–3.1 V. As a result, the ZGB achieves long-term cycling performance with a capacity retention of ~100% for over 1200 cycles at 3C and high Coulombic efficiency of ~100% in 1.0–3.1 V with no dendrites formation. Moreover, the ZGB exhibits a high working voltage of up to 2.2 V, thus contributing to both high energy density (up to 210 Wh kg −1 ) and high power density (up to 1013 W kg −1 ), superior than most reported ZIBs.

Solid Electrolyte Interphase Film on Lithium Metal Anode in Mixed-Salt System

The effect of electrolyte salt on the solid electrolyte interphase (SEI) is discussed with respect to improvement of the lithium metal anode. Lithium bis(fluorosulfonyl)imide (LiFSI) and lithium nitrate (LiNO3) were dissolved together in dimethyl sulfoxide (DMSO), in which the ratios of LiNO3:LiFSI (x:100-x mol%) were in the range of 0<x<100. Electrochemical lithium plating/stripping was tested for various x-values. A LiNO3 single salt electrolyte yielded small polarizations in the initial cycles; however, the polarization became larger with the cycle number. A LiFSI single salt electrolyte showed larger polarizations, but maintained an almost constant magnitude during all cycles. LiNO3 and LiFSI salt-mixtures gave better cycle performance with low and stable polarizations compared to the single salt electrolytes. X-ray photoelectron spectroscopy (XPS) analyses revealed that LiNO3 gave a Li2O-rich SEI membrane, while LiFSI gave a LiF-rich membrane. For LiNO3 and LiFSI salt-mixtures, the ratio of these components changed according to the x value. The use of multiple lithium salts is thus an effective way to control the SEI properties and improve the cycle performance of a lithium metal anode.

Capacitance of porous carbon electrode in mixed salt non-aqueous electrolytes

Capacitances of a porous carbon electrode in non-aqueous electrolytes containing tetraethylamonium tetrafluoroborate (TEABF 4) and a lithium salt with various compositions have been investigated for the potential use in electric double layer capacitor. In the electrolyte prepared by dissolving TEABF 4 and LiBF 4 into the mixed solvent of ethylene carbonate (EC) with diethyl carbonate (DMC), an activated carbon fiber (ACF) electrode exhibits a larger capacitance than in TEABF 4 single salt electrolyte on cyclic voltammograms. The symmetrical capacitor cell containing the LiBF 4–TEABF 4 mixed salt electrolyte also exhibits larger capacitance on a constant-current test compared with that containing the TEABF 4 single salt electrolyte, while the capacitance degradation is observable for this cell at a significant extent, while the test under controlled potential of the ACF electrode to −0.2 to 1.0 V vs. Ag provides somewhat stable capacitance over 30 cycles.

Modeling aqueous electrolyte solutions: Part 1. Fully dissociated electrolytes

Liquid densities (pvT), vapor pressures (VLE), and mean ionic activity coefficients (MIAC) at 25 °C of 115 single-salt electrolyte solutions containing univalent up to trivalent ions are modeled with the ePC-SAFT equation of state proposed by Cameretti et al. [L.F. Cameretti, G. Sadowski, J.M. Mollerup, Ind. Eng. Chem. Res. 44 (2005) 3355–3362; ibid., 8944]. For each ion, only two model parameters were adjusted to experimental density and MIAC data. Without using any additional binary parameters, ePC-SAFT is able to reproduce experimental data of the respective salt solutions up to high electrolyte molalities. Moreover, it is even able to describe the reversed MIAC series for alkali hydroxides and fluorides.

An improved electrolyte for the LiFePO 4 cathode working in a wide temperature range

A LiBF 4–LiBOB (lithium bis(oxalato)borate) salt mixture was used to formulate an electrolyte for the operation of a LiFePO 4 cathode over a wide temperature range (−50 to 80 °C) by employing a solvent mixture of 1:1:3 (wt.) propylene carbonate (PC)/ethylene carbonate (EC)/ethylmethyl carbonate (EMC). In comparison with the ionic conductivity of a single salt electrolyte, LiBF 4 electrolyte has a higher conductivity below −10 °C while the LiBOB electrolyte is higher above −10 °C. For cell performance, LiBF 4 cell has a better low temperature performance and a higher power capability, but it cannot survive above 60 °C. In contrast, the LiBOB cell performs very well at high temperature even up to 90 °C, but it fails to perform below −40 °C. We found that the temperature performance of Li/LiFePO 4 cells could be optimized by using a LiBF 4–LiBOB salt mixture. At 1 C and at −50 °C, for example, a Li/LiFePO 4 cell using 90:10 (in mole) LiBF 4–LiBOB salt mixture could provide up to ∼30% of capacity at ∼3.0 V and it still could be cycled at 90 °C. In addition, we observed and explained an opposite correlation between the ionic conductivity of the electrolyte and the power capability of the cell. That is, the LiBF 4 cell at 20 °C discharges at a higher plateau voltage than the LiBOB cell, whereas the LiBF 4 electrolyte has a lower ionic conductivity.

Modeling of Aqueous Electrolyte Solutions with Perturbed-Chain Statistical Associated Fluid Theory

The vapor pressures and liquid densities of single-salt electrolyte solutions containing NaCl, LiCl, KCl, NaBr, LiBr, KBr, NaI, LiI, KI, Li2SO4, Na2SO4, and K2SO4 were modeled with an equation of state based on perturbed-chain statistical associated fluid theory (PC-SAFT). The PC-SAFT model was extended to charged compounds using a Debye−Hückel term for the electrostatic interactions. Two model parameters for each ion were fitted to experimental pVT and vapor-pressure data. The model is able to excellently reproduce the experimental data up to high salt molalities and even to predict vapor pressures in mixed-salt solutions.

Electrolytes. Properties of Solutions. Methods for Calculation of Multicomponent Systems and Experimental Data on Thermal Conductivity and Surface Tension. By G. G. Aseyev. Begell House, Inc., New York. 1998. 611 pp. $275.50. ISBN 1-56700-106-8.

This volume is the sixth handbook by the author and others on the compilation and calculation of physical and chemical properties of inorganic substances and electrolyte solutions. In this volume, correlations of thermal conductivity and surface tension of multicomponent electrolyte solutions are presented. These correlations use water as the reference fluid for calculations. The correlations cover the range in temperature 0 to 350 C and a wide range of concentrations. Correlation coefficients for thermal conductivity are presented for approximately 120 electrolytes, and the calculation method is presented with examples. The overall deviations from experimental data are presented for single-salt electrolyte solutions only, and the validity of the equation for multicomponent mixtures is examined for one mixture only. Correlation coefficients for the surface tension are presented for over 150 electrolytes. An example calculation is presented, but the result is not compared to experimental data. Correlations of this type are most useful when they are based on well validated experimental data and the representation of the data by the correlation is completely evaluated. This enables users to determine the validity of the correlation in their applications and estimate the expected accuracy of the prediction. The deviations of the correlations are presented for single-salt electrolyte solutions only; the extension to multicomponent systems is not discussed.