Ex-situ X-ray Photoelectron Spectroscopy Research Articles

Heterostructure of Ta5+-substituted Na3V2(PO4)3–TaN promoting the activation of V4+/V5+ redox couple for high performance sodium-ion batteries

Currently, low capacity with poor kinetics seriously hinders the development of Na3V2(PO4)3 (NVP). Herein, a simultaneous optimized scheme of Ta5+ substitution and carbon nanotubes (CNTs) enwrapping is proposed. The substitution of hypervalent Ta5+ at V3+ site introduces a favorable n-type doping effect to generate extra electrons, increasing electron concentration to accelerate electronic conductivity. Ta5+ behaves as a pillar ion to expand Na + migration channel and stabilize the skeleton. Moreover, a new phase of TaN is produced, which embeds into the Na3V2(PO4)3 phase to generate grain boundary. Benefiting from this heterojunction, Na+ diffusion rate could be effectively promoted. The addition of CNTs further restricts agglomeration growth of particles, making the grains smaller and more uniform. Benefiting from the synergetic improved kinetics, a higher voltage platform at 3.9 V is activated. Due to the investigations of ex-situ X-ray photoelectron spectroscopy, the extra plateau is derived from the V4+/V5+ redox couple. Moreover, Density Functional Theoretical calculation suggests the favorable Ta5+ substitution optimizes the electronic structure of NVP to reduce the band gap. Accordingly, the modified NVPT/C@CNTs0.15 submits 125.5 mA h g−1 at 0.1C, and delivers a high value of 77.5 mA h g−1 at 100 C with retention rate of 81.03% after 12000 cycles.

Amorphous nanoscale antimony-vanadium oxide: A high capacity anode material for potassium ion batteries

Antimony (Sb)-based materials, as a kind of potential high capacity and low cost materials, are the focus of attention in the anode materials of potassium ion batteries. However, at present, studies on Sb-based anode materials mainly focus on Sb metal, Sb alloy and Sb chalcogenides, while reports on Sb-based oxides are relatively rare. In addition, the development of Sb-based materials is limited by their large volume variation and poor reaction kinetics for potassium storage. Herein, a novel amorphous Sb2VO5 (A-SbVO) as bimetallic antimony vanadium oxide has been synthesized by solvothermal method. The A-SbVO exhibits high K storage activity and capacity due to its nanoscale and amorphous structure. Moreover, ex-situ transmission electron microscopy and X-ray photoelectron spectroscopy revealed the evolution of the A-SbVO in the potassium storage process as follows: A-SbVO → Sb → K3Sb → Sb → Sb + Sb2VO5. After compounding with reduced graphene oxide (rGO), the as-prepared A-SbVO/rGO shows better K storage stability, with discharge specific capacities of 313.0 and 248. 8 mAh/g at 500 and 1000 mA g−1, respectively. After 300 cycles at 200 mA g−1, the A-SbVO/rGO still has a high discharge specific capacity of 382.1 mAh/g.

Polypyrrole pre-intercalation engineering-induced NH4+ removal in tunnel ammonium vanadate toward high-performance zinc ion batteries

Ammonium vanadate with stable bi-layered structure and superior mass-specific capacity have emerged as competitive cathode materials for aqueous rechargeable zinc-ion batteries (AZIBs). Nevertheless, fragile NH…O bonds and too strong electrostatic interaction by virtue of excessive NH4+ will lead to sluggish Zn2+ ion mobility, further largely affects the electro-chemical performance of ammonium vanadate in AZIBs. The present work incorporates polypyrrole (PPy) to partially replace NH4+ in NH4V4O10 (NVO), resulting in the significantly enlarged interlayers (from 10.1 to 11.9 Å), remarkable electronic conductivity, increased oxygen vacancies and reinforced layered structure. The partial removal of NH4+ will alleviate the irreversible deammoniation to protect the laminate structures from collapse during ion insertion/extraction. The expanded interlayer spacing and the increased oxygen vacancies by the virtue of the introduction of polypyrrole improve the ionic diffusion, enabling exceptional rate performance of NH4V4O10. As expected, the resulting polypyrrole intercalated ammonium vanadate (NVOY) presents a superior discharge capacity of 431.9 mAh g−1 at 0.5 A g−1 and remarkable cycling stability of 219.1 mAh g−1 at 20 A g−1 with 78 % capacity retention after 1500 cycles. The in-situ electrochemical impedance spectroscopy (EIS), in-situ X-ray diffraction (XRD), ex-situ X-ray photoelectron spectroscopy (XPS) and ex-situ high resolution transmission electron microscopy (HR-TEM) analysis investigate a highly reversible intercalation Zn-storage mechanism, and the enhanced the redox kinetics are related to the combined effect of interlayer regulation, high electronic conductivity and oxygen defect engineering by partial substitution NH4+ of PPy incorporation.

