Ex-situ X-ray Photoelectron Spectroscopy Research Articles

Zinc hexacyanoferrate with open framework for efficient aqueous cobalt ions storage

In this work, we report a high-performance aqueous Co-ion battery with zinc hexacyanoferrate as Co2+ storage material. Owing to the open framework, zinc hexacyanoferrate exhibits excellent electrochemical performance. The reversible capacity of zinc hexacyanoferrate is up to 62.4 mAh g−1 at 5C with ultralow capacity decay (0.0084 % per cycle) within 500 cycles. Even cycled at a higher rate of 10C, zinc hexacyanoferrate still can remain a high capacity retention of 98.8 % after 700 cycles. The excellent electrochemical performance is attributed to the rapid kinetics behavior of Co2+ in the open and stable framework structure. Besides, a joint analysis of in-situ X-ray diffraction, ex-situ Fourier transform infrared spectroscopy and ex-situ X-ray photoelectron spectroscopy verifies the highly reversible structural change of zinc hexacyanoferrate during charge/discharge process. All these evidences suggest that zinc hexacyanoferrate may be a promising host material for Co2+ storage in aqueous rechargeable batteries.

Biomass derived 3D N, P co-doped porous carbon incorporated with Ni-Cu bimetallic phosphide: Synergistic effect of Ni-Cu boosting Na+ storage performance

Transition metal phosphides (TMPs) as promising anode materials for sodium-ion batteries (SIBs) due to their amazing properties such as high theoretical specific capacity, various bond types and good electrical conductivity. However, TMPs are still facing poor cycling stability and unsatisfactory specific capacity, which restrict their practical application. Herein, NixCu3-xP incorporated in biomass derived 3D N, P co-doped porous carbon (NixCu3-xP-NPC) is constructed as SIB anode and the electrochemical behaviors with various Ni/Cu ratios are explored. The synergistic effect of Ni-Cu in NixCu3-xP is approved by the resulting investigation, and density functional theory (DFT) calculation further confirmed its important influence in enhancing electronic conductivity and boosting Na+ storage. Evidently, the optimum synergistic effect was observed when Ni0.15Cu2.85P/NPC is utilized for SIB anode. It exhibits a reversible specific capacity of 663 mAh g−1 after 200 cycles at 0.2 A g−1, long cycling stability (467 mAh g−1 after 1000 cycles at 1.0 A g−1), and excellent rate capability (432 mAh g−1 at 2.0 A g−1). The ex-situ X-ray diffraction and ex-situ X-ray photoelectron spectroscopy verify the combined conversion mechanism of Ni and Cu during sodiation/desodiation processes, which is greatly favorable for high specific capacity and cycling stability.

High-capacity and high-stability capacitive desalination with dual redox-active MnCo2S4/g-C3N4 heterojunction electrode

Capacitive deionization (CDI) utilizing dual redox-active electrodes has shown significant promise in desalinating low-concentration brackish waters, which is crucial for addressing global freshwater shortages. However, improvements in salt adsorption capacity and long-term operational stability are still required. In this study, we introduce, for the first time, a binary metal sulfide MnCo2S4/g-C3N4 (MCS-CN) heterojunction as a CDI electrode. The innovative integration of dual redox-active centers and heterojunction structures in the MCS-CN composite electrodes underscores their potential for achieving both high capacity and stability in capacitive desalination applications. The microscopic morphology, crystal structure, pore structure, and surface valence properties of the MCS-CN heterojunction composite materials were extensively characterized using various analytical techniques. In-situ X-ray diffraction, refined ex-situ X-ray photoelectron spectroscopy, three-electrode electrochemical analysis, and theoretical calculations were employed to elucidate the electrosorption and desorption mechanisms of sodium ions with the MCS-CN electrodes and to clarify the enhanced desalination performance of the binary metal sulfide-based heterojunction structure. As a result, the optimal MCS-CN-40 electrode exhibited the highest salt removal capacity of 71.64 mg g−1 and maintained stable desalination performance over 100 cycles in a 500 mg L−1 NaCl solution. This innovative approach provides a noval perspective for developing heterojunction electrodes with high redox activity and efficient desalination performance.

