Ion Diffusion Properties Research Articles

General Liquid‐Driven Coaxial Flow Focusing Preparation of Novel Microcapsules for Rechargeable Magnesium Batteries

Magnesium batteries have been considered promising candidates for next‐generation energy storage systems owing to their high energy density, good safety without dendrite formation, and low cost of magnesium resources. However, high‐performance cathodes with stable capacity, good conductivity, and fast ions transport are needed, since many conventional cathodes possess a low performance and poor preparation controllability. Herein, a liquid‐driven coaxial flow focusing (LDCFF) approach for preparing a novel microcapsule system with controllable size, high loading, and stable magnesium‐storage performance is presented. Taking the MoS2‐infilled microcapsule as a case study, the magnesium battery cathode based on the microcapsules displays a capacity of 100 mAh g−1 after 100 cycles. High capacity retention is achieved at both low and high temperatures of −10, ‒5, and 45 °C, and a stable rate‐performance is also obtained. The influences of the liquid flow rates on the size and shell thickness of the microcapsules are investigated; and electron and ion diffusion properties are also studied by first‐principle calculations. The presented LDCFF method is quite general, and the high performance of the microcapsules enables them to find broad applications for making emerging energy‐storage materials and secondary battery systems.

A Conjugated Copolymer Bearing Imidazolium-based Ionic Liquid: Electrochemical Synthesis and Electrochromic Properties

An imidazolium-based ionic liquid (IL) modified triphenylamine derivative, namely 1-(4-((4-(diphenylamino)benzoyl) oxy)butyl)-3-methyl imidazole tetrafluoroborate (TPAC6IL-BF4), was designed and synthesized, and further applied with 3,4-ethylene dioxythiophene (EDOT) to prepare conjugated copolymer P(EDOT:TPAC6IL-BF4) via electrochemical polymerization. The cyclic voltammetry curves show that the copolymer P(EDOT:TPAC6IL-BF4) possesses two pairs of redox peaks, which should be ascribed to the redox behaviors of EDOT and triphenylamine. The ultraviolet-visible (UV-Vis) absorption spectrum of P(EDOT:TPAC6IL-BF4) exhibits one maximum absorption peak at 580 nm and a small shoulder characteristic peak at 385 nm under neutral state which are assigned to π-π* conjugated structure of EDOT and triphenylamine. After being applied at the positive voltage, the copolymer color changes from dark blue to light blue, which is close to the color of poly(3,4-ethylenedioxythiophene) (PEDOT). Surprisingly, the copolymer P(EDOT:TPAC6IL-BF4) shows shorter switching time of 0.37 s, 0.30 s at 580 nm and 0.38 s, 0.45 s at 1100 nm compared with PEDOT. It is more intriguing that the copolymer P(EDOT:TPAC6IL-BF4) exhibits electrochromism even in free supporting electrolyte. The results confirm that the existence of imidazolium-based ionic liquid has an improvement on the ion diffusion properties and the switching time of conjugated polymer, which may provide a potential direction for the preparation of high-performance electrochromic materials.

Propelling electrochemical kinetics of transition metal oxide for high-rate lithium-ion battery through in situ deoxidation

To engineer advanced anodes for high-rate lithium-ion battery, rational structural design with insightful understanding of rapid reaction kinetics is important and still highly desirable. In this work, a high-temperature in situ deoxidation strategy is used to propel electrochemical kinetics of NiO through incorporating an intrinsic Ni component. Both theoretical calculation and experimental study demonstrate that the Ni-NiO heterojunction significantly enhances the electronic conductivity and ion diffusion properties. Accordingly, the lithium-ion battery modified with the heterostructured Ni-NiO shows remarkably improved charge transfer efficiency and rate performance, substantially outperforming many reported NiO-based anodes. This work opens up the exploration of heterostructured metal compounds as kinetic regulators for high-rate lithium-ion battery and also enlightens the understanding of defect chemistry in propelling electrochemical reactions.

