Excellent Comprehensive Performance of Na‐Based Layered Oxide Benefiting from the Synergetic Contributions of Multimetal Ions

Na‐ion batteries are promising for large‐scale energy storage applications, but few cathode materials can be practically used because of the significant difficulty in synthesizing an electrode material with superior comprehensive performance. Herein, an effective strategy based on synergetic contributions of rationally selected metal ions is applied to design layered oxides with excellent electrochemical performances. The power of this strategy is demonstrated by the superior properties of as‐obtained NaFe_0.45Co_0.5Mg_0.05O₂ with 139.9 mA h g^?1 of reversible capacity, 3.1 V of average voltage, 96.6% of initial Coulombic efficiency, and 73.9 mA h g^?1 of capacity at 10 C rate, which benefit from the synergetic effect of Fe³⁺ (high redox potential), Co³⁺ (good kinetics), and inactive Mg²⁺ with compatible radii (stabilizing structure). Moreover, it is clarified that the superior property is not the simple superposition of performance for layered oxides with single metal ions. With the assistance of density functional theory calculations, it is evidenced that the wide capacity range (>70%) of prismatic Na⁺‐occupied sites during sodiation/desodiation is responsible for its high rate performance. This rational strategy of designing high‐performance cathodes based on the synergetic effect of various metal ions might be a powerful step forward in the development of new Na‐ion‐insertion cathodes.     

Revealing the Intercalation Mechanisms of Lithium,Sodium, and Potassium in Hard Carbon

Hard carbon is the most promising anode material for sodium‐ion batteries and potassium‐ion batteries owing to its high stability, widespread availability, low‐cost, and excellent performance. Understanding the carrier‐ion storage mechanism is a prerequisite for developing high‐performance electrode materials; however, the underlying ion storage mechanism in hard carbon has been a topic of debate because of its complex structure. Herein, it is demonstrated that the Li⁺‐, Na⁺‐, and K⁺‐ion storage mechanisms in hard carbon are based on the adsorption of ions on the surface of active sites (e.g., defects, edges, and residual heteroatoms) in the sloping voltage region, followed by intercalation into the graphitic layers in the low‐voltage plateau region. At a low current density of 3 mA g^–1, the graphitic layers of hard carbon are unlocked to permit Li⁺‐ion intercalation, resulting in a plateau region in the lithium‐ion batteries. To gain insights into the ion storage mechanism, experimental observations including various ex situ techniques, a constant‐current constant‐voltage method, and diffusivity measurements are correlated with the theoretical estimation of changes in carbon structures and insertion voltages during ion insertion obtained using the density functional theory.     

Boosting Sodium Storage in TiF3/Carbon Core/Sheath Nanofibers through an Efficient Mixed‐Conducting Network

Sodium‐ion batteries (SIBs) are considered to be promising energy storage devices for large‐scale grid storage application due to the vast earth‐abundance and low cost of sodium‐containing precursors. Designing and fabricating a highly efficient anode is one of the keys to improve the electrochemical performance of SIBs. Recently, fluoride‐based materials are found to show an exceptional anode function with high theoretical specific capacity, based on open‐framework structure enabling Na insertion and also exhibiting improved safety. However, fluoride‐based materials suffer from sluggish kinetics and poor capacity retention essentially due to low electric conductivity. Here, an efficient mixed‐conducting network offering fast pathways is proposed to address these issues. This network relies on titanium fluoride?carbon (TiF₃?C) core/sheath nanofibers that are prepared via electrospinning. Such highly interconnected electrodes exhibit an enhanced and faster sodium storage performance. Carbon sheath nanofibers are key to an efficient ion‐ and electron‐conducting network that enable Na⁺/e^? transfer to reach the nanosized TiF₃. In addition, in‐situ‐converted Ti and NaF particles embedded in the carbon matrix allow high reversible interfacial storage. As a result, the TiF₃?C core/sheath electrode exhibits a high capacity of 161 mAh g^?1 at a high current density of 1000 mA g^?1 over 2000 cycles.     

