Alkali Metal Deposition Research Articles

Incoherence-to-coherence crossover observed in charge-density-wave material 1T-TiSe2

Analogous to the condensation of Cooper pairs in superconductors, the Bose–Einstein condensation (BEC) of electron–hole pairs in semiconductors and semimetals leads to an emergence of an exotic ground state — the excitonic insulator state. In this paper, we study the electronic structure of 1T-TiSe2 utilizing angle-resolved photoemission spectroscopy and alkali-metal deposition. Alkali-metal adatoms are deposited in-situ on the sample surface, doping the system with electrons. The conduction bands of 1T-TiSe2 are thereby pushed down below the Fermi energy, which enables us to characterize its temperature dependence with precision. We found that the formation of the charge density wave (CDW) in 1T-TiSe2 at ~ 205 K is accompanied by a significant increase of the band gap, supporting the existence of excitonic pairing in the CDW state of 1T-TiSe2. More importantly, by analyzing the linewidth of the single-particle excitation spectrum, we unveiled an incoherence-to-coherence crossover at 165 K, which could be attributed to a possible exciton condensation that occurs beneath the CDW transition in 1T-TiSe2. Our results not only explain the exotic transport properties of 1T-TiSe2, but also highlight the possible existence of an excitonic condensate in this semiconducting material.

Progressive Control of Rashba State on Topological Dirac Semimetal KZnBi.

Rashba states have been actively revisited as a platform for advanced applications such as spintronics and topological quantum computation. Yet, access to the Rashba state is restricted to the specific material sets, and the methodology to control the Rashba state is not established. Here, we report the Rashba states on the (001) surface of KZnBi, a 3D Dirac semimetal. Using angle-resolved photoemission spectroscopy and first-principles calculations, we investigated the evolution of Rashba states under different surface conditions controlled by alkali metal deposition. We observed that restoring surface ordering enables a Rashba state, which is absent in freshly cleaved surfaces. Interestingly, we were able to modify the dispersion of the Rashba state from an ordinary parabolic dispersion to a linearly dispersing Dirac-like state by additional alkali-metal deposition. Our findings provide a methodology for engineering the properties of Rashba states for advanced applications and redefine topological systems as generic hosts of Rashba states.

Constructing Three-Dimensional Architectures to Design Advanced Copper-Based Current Collector Materials for Alkali Metal Batteries: From Nanoscale to Microscale.

Alkali metals (Li, Na, and K) are deemed as the ideal anode materials for next-generation high-energy-density batteries because of their high theoretical specific capacity and low redox potentials. However, alkali metal anodes (AMAs) still face some challenges hindering their further applications, including uncontrollable dendrite growth and unstable solid electrolyte interphase during cycling, resulting in low Coulombic efficiency and inferior cycling performance. In this regard, designing 3D current collectors as hosts for AMAs is one of the most effective ways to address the above-mentioned problems, because their sufficient space could accommodate AMAs' volume expansion, and their high specific surface area could lower the local current density, leading to the uniform deposition of alkali metals. Herein, we review recent progress on the application of 3D Cu-based current collectors in stable and dendrite-free AMAs. The most widely used modification methods of 3D Cu-based current collectors are summarized. Furthermore, the relationships among methods of modification, structure and composition, and the electrochemical properties of AMAs using Cu-based current collectors, are systematically discussed. Finally, the challenges and prospects for future study and applications of Cu-based current collectors in high-performance alkali metal batteries are proposed.

Rational Design of Janus Metal Atomic‐Site Catalysts for Efficient Polysulfide Conversion and Alkali Metal Deposition: Advances and Prospects

