Organic Ionic Plastic Crystals Research Articles

Bis-imidazolium iodide organic ionic plastic crystals and their applications to solid state dye-sensitized solar cells

Novel dicationic bis-imidazolium iodide salts have been discovered as new organic ionic plastic crystalline materials. Most of them show multiple solid-solid phase transitions below their melting temperatures. Their phase transition temperatures are dependent on the imidazolium cation structure. According to Timmermans' definition of plastic crystals, bis-imidazolium iodide salts with either n-heptyl or n-octyl side arms can be classified as “true plastic crystals” because of their low ΔSf values (<20 J mol−1 K−1). The bis-imidazolium iodide salts are stable up to 260 °C under thermal gravimetric analysis. The ionic conductivities, investigated using dielectric relaxation spectroscopy, follow the Arrhenius temperature dependence with discontinuities and changes in slopes at the observed solid–solid phase transition temperature. Dye-sensitized solar cells (DSSCs) fabricated by a whole solid-state electrolyte consisting of n-hexyl side-armed bis-imidazolium iodide (BII-6) show a 4.93% power conversion efficiency (η): a remarkable result for the solid-state electrolyte system compared to that obtained using an liquid electrolyte with 1-butyl-3-methylimidazolium iodide (η = 8.00%) as a reference composition.

1H-31P CPVC NMR method under Very Fast Magic Angle Spinning for analysis of dipolar interactions and dynamics processes in the crystalline phosphonium tetrafluoroborate salts

We present an NMR methodology which can be used to study the dynamical processes occurring in organophosphorus compounds that belong to the group of the organic ionic plastic crystals (OIPCs). As model samples we employed two phosphonium tetrafluoroborate salts; (t-Bu)3PH+BF4− (1) and (Me)3PH+BF4− (2). Both samples possess in their structures direct H-P bonds, and both undergo complex thermal processes in the solid state, forming below the melting point three or four phases, respectively. 1H-31P CPVC (Cross-Polarization Variable Contact) measurements were performed under Very Fast Magic Angle Spinning with speed equal to 50 or 60 kHz, in order (i) to establish the hydrogen-phosphorus dipolar couplings, and (ii) to correlate the dipolar splitting values with molecular motions of the cation.Our project is divided into three sections. In the first part we present DSC studies of (1) and (2), to verify whether these samples fulfill the requirements that define them as OIPC. The second part is dedicated to a discussion of the theoretical aspects of 1H-31P CPVC and especially an analysis of the influence of different parameters, e.g. CSA31P, H-H mismatch, rf-inhomogeneity, dipolar truncation, and the type of dynamics through the motionally averaged <ηD> asymmetry value on the NMR response. The third part shows experimental 1H-31P CPVC data and applicability of these measurements to study H-P distances and dynamics. The complex molecular motion for sample (2), including rotation and diffusion, versus temperature is then postulated on the bases of the changes of H-P dipolar splitting.

Preparation and crystal structure of tetraoctylphosphonium tetrakis(pentafluorophenyl)borate ionic liquid for electrochemistry at its interface with water

With ongoing and expending global energy needs, nuclear power is likely to be a key energy source for many more generations. A key question is still the fate of spent nuclear fuel (SNF). SNF contains a great deal of valuable material. In order to improve safety and handling, herein is proposed relatively high melting point ionic liquid (IL) or organic ionic plastic crystals (OIPCs) for biphasic water|IL metal ion extraction. The proposed IL, tetraoctylphosphonium tetrakis(pentafluorophenyl)borate, P8888(C6F5)4, was discovered to have a melting point of ∼55°C and a high degree of order by differential scanning calorimetry and X-ray diffraction (CCDC 1550126), respectively. In this way, the IL/OIPC could be used in ligand assisted metal ion extraction from water solutions at elevated temperatures and then ‘frozen’ at ambient conditions for facile manipulation and transport of the SNF. To test the feasibility of this, electrochemistry such as cyclic voltammetry at a water|IL micro-interface (25 mm in diameter) was employed to assess the thermodynamics of K+ ligand assisted transfer. It was revealed that the TRUEX (Transuranium Extraction) ligand octyl(phenyl)-N,N’-diisobutylcarbamoylphosphine oxide (CMPO) has a high to moderate coordination to K+ at the w| P8888(C6F5)4, micro-interface. Two ligand to K+ stoichiometries were determined to be 3:1 and 2:1, respectively.

Conformational Dynamics in an Organic Ionic Plastic Crystal.