BN-codoped CNT based nanoporous brushes for all-solid-state flexible supercapacitors at elevated temperatures

Porous graphitic carbon based nanostructured electrodes offer several advantages for energy storage applications, such as, high specific surface area, high active charge storage sites, suitable ion diffusion and excellent charge transport properties. Vertically aligned carbon nanotubes (CNTs) have widely been exploited for electrochemical energy storage in different architectures using various electrolytes. However, a 3D carbon based electrode with high mechanical flexibility, reliability along with high charge storage capacity with solid-state electrolyte have yet to be realized. Here we develop a simple spray pyrolysis process for synthesizing nanoporous brush-like CNTs grown radially on individual carbon fibers of a carbon cloth (CC) substrate and simultaneously codoping with boron (B) and nitrogen (N) heteroatoms. The obtained BNCNT-CC electrodes were utilized to fabricate highly flexible all solid state symmetrical supercapacitor cells. The cells demonstrated high aerial capacitance of 106.8 mF/cm2 (~21.4 F/cm3), excellent flexibility without any performance degradation, attractive capacitance retention (86.4%) even after 5000 charge/discharge cycles, stability above room temperature, 741.8 mWh/cm3 specific energy at 25 W/cm3 specific power and conservation of 56% of its initial energy at specific power of 1 kW/cm3. The results are distinctly better than previous reports as a whole in terms of different performance parameters and are attributed to the unique nanoporous structure, low combined series resistance, BN-codoping and diffusion controlled modulation in electrochemical energy storage characteristics.

Mechanical alloy coating of LATP decorated porous carbon on LiFe1/3Mn1/3Co1/3PO4/C composite cathode for high-voltage Li-ion battery

Mixed ionic (Li1.4Al0.4Ti1.6(PO4)3; LATP) and electronic (porous carbon; C) conductor based composite coating is demonstrated on LiFe1/3Mn1/3Co1/3PO4/C olivine-type (LFMCP) composite cathode materials, for the first time, by dry particle coating method using novel mechanofusion treatment. The LFMCP cathode material is prepared through one-time (LFMCP#1) and two-time (LFMCP#2) ball-mill plus spray dry method by adding transition metal precursors with citric acid and sucrose as reducing agent and carbon source. Later, the LFMCP#2 sample is dry coated with 2 wt.% LATP@C composite filler to enhance the electrochemical performance. The initial charge-discharge result reveals the discharge capacity of the LFMCP#2-LATP@C is around 151.87 mAh g−1 at 0.1C rate which is comparatively higher than the LFMCP#1 and LFMCP#2 electrodes. Besides, LFMCP#2-LATP@C/Li cell achieved superior capacity retention value around 92.20%, after 30 cycles at 0.1C/0.1C and 81.01% for 100 cycles at 1C/1C rate. The excellent cycle stability is archived due to the improved interface properties between the LATP@C coated LFMCP materials and electrolytes. AC impedance analysis confirms the lower charge transfer resistance and higher Li+ ion diffusion properties of LFMCP#2-LATP@C materials. The results suggested that the dry particle coating of LiFe1/3Mn1/3Co1/3PO4 material with LATP@C coating layer can used as a potential candidate for the high voltage lithium battery.

A concise pore structure model for predicting the effective ion diffusion coefficients of cementitious materials

Ion diffusion property prediction of cementitious materials by modeling pore structure is a hotspot and challenge for cement and concrete research. In a recent paper, Yio et al. examined the 3D structure of capillary pores (>0.24 μm) within 1003 μm3 blended cement paste for the first time using laser scanning confocal microscopy (LSCM). The main advantage of LSCM is the ability to characterize the 3D structure of interconnected pores and then to improve the possibility of establishing more effective pore structure models. This contribution proposes a novel and concise pore structure model named accessible cylindrical tortuous pore model (ACTPore model) for describing the physical connections among accessible porosity, mean pore diameter, tortuosity and pore specific surface area. The ACTPore model is proved to be rational and verified by LSCM experimental results.

Electronic structure, ion diffusion and cation doping in the Na4VO(PO4)2 compound as a cathode material for Na-ion batteries.

