Johan Scheers

Anions for lithium battery electrolytes: A spectroscopic and theoretical study of the B(CN)4- anion of the ionic liquid C2mim[B(CN)4]

On the basis of computations, the B(CN)4 - (bison) anion is shown to be of interest as a fluorine-free alternative in lithium-conducting electrolytes. Compared to PF6 - the bison anion has an equally high stability toward oxidation, while at the same time offering a large reduction of the lithium-ion pair dissociation energy. The bison anion is readily available in a number of ambient-temperature ionic liquids (ILs). In this work, the Raman spectrum of the IL C2mim [B(CN)4] reveals an almost unperturbed bison anion and, consequently, the effects of the anion on the Raman shifts of C2mim + are also very small.

Ionic liquid based lithium battery electrolytes: fundamental benefits of utilising both TFSI and FSI anions?

Several IL based electrolytes with an imidazolium cation (EMI) have been investigated trying to elucidate a possible beneficial effect of mixing FSI and TFSI anions in terms of physico-chemical properties and especially Li(+) solvation. All electrolytes were evaluated in terms of phase transitions, densities and viscosities, thermal stabilities, ionic conductivities and local structure, i.e. charge carriers. The electrolytes with up to 20% of Li-salts showed to be promising for high temperature lithium ion battery application (ca. 100 °C) and a synergetic effect of having mixed anions is discernible with the LiTFSI0.2EMIFSI0.8 electrolyte giving the best overall performance. The determination of the charge carriers revealed the SN to be ca. 2 for all analysed electrolytes, and proved the analysis of the mixed anion electrolytes to be challenging and inherently leads to an ambiguous picture of the Li(+) solvation.

Ion–ion and ion–solvent interactions in lithium imidazolide electrolytes studied by Raman spectroscopy and DFT models

Molecular level interactions are of crucial importance for the transport properties and overall performance of ion conducting electrolytes. In this work we explore ion-ion and ion-solvent interactions in liquid and solid polymer electrolytes of lithium 4,5-dicyano-(2-trifluoromethyl)imidazolide (LiTDI)-a promising salt for lithium battery applications-using Raman spectroscopy and density functional theory calculations. High concentrations of ion associates are found in LiTDI:acetonitrile electrolytes, the vibrational signatures of which are transferable to PEO-based LiTDI electrolytes. The origins of the spectroscopic changes are interpreted by comparing experimental spectra with simulated Raman spectra of model structures. Simple ion pair models in vacuum identify the imidazole nitrogen atom of the TDI anion to be the most important coordination site for Li(+), however, including implicit or explicit solvent effects lead to qualitative changes in the coordination geometry and improved correlation of experimental and simulated Raman spectra. To model larger aggregates, solvent effects are found to be crucial, and we finally suggest possible triplet and dimer ionic structures in the investigated electrolytes. In addition, the effects of introducing water into the electrolytes-via a hydrate form of LiTDI-are discussed.

Superior Ion-Conducting Hybrid Solid Electrolyte for All-Solid-State Batteries

Herein, we developed a high-performance lithium ion conducting hybrid solid electrolyte, consisted of LiTFSI salt, Py14 TFSI ionic liquid, and TiO2 nanoparticles. The hybrid solid electrolyte prepared by a facile method had high room temperature ionic conductivity, excellent thermal stability and low interface resistance with good contact. In addition, the lithium transference number was highly increased by the scavenger effect of TiO2 nanoparticles. With the hybrid solid electrolyte, the pouch-type solid-state battery exhibited high initial discharge capacity of 150 mA h g(-1) at room temperature, and even at 1 C, the reversible capacity was as high as 106 mA h g(-1) .

Nano-fibrous polymer films for organic rechargeable batteries

We propose a nano-fibrous polymer (NFP) film, fabricated by electrospinning poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate) (PTMA), as a key component in high performance organic batteries. The new strategy with a NFP film enables extraordinary rate capability and excellent cyclability, due to its special morphology. Moreover, the NFP film enhances the flexibility of the electrode at a low cost and prevents dissolution of PTMA into the electrolyte.

The Quest for Polysulfides in Lithium–Sulfur Battery Electrolytes: An Operando Confocal Raman Spectroscopy Study

Confocal Raman spectra of a lithium-sulfur battery electrolyte are recorded operando in a depth-of-discharge resolved manner for an electrochemical cell with a realistic electrolyte/sulfur loading ratio. The evolution of various possible polysulfides is unambiguously identified by combining Raman spectroscopy data with DFT simulations.

