Expanded Interlayer Spacing Research Articles

Sulfur-grafted hard carbon with expanded interlayer spacing and increased defects for high stability potassium-ion batteries

Carbon materials have been proven to be an effective anode for potassium-ion batteries (PIBs) due to their high safety, low cost, and environmental benignity. However, the repeated insertion/extraction of K-ions with a larger size into/from electrode at low voltage region will inevitably cause obvious volume expansion, easily resulting in poor cycle stability. Hence, we synthesize S-doped hard carbon material (NSHCM2) using biomass as carbon and thiourea as S sources. Various characterizations demonstrate that the introduced S-heteroatom not only expands the distance between carbon layers, but also creates more defects. The former ensures the free intercalation/deintercalation of K-ions without structure deformation, while the latter can provide numerous active sites to adsorb K-ions, all these together contribute to structure stability and reversible capacity. As a result, the optimized NSHCM2 electrode delivers a high capacity of 294 mAh g−1 at 200 mA g−1 and an ultra-long cycling stability by achieving 220 mAh g−1 at 2000 mA g−1 over 5000 cycles. This simple and high effective synthesis route makes durable and fast potassium storage possible.

Disorder and hydrogenation in graphene nanopowder revealed by complementary X-ray and neutron scattering

Functionalization of graphene's two-dimensional sheets can be used to modify the physical properties of graphene, such as changing its conductivity or inducing ferromagnetism, which is of broad interest for a myriad of applications. However, functionalized graphene can possess significant structural disorder that is often overlooked and is difficult to characterize quantitatively. Here we investigate hydrogenated graphene nanopowder (H-Gr) produced by Birch reduction of graphene oxide. By combining complementary x-ray and neutron diffraction, we show how to quantitatively characterize the H-Gr nanostructure, including the hydrogen content. We show that the majority of the H-Gr consists of highly disordered molecular-scale carbon while a small portion of the sample contains few-layered graphene having an expanded interlayer spacing. Modeling the coherent diffuse scattering for both x-ray and neutron diffraction, and comparing it with the incoherent neutron scattering, the hydrogen to carbon ratio was measured and it was determined that most of the hydrogen resides within the disordered carbon rather than in the graphene. Evidence is presented for hydrogen clustering as well as for hydrogen bonded perpendicular to the plane of molecular-carbon bonds. Our quantitative approach to characterizing carbon nanopowders has broad relevance to understanding disorder and bonding of hydrogen in graphitic carbons and other nanomaterials.

Halogenated and chalcogenated Ti2C MXenes: High capacity electrode materials for lithium-ion batteries

Inspired by the recent successful growth of Ti2C monolayers, we investigated the effects of Ti2CT2 (T = F, Cl, Br, O, S and Se) anode in lithium-ion batteries (LIBs) by first-principles calculations. The results revealed that Ti2CT2 MXenes exhibit metallic conductivity with higher structural stability and mechanical strength than Ti2C. Compared with other Ti2CT2 monolayers, Ti2CS2 monolayer display lower diffusion barrier, larger elastic modulus, lower open circuit voltage and higher storage capacity. Moreover, surface sulfuration yields the expanded interlayer spacing, which can improve Li-ion accessibility in double-layer Ti2CS2.

Nb2C MXenes with surface chalcogenation and halogenation as high capacity electrode materials for lithium-ion batteries

MXenes show extremely competitive potential applications in electrode materials for lithium-ion batteries (LIBs) due to their excellent specific surface area, high electrical conductivity, and compositional tunability. However, limited interlayer spacing and undesired surface functional group on MXene surface impede the Li-ions accessibility and mobility. Herein, the structural, electronic, mechanical and electrochemical properties of the representative Nb2C MXene with surface chalcogenation and halogenation resulting in the formation of Nb2CT2 ([Formula: see text], S, Se, Cl and Br) materials as anodes for LIBs were investigated using first-principles calculations based on density functional theory. The results reveal that Nb2CT2 can exhibit metallic conductivity with improved mechanical strength, which renders the enhanced rate performance and endures the repeated lattice expansion and contraction during charge/discharge process, respectively. In particular, Nb2CS2 and Nb2CCl2 render the enhanced Li-ion storage and mobility with a theoretical Li storage capacity of 613.76 mA[Formula: see text]h/g and 597.79 mA[Formula: see text]h/g and diffusion energy barrier of 0.275 eV and 0.294 eV, respectively. Moreover, chalcogenation and halogenation yield the expanded interlayer spacing, which improve the Li-ions accessibility in Nb2CT2. The results demonstrate that sulfurized and chlorinated Nb2C MXenes are the promising anode materials with high capacity, low diffusion barrier and lower open circuit voltage for next-generation LIBs.