AbstractAlthough metal–sulfur batteries (M–S batteries, M = Li, Na, K) are promising next‐generation energy‐storage devices because of ultrahigh theoretical energy density, low cost, and environmentally friendliness, their practical applications are significantly hindered by the shuttle effect of polysulfides and growth of alkali metal dendrites. These issues can be mitigated by using Janus metal atomic‐site catalysts, which possess the maximum atom utilization efficiency (≈100%), adjustable electronic structures, and tailorable catalytic sites, thereby effectively improving the electrochemical performance of M–S batteries. In this review, the recent progress and development of Janus metal atomic‐sites on the properties, synthesis, and characterizations are reviewed. Then, the recent advances in Janus metal atomic‐site catalysts intended for accelerating polysulfide conversion and regulating alkali metal deposition, briefly introducing the working principles of the Janus metal atomic‐site catalysts in M–S batteries, are systematically summarized. Furthermore, a high emphasis is placed on effective regulation strategies for the rational design of Janus metal atomic‐site catalysts in M–S batteries. Finally, the current challenges and future research directions are also presented to develop high‐efficiency Janus metal atomic‐site catalysts for high‐energy M–S batteries.

Electrochemical Signatures of Potassium Plating and Stripping

Alkali metal anodes can enable unmatched energy densities in next generation batteries but suffer from insufficient coulombic efficiencies. To deduce details about processes taking place during galvanostatic cycling, voltage profiles are commonly analyzed, however the interpretation is not straightforward as multiple processes can occur simultaneously. Here we provide a route to disentangle and interpret features of the voltage profile in order to build a mechanistic understanding on alkali metal stripping and deposition, by investigating potassium metal deposition as a model case where processes and reactions are exaggerated due to the high reactivity of potassium. In particular, the importance of separating SEI formation and nucleation to correctly estimate the energy barrier for nucleation is demonstrated. Further, we show how the native layer formed on alkali metal foils gives rise to strong features in the voltage profile and propose forming alkali metal electrode through electrodeposition to mitigate these effects.

Comparison of electrochemical lithium and sodium metal deposition: A surface plasmon resonance spectroscopy investigation

Electrochemical deposition of alkali metals on the electrode surface is important for the development of metal-based batteries with high-energy density. Here, we investigate using electrochemical surface plasmon resonance spectroscopy (EC-SPR) to compare the deposition mechanisms of lithium and sodium metal. The SPR spectrum of the Cu film electrode was clearly observed for both LiPF6 and NaPF6 based organic electrolytes. The corresponding SPR spectra for both Li and Na system were dramatically red-shifted at 1st metal deposition process, indicated direct metal deposition on Cu surface. The Li system repeatedly showed similar red shift until at least the 2nd cycle, while similar red shift was not observed at all in the Na system. This indicated that direct Na-metal deposition on the Cu electrode surface was prevented by some passivation film, formed at 1st deposition process. The complex nature of Na-metal deposition, including the surface film phenomena, is responsible for the instability at the interface between the negative electrode and electrolyte in a Na-based battery system. This suggests that Na-based systems need to be more carefully designed and managed than Li-based systems.

Deposition of Sodium Metal at the Copper‐NaSICON Interface for Reservoir‐Free Solid‐State Sodium Batteries

Abstract“Anode‐free” solid‐state battery concepts are explored extensively as they promise a higher energy density with less material consumption and simple anode processing. Here, the homogeneous and uniform electrochemical deposition of alkali metal at the interface between current collector and solid electrolyte plays the central role to form a metal anode within the first cycle. While the cathodic deposition of lithium has been studied intensively, knowledge on sodium deposition is scarce. In this work, dense and uniform sodium layers of several microns thickness are deposited at the Cu|Na3.4Zr2Si2.4P0.6O12 interface with high reproducibility. At current densities of ≈1 mA∙cm−2, relatively uniform coverage is achieved underneath the current collector, as shown by electrochemical impedance spectroscopy and 3D confocal microscopy. In contrast, only slight variations of the coverage are observed at different stack pressures. Early stages of the sodium metal growth are analyzed by in situ transmission electron microscopy revealing oriented growth of sodium. The results demonstrate that reservoir‐free (“anode‐free”) sodium‐based batteries are feasible and may stimulate further research efforts in sodium‐based solid‐state batteries.

