Fast Ion Research Articles

Biexponential I = 3/2 Spin-Lattice Relaxation in the Solid State: Multiple-Quantum 7Li NMR as a Probe of Fast Ion Dynamics.

Spin-lattice relaxation measurements are used in 7Li NMR studies of materials of potential use in solid-state Li-ion batteries as a probe of ion mobility on a fast (nanosecond to picosecond) time scale. The relaxation behavior is often analyzed by assuming exponential behavior or, equivalently, a single T1 time constant. However, the spin-lattice relaxation of spin I = 3/2 nuclei, such as 7Li, is in general biexponential; this is a fundamental property of I = 3/2 nuclei and unrelated to any compartmentalization within the solid. Although the possibility of biexponential 7Li (and other I = 3/2 nuclei) spin-lattice relaxation in the solid state has been noted by a number of authors, it can be difficult to observe unambiguously using conventional experimental NMR techniques, such as inversion or saturation recovery. In this work, we show that triple-quantum-filtered NMR experiments, as previously exploited in I = 3/2 NMR of liquids, can be used in favorable circumstances to observe and readily quantify biexponential 7Li spin-lattice relaxation in solids with high ion mobility. We demonstrate a triple-quantum-filtered inversion-recovery experiment on the candidate solid electrolyte material Li2OHCl at 325 K, which has previously been shown to exhibit fast ion mobility, and we also introduce a novel triple-quantum-filtered saturation-recovery experiment. The results of these solid-state NMR experiments are less straightforward than those in liquids as a consequence of the unwanted direct excitation of triple-quantum coherences by the weak (compared with the unaveraged 7Li quadrupolar interaction) pulses used, but we show that this unwanted excitation can be accounted for and, in the example shown here, does not impede the extraction of the two 7Li spin-lattice relaxation times.

Fe2O3 nanoparticles encapsulated in the inner walls of integrated 3D carbon tube grid as high-performance anode for lithium-ion batteries

Ferric oxide (Fe2O3) holds huge potential as a promising anode material for lithium-ion batteries (LIBs) due to its high theoretical capacity and low cost, however, its battery performance is still limited by the intrinsic poor conductivity and huge volume variation during lithiation and de-lithiation processes. Herein, we developed a self-standing 3D interconnected vertical and lateral carbon tube (3D-CT) grid with Fe2O3 nanoparticles (NPs) encapsulated in the wall of CT (denoted as 3D-CT@Fe2O3-NPs@C), as structurally-integrated anode without any inactive components. The 3D-interconnected vertical and lateral CTs with open channels not only provide plenty of attachment sites for the Fe2O3 NPs and accommodate the strain generated by the volume variation of Fe2O3, but also facilitate the fast ions and electrons transfer. Therefore, the self-supported 3D-CT@Fe2O3-NPs@C electrode delivers superior cycling and high-rate performance with a high stable specific capacity of 896.2 mAh g−1 at the current density of 1.0 A g−1 after 700 cycles. Even at the high current density of 4.0 A g−1, a reversible capacity of 488.1 mAh g−1 can be reached based on the mass of the electrode. This study provides a facile and efficient strategy to improve the electrochemical performance of LIBs through the design of structurally-integrated grid electrode.

Rational Design of Naphthol Groups Functionalized Bipolar Polymer Cathodes for High Performance Alkali-Ion Batteries.

Redox-active organic compounds gather significant attention for their potential application as electrodes in alkali ion batteries, owing to the structural versatility, environmental friendliness, and cost-effectiveness. However, their practical applications of such compounds are impeded by insufficient active sites with limited capacity, dissolution in electrolytes, and sluggish kinetics. To address these issues, a naphthol group-containing triarylamine polymer, namely poly[6,6'-(phenylazanediyl)bis(naphthol)] (poly(DNap-OH)) is rationally designed and synthesized, via oxidative coupling polymerization. It is capable of endowing favorable steric structures that facilitate fast ion diffusion, excellent chemical stability in organic electrolytes, and additional redox-active sites that enable a bipolar redox reaction. By exploiting these advantages, poly(DNap-OH) cathodes demonstrate remarkable cycling stability in both lithium-ion batteries (LIBs) and potassium-ion batteries (PIBs), showcasing enhanced specific capacity and redox reaction kinetics in comparison to the conventional poly(4-methyltriphenylamine) cathodes. Overall, this work offers insights into molecular design strategies for the development of high-performance organic cathodes in alkali-ion batteries.