Novel high-voltage cathode for aqueous zinc ion batteries: Porous K0.5VOPO4·1.5H2O with reversible solid-solution intercalation and conversion storage mechanism

Cathode materials that possess high output voltage, as well as those that can be mass-produced using facile techniques, are crucial for the advancement of aqueous zinc-ion battery (ZIBs) applications. Herein, we present for the first time a new porous K0.5VOPO4·1.5H2O polyanionic cathode (P-KVP) with high output voltage (above 1.2 V) that can be manufactured at room temperature using straightforward coprecipitation and etching techniques. The P-KVP cathode experiences anisotropic crystal plane expansion via a sequential solid-solution intercalation and phase conversion pathway throughout the Zn2+ storage process, as confirmed by in-situ synchrotron X-ray diffraction and ex-situ X-ray photoelectron spectroscopy. Similar to other layered vanadium-based polyanionic materials, the P-KVP cathode experiences a progressive decline in voltage during the cycle, which is demonstrated to be caused by the irreversible conversion into amorphous VOx. By introducing a new electrolyte containing Zn(OTF)2 to a mixed triethyl phosphate and water solution, it is possible to impede this irreversible conversion and obtain a high output voltage and longer cycle life by forming a P-rich cathode electrolyte interface layer. As a proof-of-concept, the flexible fiber-shaped ZIBs based on modified electrolyte woven into a fabric watch band can power an electronic watch, highlighting the application potential of P-KVP cathode.

High-capacity all-solid-state Li-ion battery using MOF-derived carbon-encapsulated iron phosphide as anode material

Iron Phosphide (Fe2P) particles embedded within in-situ generated tubular carbon structures uniformly doped with nitrogen heteroatoms (Fe2P @ NC) have been investigated as an anode in all-solid-state lithium-ion batteries (ASSLIBs). The designed morphology offered a number of suitable features, such as high conductivity, robust framework, and abundant redox active sites for augmenting overall battery performance. As anode, Fe2P @ NC has provided a high lithiation/delithiation capacity of 1214.8 mA h/g /1367.01 mA h/g at a current density of 66.6 mA/g (100 μA) with a high coulombic efficiency (>100%). Further, Fe2P @ NC also demonstrated an excellent rate performance and moderate structural stability during cycling. The charge storing mechanism for Fe2P @ NC investigated via ex-situ X-ray diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS) studies indicates irreversible conversion of Fe2P → Li3P & Fe in the initial cycle and reversible Li3P ↔ LiP reaction in subsequent cycles. Analysis of reaction kinetics for Fe2P @ NC nanocomposite is carried out using CV measurements at different scan rates. This study explores the possibility of MOF-derived iron-phosphide-based composite material as a high-performance anode for ASSLIBs.

Structural and Electrochemical Investigation of 3D Tunnel Type Li0.44MnO2 Cathode Material for Secondary Li-Ion Batteries