Study on a new reed-coal coupled power generation system in Wuliangsuhai Lake wetland —Life cycle assessment and economic and technical analysis

As a major hydrophyte in wetlands, reeds purify water by reducing water eutrophication and have high value-added potential as biomass fuel for power generation. Based on pyrolysis experiments, reed has the maximum bio-oil yield of 57.11% at 550 °C. In this study, the optimal temperature conditions were used for the pyrolysis of reeds coupled with thermal power generation (BP-TPG). The BP-TPG process is relatively independent and avoids the deposition of alkali metals from biomass on the surface of the steam generator directly. The BP-TPG and biomass gasification coupled thermal power Generation (BG-TPG) were further investigated by process simulation and life cycle assessment. The GWP values of BP-TPG systems could be reduced by at least 4.8% than that of TPG. As the growth of reeds absorbed total nitrogen (TN) and total phosphorus (TP) from the wetland water, the eutrophication potential was reduced by 0.333 kg PO4/MWh less than that of the use of corn straw feedstocks. Economic and technical analysis showed that the BP-TPG-G system had the lowest cost of electricity generation at 386 ¥/MWh. Sensitivity analysis showed that the impact of coal prices on power generation costs cannot be ignored.

Cathode reaction models for Braga-Goodenough Na-ferrocene and Li-MnO2 rechargeable batteries

Braga-Goodenough all-solid-state Na-Fc and Li-MnO2 batteries demonstrate deposition of Na and Li on the cathode during discharge. These reaction mechanisms were investigated in light of the generalized charge neutrality level and the experimental results of Braga et al., and two new types of mechanisms were proposed. The Na-Fc mechanism is represented by a multi-step C[(CE)cC]n mechanism where C is the chemical step, E is the electrochemical step, c is the catalytic (CE) step, and n denotes the number of [(CE)cC] part cycles. The nth cycle corresponds to n moles of Na and Li deposition. For Li-MnO2, two mechanisms were considered. One is the C[(CE)cC]n mechanism which is the same as Na-Fc, and the other is the C[2(CE)cC]n mechanism, which involves two consecutive (CE)c steps. In the C step of (CE)c of both mechanisms, Fc and MnO2 reduce Na+(sf) and Li+(sf) (sf - surface states) to deposit Na and Li, respectively, which are intramolecular charge transfer reactions within the adsorbed molecules. Fc and MnO2 are oxidized to inter­mediates immediately reduced to Fc and MnO2 by their anodes in the subsequent E step. Based on these mechanisms, these batteries' discharge capacity and cathode alkali metal deposition were examined in detail.

Electric Control of 2D Van Hove Singularity in Oxide Ultra-Thin Films.

Divergent density of states (DOS) can induce extraordinary phenomena such as significant enhancement of superconductivity and unexpected phase transitions. Moreover, van Hove singularities (VHSs) lead to divergent DOS in 2D systems. Despite recent interest in VHSs, only a few controllable cases have been reported to date. In this work, by utilizing an atomically ultra-thin SrRuO3 film, the electronic structure of a 2D VHS is investigated with angle-resolved photoemission spectroscopy and transport properties are controlled. By applying electric fields with alkali metal deposition and ionic-liquid gating methods, the 2D VHS and the sign of the charge carrier are precisely controlled. Use of a tunable 2D VHS in an atomically flat oxide film could serve as a new strategy to realize infinite DOS near the Fermi level, thereby allowing efficient tuning of electric properties.

Unravelling the Effect of Alkali Metal Deposition on Co3O4 for Catalytic Decomposition of N2O

AbstractIn this paper, the effect of alkali metal deposition on the activity of x‐Co3O4 (x=Na, K, Rb, Cs) catalysts for the N2O catalytic decomposition was systematically explored by DFT calculation and various experimental characterization methods. The results demonstrated that the deposition of alkali metal Na improved the activity of the Na‐Co3O4 catalyst for N2O catalytic decomposition at low temperatures. By contrast, the deposition of other alkali metals (K, Rb and Cs) suppressed the catalytic decomposition of N2O perceptibly. Analysis of the results of XRD, FT‐IR, SEM, TEM, XPS, O2‐TPD and H2‐TPR characterization of x‐Co3O4 catalysts showed that the deposition of alkali metals did not affect the morphology and structure of the catalysts. However, it affected the chemical environment around the Co ion in the x‐Co3O4 catalyst, where the deposition of alkali metal Na not only facilitated the reduction of Co3+ to Co2+, but also promoted the surface decomposition step of N2O (i. e., the oxidation of Co2+ to Co3+ by giving electrons) at low temperatures, indicating that alkali metal Na improved the electron donating capability of the catalyst active center and enhanced the performance of the Na‐Co3O4 catalyst for the DCD of N2O at low temperatures. The deposition of other alkali metals did not show the same results as that of alkali metal Na, indicating that the promotion of different alkali metals was different and would directly affect the catalytic effect. At low temperatures, the catalytic activity of catalysts deposited with the alkali metal Na was greater than that of catalysts deposited with other alkali metals.

