Enlarged Layer Spacing Research Articles

Interfacial modulation of Ti3C2Tx MXene using functionalized cellulose nanofibrils for enhanced electrochemical actuation

Electrochemical actuators (ECAs) with low voltage actuation and large deformation ranges generally require electrode materials with high ion kinetic energy transport, high charge storage, and excellent electrochemical-mechanical properties. However, the fabrication of such actuators remains a major challenge. In the present work, hybrid electroactive films were fabricated by self-assembling one-dimensional functionalized cellulose nanofibrils (CNFs) with two-dimensional MXene (Ti3C2Tx). The obtained ECA actuators fabricated by carboxymethylated cellulose nanofibrils (consisting of -CH2COO−surface groups) with Ti3C2Tx integrate excellent curvature (0.1041 mm−1), mechanical strength (21.68 MPa), a bending strain of 0.50 %, and a good actuation displacement of 9.3 mm at a low voltage range of −0.6 to 0.3 V. This may be attributed to the enlarged layer spacing (15.34 Å), which makes the embedding and transport of H+ easier, and excellent adaptivity of mechanical properties achieved by molecular-scaled strong hydrogen bonding, leading to better actuation performance. This study provides a potential research direction for the preparation of ECAs with large actuation deformation.

Zr-doped O3-type NaNi1/3Fe1/3Mn1/3O2 cathodes with enhanced structure stability for sodium-ion batteries

O3-type NaTMO2 (TM = transition metal) is highly anticipated as a cathode for sodium-ion batteries due to its high theoretical specific capacity and low cost. However, the irreversible phase transition during sodiation/desodiation and the Jahn-Teller effect induced by Mn3+ have hindered its steps towards industrialization. Herein, we propose a doping strategy to enhance the structural stability of O3-type NaNi1/3Fe1/3Mn1/3O2 through Zr doping. On the one hand, the Na+ transport channels are broadened due to the enlarged layer spacing, which accelerates the kinetic processes. On the other hand, Zr doping maintains structural integrity, inhibiting the decay of the layered structure. As a result, the uniquely designed material NNFMZO-6000 exhibited a discharge specific capacity of 113.8 mAh g−1 at 1 C and a capacity retention of 67.54 % after 200 cycles. This work presents an effective modification method to optimize the properties of O3-type NaTMO2 materials.

Linker-induced hollow MOF embedded into arginine-modified montmorillonite for efficient urea removal: Adsorption behavior and mechanism analysis

The precise regulation of hollow metal–organic framework (HMOF) and the effective assembly with excellent guest materials present limitless potential for pollutant removal. In this work, the arginine-modified montmorillonite (AMMT) was preferentially prepared via room temperature impregnation approach, and then the AMMT-HMOF composite was effectively constructed through a one-pot method. During this process, linker-induced MOF to MOF route was proposed, i.e., solid ZIF-67 transformed into hollow MOF-74 (thicknesses: ∼25 nm). Of note, this route involves the transition from solid to hollow structures, as well as the change between different topologies. Next, the AMMT-HMOF composite was evaluated for adsorption experiments with urea in aqueous solution as the target molecule. Further speaking, the optimization experiments were conducted to analyze the impact of pH, contact time, adsorbent mass and original urea concentration towards the adsorption process. The as-fabricated absorbent presented a maximum adsorption capacity of 298.5 mg/g within 1 h, demonstrating adherence to pseudo-second-order kinetics and the Langmuir model. The excellent adsorption performance can be ascribed to the enlarged layer spacing of AMMT, as well as the fast mass transport and abundant diffusion channels in HMOF. Additionally, the mechanistic analyses revealed the existence of hydrogen bonding interactions between the adsorbent and urea. Meanwhile, the adsorbent displayed the outstanding morphological and structural stability after usage. According to our survey, this is the first time to use this linker-induced MOF-to-MOF strategy and predictably assemble with functionalized montmorillonite to construct the hollow MOF composite for urea adsorption.

Heteroatom doping-induced formation of closed pores for high-performance sodium storage hard carbon anodes.

