Slow Diffusion Kinetics Research Articles

A pinning structure via composing laminar rGO with fragmented MoS2 toward fast and stable sodium and lithium-ion storage

The diffusion of lithium ions and sodium ions in the anode materials is the main factor limiting the fast-charging performance of lithium and sodium-ion batteries. Due to the slow diffusion kinetics, taking lithium-ion batteries as an example, lithium ions and electrons accumulate locally in and on the surface of anode materials, especially in the process of fast-charging, resulting in uneven lithiation reaction and enormous transient stress, which leads to poor fast-charging performance. In this work, from the aspect of solving the ion diffusion rate, a capacitive type of energy storage is introduced by designing MoS2/rGO composite materials with pinned structures as fast-charging and stable anode materials for lithium-ion batteries and sodium-ion batteries. Combining the high ion conductivity and structural rigidity of the rGO conductive network with a few-layer MoS2 provides a high ion diffusion rate and capacity. As expected, it can charge to 69 % in 25 min and 44 % in 3.2 min, respectively, providing a high capacity of 214.2 mAh g−1 at 10 A g−1 and a high-capacity retention of 85.31 % after 1, 000 cycles at the current density of 3 A g−1 in sodium-ion batteries. Similarly, the high reversible capacity of 910.5 mAh g−1 is achieved in the lithium-ion batteries, and there is almost no capacity loss after 1, 000 cycles at a high current density of 2 A g−1. This work may provide a reference for designing more fast-charging anode materials with high capacity.

Organic Intercalation Induced Kinetic Enhancement of Vanadium Oxide Cathodes for Ultrahigh-Loading Aqueous Zinc-Ion Batteries.

Vanadium-based oxides have attracted much attention because of their rich valences and adjustable structures. The high theoretical specific capacity contributed by the two-electron-transfer process (V5+ /V3+ ) makes it an ideal cathode material for aqueous zinc-ion batteries. However, slow diffusion kinetics and poor structural stability limit the application of vanadium-based oxides. Herein, a strategy for intercalating organic matter between vanadium-based oxide layers is proposed to attain high rate performance and long cycling life. The V3 O7 ·H2 O is synthesized in situ on the carbon cloth to form an open porous structure, which provides sufficient contact areas with electrolyte and facilitates zinc ion transport. On the molecular level, the added organic matter p-aminophenol (pAP) not only plays a supporting role in the V3 O7 ·H2 O layer, but also shows a regulatory effect on the V5+ /V4+ redox process due to the reducing functional group on pAP. The novel composite electrode with porous structure exhibits outstanding reversible specific capacity (386.7 mAh g-1 , 0.1 A g-1 ) at a high load of 6.5mg cm-2 , and superior capacity retention of 80% at 3 A g-1 for 2100 cycles.

Impact of lithium diffusion paths on electrochemical behavior of LiNi0.6Co0.2Mn0.2O2 cathode for lithium-ion batteries

Severe microcracks of polycrystal LiNixCoyMnzO2 cathodes during cycling have led to increasing attention to the development of single-crystal cathodes. The single-crystal cathode particle is considered to induce a straight Li-ion diffusion through two-dimensional pathways in bulk compared with the pathways of grain boundary and cracks inside polycrystal particles. However, the effect of different paths on diffusion kinetics and the resulting electrochemical properties still needs to be better understood. In this work, the electrochemical performance of polycrystal and single-crystal cathodes caused by different diffusion paths was compared in detail. The results showed that grain boundaries and cracks of polycrystalline cathodes facilitate Li-ion diffusion. In contrast, relatively slow Li-ion diffusion occurs in the single-crystal cathode particles due to long diffusion paths. Moreover, the single-crystal cathode particles experience severe structural inhomogeneity due to the slow diffusion kinetics and inhomogeneous Li concentrations, resulting in structural distortion and localized strain increasing during cycling.

Multi-Channel Hollow Carbon Nanofibers with Graphene-Like Shell-Structure and Ultrahigh Surface Area for High-Performance Zn-Ion Hybrid Capacitors.