Engineering current collectors for advanced alkali metal anodes: A review and perspective

AbstractAlkali metal batteries (AMBs) are promising next‐generation high‐density electrochemical energy storage systems. In addition, current collectors play important roles in enhancing their electrochemical performances. Thus, it is essential to have a critical review of the most recent advances in engineering the current collectors for high‐performance AMBs. In this review paper, the fundamentals of alkali metal deposition on current collectors will be introduced first. Then recent advances in the development of advanced metal and carbon‐based current collectors are examined for boosting the stability and cycle life of lithium metal batteries (LMBs) in terms of various strategies including 3D architectural design and functional modifications. Thereafter, the research progress in design of advanced current collectors will be analyzed for sodium/potassium metal batteries, especially the counterparts that do not follow the paradigms established in LMBs. Finally, the major challenges and key perspectives will be discussed for the future development of current collectors in AMBs.image

Ubiquitous stripe phase and enhanced electron pairing in the interfacial high- Tc superconductor FeSe/BaTiO3

Monolayer FeSe grown on SrTiO$_3$ provides a new playground for high-Tc superconductivity. A recent study shows the importance of stripy instability for superconductivity enhancement in FeSe/SrTiO3. However, it is still under debate whether such a stripe phase is ubiquitously bound to the interfacial superconductivity. Here, we report on molecular beam epitaxy growth and low-temperature scanning tunneling microscopy study of FeSe films on BaTiO$_3$(001). We find that the stripe phase is more prominent in FeSe/BaTiO$_3$. Long-range stripes exist in bilayer and triple-layer FeSe films at 4 K and even persist up to 77 K in the case of bilayer FeSe, with enlarged superconducting gaps upon alkali-metal deposition. The results point out an intimate correlation between the interfacial superconductivity and the stripe phase.

Unravelling the Effect of Alkali Metal Deposition on Co3o4 for Catalytic Decomposition of N2o

Unravelling the Effect of Alkali Metal Deposition on Co3o4 for Catalytic Decomposition of N2o

Atomic and Molecular Layer Deposition of Alkali Metal Based Thin Films.

Atomic layer deposition (ALD) is the fastest growing thin-film technology in microelectronics, but it is also recognized as a promising fabrication strategy for various alkali-metal-based thin films in emerging energy technologies, the spearhead application being the Li-ion battery. Since the pioneering work in 2009 for Li-containing thin films, the field has been rapidly growing and also widened from lithium to other alkali metals. Moreover, alkali-metal-based metal–organic thin films have been successfully grown by combining molecular layer deposition (MLD) cycles of the organic molecules with the ALD cycles of the alkali metal precursor. The current literature describes already around 100 ALD and ALD/MLD processes for alkali-metal-bearing materials. Interestingly, some of these materials cannot even be made by any other synthesis route. In this review, our intention is to present the current state of research in the field by (i) summarizing the ALD and ALD/MLD processes so far developed for the different alkali metals, (ii) highlighting the most intriguing thin-film materials obtained thereof, and (iii) addressing both the advantages and limitations of ALD and MLD in the application space of these materials. Finally, (iv) a brief outlook for the future perspectives and challenges of the field is given.