One-Step Urothermal Synthesis of Li+-Intercalated SnS2 Anodes with High Initial Coulombic Efficiency for Li-Ion Batteries

Tin sulfide, as a promising anode material for Li-ion batteries, suffers from high-capacity loss during cycling and low initial Coulombic efficiency, which limits its further application. In order to solve these problems, Li+-intercalated SnS2 with expanded interlayer spacing (0.89 nm) was prepared by the one-step urothermal method. The successful synthesis of Li+-intercalated SnS2 is confirmed by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, inductively coupled plasma emission spectrometer test, and exfoliation experiment. Compared with pure SnS2, the Li+-intercalated SnS2 electrode displays a higher initial Coulombic efficiency (79.3%) than the pure SnS2 electrode (55%). Also, Li+-intercalated SnS2 exhibits more excellent rate performance (548.4 mAh g–1 at 2 A g–1 and 216.6 mAh g–1 at 10 A g–1) and cycling performance (647.7 mAh g–1 at 0.1 A g–1 after 100 cycles).

Bulk substitution of F-terminations from Ti3C2Tx MXene by cation pillaring and gas hydrolysation

Applications of 2D MXenes are limited by the difficulty of controlling bulk termination groups after the initial HF etching step without forming surface oxides. Here, we report on gas hydrolysation using a continuous flow of Ar (g) with a controlled partial pressure of H2O (g) as a new method to change the terminations of multilayered Ti3C2Tx MXene particles (T = O, OH and F), and demonstrate pre-intercalation of cations as a necessity for successful hydrolysation as it enables water molecules to enter the Ti3C2Tx MXene structure. Hydrolysation of pristine HF-etched Ti3C2Tx shows no compositional change before oxidation into a TiO2/C composite starts at T > 300 ˚C. However, by pre-intercalating various cations into the MXene, a pillaring of the structure is achieved, which for certain cations (K+ and Na+) remains even after hydrolysation at 300 ˚C. By hydrolysing K-intercalated Ti3C2Tx at 300 ˚C, a significant bulk F reduction of 78 % was achieved, accompanied by a comparable increase in O content and insignificant surface oxidation of the particles. For other cations (Mg2+, Li+ and TBA+) the expanded interlayer spacing collapsed upon hydrolysation, resulting in no significant compositional changes. Moreover, hydrolysation is shown to give higher selectivity towards F removal compared to air annealing, which instead resulted in the oxidation of C to CO2 and the formation of TiOF2. In Li-ion battery half cells, the intercalation of K-ions reduces both the capacity and energy efficiency compared to pristine Ti3C2Tx. Nevertheless, hydrolysation increases the capacity and intercalation voltage, and is thus a feasible method to control the electrochemical performance of Ti3C2Tx MXene. In summary, gas hydrolysation is demonstrated as a selective and efficient method to substitute F terminations with O-related terminations in multilayered MXene particles and pave the way for utilisation on other MXene compositions.

Wafer-biscuits-like few-graphene-layers carbon with N, P, S triple-doping for efficient and stable sodium-ion storage

Carbon-based materials are one of the most attractive anodes for sodium-ion batteries because of their wide availability, facile synthesis, and low cost. However, rational designing carbon-based architecture towards upgrading the electrochemical performance of anodes for sodium storage has been a great challenge. Herein, we prepared N, P, S triple-doped few-graphene-layers carbon with expanded interlayer spacing via a scalable template approach. The few-graphene-layers carbon negatively replicates the structure of the layered template to generate a wafer-biscuit-like architecture, which prevents the restack of carbon nanosheets. The interlayer spacing and heteroatom contents of wafer-biscuit-like carbon architecture can be modulated by varying carbonization temperatures. Consequently, the optimum carbon anode delivers a high reversible capacity of 329 mAh g−1, good rate capability, and long-term stability of 300 cycles at 1 A g−1. Furthermore, the sodium storage mechanism of wafer-biscuit-like carbon anodes has been systematically explored.