Native Vacancy Enhanced Oxygen Redox Reversibility and Structural Robustness

Cathode materials with high energy density, long cycle life, and low cost are of top priority for energy storage systems. The Li‐rich transition metal (TM) oxides achieve high specific capacities by redox reactions of both the TM and oxygen ions. However, the poor reversible redox reaction of the anions results in severe fading of the cycling performance. Herein, the vacancy‐containing Na_4/7[Mn_6/7(?_Mn)_1/7]O₂ (?_Mn for vacancies in the Mn? O slab) is presented as a novel cathode material for Na‐ion batteries. The presence of native vacancies endows this material with attractive properties including high structural flexibility and stability upon Na‐ion extraction and insertion and high reversibility of oxygen redox reaction. Synchrotron X‐ray absorption near edge structure and X‐ray photoelectron spectroscopy studies demonstrate that the charge compensation is dominated by the oxygen redox reaction and Mn³⁺/Mn⁴⁺ redox reaction separately. In situ synchrotron X‐ray diffraction exhibits its zero‐strain feature during the cycling. Density functional theory calculations further deepen the understanding of the charge compensation by oxygen and manganese redox reactions and the immobility of the Mn ions in the material. These findings provide new ideas on searching for and designing materials with high capacity and high structural stability for novel energy storage systems.     

Construction of Hierarchical K1.39Mn3O6 Spheres via AlF3 Coating for High‐Performance Potassium‐Ion Batteries

Potassium‐ion batteries are attracting great interest for emerging large‐scale energy storage owing to their advantages such as low cost and high operational voltage. However, they are still suffering from poor cycling stability and sluggish thermodynamic kinetics, which inhibits their practical applications. Herein, the synthesis of hierarchical K_1.39Mn₃O₆ microspheres as cathode materials for potassium‐ion batteries is reported. Additionally, an effective AlF₃ surface coating strategy is applied to further improve the electrochemical performance of K_1.39Mn₃O₆ microspheres. The as‐synthesized AlF₃ coated K_1.39Mn₃O₆ microspheres show a high reversible capacity (about 110 mA h g^?1 at 10 mA g^?1), excellent rate capability, and cycling stability. Galvanostatic intermittent titration technique results demonstrate that the increased diffusion kinetics of potassium‐ion insertion and extraction during discharge and charge processes benefit from both the hierarchical sphere structure and surface modification. Furthermore, ex situ X‐ray diffraction measurements reveal that the irreversible structure evolution can be significantly mitigated via surface modification. This work sheds light on rational design of high‐performance cathode materials for potassium‐ion batteries.     

Additive Modulation of DNA-DNA Interactions by Interstitial Ions

Quantitative understanding of biomolecular electrostatics, particularly involving multivalent ions and highly charged surfaces, remains lacking. Ion-modulated interactions between nucleic acids provide a model system in which electrostatics plays a dominant role. Using ordered DNA arrays neutralized by spherical cobalt³⁺ hexammine and Mg²⁺ ions, we investigate how the interstitial ions modulate DNA-DNA interactions. Using methods of ion counting, osmotic stress, and x-ray diffraction, we systematically determine thermodynamic quantities, including ion chemical potentials, ion partition, DNA osmotic pressure and force, and DNA-DNA spacing. Analyses of the multidimensional data provide quantitative insights into their interdependencies. The key finding of this study is that DNA-DNA forces are observed to linearly depend on the partition of interstitial ions, suggesting the dominant role of ion-DNA coupling. Further implications are discussed in light of physical theories of electrostatic interactions and like-charge attraction.     

Utilization of fluorescent lanthanide ions for the study of cation binding to extracellular sites in frog skeletal muscle.