In-situ doped and activated N, S co-doped porous carbon derived from organic salt for application in high-performance potassium-ion batteries

Owing to its abundance in nature and low cost, potassium has attracted considerable attention as a substitute for lithium in the manufacture of secondary-ion batteries. However, developing amorphous carbon materials that show fast K+ ion kinetics for application in high-performance potassium-ion battery (PIB) anodes remains challenging. In this study, we designed and synthesized a 3-D hierarchical nitrogen and sulfur co-doped porous carbon electrode via in-situ doping and activation using acesulfame potassium. Owing to its prominent structural advantages, the as-prepared N, S co-doped electrode showed a high reversible capacity (459.8 mAh g−1 at 0.05 A g−1) and long-term cycle stability (205 mAh g−1 after 1000 cycles at 0.5 A g−1). Further, the results of ex-situ Raman spectroscopy and X-ray photoelectron spectroscopy verified the advantages of N and S co-doping with respect to K+ ion intercalation and adsorption/desorption properties within the carbon matrix. Therefore, our findings enhance understanding regarding the advantages of the dual-doped system with respect to K+ ion storage and highlight an efficient strategy for developing high-performance and durable carbon anode materials for PIBs.

Cu/F Dual-Doping on the Ni–Mn Based Layered Oxide As Cathode Material for Sodium-Ion Batteries

As demands for energy storage are ever-increasing, sodium ion batteries (SIB) have been widely conducted for superior electrochemical performance and reduction in cost compared to lithium ion batteries (LIBs), one of the most commonly used energy storage devices nowadays. Among all the parts in batteries, cathode materials play a crucial role with regard to performance. Here, layered transition metal oxides (LTMOs) (NaxTMO2, TM = Cu, Mn, Fe, Ti, Co, Cr, Ni, etc.) have kept catching researchers’ eyes due to their mature developments in commercial LIBs over decades.P2-type Ni/Mn-based LTMOs (such as Na0.67Ni0.33Mn0.67O2, NNMO) exhibit high theoretical specific capacity (~173 mAh g− 1) with environmentally friendly and cheap elements. However, they show limited stability upon charging over 4.2 V, directly restricting their energy density and lowering operating voltage. Besides, disadvantages such as poor rate performance and air/moisture sensitivity are remaining improvements for commercialization. Hence, our study mainly focuses on improvements for shortages of NNMO by applying a facile cation-and-anion co-doping strategy. Via transition metal Cu ion doping, the cycling stability of NNMO can be improved without sacrificing too much capacity, and the air stability can also be improved. In addition, F doping to replace oxygen can further enhance the structural stability and increase the rate performance by modifying interlayer spacing of the layered structure. A facile sol-gel method with heat treatment is used to synthesize cation-and-anion co-doped NNMO. The material characterization shows successful synthesis after cation and anion doping. In addition, the long cycle test shows that capacity retention increases from ~50% to ~90% over 100 cycles after Cu doping. The specific discharge capacity also increases from ~110 mAh/g to ~130 mAh/g at 0.1C with a slight increase in cycle retention from ~75% to ~77% after F doping. Also, the capacity at 20C could be maintained at ~50 mAh/g, around 45% of the initial capacity at 0.1C. The detailed charge storage mechanism will be studied by applying operando X-ray absorption spectroscopy and ex-situ X-ray photoelectron spectroscopy. As for the moisture sensitivity part, the XRD spectra indicate that no noticeable structural changes or impurity formation occurred after air exposure for one month, showing good air stability. Furthermore, operando XRD is conducted to confirm structural reversibility during charging and discharging.In summary, by applying a simple Cu/F co-doping strategy, Na0.67Ni0.13Cu0.20Mn0.67O2-xFx exhibits sufficient cycle stability for over 100 cycles as well as excellent rate capability even at a high current density of 20C, which proves itself a promising candidate as high-performance cathode material in SIBs. In addition, the cheap and environmentally friendly elemental usage (Ni, Mn and Cu) and air-stability enhancement also increase possibility of this material for large-scale energy storage application in industry.

