Organic Ionic Plastic Crystal Electrolytes Research Articles

Fast Charge and High Stability of Solid‐State Graphite Organic Ionic Plastic Crystal Composite Anodes

AbstractInvited for this month's cover picture is the group of Dr. Hiroyuki Ueda and Prof. Patrick C. Howlett at Deakin University (Australia) jointly working with Toyota Motor Corporation (Japan). The cover picture shows the fast lithium‐ion conduction pathways in the graphite anode of all‐solid‐state batteries (ASSBs) enabled by the incorporation of an organic ionic plastic crystal (OIPC) electrolyte. Read the full text of the Research Article at 10.1002/batt.202200057.

Cover Picture: Fast Charge and High Stability of Solid‐State Graphite Organic Ionic Plastic Crystal Composite Anodes (Batteries & Supercaps 7/2022)

The Front Cover shows a solid-state graphite composite anode containing an organic ionic plastic crystal electrolyte as a multifunctional lithium-ion conductor by which the electrolyte/electrode and electrode/current collector contacts are improved, enabling fast lithiation and stable cycling. More information can be found in the Research Article by H. Ueda, P. C. Howlett and co-workers.

Efficient and Stable Solid-State Dye-Sensitized Solar Cells by the Combination of Phosphonium Organic Ionic Plastic Crystals with Silica

Remarkably efficient quasi-solid-state dye-sensitized solar cells (DSSCs) have been fabricated using organic ionic plastic crystal electrolytes based on a small triethyl(methyl)phosphonium [P1222] cation and two types of sulfonamide anions, bis(fluorosulfonyl)amide (FSA) and bis(trifluoromethanesulfonyl)amide (TFSA), in combination with varying amounts of silica (SiO2). Solar cell efficiencies of up to 7.4% were obtained, which is comparable to our benchmark efficiencies of liquid (acetonitrile) electrolyte-based devices. Such a high efficiency for DSSCs using quasi-solid-state electrolytes is attributed to improved ionic conductivity, enhanced redox couple transport, improved interfacial interaction between the electrolyte and the electrode as well as decreased resistance at both electrode interfaces. Notably, the devices with the silica-containing electrolytes displayed excellent stability after 5 months of storage, with the most stable devices, formed with either plastic crystal electrolyte containing 2% silica, showing no decrease in efficiency.

The influence of the size and symmetry of cations and anions on the physicochemical behavior of organic ionic plastic crystal electrolytes mixed with sodium salts.

The phase behaviour, ionic conductivity, electrochemical stability and diffusion coefficients of mobile components in three organic ionic plastic crystals (OIPCs): triisobutylmethylphosphonium bis(fluorosulphonyl)amide (P1i444FSI), triisobutylmethylphosphonium bis(trifluromethanesulphonyl)amide (P1i444NTf2) and trimethylisobutylphosphonium bis(trifluoromethanesulphonyl)amide (P111i4NTf2) are compared to study the effect of the anions and cations on phase behaviour and dynamics. The FSI-based OIPC shows lower melting point and higher conductivity values most likely because of the higher degree of charge distributions and weaker ion-ion interactions compared to NTf2 anion-based OIPCs. Cyclic voltammetry of electrolytes consisting of these OIPCs with 70 mol% sodium salt incorporated indicates stable sodium plating/stripping behaviour at 70 and 50 °C for all samples. The magnitude of the peak currents, however, are much higher for the FSI-based electrolyte.

ChemInform Abstract: New Insights into Ordering and Dynamics in Organic Ionic Plastic Crystal Electrolytes

AbstractReview: 39 refs.

New insights into ordering and dynamics in organic ionic plastic crystal electrolytes

Solid state phases of organic salts, whose chemistry is closely related to that of ionic liquids, often show interesting phase behavior and dynamics resulting in solid-state conductors that have potential application in electrochemical devices such as solid state batteries. The mechanism of conduction in these solid-state plastic crystal phases is still not entirely understood. We have recently shown using molecular dynamics (MD) simulations that the introduction of defects, such as vacancies, leads to heterogeneous dynamics in the OIPC arising from amorphous and mobile domains in these materials. Advanced magnetic resonance imaging (MRI) analysis indicates that these domains can exhibit distinct orientations, leading to anisotropic ionic conductivity with enhanced values in a particular direction. This paper will review this new understanding, drawing links between the molecular and macroscopic-level information provided by these two techniques.

1,2,4-Triazolium perfluorobutanesulfonate as an archetypal pure protic organic ionic plastic crystal electrolyte for all-solid-state fuel cells

Protic organic ionic plastic crystals (POIPCs) are shown to be novel anhydrous solid-state proton conductors for fuel cells.

An organic ionic plastic crystal electrolyte for rate capability and stability of ambient temperature lithium batteries

For the first time, practical lithium cell performance is achieved at ambient temperature with an organic ionic plastic crystal solid electrolyte.