Sodium-ion batteries are considered one of the most promising alternatives to lithium-ion batteries owing to the low cost and wide abundance of sodium. Phosphate compounds are promising materials for sodium-ion batteries because of their high structural stability, energy densities and capacities. Vanadium phosphates have shown high energy densities, but their sodium-ion diffusion and cation doping properties are not fully rationalized. In this work, we combine density functional theory calculations and molecular dynamics simulations to study the electronic structure, ion diffusion and cation doping properties of the Na4VO(PO4)2 compound. The calculated Na-ion activation energy of this compound is 0.49 eV, which is typical for Na-based cathode materials, and the simulations predict a Na-ion diffusion coefficient of 5.1 × 10-11 cm2 s-1. The cell voltage trends show a voltage of 3.3 V vs. Na/Na+. Partial substitution of vanadium atoms by other metals (Al3+, Co2+, Fe3+, Mn4+, Ni2+ or Ti4+) increases the cell voltage up to 1.1 V vs. Na/Na+. These new insights will help us to understand the ion transport and electrochemical behaviour of potential phosphate cathode materials for sodium-ion batteries.

Ag diffusion effect on the crystal structure, band structure, and optical property of α-CsPbI3 perovskite materials

Organic-inorganic perovskite solar cell materials have attracted considerable attention in recent years. Ag and Au are commonly employed as the counter electrode in such cells. In this study, molecular dynamics simulation were used to investigate the diffusion properties of Ag ions in α-CsPbI3. Ag ions have the highest diffusion coefficient at temperatures between 318 K and 358 K. Density functional theory calculations were performed to study the effects of Ag diffusion on the band structures, crystal structures and optical absorption spectra of α-CsPbI3 materials. The results suggest that, Ag ions have diffusion coefficients ranging from 0.6 × 10−6 cm2 × s−1 to 1.1 × 10−6 cm2 × s−1 in α-CsPbI3 at temperatures between 278 K and 398 K. Ag doping can insert a Ag dopant level in α-CsPbI3 and reduce the band gap of α-CsPbI3. Furthermore, increasing the Ag content could reduce the energy gap between the Ag dopant level and the valence band or conduction band.

Layer Charge Effects on Adsorption and Diffusion of Water and Ions in Interlayers and on External Surfaces of Montmorillonite

Molecular simulations using classical force fields were performed to study the adsorption and diffusion properties of water and ions in the high-charge (Arizona-type) montmorillonite clays with var...

A high energy storage supercapacitor based on nanoporous activated carbon electrode made from Argan shells with excellent ion transport in aqueous and non-aqueous electrolytes

Abstract A high-performance supercapacitor electrode was obtained from waste biomass, Argan shells. This electrode was fabricated using a simple activation technique; demonstrating an industry-friendly process, which is capable of having precise control over pore size distribution of the activated carbon derived from a natural resource. The obtained samples exhibited different pore size distributions, based on different activating agents and different activation routes used in the process. Two distinctly different pore size distributions were obtained from a single source and same synthesis routes, only by exploiting the size differences of the activating agents, which are potassium (KOH) and sodium (NaOH) ions respectively. This process enabled a significant enhancement of specific energy, with no or very negligible change in specific power. Thanks to the fact that there was almost no loss in ion diffusion properties within the porous network of the electrodes even after a change in the electrolytes, to the more viscous ionic liquid (Ethyl-Methyl Imidazolium Tetrafluoroborate), from comparatively less viscous aqueous and organic-based electrolytes. This size-controlled activation enabled us obtaining appropriate pore size distribution, which is a combination of a large number of micropores and a sufficient number of mesopores. This provided a very high specific surface area of 2251 m2/g with a total pore volume of 1.04 cm3/g. Very high specific capacitance of ∼179 F/g in aqueous electrolyte (0.5 M K2SO4) was obtained. The excellent porosity resulted in very high specific energy of ∼65 Wh/kg and high specific power of ∼2 kW/kg in ionic liquid electrolyte for 3.5 V operating voltage.