Porous carbon is the most promising cathode material for Zn-ion hybrid capacitors (ZIHCs), but is limited by insufficient active adsorption sites and slow ion diffusion kinetics during charge storage. Herein, a pore construction-pore expansion strategy for synthesizing multi-channel hollow carbon nanofibers (MCHCNF) is proposed, in which the sacrificial template-induced multi-channel structure eliminates the diffusion barrier for enhancing ion diffusion kinetics, and the generated ultrahigh surface area and high-density defective structures effectively increase the quantity of active sites for charge storage. Additionally, a graphene-like shell structure formed on the carbon nanofiber surface facilitates fast electron transport, and the highly matchable pore size of MCHCNF with electrolyte-ions favors the accommodation of charge carriers. These advantages lead to the optimized ZIHCs exhibit high capacity (191.4mAhg-1 ), high energy (133.1Whkg-1 ), along with outstanding cycling stability (93.0% capacity retention over 15000 cycles). Systematic ex situ characterizations reveal that the dual-adsorption of anions and cations synergistically ensures the outstanding electrochemical performance, highlighting the importance of the highly-developed porous structure of MCHCNF. This work not only provides a promising strategy for improving the capacitive capability of porous materials but also sheds light on charge storage mechanisms and rational design for advanced energy storage devices.

Proton-self-doped PANI@CC as the cathode for high-performance aqueous zinc-ion battery

Aqueous zinc-ion batteries (AZIB) have several advantages such as low cost, large theoretical capacity and good safety. However, the development of polyaniline (PANI) cathode materials has been limited by slow diffusion kinetics. Herein, proton-self-doped polyaniline@carbon cloth (CC) (PANI@CC) was prepared via in-situ polymerization, where polyaniline was deposited on an activated carbon cloth. The PANI@CC cathode exhibits a high specific capacity of 234.3 mA h g−1 at 0.5 A g−1, and excellent rate performance, delivering a capacity of 143 mA h g−1 at 10 A g−1. Furthermore, the reversible redox conversion during the charge–discharge process was studied using ex-situ X-ray photoelectron spectroscopy (XPS) and ex-situ Raman spectra. The results show that the excellent performance of the PANI@CC battery can be attributed to the formation of a conductive network between the carbon cloth and polyaniline. Also, a mixing mechanism involving insertion/extraction of Zn2+/H+ and a double-ion process is proposed. PANI@CC electrode is a novel idea for developing high-performance batteries.

Exploring Cathode Materials for Zn-Ion Batteries: A First-Principles Investigation

Aqueous zinc-ion batteries (ZIBs) are a promising technique for large-scale energy storage, however, the large ionic potential of Zn2+ ions leads to slow diffusion kinetics of Zn2+ ions in cathode hosts. To address this issue, we predicted two vanadium-based compounds for potential applications as cathode materials for ZIBs through the evolutionary algorithm. The dynamic, mechanical, and thermodynamic stabilities of the newly discovered ZnVO3 polymorphs were confirmed by ab initio calculations. CI-NEB results show impressively low Zn2+-ion migration barriers of 0.44 and 0.40 eV for the predicted P2/c and P21/c polymorphs, respectively. Furthermore, the P21/c-structured ZnVO3 exhibits a small band gap of 1.62 eV, a high voltage plateau of 1.16 V, and a trivial volume change upon charging, which may suggest excellent rate performance and a long cycle life when functioning as a cathode material for ZIBs. The work may provide fundamental guidance for the design and development of electrode materials featuring intrinsic fast Zn2+ ion transportation.

强耦合氧化钼氮碳复合材料的制备及其锂离子存储性能研究

Molybdenum oxide (MoO3) is an attractive anode material for lithium-ion batteries (LIBs); however, its low electrical conductivity, large volume expansion after lithiation, and slow Li-ion diffusion kinetics severely limit its practical applications. Here, ultrafine MoO3 nanoparticles (NPs) (10–15 nm) are synthesized from heavily Mo/N-doped carbonaceous precursors, resulting in MoO3 NPs confined in an N-doped carbon network. This design allows fast electron conduction and short Li-ion diffusion paths; meanwhile, abundant N species and O vacancies on the MoO3 surface lower the Li-ion adsorption barrier and together contribute to the durable Li-ion storage at high current rates. Notably, the obtained nanocomposite NC-MoO3 exhibits a high capacity of 1362 mA h g−1 (0.1 A g−1) and maintains a reversible capacity of 394 mA h g−1 at 10.0 A g−1. A coin-type full LiFePO4//NC-MoO3-400 cell obtains a large specific capacity of 81 mA h g−1 at 5 C. Our work inspires the design and confinement synthesis of other transition metal oxides embedded in conducting carbon networks for practical LIB applications.

