Complex Phase Transitions Research Articles

First-principles investigation of phase stability in layered NaxCrO2

Layered oxide intercalation compounds continue to attract interest as electrode materials for Na-ion batteries. However, many of these materials undergo complex phase transitions during cycling that influence battery performance but are still not completely understood. We have conducted a first-principles study of layered ${\mathrm{Na}}_{x}{\mathrm{CrO}}_{2}$ $(0\ensuremath{\le}x\ensuremath{\le}1)$ to assess phase stability between various Na-vacancy ordered phases in the O3 and P3 host structures. We predict that many of the low-energy phases belong to families of Na orderings that follow specific patterns. At high $x$, we identify families of vacancy row orderings in O3, which may also couple to magnetic orderings of the Cr spins. We predict similar orderings at intermediate $x$ in P3 that contain antiphase boundaries between regions of the $x=1/2$ ordering. In both cases, the average spacing between rows/boundaries is set by the overall composition. At $x=0$, we find a strong preference for charge disproportionation and migration of Cr to tetrahedral sites in the intercalation layers. We obtain generally good agreement with experimental observations and rationalize key discrepancies.

Study of Synergistic Effects of Cu and Fe on P2-Type Na0.67MnO2 for High Performance Na-Ion Batteries.

P2-type Na0.67MnO2 with a stable structure and an open framework can provide numerous channels for fast Na+ de/intercalation, for which it is considered to be advantageous in application of the cathode material for Na-ion batteries. However, the complex phase transition occurring during cycling and the lattice distortion triggered by the Jahn-Teller effect severely restrict its development. Herein, the modified Na0.67MnO2 with Cu or Fe single-element doping as well as Cu and Fe double-element doping was synthesized by the sol-gel method, and the effects of doping on the crystal structure and electrochemical performances of Na0.67MnO2 were studied. It was demonstrated that the phase of the material did not change after the introduction of Cu and Fe elements, and the cycling stability and rate performance were greatly improved by Cu and Fe double-doping owing to their synergistic effect. The Na0.67Mn0.92Fe0.04Cu0.04O2 (NMFCO) cathode delivers discharge specific capacities of 110.5 mA h g-1 at 5 C and 91.8 mA h g-1 at 10 C and exhibits the high-capacity retention of 94.35% at 1 C and 90.68% at 5 C after 100 cycles. Overall, this study offers a guiding direction for accelerating the modification of P2-type Na0.67MnO2 as a cathode active material for high performance Na-ion batteries.

Stabilizing Lattice Oxygen in Slightly Li-Enriched Nickel Oxide Cathodes Toward High-Energy Batteries