Tunnel-Oriented VO2 (B) Cathode for High-Rate Aqueous Zinc-Ion Batteries.

Tunnel-type vanadium oxides are promising cathodes for aqueous zinc ion batteries. However, unlike layer-type cathodes with adjustable layer distances, enhancing ion-transport kinetics in tunnels characterized by fixed sizes poses a considerable challenge. This study highlights that the macroscopic arrangement of the electrode crucially determines tunnel orientation, thereby influencing ion transport. By changing the material morphology, the tunnel orientation can be optimized to facilitate rapid ion diffusion. In a proof-of-concept demonstration, it is revealed that (00l) facets-dominated VO2 (B) nanobelts with dispersive morphology (VO2-D) tend to adopt a stacking pattern with directional ion transport along the c-axis on the electrode and guarantee fast ion diffusion. Compared with the aggregated sample (VO2-A) that tends to random arrangement on the electrode with isotropic and slow ion transfer behavior, the electrode featuring dispersive (00l) facets-dominated VO2 (B) nanobelts displays directional and fast ion diffusion behavior, thus exhibits an ultrahigh-rate performance (420.8 and 344.8 mAh g-1 at 0.1 and 10 A g-1, respectively) and long cycling stability (84.3% capacity retention under 5000 cycles at 10 A g-1). The results suggest that simultaneous manipulation of exposed crystal facet and morphology-related electrode arrangement should be promising for boosting the ion-transport kinetics in tunnel-type vanadium oxide cathodes.

Pyridine N‐Modulated Adsorption Equilibrium of Highly Dispersed Atomic W‐P Clusters toward Advanced Potassium‐Ion Hybrid Capacitors

AbstractImproving the atomic utilization of storage sites and developing isotropic transport characteristics become crucial to enhance the performance of potassium‐ion hybrid capacitors (PIHCs), and the disordered strategy and coordination modulation of the electrodes can satisfy the above structure‐activity requirements. Herein, the highly dispersed atomic W‐P clusters are chosen as a platform for the electronic restructuring. Studies and calculations indicate that replacing O in W‐O2/P2 with pyridine N can modulate the electron distribution and electronegativity, and enrich the edge‐dangling bonds of the amorphous clusters (W‐N2/P2), resulting in proper adsorption equilibrium and high affinity for K+ storage. In addition, the clusters have isotropic and bulk‐phase‐indifferent fast ion storage, and in situ protection of carbon nanosheets can provide stable support for ion storage and electron transfer in the clusters. As an anode, the composite (W‐N/P@C) exhibits superior storage properties of K+ (reversible capacity of 181.6 mAh g−1 after 3000 cycles at 5.0 A g−1), with high energy density (163.7 Wh Kg−1) at the high‐power output (3500 W Kg−1) in PIHCs. This work systematically delineates the effects of disordered design and pyridine N‐coordination on energy storage, and provides new research ideas for studying high‐performance PIHCs.

Hydride ion diffusion along grain boundaries in titanium nitride

Density functional theory (DFT) simulations are utilized to study the absorption and diffusion of hydride ions along four types of titanium nitride grain boundaries: open and compact structures of Σ5 (210)[001] and Σ5 (310)[001]. The absorption energy into bulk vacancies ranges from approx. −0.7 eV in TiN0.7 to −0.38 eV for a single vacancy in TiN, and shows a minor dependence on the hydrogen content in the structure. The absorption energy for vacancy sites at the grain boundaries ranges from −0.44 eV to −0.66 eV. Hydrogen absorption into interstitial sites at the grain boundaries is less favourable, in part due to a positive and fairly large zero-point energy contribution, with absorption enthalpies between −0.09 eV and 0.06 eV. The interstitial diffusion barriers are 1.34 eV and 0.83 eV in the open Σ5 (310) and Σ5 (210) grain boundaries, respectively. In the compact grain boundaries, the migrating hydrogen species changed oxidation state from a hydride ion (H0.5−) to a proton (H0.3+) at the transition state as it formed bonds to nitrogen along the diffusion path. The diffusion barriers are larger than in the corresponding open structures: 1.75 eV and 1.02 eV in the compact Σ5 (310) and Σ5 (210) structures, respectively. The considered grain boundaries and diffusion pathways cannot explain the fast interfacial hydride ion transport reported for hydrogen separation membranes based on TiNx thin films with columnar microstructure.