Controlled growth of Co9S8 nanoparticle-embedded carbon nanosheets/carbon nanofibers toward high-performance sodium storage

Transition metal sulfides (TMSs) are considered as promising anodes for sodium-ion batteries (SIBs) due to their high theoretical capacity and low cost. However, TMSs suffer from massive volume expansion, slow sodium-ion diffusion kinetics, and poor electrical conductivity, which severely restrict their practical application. Herein, we design self-supporting Co9S8 nanoparticles embedded carbon nanosheets/carbon nanofibers (Co9S8@CNSs/CNFs) as anode materials for SIBs. The electrospun carbon nanofibers (CNFs) provide continuous conductive networks to accelerate the ion and electron diffusion/transport kinetics, while MOFs-derived carbon nanosheets (CNSs) buffer the volume variation of Co9S8, consequently improving the cycle stability. Benefitting from the unique design and pseudocapacitive features, Co9S8@CNSs/CNFs deliver a stable capacity of 516 mAh g−1 at 200 mA g−1 and a reversible capacity of 313 mAh g−1 after 1500 cycles at 2 A g−1. Note that, it also displays excellent sodium storage performance when assembled into a full cell. The rational design and excellent electrochemical properties endow Co9S8@CNSs/CNFs with the potential stepping into commercial SIBs.

Spectroelectrochemical Investigation of the Local Alkaline Environment on the Surface-Nanostructured Au for the Conversion of CO2 to CO

The electrocatalytic conversion of carbon dioxide (CO2) into fuels could potentially achieve a sustainable carbon-based economy. The engineering of nanostructured metal electrodes can enhance their activity and selectivity by controlling their local chemical environment; however, direct observation is challenging. In this study, we investigate the molecular-level reaction mechanism of a nanoporous-structured Au electrode for the conversion of CO2 to carbon monoxide (CO) using surface-enhanced infrared absorption spectroscopy (SEIRAS). We designed a well-structured nanoporous Au layer (with a depth distribution of 56.3 nm) on a Si prism using a high-temperature non-aqueous anodization process and characterized the nanoporous Au electrode using atomic force microscopy (AFM) and X-ray absorption spectroscopy (XAS). The in situ SEIRAS results demonstrated that the nanoporous Au electrode has a dominant active site, promoting the linear CO intermediate and suppressing the bridging CO intermediate when compared with the non-structured Au electrode. We also revealed a high local pH at a reaction potential of −0.9 V and the slow diffusion kinetics of local CO32– at an open-circuit potential. These findings provide deeper insights into the electrochemical kinetics and corresponding mechanisms occurring in the electric double layers and highlight the potential for the design of efficient electrocatalysts for CO2 reduction.

Sub-10 nm Mixing and Alloying of Cu-Ag and Cu-Ni via Accelerated Solid Diffusion.

Development of nanoscale multicomponent solid inorganic materials is often hindered by slow solid diffusion kinetics and poor precursor mixing in conventional solid-state synthesis. These shortcomings can be alleviated by combining nanosized precursor mixtures and low temperature reaction, which could reduce crystal growth and accelerate the solid diffusion at the same time. However, high throughput production of nanoparticle mixtures with tunable composition via conventional synthesis is very challenging. In this work, we demonstrate that ∼10 nm homogeneous mixing of sub-10 nm nanoparticles can be achieved via spark nanomixing at room temperature and pressure. Kinetically driven Spark Plasma Discharge nanoparticle generation and ambient processing conditions limit particle coarsening and agglomeration, resulting in sub-10 nm primary particles of as-deposited films. The intimate mixing of these nanosized precursor particles enables intraparticle diffusion and formation of Cu/Ni nanoalloy during subsequent low temperature annealing at 100 °C. We also discovered that cross-particle diffusion is promoted during the low-temperature sulfurization of Cu/Ag which tends to phase-segregate, eventually leading to the growth of sulfide nanocrystals and improved homogeneity. High elemental homogeneity, small diffusion path lengths, and high diffusibility synergically contribute to faster diffusion kinetics of sub-10 nm nanoparticle mixtures. The combination of ∼10 nm homogeneous precursors via spark nanomixing, low-temperature annealing, and a wide range of potentially compatible materials makes our approach a good candidate as a general platform toward accelerated solid state synthesis of nanomaterials.