Ionic liquids and oligomer electrolytes based on the B(CN)4− anion; ion association, physical and electrochemical properties

The role of B(CN)(4)(-) (Bison) as a component of battery electrolytes is addressed by investigating the ionic conductivity and phase behaviour of ionic liquids (ILs), ion association mechanisms, and the electrochemical stability and cycling properties of LiBison based electrochemical cells. For C(4)mpyrBison and C(2)mimBison ILs, and mixtures thereof, high ionic conductivities (3.4 ≤σ(ion)≤ 18 mS cm(-1)) are measured, which together with the glass transition temperatures (-80 ≤T(g)≤-76 °C) are found to shift systematically for most compositions. Unfortunately, poor solubility of LiBison in these ILs hinders their use as solvents for lithium salts, although good NaBison solubility offers an alternative application in Na(+) conducting electrolytes. The poor IL solubility of LiBison is predicted to be a result of a preferred monodentate ion association, according to first principles modelling, supported by Raman spectroscopy. The solubility is much improved in strongly Li(+) coordinating oligomers, for example polyethylene glycol dimethyl ether (PEGDME), with the practical performance tested in electrochemical cells. The electrolyte is found to be stable in Li/LiFePO(4) coin cells up to 4 V vs. Li and shows promising cycling performance, with a capacity retention of 99% over 22 cycles.

Physical Properties, Ion–Ion Interactions, and Conformational States of Ionic Liquids with Alkyl-Phosphonate Anions

We investigate the ionic conductivities, phase behaviors, conformational states, and interactions of three ionic liquids based on imidazolium cations and phosphonate anions with varying alkyl chain lengths. All three ionic liquids show high conductivities, with 1,3-dimethylimidazolium methyl-phosphonate [DiMIm(MeO)(H)PO2] being the most conductive (7.3 × 10(-3) S cm(-1) at 298 K). The high ionic conductivities are a result of the low glass-transition temperatures, Tg, which do not change significantly upon changing the cation and/or anion size. However, there is a slight dependence of the temperature behavior of the conductivity on the size of the ions, as seen from the fragility parameter (D) obtained from fits to the Vogel-Fulcher-Tammann equation. The molecular-level structure and interactions of the phosphonate anions were examined by Raman spectroscopy and first-principles calculations. The calculations identify two stable conformations for the methyl- and ethyl-phosphonate anions by rotation of the methyl and ethyl groups, respectively. The broad Raman signatures of the anions suggest the coexistence of two anion conformers in the ionic liquids and non-negligible cation-anion interactions, with a dependence on the position and shape of the bands of the cation species and the alkyl group of the anion.

A layer-built rechargeable lithium ribbon-type battery for high energy density textile battery applications

We designed a novel layer-built rechargeable lithium ribbon-type battery intended for textile or cloth based applications. The ribbon-type battery, 2.4 mm (or 1 mm) wide and 10 cm long, is composed of a double layer LiFePO4 cathode and an amorphous silicon nanofilm. The double layer LiFePO4 and amorphous silicon electrodes were prepared using the doctor blade method and a vertical deposition technique, respectively. The structure and morphology of the LiFePO4 and the silicon thin film were characterized by Rietveld refinement, SEM and TEM. At room temperature the ribbon-type battery exhibited an initial discharge capacity of 166.4 and 132.7 mA h g−1 at 0.5 and 1 C-rate, respectively. A reasonably good cycling performance and high coulombic efficiency under the high current density of 1 C-rate could be obtained with the Si/LiFePO4 ribbon-type battery. Also, a high volumetric capacity of 336 mA h cm−3 at 0.5 C-rate was achieved, which makes the ribbon-type battery suitable for practical use.

Properties of N-butyl-N-methyl-pyrrolidinium Bis(trifluoromethanesulfonyl) Imide Based Electrolytes as a Function of Lithium Bis(trifluoromethanesulfonyl) Imide Doping

In this study we have investigated the Li-ion coordination, thermal behavior and electrochemical stability of N-butyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide () with lithium bis(trifluoromethanesulfony)imide (LiTFSI) doping intended for use as electrolytes for lithium batteries. The ionic conductivity is reduced and glass transition temperature () increases with LiTFSI doping concentration. Also, the electrochemical stability increases with LiTFSI doping. A high LiTFSI doping could enhance the electrochemical stability of electrolytes for lithium batteries, whereas the decrease in the ionic conductivity limits the capacity of the battery.