LiNiO2 (LNO, 100% Ni) is an old material first identified in the early 1990s (as a higher-capacity and lower-cost alternative to LiCoO2) but has yet to fulfill its potential. Despite intense research efforts for more than two decades, LNO still exhibits rapid capacity loss during cycling and poor thermal stability (1-3). The traditional LNO is generally prepared by solid-state reactions and recognized as Li-deficient Li1-yNi1+yO2 (4). Ex situ characterizations indicated that the performance degradation originates from the detrimental phase transition (layered to rock-salt structure) during electrochemical cycling (5-7), which is closely related to the lattice-oxygen release during charge (8, 9). To improve the performance of LNO, the structure is commonly modified by lattice doping or surface coating, which have led to improved cycle stability but at the cost of capacity loss (10). Meanwhile, these modification approaches failed to address the lattice oxygen instability, as the O2 release was still detected for the doped or surface-coated layered cathodes (11, 12).Here, we demonstrate an Li-enrichment strategy to produce a trigonal-structured layered Li-enriched LNO (Li1.04Ni0.96O2, LR-LNO) with a slight excess of Li to occupy the Ni sites, which is a possible phase according to the Li-Ni-O phase diagram but has never been experimentally synthesized (Figure 1). LR-LNO (Figure 1) enables a combination of a high specific energy density of 904 Wh kg-1, outstanding cyclability (~80% capacity retention after 400 cycles in full cells versus 35 cycles for LNO), and significantly enhanced thermal stability (>70 °C increase in thermal-runaway temperature over LNO).We further designed a double-tilt electrochemical liquid cell inside a transmission electron microscope (TEM) to track the local structural changes at the surface of individual particles during galvanostatic cycling (Figure 2), revealing the performance-enhancing mechanism behind the slight change in the material composition. Excess Li ions in the Ni layer promoted intralayer migration of Ni ions during delithiation in LR-LNO, generating vacancy clusters to trap the electrochemically oxidized molecular O2 in the near-surface lattice. Consequently, the oxygen redox reaction became highly reversible, and the detrimental layered-to-rock-salt phase transition are effectively inhibited, thus improving the structural reversibility of LR-LNO during cycling and the thermal stability.Our results provide a composition fine-tuning strategy to produce highly-reversible cathodes for high energy-density, low-cost and safe batteries. Beyond batteries, the double-tilt operando TEM technique will facilitate studies into complex phase transitions in a wide range of materials. Figure 1 Pristine structure and outstanding performance of LR-LNO References M. M. Thackeray, K. Amine, Layered Li–Ni–Mn–Co oxide cathodes. Nature Energy 6, 933-933 (2021). A. Manthiram, J. B. Goodenough, Layered lithium cobalt oxide cathodes. Nature Energy 6, 323-323 (2021). K. Turcheniuk, D. Bondarev, V. Singhal, G. Yushin, Ten years left to redesign lithium-ion batteries. Nature 559, 467-470 (2018). J.-H. Kim, K.-J. Park, S. J. Kim, C. S. Yoon, Y.-K. Sun, A method of increasing the energy density of layered Ni-rich Li[Ni1−2xCoxMnx]O2 cathodes (x = 0.05, 0.1, 0.2). Journal of Materials Chemistry A 7, 2694-2701 (2019). C. S. Yoon, D.-W. Jun, S.-T. Myung, Y.-K. Sun, Structural stability of LiNiO2 cycled above 4.2 V. ACS Energy Lett. 2, 1150-1155 (2017). D.-W. Jun, C. S. Yoon, U.-H. Kim, Y.-K. Sun, High-energy density core-shell structured Li[Ni0.95Co0.025Mn0.025]O2 cathode for lithium-ion batteries. Chem. Mater. 29, 5048-5052 (2017). C. S. Yoon, M. H. Choi, B. B. Lim, E. J. Lee, Y.-K. Sun, Review—high-capacity Li[Ni1-xCox/2Mnx/2]O2 (x = 0.1, 0.05, 0) cathodes for next-generation Li-ion battery. J. Electrochem. Soc. 162, A2483-A2489 (2015). N. Li et al., Unraveling the cationic and anionic redox reactions in a conventional layered oxide cathode. ACS Energy Lett. 4, 2836-2842 (2019). S. S. Zhang, Problems and their origins of Ni-rich layered oxide cathode materials. Energy Storage Materials 24, 247-254 (2020). M. Bianchini, M. Roca-Ayats, P. Hartmann, T. Brezesinski, J. Janek, There and back again-the journey of LiNiO2 as a cathode active material. Angew. Chem., Int. Ed. 58, 10434-10458 (2019). N. Li et al., Correlating the phase evolution and anionic redox in Co-Free Ni-Rich layered oxide cathodes. Nano Energy 78, (2020). F. Strauss et al., Li2ZrO3-Coated NCM622 for Application in Inorganic Solid-State Batteries: Role of Surface Carbonates in the Cycling Performance. ACS applied materials & interfaces 12, 57146-57154 (2020). Figure 1

Improved electrochemical performance of B doped O'3-NaMnO2 for Na-ion battery

O'3-NaMnO2 possesses a high theoretical capacity due to its high initial sodium content as a cathode material in Na-ion batteries. However, complex phase transition from O'3 to P3, even to O1 phase caused by the gliding of layered structure occurred during Na extraction, leads to the collapse of the layered structure, and causes loss of battery capacity. To improve the structural stability of layered O'3-NaMnO2 cathode, the electrochemically inert B3+ with good affinity for oxygen was selected to substitute the Mn3+ in O'3-NaMnO2 and a series of O'3-NaBxMn1-xO2 (x=0, 0.05, 0.1, 0.15, 0.25) oxides were obtained by optimized preparation methods. The average effective radius of the transition-metal layer is reduced after B doping, making the structure more stable. At the same time, B inhibits the Jahn-Teller distortion caused by Mn3+. Among them, NaB0.1Mn0.9O2 shows improved cycle and rate performance. In-situ XRD and EIS results reveal that the enhanced electrochemical performance is resulted from the higher structure reversibility than O'3-NaMnO2.