Superlithiation Performance of Pyridinium Polymerized Ionic Liquids with Fast Li+ Diffusion Kinetics as Anode Materials for Lithium-Ion Battery.

Polymerized ionic liquids (PILs) with super ion diffusion kinetics have aroused considerable attention in rechargeable batteries, which are very promising to solve the problem of the slow ion diffusion kinetics in organic electrode materials. Theoretically, PILs incorporated redox groups are very suitable as anode materials to realize "superlithiation" performance, achieving high lithium storage capacity. In this study, redox pyridinium-based PILs (PILs-Py-400) have been synthesized through trimerization reactions by pyridinium ionic liquids with cyano groups under an appropriate temperature (400 °C). The positively charged skeleton, extended conjugated system, abundant micropores, and amorphous structure for PILs-Py-400 can boost the utilization efficiency of redox sites. A high capacity of 1643 mAh g-1 at 0.1 A g-1 (96.7% of the theoretical capacity) has been obtained, indicating intriguing 13 Li+ redox reactions in per repeating unit of one pyridinium ring, one triazine ring, and one methylene. Moreover, PILs-Py-400 exhibit excellent cycling stability with a capacity of around 1100 mAh g-1 at 1.0 A g-1 after 500 cycles, and the capacity retention is 92.2%.

Phase engineering of nickel-based sulfides toward robust sodium-ion batteries

Nickel-based sulfides are considered promising materials for sodium-ion batteries (SIBs) anodes due to their abundant resources and attractive theoretical capacity. However, their application is limited by slow diffusion kinetics and severe volume changes during cycling. Herein, we demonstrate a facile strategy for the synthesis of nitrogen-doped reduced graphene oxide (N-rGO) wrapped Ni3S2 nanocrystals composites (Ni3S2-N-rGO-700 °C) through the cubic NiS2 precursor under high temperature (700 ℃). Benefitting from the variation in crystal phase structure and robust coupling effect between the Ni3S2 nanocrystals and N-rGO matrix, the Ni3S2-N-rGO-700 °C exhibits enhanced conductivity, fast ion diffusion kinetics and outstanding structural stability. As a result, the Ni3S2-N-rGO-700 °C delivers excellent rate capability (345.17 mAh g−1 at a high current density of 5 A g−1) and long-term cyclic stability over 400 cycles at 2 A g−1 with a high reversible capacity of 377 mAh g−1 when evaluated as anodes for SIBs. This study open a promising avenue to realize advanced metal sulfide materials with desirable electrochemical activity and stability for energy storage applications.

Electronic structure engineering on NiSe2 micro-octahedra via nitrogen doping enabling long cycle life magnesium ion batteries

Multivalent ion batteries have attracted great attention because of their abundant reserves, low cost and high safety. Among them, magnesium ion batteries (MIBs) have been regarded as a promising alternative for large-scale energy storage device owing to its high volumetric capacities and unfavorable dendrite formation. However, the strong interaction between Mg2+ and electrolyte as well as cathode material results in very slow insertion and diffusion kinetics. Therefore, it is highly necessary to develop high-performance cathode materials compatible with electrolyte for MIBs. Herein, the electronic structure of NiSe2 micro-octahedra was modulated by nitrogen doping (N-NiSe2) through hydrothermal method followed by a pyrolysis process and this N-NiSe2 micro-octahedra was used as cathode materials for MIBs. It is worth noting that N-NiSe2 micro-octahedra shows more redox active sites and faster Mg2+ diffusion kinetics compared with NiSe2 micro-octahedra without nitrogen doping. Moreover, the density functional theory (DFT) calculations indicated that the doping of nitrogen could improve the conductivity of active materials on the one hand, facilitating Mg2+ ion diffusion kinetics, and on the other hand, nitrogen dopant sites could provide more Mg2+ adsorption sites. As a result, the N-NiSe2 micro-octahedra cathode exhibits a high reversible discharge capacity of 169 mAh g−1 at the current density of 50 mA g−1, and a good cycling stability over 500 cycles with a maintained discharge capacity of 158.5 mAh g−1. This work provides a new idea to improve the electrochemical performance of cathode materials for MIBs by the introduction of heteroatom dopant.