(Invited) A Study of the SEI Layer Cross-Talk in Si/C Composite Li-Ion Anodes

Composite electrodes, especially silicon/carbon (Si/C) anodes, present significant opportunities for advancing the energy density of lithium-ion batteries (LIBs). However, challenges emerge, particularly in performance metrics when a high weight percentage of Si beyond 8-10 wt.% is employed 1. A nuanced understanding of the solid electrolyte interphase (SEI) in Si/C composites is imperative to overcome these limitations and enhance energy density. Conventional techniques such as ex-situ X-ray photoelectron spectroscopy and cryogenic electron microscopy face inherent drawbacks, including exposure to ultrahigh vacuum and the need for solvent washing, potentially altering the SEI layer 2. In contrast, nano-FTIR, utilizing Fourier transform infrared near-field spectroscopy, overcomes these challenges, enabling non-destructive probing of the SEI layer's chemistry and structure at room temperature within an inert atmosphere 3–5.In this study, we engineer custom-patterned electrodes featuring amorphous Si on atomically flat highly ordered pyrolytic graphite (HOPG) to emulate model composite electrodes. Leveraging nano-FTIR spectroscopy, near-field nanoscale white-light imaging, and atomic force microscopy measurements, our investigation reveals that the SEI on HOPG is enriched in organic lithium ethylene decarbonate (LiEDC), while the SEI on lithiated silicon unveils the presence of inorganic Li2CO3. Notably, we unveil a unique "mixed" SEI layer zone at the Si/HOPG interface, comprising a mixture of dominant SEI species from the surfaces of both the lithiated Si and the HOPG. The coexistence of these species suggests the formation of an SEI layer with presumably unique physicochemical properties, forming along Si-C interfaces in Si/C composite electrodes. These findings provide a comprehensive approach to studying model composite electrodes and offer valuable insights into optimizing the surface passivation of Si/C composite electrodes for high-performance LIBs. Acknowledgments This research was supported by the US Department of Energy (DOE)’s Vehicle Technologies Office under the Silicon Consortium Project directed by Brian Cunningham and managed by Anthony Burrell. References V. G. Khomenko and V. Z. Barsukov, Electrochim Acta, 52, 2829–2840 (2007).J. Wu, M. Ihsan-Ul-Haq, Y. Chen, and J. K. Kim, Nano Energy, 89, 106489 (2021).X. He, J. M. Larson, H. A. Bechtel, and R. Kostecki, Nat Commun, 13, 1398 (2022).I. Yoon, J. M. Larson, and R. Kostecki, ACS Nano, 17, 6943–6954 (2023).A. Dopilka, Y. Gu, J. M. Larson, V. Zorba, and R. Kostecki, ACS Appl Mater Interfaces, 15, 6755–6767 (2023).

Extended Cycle Life Pb-Ion Batteries with High Coulombic Efficiency Exceeding 99.96% from Al/Pb Bimetallic Eutectic Electrolyte

