Fast Ion Research Articles

Strain Engineering of Ion-Coordinated Nanochannels in Nanocellulose.

Expanding the interlayer spacing plays a significant role in improving the conductivity of a cellulose-based conductor. However, it remains a challenge to regulate the cellulose nanochannel expanded by ion coordination. Herein, starting from multiscale mechanics, we proposed a strain engineering method to regulate the interlayer spacing of the cellulose nanochannels. First-principles calculations were conducted to select the most suitable ions for coordination. Large-scale molecular dynamics simulations were performed to reveal the mechanism of interlayer spacing expansion by the ion cross-linking. Combining the shear-lag model, we established the relationship between interfacial cross-link density and interlayer spacing of an ion-coordinated cellulose nanochannel. Consequently, fast ion transport and current regulation were realized via the strain engineering of nanochannels, which provides a promising strategy for the current regulation of a cellulose-based conductor.

Perfect confinement of crown ethers in MOF membrane for complete dehydration and fast transport of monovalent ions.

Fast transport of monovalent ions is imperative in selective monovalent ion separation based on membranes. Here, we report the in situ growth of crown ether@UiO-66 membranes at a mild condition, where dibenzo-18-crown-6 (DB18C6) or dibenzo-15-crown-5 is perfectly confined in the UiO-66 cavity. Crown ether@UiO-66 membranes exhibit enhanced monovalent ion transport rates and mono-/divalent ion selectivity, due to the combination of size sieving and interaction screening effects toward the complete monovalent ion dehydration. Specifically, the DB18C6@UiO-66 membrane shows a permeation rate (e.g., K+) of 1.2 mol per square meter per hour and a mono-/divalent ion selectivity (e.g., K+/Mg2+) of 57. Theoretical calculations and simulations illustrate that, presumably, ions are completely dehydrated while transporting through the DB18C6@UiO-66 cavity with a lower energy barrier than that of the UiO-66 cavity. This work provides a strategy to develop efficient ion separation membranes via integrating size sieving and interaction screening and to illuminate the effect of ion dehydration on fast ion transport.

Influence of sawtooth oscillations on fast ions in a stellarator

Sawtooth oscillations in tokamaks frequently lead to the redistribution of energetic ions, mainly on passing orbits, causing their expulsion from the core. This paper discusses the first measurements of the interaction of fast ions and sawteeth in the Large Helical Device. The crashes were caused by the plasma current induced by Electron Cyclotron Current Drive and Neutral Beam Current Drive. Despite these crashes, there was no detectable redistribution effect on fast ions in either the core or at the edge of the plasma.

Velocity-space distribution function of fast ions in a sawtoothing plasma

Abstract This study explores the influence of sawtooth oscillations on the velocity space distribution of fast ions in tokamak plasma discharges. The relevant Fokker-Planck equation for fast ions is solved analytically. Two distinct effects arising from the temperature drop associated with a sawtooth crash and their impact on the distribution function of fast ions are considered. The first effect involves the modulation of the fusion alpha particle source on the timescale of the sawtooth period, linked to the drop in fusion yield resulting from the sawtooth temperature relaxations. The second effect is tied to the increase of the slowing-down time during the sawtooth ramp, causing particles born later in the sawtooth cycle to experience reduced slowing down compared to those born right after the crash, creating an accumulation-like mechanism at higher energies.
In regimes where the sawtooth period is shorter than the fast ion slowing-down time, the combined influence of these effects gives rise to fast ion distribution functions that transiently exhibit positive slopes in velocity space.

Numerical simulations on loss of ICRF-heated NBI ions in EAST

Abstract The loss of ICRF-heated NBI ions in EAST tokamak was numerically investigated by ORBIT code simulations. The effects of collisions and ripples on particle losses taken into account, and the distributions of fast ions generated by different beams in combination with ICRF heating were calculated using the TRANSP code. Results showed that ICRF waves altered the orbital distributions of beam ions, causing an increase in trapped ions and fast ion losses. Additionally, for co-current injected beams, perpendicular injection resulted in higher fast ion losses in synergistic heating than tangential injection. The study also found that the synergistic effect of collisions and ripples enhanced fast ion losses, which were highly localized and generated a maximum heat load of 0.165 MW/m2 on the first wall. However, conducting synergy heating experiments at high plasma currents and low effective ion charge numbers can significantly reduce the loss of fast ions.