Water‐Resistant, Solid‐State, Dye‐Sensitized Solar Cells Based on Hydrophobic Organic Ionic Plastic Crystal Electrolytes

Water-resistant, solid-state, dye-sensitized solar cells with excellent long-term stability at 100% relative humidity and at 50 °C are fabricated on the basis of a novel hydrophobic organic ionic plastic crystal electrolyte and hybrid redox couple.

A novel organic ionic plastic crystal electrolyte for solid-state dye-sensitized solar cells

An organic ionic plastic crystal (OIPC) 2-hydroxyethyltrimethylammonium iodide (choline iodide) as an important component in solid electrolyte is synthesized and applied in dye-sensitized solar cells. It allows relatively rapid diffusion of the redox couple through the plastic crystal phase that is critical to the cell performance. The novel material, utilizing strong quaternary ammonium cation 2-hydroxyethyltrimethylammonium (HETA+) as a cation donor, is treated as matrix in electrolyte. At optimal condictions, the cell gives a short-circuit photocurrent density (Jsc), open-circuit voltage (Voc) and fill factor (FF) of 6mAcm−2, 0.69V and 63%, respectively. The corresponding overall conversion efficiency (η) is 2.5%. The results suggest that the OIPC is a promising solid electrolyte material for dye-sensitized solar cells applications.

Silica Nanoparticle Doped Organic Ionic Plastic Crystal Electrolytes for Highly Efficient Solid-State Dye-Sensitized Solar Cells

Organic ionic plastic crystal, 1-propyl-1-methylpyrrolidinium iodide (P₁₃I), which possesses a broad plastic phase from -36 to 135 °C, was doped with silica nanoparticles (SiO₂ NPs) and 1-ethyl-3-methylimidazolium iodide (EMII), for the preparation of SiO₂/EMII/P₁₃I solid-state electrolytes for dye-sensitized solar cells (DSSCs). The thermal properties of all the electrolytes, including solid-solid phase transitions and melting temperatures, were investigated by differential scanning calorimetry (DSC). The effect of silica particles on the ionic conductivity, diffusion of I⁻/I₃⁻ redox couple in electrolytes, and photovoltaic performance for solid-state DSSCs were investigated. The fabricated solid-state DSSCs yielded a high power conversion efficiency of 5.25% under simulated air mass 1.5 solar spectrum illuminations at 50 mW cm⁻². Furthermore, the DSSCs based on SiO₂/EMII/P₁₃I solid-state electrolytes show good stability after an accelerating aging test, demonstrating potential practical applications.

Recent progress in the development and use of organic ionic plastic crystal electrolytes

Significant progress has been made recently in the development of Organic Ionic Plastic Crystals (OIPCs), a unique family of solid state electrolytes with applications in electrochemical devices such as lithium batteries and dye-sensitised solar cells. The negligible volatility of OIPCs renders them more suitable than molecular species for long-term device use, while the high thermal and electrochemical stability of many OIPCs fulfils an essential requirement for solid state electrolytes for many device applications. However, the complex mechanisms of conduction through these materials, both in their pure state and in the presence of a small amount of a second component (such as lithium salts to enable their use in lithium batteries) are still not fully understood. At the same time, the range of anions and cations utilised in the synthesis of plastic crystal phases continues to increase. This perspective concentrates on recent research into both fundamental and device-oriented aspects of these materials. Important fundamental understanding of the physical properties and transport mechanisms of different OIPCs has been achieved through use of techniques including variable temperature solid-state NMR and crystallographic analysis, as well as detailed molecular dynamics simulations. In parallel, the applicability of these materials as electrolytes for dye-sensitised solar cells and lithium batteries is being more widely demonstrated. The possibility of using OIPCs as solid state electrolytes for fuel cells is also discussed.

High‐Temperature Solid‐State Dye‐Sensitized Solar Cells Based on Organic Ionic Plastic Crystal Electrolytes

Organic ionic plastic crystal, 1-ethyl-1-methyl pyrrolidinium iodide (P(12) I), is employed as the solid-state electrolytes for dye-sensitized solar cells. The fabricated solid-state devices show an overall power conversion efficiency of ~5.8% under AM 1.5 radiation (50 mW/cm(2) ) and excellent long-term stability at 80 °C.

Optimising organic ionic plastic crystal electrolyte for all solid-state and higher than ambient temperature lithium batteries

Organic ionic plastic crystal (OIPC) electrolytes are among the key enabling materials for solid-state and higher than ambient temperature lithium batteries. This work overviews some of the parameter studies on the Li|OIPC interface using lithium symmetrical cells as well as the optimisation and performance of Li|OIPC|LiFePO4 cells. The effects of temperature and electrolyte thickness on the cycle performance of the lithium symmetrical cell, particularly with respect to the interfacial and bulk resistances, are demonstrated. Whilst temperature change substantially alters both the interfacial and bulk resistance, changing the electrolyte thickness predominantly changes the bulk resistance only. In addition, an upper limit of the current density is demonstrated, above which irreversible processes related to electrolyte decomposition take place. Here, we demonstrate an excellent discharge capacity attained on LiFePO4|10 mol% LiNTf2-doped [C2mpyr][NTf2]|Li cell, reaching 126 mAh g-1 at 50 °C (when the electrolyte is in its solid form) and 153 mAh g-1 at 80 °C (when the electrolyte is in its liquid form). Most remarkably, at high temperature operation, the capacity retention at long cycles and high current is excellent with only a slight (3%) drop in discharge capacity upon increasing the current from 0.2 C to 0.5 C. These results highlight the real prospects for developing a lithium battery with high temperature performance that easily surpasses that achievable with even the best contemporary lithium-ion technology.