The binding of Tb³⁺ ions to frog muscle has been studied, using fluorescence measurements. Kinetic evidence suggests that Tb³⁺ binds to the muscle at multiple sites. Two major classes can be distinguished: One having relatively fast kinetics and saturating within a few minutes; the second type being either very slow (hours) or consisting of an infinite pool. Binding to the first class of sites is readily reversible and is probably extracellular. It is shown that part of the slow type of binding is also reversible, and is also associated with extracellular binding sites.The binding of terbium is antagonized by other metal ions, their order of effectiveness being: La³⁺, Eu³⁺ > Mn²⁺, Hg²⁺ ? Ca²⁺ > Mg²⁺. A comparison with other studies suggests that part of the binding sites are located at the surface membrane of the muscle. Our experiments raise the possibility that part of the slowly exchanged calcium ions may well be of extracellular origin rather than intracellular one. The limitations and advantages of such studies, as a means to probe ion interactions in complex biological systems are discussed.     

Ion Competition in Condensed DNA Arrays in the Attractive Regime

Physical origin of DNA condensation by multivalent cations remains unsettled. Here, we report quantitative studies of how one DNA-condensing ion (Cobalt³⁺ Hexammine, or Co³⁺Hex) and one nonDNA-condensing ion (Mg²⁺) compete within the interstitial space in spontaneously condensed DNA arrays. As the ion concentrations in the bath solution are systematically varied, the ion contents and DNA-DNA spacings of the DNA arrays are determined by atomic emission spectroscopy and x-ray diffraction, respectively. To gain quantitative insights, we first compare the experimentally determined ion contents with predictions from exact numerical calculations based on nonlinear Poisson-Boltzmann equations. Such calculations are shown to significantly underestimate the number of Co³⁺Hex ions, consistent with the deficiencies of nonlinear Poisson-Boltzmann approaches in describing multivalent cations. Upon increasing the concentration of Mg²⁺, the Co³⁺Hex-condensed DNA array expands and eventually redissolves as a result of ion competition weakening DNA-DNA attraction. Although the DNA-DNA spacing depends on both Mg²⁺ and Co³⁺Hex concentrations in the bath solution, it is observed that the spacing is largely determined by a single parameter of the DNA array, the fraction of DNA charges neutralized by Co³⁺Hex. It is also observed that only ∼20% DNA charge neutralization by Co³⁺Hex is necessary for spontaneous DNA condensation. We then show that the bath ion conditions can be reduced to one variable with a simplistic ion binding model, which is able to describe the variations of both ion contents and DNA-DNA spacings reasonably well. Finally, we discuss the implications on the nature of interstitial ions and cation-mediated DNA-DNA interactions.     

KVOPO4: A New High Capacity Multielectron Na‐Ion Battery Cathode

Sodium ion batteries have attracted much attention in recent years, due to the higher abundance and lower cost of sodium, as an alternative to lithium ion batteries. However, a major challenge is their lower energy density. In this work, we report a novel multi‐electron cathode material, KVOPO₄, for sodium ion batteries. Due to the unique polyhedral framework, the V³⁺ ? V⁴⁺ ? V⁵⁺ redox couple was for the first time fully activated by sodium ions in a vanadyl phosphate phase. The KVOPO₄ based cathode delivered reversible multiple sodium (i.e. maximum 1.66 Na⁺ per formula unit) storage capability, which leads to a high specific capacity of 235 Ah kg^?1. Combining an average voltage of 2.56 V vs. Na/Na⁺, a high practical energy density of over 600 Wh kg^?1 was achieved, the highest yet reported for any sodium cathode material. The cathode exhibits a very small volume change upon cycling (1.4% for 0.64 sodium and 8.0% for 1.66 sodium ions). Density functional theory (DFT) calculations indicate that the KVOPO₄ framework is a 3D ionic conductor with a reasonably, low Na⁺ migration energy barrier of ≈450 meV, in line with the good rate capability obtained.     

