Plastic Crystalline Phase Research Articles

Polar groups promoting in-situ polymerization phase separation for solid electrolytes enabling solid-state lithium batteries

Plastic-crystal-embedded elastomer electrolytes (PCEEs), produced through polymerization-induced phase separation (PIPS), are gaining popularity as solid polymer electrolytes (SPEs). However, it remains to be investigated whether all monomer molecules can achieve polymerization-induced phase separation and the corresponding differences in lithium metal battery performance. Herein, we prepared PCEEs with different functional groups (OH, CN, F) through in situ polymerization. Research findings show that PCEE containing – CN or – F achieves the separation of the plastic crystalline phase and succinonitrile (SN) phase, whereas PCEE containing OH cannot due to hydrogen bonding with the SN phase. Notably, the PCEE synthesized with the F monomer (FBA-PCEE) exhibited exceptional interfacial stability with lithium metal anodes and lithium iron phosphate (LFP) cathodes, due to its unique coordination mechanism with lithium ions. The FBA-PCEE demonstrated a high ionic conductivity (2.02 × 10−3 S cm−1) and lithium-ion migration number (tLi+ = 0.75). Moreover, lithium symmetric cells incorporating FBA-PCEE demonstrated stable cycling performance for more than 1000 h at a current density of 0.1 mA cm−2, resulting in the development of a solid electrolyte interphase (SEI) rich in LiF, Li3N, and Li2CO3 over time. Additionally, incorporating FBA-PCEE facilitated the stable cycling of LPF over 1000 cycles at 0.5C, maintaining a capacity retention of 77.38 % after 500 cycles. When coupled with high-voltage Nickel Cobalt Manganese Oxide (NCM-622) cathodes and lithium metal anodes, a discharge capacity of 119.70 mAh g−1 at 0.1C was sustained after 100 cycles, exhibiting a capacity retention of 78.95 %. This study elucidates the critical role of monomer design in achieving PIPS, offering valuable insights into developing high-performance polymer composite electrolytes for advanced lithium metal batteries.

Solvent-assisted mechanochemical crystallization of the metal-free perovskite solid solution (H2dabco, H2hmta)NH4(BF4)3.

All-proportional solid solutions of the metal-free perovskite (H2dabco1-y, H2hmtay)(NH4)(BF4)3 ((d,h)-BF4) were crystallized via a mechanochemical method. Their molecular dynamics depend on the ratio y with a compositional boundary at y = 0.43, where H2dabco2+ was deduced to be at a dynamic disorder state, even below phase transition temperature to a plastic crystalline phase seen at y = 0.

Nuclear Magnetic Resonance Study on Relationship between Phase Behavior and Rotational and Translational Dynamics of an Ionic Liquid with a Plastic Crystal Phase: N-Butyl-N-methylpiperidinium Hexafluorophosphate

Abstract N-butyl-N-methylpiperidinium hexafluorophosphate, [C1C4pip]PF6, is an ionic liquid with a plastic crystal (PC) phase. To investigate the dynamics of the phase transition between crystalline, plastic crystalline, and liquid phases of [C1C4pip]PF6, we measured the temperature dependences of longitudinal and transverse relaxation times (T1 and T2, respectively) for 1H and 19F using low-frequency pulse nuclear magnetic resonance (NMR) methods. T1 and T2 changes are sensitive to the rotational and translational dynamics of ions, respectively. Since H and F atoms are only present in the cation and anion, respectively, the dynamic behaviors of each ionic molecule can be investigated separately. In the phase transition between the PC and liquid phase, the temperature-dependent curves of 1H-T1 were smoothly connected, indicating the same rotational motion for the cation occurred in both phases. The curves of 19F-T1 yielded the same conclusion for the rotational motion of the anion in both phases. The temperature-dependent curves of 1H-T2 and 19F-T2 jumped abruptly from phase to phase, indicating different modes of translational motion in each phase. We observed the appearance of a translationally mobile component in both the PC phase and the crystalline phase. This was concluded to be surface or interfacial melting.

Densest-known packings and phase behavior of hard spherical capsids.