MEAM interatomic potential for thermodynamic and mechanical properties of lithium allotropes

Li has relatively simple electronic structure but exhibits complex allotropic phase transitions. Atomistic modeling is important to reveal thermodynamic and mechanical properties at grain and interface scales in multi-phase Li. However, extant interatomic potentials have limited accuracy in reproducing properties in the FCC, BCC and HCP phases of Li. Here, we develop a new interatomic potential for multi-phase Li using the classical MEAM approach. The new potential is fit to key properties of all three phases based on both extant and new DFT calculations. An extensive range of simulations are performed to validate the new potential. Good accuracy and transferability are demonstrated in all three phases and over a wide range of temperatures. The current potential is thus suitable for modeling both thermodynamic and mechanical behavior of Li and can be applied generally in a wide range of applications.

The dispersion and propagation of topological Langmuir-cyclotron waves in cold magnetized plasmas

The topological Langmuir-cyclotron wave (TLCW) is a recently identified topological surface excitation in magnetized plasmas. We show that TLCW originates from the topological phase transition at the Langmuir wave-cyclotron wave resonance. By isofrequency surface analysis and two- and three-dimensional time-dependent simulations, we demonstrate that the TLCW can propagate robustly along complex phase transition interfaces in a unidirectional manner and without scattering. Because of these desirable features, the TLCW could be explored as an effective mechanism to drive current and flow in magnetized plasmas. The analysis also establishes a close connection between the newly instituted topological phase classification of plasmas and the classical Clemmow-Mullaly-Allis (CMA) diagram of plasma waves.

Precisely modulating the structural stability and redox potential of sodium layered cathodes through the synergetic effect of co-doping strategy

Although P2-type Na0.67Ni0.33Mn0.67O2 (NNMO) is a promising cathode material for sodium-ion batteries (SIBs), it usually suffers from complex phase transition, multiple ordering rearrangements, and irreversible oxygen loss upon electrochemical cycling, incurring rapid voltage decay and capacity degradation. Herein, a novel optimization strategy with simultaneous modulation of the crystal and electronic structure of NNMO is realized through Zn/Cu synergistic doping. It is revealed that partial substitution of Ni with inert Zn possessing similar ionic radii but different Fermi levels suppresses the unfavorable phase transition and disrupts the Na+/vacancy ordering, while active Cu doping not only elevates the redox potential but also alleviates the irreversible oxygen redox through reinforced orbital hybridization. Moreover, the cooperation of Zn and Cu inhibits the Ni/Mn ordering distribution, thereby promoting the Na+ transportation kinetics. Benefiting from the cooperative advantages, the resultant Na0.67Ni0.21Mn0.67Cu0.05Zn0.07O2 exhibits a complete solid-solution reaction upon cycling, a high operating voltage of 3.65 V with a low decay rate of 0.48 mV per cycle, and a superior rate capability of 84.1 mAh/g at 20 C. This work demonstrates the promise of co-doping strategy for optimizing the structural stability and redox potential from the atomic and orbital levels to construct high-energy cathode materials for SIBs.

Ion Substitution Strategy of Manganese-Based Layered Oxide Cathodes for Advanced and Low-Cost Sodium Ion Batteries.

Sodium ion batteries (SIBs) have recently been promising in the large-scale electric energy storage system, due to the low cost, abundant sodium resources. Mn-based layered oxide cathode materials have been widely investigated, because of the high theoretical specific capacity, low cost, and abundant reserves. However, their development is limited by the problems of Jahn-Teller distortion, Na+ /vacancy ordering, complex phase transitions, and irreversible anionic redox during cycling. Ion substitution strategy is one simple and effective way to regulate the crystal structure and boost sodium-storage performances of Mn-based cathode materials. In this review, we summarize the progress and mechanism of ion-substituted Mn-based oxides, establish a composition-crystal structure-electrochemical performance relationship, and also offer perspectives for guiding the design of high-performance Mn-based oxides for SIBs.