The design of new cathode materials remains a key goal in the development of (post) Li-ion batteries. In that regard, densely packed structures like Li0.44MnO2 are judicious for study. The presence of Mn as a transition metal makes it more attractive due to its sustainable nature, low cost, elemental abundance, structural diversity/polymorphism, and rich oxidation states (2+ to 7+) offering tunable redox potential [1]. Here, we have investigated Mn-based tunnel-type Li0.44MnO2 oxide for secondary LIBs. i) Li44MnO2 (LMO) was prepared by a soft chemical method using the corresponding sodium manganese oxide (Na0.44MnO2) as a parent compound [2]. The crystal structure of Li0.44MnO2 maintains the parent Na0.44MnO2-type tunnel structure which is analogous to Na4Mn4Ti5O18 having an orthorhombic (s.g. Pbam) crystal system [3]. To understand redox chemistry, this material was studied for both cationic (Mn) and anionic (O) redox reactions using ex-situ X-ray photoelectron spectroscopy. The lithium (de)insertion mechanism of Li0.44MnO2 was explored involving ab initio calculations and in-situ X-ray diffraction experiments. Combined with electrochemical measurements, structural characterizations, and first principles DFT calculations revealed the capacity correlated strongly with both cationic and anionic redox reactions. ii) We have studied the phase transition of Li44MnO2 from a 3D tunnel-type structure to a cubic spinel structure by in-situ X-ray diffraction and Raman spectroscopy. The mechanism of transformation was elucidated by employing transmission electron microscopy. In this case, diffusion-less transformation occurs involving the rearrangement of atoms during heating [4]. An increase in the average redox potential from the pristine orthorhombic phase to the final spinel phase was observed by electrochemical studies. iii) Further to improve the electrochemical performance of Li0.44MnO2, Ti was used as a dopant. The Li0.44[Mn1-xTix]O2 (x=0, 0.11, 0.22, 0.33, 0.44, 0.56) series were obtained with chemical ion exchange from Na precursors. The Na precursors (Na0.44[Mn1-xTix]O2) were prepared via a simple solid-state route. Ti-substituted compositions exhibited similar crystal structures to their parent LMO i.e. orthorhombic framework with Pbam symmetry. A tunnel-type morphology was observed in all cases. The electrochemical performance of Ti-substituted LMO as cathode material for LIBs was studied in a half-cell configuration. The structure and electrochemical properties of Ti-doped LMO, reaching the highest capacity of 128 mAh/g, will be described. Keywords: batteries; cathode; tunnel type manganese oxides; phase transformation; doping

Investigation of Heteroatom Doped Graphene Anode for High-Capacity Alkali Metal-Ion Batteries

The drastic growth of Li-ion batteries (LIBs) in global electronic market and low crustal abundance of Li demands for more abundant alternatives such as sodium and potassium having similar electrochemical properties. Sodium-ion battery (SIB) and potassium-ion battery (PIB) can be used “side-by-side” to LIB which can help battery technology progress efficiently. 1Graphite has been a commercial anode in LIB due to its low cost, high abundance, high electrical conductivity, with a theoretical storage capacity (LiC6) of 372 mAh g-1. In contrast the utilization of graphite in SIBs and PIBs is challenging. This is due to the large radius and unstable graphite-intercalation compounds (NaC64) giving very low theoretical capacity of 30 mAh g-1. In PIBs, graphite exhibits a theoretical capacity of 279 mAh g-1 but suffers from poor stability due to huge volume expansion (60%) in fully potassiated state (KC8). Thus, focus is now shifted on to class of amorphous carbon materials such as hard carbon, soft carbon, graphene etc. with variations in micro-structures, larger interlayer spacing, and defect rich sites promoting enhanced capacity and stability even at high current densities. 2 In my presentation I will be discussing about the synthesis of heteroatom doped graphene with high charge storage and stability for LIB, SIB and PIB compared to graphite. The heteroatom doped graphene exhibits nearly 1000 mAh g-1 (LIB), 380 mAh g-1 (SIB) and 379 mAh g-1 (PIB) at a low current density of 25 mAg-1. Additionally, the elastic nature of ultrathin graphene nanosheets aids in attaining long term cyclability at 1 A g-1 with high-capacity retention of 83% for 300 cycles (LIB), 73% for 400 cycles (SIB) and 91% for 600 cycles (PIB). The enhanced stability in case of PIB, is attributed to optimizing solid electrolyte interphase (SEI) components and improving interfacial reaction kinetics at high current densities. Choice of high concentrated electrolyte (HCE) over conventional KPF6 in EC:DEC determines the nature of SEI and thereby helps in achieving cycling stability. The stability in SEI is characterized via voltage profile and understanding chemical composition by ex-situ X-ray photoelectron spectroscopy. Robust SEI in HCE is due to difference in anion structure studied by Raman spectroscopy.Furthermore, the charge-discharge mechanism, alkali ion diffusion kinetics and structure-activity relationship of electrode materials was investigated using various techniques like cyclic voltammetry profiles at different scan rates and Galvanostatic intermittent titration technique (GITT). Additionally, deeper insights into the fundamental understanding of interfacial and bulk behavior were provided with the help of in-situ Raman spectroscopy and in-situ potentiostatic electrochemical impedance spectroscopy (PEIS) analysis. The investigation of peak area and shift in D (defect) and G (graphitic) band analyzed from in-situ Raman studies helped in understanding the evolution and reversibility of alkali ion storage behavior during charging and discharging. PEIS analysis gave us a thorough understanding of the evolution of stable SEI on charging-discharging and after cycling, which helps us to understand the long-term stability in LIB, SIB and PIB.

