Diffusion Coefficients Of Na Research Articles

Large scale atomistic and quantum mechanical study of Na+ ion transport in liquid electrolytes for batteries

Lithium–ion batteries (LIBs) have long dominated energy storage markets due to their high energy density and reliability. However, concerns over lithium scarcity and geographic distribution necessitate alternatives. Sodium-ion batteries (SIBs) offer a promising solution due to sodium's abundance, cost-effectiveness, and favorable electrochemical properties. This study investigates Na+ ion transport, aggregation, and performance in various organic electrolytes using molecular dynamics (MD) simulations and density functional theory (DFT) calculations. The electrolytes studied include ethylene carbonate (EC), propylene carbonate (PC), dimethoxyethane (DME), and dimethyl carbonate (DMC) at 320 K. We focused on conductivity, diffusivity, and survival probability of Na+ ions at different salt concentrations. Furthermore, the solvation structure and the binding energy of ions in the electrolytes are thoroughly analyzed. Key findings reveal that at 2 M salt concentration, Na+ ion diffusivity and ionic conductivity follow the order EC>PC>DME>DMC. Increasing salt concentration decreases self–diffusion coefficients of Na+ and PF6− ions across all electrolytes, affecting conductivity. EC shows the highest ionic conductivity at both 1 M and 2 M salt concentrations. These insights suggest that a 2 M NaPF6 concentration in EC optimizes ionic conductivity, making it ideal for high–performance SIBs. This study provides crucial understanding for optimizing electrolytes in SIBs, advancing their development for scalable energy storage solutions.

Revealing sodium storage mechanism of graphitic carbons with various dimensions by a new strategy

Two kinds of graphitic carbon materials without closed pores were obtained by a new strategy in an effort to thoroughly characterize the sodium storage mechanism in the graphitic carbon anodes of sodium-ion batteries. In the first strategy, the interlayer distance is constant, but the defect concentration varies, while in the second strategy, the defect concentration is constant, but the interlayer distance varies and the graphitic crystallites are of different sizes. In situ X-ray diffraction (XRD) analysis was employed to detect the intercalation/de-intercalation process of Na+ ions in these graphitic carbon materials. The results showed that Na+ intercalation in the interlayer space proceeds in two stages at 1.0–0.5 V and 0.5–0 V, contributing to both sloping and plateau capacity profiles. Moreover, the size of the graphene layers in the graphitic crystallites exerts an effect on the slope and plateau capacities in addition to the interlayer distance and defect concentration. Furthermore, the rate performance of a graphitic anode is mainly determined by the defect content, polar groups, and surface area, rather than the interlayer distance. This is due to the influence of defects and polar groups on the diffusion coefficients of Na+ in the insertion/extraction process in the interlayer space and in the Na+ adsorption/desorption process. This work provides new insight for the design of hard carbon anode materials for high-energy-density sodium-ion batteries.

Employing Na<sub>2</sub>CO<sub>3</sub> and NaCl as sources of sodium in NaFePO<sub>4</sub> cathode: A comparative study on structure and electrochemical properties

<abstract> <p>Encouraged by the tremendous success of lithium iron phosphate (LiFePO<sub>4</sub>), analogous NaFePO<sub>4</sub> has been predicted to show identical properties as LiFePO<sub>4</sub>. Synthesis of NaFePO<sub>4</sub> materials in the maricite phase has been carried out using the sol-gel method with variations of calcination temperature and starting materials as sources of sodium Na<sub>2</sub>CO<sub>3</sub> and NaCl. The resulted NaFePO<sub>4</sub> maricite phase with the purity between 40% and 85%, according to X-ray diffractometry (XRD) characterization was obtained. The morphology and grain size of the particles in samples, as observed by a scanning electron microscope (SEM), tend to enlarge upon calcination at higher temperatures. The increment of calcination temperature increases the NaFePO<sub>4</sub> maricite phase content in the sample. The impedance data analysis shows that the diffusion coefficient of Na<sup>+</sup> ions and the electrical conductivity of a sample using Na<sub>2</sub>CO<sub>3</sub> is higher than that of NaCl. This comprehensive study provides a feasible method and opens new opportunities for the continuous study of Na-ion batteries.</p> </abstract>

New insights from nanoscale in-depth investigation into wettability modification in oil-wet porous media