Alkali-Ion-Assisted Activation of ε-VOPO4 as a Cathode Material for Mg-Ion Batteries.

Rechargeable multivalent-ion batteries are attractive alternatives to Li-ion batteries to mitigate their issues with metal resources and metal anodes. However, many challenges remain before they can be practically used due to the low solid-state mobility of multivalent ions. In this study, a promising material identified by high-throughput computational screening is investigated, ε-VOPO4, as a Mg cathode. The experimental and computational evaluation of ε-VOPO4 suggests that it may provide an energy density of >200Whkg-1 based on the average voltage of a complete cycle, significantly more than that of well-known Chevrel compounds. Furthermore, this study finds that Mg-ion diffusion can be enhanced by co-intercalation of Li or Na, pointing at interesting correlation dynamics of slow and fast ions.

Discovering the Order-Disorder Transition in Quinoline Intercalated Vanadium Oxide with Superior Calcium Storage via Polyhedral Distortion.

Calcium-ion batteries (CIBs) are considered as potential next-generation energy storage systems due to their abundant reserves and relatively low cost. However, irreversible structural changes and weak conductivity still hinder in current CIBs cathode materials. Herein, an organic molecular intercalation strategy is proposed, in which V2O5 regulated with quinoline, pyridine, and water molecules are studied as cathode material to provide fast ion diffusion channels, large storage host, and high conductivity for Ca ions. Among them, V2O5-quinoline (QVO) owns the largest interplanar spacing of 1.25 nm and the V-O chains are connected with organic molecular by hydrogen bond, which stabilizes the crystal structure. As a result, QVO exhibits a specific capacity of 168 mAh g-1 at 1 A g-1 and capacity retention of 80% after 500 cycles at 5 A g-1 than the other materials. Furthermore, X-Ray diffraction and X-ray absorption spectroscopy results reveal a reversible order-disorder transformation mechanism of Ca2+ for QVO, which can make full use of the abundant active sites for high capacity and simultaneously achieve fast reaction kinetics for excellent rate performance. These results demonstrate that QVO is a promising cathode material for CIBs, providing more choices for the development of high-performance CIBs.

Hydrated Calcium Vanadate Nanoribbons with a Stable Structure and Fast Ion Diffusion as a Cathode for Quasi-Solid-State Zinc-Ion Batteries.

We demonstrated the use of hydrated calcium vanadate (CaV6O16·3H2O, denoted as CaVO-2) as a cathode for aqueous zinc-ion batteries (AZIBs). Nanoribbons of hydrated calcium vanadate facilitated shortening of the Zn2+ transport distance and accelerated zinc-ion insertion. The introduction of interlayer structure water increased the interlayer spacing of calcium vanadate and as a "lubricant". Ca2+ insertion also expanded the interlayer spacing and further stabilized the interlayer structure of vanadium-based oxide. The density functional theory results showed that the introduction of Ca2+ and structured water could effectively improve the diffusion kinetics, resulting in the rapid transport of zinc ions. As a result, AZIBs based on the CaVO-2 cathode offered high specific capacity (329.6 mAh g-1 at 200 mA g-1) and fast charge/discharge capability (147 mAh g-1 at 10 A g-1). Impressively, quasi-solid-state zinc-ion batteries based on the CaVO-2 cathode and polyacrylamide-cellulose nanofiber hydrogel electrolytes maintained an outstanding specific capacity and long cycle life (162 mAh g-1 over 10 000 cycles at 5 A g-1). This study provided a reliable strategy for metal-ion insertion and the structural water introduction of oxides to produce a high-quality cathode for ZIBs. Meanwhile, it provides ideas for the combination of vanadium-based materials and gel electrolytes to construct solid-state zinc-ion batteries.

Synergistic Cathode Design for High-Performance Dual-Salt Magnesium/Lithium-Ion Batteries Using 2D/2D 1T/2H-MoS2@Ti3C2Tx MXene Nanocomposite.