Unraveling the Lithium Storage Mechanism at Low Potentials in Niobium Pentoxide Anodes for Lithium-Ion Batteries

State-of-the-art lithium-ion anodes based on graphite exhibits high specific capacity and a low de-/lithiation potential, thus, enabling very high energy densities at full-cell level. However, the rather sluggish lithiation kinetics render them less suitable for fast-charging batteries[1]. A potential alternative that has gathered increasing interest in recent years is Nb2O5, but the commonly employed lower cut-off voltage of 1.0 V vs. Li+/Li in combination with the lower capacity compared to graphite limit the achievable energy density[2,3].Herein, the extended lithiation to lower cut-off voltages is reported, resulting in increased capacities while maintaining a very stable cycle life. Remarkably, this behavior is generally independent from the initial polymorph, and both monoclinic and orthorhombic Nb2O5 show a substantial increase in capacity for several hundred cycles. To elucidate the underlying storage mechanism, comprehensive characterization via operando/ex-situ X-ray diffraction (XRD), operando Raman spectroscopy, operando isothermal microcalorimetry (IMC), ex-situ X-ray absorption spectroscopy (XAS), and ex-situ X-ray photoelectron spectroscopy (XPS) was conducted. It appears that the occurrence of an additional phase transition at low potentials plays a decisive role for the enhanced capacity and superior cycling stability. Reference [1] J. Asenbauer, T. Eisenmann, M. Kuenzel, A. Kazzazi, Z. Chen, D. Bresser, Sustain. Energy Fuels 2020, 4, 5387–5416.[2] P. Jing, K. Liu, L. Soule, J. Wang, T. Li, B. Zhao, M. Liu, Nano Energy 2021, 89, 106398.[3] T. Li, G. Nam, K. Liu, J. H. Wang, B. Zhao, Y. Ding, L. Soule, M. Avdeev, Z. Luo, W. Zhang, T. Yuan, P. Jing, M. G. Kim, Y. Song, M. Liu, Energy Environ. Sci. 2022, 15, 254–264.

Development of Iron Fluoride Based Nanocomposite Materials to Enable High Performance Aluminium-Ion Batteries