By mostly using Monte Carlo numerical simulation, this work investigates the densest-known packings and phase behavior of hard spherical capsids, i.e., hard infinitesimally thin spherical caps with a subtended angle larger than the straight angle. The infinitely degenerate densest-known packings are all characterized by hard spherical capsids that interlock and can be subdivided into three families. The first family includes crystalline packings that are constructed by suitably rotating and stacking layers of hexagonally arranged and suitably tilted hard spherical capsids; depending on the successive rotations, the crystalline packings of this family can become the face-centered cubic crystal, the hexagonal close-packed crystal, and their infinitely degenerate variants in the hard-sphere limit. The second family includes crystalline packings that are characterized by rhombic motifs; they all become the face-centered cubic crystal in the hard-sphere limit. The third family includes crystalline packings that are constructed by suitably shifting and stacking layers in which hard spherical capsids are arranged in tightly packed, straight or zigzag, columns; depending on the successive shifts, the crystalline packings of this family can become the face-centered cubic crystal, the hexagonal close-packed crystal, and their infinitely degenerate variants in the hard-sphere limit. In the plane number density vs subtended angle, the phase diagram of hard spherical capsids features a hexagonal columnar liquid-crystalline phase, toward the hard-hemispherical-cap limit, and a plastic-crystalline phase, toward the hard-sphere limit, in addition to the isotropic fluid phase and crystalline phases. On departing from the hard-sphere limit, the increasing propensity of hard spherical capsids to interlock progressively disfavors the plastic-crystalline phase while favoring auto-assemblage into mostly dimeric interlocks in the denser isotropic fluid phase so that a purely entropic isotropic-fluid-plastic-crystal-isotropic-fluid re-entrant sequence of phase transitions is observed in systems of hard spherical capsids with a subtended angle intermediate between the straight angle and the complete angle.

Solid state 1H, 7Li, and 13C NMR studies on new ionic plastic crystals of crown ether-Li-TFSA complexes.

This study provides the first evidence that a Li ion can form ionic plastic crystals using crown ether with a bis-(trifluoromethanesulphonyl) amide (TFSA) anion. 1H, 7Li, and 13C nuclear-magnetic-resonance (NMR) measurements of the 15-crown-5-Li-TFSA complex revealed that the constituents underwent isotropic reorientation in the plastic crystalline phase. The NMR data of the 12-crown-4-Li-TFSA salt showed that the complex is a rotator crystal (the complexes are denoted as [Li 15C5] and [Li 12C4] in this paper). The X-ray diffraction (XRD) reflection patterns of the [Li 15C5] crystal recorded in the highest-temperature solid phase (plastic phase) could be indexed to a cubic structure. Conversely, [Li 12C4] could be fitted to a trigonal structure. In this study, [M (3n)Cn] (M = Li, Na, K; n = 4-6) complexes were also prepared, and NMR, DSC, XRD, and electrical conductivity measurements were performed. Based on these results, we additionally revealed that the [Na 15C5] and [K (15C5)2] complexes are also new rotator crystals. Single-crystal XRD measurements also revealed that the [Na 15C5] compound has two stable sites in the crystal. Activation energies of molecular motions in the [M (3n)Cn] crystals were estimated using 1H NMR relaxation time (T1 and T2) measurements. The electrical conductivity measurements of [Li 12C4], [Li 15C5], and [Na 15C5] showed high ionic conductivities (∼10-2 S cm-1).

Solid-state 1H and 13C NMR studies of novel ionic rotator-crystals of [NEt x Me(3−x)R][BEt4] (R = Pr, Bu. x = 1, 2)

Abstract Four new ionic rotator-crystals of [NEt x Me(3−x)R][BEt4] (R = Pr, Bu; x = 1, 2) were observed. Rotator crystals (two-dimensional plastic crystals) are mesophases between solid and isotropic liquid phases. Solid-state 1H and 13C nuclear magnetic resonance (NMR) measurements revealed that the ellipsoidal cations of [NEt x Me(3−x)R]+ undergo uniaxial rotation about their N–R axis and libration motion of the axis, and the anions perform isotropic reorientations in the highest-temperature solid-phase (rotator phase). Differential scanning calorimetry (DSC) measurements showed small entropy changes of 8–11 J K−1 mol−1 at the melting point of the compounds. These results suggest that the cations and anions have large degrees of freedom of motion in the rotator phase. The diffraction patterns of X-ray diffraction (XRD) could be indexed to the trigonal structure (space group of P31c). Compared with the reported data for [NEt x Me(3−x)Pr][BEt3Me] (x = 1, 2) compounds, which also have rotator-crystal phases and transform to a plastic crystalline phase, a model that explains why the cations of [BEt4] salts hardly perform isotropic reorientation in the solid phases was proposed.