In the context of fluid-surface studies of oil reservoirs, wettability alteration plays an important role, especially in carbonate reservoirs. This investigation, utilizing molecular dynamics simulation, delves into the effect of oil movement during interactions with brine ions. The calculation of adsorption energy, radial distribution function, diffusion coefficient, and configurational changes of the NaCl brine molecules allowed for an examination of the role of ions in oil movement from an oil-wet calcite surface. Findings indicate that the polarity of oil has a marked influence on oil detachment, as evidenced by the more than 30% adsorption energy for the acrylic acid system compared to the decane system. The diffusion coefficient of Na[Formula: see text] ions in the acrylic acid system was found to be five times as high as in the decane system. Configuration changes showed that brine ions are more active — in a regular eight shape — in interacting with the acrylic acid-wet surface as opposed to the decane-wet surface. The hierarchical significance of oil polarity [Formula: see text] brine ions [Formula: see text] mineral surface in altering the wettability of the system demonstrates the significance of sodium ions in the presence of the polar oil component. The findings greatly contribute to the development of effective Smart Water flooding technology.

Structural, Electrical, and Electrochemical Properties of a Na2O-V2O5 Ceramic Nanocomposite as an Active Cathode Material for a Na-Ion Battery

In this paper, a relationship between the structure and the electrical properties of a nanocrystalline composite ceramics xNa2O·(100 − x)V2O5 with ‘x’ of 5, 15, 25, 35, and 45 mol%, abbreviated as xNV, was investigated by X-ray diffractometry (XRD), X-ray absorption spectroscopy (XAS), Cyclic Voltammetry (CV), Electrochemical impedance spectroscopy (EIS), and cathode active performance in Na-ion battery (SIB). For the expected sodium vanadium bronzes (NaxV2O5) precipitation, the preparation of xNV was performed by keeping the system in the molten state at 1200 °C for one hour, followed by a temperature decrease in the electric furnace to room temperature at a cooling rate of 10 °C min−1. XRD patterns of the 15NV ceramic exhibited the formation of Na0.33V2O5 and NaV3O8 crystalline phases. Moreover, the V K-edge XANES showed that the absorption edge energy of ceramics 15NV recorded at 5479 eV is smaller than that of V2O5 at 5481 eV, evidently indicating a partial reduction from V5+ to V4+ due to the precipitation of Na0.33V2O5. In the cyclic voltammetry, reduction peaks of 15NV were observed at 1.12, 1.78 V, and 2.69 V, while the oxidation peak showed up only at 2.36 V. The values of the reduction peaks were related to the NaV3O8 crystalline phase. Moreover, the diffusion coefficient of Na+ (DNa+) gradually decreased from 8.28 × 10−11 cm2 s−1 to 1.23 × 10−12 cm2 s−1 with increasing Na2O content (x) from 5 to 45 mol%. In the evaluation of the active cathode performance of xNV in SIB, ceramics 15NV showed the highest discharge capacity 203 mAh g−1 at a current rate of 50 mA g−1. In the wider voltage range from 0.8 to 3.6 V, the capacity retention was maintained at 50% after 30 cycles, while it was significantly improved to 90% in the narrower voltage range from 1.8 to 4.0 V, although the initial capacity decreased to 56 mAh g−1. It is concluded that the precipitation of the Na0.33V2O5 phase improved the structural and electrical properties of 15NV, which provides a high capacity for the Na-ion battery when incorporated as a cathode active material.

Ti, F Codoped Sodium Manganate of Layered P2-Na 0.7 MnO 2.05 Cathode for High Capacity and Long-Life Sodium-Ion Battery

Ti, F Codoped Sodium Manganate of Layered P2-Na _0.7 MnO _2.05 Cathode for High Capacity and Long-Life Sodium-Ion Battery

Spectral induced polarization monitoring of induced calcite precipitation in subsurface sediments