Controlling Phase Transition toward Future Low-Cost and Eco-friendly Printing of Perovskite Solar Cells.

Perovskite solar cells (PSCs) have grown increasingly popular over the past few years and are considered to be game-changers in the energy conversion market. It has became vital to transfer the deep understanding of the perovskite film formation process during lab-scale fabrication to large-scale production. Complex phase transition during film formation has been revealed by in situ strategies. However, there is still debate which phase transition is the right route for a future scalable approach. Herein, we briefly summarize perovskite crystallization during scalable printing processes. The critical information about the intermediates involved in phase transition from precursors to perovskite crystals are discussed because it deeply impacts the morphology of printed films. Finally, important strategies to control phase transition and challenges toward future low-temperature and eco-friendly printing of perovskite solar cells are proposed. The information provided by this Perspective will assist the screening and development of the perovskite phase transition for future cost-efficient printed perovskite panels.

Temperature-induced electride transition in dense lithium

As a prototypical light metal, lithium shows various and intriguing behaviors including electride character under high pressure. It has a pronounced melting line depression from 40 to 60 GPa, yet a precise and detailed understanding of this melting minimum remains elusive. Here, using computations that include metadynamics, crystal structure searching, and molecular dynamics with machine learned potentials, we demonstrate a temperature-induced electride (pocketlike to tubelike) transition accompanied by complex structural phase transitions in dense premelting lithium. The possible rearrangement of nearest neighbors from three-coordinated net to dimers and the premelting collective atomic motion affected by this electronic transition demonstrates the combined influence of temperature and electronic structure on the high-pressure behaviors of metals.

Effect of bed shrinkage on iron ore sintering process

There exist complex chemical reactions and phase transition processes—melting and solidification—in the iron ore sintering process. This will result in bed shrinkage and has an important impact on the sintering process and sinter properties. Numerical simulation was carried out in this paper, and it is based on the porous medium and double-energy equation model, coupled with the porosity shrinkage model. The influence of bed shrinkage on the sintering process was explored and revealed by comparing the calculation results, considering and neglecting bed shrinkage. The results indicate that bed shrinkage has less influence on the highest temperature in the area above 0.15 m of the sintered bed but it severely decreases by about 60 K below 0.15 m. Bed shrinkage makes the thickness of the combustion zone reduce by about 1.367, 1.398, and 4.367 cm at 500, 1000, and 1500 s, respectively. Bed shrinkage reduces the vertical sintering velocity, and the highest temperature of flue gas decreased by 77 K approximately; in addition, it also has a delay of 50 s to reach the highest temperature. The volume concentration of SO2 in the flue gas remains unchanged considering bed shrinkage, but it has a delay of about 50 s to reach the maximum value.

Cyanostilbene‐Based AIEgen Smart Film: Optical Switching by Engineering Molecular Packing Structure and Molecular Conformation Through Thermal and Photoinduced Monotropic Phase Transition

AbstractThe optical properties of newly synthesized cyanostilbene‐based AIEgen (D4CS) exhibiting a unique monotropic phase transition are modulated by engineering molecular packing structure and molecular conformation through temperature change and light irradiation. D4CS exhibits only a low‐ordered smectic liquid crystal (SmA) phase over a wide temperature range during cooling and subsequent heating processes, while D4CS crystallizes after a significantly long annealing time at room temperature. Crystallized D4CS exhibits a complex phase transition (SmCr–SmB–SmA–Iso) in the subsequent heating process. In addition, the photoisomerization behavior of D4CS from trans to cis conformer can induce a phase transition to the isotropic (Iso) state, and the reverse isomerization can occur by high‐temperature heat treatment. This unique thermal and photoinduced phase transition of D4CS is accompanied by changes in optical properties including transmittance and luminescence. Based on the optical switching behavior of D4CS, photopatternable temperature and time‐dependent optical films are demonstrated. The newly developed cyanostilbene‐based AIEgen is a smart optical material with great potential for advanced optical sensors, anti‐counterfeiting ink and smart display system.