Understanding the short-range molecular motions of organic ionic plastic crystals is critical for the application of these materials as solid-state electrolytes in electrochemical devices such as lithium batteries. However, the theory of short-range-motions was originally developed for simple molecular plastic crystals and does not take account of strong interionic interactions that are present in organic ionic plastic crystals. Here we report a fundamental investigation of the dynamic behavior of an archetypal example triethyl(methyl)phosphonium bis(fluorosulfonyl)amide ([P1222][FSI]) through calorimetry, impedance spectroscopy, synchrotron X-ray diffraction, and solid-state NMR and Raman spectroscopies. For the first time, we show the presence of conformational dynamics in the solid state for the FSI anion. We relate the dynamics to a unique second-order displacive phase transition of [P1222][FSI]. This detailed analysis suggests a new disorder mechanism involving cooperative motion between the cation and FSI anion in the plastic crystal due to strong interionic interactions.

Organic Ionic Plastic Crystal‐Based Composite Electrolyte with Surface Enhanced Ion Transport and Its Use in All‐Solid‐State Lithium Batteries

Solid‐state electrolytes have been identified as one of the most attractive materials for the fabrication of reliable and safe lithium batteries. This work demonstrates a facile strategy to prepare highly conductive organic ionic plastic crystal (OIPC) composites by combination of a low weight fraction of Li+ doped OIPC (N‐ethyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)amide, [C2mpyr][FSI]) with commercial poly(vinylidene difluoride) (PVDF) powder. Benefiting from the enhancement of lithium ion dynamics, as evidenced by the solid‐state NMR measurements, the composite electrolyte shows an order of magnitude higher conductivity than that of the bulk material. Lithium metal/LiFePO4 cells incorporating the prepared composite electrolytes show impressively high specific capacity and good cycling stability (99.8% coulombic efficiency after 1200 cycles at 2 C, room temperature), which is the first demonstration of long‐term cycling performance at such high rate for an OIPC‐based electrolyte. The high voltage cathode, LiCo1/3Ni1/3Mn1/3O2 was tested and good rate performance and stable capacities have been achieved.

N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide-electrospun polyvinylidene fluoride composite electrolytes: characterization and lithium cell studies.

Using the organic ionic plastic crystal N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide ([C2mpyr][FSI]) with electrospun nanofibers, LiFSI doped [C2mpyr][FSI]-PVdF composites were developed as solid state, self-standing electrolyte membranes. Different lithium salt concentration were investigated, with 10 mol% LiFSI found to be optimal amongst those assessed. Composites with different weight ratios of plastic crystal and polymer were prepared and 10 wt% polymer gave the highest conductivity. In addition, the effects of PVdF incorporation on the morphological, thermal, and structural properties of the organic ionic plastic crystal were investigated. Ion mobilities were also studied using solid-state nuclear magnetic resonance techniques. The electrolytes were then assembled into lithium symmetric cells and cycled galvanostatically at 0.13 mA cm-2 at both ambient temperature and at 50 °C, for more than 500 cycles.

Effect of secondary phase on thermal behaviour and solid-state ion conduction in lithium doped N-ethyl-N-methylpyrrolidinium tetrafluoroborate organic ionic plastic crystal

Microstructural features significantly affecting lithium ion dynamics and conduction within the crystalline structure of pyrrolidinium based organic ionic plastic crystals.

Proton Hopping Mechanisms in a Protic Organic Ionic Plastic Crystal

We elucidate the dynamics and mechanism of proton transport in a protic organic ionic plastic crystal (POIPC) [TAZ][pfBu] by means of Born–Oppenheimer molecular dynamics simulations at 400 K and zero humidity. The arrangement of ionic species in the crystal offers a two-dimensional hydrogen bond network along which an acidic proton can travel from one cation to another through a sequence of molecular reorientations. The results suggest spontaneous autodissociation of the N–HN bond in the cation and multiple proton shuttle events from the cation’s nitrogen to the anion’s oxygen site in a native crystal. A complete proton transfer event is observed in simulations of a defective crystal with a single proton hole created in the cation. The barrier for proton transfer is determined using ab initio metadynamics simulations to be 7 kcal/mol, in agreement with experimental conductivity data. Using gas phase quantum chemical calculations, we propose [TAZ][CF3CF2CH2CF2SO3] as a compound that can show enhanced conductivity compared to that of [TAZ][pfBu].