Efficient interlayer confined nitrate reduction reaction and oxygen generation enabled by interlayer expansion.

Electrochemically converting nitrate ions back to ammonia can not only eliminate water pollution but also obtain valuable ammonia without a serious carbon footprint, and is thus deemed as an efficient supplement to the traditional Haber-Bosch process. Currently reported catalysts can achieve a single electrode reaction in the electrochemical nitrate reduction reaction. However, the bifunctionality of a single catalyst for both cathodic and anodic reactions has not yet been reported. Herein, we report Fe-doped layered α-Ni(OH)2 with expanded interlayer spacing as an efficient bifunctional catalyst for the nitrate reduction reaction and oxygen evolution reaction. The expanded interlayer spacing facilitates in situ electrochemical potassium ion intercalation between layers. In situ Raman spectroscopy characterization confirms that both the nitrate reduction reaction and oxygen evolution reaction are confined between layers and are triggered by the accumulation of potassium ions. The obtained α-Ni0.881Fe0.119(OH)2 nanosheets deliver an ammonia yield rate of 8.1 mol gcat.-1 h-1 with a NO3--to-NH3 faradaic efficiency of 97.5% at the cathode. The overpotential of oxygen generation at 10 mA cm-2 is reduced to 254 mV at the anode. As a bifunctional catalyst in overall electrolysis, the current density of α-Ni0.881Fe0.119(OH)2 reaches 24.8 mA cm-2 at a voltage of 2.0 V and performs continuously for 50 h with a current retention of 80.2%.

Mo-Pre-Intercalated MnO2 Cathode with Highly Stable Layered Structure and Expanded Interlayer Spacing for Aqueous Zn-Ion Batteries

Although manganese-based oxides possess high voltage and low cost, the sluggish reaction kinetics and poor structural stability hinder their applications in aqueous rechargeable Zn-ion batteries (ZIBs). Herein, a molybdenum (Mo) pre-intercalation strategy is proposed to solve the above issues of δ-MnO2. The pre-intercalated Mo dopants, acting as the interlayer pillars, can not only expand the interlayer spacing but also reinforce the layered structure of δ-MnO2, finally achieving enhanced reaction kinetics and superb cycling stability during carrier (de)intercalation. Moreover, oxygen defects, introduced due to Mo-pre-intercalation, play a critical role in the fast reaction kinetics and capacity improvement of the Mo-pre-intercalated δ-MnO2 (Mo-MnO2) cathode. Therefore, the Mo-MnO2 cathode displays a high energy density of 451 Wh kg-1 (based on cathode mass), excellent rate capability, and admirable long-term cycling performance with a high capacity of 159 mAhg-1 at 1.0 A g-1 after 1000 cycles. In addition, the energy storage mechanism of Zn2+/H+ stepwise reversible (de)intercalation is also revealed by ex situ experiments. This work provides an insightful guide for boosting the electrochemical performance of Mn-based oxide cathodes for ZIBs.

Hard carbon anodes derived from phenolic resin/sucrose cross‐linking network for high‐performance sodium‐ion batteries

AbstractHard carbons are widely studied as anode materials for sodium‐ion batteries (SIBs) due to their high Na‐storage capacity, long cycle life, and low cost. However, the low initial coulombic efficiency (ICE) and poor cycle performance remain bottleneck concerns that necessitate a comprehensive material engineering solution. Herein, we propose a facile strategy to synthesize amorphous carbons with pseudo‐graphitic dominated crystalline, expanded interlayer spacing, and reduced surface defects via carbonization of the cross‐linking network of phenolic resin and sucrose. An elaborate structural and electrochemical characteristics analysis has been investigated against different sucrose contents and carbonization temperatures. The representative PF‐S‐55‐1200 with the optimum cross‐linking degree as well as carbonization temperature realizes a high reversible Na‐storage capacity of 323.0 mAh g−1 with an ICE as high as 86.4%, much superior to the pristine phenolic resin pyrolytic carbon with a capacity of 267.1 mAh g−1 and an ICE of 46.3%. The hybrid hard carbons also exhibit robust structural stability with a prolonged cycle lifespan evidenced by a retained capacity of 238.3 mAh g−1 at a current density of 200 mA g−1 over 1500 cycles. The proposed route promises low‐cost and high‐performance hybrid hard carbons with optimized structural configuration for advanced SIBs.