A charge‐sensitive loop in the FKBP38 catalytic domain modulates Bcl‐2 binding

The Bcl‐2 inhibitor FKBP38 is regulated by the Ca²⁺‐sensor calmodulin (CaM). Here we show a hitherto unknown low‐affinity cation‐binding site in the FKBP domain of FKBP38, which may afford an additional level of regulation based on electrostatic interactions. Fluorescence titration experiments indicate that in particular the physiologically relevant Ca²⁺ ion binds to this site. NMR‐based chemical shift perturbation data locate this cation‐interaction site within the β5–α1 loop (Leu90–Ile96) of the FKBP domain, which contains the acidic Asp92 and Asp94 side‐chains. Binding constants were subsequently determined for K⁺, Mg²⁺, Ca²⁺, and La³⁺, indicating that the net charge and the radius of the ion influences the binding interaction. X‐ray diffraction data furthermore show that the conformation of the β5–α1 loop is influenced by the presence of a positively charged guanidinium group belonging to a neighboring FKBP38 molecule in the crystal lattice. The position of the cation‐binding site has been further elucidated based on pseudocontact shift data obtained by NMR via titration with Tb³⁺. Elimination of the Ca²⁺‐binding capacity by substitution of the respective aspartate residues in a D92N/D94N double‐substituted variant reduces the Bcl‐2 affinity of the FKBP38^35–153/CaM complex to the same degree as the presence of Ca²⁺ in the wild‐type protein. Hence, this charge‐sensitive site in the FKBP domain participates in the regulation of FKBP38 function by enabling electrostatic interactions with ligand proteins and/or salt ions such as Ca²⁺. Copyright © 2010 John Wiley & Sons, Ltd.     

Ion Competition in Condensed DNA Arrays in the Attractive Regime

Physical origin of DNA condensation by multivalent cations remains unsettled. Here, we report quantitative studies of how one DNA-condensing ion (Cobalt³⁺ Hexammine, or Co³⁺Hex) and one nonDNA-condensing ion (Mg²⁺) compete within the interstitial space in spontaneously condensed DNA arrays. As the ion concentrations in the bath solution are systematically varied, the ion contents and DNA-DNA spacings of the DNA arrays are determined by atomic emission spectroscopy and x-ray diffraction, respectively. To gain quantitative insights, we first compare the experimentally determined ion contents with predictions from exact numerical calculations based on nonlinear Poisson-Boltzmann equations. Such calculations are shown to significantly underestimate the number of Co³⁺Hex ions, consistent with the deficiencies of nonlinear Poisson-Boltzmann approaches in describing multivalent cations. Upon increasing the concentration of Mg²⁺, the Co³⁺Hex-condensed DNA array expands and eventually redissolves as a result of ion competition weakening DNA-DNA attraction. Although the DNA-DNA spacing depends on both Mg²⁺ and Co³⁺Hex concentrations in the bath solution, it is observed that the spacing is largely determined by a single parameter of the DNA array, the fraction of DNA charges neutralized by Co³⁺Hex. It is also observed that only ∼20% DNA charge neutralization by Co³⁺Hex is necessary for spontaneous DNA condensation. We then show that the bath ion conditions can be reduced to one variable with a simplistic ion binding model, which is able to describe the variations of both ion contents and DNA-DNA spacings reasonably well. Finally, we discuss the implications on the nature of interstitial ions and cation-mediated DNA-DNA interactions.     

One‐Step Synthesis of 2‐Ethylhexylamine Pillared Vanadium Disulfide Nanoflowers with Ultralarge Interlayer Spacing for High‐Performance Magnesium Storage

Rechargeable magnesium batteries (RMBs) are attractive candidates for large‐scale energy storage owing to the high theoretical specific capacity, rich earth abundance, and good safety characteristics. However, the development of desirable cathode materials for RMBs is constrained by the high polarity and slow intercalation kinetics of Mg²⁺ ions. Herein, it is demonstrated that 2‐ethylhexylamine pillared vanadium disulfide nanoflowers (expanded VS₂) with enlarged interlayer distances exhibit greatly boosted electrochemical performance as a cathode material in RMBs. Through a one‐step solution‐phase synthesis and in situ 2‐ethylhexylamine intercalation process, VS₂ nanoflowers with ultralarge interlayer spacing are prepared. A series of ex situ characterizations verify that the cathode of expanded VS₂ nanoflowers undergoes a reversible intercalation reaction mechanism, followed by a conversion reaction mechanism. Electrochemical kinetics analysis reveal a relatively fast Mg‐ion diffusivity of expanded VS₂ nanoflowers in the order of 10^?11–10^?12 cm² s^?1, and the pseudocapacitive contribution is up to 64% for the total capacity at 1 mV s^?1. The expanded VS₂ nanoflowers show highly reversible discharge capacity (245 mAh g^?1 at 100 mA g^?1), good rate capability (103 mAh g^?1 at 2000 mA g^?1), and stable cycling performance (90 mAh g^?1 after 600 cycles at 1000 mA g^?1).     