Mixed Phase Solid‐State Plastic Crystal Electrolytes Based on a Phosphonium Cation for Sodium Devices

Na batteries are seen as a feasible alternative technology to lithium ion batteries due to the greater abundance of sodium and potentially similar electrochemical behavior. In this work, mixed phase electrolyte materials based on solid‐state compositions of a trimethylisobutylphosphonium (P111i4) bis(trifluromethanesulphonyl)amide (NTf2) organic ionic plastic crystal (OIPC) and high concentration of NaNTf2 that support safe, sodium metal electrochemistry are demonstrated. A Na symmetric cell can be cycled efficiently, even in the solid state (at 50 °C and 60 °C), for a 25 mol% (P111i4NTf2)–75 mol% NaNTf2 composition at 0.1 mA cm−2 for 100 cycles. Thus, these mixed phase materials can be potentially used in Na‐based devices under moderate temperature conditions. It is also investigated that the phase behavior, conductivity, and electrochemical properties of mixtures of NaNTf2 with this OIPC. It is observed that these mixtures have complex phase behavior. For high compositions of the Na salt, the materials are solid at room temperature and retain a soft solid consistency even at 50 °C with remarkably high conductivity, approaching that of the pure ionic liquid at 50 °C, i.e., 10−3–10−2 S cm−1.

Ionic Liquids and Organic Ionic Plastic Crystals Based on Tris(fluorosulfonyl)methide

Ionic liquids (ILs) composed of low coordinating anions such as perfluoroanions have been studied as a unique electrolyte for a lithium battery for past two decades.[1] The best performance of a lithium battery system using only ILs was achieved by bis(fluorosulfonyl)amide (FSI-, FSA- or f2N-) [2]. The existence of FSO2- group in f2N- might cause such a good performance. In this study, we tried to prepare new perfluoromethide, tris(fluorosulfonyl)methide (f3C-) to investigate the effect of FSO2 - group on physicochemical and electrochemical properties of onium salts composed of f3C-. The physical, thermal and electrochemical properties of the ILs were compared to another similar methide anion (tris(trifluoromethylsulfonyl)methide, Tf3C-). The Tf3C- could form ILs with conventional cations such as N-ethyl-N-methylimidazolium (C1C2im+) and N,N-dimethyl-N-methyl-N-(2-ethoxymethyl)ammonium (N2,2,1,2O1 +), however, It was quite interesting that the f3C- had a tendency to form organic ionic plastic crystals (OIPCs) rather than ILs. As far as we know, the N2,2,1,2O1 + forms ILs with various anions even PF6 - [3] however, the f3C- forms good OIPCs with N2,2,1,2O1 + (T m = 69 °C, T s-s = -29 °C). The cathodic limiting potential of a ILs composed of N-ethyl-N-methylimidazolium (C1C2im+) and f3C- was about 1.0 V shifted toward negative potential with adding Lif3C and stable lithium deposition and redissolution cycle could be successfully observed. The apparent charge transfer resistance at an interface between a Li metal and [C1C2im][f3C] was more stable over 18 months than that for [C1C2im][Tf3C], which indicated that the existence of FSO2- group in a perfluoroanion must be importance to maintain a stable SEI on the lithium metal as previously reported in a bis(fluorosulfonyl)amide based melts.[3] Furthermore, the apparent charge transfer resistance at a charged LiCoO2 composite electrode (4.2 V vs Li/Li+) in the [C1C2im][f3C] was almost the same value during over 500 charge and discharge cycles, which suggested that the good electrochemical stability not only for a lithium metal but also for the charged cathode were achieved with using the new methide f3C- composed of FSO2 - group as in bis(fluorosulfonyl)amide based melts. These results suggest that the FSO2 - group have an essential moiety to design an novel perfluoroanions for a lithium battery electrolyte. The f3C-provided not only ILs as a novel lithium battery electrolyte but also OIPCs and the molecular design rules, which have not yet been clearly understood. Acknowledgment This study was financially supported by JST, ALCA-SPRING project.

Ionic Liquids and Organic Ionic Plastic Crystals Based on Tris(fluorosulfonyl)methide

New ionic liquids and organic ionic plastic crystals based on tris(fluoromethylsulfonyl)methide were prepared and the physico-chemical, thermal and electrochemical properties were investigated and compared to that of the corresponding tris(trifluoromethyl-sulfonyl)methide salts.

Modelling of Li+ and Na+ Conduction Under Electric Fields in Organic Ionic Plastic Crystals

Solid electrolytes are a promising topic, which could replace the flammable solvents currently used for both Li-ion battery electrolytes, and their Na-counterpart (still under development). Thus the transport properties of such solid electrolytes must be understood. Here, we studied the effect of applying an external electric field to an organic ionic plastic crystal, P1224PF6, previously reported to have interesting alkali-ion transport properties[i]. The study employed molecular dynamics (using a previously reported force field[ii]). The roles of electric field strength and Li+/Na+ concentration were explored. Furthermore, system polarisation was explored by adding a surface/electrode to the system. This was done both on the basis of an external electric field and one due to electrode charge. [i] Chen, F., Pringle, J.M., Forsyth, M. Chem. Mater. 2015, 27, 2666-2672. [ii] Chen, F., Jin, L., de Leeuw, S.W., Pringle, J.M., Forsyth, M. J. Chem. Phys. 2013, 138, 244503.