SUMMARY Co-precipitation of contaminants within the crystalline structure of calcite is a promising natural attenuation or remedial technology being considered at contaminated sites. We explore the sensitivity of the spectral induced polarization (SIP) method to induced calcite precipitation in natural sediments as a path forward to non-invasively monitor these sites. We performed time-lapse column experiments using phased (I–IV) injections over 40 d on natural sediments from the Hanford Site (WA, USA). In the phased injections, abiotic calcite precipitation was induced and confirmed to have occurred. Previous work on glass beads and homogeneous sand was limited to high frequency detection of calcite, however in this work we observed the development of two polarization mechanisms, one at high frequency (>100 Hz) and one at low frequency (<100 Hz). Based on the characteristic frequencies from the SIP high and low frequency regimes, characteristic length scales (L) were computed where the adsorption mode of Na+ versus Ca2+ was compared by using diffusion coefficients corresponding to Na+ versus an arithmetically averaged value for Na+ and Ca2+. Using the diffusion coefficient of Na+, the high frequency L was found to correlate well with the size of the calcite crystals. The low frequency L correlated well with the individual natural sediment grain sizes within the columns. During late experimental times (day 36 and 40), the characteristic low frequency in two of the experimental columns shifted to lower frequencies (<0.001 Hz) which may signify SIP sensitivity of the formed calcite with the sediment grains. In field applications, the development of a low frequency polarization length scale to monitor calcite precipitation is promising for field monitoring applications, however further laboratory work needs to be performed to examine the SIP sensitivity of calcite formation in the presence of natural sediments.

Electrochemical Properties and Ex Situ Study of Sodium Intercalation Cathode P2/P3-NaNi1/3Mn1/3Co1/3O2

In recent work, P2/P3-NaNi1/3Mn1/3Co1/3O2 (NaNMC) was obtained by the sol-gel process followed by calcination of the precursor at 900°C for 12 h. The electrochemical properties of NaNMC were investigated in the voltage range of 2.0–4.0 V. The material exhibited an initial discharge capacity of 107 mAh·g−1 and good capacity retention of 82.2% after 100 cycles. Ex situ XRD performance showed that the P3-phase transformed from the P3- to O1-phase and vice versa, while the P2-phase remained stable during the sodium intercalation. The kinetic of sodium intercalation of NaNMC upon reversible Na+ insertion/deinsertion was evaluated via a Galvanostatic Intermittence Titration Technique (GITT) and Electrochemical impedance spectroscopy (EIS). The diffusion coefficients of Na+ ion deduced from the GITT curve have a broad distribution ranging from 10−10 to 10−11 cm2·s−1 for the charging/discharging process. Besides, the evolution of diffusion coefficient and charge transfer resistance is consistent with the complex phase transition generally observed in sodium layered oxides.

Lab-scale and pore-scale study of low-permeability soil diffusional tortuosity

Diffusion coefficients for Na+ was measured in low-permeability samples (diameter of 3 cm and average length of 7 cm) from the deep disposal site of the Siberian Chemical Combine (SCC) using the end-diffusion technique. The direction of diffusion was perpendicular to the direction of bedding. Special equipment was designed and constructed for the experiment. Two types of concentration observations were used. For non-sorbing Na+, EC sensors and the length distribution of sorbed elements were used. The synthetic solution used in the experiments was a model of the low-activity contaminant of the SCC and consisted of NaNO3 (25 g/L) and nitrate compounds of Cs+, Ni2+, Co2+, and Sr2+ (100 mg/L each). The measured values of the effective diffusion coefficients De for Na+ from 1.92 × 10−11 to 1.70 × 10−10 m2/s. The microstructure was studied with X-ray microtomography for the same cores. Image shooting was performed on undisturbed microsamples with a size of 0.913 mm (7003 vox). Spatial correlation analysis was performed after the binarization of each obtained 3-D structure. This analysis showed that the spatial correlation scale of the indicator variogram is considerably smaller than the microsample length. Then, a numerical simulation of the Laplace equation with binary coefficients for each microsample was performed. The results were analysed in the form of a plot of the tortuosity versus the porosity. Pore-scale simulations show a nonlinear decrease in the tortuosity with decreasing porosity. Exponential values in the range between 1.8 and 2.4 were found by fitting this graph with Archie's model. Anisotropic tortuosity is also detected in the horizontal and vertical directions. The diffusion coefficients of non-sorbing Na+ measured in this study agree with those of the pore-scale diffusion simulation of the microtomography data.