A resin-based hard carbon with rich closed pores is prepared by the in situ reconstruction of cavities formed after heteroatoms evaporated during a high-temperature carbonization process. Various characterization results confirm that rich defect sites and micropores and enlarged layer spacing in hard carbon promote Na+ transport and facilitate high-performance Na+ storage.

Realization of Mg2+ intercalation in a thermodynamically stable layer-structured oxide.

Magnesium batteries have emerged as one of the considerable choices for next-generation batteries. Oxide compounds have attracted great attention as cathodes for magnesium batteries because of their high output voltages and ease of synthesis. However, a majority of the reported results are based on metastable nanoscale oxide materials. This study puts forward a thermodynamically stable layer-structured oxide K0.5MnO2 with an enlarged lattice spacing as a model cathode material employing optimized electrolytes, enabling Mg2+ intercalation into the K0.5MnO2 framework in a real magnesium battery directly using Mg foil as the anode. First-principles calculations implied that the enlarged layer spacing could decrease the migration energy barrier of Mg2+ in the layered oxide. This work can pave the way to understanding the fundamental intercalation behavior of Mg2+ in magnesium batteries.

Interlayer spacing expansion for V2O5 towards ultra-stable zinc anode-based flexible electrochromic displays in Zn2+/Li+-PC organic electrolyte

To enhance the electrochemical stability and kinetics of V2O5, 3,4-ethylenedioxythiophene (EDOT) was in-situ polymerized within V2O5 interlayers, rendering PEDOT@V2O5 with enlarged layer spacing, increased stability in organic electrolyte, superior electrochemical...

Employing the optimized pre-intercalation strategy to design functional Mo pre-intercalated hydrated vanadium oxide for aqueous zinc-ion batteries

The traditional metal ions (K+, Na+, Ca2+, etc.) pre-intercalated strategy is widely used to optimize the structure of vanadium oxides as the cathode materials for aqueous zinc-ion batteries (AZIBs). However, these intercalated ions with a single valence state between the layers of vanadium oxides occupy the original active sites and merely act as ‘pillars’ without redox reactions for energy storage. Herein, we employ the optimized pre-intercalation strategy to fabricate a series of Mo pre-intercalated hydrated vanadium oxide materials (x-MoVOH) as the cathode of AZIBs. The intercalated functional Mo ions can not only effectively enlarge the interlayer spacing to expose more active sites for insertion and de-insertion of hydrated Zn2+, but also provide additional electrochemical performance through the redox reactions of Mo4+/Mo5+/Mo6+. The finest material (Mo3V15O35·nH2O, 5-MoVOH) exhibits the electrochemical performance of the specific capacity of 430 mAh·g−1 at 100 mA·g−1 and the capacity retention proportion of 95 % after 1000 cycles at 2 A·g−1. Additionally, the galvanostatic intermittent titration technique (GITT) further confirms that the enlarged layer spacing facilitates the rapid diffusion of hydrated Zn2+. This work provides a novel and feasible way to further enhance the performance of vanadium oxides in AZIBs.

Soft Carbon-Thiourea with Fast Bulk Diffusion Kinetics for Solid-State Lithium Metal Batteries.

The development of all-solid-state lithium-metal batteries (ASSLMBs) is impeded by low coulomb efficiency, short lifetime, poor rate performance, and other problems caused by the rapid growth of lithium (Li) dendrites. Herein, a multiple-diffusion-channel N,S-doped soft carbon with expanded layer spacing is designed/developed by thiourea calcination for dendrite-free anodes. Since the enlarged layer spacing can improve Li+ transportation rate within the layers and N,S-doping can facilitate Li+ transport between the layers, the bulk phase diffusion (not just surface diffusion) kinetics can be improved, which in turn reduces the local current density, inhibits the growth of Li dendrites, and improves the rate performance. The resulting ASSLMB achieves record-high current density (15mA cm-2 ), areal capacity (20 mAh cm-2 ), energy density (403Wh kg-1 ), and ultra-long cycle life (13000 cycles). >305Wh kg-1 pouch cells are realized, representing one of the most critical breakthroughs for real-world application of ASSLMBs.