3D Amorphous Carbon with Controlled Porous and Disordered Structures as a High‐Rate Anode Material for Sodium‐Ion Batteries

Sodium‐ion batteries (SIBs) have a promising application prospect for energy storage systems due to the abundant resource. Amorphous carbon with high electronic conductivity and high surface area is likely to be the most promising anode material for SIBs. However, the rate capability of amorphous carbon in SIBs is still a big challenge because of the sluggish kinetics of Na⁺ ions. Herein, a three‐dimensional amorphous carbon (3DAC) with controlled porous and disordered structures is synthesized via a facile NaCl template‐assisted method. Combination of open porous structures of 3DAC, the increased disordered structures can not only facilitate the diffusion of Na⁺ ions but also enhance the reversible capacity of Na storage. When applied as anode materials for SIBs, 3DAC exhibits excellent rate capability (66 mA h g^?1 at 9.6 A g^?1) and high reversible capacity (280 mA h g^?1 at a low current density of 0.03 A g^?1). Moreover, the controlled porous structures by the NaCl template method provide an appropriate specific surface area, which contributes to a relatively high initial Coulombic efficiency of 75%. Additionally, the high‐rate 3DAC material is prepared via a green approach originating from low‐cost pitch and NaCl template, demonstrating an appealing development of carbon anode materials for SIBs.     

Redistribution of Terbium Ions Across Acetylcholine Receptor-Enriched Membranes Induced by Agonist Desensitization

Using small-angle x-ray diffraction from centrifugally oriented acetylcholine receptor (AChR) enriched membranes coupled with anomalous scattering from terbium ions (Tb³⁺) titrated into presumed Ca²⁺ binding sites, we have mapped the distribution of Tb³⁺ perpendicular to the membrane plane using a heavy atom refinement algorithm. We have compared the distribution of Tb³⁺ in the closed resting state with that in the carbamylcholine-desensitized state. In the closed resting state we find 45 Tb³⁺ ions distributed in 10 narrow peaks perpendicular to the membrane plane. Applying the same refinement procedure to the data from carbamylcholine desensitized AChR we find 18 fewer Tb³⁺ ions in eight peaks, and slight rearrangements of Tb³⁺ density in the peaks near the ends of the AChR ion channel pore. These agonist dependent changes in the Tb³⁺ stoichiometry and distribution suggest a likely role for multivalent cations in stabilizing the different functional states of the AChR, and the changes in the Tb³⁺ distribution at the two ends of the pore suggest a potential role for multivalent cations in the gating of the ion channel.     

Mechanistic Insight into the Electrochemical Performance of Zn/VO2 Batteries with an Aqueous ZnSO4 Electrolyte

Rechargeable aqueous zinc‐ion batteries (ZIBs) are promising for cheap stationary energy storage. Challenges for Zn‐ion insertion hosts are the large structural changes of the host structure upon Zn‐ion insertion and the divalent Zn‐ion transport, challenging cycle life and power density respectively. Here a new mechanism is demonstrated for the VO₂ cathode toward proton insertion accompanied by Zn‐ion storage through the reversible deposition of Zn₄(OH)₆SO₄·5H₂O on the cathode surface, supported by operando X‐ray diffraction, X‐ray photoelectron spectroscopy, neutron activation analysis, and density functional theory simulations. This leads to an initial discharge capacity of 272 mAh g^?1 at a current density of 3.0 A g^?1, of which 75.5% is maintained after 945 cycles. It is proposed that the competition between proton and Zn‐ion insertion in the VO₂ host is determined by the solvation energy of the salt anion and proton insertion energetics, where proton insertion has the advantage of minimal structural distortion leading to a long cycle life. As the discharge kinetics are capacitive for the first half of the process and diffusion limited for the second half, the VO₂ cathode takes the middle road possessing both fast kinetics and high practical capacities revealing a reaction mechanism that provides new perspective for the development of aqueous ZIBs.     