Effect of 3D Metal on Electrochemical Properties of Sodium Intercalation Cathode P2-NaxMe1/3Mn2/3O2 (M = Co, Ni, or Fe)

This research aims to evaluate the influence of different 3D metals (Fe, Co, and Ni) substituted to Mn on the electrochemical performance of P2-NaxMe1/3Mn2/3O2 material, which was synthesized by the coprecipitation process followed by calcination at high temperature. X-ray diffraction (XRD) results revealed that the synthesized Mn-rich materials possessed a P2-type structure with a negligible amount of oxide impurities. The materials possessed their typical cyclic voltammogram and charge-discharge profiles; indeed, a high reversible redox reaction was obtained by NaxCo1/3Mn2/3O2 sample. Both NaxCo1/3Mn2/3O2 and NaxFe1/3Mn2/3O2 provided a high specific capacity of above 140 mAh·g−1; however, the former showed better cycling performance with 83% capacity retention after 50 cycles at C/10 and high rate capability. Meanwhile, the Ni-sub NaxNi1/3Mn2/3O2 exhibited excellent cycling stability but a low specific capacity of 110 mAh·g−1 and inferior rate capability. The diffusion coefficient of Na+ ions into the structure tended to decrease with a depth of discharge; those values were in the range of 10−10–10−9 cm2·s−1 and 10−11–10−10 cm2·s−1 in the solid solution region and biphasic region, respectively.

Origin of anomalous high-rate Na-ion electrochemistry in layered bismuth telluride anodes

Summary van der Waals layered metal chalcogenide Bi2Te3 has shown exceptional capacity and rate capability in alkali-ion batteries but the underlying reaction mechanism with Li+, Na+, and K+ remains undiscovered. It is unexpected that Na+ electrochemistry outperforms Li+ and K+ at high current densities. Here, in situ transmission electron microscopy is used to uncover nanoscale transformations during lithiation, sodiation, and potassiation, which follows two-step conversion and alloying reactions with Li+ and Na+, and three-step intercalation-conversion-alloying reactions with K+. Counterintuitively, sodiation exhibits the highest reaction kinetics, and its origin can be elucidated by first-principles and finite-element simulations in two aspects. The lower interfacial strain accommodation energy between Bi2Te3 and its Na-conversion products allows more facile sodiation phase transformation than Li- and K-ion reactions. The higher electrochemo-mechanical stress concentration at the concave-shaped sodiation reaction front facilitates continued Na-ion diffusion and reaction propagation. These fundamental insights are essential for fast-charging alkali-ion batteries.

Effects of calcination temperature on electrochemical properties of cathode material Na4MnV(PO4)3/C synthesized by sol-gel method for sodium-ion batteries

The effects of calcination temperature on the physical and electrochemical performance of the Na4MnV(PO4)3/C composites, which are prepared by a sol-gel method combined with the subsequent calcination in inert atmosphere, are reported in this work. The Na4MnV(PO4)3/C composites are investigated by x-ray diffraction (XRD), N2 adsorption/desorption isothermal, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy and electrochemical measurements. The specific surface area, disorder of carbon, diffusion coefficients of Na+ (DNa) and electrochemical performance of Na4MnV(PO4)3/C composites are greatly influenced by the calcination temperature. The surface area and disorder of carbon of Na4MnV(PO4)3/C substantially decrease with the calcination temperature increasing. While the DNa and electrochemical performance of Na4MnV(PO4)3/C composites improve with the calcination temperature from 650 to 750 °C and then degrade with the calcination temperatures from 750 to 850 °C. The results reveal that the optimal calcination temperature for the Na4MnV(PO4)3/C composites is 750 °C and the corresponding Na4MnV(PO4)3/C composite possesses the highest capacity and the best rate capability and cyclability amongst all these Na4MnV(PO4)3/C composites in this work.

Effects of organic pollutants on the fractional crystallization of NaNO3 from high-saline wastewater