Multiple glassy dynamics of a homologous series of triphenylene-based columnar liquid crystals – A study by broadband dielectric spectroscopy and advanced calorimetry

Hexakis(n-alkyloxy)triphenylene) (HATn) consisting of an aromatic triphenylene core and alkyl side chains are model discotic liquid crystal (DLC) systems forming a columnar mesophase. In the mesophase, the molecules of HATn self-assemble in columns, which has one-dimensional high charge carrier mobility along the columns. Here, a homologous series of HATn with different length of the alkyl chain (n = 5,6,8,10,12) is investigated using differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS) and advanced calorimetric techniques including fast scanning calorimetry (FSC) and specific heat spectroscopy (SHS). The investigation of the phase behavior was done utilizing DSC experiments and the influence of the alkyl chain length on the phase behavior was revealed. By the dielectric investigations probing the molecular mobility, a γ-relaxation due to localized fluctuations as well as two glassy dynamics, the αcore- and αalkyl-relaxation, were observed in the temperature range of the plastic crystalline phase. Moreover, the observed glassy dynamics were further studied employing advanced calorimetry. All observed relaxation processes are attributed to the possible specific molecular fluctuations and discussed in detail. From the results a transition at around n = 8 from a rigid constrained (n = 5,6) to a softer system (n = 10,12) was revealed with increasing alkyl chain length. A counterbalance of two competing effects of a polyethylene-like behavior of the alkyl chains in the intercolumnar domains and self-organized confinement is discussed in the context of a hindered glass transition.

Dynamics in the plastic crystalline phase of cyanocyclohexane and isocyanocyclohexane probed by 1H field cycling NMR relaxometry.

Proton Field-Cycling (FC) nuclear magnetic resonance (NMR) relaxometry is applied over a wide frequency and temperature range to get insight into the dynamic processes occurring in the plastically crystalline phase of the two isomers cyanocyclohexane (CNCH) and isocyanocyclohexane. The spin-lattice relaxation rate, R1(ω), is measured in the 0.01-30MHz frequency range and transformed into the susceptibility representation χNMR ″ω=ωR1ω. Three relaxation processes are identified, namely, a main (α-) relaxation, a fast secondary (β-) relaxation, and a slow relaxation; they are very similar for the two isomers. Exploiting frequency-temperature superposition, master curves of χNMR ″ωτ are constructed and analyzed for different processes. The α-relaxation displays a pronounced non-Lorentzian susceptibility with a temperature independent width parameter, and the correlation times display a non-Arrhenius temperature dependence-features indicating cooperative dynamics of the overall reorientation of the molecules. The β-relaxation shows high similarity with secondary relaxations in structural glasses. The extracted correlation times well agree with those reported by other techniques. A direct comparison of FC NMR and dielectric master curves for CNCH yields pronounced difference regarding the non-Lorentzian spectral shape as well as the relative relaxation strength of α- and β-relaxation. The correlation times of the slow relaxation follow an Arrhenius temperature dependence with a comparatively high activation energy. As the α-process involves liquid-like isotropic molecular reorientation, the slow process has to be attributed to vacancy diffusion, which modulates intermolecular dipole-dipole interactions, possibly accompanied by chair-chair interconversion of the cyclohexane ring. However, the low frequency relaxation features characteristic of vacancy diffusion cannot be detected due to experimental limitations.