On the use of organic ionic plastic crystals in all solid-state lithium metal batteries

We show that a previously observed low current, pre-conditioning behavior which allows increased lithium flux through a solid state, symmetric lithium cell containing a pyrrolidinium bis(trifluoromethyl)sulfonamide electrolyte is a more general phenomenon for organic ionic plastic crystal electrolytes. Furthermore, the mechanism of the preconditioning behavior has been highlighted via a post-mortem characterisation of the cells. Differential scanning calorimetry (DSC) indicated a decrease in the melting point by 1.9 °C after 35 h of 0.01 mA cm − 2 cycling and scanning electron microscopy (SEM) images revealed that substantial changes to the OIPC microstructure, in particular grain size, had occurred. Both of these phenomena would lead to an enhancement of lithium ion transport near the Li/electrolyte interface. In a preliminary experiment incorporating a LiFePO 4 cathode, similar preconditioning behavior was observed. Furthermore, good battery performance can be achieved, between 129 and 110 mAh g − 1 during 50 cycles at 0.2 C, denoting the promise of these plastic crystal electrolytes in highly stable, all solid-state lithium metal batteries.

An organic ionic plastic crystal electrolyte based on the triflate anion exhibiting high proton transport

A novel organic ionic plastic crystal (OIPC) electrolyte based on a quaternary ammonium cation and the triflate anion has been synthesized, which shows fast proton transport and high thermal stability in the solid state when doped with triflic acid.

Organic ionic plastic crystal electrolytes; a new class of electrolyte for high efficiency solid state dye-sensitized solar cells

Dye-sensitized solar cells are an increasingly promising alternative to conventional silicon solar cells as a method of converting solar energy to electricity and thus providing an effectively inexhaustible energy source. However, the most efficient of these devices currently utilize liquid electrolytes, which suffer from the associated problems of leakage and evaporation. Hence, significant research is currently focused on the development of solid state alternatives. Here we report a new class of solid state electrolyte for these devices, organic ionic plastic crystal electrolytes, that allow relatively rapid diffusion of the redox couple through the matrix, which is critical to the cell performance. A range of different organic ionic plastic crystal materials, utilizing different cation and anion structures, have been investigated and the conductivities, diffusion rates and photovoltaic performance of the electrolytes are reported. The best material, utilizing the dicyanamide anion, achieves efficiencies of more than 5%.

Lithium-doped, organic ionic plastic crystal electrolytes exhibiting high ambient-temperature conductivities

Film-forming, ionic plastic crystal— N, N-diethyl- N-methyl- N-( n-propyl)ammonium trifluoromethyltrifluoroborate (N 1223[CF 3BF 3])—has been doped with Li[CF 3BF 3] salt to prepare stable Li-ion conducting plastic crystal electrolytes. Solid-state conductivities as high as 10 −4–10 −3 S cm −1 have been obtained within the ambient-temperature plastic crystalline phase of the Li-doped materials. Solid-state Li deposition/dissolution based on these materials has been realized at 25 °C. The outstanding properties of these materials make them attractive candidates for all-solid-state Li batteries.

Defect-assisted conductivity in organic ionic plastic crystals

In order to determine the role of defects (vacancies and extended lattice defects) in the conductivity mechanism of a well studied organic ionic plastic crystal electrolyte, conductivity and mean defect volumes were measured. The ionic conductivity of the salt showed a characteristic phase dependence. Defect volumes, as measured by positron annihilation lifetime spectroscopy, showed increasing rates of expansion with increasing rotational disorder. The dependence of ionic conductivity on defect volume was observed to be phase dependent. Increases in mean defect volume size below approximately 100 cm(3) mol(-1) did not always facilitate ionic conductivity. It was shown that the material undergoes a solid-solid phase transition to the most disordered phase (a plastic crystalline phase with the highest conductivity) when the mean defect volume becomes larger than the molar volume of either the rotating anionic or cationic species. Conductivity in this phase had the strongest dependence on defect volume. Critical volumes calculated from the free volume model of Cohen and Turnbull were unrealistically large.

Supercritical CO2 modified organic ionic plastic crystals

The treatment of an organic ionic plastic crystal electrolyte N-methyl-N-ethylpyrrolidinium tetrafluoroborate (P1,2BF4) with supercritical CO2 resulted in a substantial increase in ionic conductivity, especially in the more highly ordered solid phases of the material, and also stabilised the most ordered phase to lower temperatures.