A bimetal strategy for suppressing oxygen release of 4.6V high-voltage single-crystal high-nickel cathode

High-voltage cathode materials, such as single-crystal high-nickel layered oxide materials, are a necessary condition for achieving high energy density lithium-ion batteries, but they have to be accompanied by the structural instability and irreversible release of lattice oxygen during operation, posing serious safety hazards. Here, to solve the lattice oxygen release issue of single-crystal high-nickel cathode, we propose an improved strategy for overall cathode by synchronously addressing interface and lattice instability, ensuring stable operation at a high voltage up to 4.6 V. By Al-doping, in the bulk phase, we intensify the charge transfer between transition metals and oxygen, and the columnar effect caused by doped atoms effectively alleviates internal strain, thereby significantly limiting lattice shrinkage and then suppressing oxygen release. On the other hand, the protective layer of LiNbO3 as the fast ion conductor formed at the cathode interface suppresses parasitic reactions and hinders lattice oxygen loss caused by dissolution of transition metals. Therefore, after 200 cycles at a cut-off voltage of 4.6 V, our cathode material still maintains a capacity retention rate of 89.1%. Density functional theory (DFT) calculations predict the effective suppression of oxygen release for the modified cathode materials, which has been further confirmed by differential electrochemical mass spectrometry (DEMS) tests. This work provides a new perspective for solving the problem of oxygen release under high cut-off voltage conditions for single crystal high nickel cathode.

In-situ cathode coating for all-solid-state batteries by freeze-drying technology

All solid-state batteries (ASSBs) are considered in the next generation of energy storage, but their active material ratio is low and cathode interface reactions are severe.To overcome these two challenges, a layer of fast ion conductor Li3InCl6 is in-situ synthesized to realize uniform coating on LiCoO2 surface by freeze drying technology, which effectively improves active material proportions/ion transportation capability in the cathode, and prevents interfacial degradation between sulfide solid electrolyte and LiCoO2. The resultant Li-anode ASSBs show excellent electrochemical performances, including 7000 cycles at 20 C (9.4 mA/cm2), unprecedented current rates of 70 C and high loading of 15 mAh/cm2 (110 mg/cm2). The ASSB achieved an energy density of 340 Wh/kg. These encouraging results make future practical applications of high-energy-density ASSB with high cathode loadings and fast-charging capabilities possible.

Halide Superionic Conductors with Non‐Close‐Packed Anion Frameworks

AbstractHalide superionic conductors (SICs) are drawing significant research attention for their potential applications in all‐solid‐state batteries. A key challenge in developing such SICs is to explore and design halide structural frameworks that enable rapid ion movement. In this work, we show that the close‐packed anion frameworks shared by traditional halide ionic conductors face intrinsic limitations in fast ion conduction, regardless of structural regulation. Beyond the close‐packed anion frameworks, we identify that the non‐close‐packed anion frameworks have great potential to achieve superionic conductivity. Notably, we unravel that the non‐close‐packed UCl3‐type framework exhibit superionic conductivity for a diverse range of carrier ions, including Li+, Na+, K+, and Ag+, which are validated through both ab initio molecular dynamics simulations and experimental measurements. We elucidate that the remarkable ionic conductivity observed in the UCl3‐type framework structure stems from its significantly more distorted site and larger diffusion channel than its close‐packed counterparts. By employing the non‐close‐packed anion framework as the key feature for high‐throughput computational screening, we also identify LiGaCl3 as a promising candidate for halide SICs. These discoveries provide crucial insights for the exploration and design of novel halide SICs.

Halide Superionic Conductors with Non-Close-Packed Anion Frameworks.