Magnesium-ion batteries (MIBs) and dual-salt magnesium/lithium-ion batteries (MLIBs) have emerged as promising contenders for next-generation energy storage. In contrast to lithium metal anode in lithium metal batteries, magnesium metal anode in MIBs and MLIBs presents a safer alternative due to the limited dendrite growth and higher volumetric capacity, along with higher natural abundance. This study explores a MLIB configuration with a novel cathode design by employing a 2D/2D nanocomposite of 1T/2H mixed phase MoS2 and delaminated Ti3C2Tx MXene (1T/2H-MoS2@MXene) to address challenges associated with slow kinetics of magnesium ions during cathode interactions. This cathode design takes advantage of the high electrical conductivity of Ti3C2Tx MXene and the expanded interlayer spacing with enhanced conductivity of the 1T metallic phase in 1T/2H mixed phase MoS2. Through a designed synthesis method, the resulting nanocomposite cathode maintains structural integrity, enabling the stable and reversible storage of dual Mg2+ and Li+ ions. The nanocomposite cathode demonstrates superior performance in MLIBs compared to individual components (253 mAh g-1 at 50 mA g-1, and 36% of capacity retention at 1,000 mA g-1), showcasing short ion transport paths and fast ion storage kinetics. This work represents a significant advancement in cathode material design for cost-effective and safeMLIBs.

Isofield plasma expansion in kJ petawatt laser-driven ion acceleration with a tailored fast electron temperature

Kilojoule-class relativistic intensity lasers, having multi-picosecond (ps) pulse durations, enable efficient ion acceleration in the interaction with thin foil targets. The foil plasma expands under the laser energy input over picoseconds where fast electrons keep increasing their effective temperature, while they convert a part of the energy into fast ions through generation of a sheath electric field. The temporal evolution of the sheath electric field is the key to understanding the efficient ion acceleration seen in kJ-class laser experiments. Here, we extend the non-isothermal plasma expansion model by introducing a temporal function of the effective temperature of fast electrons to obtain the sheath electric field in the expanding plasma. We theoretically derived that when the effective temperature of fast electrons increases in proportional to the square of the time, the strength of the sheath electric field is kept constant without depletion during the expansion. This ‘isofield’ expansion is confirmed by a quasi-one-dimensional particle-in-cell simulation. The isofield expansion results in a high energy ion acceleration with a small expansion length, which is favorable for realizing an efficient ion acceleration with less lateral energy loss in multi-dimensional situations.

Eliminating lithium dendrites via dependable ion regulation of charged nanochannels

Reviving lithium metal anode is of great significance to developing high-energy-density batteries after addressing the lithium dendrite. Constructing functional separator with charged nanochannel configuration has been proven to be an effective way to inhibit nucleation of lithium dendrites due to the achievement of a fast and selective lithium ion transport. While the ion regulation capability of existing functional separators cannot be maximized because their nanochannels are much larger than the electric double layer (EDL) regions that dominate ion transport. Considering the tiny EDL thickness (∼1 nm) formed in the electrolyte, the sulfonate-rich covalent organic framework (COF) is developed as functional separator to achieve a dependable ion regulation based on the nano-confined channel (∼1.55 nm) and surface negative charges. Consequently, a high Li+ transference number tLi+ (0.85) and sufficient ionic conductivity (0.53 mS cm−1) are obtained simultaneously, which effectively alleviates dendrite nucleation and growth of lithium metal anode for over 1000 h. Moreover, the principle for fast and selective lithium-ion transport is revealed from a new perspective of EDL region embedded in the nanochannel. Overall, this work demonstrates a strategy to eliminate lithium dendrites via ion regulation of charged nanochannels, which is anticipated to promote the practical application of lithium metal batteries.