Following renewable energy development, batteries are the most crucial way to establish an energy storage system. In the past hundred years, lead-acid batteries have been widely applied in industrial and vehicle applications. Their low cost, simple manufacturing, and good safety can compete with lithium-ion batteries. However, some challenges still exist, e.g., poor low-temperature performance and short cycle life; aqueous solution is the reason that oxygen evolves from positive electrodes, resulting in positive active material detached from the electrode. Thus, developing novel lead-ion batteries to replace lead-acid batteries is a significant issue. In metal-ion batteries research, deep eutectic solvent (DES) has been well developed in recent years due to its high thermal stability and wide electrochemical window. Herein, a new Al/Pb bimetallic eutectic electrolyte (BEE) composed of aluminium perchlorate (Al(ClO4)3·9H2O), lead perchlorate (Pb(ClO4)2·3H2O), and succinonitrile (SN) with acetonitrile (ACN) as an additive, mixing in molar ratio. To realize the medium effect in this electrolyte, the BEE is compared with concentrated Pb(ClO4)2 aqueous solution. The ion conductivity, viscosity, and thermal stability depend on the metallic salt/SN ratio, and we proposed that the optimized molar ratio is 1:1:12:5. It exhibits outstanding thermal stability within − 50 to 50 °C. From Fourier-transform infrared spectroscopy (FTIR) spectrum analysis in BEE, the O-H stretching decreased, and the ClO4 - stretching band increased, compared to the concentrated Pb(ClO4)2 aqueous solution; it can be understood that O-H interaction between Pb2+ and ClO4 - is weakened; meanwhile, ClO4 - ions participated in first solvation shell. This variation reduces the desolvation energy of Pb2+ to facilitate smoother lead plating/stripping and enables better electrochemical performance. To validate the effect of the solvation structure variation, assembling the Pb/Pb symmetric cell and Pb/Platinum (Pt) asymmetric cell are essential methods. Pb/Pb cell maintains a stable voltage hysteresis of about 20 mV even cycling 2500 h at the current density of 0.5 mA cm-2, Pb/Pt cell under galvanostatic conditions successfully performs highly reversible Pb plating/stripping, achieved average coulombic efficiency (ACE) >99.96% in BEE for more than 1000 h at current density 0.5 mA cm-2. Furthermore, we utilize BEE in Na3V2(PO4)3(NVP) and natural graphite (NG) as cathode material; the reversible Pb2+ and ClO4 - (de-)intercalation are respectively observed in Pb/NVP and Pb/NG full cell, Pb/NVP cell exhibited long-term cycling stability with 80.95% capacity retention and 98.21% ACE after 600 cycles at a current density of 100 mA g-1, then Pb/NG cell remains high discharge voltage plateau (≈1.7V) with 72% capacity retention after 200 cycles at a current density of 100 mA g-1. Electrochemical impedance spectroscopy (EIS) of Pb/NVP in BEE-1:1:12:0 and 1:1:12:5 shows that adding the ACN additive can decrease the solution resistance (Rs) and charge transfer resistance (Rct) of the cell. Ex-situ X-ray photoelectron spectroscopy (XPS) was performed on the Pb surface at the charging state, observing that Al species are co-deposited, revealing the synergistic effect between Aluminium perchlorate and Lead perchlorate. From the ex-situ X-ray diffraction (XRD) patterns of cycled NVP and NG cathode at charge/discharge states, some irreversible variation of peak position occurred, indicating that ion (de-)intercalation after operation; these results demonstrate BEE performed bi-functional ion (Pb2+ and ClO4 -) intercalation phenomenon. To further confirm the Pb2+ dynamic in the NVP cathode at charge/discharge progress, the X-ray absorption spectroscopy (XAS) characterization was applied. The comparison of XANES spectra collected at the V K-edge, the XANES shift to lower energy during discharging, this exhibition is consistent with reduction reaction of V4+ to V3+, the EXAFS spectra show the local structure change of V-P/Na/Pb bonds. The EXAFS spectra at the Pb LIII-edge indicated that the Pb-O distance is shortened during discharging; the abovementioned results demonstrate the Pb2+ (de-)intercalation process in the NVP structure.In conclusion, this work proposed a novel bimetallic eutectic electrolyte for potential lead-ion batteries that enables stable Pb plating/stripping. The cycle-life and capacity retention of Pb/NVP and Pb/NG full-cell with BEE is significantly improved by adding acetonitrile (ACN) additive. The XAS characterization further confirmed the (de-)intercalation of Pb2+ in the NVP cathode. A stable, high-voltage, and high-capacity positive electrode is needed, allowing the reuse of secondary lead metal to be applied to next-generation energy storage. Figure 1

Systematic Investigations of Surface Oxygen Functional Groups on Spherical Hard Carbon for Sodium-Ion Batteries