In this study, the effect of organic pollutants on the fractional crystallization of NaNO3 from high-saline wastewater was investigated by experiments and theoretical methods. Prior to the investigation, the optimal condition of cooling rate, 10 K/h, stirring intensity, 200 rpm, and aging time, 10 min, were acquired for pursuing a high purity, large crystal particle and uniform size distribution. Based on the optimized process operation, different contents of organic contaminants represented by phenol and quinoline were added for NaNO3 crystallization. It is clear that both phenol and quinoline have no effect on the product morphology, while their negative effects on the crystal size are significant. The averaged crystal size decrease from 717 μm to 162 μm, when the phenol content reaches 2.0%. Similarly, the addition of 0.2% quinoline cause an obvious decline of the mean size to 197 μm. The results of XRD characterization, carbon content analysis and infraredspectrum show that phase transformation, incorporation into crystal lattice and selective adsorption are not the main modification mechanisms for the influence of organic matters on the crystal size. Hence, the reduced crystal size is mainly attributed to the inhibition of solute diffusion caused by the presence of organic pollutants. This was further verified by the molecular dynamics simulation. The calculated results indicate that when the system contains 40 Na+ ions, 40 NO3− ions, 20 phenol or quinoline molecules, the diffusion coefficient of Na+ reduce by 8.67% and 30.86%, while the diffusion coefficient of NO3− decrease by 29.33% and 39.51%, respectively. Related results provide an important reference for the industrial process control of high-saline wastewater fractional crystallization.

A study of the electrochemical kinetics of sodium intercalation in P2/O1/O3-NaNi1/3Mn1/3Co1/3O2

Sodium ternary layered oxides, typically NaNi1/3Mn1/3Co1/3O2 (NMC), are layered structures analogous to LiNi1/3Mn1/3Co1/3O2, and have been utilized extensively in sodium-ion batteries (SIBs). The cathode material was successfully synthesized by a sol-gel process followed by a calcination step at 900 °C for 12 h. The triple-phase integration denoted as P2, O1 and O3 in the NMC sample was evidently revealed on XRD diagrams. The composite cathode material acted as an O3 purity phase that exhibited relatively good performance that delivered an initial capacity of 140 mAh g−1 and sustained reversible capacities of nearly 110 mAh g−1 after 100 cycles. The kinetics of sodium intercalation of sol-gel NMC upon reversible Na+ insertion/de-insertion was evaluated via galvanostatic intermittence titration technique (GITT) and electrochemical impedance spectroscopy (EIS). The diffusion coefficients of Na+ deduced from the GITT curve were found to lie within a wide range, 10−9–10−12 cm2 s−1 for the charge process and 10−13–10−17 cm2 s−1 for the discharge process. This implies that the kinetics of Na+ extraction out of the NaxNi1/3Mn1/3Co1/3O2 host could be much more favored than Na+ insertion. Additionally, the evolution of diffusion coefficient and charge transfer resistance are consistent with the complex phase transition generally observed in sodium layered oxides.

Synthesis and electrochemical studies on sodium ion conducting PVP based solid polymer electrolytes

The flexible solid polymer electrolytes based on polyvinyl pyrrolidone (PVP) complexed with sodium nitrate have been developed for battery applications. The amorphous natures of the prepared films have been discussed by X-ray diffraction studies. The maximum ionic conductivity value of 1.21 × 10−5 S/cm is obtained for 6 wt% of NaNO3 doped system. The prepared membranes are ionic conductors which is proved by transport studies. The mobility and diffusion coefficient of Na+ ions in the prepared SPEs were estimated. Electrochemical characterization has been carried out by assembling Na-ion conducting symmetry cell. The pseudo-capacitance behavior of the electrolyte is also confirmed by cyclic-voltammetry studies. The solid state battery (Na||94PVP:06NaNO3||I2 + C) has been constructed using the higher conducting membrane and its properties are studied.

Experimental study of multicomponent diffusion in low permeable sediments

Diffusion coefficients for Na+ and distribution coefficients for Cs+, Ba2+, Ni2+, CO2+, Sr2+ were measured on low permeable samples (3 cm diameter, average length 7 cm) from the deep disposal site Siberian Chemical Combine (SSC) using the end-diffusion technique. The direction of diffusion was perpendicular to bedding. Special equipment for experiment were designed and constructed. Two types of concentration observation were used. For non-sorbing Na+ in time used EC sensors and length distribution of sorbed elements. The synthetic solution used in the experiments was a model of low-activity contaminant of the SSC, and consist NaNO3 (25 g/l) and nitrate compounds: Cs+, Ba2+, Ni2+, Co2+, Sr2+ (100 mg/l each). The measured values of the effective diffusion coefficients De) for Na+ from 7.60×10-7 to 1.51×10-5 m2/day and volumetric dimensionless distribution coefficients (Kdρ) are: Cs+ from 0.21 to 22.1, Ba2+ from 1.1 to 1.45, Ni2+ from 0.3 to 16.4, Co2+ from 1.98 to 24.7, Sr2+ from 1.9 to 14.3. The values of the diffusion coefficient show a large degree of variability. The diffusion coefficients of non-sorbing Na+ measured in this study are in good agreement with pore-scale diffusion simulation on microtomography data.