Aliovalent doping and structural design of MoSe2 with fast reaction kinetics for high-stable sodium-ion half/full batteries

The development of high-quality anode materials is critical for the advancement of sodium-ion batteries (SIBs). MoSe2 is a candidate anode for SIBs, while its inherent limitations, such as the agglomeration of nanosheets, poor electron conductance and mechanical strain due to volume changes during cycling, which can lead to decreased performance and durability in SIBs. To overcome the challenges, a novel aliovalent doping and structural engineering was taken to prepare reduced graphene oxide (rGO) functionalized and phosphorus-doped MoSe2 flake (P-MoSe2@rGO) via in situ growth technique. The unique structural design of P-MoSe2@rGO addresses material limitations and optimizes performance by providing a high conductive grid for ion/electron transfer, a large surface area for full electrolyte penetration, and effective suppression of MoSe2 nanosheet agglomeration and mechanical strain due to volume change during charge/discharge in SIBs. The P-MoSe2@rGO inherits the enhanced electronic conductivity and enlarged layer spacing (from 0.652 to 0.668 nm), which boosts the reaction kinetics and facilitates the insertion/extraction of sodium ions. The P-MoSe2@rGO exhibits excellent long-cycle properties with a high reversible capacity of 384 mAh/g at 2 A/g and 338 mAh/g at 10 A/g after 1450 circulations. Detailed discussion of reaction kinetics is conducted. Theoretical calculations prove that doping of P atoms in MoSe2 reduces the forbidden band gap from 1.443 to 1.397 eV and accelerates ion and electron migration. Furthermore, the full cell P-MoSe2@rGO//Na3V2(PO4)3@C (NVP@C) demonstrates a remarkable cycling durability of 326 mAh/g after 200 cycles and a high energy density of 159.6 Wh kg−1. This process provides a reference for the adjustment and modification of MoSe2 to adapt to high performance SIBs anode.

Interlayer Nano-Dots Induced High-Rate Supercapacitors.

The fast OH- transfer between hydroxide layers is the key to enhancing the charge storage efficiency of layered double hydroxides (LDH)-based supercapacitors (SCs). Constructing interlayer reactive sites in LDH is much expected but still a huge challenge. In this work, CdS nano-dots (NDs) are introduced to interlayers of ultra-thin NiFe-LDH (denoted CdSinter. -NiFe-LDH), promoting the interlayer ions flow for higher redox activity. The excellent performance is not only due to the enlarged layer spacing (from 0.70 to 0.81nm) but also stems from anchored interlayer reactive units and the undamaged original layered structure of LDH, which contribute to the improvement of OH- diffusion coefficient (1.6×10-8 cm2 s-1 ) and electrochemical active area (601mFcm-2 ) better than that of CdS NDs on the surface of NiFe-LDH (2.1×10-9 cm2 s-1 and 350mFcm-2 ). The champion CdSinter. -NiFe-LDH electrode displays high capacitance of 3330.0Fg-1 at 1Ag-1 and excellent retention capacitance of 90.9% at 10Ag-1 , which is better than the NiFe-LDH with CdS NDs on the surface (1966.6Fg-1 ). Moreover, the assembled asymmetric SCs (ASC)device demonstrate an outstanding energy density/power density (121.56Whkg-1 /754.5Wkg-1 ).

Defect engineered Ti3C2Tx MXene electrodes by phosphorus doping with enhanced kinetics for supercapacitors

Supercapacitors (SCs) have attracted increasing attention due to high power density, rapid charge/discharge, excellent cyclic stability, and withstands adverse environments. Two-dimensional (2D) Ti3C2Tx MXene is considered as a promising electrode material for electrochemical energy storage. However, undesirable low specific capacitance issues limit its practical applications. Herein, a facile heteroatom doping strategy is proposed to construct defect-rich Ti3C2Tx MXene with abundant active cites. Hence, P-doped Ti3C2Tx MXene was synthesized by a simple annealing method. The prepared P-doped Ti3C2Tx was used as the electrode material of SC, and it was found that the P-doped Ti3C2Tx exhibits enhanced electrochemical performance compare to the pristine Ti3C2Tx MXene, the P-doped Ti3C2Tx electrode could deliver a high specific capacity of 31.11 mA h g−1 at 1 A g−1 in 1 M KOH electrolyte. Furthermore, a P-doped Ti3C2Tx based symmetric SC device is fabricated and displays excellent energy density of 8.2 Wh L−1 at a power density of 303.4 W L−1. This study provides a straightforward strategy to design and construct MXene-based electrode materials with enlarged layer spacing structure for high-performance K+ storage and even in other metal ion storages.