The surface activity of hard carbons and its effect on the formation of a stable solid electrolyte interface (SEI) in sodium ion batteries has gained significant interest in the scientific community over the last years. The surface of hard carbons thus plays a pivotal role within the cell, as it constitutes the interface between the bulk material and the electrolyte. Following pyrolysis of the carbon-rich precursor at high temperatures, various oxygen functional groups (OFGs) and defects, such as five- or seven-membered rings, are present on the surface of the resulting hard carbons. The influence of OFGs on the surface is however controversially discussed. On the one hand, irreversible reactions of sodium ions with OFGs lower the initial coulombic efficiency (ICE), which leads to a decreased energy density. On the other hand, OFGs may also serve as nucleation sites for the SEI leading to a more conductive interfacial phase for sodium ions. Although many approaches of additional oxygen functionalization on the surface of hard carbons have already been reported, they mostly employ harsh reaction conditions disregarding the morphological impact on the carbon surface.In our studies, oxo-functionalized polycyclic aromatic hydrocarbons (PAHs) are adsorbed on the surface to serve as model OFGs on surface oxygen deficient hard carbons. The versatility of functionalized pyrenes in combination with nondestructive adsorption enables independent investigations on the oxygen functionalization of the hard carbon surface. In the first step, native surface oxygen groups are cleaved from the pristine hard carbon through a high-temperature post-treatment in hydrogen atmosphere. Afterwards, selective re-introduction of surface OFGs is achieved through adsorption of oxo-functionalized pyrene derivatives such as 1-hydroxypyrene or 1-pyrenecarboxylic acid to simulate hydroxy or carboxylic surface functionalities. Additionally, various spatially configurations of surface OFGs can be mimicked by elongating the distance between the oxygen functionality and the pyrene backbone through a short alkyl chain (e.g. 1-pyrenebutyric acid).Our systematic approach of selectively re-introducing surface OFGs allows the discrimination between different surface OFGs and their influence on the SEI. The surface of our modified hard carbons is characterized by X-Ray photoelectron spectroscopy (XPS) and Raman spectroscopy to evaluate the oxygen content and determine the defect concentration. The electrochemical performance is assessed by rate performance tests and cyclic voltammetry in three-electrode half-cells with sodium metal as counter and reference electrode. Initial findings validate the correlation between surface oxygen functionalization determined by XPS and the electrochemical formation potential of the SEI during the first cycle. After high-temperature treatment in a hydrogen atmosphere, the surface oxygen content decreases from ~5% to 2%, leading to a significant lowering of the plateau capacity. Simultaneously, the ICE decreases from 79% to 55%. Cyclic voltammetry of deoxygenated hard carbon reveals that the SEI formation potential is shifted from ~1.0 V vs. Na towards lower potentials of ~0.3 V vs. Na indicating that different decomposition products are formed. Furthermore, rate performance is substantially deteriorated by the development of a modified SEI. Ex-situ XPS of cycled electrodes and electrochemical impedance spectroscopy are used to identify differences in the SEI composition and link them to the electrochemical performance of our spherical hard carbons.Figure: 1-Pyrenebutyric acid adsorbed on the surface of hard carbon highlighting the different possible spatially orientations of the oxygen functional group. Figure 1

V2O3/VO2@S/N-C nanofibers with excellent cycling stability and superior rate capability in aqueous zinc ion batteries

The development of aqueous zinc-ion batteries (AZIBs) marks a significant advancement in the field of sustainable and environmentally friendly energy storage. To address the challenges faced by single-phase vanadium-based oxides, such as poor conductivity and dissolution in electrolytes, this study introduces vacuum S/N doping to fabricate V2O3/VO2@S/N-C nanofibers, improving the cycling stability and enhancing the capacity. The V2O3/VO2@S/N-C electrode exhibits exceptional cyclic stability, retaining a capacity of 133.3 mA h g−1 after 30,000 cycles at a high current density of 100 A g−1 and a capacity retention of 81.8% after 150,000 cycles at 200 A g−1. Characterizations using ex-situ X-ray diffraction and ex-situ X-ray photoelectron spectroscopy reveal co-intercalation of H+ and Zn2+ in the V2O3/VO2@S/N-C electrode. Due to the presence of S22-, more phases changed to V10O24·12H2O, making the V2O3/VO2@S/N-C electrode better reversible. By elucidating the zinc storage mechanism and demonstrating the stable performance of the doped electrode, this work contributes valuable insights into the optimization of the electrode materials for future energy storage solutions.

Structural Regulation of NiFe LDH under Spontaneous Corrosion to Enhance the Oxygen Evolution Properties.