Probing calorimetric heat transfer phenomena in multi-nanophase substances: A case study of some over-stoichiometric nanoarsenicals

Thermochemical events recognized from heat flux DSC measurements involving dynamic and progressive step-cycling are identified in multi-nanophase substances exemplified by melt-quenched and nanomilling-derived AsxS100-x arsenicals enriched in As over As4S3 composition (As60S40, As62S38, As64S36). Thermal-alteration heat transfer in these alloys composed of normal- and plastic-crystalline phases supplemented by dual-nature amorphous substance are complicated by transformations in nanocrystalline dimorphite-type As4S3 and realgar-type As4S4 phases. Primary calorimetric events in the examined nanoarsenicals are shown to be as follows: (i) reduction in onset temperature from normal- (α′-As4S3) to plastic-crystalline (β-As4S3) phase; (ii) depression in pre-melting temperature of β-As4S3 phase; (iii) decrease in decomposition temperature of dimorphite-type phase supplemented by appearance of realgar-type β-As4S4 and amorphous phase, (iv) increase in crystallization temperature of β-As4S3 phase; (v) high-temperature shift in relaxation from liquid to stabilized heterogeneous state. The multiphase occurrence of nanoarsenicals results in unexpected increase in some heat transfer events detected in reheating modes.

Brillouin light scattering study of microscopic structure and dynamics in pyrrolidinium salt based ionic liquids

Pyrrolidinium salts based ionic liquids are known to be good ionic conductors even in solid-state around room temperature, which is attributed to the highly disordered plastic crystalline phase. Moreover, these salts are characterized by multiple phase transitions which include plastic, structural glass, and glassy crystal phases with varying levels of molecular disorder. Temperature-dependent Brillouin light scattering is used to investigate the phase transitions in a series of alkylmethylpyrrolidinium Bis(trifluoromethanesulfonyl) imides (P1nTFSI, n = 1,2,4). Brillouin spectral features such as the number of acoustic modes, their shape, and linewidths provide the picture of different disordered phases resultant of dynamics at the microscopic scale. The longitudinal and transverse acoustic velocities in different phases are determined from the corresponding acoustic mode frequencies (Brillouin shift). Extremely low acoustic velocities in the solid phase of P11TFSI and P12TFSI are a consequence of a high degree of disorder and plasticity present in these systems. Anomalous temperature-dependent behavior of linewidths and asymmetric (Fano) line shape of acoustic modes observed in certain phases of P1nTFSI could be due to the strong coupling between the Brillouin central peak and the acoustic phonons. The present results establish that the Brillouin light scattering technique can be efficiently used to understand the complex phase behavior, microscopic structure, and dynamics of ionic liquids.

Molecular dynamics and electrical conductivity of Guanidinium based ionic liquid crystals: Influence of cation headgroup configuration

Molecular mobility and conductivity of four bent shaped tetramethylated guanidinium based ionic liquid crystals (ILCs) with varying head group configuration (cyclic or acyclic) and alkyl chain length is investigated by a combination of broadband dielectric spectroscopy (BDS) and specific heat spectroscopy (SHS). Two dielectrically active processes observed in the plastic crystalline phase at low and high temperatures are denoted as γ and α1 relaxation. The former is assigned to localized fluctuations of methyl groups including nitrogen atoms in the guanidinium head groups. SHS investigations reveal one calorimetrically active process termed as α2 relaxation process. The temperature dependencies of the relaxation rates of α1 and α2 are similar for the cyclic ILC while for the acyclic counterpart they are different. Possible molecular assignments for the α1 and α2 relaxation are discussed in detail. Alongside relaxation processes, a significant conductivity contribution was observed for all ILCs, where the absolute value of DC conductivity increases by 4 orders of magnitude at the transition from the crystalline to the hexagonal columnar phase. The increase is traced to the change in the underlying conduction mechanism from the delocalized electrical conduction in the Cry phase to ionic conduction in the quasi 1D ion columns formed in the hexagonal columnar mesophase.

Plastic Crystal-to-Crystal Transition of Janus Particles under Shear.

Colloidal Janus spheres in the bulk typically spontaneously assemble into plastic crystalline phases, while particle orientations exhibit glasslike dynamics without long-range order. Through Brownian dynamics simulations, we demonstrate that shear can trigger a phase transition from an isotropic crystal with orientational disorder to an orientationally ordered crystal with lamellae along the shear direction. This nonequilibrium transition is accompanied with the orientational ordering following a nucleation and growth mechanism. By performing a phenomenological extension of free energy analysis, we reveal that the nucleation originates from the orientation fluctuations induced by shear. The growth of the orientationally crystalline cluster is examined to be disklike, captured by developing a lattice model with memoryless state functions. These findings bring new insights into the mechanisms for the ordering transition of anisotropic particles at nonequilibrium states.