Delicate Co-Control of Shell Structure and Sulfur Vacancies in Interlayer-Expanded Tungsten Disulfide Hollow Sphere for Fast and Stable Sodium Storage.

Hollow multishelled structure (HoMS) is a promising multi-functional platform for energy storage, owing to its unique temporal-spatial ordering property and buffering function. Accurate co-control of its multiscale structures may bring fascinating properties and new opportunities, which is highly desired yet rarely achieved due to the challenging synthesis. Herein, a sequential sulfidation and etching approach is developed to achieve the delicate co-control over both molecular- and nano-/micro-scale structure of WS2- x HoMS. Typically, sextuple-shelled WS2- x HoMS with abundant sulfur vacancies and expanded-interlayer spacing is obtained from triple-shelled WO3 HoMS. By further coating with nitrogen-doped carbon, WS2- x HoMS maintains a reversible capacity of 241.7 mAh g-1 at 5 A g-1 after 1000 cycles for sodium storage, which is superior to the previously reported results. Mechanism analyses reveal that HoMS provides good electrode-electrolyte contact and plentiful sodium storage sites as well as an effective buffer of the stress/strain during cycling; sulfur vacancy and expanded interlayer of WS2- x enhance ion diffusion kinetics; carbon coating improves the electron conductivity and benefits the structural stability. This finding offers prospects for realizing practical fast-charging, high-energy, and long-cycling sodium storage.

Engineering of the Crystalline Lattice of Hard Carbon Anodes Toward Practical Potassium‐Ion Batteries

AbstractHard carbons have attracted increased interest as an alternative of graphite for the anodes of potassium‐ion batteries (PIBs). However, the practical applications of hard carbon anodes are hampered by their low capacities, high potential platforms, and large potential hysteresis. Hard carbons coupled with graphitic nanodomains can achieve stable potassium‐ion storage behaviors with low potential platforms and low potential hysteresis. Herein, the crystalline lattice in hard carbon anodes is tuned by incorporating graphene oxide in renewable lignin precursors. The modified hard carbon (i.e., QLGC) anodes show graphitized nanodomains in the carbon matrix with an expanded interlayer spacing (0.42 nm) in the amorphous regions, which results in a stable potassium‐ion (de)intercalation behavior. Thus, the QLGC anodes exhibit a high capacity of 164 mAh g−1 with low potential hysteresis in the low potential platform region. Moreover, the QLGC anode delivered a highly stabilized capacity of 283 mAh g−1 at 50 mA g−1, a high‐rate capability, and stable cycling performance. Furthermore, the charge storage mechanisms of QLGC anode are elucidated by electro‐kinetic analysis and ex/in situ physicochemical characterizations. This study opens a new avenue for designing hard carbon anodes with engineered crystalline lattices toward practical PIBs.

Anomalous Zn2+ Storage Behavior in Dual‐Ion‐In‐Sequence Reconstructed Vanadium Oxides

AbstractVanadium oxides with fast and stable Zn2+ storage are of great significance to the development of high‐performance aqueous zinc ion batteries (ZIBs), and yet they commonly suffer from structural instability and sluggish diffusion kinetics. Herein, a new “dual‐ion‐in‐sequence” intercalation strategy based on quenching is proposed to address these issues. Interestingly, it is found that the Zn2+ storage mechanism evolves from the common solid‐state ion diffusion kinetic into an intercalation pseudocapacitance as a result of the enlarged interlayer spacing of V2O5. Together with the expanded interlayer spacing arising from the “dual‐ion‐in‐sequence” intercalation, oxygen defects are simultaneously generated at the sub‐surface of the reconstructed Li@MnVO materials. Benefitting from the improved ionic diffusivity, intercalation pseudocapacitance, and fast charge transferability, full cell based on Li@MnVO cathode shows impressive rate capability and excellent cycling stability of 5000 cycles with a high energy density of 253 Wh kg‐1 at 10 A g‐1. More importantly, the capacity can maintain at 125 mAh g‐1 at 4 A g‐1 even under a raised mass loading of 10 mg cm‐2. The proposed “dual‐ion‐in‐sequence” intercalation strategy of manipulating V2O5 structure at atomic scales is a viable pathway for the high‐performance layered metal oxides, not only for ZIBs but also for other energy storage systems.