Developing grid-scale energy storage is important for the penetration of intermittent renewable energies such as wind and solar, but remains one of the biggest challenges in the field of electrochemical energy storage [1]. The application of mature lithium-ion batteries (LIBs) to grid energy storage is controversial due to the limited Li resources and geographical distribution, high cost of materials (e.g., Co, Li), limited lifetime, and safety concerns [2]. Rechargeable aluminium ion batteries (AIBs), which normally utilises aluminium (Al) metal as anode, are one of the most promising battery technologies for future large-scale energy storage, due to the high theoretical volumetric capacity (8046 mAh cm−3), high safety, and low cost and high abundance of aluminium (the third most abundant metal in the earth crust) [3].AIBs have achieved long cycle life (>7500 cycles) when using graphite and graphene as cathode materials [4-5]. Nevertheless, the reported graphite-based cathodes have intrinsically low storage capacities (60–200 mAh g-1) due to the intercalation mechanism of the solvated ions rather than the multivalent Al3+ transformation. Extensive efforts have been made to develop new cathode materials to promote the specific/volumetric capacity of AIBs, including transition metal oxides [6], sulfides [7], selenides [8] and others. These AIBs based on non-graphite cathodes usually demonstrate either low discharge voltage, or high initial capacity but significant capacity decay and poor cycle life. To further improve the performance of AIBs, new cathode materials with high storage capacity and long cycle life needs to be developed.In this paper, we report the development of a nanoscale FeF3@expaned graphite (EG) composite as a novel conversion-type cathode material for AIBs [9]. AIB coin cells were assembled using high-purity Al foil as the anode, the ionic liquid [EMIm]Cl/AlCl3 as the electrolyte, and the FeF3@EG composite as cathode. The conversion reaction between the Al3+ ions and FeF3 through transferring three electrons for per Al3+ ion reacted could boost the storage capacity of AIBs. A single-wall carbon nanotube-modified separator was introduced into the system, to significantly restrict the shuttle effect of the intermediate product of FeF3. The assembled AIBs exhibited a satisfactory reversible specific capacity of 266 mAh g-1 at a current density of 60 mA g-1 after 200 cycles, and a good Coulombic efficiency approaching 100% after 400 cycles at a current density of 100 mA g-1 [9]. Ex-situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) have been applied to explore the energy storage mechanism of FeF3 in AIBs for the first time [9].To further overcome the corrosion issue of ionic liquid, a gel polymer electrolyte (GPE) has been successfully synthesised via an innovative method where no solvent or initiator was utilised in the polymerisation process. The application of GPE significantly reduced the corrosivity and enhances the moisture sensitivity of EMIC ionic liquid, as well as improving the reversible ability of the AIBs. The FeF3@EG-based AIB with 0.8g-EMIC-gel electrolyte exhibits a reversible capacity of 204.5 mAh g-1after 1000 cycles at a current density of 100 mA g-1 and stable rate performance for 600 cycles with a Coulombic efficiency of approximately 95%.This work provides unprecedented insight into novel conversion type cathode materials for AIBs. The findings in this work can serve as guidance for the successful design of low cost and high discharge capacity AIBs for large-scale energy storage and are also meaningful for the fundamental understanding of the metal fluorides cathodes for AIBs.

Na3(VO)2(PO4)2F coated carbon nanotubes: A cathode material with high-specific capacity for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are one of the candidate technologies for large-scale energy storage systems due to their environmental friendliness, safety and resourcefulness. However, designing and synthesizing high-performance cathode materials with practical application value is currently a great challenge. Herein, we synthesize a carbon-nanotube-coated Na3(VO)2(PO4)2F (Na3(VO)2(PO4)2F@CNT) cathode material for AZIBs, which has a continuous and interconnected ion transport channel structure. A Zn2+/H+ co-intercalation mechanism is revealed by ex-situ X-ray diffraction (XRD) and ex-situ X-ray photoelectron spectroscopy (XPS) characterizations. The Na3(VO)2(PO4)2F@CNT cathode material exhibits a high specific capacity of 143 mAh‧g Wan et al. (2019). at 0.2 C in the electrolyte of 3 M Zn(OTf)2 aqueous solution. In addition, Na3(VO)2(PO4)2F@CNT shows a good low-temperature electrochemical performance in the electrolyte of 2 M Zn(OTf)2 deionized water/ethylene glycol (DIW/EG) mixed solution with a different ion storage mechanism. This study provides a new polyanionic cathode material for AZIBs and an idea to modulate the electrolyte polarity to enhance the zinc storage capacity of the cathode material.

A rational proton compensation strategy of polyaniline-MnO2 hybrid structure for promoting dual ion storage of Zn-ion battery

Manganese dioxide is the most potential cathode material for aqueous zinc-ion batteries (ZIBs). Unfortunately, the terrible structure stability and slow kinetic response of manganese dioxide limit their further application. Here, polyaniline (PANI) and manganese dioxide (MnO2) composites are devised as high-performance cathodes for ZIBs. It is demonstrated that the composite exhibits the characteristics of high conductivity, long discharge platform and stable circulation. At the same time, according to the ex-situ X-ray diffraction and X-ray photoelectron spectroscopy, polyaniline can provide additional H+ ions to participate in the reaction, thus increasing the specific capacity. Due to these attractive merits, the PANI-MnO2(1 h)@CC cathode acquires high discharge capacity of 479.9 and 121.2 mAh g–1 at 0.2 and 4 A g–1, respectively. This study supplies a new view to improve the specific capacity of MnO2 cathodes.