Edge-enriched and S-doped carbon nanorods to accelerate electrochemical kinetics of sodium/potassium storage

Hard carbon is regarded as a promising anode material for sodium/potassium-ion batteries, which have attracted much attention in grid-scale energy storage. However, it still suffers from the sluggish electrochemical kinetics rooted in the turbostratic structure of carbon, leading to an inferior rate capacity. Herein we utilize a facile strategy to fabricate the edge-enriched and S-doped carbon nanorods (SCNs) with controllable diameter and highly-oriented carbon layer arrangement. The abundant edges lead to the shorter diffusion path of ions, as well as the enlarged layer spacing, both contribute to the rapid kinetics of ionic insertion/desertion. Such a unique highly-oriented structure enables the SCNs anodes to deliver excellent rate capacities and long-lasting cycling life for both sodium and potassium ion storage. The density functional theory (DFT) results demonstrate the enhanced adsorption and reduced ions diffusion energy barrier of Na+ ions near the S-doped active sites, which substantiates the promoted electrochemical kinetics of SCNs electrodes. This work inspires more ideas for rational design of advanced electrodes and provides an in-depth insight into the reaction kinetics of carbonaceous anodes.

Highly Graphitized Porous Carbon Microspheres Derived from Copolymer of Glucose and Melamine for Advanced Electrodes

AbstractThe N/O co‐doped hierarchical porous graphitized carbon microspheres (N/O‐PCs) are successfully prepared by condensation polymerization of 5‐hydroxymethylfurfural and melamine, and subsequent KOH activation strategy. The obtained carbon materials have a high specific surface area (1685.58 m2 g–1), rich micro‐ and mesopores, and appropriate pore volume (0.828 cm3 g–1). The degree of graphitization for N/O‐PCs is improved because the ratio of IG and ID increases from 0.88 to 1.03. The layer spacing of the lattice plane (002) for the N/O‐PCs is enlarged, facilitating the transmission of electrolyte ions. The high graphitization degree and enlarged layer spacing bring excellent electrical conductivity and wettability for N/O‐PCs as electrode materials. Besides, owing to the higher N (3.59 at%) and O (12.67 at%) content, the N/O‐PCs show excellent specific capacitances of 412 and 284 F g–1 at the current densities of 1 and 10 A g–1 in 2 m H2SO4 aqueous electrolytes, respectively. Outstanding rate performance (200 F g–1 at 50 A g–1) and ideal cycle stability (>10 000 cycles) are achieved. Moreover, the N/O‐PCs‐based symmetric supercapacitor exhibits an energy density of 9.6 Wh kg–1 at 100.8 W kg–1. Thus, the N/O‐PCs provide the potential for high‐performance supercapacitor electrodes.

Hydration kinetics and phase evolution of Portland cement composites containing sodium-montmorillonite functionalized with a Non-Ionic surfactant

This study investigates the hydration behavior and phase evolution of portland cement composites containing montmorillonite (MT) with an objective to address the poor dispersion and improve physical features and chemical reactivity of MT through functionalization with a non-ionic surfactant (polyethylene glycol ether). After functionalization, the MT exhibited an enlarged layer spacing (122%), organic chemical bonds intercalated, improved dispersion in concrete pore solutions, reduced moisture sorption capacity. The cement composites containing the functionalized MT showed enhanced cement hydration, less portlandite, more calcium silicate hydrates (C-S-H) and aluminum-containing hydrates, a more densified microstructure, and higher strength than the composites with raw MT.