A Novel Graphene Oxide Wrapped Na2Fe2(SO4)3/C Cathode Composite for Long Life and High Energy Density Sodium‐Ion Batteries

AbstractThe cathode materials in the Na‐ion battery system are always the key issue obstructing wider application because of their relatively low specific capacity and low energy density. A graphene oxide (GO) wrapped composite, Na2Fe2(SO4)3@C@GO, is fabricated via a simple freeze‐drying method. The as‐prepared material can deliver a 3.8 V platform with discharge capacity of 107.9 mAh g−1 at 0.1 C (1 C = 120 mA g−1) as well as offering capacity retention above 90% at a discharge rate of 0.2 C after 300 cycles. The well‐constructed carbon network provides fast electron transfer rates, and thus, higher power density also can be achieved (75.1 mAh g−1 at 10 C). The interface contribution of GO and Na2Fe2(SO4)3 is recognized and studied via density function theory calculation. The Na storage mechanism is also investigated through in situ synchrotron X‐ray diffraction, and pseudocapacitance contributions are also demonstrated. The diffusion coefficient of Na+ ions is around 10−12–10−10.8 cm2 s−1 during cycling. The higher working voltage of this composite is mainly ascribed to the larger electronegativity of the element S. The research indicates that this well‐constructed composite would be a competitive candidate as a cathode material for Na‐ion batteries.

Probing the Role of Electronic Conduction during the Apparent Diffusion of Cations in Nickel Hexacyanoferrate

Nickel hexacyanoferrate (NiHCF) is an attractive candidate intercalation host compound for grid scale sodium-ion batteries1,2 and for efficient electrochemical desalination of sea and brackish water resources.3,4 Its open-framework crystal structure and facile intercalation kinetics produce long life with high capacity retention, while achieving charge capacities between 60 to 70 mAh/g.1 However, to improve the in operando rate capability and selectivity of cation intercalation within NiHCF, and similar Prussian Blue analogues (PBAs), transport and kinetic processes must be characterized to identify rate-limiting mechanisms. In particular, a lack of clarity exists with respect to apparent diffusion that takes place during (de)-intercalation of cations. In the present work we explore this phenomenon through a combination of experimental characterization and particle-scale transport modelling. Most significantly, our preliminary results reveal that slow electronic conduction in NiHCF nanoparticle agglomerates limits apparent diffusion, rather than crystal-scale diffusion of cations themselves.We also show that experimental measurement of the apparent diffusion time scale (τ D =R 2/D app where R and D app are particle radius and the apparent diffusion coefficient) is more insightful and reliable, compared to measurements of diffusion coefficients alone.Previous research has focused on the measurement of PBA electronic conductivity σ and bulk Diffusivity D for fully dense thin films, while electron and cation transport within PBAs in the nanoparticulate formats needed for economically constrained applications (which require simultaneously high charge capacity and current density) have not been explored in detail. Prussian Blue thin films are known to have slow electronic conduction with σ≅5x10-5S/m.5 Diffusion coefficients of Na+ and Rb+ in NiHCF6 and of K+ in copper hexacyanoferrate (CuHCF)7 thin films were approximately 10-9 cm2/s using chronoamperometry,6 cyclic voltammetry,7 and impedance spectroscopy.7 Further, the coupling of cation diffusion and electron hopping inhibits isolation of these two effects using electrochemical characterization techniques.7 Presently we characterize cation diffusion rates within slurry-cast porous electrodes that contain NiHCF nanoparticles, electronically conductive carbon, and polymer binder. We use the potentiostatic intermittent titration technique (PITT) to determine the apparent diffusion time scales by fitting current/time response to closed-form expressions8 derived for porous electrodes having kinetic and diffusive transport limitations. We probed the effect of agglomeration of NiHCF nanoparticles by fabricating two types of electrodes. In particular, NiHCF powder was mixed with conductive carbon using either (1) a mortar/pestle or (2) a vortex mill with 5mm steel beads. Microscopy of cast electrodes revealed a larger agglomerate size and higher size dispersity for milled electrodes than for unmilled ones. Consequently, the milled electrode showed a significantly poorer galvanostatic rate capability and longer diffusion time scales. For both electrodes, Dapp varied with a concave-up profile with respect to the degree of intercalation (x in Na1+ x NiFe(CN)6). Transport modelling of these diffusion processes during galvanostatic (dis)charge, which predicts the spatiotemporal variation of of x within NiHCF nanoparticles, showed consistent scaling of charge utilization with C-rate. To explain the variation of diffusion coefficients with intercalant fraction, a new theoretical model is presented. Assuming facile crystal scale diffusion and interfacial kinetics, we find that Dapp varies (1) in inverse proportion with the volumetric differential capacitance Cdiff of NiHCF and (2) in proportion to the effective electronic conductivity of NiHCF nanoparticle agglomerates: D app = σ/ Cdiff . Here, Cdiff varies inversely with the slope of intercalation potential with respect to x and thus, is responsible for the concave-up variation of Dapp with x. Furthermore, electronic conductivity of dry porous NiHCF compacts was measured, based upon predicted values of Dapp , based on our theory, were consistent with measured values from PITT. These findings confirm that apparent diffusion in NiHCF is indeed limited by slow electronic conduction and motivate further studies to enhance diffusion rates and to explore selectivity. Acknowledgements: We are grateful for funding and support by the College of Engineering, UIUC and Mechanical Science and Engineering Department at UIUC References S. V. . 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Sb-doped SnO2/graphene-CNT aerogels for high performance Li-ion and Na-ion battery anodes