Ester-based anti-freezing electrolyte achieving ultra-low temperature cycling for sodium-ion batteries

With the continuous advancement of industrialization, sodium-ion batteries (SIBs) need to operate in various challenging circumstances, particularly in extremely cold conditions. However, at ultra-low temperatures, the reduced ionic conductivity and sluggish Na+ migration of commonly carbonate-based electrolytes will inevitably lead to a sharp decrease in the capacity of SIBs. Herein, we design a carboxylate ester-based electrolyte with excellent ultra-low temperature performance by straightforward cosolvent strategy. Due to the low viscosity, melting point, and sufficient ionic conductivity of the designed electrolyte, the resulting Na||Na3V2(PO4)2O2F can achieve the capacity retention of 96% (100 cycles at 0.1 C) at –40 °C and can also operate stably even at –50 °C. Besides, galvanostatic intermittent titration technique (GITT), ex-situ X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (TEM) tests are employed to analyze and confirm that the carboxylate ester-based electrolyte promotes robust and uniform cathode/electrolyte interface layer formation and accelerates ion diffusion kinetics, which collectively facilitates the better low-temperature performance. In addition, the assembled hard carbon||NVPOF full cells further prove the practicability of the carboxylate ester-based electrolyte at low-temperature, which delivers high discharge capacity of 108.4 and 73.0 mAh g–1 at –25 and –40 °C. This work affords a new avenue for designing advanced low-temperature electrolytes for SIBs.

Construction of 2D sandwich-like Na2V6O16·3H2O@MXene heterostructure for advanced aqueous zinc ion batteries

Aqueous zinc ion batteries (AZIBs) have attained enormous attention in the last few years. The cathode materials of aqueous zinc ion batteries play a vital effect in their electrochemical and battery properties. In this manuscript, Sandwich-like MXene@Na2V6O16·3H2O (NVO@MXene) heterostructure was successfully prepared by the combination and cooperation of the layer lattice structure of Na2V6O16·3H2O and the high conductivity of MXene. When used as the cathode material for AZIBs, NVO@MXene demonstrates preeminent rate capability and excellent reversible capacity of 175 mAh/g after 3000 cycles at 5 A/g with a retention rate of 88.9 % of initial discharge capacity. The outstanding battery performance can be attributed to the MXene layers with high conductivity for accelerating the ion diffusion rate and reducing the agglomeration of Na2V6O16·3H2O nanowires during the (dis)charge process. Meanwhile, the stable layered structure of Na16V6O6·3H2O with wide interlamellar spacing (d = 7.9 Å) is also favorable for the s fast intercalation/deintercalation of Zn2+. Finally, ex-situ X-ray diffraction and X-ray photoelectron spectroscopy were applied to study and reveal the energy storage mechanism of this novel material for aqueous zinc ion batteries.

Controllable phase transition of two-dimensional ferromagnetic chromium telluride thin films grown by molecular beam epitaxy

Two-dimensional (2D) Cr(1+δ)Te2 materials exhibit strong magnetic ordering and high Curie temperatures, making them attractive for various applications. It is crucial to achieve controllable synthesis for their successful integration into device technologies. In this study, we present the synthesis of phase-controllable 2D Cr(1+δ)Te2 films on the Si (111) substrate via molecular beam epitaxy. The composition and phase transition of the as-grown Cr(1+δ)Te2 films are characterized by using in-situ reflection high-energy electron diffraction, scanning tunneling microscopy, ex-situ X-ray photoelectron spectroscopy, X-ray diffraction, and theoretical calculations. At low growth temperatures, by carefully adjusting the film thickness from 2 to more than 3 layers, we achieve precise control over the phase of Cr(1+δ)Te2, from CrTe2 to Cr intercalated Cr2Te3. At a relatively elevated growth temperature, it is demonstrated that the Cr(1+δ)Te2 phase is independent of the film thickness, only Cr2Te3 forms and its growth mode is thickness-dependent. These phase transitions at low growth temperatures and growth mode changes at elevated growth temperatures are attributed to interfacial effects and the phase stability of Cr(1+δ)Te2 compounds. Additionally, we utilize scanning tunneling spectroscopy and computations to gain insights into the electronic properties of Cr2Te3. The magnetic measurements reveal that the 30-nm Cr2Te3 film exhibits ferromagnetic behavior with a Curie temperature of about 180 K. Our work offers a robust method for the controllable growth of high-quality 2D Cr(1+δ)Te2 films on Si substrates, providing an ideal platform for investigating their intrinsic properties and advancing the development of 2D magnet-based spintronics devices.