Dual sulfur-doped sites boost potassium storage in carbon nanosheets derived from low-cost sulfonate

• Dual S-doped carbon sheets are obtained by one-step low-cost pyrolysis. • C-S bonds and ultrafine sulfate are tailored on enlarged d-spacing carbon sheets. • High-capacity, long-life and high-rate K-ion battery is obtained. • Ex-situ XPS and capacity-contribution analysis reveal storage mechanism. As a new energy storage system, K-ion batteries (KIBs) have the advantages of low price and competitive high energy density. However, due to the large radius of K + , in the process of intercalation/deintercalation, the traditional carbon anode materials usually display insufficient cycle life and poor rate performance in KIBs. In this work, inexpensive and widely-sourced sodium p-toluenesulfonate (CH 3 C 6 H 4 SO 3 Na) is used as raw material to synthesize dual sulfur-doped carbon nanosheets (DS-CN) by a simple one-step carbonization method. The nanosheets possess an enlarged interlayer distance (4.25 Å) which allows large K + to intercalate. C-S bonds and the embedded ultrafine sulfate provide active sites to enhance capacity and accelerate kinetics. Moreover, a high S/O ratio would reduce the irreversible reactions caused by oxygen functional groups. The high reversible specific capacity (331.9 mA h g −1 at 50 mA g −1 ), good rate performance (165.3 mA h g −1 at 1000 mA g −1 ) and long cycle stability (0.011% capacity decay per cycle) are attributed to the multiple synergistic effects of enlarged layer spacing, reaction between C-S bonds and K + , as well as more active -C-SO 2 - bonds, as confirmed by ex-situ XPS and electrochemical analysis. Our work shows a feasible and effective way to develop low-cost, high-performance carbon anode materials for KIBs.

Modulating visible-near-infrared reflectivity in ultrathin graphite by reversible Li-ion intercalation

Two-dimensional materials with optical turnability have wide prospect in related applications such as electrochromic coating and thermal camouflage. Here we report a Li-intercalated ultrathin graphite device with tunable visible-near-infrared reflectivity. After Li-ion intercalation, the Fermi surface of ultrathin graphite will move to a higher level, which prevents the interband optical transitions below it. Therefore, it is possible to change the absorptivity or emissivity of ultrathin graphite through reversible Li-ion intercalation, which accomplishes the modification to reflectivity indirectly. In our experiment, the strong fluorescence background and Peak shifts in Raman spectra, as well as the enlarged layer spacing in XRD spectra, together confirmed that Li-ions were successfully intercalated into the graphite layers. The relative reflectivity of ultrathin graphite increased sharply in a wide range from 460 nm to 1500 nm after complete Li-ion intercalation. At a typical near-infrared wavelength 1500 nm for instance, the relative reflectivity is 0.28 for pristine graphite while 0.70 for fully lithiated graphite. Such reversible intercalated modulation in visible-near-infrared reflectivity of ultrathin graphite might provide a new way to design electrochromic coating, thermal camouflage or radar stealth systems, which also promotes further understanding and optical applications of graphene and other 2D materials. • Systematic investigation into visible-near-infrared reflectivity modulation of intercalated ultrathin graphite. • The relative reflectivity of ultrathin graphite increased sharply in a wide wavelength range after Li-ion intercalation. • Such prominent modulation of ultrathin graphite might be ascribed to uplifted Fermi level in intercalated graphene layers.

Efficient regeneration and reutilization of degraded graphite as advanced anode for lithium-ion batteries

As a burgeoning solid waste, it is of great significance for spent lithium-ion batteries (LIBs) that recovering graphite anode and valuable lithium simultaneously to achieve resource utilization and environmental protection. However, two major troubles, difficult separation and degraded structure, have stagnated the recycling of spent graphite anode. Hence, we propose an approach to achieve the separation of collector/graphite and structural restoration of graphite anode synchronously. Benefited from the acidity and oxidability of ammonium persulfate, the recovered graphite with enlarged layer spacing is successfully obtained. When assembled in coin-cell, it exhibits excellent lithium storage performance with high reversible capacity (365.3 mA h g−1 after 100 cycles at 0.03 A g−1) and long cyclic life (330.2 mA h g−1 after 500 cycles at 0.3 A g−1), which is apparently higher than that of spent graphite and closed to that of commercial graphite. Furthermore, renewed graphite anode also demonstrates negligible difference with commercial graphite in electrochemical performance for full-cells, manifesting the sustainable meritoriousness of this recycling process. This recycling approach with the advantages of green, efficiency, and conciseness has the application prospects for industrial recycling of graphite anode of spent LIBs.