Halide superionic conductors (SICs) are drawing significant research attention for their potential applications in all-solid-state batteries. A key challenge in developing such SICs is to explore and design halide structural frameworks that enable rapid ion movement. In this work, we show that the close-packed anion frameworks shared by traditional halide ionic conductors face intrinsic limitations in fast ion conduction, regardless of structural regulation. Beyond the close-packed anion frameworks, we identify that the non-close-packed anion frameworks have great potential to achieve superionic conductivity. Notably, we unravel that the non-close-packed UCl3-type framework exhibit superionic conductivity for a diverse range of carrier ions, including Li+, Na+, K+, and Ag+, which are validated through both ab initio molecular dynamics simulations and experimental measurements. We elucidate that the remarkable ionic conductivity observed in the UCl3-type framework structure stems from its significantly more distorted site and larger diffusion channel than its close-packed counterparts. By employing the non-close-packed anion framework as the key feature for high-throughput computational screening, we also identify LiGaCl3 as a promising candidate for halide SICs. These discoveries provide crucial insights for the exploration and design of novel halide SICs.

Electron distribution near the fast ion track in silicon

A model is proposed to describe the distribution of electrons near the track of a fast ion. The dependence of the fast electron flux on time, layer depth, and radial variable is modeled taking into account the statistical weight of each trajectory. It has been found that the pulse duration in the electron flux distribution is fractions of picoseconds, and the radial size of the cylindrical region where fast electrons are transported reaches tens of angstroms.

MARS-F/K modeling of plasma response and fast ion losses due to RMP in KSTAR

The toroidal single-fluid magnetohydrodynamic (MHD) code MARS-F (Liu et al 2000 Phys. Plasmas 7 3681) and the MHD-kinetic hybrid code MARS-K (Liu et al 2008 Phys. Plasmas 15 112503) are utilized to study the plasma response to the n = 1 (n is the toroidal mode number) resonant magnetic perturbation (RMP), applied to suppress the type-I edge localized mode (ELM) in a KSTAR discharge. Both the resistive-rotating and ideal-static plasma models identify strong screening of the resonant radial field harmonics of the applied RMP due to the plasma response, and predict a strong edge-peeling response of the plasma which is consistent with the optimal ELM control coil current configuration adopted in experiment. The RMP-induced radial displacement of the plasma, computed by the resistive-rotating plasma model, agrees reasonably well with that reconstructed from the measured data in the plasma core. Taking into account the drift kinetic response of fast ions, MARS-K hybrid modeling also finds quantitative agreement of the plasma core fluid pressure perturbation with experiment. Based on the MARS-F computed plasma response, a guiding-center orbit-tracing simulation finds about 0.3% of fast ion losses due the n = 1 RMP in the KSTAR ELM control experiment considered. Most losses are associated with counter-current fast ions located near the plasma edge.

Real-time control of NBI fast ions, current-drive and heating properties

Conventionally, neutral beam injection (NBI) in tokamaks is controlled via engineering parameters such as injection voltage and power. Recently, the high-fidelity real-time NBI code RABBIT has been coupled to the discharge control system of ASDEX Upgrade. It allows to calculate the NBI fast-ion distribution and hence the properties of NBI in real-time, making it possible to control them directly. We successfully demonstrate control of driven current, ion heating and stored fast-ion energy by modifying the injected beam power. A combined ECRH and NBI controller is also successfully tested, which is able to adjust the heating mix between ECRH and NBI to match a certain desired ion heating fraction at given total power. Further experiments have been carried out towards control of the ion heat flux (i.e. ion heating plus collisional heat transfer between ions and electrons). They show good initial success, but also leave room for future improvements as the controller runs into instabilities at too high requests.

Experimental issues of energy balance in open magnetic trap

The paper presents an overview of experimental results of an investigation of different energy loss channels in the gas dynamic trap (GDT), which is a magnetic mirror plasma confinement device in the Budker Institute of Nuclear Physics. Energy losses along magnetic field lines are considered as well as losses onto radial limiters, which restrict the plasma column radius and provide its magnetohydrodynamic stability via the ‘vortex confinement’ mechanism. The losses along the field lines were measured using a set of pyroelectric bolometers on the plasma absorber and the losses onto the limiters were determined with thermistors from their temperature rise. Additionally, the losses due to charge exchange of fast plasma ions on the residual neutral gas in the GDT were measured using a longitudinal array of pyroelectric bolometers mounted on the wall of the central cell. An attempt was made to draw up the energy balance in the GDT in order to identify the predominant loss channels and reduce those losses in the future.