Enhancing oxide scale growth and adhesion via electrochemically regulating ion diffusion

Pre-oxidation is a common surface treatment approach to enhance the corrosion resistance of metals, which suffers from slow ion diffusion kinetics, bad oxide scale adhesion, and weak compactness. Herein, we propose an electrochemical oxidation approach in molten carbonate to improve the oxide scale growth and adhesion via electrochemically regulating ion diffusion in the formed oxide scale. An anodic polarization applied at the metal substrate enlarges the chemical potential gradient of oxygen and offers a favorable electric field across the metal/oxide interface to the oxide scale/molten salt interface, thereby speeding up the oxide scale growth rate in terms of increasing the diffusion rate of metal cations and oxygen ions through the oxide scale. At the same time, the oxide scale adhesion is remarkedly improved because the metal vacancies at the oxide/alloy interface are filled by the newly formed oxide. After being treated by electrochemical oxidation, the corrosion rate of the Ni-16Fe-4Mo alloys in molten Li2CO3-Na2CO3-K2CO3 decreased ten-fold. Overall, electrochemical oxidation enables the rapid formation of an adherent and corrosion-resistant oxide scale on the metal substrate, offering a general and effective way to fabricate corrosion-resistant films to survive in various aggressively corrosive media.

Structural Water in Amorphous Tungsten Oxide Hydrate Enables Fast and Ultrastable Regulation of Near‐Infrared Light Transmittance

AbstractAmorphous tungsten oxides typically show low near infrared (NIR) light selectivity owing to the overlapped modulation of visible and NIR light originating from ion insertion induced polaronic adsorption, and poor cycling stability due to the ion trapping effects during the repeated ion insertion/extraction. Here it is reported that the structural water in amorphous tungsten oxide hydrate can induce selective and fast modulation of NIR light with extremely high cycling stability. The enhanced NIR electrochromic (EC) capability is found to be associated with the dominant pseudocapacitive behavior promoted by the structural water. The pseudocapacitive EC process avoids the deep ion insertion, slow ion diffusion kinetics, and ion trapping effects that typically occur in conventional diffusion‐controlled EC process, leading to high NIR light selectivity, fast response speed, and exceptional cycling stability. By tuning the amount of structural water, it is found that WO3·0.9H2O films show the optimum NIR EC performance with optical modulation of 69%, response times <3 s, coloration efficiency of 312 cm2 C−1, and cycling stability of 12 000 cycles at the wavelength of 1100 nm, which represents the state‐of‐the‐art NIR EC performance for the tungsten oxide‐based EC materials, making it a promising material for managing solar heat.

MoSe2 Complex with N and B Dual-Doped 3D Carbon Nanofibers for Sodium Batteries

The sodium battery is one of the best energy storage technologies due to its abundant resource reserves and excellent energy storage ability. As a two-dimensional layered transition metal, molybdenum selenide (MoSe2) has large interlayer spacing and a high theoretical capacity (470 mAh∙g−1). Its structure is suitable for the negative electrode of sodium-ion batteries, with a large ionic radius and slow ion diffusion kinetics. However, it is difficult for the rate capability and cycling performance of MoSe2 to meet practical needs due to a weak intrinsic electron transport ability and volume expansion during sodium absorption. The hydrothermal synthesis method was used to synthesize the MoSe2 complex based on boron and nitrogen dual-doped 3D carbon fibers obtained from bacterial cellulose membranes (MoSe2/N&B-BCM) for sodium batteries. Additionally, electrochemical analysis and experimental characterization were performed. In summary, the experimental analysis shows that MoSe2/N&B-BCM has excellent conductivity, structural integrity, cyclability (328 mAh∙g−1 after 100 cycles at a 0.5 c constant rate), and rate stability.