1H and 13C NMR Studies on New Ionic Plastic Crystals Constructed by Ellipsoidal Cations with [BEt3Me] Anion

Abstract Two new ionic plastic crystals of [NEtMe2Pr][BEt3Me] and [NEt2MePr][BEt3Me] were found. In contrast, the highest-temperature solid-phase of [NEtMe2Bu][BEt3Me] and [NEt2MeBu][BEt3Me] were assigned to rotator phases. Solid-state 1H and 13C nuclear magnetic resonance (NMR) measurements revealed that both the cations and anions perform isotropic reorientations in the plastic phase. Conversely, the cations of [NEtMe2Bu] and [NEt2MeBu] undergo rotation about an axis. Based on these results, it is revealed that ellipsoidal cations of [NEtMe2Pr]+ and [NEt2MePr]+ can form plastic crystalline phases with [BEt3Me]−. In the lower temperature solid-phase of the plastic phase, a rotator phase was also found in [NEtMe2Pr][BEt3Me] and [NEt2MePr][BEt3Me] salts. This is rarely reported in alkylammonium compounds with [BEt3Me]. 1H NMR spin-lattice relaxation time (T1) measurements showed that activation energies of isotropic reorientation were slightly large when compared to those reported in other ionic plastic crystals constructed with globular cations. This difference can be explained by assuming the aspect ratio. On differential scanning calorimetry (DSC) charts, small entropy changes were recorded at melting points of four compounds. These results support the observation that cations and anions have large degrees of freedom of motion in the highest-temperature solid-phases (plastic and rotator phases).

UV-curable-based plastic crystal polymer electrolyte for high-performance all-solid-state Li-ion batteries

An all-solid-state polymer electrolyte has been prepared by polymerizing a monomer ethoxylated trimethylolpropane triacrylate (ETPTA) using ultraviolet irradiation (UV-curing) into crystal electrolyte (referred to as UV-PCCE) in this paper, which has the merit of outstanding interfacial compatibility with electrode materials. Otherwise, on account of the appearance of a unique plastic-crystalline phase, this polymer electrolyte presents a great electrochemical window (4.78 V vs Li/Li+) and a high ionic conductivity at ambient temperature. The cell of LiFePO4/UV-PCCE/Li displays a high initial discharge capacity of 147.1 mAh g−1 at 0.5 C and 118.0 mAh g−1 at a rate of 8.0 C at room temperature. At the same time, it may deliver a high initial discharge capacity of 150.0 mAh g−1 and the coulombic efficiency approximate 100% over 120 cycles at 2.0 C at 55 °C. Its superior performances demonstrate that the UV-PCCE-based electrolyte via an ultraviolet irradiation is applied to the actual, which can be used for high-performance lithium-ion batteries. This technology can also be compatible with existing lithium-ion battery equipment.

Dynamics of Dimethylbutanols in Plastic Crystalline Phases by Field Cycling 1H NMR Relaxometry.

2,2-Dimethylbutan-1-ol (2,2-DM-1-B), 3,3-dimethylbutan-1-ol (3,3-DM-1-B), and 3,3-dimethylbutan-2-ol (3,3-DM-2-B) show a rich solid-state polymorphism, which includes one or more plastic crystalline phases (also referred to as orientationally disordered crystalline (ODIC) phases) and glass of the liquid or ODIC phases. In this work, the dynamics of the three isomeric alcohols was investigated in the liquid and plastic crystalline phases by fast field cycling 1H NMR relaxometry in the temperature range between 213 and 303 K. The analysis of the nuclear magnetic relaxation dispersion curves (i.e., longitudinal relaxation rate R1 vs 1H Larmor frequency) acquired for the different alcohols at different temperatures gave quantitative information on internal motions, overall molecular reorientations, and molecular self-diffusion. Self-diffusion coefficients were also determined in the liquid phase and in some ODIC phases of the samples from the trends of 1H R1 as a function of the frequency square root at low frequencies. Remarkable changes in the temperature trends of correlation times and self-diffusion coefficients were found at the transition between the liquid and the ODIC phase for 2,2-DM-1-B and 3,3-DM-1-B, and between ODIC phases for 3,3-DM-2-B, the latter sample showing a markedly different dynamic and phase behavior.