Understanding the Inorganic‐Rich Feature of Anion‐Derived Solid Electrolyte Interphase

AbstractAnion‐derived solid‐electrolyte interphase (SEI) has received growing attention owing to its appealing properties like fast ion transport and excellent passivation effect. However, a sophisticated understanding of anion‐derived SEI is lacking. To common wisdom, anion‐derived SEI features an inorganic‐rich composition. Herein, it is reveal that the freshly formed anion‐derived SEI consists of a polymer‐rich outer layer and an inorganic inner layer. Then, the organic components dissolve during the discharge process, while the inorganic species with low solubility are retained in the empty SEI husk. The accumulation of empty SEI husks during cycling forms a reacted lithium (Li) layer, which features a much higher content of anion‐derived inorganic species than the newly formed SEI. Therefore, the acknowledged “anion‐derived inorganic‐rich SEI” actually refers to the reacted Li layer instead of the freshly formed SEI. This work provides fruitful insights on the compositional features of anion‐derived SEI.

Antimony Doping Enabled Radially Aligned Microstructure in LiNi0.91Co0.06Al0.03O2 Cathode for High‐Voltage and Low‐Temperature Lithium Battery

AbstractNi‐rich layered oxide cathode material with Ni contents greater than 90% is considered as a highly promising candidate for lithium‐ion batteries (LIBs) owing to its remarkable specific capacity and cost‐efficiency. However, severe capacity degradation caused by the structural collapse and interfacial instability with electrolyte under high voltage greatly hinders the practical application. Here, an antimony (Sb)‐doped LiNi0.91Co0.06Al0.03O2 (Sb‐NCA91) cathode is proposed, where the Sb doping modifies the morphology of primary particles and enables the radially aligned microstructure. This unique microstructure can disperse the anisotropic mechanical stress caused by the H2‐H3 phase transformation, and mitigate the shrinkage and expansion of the primary particles during high‐voltage and low‐temperature cycling, thus inhibiting the formation of microcracks and structural deterioration. Meanwhile, the closely arranged radial spokes allow fast ion transport in the secondary particles and effectively improve the rate performance and low‐temperature performance of the cathodes. As a result, the Sb modified cathode demonstrates superior capacity retention of ≈84% at 1 C after 200 cycles in 2.7–4.5 V at 25 °C, while the pristine NCA91 cathode only retains ≈79%. Additionally, the capacity retention at −20 °C is significantly increased from ≈61% (NCA91) to ≈88% (Sb‐NCA91) after 100 cycles.

Tailoring moldy-mulberry-derived carbons for ionic liquid-based supercapacitors with ultrahigh energy density

Developing low cost and renewable materials for energy storage is becoming critical for modern society. Biomass-derived porous carbons are promising candidates for constructing high-performance supercapacitors and batteries. To overcome challenges such as the low energy density of carbon, herein three-dimensional interconnected N/P/O co-doped hierarchical porous carbon is fabricated from moldy mulberry/melamine mixture, which possesses a large specific surface area, enhanced surface wettability and fast ions transportation. The thus-improved microstructural properties of N/P/O co-doped carbon boost their supercapacitive performances in aqueous and ionic liquid electrolytes, where specific capacitance of 340 F g−1 at 1.0 A g−1 in KOH solution and capacitance retention of 95.0 % after 25,000 cycles are achieved. Symmetric supercapacitors assembled with such carbon electrodes produce an energy density of 15.5 Wh kg−1 at the power density of 162.3 W kg−1 in KOH solution, and an ultrahigh energy density of 147.6 Wh kg−1 at 900 W kg−1 in EMIMBF4 electrolyte. DFT calculations illustrate that the high N/P doping enhances the electrical conductivity and promotes binding sites for EMIM+ adsorption, hence greatly boosting their supercapacitive capability. These gratifying results demonstrate the feasibility of significantly enhancing electrochemical properties of biomass-derived hierarchical porous carbons with a simple and scalable doping method.