Suppressing lithium dendrites by coating MoS2 with different layer spacings: A multiscale simulation study

MoS2 coating is an effective way to suppress the growth of lithium dendrites, but the study of the layer spacing effect is still lacking. In this work, the diffusion and adsorption of lithium ions on the MoS2 were studied by multiscale simulations. The transport of lithium ions on the MoS2 was investigated by a continuum method, which shows that the smaller layer spacing of 1 nm can enhance the ion diffusion. The QDFT method was used to study the lithium ions transport on 1T- and 2H- MoS2 with layer spacing of 0.65 nm - 1.15 nm. Results indicate that lithium dendrites are more difficult to grow on 2H- MoS2. For both types of MoS2, enlarged layer spacing can reduce lithium dendrites growth and 0.75 nm is the most suitable interlayer distance for MoS2 expanding. We hope our results can provide guidance to the synthesis of dendrite-free lithium metal batteries.

Facile Fabrication and High Field Emission Performance of 2-D Ti₃C₂Tₓ MXene Nanosheets for Vacuum Electronic Devices

Although Ti3C2T x has been widely studied in applications such as electrical storage devices, there are very few reports about the field emission properties of Ti3C2T x . In this work, 2-D Ti3C2T x MXene was fabricated by simple etching Al layer from Ti3AlC2 in hydrofluoric acid (HF) at room temperature and employed as a cold cathode for field emission devices. The device presents a high field emission performance with a low turn-on field of 2.7 V/ $\mu \text{m}$ and excellent stability, much lower than the reported value of the former work (around 5 V/ $\mu \text{m}$ ), its relative 1-D TiC nanowires (7.1 V/ $\mu \text{m}$ ), and most of other 2-D cathode materials, such as MoS2 and graphene, which is found due to its unique accordion structure with evenly distributed sharp edges and enlarged layer spacing reducing the field screening effect. The results confirmed by numerical simulation demonstrate that the local electric intensity at sharp edges indeed significantly higher than that of elsewhere. In other words, more sharp edges owning to the increased interlayer spacing exposed, which can considerably boost field emission performance. Based on experimental data and simulation analysis, the edge effect was found to correspond well with other former reports. Hence, 2-D MXene can be a promising candidate for vacuum electronic applications other than energy storage and conversion devices.

Alternate‐stacked Li4Ti5O12 nanosheets/d‐Ti3C2 flexible film as a current collector‐free, high‐capacity and robust cathode for rechargeable Mg batteries

AbstractRechargeable magnesium batteries (RMBs) have gained increasing attention owing to its high volumetric capacity, crust abundance, and safety from dendrite‐free characteristic. However, the lack of development of high‐performance cathode materials with long cycling stability and satisfactory capacity has greatly restricted the development of RMBs. Herein, a self‐supported, current collector‐free and soft electrode is prepared with delaminated Ti3C2 (d‐Ti3C2) and Li4Ti5O12 nanosheets by simple vacuum filtration as flexible cathode in RMBs. Fabricated into a full cell with hybrid AlCl3/MgCl2/Mg(TFSI)2 electrolyte and Mg anode (a thin Mg foil with thickness of 50 μm), the flexible cathode shows high initial specific capacity of 320 mAh g−1 at 20 mA g−1, excellent cycling stability (good retention even after 1000 cycles) and outstanding rate performance. Detailed mechanistic studies reveal that introduction of d‐Ti3C2 provide fast transport paths for electrons and Mg2+. The enlarged layer spacing of composited d‐Ti3C2 accounts for significant increment in capacity. Benefiting from above‐mentioned advantages, the best performance among Ti‐based electrode materials is realized and make wearable devices powered by RMBs possible, thus circumventing the safety issues of lithium batteries.