Dynamics in the Plastic Crystalline Phases of Cyclohexanol and Cyclooctanol Studied by Quasielastic Neutron Scattering.

Plastic crystals are a promising candidate for solid state ionic conductors. In this work, quasielastic neutron scattering is employed to investigate the center of mass diffusive motions in two types of plastic crystalline cyclic alcohols: cyclohexanol and cyclooctanol. Two separate motions are observed which are attributed to long-range translational diffusion (α-process) and cage rattling (fast β-process). Residence times and diffusion coefficients are calculated for both processes, along with the confinement distances for the cage rattling. In addition, a binary mixture of these two materials is measured to understand how the dynamics change when a second type of molecule is added to the matrix. It is observed that, upon the addition of the larger cyclooctanol molecules into the cyclohexanol solution, the cage size decreases, which causes a decrease in the observed diffusion rates for both the α- and fast β-processes.

Crystal structures of ordered and plastic-crystalline phases of iso-butyllithium by X-ray powder diffraction

Donor-unsupported iso-butyllithium consists of hexamers with an ordered triclinic structure at -80 °C (α-phase). At ambient temperature, the compound exists as an orthorhombic, remarkably stable, plastic-crystalline γ-phase, which is built by disordered hexamers adopting a distorted face-centred cubic packing. Both structures were determined by X-ray powder diffraction. Additionally, an intermediate β-phase is observed.

Variation of ionic conductivity in a plastic-crystalline mixture.

Ionically conducting plastic crystals (PCs) are possible candidates for solid-state electrolytes in energy-storage devices. Interestingly, the admixture of larger molecules to the most prominent molecular PC electrolyte, succinonitrile, was shown to drastically enhance its ionic conductivity. Therefore, binary mixtures seem to be a promising way to tune the conductivity of such solid-state electrolytes. However, to elucidate the general mechanisms of ionic charge transport in plastic crystals and the influence of mixing, a much broader database is needed. In the present work, we investigate mixtures of two well-known plastic-crystalline systems, cyclohexanol and cyclooctanol, to which 1 mol. % of Li ions were added. Applying differential scanning calorimetry and dielectric spectroscopy, we present a thorough investigation of the phase behavior and the ionic and dipolar dynamics of this system. All mixtures reveal plastic-crystalline phases with corresponding orientational glass-transitions. Moreover, their conductivity seems to be dominated by the "revolving-door" mechanism, implying a close coupling between the ionic translational and the molecular reorientational dynamics of the surrounding plastic-crystalline matrix. In contrast to succinonitrile-based mixtures, there is no strong variation of this coupling with the mixing ratio.

The plastic crystalline A15 phase of dimethylaminoalane, [N(CH3)2-AlH2]3.

A plastic crystalline phase of dimethylaminoalane has been discovered at T > 332 K. The phase transitions solid - plastic phase - liquid are fully reversible. The plastic crystalline phase exhibits a cubic unit cell, space group Pm3[combining macron]n, in which the dimethylaminoalane molecules rotate and adopt a structural arrangement reminiscent of the A15 phase.

An All-Solid-State Electrochemical Double-Layer Capacitor Based on a Plastic Crystal Electrolyte

A plastic crystal, solid electrolyte was prepared by mixing tetrabutylammonium hexafluorophosphate salt, (C4H9)4NPF6, (10 molar %) with succinonitrile, SCN, (N C−CH2−CH2−C N), [SCN-10%TBA-PF6]. The resultant waxy material shows a plastic crystalline phase that extend from -36 °C up to its melting at 23 °C. It shows a high ionic conductivity reaching 4 × 10−5 S/cm in the plastic crystal phase (15 °C) and ~ 3 × 10−3 S/cm in the molten state (25 °C). These properties along with the high electrochemical stability rendered the use of this material as an electrolyte in an electrochemical double-layer capacitor (EDLC). The EDLC was assembled and its performance was tested by cyclic voltammetry, AC impedance spectroscopy and galvanostatic charge-discharge methods. Specific capacitance values in the range of 4-7 F/g. (of electrode active material) were obtained in the plastic crystal phase at 15 °C, that although compare well with those reported for some polymer electrolytes, can be still enhanced with further development of the device and its components, and only demonstrate their great potential use for capacitors as a new application.