Ti3C2Tx constrained Sb2S3 composite biomass-derived carbon ribbon film achieves stable sodium storage for flexible quasi-solid full-battery

Optimizing electrode structure, reducing the proportion of inactive substances, and fabricating a flexible free-standing electrode without fluid collection are desirable to enhance the energy density, fast charging, and cycling stability of flexible batteries. In this study, we utilized the biological characteristics of Aspergillus niger to synthesize one-dimensional (1D) Sb2S3 nanoparticle composite N-doped C ribbons. Subsequently, vacuum filtration was employed to blend and assemble these 1D composite C ribbons with Ti3C2Tx nanosheets into a free-standing flexible anode for Sodium-ion batteries (SIBs). Using 1D C ribbons can effectively inhibit the stacking of 2D MXenes, thereby facilitating the penetration of Na+ into Sb2S3@NCR through the interlamellar pores. Ex-situ X-ray photoelectron spectroscopy analyses indicated that the MXene layers were not only physically confined but also effectively suppressed polysulfide diffusion through chemical confinement. Consequently, the energy density and cycling stability of the Sb2S3@NCR composite electrode were enhanced. The Sb2S3@NCR/MXene||CGPFE||NVP@CNF full battery, consisting of an Sb2S3@NCR/MXene anode, free standing NVP@CNF cathode, and PVDF-HFP fiber quasi-solid-state polymer electrolyte prepared via electrospinning, achieved 1,000 stable cycles at a current density of 1 Ag−1. Additionally, the flexible quasi-solid-state bag-type battery could power an LED lamp at a bending angle of 0°–180°.

In-depth investigation on the influence of iron impurity on the oxygen evolution performance of iron-based catalysts

It is well-known that Fe3+ impurities in the electrolyte can significantly promote the oxygen evolution reaction (OER) activity of Co-based and Ni-based electrocatalysts. However, it is not clear if they work for single-metal Fe-based catalysts. Here, we systematically investigate the influence of Fe3+ ions in the electrolyte on the OER activity of core-shell FeOx@C catalytic system. We find that the absorbed Fe3+ can induce the generation of surface oxygen vacancies and regulate the electronic structure of active sites, thus increasing the OER kinetics and decreasing the energy barrier. Combining with in-situ Raman and ex-situ X-ray photoelectron spectroscopy (XPS) analysis, we disclose that Fe4+ species is the active species for the OER and positively correlate the characteristic content of the high-valence Fe species and OER activity.

In-situ rooting biconical-nanorods-like Co-doped FeP @carbon architectures toward enhanced lithium storage performance

With desirable high capacity, theoretical work voltage and abundant resources, iron phosphide (FeP) has been garnered much consideration as a hopeful anode material for lithium-ion batteries (LIBs). Nevertheless, structural stability and low electronic conductivity restrict its application. Herein, metal organic frameworks (MOFs)-derived biconical-nanorods-like Co-doped FeP confined by phosphorus-doped carbon (Co-doped FeP@P-C) is successfully prepared. The unique biconical-nanorods-like structure, MOFs in-situ derived carbon coating and Co-doping can accelerate the ion and electron transport efficiency, supply abundant reaction active sites and moderate the volume expansion of FeP material. Benefiting from these merits, the as-prepared Co-doped FeP@P-C anode manifests a high Li+ storage capacity (784 mAh/g at 0.2 A g−1) and long-term stability (555.6 mAh/g at 1 A g−1 after 700 cycles). The experimental studies coupled with density functional theory (DFT) theoretical calculations uncover the effect of Co-doping on boosting charge transfer and enriching the reaction active sites in FeP@P-C anode. Furthermore, the electrochemical kinetic analysis revealed the underlying mechanism of lithium storage in detail, ex-situ X-ray diffraction and X-ray photoelectron spectroscopy analysis. LiCoO2//Co-doped FeP@P-C full-cells are successfully assembled and exhibit relatively high reversible capacity. The present work can provide a rational design and promising cation doping strategy for other metal phosphide anode materials for LIBs.