Free-standing vanadium oxide hydration/reduced graphene oxide film for ammonium ion supercapacitors

Aqueous ammonium-ion energy storage systems have recently gained continuous attention owing to the advantages of sustainability and environmental-friendliness in the grid-scale application. However, ammonium-ion supercapacitors are still in their infancy, and it is of great challenge in developing suitable materials for application in wearable energy storage devices. Herein, we develop a vanadium oxide hydration (V2O5·nH2O)/reduced graphene oxide (rGO) composite film (denoted as VGF) as a free-standing paper-like electrode for ammonium-ion storage, where V2O5·nH2O shows an expanded interlayer spacing and is sandwiched by rGO through chemical bonds. As a result, the designed VGF exhibits a capacitance of 600F·g−1 at 0.2 A·g−1 and good cyclability of over 10,000 cycles with a retention of 93 % using PVA/NH4Cl gel electrolyte. Meanwhile, the ammonium-ion storage mechanism in VGF electrode is further verified to be dominated by the intercalation pseudocapacitance and electric double-layer capacitance. Furthermore, the quasi-solid-state symmetric supercapacitor (SSC) has been also assembled to assess the feasibility of practical applications in wearable devices. As expected, the SSC possesses an areal capacitance of 241 mF·cm−2 at 0.1 mA·cm−2 (0.82 Wh·m−2 at 0.09 W·m−2) and an excellent cyclability of 20,000 cycles with a retention of 92 %, which is comparable to that achieved in the vanadium oxides powder-made electrodes and the SSC made of. Together with the excellent flexibility and feasibility of parallel/series combination, the VGF SSC devices shows great possibility for the applications in wearable devices, which further proves the great potential of this designed VGF free-standing electrode for ammonium-ion storage.

Methyl-functionalized hydrangea-like vanadium pentoxide cathode for aqueous zinc ion batteries with high-rate and long-term cycling stability

Vanadium Pentoxide (V 2 O 5 ) is an appealing cathode candidate for Zinc-ion batteries (ZIBs) owing to its modifiable interlayer structure and changeable chemical redox states. However, the extensive practical application is deeply plagued by either poor rate capability or cycling stability performance. Herein, the methyl group decorated V 2 O 5 with hydrangea-like morphology was successfully fabricated by a facile solvothermal method to solve the problem. Such a hydrangea-shaped architecture containing numerous nanosheets is advantageous for the rapid ions/electrons transfer. The extended interlayer distance stemmed from the pillar effect of the methyl-functionalized V 2 O 5 contributes a comparatively steady and rapid Zn 2+ intercalation/deintercalation. When applied in ZIBs, it delivers a superior rate capability (123 mA h g −1 at 4.0 A g −1 ) and an excellent long-life cycling (capacity retention of 112.7 % after 1000 cycles at 4.0 A g −1 ). Electrochemical kinetics investigations of methyl-functionalized V 2 O 5 microsphere show that the capacity is dominantly contributed from pseudocapacitance. As well, mechanism of zinc ion storage has been explored. Such a structural design of electrode materials can be exploited to promote extensive applications of ZIBs in future. Pillaring effect of methyl group in the hydrangea-like V 2 O 5 microsphere ensures the expanded interlayer spacing for advanced Zn storage. • Methyl-functionalized V 2 O 5 is successfully prepared via a simple solvothermal method. • Pillaring effect of methyl group endows the favorable interlayer expansion and structural stability. • Methyl-functionalized V 2 O 5 is a promising cathode material for Zn-ion batteries.