Fast Conduction of Organic Cations in Metal Sulfate Frameworks

We demonstrated a new method of synthesizing crystalline organic cation conductors. The conductivities of various organic cations involved in a one-dimensional zinc sulfate framework were studied. The optimized structure (EMIm)2[Zn(SO4)2] exhibited an ionic conductivity of 3.8 × 10–3 S cm–1 at 210 °C, which is comparable to that of highly conductive organic ionic plastic crystals. The high ionic conductivity is attributable to the defect structures of the organic cations in the inorganic frameworks. The pulsed-field gradient solid-state NMR technique revealed that the self-diffusion coefficient of organic cations in the zinc sulfate at 80 °C is comparable to that of the popular ionic liquid EMIm-BF4 at 30 °C, which indicates that liquid-like fast transporting of organic cation is achieved in the robust crystal structure.

In Situ MRI of Operating Solid-State Lithium Metal Cells Based on Ionic Plastic Crystal Electrolytes

Solid-state ion conductors based on organic ionic plastic crystals (OIPCs) are a promising alternative to conventional liquid electrolytes in lithium battery applications. The OIPC-based electrolytes are safe (nonflammable) and flexible in terms of design and operating conditions. Magnetic resonance imaging (MRI) is a powerful noninvasive method enabling visualization of various chemical phenomena. Here, we report a first quantitative in situ MRI study of operating solid-state lithium cells. Lithium ion transfer into the OIPC matrix during the ongoing discharge of the anode results in partial liquefaction of the electrolyte at the metal interface. The developed liquid component enhances the ion transport across the interface and overall battery performance. Displacement of the liquefaction front is accompanied by a faster Li transfer through the grain boundaries and depletion at the cathode. The demonstrated solid–liquid hybrid properties, inherent in many OIPCs, combine benefits of highly conductive ioni...

Ionic liquids and their solid-state analogues as materials for energy generation and storage

Ionic liquids and their solid-state analogues, organic ionic plastic crystals, have recently emerged as important materials for renewable energy applications. This Review highlights recent advances in the synthesis of these materials and their application as electrolytes for batteries, capacitors, photovoltaics, fuel cells and CO2 reduction.

Enhancement of ion dynamics in organic ionic plastic crystal/PVDF composite electrolytes prepared by co-electrospinning

Organic ionic plastic crystal (OIPC) modified poly(vinylidene difluoride) (PVDF) composite fiber membrane with enhanced ion dynamics and almost pure β-PVDF are demonstrated.

A novel class of gas separation membrane based on organic ionic plastic crystals.

The first use of organic ionic plastic crystals (OIPCs) as CO2 separation membranes is reported. The novel OIPC/PVDF nanofiber composites show CO2/N2 ideal selectivities of 30 at 35 °C. The dependence of gas permeability on the thermal phase of the plastic crystals is discussed.

Guanidinium nonaflate as a solid-state proton conductor

Guanidinium nonaflate, a novel pure protic organic ionic plastic crystal (POIPC) with an elegant symmetrical cation, is discovered to be a new solid-state proton conductor.

Protic organic ionic plastic crystals based on a difunctional cation and the triflate anion: a new solid-state proton conductor.

Two protic organic ionic plastic crystalline materials based on the mono- and di-protonated cations of N,N-dimethylethylenediamine, (DMEDA) and the triflate anion have been studied. The symmetrical di-protonated cation salt shows 54 °C higher melting point and 24-fold higher conductivity at room temperature as compared to the mono-protonated cation salt, making it a promising candidate for a solid-state proton conductor. The conductivity of this salt was further enhanced by acid doping.

Thermal phase behavior and ion hopping in a 1,2,4-triazolium perfluorobutanesulfonate protic organic ionic plastic crystal.

Critical aspects of thermal behavior and the electrolytic properties of solid-state Protic Organic Ionic Plastic Crystals (POIPCs) are unknown. We present molecular dynamics (MD) simulations on a perfect crystal and a vacancy model to probe such physical phenomena in POIPCs using 1,2,4-triazolium perfluorobutanesulfonate ([TAZ][pfBu]) as an example. The results show the existence of a rotator phase wherein the cations, although translationally ordered are disordered rotationally and exhibit a tumbling motion which significantly affects hydrogen bond lifetimes. van Hove correlation functions characterize the concerted hopping of ions (cation or anion) at 500 K. These results are substantiated by calculated free energy barriers (cation = 2.5 kcal mol(-1) and anion = 6 kcal mol(-1)) and suggest that proton and ion transport influenced by facile hydrogen bond dynamics in the rotator phase contribute to the solid-state conductivity of POIPCs.