Investigating the role of edge neutrals in exciting tearing mode activity and achieving flat temperature profiles in LTX-β

We present observations, numerical simulations, and analysis from experiments in the Lithium Tokamak Experiment-Beta (LTX-β) in which the electron temperature profile (Te (r)) shifts from flat to peaked and a tearing mode is also destabilized when the average density (ne ave ) exceeds ∼1019 m−3. Flat Te (r) is obtained routinely in LTX-β, with a lithium coated, low-recycling first wall, once the external fueling is stopped and density decays [Boyle et al 2023 Nucl. Fusion 63 056020]. In the present experiment, flat Te profiles can be sustained while maintaining constant ne ave below a line averaged density threshold (ne ave th ) of ∼1019 m−3. Above ne ave th, Te (r) shifts from flat to peaked and a tearing mode is destabilized. Due to low recycling, the achieved ne ave can be controlled precisely by external fueling and hence, a certain threshold of the edge neutral inventory from the external fueling is experimentally manifested through ne ave th . The goal of the present work is to investigate the role of edge neutrals in determining Te (r) and MHD stability in the unique low-recycling regime of LTX-β. Our hypothesis is that the peaking of Te (r) beyond ne ave th is due ultimately to the edge cooling by the cold neutrals beyond a critical fueling flux. At lower fueling flux, flat Te (r) results in broader pressure profile and lower resistivity, which in turn stabilizes the tearing mode. This hypothesis is supported by edge neutral density estimation by DEGAS 2 code. Mode analysis by singular value decomposition confirms the tearing mode structure to be m/n = 2/1 (m and n being the poloidal and toroidal mode numbers). Linear tearing stability analysis with M3D-C1 predicts that plasmas with ne ave > 1019 are highly susceptible to a n = 1 tearing mode. ORBIT simulations, however, confirmed that the tearing modes do not contribute to the loss of fast ions from neutral beam injection. This study shows for the first time that the neutral inventory at the edge could be one of the deciding factors for the achievability of the unique operation regime of flat Te (r) and the excitation of tearing activity that could be disruptive for the plasmas.

In Situ Construction of LiF-Li3N-Rich Interface Contributed to Fast Ion Diffusion in All-Solid-State Lithium-Sulfur Batteries.

All-solid-state lithium-sulfur batteries (ASSLSBs) have attracted wide attention due to their ultrahigh theoretical energy density and the ability of completely avoiding the shuttle effect. However, the further development of ASSLSBs is limited by the poor kinetic properties of the solid electrode interface. It remains a great challenge to achieve good kinetic properties, by common strategies to substitute sulfur-transition metal and organosulfur composites for sulfur without reducing the specific capacity of ASSLSBs. In this study, a sulfur-(Ketjen Black)-(bistrifluoromethanesulfonimide lithium salt) (S-KB-LiTFSI) composite is constructed by introducing LiTFSI into the S-KB composite. The initial discharge capacity reaches up to 1483 mA h g-1, benefited from the improved ionic conductivity and diffusion kinetics of the S-KB-LiTFSI composite, where numerous LiF interphases with a Li3N component are in situ formed during cycling. Combined with DFT calculations, it is found that the migration barriers of LiF and Li3N are much smaller than that of the Li6PS5Cl solid electrolyte. The fast ionic conductors of LiF and Li3N not only enhance the Li+ transfer efficiency but also improve the interfacial stability. Therefore, the assembled ASSLSBs operate stably for 600 cycles at 200 mA g-1, and this study provides an effective strategy for the further development of ASSLSBs.

Metal organic framework MOF-74 based solid-state electrolytes for all-solid-state sodium metal batteries

The all-solid-state sodium metal batteries (ASSMBs) are highly promising for their low cost. MOFs have emerged as potential solid electrolyte materials due to their abundant pores and open metal-active sites, enabling fast ion conduction. In this study, a solid electrolyte membrane Na/Mg-MOF-74 was synthesized using a simple method. The stable ion-conducting channel of Mg-MOF-74 contributed to the excellent electrochemical performance of ASSMBs coupled with Na/Mg-MOF-74 electrolyte, including high ionic conductivity (8.53 × 10−4 S cm−1 at 70 °C) and a wide potential window (1–4.3 V). This study represents the first utilization of Mg-MOF-74 for ASSMBs, marking a significant milestone in the field.