Laser induced 3D porous graphene dots: Bottom-up growth mechanism, multi-physics coupling effect and surface wettability

One-step conversion of three-dimensional (3D) porous laser-induced graphene (LIG) from carbon precursors opens a facile way to prepare graphene-related materials. Herein, a series of dots is fabricated by CO2 laser irradiation of polyimide (PI, Kapton) films to investigate the in-situ growth mechanism of LIG. Complex phase transitions combined with various physical fields lead to morphologic changes from mastoid to volcanic structure. The cross-section profile varying with laser parameters are fitted to measure the physical characteristics (e.g., top/bottom width, depth, and tilt angle) under Gauss energy distribution. With considering the highly localized heating effect and non-uniform thermal stress, a coupled physical field is established to theoretically analyze the temperature, thermal stress and deformation distribution. The micro-scale spatial effects such as nucleation, growth, escape and explosion of bubbles in the air flow field are responsible for the 3D porous structure of LIG. Inspired by the “lotus effect”, a superhydrophobic dot matrix is manufactured with static contact angle of 151.5 ± 1.3° and roll-off angle of 15.7 ± 1.2°, laying a foundation for large-scale production of LIG.

Synthesis, thermal behavior in oxidative and pyrolysis conditions, spectroscopic and DFT studies of some alkaline earth metals p-aminobenzoate complexes using TG-DTA, DSC, PXRD and EGA (TG-FTIR) techniques

p-aminobenzoic acid is a substance widely used in several areas, such as catalysis, biomarkers, magnetic materials, luminescent materials and biological applications. p-aminobenzoate complexes with alkaline earth metal were synthesized and the thermal and pyrolysis behavior was studied using thermoanalytical and spectroscopic techniques. Based on TG/DTG-DTA and EGA results, the thermal decomposition mechanisms of the compounds were proposed under both atmospheres studied. The main gaseous products identified by EGA in both study conditions were H2O, Aniline, CO and CO2. From DSC analysis, it was possible to measure the enthalpies of dehydration and evaluate the phase transitions of the magnesium complex. FTIR data suggest that metal-ligand coordination occurs through carboxylate group by different ways. The coordination modes suggested by experimental FTIR data were supported by DFT study. The X-ray diffraction powder patterns show that the barium compound was obtained in amorphous state, while the other compounds have a crystalline structure.

Hierarchical O3/P2 heterostructured cathode materials for advanced sodium-ion batteries

O3-type layered materials are considered as promising cathode materials for advanced sodium-ion batteries owing to their low cost and high energy density. However, resultant cathodes undergo complex phase transitions and severe electrochemical corrosion during cycling, causing rapid capacity decay. To overcome these limitations, a heterostructured cathode, consisting of P2-Na2/3MnO2–coated O3-NaNi0.5Mn0.5O2 that combines a high-capacity core and structurally stable shell, is rationally designed. A half cell with an optimized heterostructured cathode yields a high reversible capacity of 141.4 mA h g−1 at 0.1 C and exhibits excellent rate capability, with a capacity of 103.7 mA h g−1 at 15 C. In addition, the surface-modified cathode also shows improved cycling stability in both Na half cell (i.e. 85.3% capacity retention after 150 cycles at 1 C) and full cell systems (i.e. 83.6% capacity retention after 200 cycles at 3 C). The protective P2-Na2/3MnO2 layer not only enhances the reversibility and air/thermal stability of the cathode, but also improves the electrochemical kinetics and reduces the charge transfer resistance. Hence, the sodium storage performance of O3-NaNi0.5Mn0.5O2 is greatly improved by employing the proposed heterostructure design approach, which can be extended to other Mn-based layered oxide cathode materials.