Luminescence properties of Tm3+ ions single‐doped YF3 materials in an unconventional excitation region

According to the spectral distribution of solar radiation at the earth's surface, under the excitation region of 1150 to 1350 nm, the up‐conversion luminescence of Tm³⁺ ions was investigated. The emission bands were matched well with the spectral response region of silicon solar cells, achieved by Tm³⁺ ions single‐doped yttrium fluoride (YF₃) phosphor, which was different from the conventional Tm³⁺/Yb³⁺ ion couple co‐doped materials. Additionally, the similar emission bands of Tm³⁺ ions were achieved under excitation in the ultraviolet region. It is expected that via up‐conversion and down‐conversion routes, Tm³⁺‐sensitized materials could convert photons to the desired wavelengths in order to reduce the energy loss of silicon solar cells, thereby enhancing the photovoltaic efficiency.     

Fast and Reversible Four‐Electron Storage Enabled by Ethyl Viologen for Rechargeable Magnesium Batteries

Magnesium (Mg) batteries are the most promising “post‐lithium‐ion” energy storage technologies owing to their high theoretical energy density, low cost, and intrinsic safety with air and moisture. However, the development of Mg batteries has been limited to cathode materials leading to low power, low reversible energy density, and poor cycle life. Here, a new Mg cathode is reported based on ethyl viologen (EV), which not only has a fast redox couple EV²⁺/EV⁰ but also is capable of coupling with redox‐active anions, such as iodide (I^?), achieving a total four‐electron storage. The EV²⁺/EV⁰ redox couple demonstrates a superior rate performance (10 C) and stable cycle life (500 cycles) owing to intrinsic fast electrode kinetics. A high material utilization (>80%) can be achieved at 1.0 C under a high areal loading of 5 mg cm^?2. When coupling with iodide I^?, a reversible four‐electron storage is achieved with a high energy density (304.2 Wh kg^?1) and a stable cycle life (>100 cycles). This study provides effective strategies for designing reversible multielectron storage for high‐rate and high‐energy rechargeable Mg batteries.     

Biosorptive removal of chromium by husk of Lathyrus sativus: Evaluation of the binding mechanism,kinetic and equilibrium study

The adsorption of tri‐ and hexavalent chromium by the husk of Lathyrus sativus (HLS), which is an agro‐waste has been investigated to find a potential solution to environmental pollution. The pH‐dependent adsorption process finds the optimum values for trivalent and hexavalent chromium ions at about pH 5.0 and pH 2.0, respectively. The process is very fast initially and attains an equilibrium within 90 min following pseudo second‐order rate kinetics. Equilibrium adsorption data can best elucidated by the Langmuir–Freundlich dual model (r² = 0.998) in comparison with other isotherm models examined indicating that both physi‐ and chemisorption are components of the binding mechanism of chromium ions on HLS. The results show that one gram of HLS can adsorb 24.6 mg Cr³⁺ and 44.5 mg Cr⁶⁺. Fourier transform infrared data and functional group modification experiments indicate that –NH₂, ‐COOH, ‐OH, ‐PO₄^3? groups of the biomass interact chemically with the chromium ions. SEM‐energy dispersive X‐ray analysis and X‐ray diffraction spectrum analysis were used to further assess the morphological changes and the mechanisms of chromium ion interaction with HLS. The analysis signified that the biosorption process involved surface morphological changes, complexation and an ion exchange mechanism. The amorphous nature of HLS facilitating metal biosorption was indicated by the X‐ray diffraction analysis.