Electrochemical water splitting holds promise for sustainable hydrogen production but restricted by the sluggish reaction kinetics at the anodic oxygen evolution. Herein, we present a room-temperature spontaneous corrosion strategy to convert inexpensive iron (Fe) on iron foam substrates into highly active and stable self-supporting nickel iron layered hydroxide (NiFe LDH) catalysts. The corrosion evolution mechanisms are elucidated combining ex-situ scanning electron microscopy (SEM) and X-ray photo electron spectroscopy (XPS) techniques, demonstrating precise control over the concentration of Ni2+ and reaction time to achieve controllable micro-structures of NiFe LDH. Taking advantage of the self-supporting morphology and hierarchical micro-/nano- structure, the NiFe LDH with optimized Ni2+ concentration and reaction time exhibits significant small overpotentials of 160 mV and 200 mV for the OER at current densities of 10 mA cm-2 and 100 mA cm-2 respectively, showcasing excellent OER activities. Furthermore, this catalyst demonstrates superior reaction kinetics, high electrochemical stability, and excellent integral water splitting performance when coupled with a commercial Pt/C cathode. The energy-efficient, cost-effective, and scalable spontaneous corrosion strategy opens new avenues for the development of high-electrochemical-interface catalysts.

Construction of High-Performance Anode of Potassium-Ion Batteries by Stripping Covalent Triazine Frameworks with Molten Salt.

Covalent triazine frameworks (CTFs) are promising battery electrodes owing to their designable functional groups, tunable pore sizes, and exceptional stability. However, their practical use is limited because of the difficulty in establishing stable ion adsorption/desorption sites. In this study, a melt-salt-stripping process utilizing molten trichloro iron (FeCl3) is used to delaminate the layer-stacked structure of fluorinated covalent triazine framework (FCTF) and generate iron-based ion storage active sites. This process increases the interlayer spacing and uniformly deposits iron-containing materials, enhancing electron and ion transport. The resultant melt-FeCl3-stripped FCTF (Fe@FCTF) shows excellent performance as a potassium ion battery with a high capacity of 447 mAh g-1 at 0.1 A g-1 and 257 mAh g-1 at 1.6 A g-1 and good cycling stability. Notably, molten-salt stripping is also effective in improving the CTF's Na+ and Li+ storage properties. A stepwise reaction mechanism of K/Na/Li chelation with C═N functional groups is proposed and verified by in situ X-ray diffraction testing (XRD), ex-situ X-ray photoelectron spectroscopy (XPS), and theoretical calculations, illustrating that pyrazines and iron coordination groups play the main roles in reacting with K+/Na+/Li+ cations. These results conclude that the Fe@FCTF is a suitable anode material for potassium-ion batteries (PIBs), sodium-ion batteries (SIBs), and lithium-ion batteries (LIBs).

Rubik’s cube PBA frameworks for optimizing the electrochemical performance in alkali metal-ion batteries

PBA frameworks have stood out among metal–organic frameworks because of their easy preparation, excellent stability, porous structures, and rich redox properties. Unfortunately, their non-ideal conductivity and significant volume expansion during cycling prevent more widespread application in alkali-metal-ion (Li+, Na+, and K+) batteries. By changing the type and molar ratio of metal ions, Rubik’s PBA frameworks with infinite structural variations were obtained in this study, just like the Rubik’s cube undergoes infinite changes during the rotation. X-ray adsorption fine structure measurements have documented the existence and determined the coordination environment of the metal ions in the Rubik’s PBA framework. Benefiting from the more stable Rubik’s cube structures with diverse composition, enhanced conductivity, and greater adsorption capacity, the obtained Rubik’s cubes CoM-PBA anodes, especially CoZn-PBA deliver the enhanced cycling and rate performance in all the alkali-metal-ion batteries. The findings are supported by density functional theory calculations. Ex-situ X-ray photoelectron spectroscopy, and in-situ X-ray diffraction measurements were undertaken to explore the storage mechanism of CoZn-PBA anodes. Our results further demonstrate that the Rubik’s cube PBA framework-based materials could be widely applied in the field of alkali-metal-ion batteries.