Engineering unsaturated sulfur site in three-dimension MoS2@rGO nanohybrids with expanded interlayer spacing and disordered structure for gaseous elemental mercury trap

Rapid and effective capture of gaseous elemental mercury (Hg0) over a wide operating temperature range is significant for the green and sustainable development of nonferrous smelting industry. High mercury affinity and strong sulfur resistance of two-dimensional layered MoS2 render it an outstanding adsorbent for Hg0 trap. However, the relative lack of serviceable active sites greatly suppresses its extensive application. Herein, a feasible strategy to expand interlayer spacing, build disordered structure and engineer unsaturated sulfur adsorption sites was provided through the construction of three-dimension MoS2@rGO nanohybrids. As expected, compared with bulk and ordered MoS2, the prepared MoS2@rGO hybrid exhibits a remarkable performance improvement for Hg0 adsorption. The average Hg0 adsorption rate of MoS2@rGO is 2.28 μg/g/min and its saturated adsorption capacity reaches 20.91 mg/g. The typical components in nonferrous flue gas have almost no effect on Hg0 adsorption performance. X-ray photoelectron spectroscopy confirms that the formation of abundant unsaturated coordination sulfurs sites with high thermostability is critical for Hg0 adsorption performance improvement. Moreover, the density functional theory calculation results further demonstrate the high adsorption activity of unsaturated coordination sulfur sites for Hg0 capture. Among these sulfur sites, edge sulfur vacancy site plays a dominant role for Hg0 adsorption because of the lowest Hg0 adsorption energy. The final adsorption production is HgS which has negligible environmental toxicity due to its extreme stability. This work not only provides a promising adsorbent for Hg0 removal in industrial application, but also opens up an avenue to engineer unsaturated sulfur for other layered transition metal dichalcogenides.

Ion Exchange Conversion of Na-Birnessite to Mg-Buserite for Enhanced and Preferential Cu2+ Removal via Hybrid Capacitive Deionization.

Layered manganese oxides (LMOs) have recently been demonstrated to be one of the most promising redox-active material platforms for electrochemical removal of heavy metal ions from solution via capacitive deionization (CDI). However, the impact of interlayer spacing of LMOs on the deionization performance of electrodes in a hybrid capacitive deionization (HCDI) system with an LMO cathode and a carbon anode (i.e., LMO/C electrodes), and their phase transformation behaviors, particularly during the desalination operations, have yet to be extensively evaluated. In this study, we thoroughly evaluate Mg-buserite obtained by ion exchange of fresh Na-birnessite and Na- and K-birnessite as HCDI electrodes to remove copper ions (Cu2+) from saline solutions. Among the three LMO/C electrodes, the Mg-buserite/C (MgB/C) electrodes demonstrate the best deionization performance in terms of salt adsorption capacity (SAC), electrosorption rate, and cycling stability, followed by K-birnessite/C (KB/C) and Na-birnessite/C (NaB/C). More importantly, MgB/C exhibits the highest Cu2+ ion adsorption capacity (IAC) of 89.3 mg Cu2+ per gram electrode materials at a cell voltage of 1.2 V in 500 mg L-1 CuCl2 solution, with an IAC retention as high as 96.3% after 60 charge/discharge cycles. Given that electrosorption of Cu2+ ions is often competed by alkali and alkaline earth metal ions, our data reveal that the MgB/C electrodes demonstrate selectivities of 4.7, 7.7, and 8.1 for Cu2+ over Na+, Ca2+, and Mg2+, respectively. Moreover, X-ray diffraction and spectroscopic analyses show that the enhanced deionization performance and preference for Cu2+ are mainly attributed to the expanded interlayer spacing of LMO minerals. This study provides a promising strategy for tailoring LMO minerals for improving their electrosorption capacity and preference for copper ions from a multivalent-ion solution via an HCDI platform.

Assembly of Two-Dimensional δ-V2O5-Ti3C2Tx Heterostructure Electrodes for Li-Ion Batteries

