Cation effect on small phosphonium based ionic liquid electrolytes with high concentrations of lithium salt

Chen, Fang Fang; Kerr, Robert; Forsyth, Maria

doi:10.1063/1.5016460

Cited by 19 publications

(19 citation statements)

References 48 publications

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“…MD simulations have elucidated the stark differences between the coordination environments and lithium/sodium-ion transport in the more traditional lower salt concentrations compared to the superconcentrated cases. (33,34) Recent reports of Li coordination in related TFSI systems are consistent with our observations. (35,36) These superconcentrated electrolytes allow dendrite-free lithium and sodium metal plating at very high current densities.…”

Section: Figure 2 Schematic Of a Mixed Co-cation Conductor And The Chemical Structures Of The Bulky Quaternary Ammonium Cations Describedsupporting

confidence: 92%

Innovative Electrolytes Based on Ionic Liquids and Polymers for Next-Generation Solid-State Batteries

et al. 2019

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Electrolytes based on organic solvents used in current Li-ion batteries are not compatible with the next-generation energy storage technologies including those based on Li metal. Thus, there has been an increase in research activities investigating solid-state electrolytes, ionic liquids (ILs), polymers, and combinations of these. This Account will discuss some of the work from our teams in these areas. Similarly, other metal-based technologies including Na, Mg, Zn, and Al, for example, are being considered as alternatives to Libased energy storage. However, the materials research required to effectively enable these alkali metal based energy storage applications is still in its relative infancy. Once again, electrolytes play a significant role in enabling these devices, and research has for the most part progressed along similar lines to that in advanced lithium technologies. Some of our recent contributions in these areas will also be discussed, along with our perspective on future directions in this field. For example, one approach has been to develop single-ion conductors, where the anion is tethered to the polymer backbone, and the dominant charge conductor is the lithium or sodium countercation. Typically, these present with low conductivity, whereas by using a copolymer approach or incorporating bulky quaternary ammonium co-cations, the effective charge separation is increased thus leading to higher conductivities and greater mobility of the alkali metal cation. This has been demonstrated both experimentally and via computer simulations. Further enhancements in ion transport may be possible in the future by designing and tethering more weakly associating anions to the polymer backbone. The second approach considers ion gels or composite polymer electrolytes where a polymerized ionic liquid is the matrix that provides both mechanical robustness and ion conducting pathways. The block copolymer approach is also demonstrated, in this case, to simultaneously provide mechanical properties and high ionic conductivity when used in combination with ionic-liquid electrolytes. The ultimate electrolyte material that will enable all high-performance solid-state batteries will have ion transport decoupled from the mechanical properties. While inorganic conductors can achieve this, their rigid, brittle nature creates difficulties. On the other hand, ionic polymers and their composites provide a rich area of chemistry to design and tune high ionic conductivity together with ideal mechanical properties.

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Section: Figure 2 Schematic Of a Mixed Co-cation Conductor And The Chemical Structures Of The Bulky Quaternary Ammonium Cations Describedsupporting

confidence: 92%

Innovative Electrolytes Based on Ionic Liquids and Polymers for Next-Generation Solid-State Batteries

et al. 2019

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“…31 The Canongia Lopes-Padua (CL&P) force field parameters were used in this work for P 1222 FSI ionic liquids, which we also adopted previously for bulk phase investigation of the same IL. 32 The Lennard-Jones potential parameters (ε = 22.1333 kJ/mol and σ = 0.2629 nm) for the Au electrode were adopted from literature, which were previously validated for IL/ Au(111) interface structure analysis. 33 The bulk phase densities of all systems based on 216 ion pairs (Supporting Information (SI) Table S1) were calculated first.…”

Section: Methodsmentioning

confidence: 99%

Improving Cycle Life through Fast Formation Using a Superconcentrated Phosphonium Based Ionic Liquid Electrolyte for Anode-Free and Lithium Metal Batteries

Pathirana

Rakov

Chen

et al. 2021

ACS Appl. Energy Mater.

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Cell formation of lithium-ion cells impacts the evolution of the solid electrolyte interphase (SEI) and the cell cycle stability. Lithium metal anodes are an important step in the development of high energy density batteries owing to the high theoretical specific capacity of lithium metal. However, most lithium metal battery research has used a conventional lithium-ion formation protocol; this is time-consuming and costly and does not account for the different properties of the lithium metal electrode. Here, we have used a recently reported promising phosphonium bis(fluorosulfonyl)imide ionic liquid electrolyte coupled with an NMC622 high areal capacity cathode (>3.5 mAh/cm2) to investigate the effect of cell formation rates. A faster formation protocol comprised of a pulsed 1.25C current decreased the formation time by 56% and gave a 38% greater capacity retention after 50 cycles when compared to formation at C/20. Electrochemical impedance spectroscopy measurements showed that the fast formation gave rise to a lower resistance SEI. Column-like lithium deposits with reduced porous lithium domains between the particles were observed using scanning electron microscope imaging. To underline the excellent performance of these high energy density cells, a 56% greater stack specific energy was achieved compared to the analogous graphite-based lithium-ion cell chemistries.

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“…Ion solvation affects charge transfer [2,3], interaction with surfaces [4], and the kinetics of chemical interactions [5]. The properties of the solvation shells in solutions based on organic solvents are especially critical in the development of batteries [6][7][8][9][10][11].…”

Section: Introductionmentioning

confidence: 99%

Coordination Numbers of Bivalent Ions in Organic Solvents

Orekhov

2021

Russ. J. Phys. Chem.

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Molecular dynamic models are created for properties of bivalent ions in organic solvents. It is shown that molecules of the considered solvents bound to ions via oxygen atoms. A theoretical model is developed that describes the ion coordination number. The coordination number in this model is determined by the ratio between the sizes of the ion and the atom organic molecule bound to it. It is shown that the coordination number depends weakly on the solvent and strongly on the type of ion. A value of 0.13 nm is obtained for the effective size of an oxygen atom bound to a bivalent ion. The constructed theoretical model agrees with the results from molecular dynamic calculations and the available experimental data.

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Cation effect on small phosphonium based ionic liquid electrolytes with high concentrations of lithium salt

Cited by 19 publications

References 48 publications

Innovative Electrolytes Based on Ionic Liquids and Polymers for Next-Generation Solid-State Batteries

Innovative Electrolytes Based on Ionic Liquids and Polymers for Next-Generation Solid-State Batteries

Improving Cycle Life through Fast Formation Using a Superconcentrated Phosphonium Based Ionic Liquid Electrolyte for Anode-Free and Lithium Metal Batteries

Coordination Numbers of Bivalent Ions in Organic Solvents

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