Origin of large magnetoresistance in the topological nonsymmorphic semimetal TaSe3

$\mathrm{Ta}{\mathrm{Se}}_{3}$ is a layered van der Waals semimetal with several inverted band gaps throughout the entire Brillouin zone and nontrivial ${Z}_{2}$ topological indices, which place it at the boundary between a strong and a weak topological phase. Our transport experiments reveal a quadratic nonsaturating magnetoresistance (MR) with values reaching ${10}^{4}$% at 1.8 K and 14 T, whose origins have to be searched in the material's band structure. Here we combine angle-resolved photoelectron spectroscopy experiments, also with spin resolution, with ab initio calculations based on density functional theory in order to draw a connection between the Fermi surface topology and the measured transport properties. Simulations based on the calculated Fermi surface clarify that electron-hole compensation plays an important role for the observed MR in the bulk material. At the surface, the position of Fermi level differs, and it can be controlled by alkali metal deposition which accounts not only for the energy shift of the bands but it slightly modifies the dispersion of the valence and conduction bands. We propose that the observed band-gap renormalization might offer a route for engineering the topological phase in $\mathrm{Ta}{\mathrm{Se}}_{3}$, alternative to strain.

Effect of ash on the performance of iron-based oxygen carrier in the chemical looping gasification of municipal sludge

As sludge ash is rich in alkali metals, the oxygen carrier (OC) performance in the multi-cycle chemical looping gasification (CLG) of dried sludge is affected by simultaneously cycling and accompanying ash. Fe-based OC was used in a lab-scale fluidized-bed reactor to investigate the multi-cycle CLG of dried sludge and to study the effect of accompanied ash on OC particle. The synthesis gas, carbon conversion rate, and reaction rate were monitored over several cycles. Physicochemical characterization of the OC was accomplished to determine its effective components and the alkali metal deposition from ash. The results showed that as the number of cycles increased, the mole fractions of H2 and CO2 in synthesis gas decreased and increased, respectively, both eventually stabilizing. The carbon conversion rate reached its peak in fifth cycle. The gasification rate of sludge reached its maximum value in the 14th cycle, slowing down and then stabilizing thereafter. The OC was loaded with more alkali metal during the cycle, whose activity was enhanced at the beginning. However, once the cycle number became higher than 25, ash spheroidization and sintering occurred on its surface. Accordingly, the OCs particle size and mass became a little larger for the accumulation of unreacted lattice oxygen.

Metal-Insulator Transition and Emergent Gapped Phase in the Surface-Doped 2D Semiconductor 2H-MoTe_{2}.

Artificially created two-dimensional (2D) interfaces or structures are ideal for seeking exotic phase transitions due to their highly tunable carrier density and interfacially enhanced many-body interactions. Here, we report the discovery of a metal-insulator transition (MIT) and an emergent gapped phase in the metal-semiconductor interface that is created in 2H-MoTe_{2} via alkali-metal deposition. Using angle-resolved photoemission spectroscopy, we found that the electron-phonon coupling is strong at the interface as characterized by a clear observation of replica shake-off bands. Such strong electron-phonon coupling interplays with disorder scattering, leading to an Anderson localization of polarons which could explain the MIT. The domelike emergent gapped phase could then be attributed to a polaron extended state or phonon-mediated superconductivity. Our results demonstrate the capability of alkali-metal deposition as an effective method to enhance the many-body interactions in 2D semiconductors. The surface-doped 2H-MoTe_{2} is a promising candidate for realizing polaronic insulator and high-T_{c} superconductivity.

Regulating alkali metal deposition behavior via Li/Na-philic Ni nanoparticles modified 3D hierarchical carbon skeleton