Unlocking the potential of spinel MnV2O4 for highly durable aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have received comprehensive attention as promising candidates for large-scale energy storage owing to high security, low cost, and environmental friendliness. Developing appropriate cathode materials is of great significance for high-efficiency Zn2+ storage. Herein, we proposed an efficient in-situ electrochemical pretreatment strategy to unlock the potential of non-electrochemically active spinel MnV2O4via an irreversible phase reconstruction from crystalline structure to short-range ordered amorphous state. Specifically, the reconstructed electrodes not only deliver abundant active sites for Zn2+ ions accommodation, but also shorten diffusion paths for rapid reaction kinetics, thus achieving superior electrochemical properties. As revealed, the optimized electrodes present a prominent specific capacity of 445 mA h g−1 at 0.1 A g−1, a high capacity retention of 73.1 % over 2000 cycles at 5 A g−1, as well as exceptional energy density of 335 W h kg−1 and power density of 176 W kg−1 based on the mass of cathode. In addition, the reaction mechanism during Zn2+ ions storage process is systematically investigated by ex-situ X-ray diffraction and X-ray photoelectron spectroscopy. This in-situ electrochemical conversion mechanism sheds light on a new methodology of designing desirable cathode materials for aqueous ion batteries.

Electrochemical insertion of Ni2+ to synthesize Ca-doped β-NiV3O8 films as electrodes for sodium-ion batteries

Sodium-ion batteries (SIBs) need to address inherent limitations such as low energy densities and poor cycle stability. In the paper, a novel yet safe electrochemical method has been employed to insert Ni2+ in pre-prepared films, culminating in the synthesis of Ca-doped β-NiV3O8. The high covalency of the Ni–O bond was expected to enhance the migration rate of Na+, and in turn exhibit a higher ionic conductivity. Various doping amounts of Ca2+ were applied to investigate the differences in the kinetic behavior of β-NiV3O8 film electrodes. Throughout the discharge process, the average DNa+ of Ca-doped β-NiV3O8 was calculated to be 10−13～10−12 cm2 s−1. In addition, high-resolution transmission electron microscopy (HRTEM) and ex-situ X-ray photoelectron spectroscopy (XPS) revealed the presence of oxygen defects, which assisted interfacial electron transfer. Ex-situ X-ray diffraction (XRD) revealed partial new phases (NaV3O8·xH2O and NaVO3·1.9H2O) generation alongside diverse mechanisms of sodium ion insertion/extraction. Under a lower current density with 1 M NaClO4/PC as the electrolyte, it exhibited an initial discharge capacity of 433.2 mA h m−2 at 167 mA m−2 and 96.3 % capacity retention after 100 cycles. This electrochemical method, applicable to treating film electrodes, provides a novel idea for the preparation of high-performance electrode materials for SIBs.

Constructing Cu9S5@CuSe heterostructures under microwave irradiation for rechargeable magnesium batteries

Copper chalcogenides are believed as the prospective cathode materials for rechargeable magnesium batteries. However, their practical application is seriously restricted by slow diffusion and reaction kinetics due to the large charge/radius ratio of divalent Mg2+ ions. Herein, a simple two-step microwave-assisted synthesis method is rationally developed to construct Cu9S5@CuSe heterostructures as the capable cathode materials for rechargeable magnesium batteries. Two-dimensional CuSe nanosheets are vertically grown on the surface of single-crystal Cu9S5 substrate through selenation reaction under microwave irradiation to form the mixed-dimensional heterostructures. Electrochemical measurements reveal that the as-synthesized Cu9S5@CuSe heterostructures show high reversible capacity of 240 mAh g−1 and good long-term cyclic stability with approximate 0.013 % capacity decay per cycle at 500 mA g−1 within 1000 cycles. Furthermore, the obviously enhanced rate capability can be achieved in comparison with that of single-crystal Cu9S5 substrate and CuSe nanoparticles. Ex-situ X-ray photoelectron spectroscopy and X-ray diffraction characterizations reveal favourable electrochemical conversion reaction over the Cu9S5@CuSe heterostructure cathode. The superior electrochemical properties are attributed to the optimized diffusion kinetics within the unique heterostructure. This research offers a valuable strategy to develop high-performance cathode materials with favourable kinetics for magnesium batteries.

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.