Chitosan-derived large surface area porous carbon via Microphase separation engineering of pore-regulation and Nitrogen-doping coupling for high-performance supercapacitors

In the face of the contradiction between the shortage of fossil raw materials, global warming and growing energy demand, it is of great practical significance to apply biomass, which is widely available in nature, environmentally friendly and renewable, to energy storage. Based on the coupling mechanism of pore-regulation and N-doping, this study implements pre-carbonization through microphase separation engineering in the chitosan (CS) and aniline (AN) co-hydrothermal. Using hydrochar as the precursor, porous carbon with good electrochemical properties has been prepared by a multi-step process consisting of KOH activation, pyrolysis, pickling and water washing. The CS/AN co-doped porous carbons (1830.08-2576.53 m2/g) show an enhancement of 8.48%-52.73% in specific surface area compared to the CS porous carbon (1687.02 m2/g). The hierarchical network structure of the micro-mesoporous interconnects enables fast ion transport and the ultra-micropores further increase the specific capacitance of the electrodes. Theoretical calculation shows that N doping can effectively activate the chemically inert carbon structure and enhance the adsorption capacity of electrolyte ions, thus increasing the specific capacitance. Using 6 M KOH as the electrolyte, CS-AN60-220-800 exhibits a specific capacitance of 368.6 F/g (1.0 A/g) in the three-electrode system. In the two-electrode system, the supercapacitor device constructed with CS-AN60-220-800 demonstrates a capacitance retention of 95.32% (after 10,000 cycles) along with an energy density of 14.16 Wh/kg (with a power density of 125 W/kg), which is at a high level among similar biomass symmetric supercapacitors. The preparation strategy provides a valuable reference for the preparation of other biomass-based porous carbon, as well as for applications in energy storage.

Synergy of structural engineering and VO2 self-transformation enables ultra-high areal capacity cathodes for zinc-ion batteries

The development of cathodes with high areal capacities is a prerequisite for realizing the practical application of zinc-ion batteries (ZIBs). However, the slow ion (de)intercalation kinetics and the highly tortuous ion transport channels in the traditionally blade-coated electrodes limit the practical areal capacities of the ZIB cathodes below 3 mAh cm−2. In this work, multi-stage pore structures, including through-holes perpendicular to the electrode and submicron-scale channels along the radial direction of the printed filaments, are obtained through polyvinylidene difluoride (PVDF) phase separation assisted 3D printing procedure. In this novel electrode material, the porous network enables fast electron/ion transport and improves the accessibility of active materials for thick electrodes with high active material loadings. More importantly, a phase self-transformation of VO2 to a high oxidation state of V5O12∙6H2O is achieved by regulating the charging voltage, which significantly enhances the zinc storage capacity and provides smoother channels for fast ion (de)intercalation. With these unique features, the 3D printed VO2 cathode with a mass loading of 8.9 mg cm−2 demonstrates a high specific capacity of 478.1 mAh g−1 at 1 A g−1 and a stable life cycle for 1000 cycles at 4 A g−1. When the mass loading is increased to 29.6 mg cm−2, the electrode is still able to deliver an ultra-high areal capacity of 16.8 mAh cm−2. The strategies adopted in this work greatly boost up the performance of VO2 cathodes, especially the high areal capacity, by combining structural engineering and material activity regulation.

Investigation of fast ion effects on core turbulence in FIRE mode plasmas

Further investigation of fast ion effects on turbulence and transport in the fast ion regulated enhancement (FIRE) mode discharge (Han et al 2022 Nature 609 269–275) was performed in this work as a continuation of a previous study (Kim et al 2023 Nucl. Fusion 63 124001) that showed that the dominant turbulence suppression mechanism by fast ions is the dilution effect in the FIRE mode discharge. The current study includes (i) the impact of the fast ion relevant mode observed in the simulation of thermal energy flux, (ii) dilution effects by fast ions compared to dilution effects by other species, and (iii) fast ion effects on electron-scale turbulence. First, nonlinear gyrokinetic simulation results show that turbulence is significantly suppressed even without the fast ion relevant mode, indicating that the impact of this mode on thermal transport is not significant in this discharge. Second, further analysis on the dilution effects shows the three following results: Turbulence is not completely suppressed by the reduced main ion density fraction effect due to impurities; the reduction in energy flux can be limited by a certain impurity mode that is destabilized by a high impurity density gradient from adjusting the main ion density gradient; electrons can contribute to turbulence suppression through the main ion density gradient change, although this effect is less significant compared to other species. Third, we observe that two fast ion effects can influence the linear growth rate of the electron-scale turbulence mode. The growth rate decreases by an increase in β∗(≡(−8π/B2)dp/dr) and increases by dilution effects, suggesting that fast ion effects on electron-scale turbulence can differ depending on the operation scenario, such as the fast ion fraction. The comprehensive analysis performed in this study can enhance our understanding of fast ion physics, required for burning plasma operation in the future.