3D Printed Hierarchical Porous Carbon Aerogels for Supercapacitors at Ultralow Temperatures

Supercapacitors (SCs) represents an emerging class of fast-charging and stable energy storage devices and have been extensively studied in recent years. However, most of the previous research are focused on SCs in aqueous and room temperature conditions. Improve the performance of SCs, especially in low-temperature environments, is significantly important for prolonged space exploration. This talk will report our new findings of using 3D printing method to fabricate carbon aerogels for supercapacitors at ultralow temperatures. The 3D printed carbon aerogel electrodes with periodic large pores have shown much improved electrochemical performance than the non-3D printed counterparts at low temperatures. More importantly, hierarchical pore structure with large periodic pores, macropores, mesopores and micropores in the 3D printed carbon aerogels enable the porous electrodes to achieve an excellent capacitance of over 150 F/g even under -70 °C. Kinetic analysis further reveals the favorable ion diffusion property in the 3D printed hierarchical porous electrodes. Moreover, the effects of each type of pore structure on capacitance at low-temperature will also be talked. This talk will for the first time demonstrate the superiority of 3D printed porous electrodes for ultralow temperature energy storage, which might open a new door for the future work on high-performance fast-charging energy storage system for space missions.

Activated carbon with exceptionally high surface area and tailored nanoporosity obtained from natural anthracite and its use in supercapacitors

We have developed high performance supercapacitor electrodes while demonstrating that using one-step simple industry friendly activation technique, precise control over pore size distribution can be obtained from natural resource. Irrespective of the same staring material, natural anthracite, the obtained samples exhibited two distinctly different pore size distributions exploiting the size differences of the activating agents, which are potassium (KOH) and sodium (NaOH) ions respectively. This precise control over pore sizes enabled us to obtain an unprecedented observation of 136% enhancement of energy density while there is no loss of power density was observed. This unique observation is a result of almost no loss in ion diffusion properties within the electrodes, irrespective of the change of electrolyte to more viscous ionic liquid (Ethyl-Methyl Imidazolium Tetrafluoroborate) from a less viscous aqueous and organic based electrolytes. This size-selective activation enabled us tailoring a highly desirable pore size distribution, a combination of bigger micropores and smaller mesopores. This not only provided very high specific surface area of 2934.60 m2/g with a total pore volume of 1.33 cm3/g, and highest capacitance (198.15 F/g) in aqueous electrolyte, it has also resulted in very high energy density of 82.93 Wh/kg and high power density of ~3487 W/kg.

Influence of Fe doping on the crystal structure, electronic structure and supercapacitance performance of birnessite [(Na, K)x(Mn4+, Mn3+)2O4·1.5H2O] with high areal mass loading

The supercapacitance performance of birnessite, which is a common layered manganese oxide mineral with the general formula of (Na, K, Ca)x(Mn4+, Mn3+)2O4·1.5H2O, is greatly hindered by poor electrical conductivity, especially when the areal mass loading of the active materials is high enough for practical application. Heterogeneous atom doping is an effective way for improving the supercapacitance performance of birnessite. Herein, we mainly investigate the influence of Fe doping on the crystal structure, electronic structure and capacitance performance of birnessite [(Na, K)x(Mn4+, Mn3+)2O4·1.5H2O] in detail by combining the experiments and theoretical calculations/simulations. It is found that Fe atoms mainly substitute the central trivalent Mn in [MnO6] octahedral after doping without changing the crystalline phase of birnessite. Meanwhile, the particle size and surface area of Fe-doped birnessite continuously increase with the increase of the content of Fe dopant. On the other hand, the electronic conductivity of the doped birnessite firstly increases and then decreases with the increase of the Fe content due to the reduced indirect band gap and the increased number of the boundary/grain interfaces. Based on these results, the influences of Fe doping on the supercapacitance performance of birnessite electrode with very high areal mass loading of ∼10–12 mg cm−2 are elaborately discussed related to morphology, structure, electrical conductivity, and ion diffusion properties.