Covalent sulfur confined in mesoporous hollow carbon spheres for effective kinetic regulation of room-temperature sodium-sulfur batteries

Room-temperature sodium-sulfur batteries have attracted extensive attention as a cost-effective and high theoretical energy density next-generation energy storage systems. However, the insulating nature of sulfur, the sluggish reactivity of sulfur with sodium, and severe dissolution of polysulfide are the main challenges of this technology. Here, we propose a covalent sulfur bond breakage mechanism by bonding of sulfur chain onto the inner cavity of the sulfydryl-functionalized mesoporous hollow carbon spheres (MHCS) to efficiently promote the generation of short-chain sodium polysulfide and accelerate polysulfide redox kinetics. The covalent sulfur confined MHCS (S@MHCS) cathode delivers an unprecedented rate capability (250 mAh g−1 at 5 C) and exhibits excellent long-term cycling stability over 1000 cycles at 1 C with a high cathode loading of 5 mg cm−2. Moreover, the associated electrochemical reaction mechanism is also revealed by ex-situ X-ray photoelectron spectroscopy and theoretical calculation. This work introduces a novel sulfur cathode design to enhance the performance of room-temperature sodium-sulfur batteries.

Endogenous Nb2CTx/Nb2O5 Schottky heterostructures for superior lithium-ion storage

Schottky heterostructures have significant advantages for exciting charge transfer kinetics at material interfaces. In this work, endogenous Nb2CTx/Nb2O5 Schottky heterostructures with a large active surface area were constructed using an in-situ architectural strategy. The semiconductor Nb2O5 has a low work function, and during the construction of Nb2CTx/Nb2O5 Schottky heterostructures, there was an interfacial electron transfer, which resulted in a built-in electric field. The electrochemical reaction kinetics of Nb2CTx/Nb2O5 Schottky heterostructures were enhanced due to the rapid transfer of charge driven by the electric field. The Nb2CTx/Nb2O5 Schottky heterostructures have a large active surface area, which contributes to excellent electrolyte diffusion kinetics. Therefore, Nb2CTx/Nb2O5 Schottky heterostructures have excellent lithium-ion storage capacity with 575 mAh/g after 200 cycles at 0.10 A/g, and 290 mAh/g after 1000 cycles at 2.00 A/g, without capacity fading. Furthermore, in-situ X-ray diffraction and ex-situ X-ray photoelectron spectroscopy analyses reveal the mechanisms for structure evolution and lithium-ion storage optimization of Nb2CTx/Nb2O5 Schottky heterostructures during the electrochemical reaction. The construction of Schottky heterostructures with excited charge transport kinetics provides a novel idea for optimizing the lithium-ion storage activity of MXenes materials.

In-situ synthesis of porous Na3V2(PO4)3 with stable V[sbnd]O[sbnd]C bridge bonding by hard template method

Low electronic conductivity and poor properties at high rate have hindered the application of Na3V2(PO4)3 (NVP). Herein, a facile synthesis of NVP with porous carbon skeleton is proposed. Specifically, Na2CO3 and glucose, acting as hard templates, are introduced to the precursors after initial firing stage, and Na2CO3 particles are removed by flushing after the final heatment. Due to the thermal conductivity of Na2CO3, the secondary addition of glucose can generate distinctive graphitized porous carbon skeleton, which bonds well with the amorphous carbon coating to construct stable and conductive network. The porous construction can alleviate the stress and strain caused by the current impact through deformation. Furthermore, ex-situ EIS reveals the highly conductive carbon skeleton can significantly reduce the surface resistance and result in an increase of effective voltage to promote the de-intercalation of Na+. Moreover, the ex-situ X-ray photoelectron spectroscopy (XPS) at different potentials confirms the stabilized existence of VOC bonds. Benefiting from the unique carbon skeleton, the PC-NVP releases capacity of 116.9 mAh g−1 at 0.1C. Even at 120C, PC-NVP still exhibits a high capacity of 84.7 mAh g−1, retaining a value of 41.3 mAh g−1 after 16,000 cycles, corresponding to a low decay rate of 0.0032% per cycle.