Ni3S2 nanoparticles encapsulated in S-doped biomass-derived hierarchically porous carbon as an advanced electrode for excellent hybrid supercapacitors performance

Although extensive efforts have been made to utilize raw biomass to synthesize porous carbon for the supercapacitor (SC), its large-scale application is difficult to achieve due to its slow diffusion kinetics and insufficient storage sites. Herein, biomass-derived high-capacity/high-rate cathode and anode materials are designed to realize high-performance SC. S-doped passionfruit peel-derived porous carbon (S-PFPC) is used as support to anchor nickel sulfide (Ni3S2) nanoparticles and is developed as cathode material. It provides sufficient sites to store discharge products, S-PFPC porous channels for fast electron transport, and uniformly dispersed Ni3S2 nanoparticles for enhance charge storage capacity. Simultaneously, hierarchically porous carbon with a high specific surface area as the anode material is also obtained by simple pyrolysis of passionfruit peel. Benefiting from the well-matched anode and cathode structures, the assembled Ni3S2 @S-PFPC//PFPC hybrid supercapacitor (HSC) exhibits a high energy density of 118 W h kg−1 at a power density of 433 W kg−1. In addition, it exhibits long-life stability with excellent capacitance retention of 88.3% over 10000 cycles. The route for preparing biomass-derived electrode materials proposed in this work broadens the horizon to realize high-performance SC applications.

Co‐Substituted BiFeO3: Electronic, Ferroelectric, and Thermodynamic Properties from First Principles

AbstractBismuth ferrite, BiFeO3, is a multiferroic solid that is attracting increasing attention as a potential photocatalytic material, because the ferroelectric polarization enhances the separation of photogenerated carriers. With the motivation of finding routes to engineer the band gap and the band alignment, while conserving or enhancing the ferroelectric properties, the thermodynamic, electronic, and ferroelectric properties of BiCoxFe1−xO3 solid solutions (x = 0, 0.0625, 0.125) using density functional theory are investigated. It is shown that the band gap can be reduced from 2.9 to 2.1 eV by cobalt substitution, while simultaneously increasing the spontaneous polarization, which is associated with a notably larger Born effective charge of Co compared to Fe cations. The interaction between Co impurities is discussed, which is strongly attractive and can drive the aggregation of Co, as evidenced by Monte Carlo simulations. Phase separation into a Co‐rich phase is therefore predicted to be thermodynamically preferred, and the homogenous solid solution can only exist in metastable form, protected by slow cation diffusion kinetics. Finally, the band alignment of pure and Co‐substituted BiFeO3 with relevant redox potentials, in the context of its applicability in photocatalysis, is discussed.

Single-crystalline Mn2V2O7 anodes with high rate and ultra-stable capability for sodium-ion batteries

The abundant sodium resources provide a great potential for the practical application of sodium ion batteries (SIBs). However, the development of feasible anode materials with high-rate capability to solve the slow diffusion kinetics of Na+ has always been a major challenge for high performance SIBs. Herein, a layer-structured metal vanadate Mn2V2O7 (MnVO) with large open channel within its crystal structure frame is for the first time identified as a promising candidate for high-rate SIB anodes, which ensures a large pseudocapacitance contribution. Moreover, the prepared micron size single crystal structure of MnVO effectively shortens the diffusion and transmission paths of Na+ ions and electrons, thus accomplishing high capacity (a reversible capacity of 250 mA h g−1 at 0.2 A g−1), excellent cycling stability (125 mA h g−1 at 10 A g−1 after 3500 cycles with 98% capacity retention) and fast charge and discharge rates (120 mA h g−1 at 20 A g−1 after 5000 cycles). This work explores transition metal vanadates as SIB anodes with excellent rate performance.

Efficient separation of propane and propylene by nanocrystals of a metal–organic framework-based splitter

The separation of propane/propylene mixtures to produce polymer-grade propylene represents an important yet challenging task in the petrochemical industry. Metal-organic frameworks (MOFs) hold particular promise for the energy-efficient adsorptive separation of propane/propylene, in light of their structural diversity as well as highly tunable pore dimensions. MOFs exhibiting selective molecular exclusion for propylene over propane render exceptionally high adsorption selectivity. However, the relatively low adsorption capacity and/or slow diffusion kinetics have largely limited their separation efficiency. Here we report the fabrication of nano-sized crystals of a MOF-based splitter for propane and propylene. Compared to the micro-sized MOF samples, the nanocrystals display enhanced adsorption kinetics as well as notably improved adsorption capacity, making a new record with the highest efficiency for the separation of propane/propylene among all reported MOF-based splitters. Our study may shed light on the development of MOF-based adsorbents with optimal efficiency for industrially challenging gas separations.