Enhanced electrochemical performance of electrospun V2O5 fibres doped with redox-inactive metals

The structural and electrochemical effects of electrospun V2O5 with selected redox-inactive dopants (namely Na+, Ba2+ and Al3+) have been studied. The electrospun materials have been characterised via a range of analytical methods including X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller surface area measurements and scanning and transmission electron microscopy. The incorporation of dopants in V2O5 was further studied with computational modelling. Structural analysis suggested that the dopants had been incorporated into the V2O5 structure with changes in crystal orientation and particle size, and variations in the V4+ concentration. Electrochemical investigations using potentiodynamic, galvanostatic and impedance spectroscopy analysis showed that electrochemical performance might be dependent on V4+ concentration, which influenced electronic conductivity. Na+- or Ba2+-doped V2O5 offered improved conductivities and lithium ion diffusion properties, whilst Al3+ doping was shown to be detrimental to these properties. The energetics of dopant incorporation, calculated using atomistic simulations, indicated that Na+ and Ba2+ occupy interstitial positions in the interlayer space, whilst Al3+ is incorporated in V sites and replaces a vanadyl-like (VO)3+ group. Overall, the mode of incorporation of the dopants affects the concentration of oxygen vacancies and V4+ ions in the compounds, and in turn their electrochemical performance.

Two-dimensional mesoporous vanadium phosphate nanosheets through liquid crystal templating method toward supercapacitor application

Mesoporous vanadium phosphate (VOPO4) nanosheets have been successfully synthesized through an easy and reproducible lyotropic liquid crystals (LLC) templating approach for the first time. Using the triblock copolymer (P123) as a surfactant, VOPO4 precursor with a well-developed 2D hexagonal mesostructure can be obtained. Following complete removal of the template by calcination, crystallized VOPO4 frameworks with less-ordered mesostructure are achieved. The as-prepared mesoporous VOPO4 nanosheets exhibit superior pseudocapacitive performance (767 F g‒1 at 0.5A g‒1) by virtue of the favorable mesostructure that gives rise to abundant easily accessible redox active sites as well as reinforced charge transfer and ion diffusion properties. The charge storage mechanism of the mesoporous VOPO4 nanosheets has been experimentally demonstrated to be based on the reversible two-step redox reactions between V(V) and V(III) in acidic medium. This advantageous LLC templating strategy is expected to open up a new route for designing various mesoporous metal phosphates with superior electrochemical performance for utilization in energy storage devices.

Self-doping of Ti3+into Na2Ti3O7 increases both ion and electron conductivity as a high-performance anode material for sodium-ion batteries

As a safe, low-voltage anode material, in recent years, Na2Ti3O7 has become regarded as a highly alternative negative material for high energy room-temperature sodium ion batteries. However, its poor ion and electron conductivity produces very poor electrochemical performance of Na2Ti3O7, therefore greatly limiting its practical application in future scalable utilization. We report here a self-doping of Ti3+ into the Na2Ti3O7 electrode material, through a very simple post heat-treatment process, that is, annealing the Na2Ti3O7 precursor at an argon atmosphere containing 5% H2. By XPS characterization, it is confirmed that Ti3+ is successfully doped into Na2Ti3O7. Benefiting from this self-doped Ti3+ with larger ionic radius and better electronic conductivity, the obtained Na2Ti3O7 demonstrates improved electron conductivity and ion diffusion properties. Combined with a carbon coating, this self-doped Na2Ti3O7 electrode material exhibits superior electrochemical performance to that of non-doped electrode, e.g., this Na2Ti3O7 sample could delivers a specific capacity of 187.8 and 51.9 mAh g−1 from 0.1C to 10C at various rate of discharge, respectively. When recycled back to 0.1C, it can still reach 153 mAh g−1. Compared with numerous reported nanoscale means, we believe this approach is practical and productive, and may extend to other ti-based electrode materials.

Reliable Ge2Sb2Te5‐Integrated High‐Density Nanoscale Conductive Bridge Random Access Memory using Facile Nitrogen‐Doping Strategy

AbstractConductive bridge random access memory (CBRAM) is a possible replacement for static field‐programmable gate arrays (FPGAs) based on random‐access memory. Ge2Sb2Te5 (GST) is used in CBRAMs as a solid electrolyte due to its high diffusion properties of active ions and scalability to obtain high‐density memory devices. Here, the trade‐off between high memory window and uniformity of CBRAM based on GST is solved by introducing N atoms into the SE. Nitrogen‐incorporated GST film (N‐GST) is proposed as a replacement for the current GST‐based CBRAMs with improved performance and better opportunities for conventional FPGA technologies. A bidirectional polarity‐dependent characteristic with high ION/IOFF ratio and satisfactory operation voltage is achieved by using N‐GST thin film in a programmable metallization cell (PMC). Integration of N atoms in the GST‐based PMC with a simple structure of Ag/ N‐GST /Pt increases the resistance ratio more than 100 times compared to an undoped one. Consistent data retention is attained in both resistance states for ≥3.5 × 104 s at temperature up to 85 °C.