The bilayered phase of vanadium oxide (δ-V2O5∙nH2O or BVO) synthesized via sol-gel synthesis method is an attractive candidate to be used as a cathode material for Li-ion batteries (LIBs) due to its expanded interlayer spacing, and high theoretical capacity. However, poor electrical conductivity and rapid capacity fade present challenges for achieving high-rate performance and good cycle life during cycling in LIBs. A viable solution to mitigating these drawbacks is to fabricate two-dimensional (2D) heterostructures comprised of vanadium oxide and an additional selected 2D material. Titanium carbide (Ti3C2Tx) MXenes are particularly of interest for their high electronic conductivity (103 S cm-1) and well developed delamination protocols. Herein, we present a wet-based approach for assembling BVO and MXene nanoflakes into 2D heterostructures in suspension.In this study, we first demonstrate a simple liquid phase exfoliation technique utilizing probe ultrasonication to exfoliate bulk -LixV2O5·nH2O (LVO). Previous experiments from our group showed the exfoliation technique in n-methyl-2-pyrrolidone, an organic solvent that is toxic, flammable, and resulted in low yield during exfoliation. Here, for the first time, we have successfully performed exfoliation of LVO in aqueous media and obtained few layered nanoflakes with high yield after centrifugation. Despite the partial solubility of vanadium oxide in water, these nanoflakes suspended in aqueous media maintained chemical stability and readily assembled into a free-standing film using vacuum filtration. The LVO nanoflake films have a two-dimensional (2D) layered morphology as confirmed by SEM and maintain the bilayered structure as confirmed by XRD.Due to the hydrated nature of LVO, we also highlight the importance of controlling interlayer water content with vacuum drying for achieving better cycling stability. The comparison of a 105°C and 200°C vacuum drying temperature and corresponding interlayer water content was carried out using XRD, TGA, and Raman spectroscopy characterization methods. The 200°C vacuum dried LVO nanoflake cathode achieved an initial ion storage capacity of 212 mAh g-1 which was 32.5% higher than the sample dried at 105°C. In addition, galvanostatic cycling experiments conducted for the 200°C vacuum dried LVO nanoflake cathode show there were significant improvements in capacity retention by ~35%, compared to the 105°C dried sample, after 100 cycles at a current density of 20 mA g-1.Subsequently, dispersions of LVO and Ti3C2Tx flakes in water were combined in different weight ratios of 9:1, 4:1, and 1:1 LVO to Ti3C2Tx. The heterostructure electrostatic assembly was facilitated by the introduction of a cationic species into the mixed suspensions. Resistivity measurements showed that heterostructure films achieved electronic conductivities as high as ~105 higher than pristine LVO. Through electrochemical testing, the 9:1 heterostructure cathodes delivered the highest ion storage capacity of 167 mAh g-1. At the cost of lower capacity (125.3 mAh g-1), the 4:1 heterostructures maintain a superior capacity retention of ~96% after 10 cycles. Furthermore, rate capability experiments for the 9:1 heterostructure cathodes demonstrate that the addition of 10 wt % Ti3C2Tx to LVO enables greater tolerance to high current densities with a capacity retention of ~90% after cycling through increasing current densities. In this work we also show that increased capacities can be acquired upon the extension of the potential window below 2V covering where Ti3C2Tx exhibits redox activity.These results demonstrate an environmentally friendly and safe approach to obtaining 2D LVO nanoflakes and offers pathways to constructing novel vanadium oxide based 2D heterostructures for improving electrochemical performance in energy storage devices.

Two-dimensional Ti2CTx with expanded interlayer spacing for Na-ion storage

Highlights • The interlayer spacing of Ti 2 CTx MXene can be enlarged by dimethyl sulfoxide intercalation. • The Ti 2 CT x MXene with expanded interlayer spacing delivered superior Na storage performance than the pristine Ti 2 CT x MXene. • Electrochemical kinetic analysis revealed a capacitive dominated sodium storage process. MXenes have been regarded as promising anode materials for Na-ion batteries due to their unique layered structures. Herein, the two-dimensional Ti 2 CT x with expanded interlayer by intercalation of dimethyl sulfoxide is designed as anode material for Na-ion storage. The as-prepared interlayer-expanded Ti 2 CT x delivered an initial discharge capacity of 486 mAh g −1 and maintained a stable capacity of 176 mAh g −1 after 250 cycles at 100 mA g −1 , which are much higher than those of the pristine Ti 2 CT x .

Rational Design of Sulfur-Doped Carbon with Expanded Inter-layer Spacing toward Anode Material of Sodium-Ion Batteries

Rational Design of Sulfur-Doped Carbon with Expanded Inter-layer Spacing toward Anode Material of Sodium-Ion Batteries