Thermo‐ and Mechano‐Triggered Luminescence ON/OFF Switching by Supercooled Liquid/Crystal Transition of Platinum(II) Complex Thin Films

AbstractTrihexyltetradecylphosphonium (P6,6,6,14) salts of luminescent anionic Pt(II) complexes, (P6,6,6,14)[PtX2(ppy)] (X = Cl‐, Br‐; ppy = 2‐phenylpyridinate), are synthesized and photofunctional thin films with crystal/liquid bi‐stability are fabricated. In particular, the chloride complex provides a thin film exhibiting thermo‐ and mechano‐triggered luminescence ON/OFF switching at ambient temperature, which is based on the control of the supercooled liquid phase and bright luminescent crystalline phase. The photophysical properties of the complexes are investigated and compared with those of the bromide complex and tetra(n‐butyl)ammonium salts of the complexes. Furthermore, detailed photophysical analysis reveals a large contribution of the charge‐transfer character to the ligand‐centered 3π π* excited state, which results in intense phosphorescence in the crystal and high‐contrast luminescence ON/OFF by the phase transition of the chloride complex.

A Complex Network Clustering and Phase Transition Models for Stock Price Dynamics before Crashes

Researchers from multiple disciplines have tried to understand the mechanism of stock market crashes. Precursory patterns before crashes agree with various empirical studies published by econophysicists, namely the prolific work of Didier Sornette. We intend to add more empirical evidence of synchronization of trading and demonstrate the prospect of predicting stock market crashes by analyzing clusters’ dynamics in the period of bubble build-up leading to a crash. We apply the Potential-based Hierarchical Agglomerative (PHA) Method, the Backbone Extraction Method, and the Dot Matrix Plot on S&P500 companies daily returns. Our innovative approach is proposed in this paper, empirical results and discussion presented in another publication.

Multi-dimensional correlation of layered Li-rich Mn-based cathode materials

Lithium-rich manganese-based cathode materials are expected to promote the commercialization of lithium-ion batteries to a new stage by virtue of their ultrahigh specific capacity and energy density advantages. However, they are still restricted by complex phase transitions and electrochemical performance degradation caused by labile anion charge compensation. A deep understanding of the electrochemical properties contained in their intrinsic structures and the key driving factors of structural deterioration during cycling are crucial to guide the preparation and optimization of lithium-rich materials. Considering recent progress, this review introduces the intrinsic properties of Li-rich manganese-based cathode materials from interatomic interactions to particle morphology at multiple scales in the spatial dimension. The charge compensation mechanism and energy band reorganization of the initial charge and discharge, the structural evolution during cycling and the electrochemical reaction kinetics of the materials are analyzed in the temporal dimension. Based on the relationship between structure and electrochemical performance, preparation methods and modification methods are introduced to guide and design cathode materials. Effective characterization methods for studying anion charge compensation behavior are also demonstrated. This review provides important guidance and suggestions for making full use of the high specific capacity in these materials derived from anion redox and the maintaining of its stability.

Synthesis of heat exchanger network with complex phase transition based on pinch technology and carbon tax

The aim of this paper is to integrate carbon emissions into the synthesis of heat exchanger network for an industrial process with a four-stage pyrolysis gas compression cycle and depropanizers. Problem table is used to determine the pinch point for the design of heat exchanger network. Due to the complex phase transition of the mixture in the system, the phase transition is considered as a pseudo-stream with constant heat capacity flow rate according to its thermal load and material characteristics within several individual temperature intervals. The contribution of carbon tax is also introduced to the total annual cost to determine the suitable minimum approach temperature(△Tmin). Compared with traditional pinch point method, △Tmin is determined as 8°C instead of 9°C due to the consideration of carbon emission. The pinch point is obtained at 80.15°C for hot streams and 72.15°C for cold streams, under which the minimum hot and cold utilities required by the heat exchanger network are 28046.89 kW and 69324.05kW respectively. The total annual cost is saved by 4,446,559 USD.a−1 and the carbon emission is reduced by 96689.31t/a. Results indicate that the consideration of carbon emissions based on carbon tax is helpful to obtain a better heat exchanger network in terms of total annual cost and energy efficiency on the way to carbon neutrality.

Solvent-induced reversible high-temperature phase transition in crown ether clathrates

The phase transitions of crown ether complexes with molecular motor motion triggered by the solvent-induced effect are reported.