SnO2 has been extensively explored as a potential anode material for both Li-ion (LIBs) and Na-ion batteries (SIBs). It possesses however an extremely poor electrical conductivity, making it difficult to be used as the standalone electrode. Herein, Sb-doped SnO2 (ATO) nanoparticles are in situ grown on N-doped graphene-CNT aerogels (N-GCAs) based on a facile hydrothermal self-assembly route for the first time. The ATO/N-GCA composite presents a highly porous structure along with an electrical conductivity enhanced by over two orders of magnitude through the in situ Sb doping. The composite electrode delivers an outstanding rate capability of 659mAhg−1 at 10Ag−1 with capacity retention of 73% after 1000 cycles at 1Ag−1 in LIBs. The same electrode also maintains 74% of its capacity after 500 cycles in SIBs, confirming a promising anode for both rechargeable batteries. We reveal distinct reaction kinetics and phase transition behaviors of ATO electrodes in different rechargeable batteries. The lithiation of ATO ensues consecutive conversion and alloying reactions while only the conversion reaction takes place during sodiation. Furthermore, the diffusion coefficient of Na+ ion in ATO is nine orders of magnitude lower than that of Li+ ions. The enhanced electrical conductivity of SnO2 by Sb doping dominates the capacity enhancements in LIBs whereas the mesoporous structure of hybrid aerogel plays a more important role in enhancing the Na+ ion storage performance. These new findings may offer insights into the relatively poor performance of SIBs and will help proper structural design of high performance bi-functional anodes for alkali metal ion batteries.

Energetic and Frictional Effects in the Transport of Ions in a Cyclic Peptide Nanotube

The effects of geometric restraints and frictional parameters on the energetics and dynamics of ion transport through a synthetic ion channel are investigated using molecular dynamics (MD) simulations for several different ions. To do so, potential of mean force profiles and position‐dependent diffusion coefficients for Na+, K+, Ca2+, and Cl− transport through a simple cyclic peptide nanotube, which is composed of 4× cyclo[−(D‐Ala‐Glu‐D‐Ala‐Gln)2−] rings, are calculated via an adaptive biasing force MD simulation method and a Baysian inference/Monte Carlo algorithm. Among the restraints and parameters examined in this work, the radius parameter used in the flat‐bottom half‐harmonic restraint at the entrance and exit to channel has a great effect on the energetics of ion transport through the variation of entropy in the outside of the channel. The diffusivity profiles for the ions show a strong dependence on the damping coefficient, but the dependence on the coefficient becomes minimal inside the channel, indicating that the most important factor which affects the diffusivity of ions inside the channel is local interactions of ions with the structured channel water molecules through confinement.