Alkali metal anodes are promising anodes for constructing novel battery systems with high energy density. Nevertheless, limited nucleation sites and nonuniform local electric field caused dendrites growth and unlimited volume expansion hindered their practical implementation during electrochemical plating/stripping. Herein, a 3D N-doped carbon nanofiber skeleton wrapped with Ni nanoparticles encapsulated carbon nanotubes (CNTs-Ni@NCFs) is prepared by hydrothermal process and followed catalytic reaction under ethanol atmosphere to construct a superior Li/Na-philic host with stable chemical properties. The 3D NCF networks serve as a primary framework, providing sufficient voids for alkali metal deposition and rapid electron and ion transport. The Li/Na-philic Ni nanoparticles and catalyzed CNTs on CFs provide evenly distributed nucleation sites and uniform local electric field, leading to dendrite-free Li deposition, which is confirmed by theoretical calculations. Because of the guided deposition behavior and bare volume change, the CNTs-Ni@NCFs anode delivers an extremely low nucleation overpotential in the initial deposition and a superior plating/stripping voltage hysteresis under a high current density of 30 mA cm−2 for 300 cycles. The CNTs-Ni@NCFs-Li full cell with LiFePO4 cathodes demonstrates 94.2% capacity retention after 200 cycles under 2 C. When coupled with Na3V2(PO4)3 cathode, the CNTs-Ni@NCFs-Na cell shows a good suitability in full cell. This work shed new light on fabricating novel stable alkali metal anodes, which may also pave the way toward to other practical applications with high energy densities, such as in Li-air and Li-S batteries, etc.

A Rational Design of a Porous Copper Current Collector for Alkali Metal Anodes with a High Areal Capacity

Alkali metals are the ideal anode materials for improving the specific energy of secondary ion batteries because of the lowest redox potentials (3.04 and 2.71 VSHE for lithium and sodium, respectively) and the highest capacities (3860 and 1166 mAh g-1 for lithium and sodium, respectively). Nevertheless, using alkali metal anode is still challenging, because the dendritic growth and large volume changes of alkali metal anode cause many problems such as cell shorting, dead lithium, excessive SEI formation, and so on. Among the previously suggested solutions, the strategy to accommodate the Li or Na metal in the porous electrode has a great potential to address the aforementioned issues. [1] Particularly, the volume changes in the deposition and stripping processes of alkali metal can be minimized by adopting a porous electrode, and therefore increase the areal capacity of the anode. Furthermore, it is expected to increase the nucleation sites and impede the ununiform growth of specific position on the alkali metal by increasing the exposed surface area (that is, reducing the current density).In designing an alkali metal anode using a porous electrode, the required characteristics of the electrodes to improve the electrochemical performances such as coulombic efficiency and specific energy of full-cell are considered as follows. Firstly, the weight of the porous electrode should not be too heavy. In the case of porous Cu electrode, the porosity determines the specific capacity, as shown in Figure 1(a), thus the porous electrode having low porosity rather reduces a specific capacity. [2] Therefore, in the case of porous Cu electrode, the specific capacity of the electrode including the mass of current collector is improved when the porosity is more than 85%. Secondly, the conductivity of the thickened porous electrode should be high and uniform to achieve less voltage hysteresis, because the larger voltage hysteresis (high overpotential) of anode reduces the specific energy and energy efficiency of full-cell. [3]In this context, we focused on the control of structural characteristics of the porous Cu electrode including porosity, thickness, and surface area. As shown in Figure 1(b), the self-standing porous Cu sheet was fabricated by calendaring of the Cu/SiO2 mixture, and then followed by sintering of Cu and etching of SiO2.. Namely, the amount of SiO2 in the Cu/SiO2 mixture determines the porosity of the porous Cu electrode, leading to a facile control of the porosity of Cu.The fabricated porous Cu current collector with 15 mg cm-2 could deliver a high areal capacity of 40 mA h cm-2 at a current density of 10 mA cm-2 with high coulombic efficiency (99.98%) and low voltage hysteresis (~20 mV), as shown in Figure 1(c). The required weight of the porous Cu electrode (Cu:SiO2=1:2) for storing 4 mAh cm-2 was only 1.5 mg, whereas the porous Cu electrode (Cu:SiO2=1:0) required 3.6 mg. Furthermore, the number of cycle for reaching maximum coulombic efficiency was shorter in high porosity (90%) compared to the lower porosity (30%~80%). Therefore, the outstanding performance would be due to the high porosity and conductivity of the porous Cu electrode providing multiple nucleation sites, as well as enough space for the growth of alkali metal. This work will provide insights into the rational design of the alkali metal anode with high areal capacity and low voltage hysteresis, by providing a facile method to control of structural characteristics of the Cu current collector.