Bio-Inspired Electrodes with Rational Spatiotemporal Management for Lithium-Ion Batteries.

Lithium-ion batteries (LIBs) are currently the predominantenergy storage power source. However, the urgent issues of enhancing electrochemical performance, prolonging lifetime, preventing thermal runaway-caused fires, and intelligent application are obstacles to their applications. Herein, bio-inspired electrodes owning spatiotemporal management of self-healing, fast ion transport, fire-extinguishing, thermoresponsive switching, recycling, and flexibility are overviewed comprehensively, showing great promising potentials in practical application due to the significantly enhanced durability and thermal safety of LIBs. Taking advantage of the self-healing core-shell structures, binders, capsules, or liquid metal alloys, these electrodes can maintain the mechanical integrity during the lithiation-delithiation cycling. After the incorporation of fire-extinguishing binders, current collectors, or capsules, flame retardants can be released spatiotemporally during thermal runaway to ensure safety. Thermoresponsive switching electrodes are also constructed though adding thermally responsive components, which can rapidly switch LIB off under abnormal conditions and resume their functions quickly when normal operating conditions return. Finally, the challenges of bio-inspired electrode designs are presented to optimize the spatiotemporal management of LIBs. It is anticipated that the proposed electrodes with spatiotemporal management will not only promote industrial application, but also strengthen the fundamental research of bionics in energy storage.

CuGa2 transition phase anchored liquid GaSn achieves high-performance liquid metal battery cathode

Severe volume expansion will cause the gallium-based liquid metal cathode material to detach from the collector thus deteriorating performance. Here, we propose a strategy for preparing electrodes by anchoring the liquid metal with an intermetallic compound transition phase to avoid the problem of liquid metal shedding during cycling. The good reactive wetting between the CuGa2 transition phase and gallium can firmly anchor the liquid metal to prevent the electrode material exfoliating from the collector. On the other hand, the unique two-dimensional layer structure of CuGa2 can also limit the lithiation volume expansion of liquid gallium. Density functional theory (DFT) reveals the anchoring mechanism of the CuGa2 transition layer to liquid gallium and the reaction mechanism of Li with CuGa2 during the electrochemical reaction. As a result, O-GaSn/CF cathodes exhibit low resistance, fast ion diffusion, high reversible capacity, excellent rate performance and outstanding cycling stability.

Asymmetric capacitive deionization based on pore structures of biochar

Biochar is an affordable and sustainable material for the application of capacitive deionization. Although the desalination capability of biochar is significantly impacted by its pore size distribution, the correlation between them is challenging to explore due to the uncontrollable pore size. This study exclusively utilizes different activation mechanisms to regulate the pore size distribution of carbon derived from the same biomass precursor, and explores the role of pore structures in capacitive deionization. The specific capacitance of microporous biochar (MiB) can reach up to 319.1 F/g (0.2 A/g), with an Epzc of 0.11 V and high oxygen content, while mesoporous biochar (MeB) has a specific capacitance of only 170.4 F/g, an Epzc of 0 V, and a small charge transfer impedance. The MeB//MiB desalination cell is designed based on these characteristics and demonstrates a higher salt adsorption capacity of 17.04 mg/g at 1.2 V, compared to MiB//MiB (15.72 mg/g) and MeB//MeB (6.07 mg/g), alongside a stability of 81 % after 50 cycles. These capabilities can be attributed to the expanded voltage range resulting from the different Epzc, and the high ion storage capacity of MiB, as well as the fast ion transport capability of MeB. The oxygen/carbon ratio of the anode in MeB//MiB increased by only 42 %, whereas that in MiB//MiB increased by 370 %, confirming the oxidation inhabitation ability of the asymmetric structure and the oxidation resistance of MeB. Therefore, constructing ideal pore structures and more importantly reasonable deployment is an effective strategy for improving desalination capacity and stability.