Exploring the correlation between MoS2 nanosheets and 3D graphene-based nanostructures for reversible lithium storage

Graphene-based materials are an attractive lithium storage material for next-generation lithium-based batteries due to its high capacity, surface area and conductivity. However, one of the major problems for its broad application in batteries is a large irreversible capacity, and the poor cycle stability and low rate capability remain. Here, we report a MoS2-stabilized hierarchical three-dimensional graphene-based nanostructure, in which the MoS2 layer acts as a stabilizer as well as an active material. We show that the presence of MoS2 thin layer adjacent to the graphene surface can improve lithium storage capability by improving lithium ion diffusion property with fast Li-ion transport kinetic. On the basis of experimental and theoretical approaches, we ascribe the improved reversible lithium storage to the unusual reversible Li-MoS2 redox reaction and charge distribution on the graphene and MoS2 interlayers. These findings will provide a potential new direction in the design of electrode materials for advanced lithium storage technologies.

Novel Biohybrid Polysulfone Membranes with Physically Immobilized Gramicidin for Ion-Exchange Applications

The goal of this work was to design a system incorporating gramicidin (gA) into a polysulfone (Psf) membrane. The strategy involved immobilization of gA on the surface of two types of magnetite nanoparticles (MNPs) dispersed in a polymeric matrix. Membranes have been treated with surfactant Triton X100 (TRX) and surfactant/protein micelles (TRX/gA). MNP morphology was studied using transmission electron microscopy, and the chemical structure was confirmed by Fourier transform infrared analysis. Membrane morphology was observed under environmental scanning electron microscopy; water interactions were tested using static contact angle and water uptake, whereas ion transport was evaluated by means of a permeability test and current–voltage experiments. Depending on the type of nanoparticles used, immobilization led to either higher or lower membrane hydrophilicity but did not influence their morphology. Protein immobilization resulted in enhanced ion diffusion properties and membrane selectivity. This novel ...

Polymethacrylate-comb-copolymer electrolyte for solid-state energy storage devices

We report a highly ion-conductive polymer electrolyte, based on a poly(2-[3-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]ethyl methacrylate)-poly(oxyethylene methacrylate)-comb (PBE-comb) copolymer and the 1-ethyl-3-methylimidazolium dicyanamide (EMIM-DCA) ionic liquid, for use in a solid-state supercapacitor. Selective interactions between the poly(oxyethylene methacrylate) (POEM) chains and the EMIM-DCA induce the formation of a microphase-separated structure, as evidenced by Fourier-transform infrared spectroscopy, transmission electron microscopy, and differential scanning calorimetry. The well-defined nanostructured morphology effectively suppresses the aggregation of EMIM-DCA to provide ion-transport pathways that facilitate the fast diffusion of mobile ions. The capacitance of the solid-state supercapacitor formed with the PBE/EMIM-DCA electrolyte (125.1Fg−1) was much greater than that of the conventional poly(vinyl alcohol) (PVA)/H3PO4 electrolyte (39.5Fg−1) due to its higher ionic conductivity and superior affinity for the electrode. The fast ion-diffusion properties of the PBE/EMIM-DCA electrolyte was confirmed by its high capacitance retention (70%) at a fast scan rate, significantly higher than that observed for the PVA/H3PO4 electrolyte. Moreover, the supercapacitor composed of the PBE/EMIM-DCA electrolyte showed considerable cycling stability (91.1% after 10,000 charge-discharge cycles). The PBE/EMIM-DCA electrolyte is therefore a promising candidate for use in high-performance solid-state supercapacitors and energy-storage systems.