Can large lattice volume always facilitate ion diffusion in solids?

Large lattice volume is usually expected to expand the bottleneck size and enlarge free volume for fast Li ion transport in solids. But the universality of lattice expansion decreasing activation energy barrier for Li ion migration is still debatable. Herein, our molecular dynamics simulations and density functional theory calculations detect the unconventional phenomenon of lattice expansion increasing activation energy barrier for Li ion migration in β-Li3PS4, Li4SnS4 and Li4GeS4 sulfides with the hcp-type anion sublattice, and discover the underlying mechanism. On one hand, lattice expansion enlarges the relative energies between the octahedral and tetrahedral Li sites, and correspondingly increase activation energy barrier for tetrahedral Li ions migration along the Tet-Oct-Tet migration paths in β-Li3PS4, Li4SnS4 and Li4GeS4. On the other hand, the lattice dynamics calculations show Li energy landscapes of β-Li3PS4, Li4SnS4 and Li4GeS4 are anharmonic and enlarging lattice volume make the local minimum of Li potential energy surface flatter, simultaneously reduce the relative energy of Li occupation site, eventually resulting in the higher activation energy barrier for Li ion migration. Thus, understanding the effect of lattice volume on ion migration in solids should not only consider the factor of bottleneck size and free volume, but also combine the aspects of Li ion occupation type, Li ion migration path and anion sublattice type. These new understandings of the lattice expansion increasing activation energy barrier for ion migration would further promote the further optimization and rational design of superionic conductors by element doping or strain engineering.

Dual-Cation CuAgSe-Based Material: Rapid Mass Transfer in Synthesis and High Thermoelectric Performance Realization.

Understanding mass transfer mechanisms is vital for developing new material synthesis and densification technologies. Ion transport, serving both mass and charge transfer, is essential for the rapid preparation of high-performance fast ionic conductor thermoelectric materials like Zn4Sb3 and Cu2Q (Q = S, Se). In the case of dual-cation fast ion conductor materials like CuAgSe, exploring the relationship between cation transport becomes pertinent. In this study, copper (Cu) and selenium (Se) undergo a reaction in the presence of an electric field (∼15 A), resulting in the formation of the CuSe compound. Subsequent to this initial reaction, a subsequent thermal environment facilitates the interaction among Cu, CuSe, and Ag2Se, culminating in the rapid formation and densification of CuAgSe (with a relative density exceeding 99%) in just 30 s. Evidently, the diffusion of copper ions substantiates a pivotal role in facilitating mass transfer. As a result, CuAg1+xSe samples with different silver contents (x = 0.01, 0.02, 0.03, 0.04 and 0.05) can effectively inhibit cation vacancy, and introduce highly ordered Ag nanotwins to enhance the electrical transport performance. For CuAg1.04Se, a peak ZT value of 1.0 can be achieved at 673 K, which is comparable to the literatures. This work will guide the future electric field-assisted rapid mass transfer of materials.

High-entropy layer assisting quasi-zero-strain cathodes for P2-Na2/3Ni1/3Mn2/3O2

Layered transition metal oxides have attracted much attention for high-energy density sodium ion batteries. However, most P2-type layered oxides undergo a large volume change when they are charged at a deep desodiated state, accompanied by inevitable anisotropic stress, leading to poor structural stability and terrible ion transfer. In this work, a high entropy (HE) material with a robust structure and fast ion transportation was decorated on P2-Na2/3Ni1/3Mn2/3O2 (NM) layered oxides. The unique characteristics of HE shells with similar lattice constants could effectively depress particle crack and exfoliation through buffering severe lattice strains, thus leading to enhanced cycling stability and kinetic properties of the HE-NM electrode. In situ x-ray diffraction analysis confirms that the volume expansion of NM could be prominently restrained both under thermal treatments and electrochemical after HE decoration. The modified cathode exhibits a volume change as low as 0.5%. The findings highlight the significance and superiority of the HE coating layer and provide insight for the rational design of high-performance sodium-ion batteries.