Deintercalation Of Na Research Articles

In situ electrochemical Mn vacancies in CoMnHCF for a high level of zinc storage.

CoMnHCF is utilized in aqueous sodium/zinc mixed ion batteries and exhibits a high reversible capacity with good rate and cycle performances. At 0.05 A g-1 current density, the CoMnHCF can deliver a specific capacity for 180.4 mA h g-1, and have 99.3% capacity retention after 300 cycles at 0.3 A g-1. Such high reversible capacity profits from Mn vacancies that generate in situ during the first cycle, which provides more active sites for Zn storage. The de-intercalation of Na+ further elevates this good electrochemical performance. Co atoms in the framework are not only involved in the redox reactions, but help to support the structure, thus achieving better cycle stabilities.

Degradation Control of All-Solid-State Na Batteries by Inorganic Oxide Coated Positive Electrode Active Material

All-solid-state Na batteries (ASSBs) are attracted attention owing to their high safety and resource properties for next-generation batteries. Na has the advantage of abundant resources compared to Li. In addition, polymer electrolyte is expected to improve the safety of the battery by suppressing the risk of ignition with liquid leakage. In general, the degradation of batteries using polymer electrolyte mainly occurs at the positive electrode (PE)/electrolyte interface during charge process. In case of batteries using active material having layered structures such as NaCoO2 and polyether electrolyte, the degradation of CoO2 structure and decomposition of polyether during the deintercalation of Na+ in the active material. These PE / electrolyte interface degradations contribute to increasing resistance of the battery. To suppress interfacial degradation, inorganic oxides coating for active materials were reported in the Li-based battery[1]. In this study, Na3PO4 or Na3Zr2Si2PO12 (NZSP) coated PEs were applied for ASSBs to suppress degradation. The degradation behavior of ASSBs was investigated by charge / discharge test and XRD analysis using extracted PE sheet from cell. Furthermore, Raman spectroscopy was applied on the cell before and after charge / discharge test to investigate structural changes in active material and polymer electrolyte.NaTFSA as Na salt, P(EO/PO) as polyether-based macromonomer, and DMPA as photoinitiator were mixed into Ar-filled glovebox. NaTFSA was added by ratio of [Na]/[O]=0.1 per molar of oxygen units of P(EO/PO). Polymer electrolyte films were prepared by UV irradiation for obtained homogeneous solution. NaCoO2 (NCO) as active material, acetylene black (AB) as conductive additive, and P(EO/MEEGE)-NaTFSA as binder were mixed by 82:5:13 weight ratio. The Na3PO4 and NZSP as inorganic oxides were added 5 wt.% and 10 wt.% for NCO, respectively. Applied slurry (thick. 50 µm) onto Al foil was cut to Φ16 mm after vacuum dry. The PE sheet, Na metal negative electrode, and polymer electrolyte were assembled into coin-cell to fabricate ASSBs. The charge / discharge tests for more than 10 cycles were performed at 333K after heat-treated at 363K for 48h. After charge / discharge test, XRD analysis was applied to extracted PE sheet from the cell under a low dew point for structural evaluation. Moreover, PE, polymer electrolyte, and Na metal were initially cut to 9 mm × 9 mm and introduced into the Raman cell with observation window to observe the cross-section of the cell. Raman spectroscopy was performed to the cross-section of the cell before and after charge / discharge test in order to investigate the degradation behavior of PE and polymer electrolyte.Fig. 1 shows charge / discharge profiles of non-coated and 10 wt.% NZSP coated PE in the cells. The 1st discharge capacity was 36 mAhg-1 in the non-coated system, and was also the insufficient capacity of about 30% from the theoretical capacity (ca. 118 mAhg-1) of NCO. In contrast, the NZSP-coated PE improved the 1st discharge capacity to 60 mAhg-1, and clear plateau was observed owing to their crystal structure change of NCO. These results suggest that inorganic oxide served as sufficient ionic conduction path between PE and electrolyte, reducing the interfacial resistance. Fig. 2 shows the cycle number dependencies of capacity and Coulombic efficiency. ASSB with inorganic oxides coated PE showed high discharge capacity retention and Coulombic efficiency in comparison with non-coated system. These results are suggesting that inorganic oxides coating active material surface suppress increase of interfacial resistance and degradation of the PE/electrolyte by prevent the formation of side products such as Co3O4 [2]. NZSP has higher Na ionic conductivity than Na3PO4, and can cover more apparent area of NCO surface than Na3PO4 because of their smaller particle size. Therefore, from comparing Na3PO4 and NZSP coating, NZSP more contributes to suppressing degradation of the cell. Fig. 3 shows the results of XRD analysis for PEs after charge / discharge test. Peaks attributed to NCO were confirmed in the PE before degradation, however, peak intensity decreased after degradation, especially for (003) and (006) of NCO. The peak derived from Co3O4 was confirmed only after degradation. These results suggest that structural degradation of NCO occurs during charging and discharging of the cell, resulting in the formation of Co3O4. In addition, the inorganic oxide coating should be contributed to maintaining the structure of the active material. In this presentation, the analysis results of structural changes of PE and electrolyte before and after charge / discharge test by Raman spectroscopic measurement will be also reported.

Suppressing Vanadium Dissolution in "Water-in-Salt" Electrolytes for 3.2 V Aqueous Sodium-Ion Pseudocapacitors.

Low-cost sodium-ion-based electrochemical energy storage devices, especially vanadium-based sodium-ion pseudocapacitors, are receiving increasing attention. However, the inevitable dissolution of vanadium in aqueous electrolytes usually leads to poor cycling stability and a narrow electrochemical stability window (ESW). In this study, we prepared layered (NH4)2V10O25·8H2O with a hierarchical flower-like structure and an ultralarge layer spacing and evaluated its potential as a sodium-ion pseudocapacitive material. Ex situ X-ray diffraction (XRD) measurement and kinetic analysis demonstrate the reversible intercalation and deintercalation of Na+ in (NH4)2V10O25·8H2O in NaClO4 electrolytes. Significantly improved durability and a large voltage window of 3.2 V are achieved in the high-concentration NaClO4 electrolyte. Inductively coupled plasma-optical emission spectroscopy (ICP-OES) analysis and molecular dynamics (MD) simulations reveal that the dissolution of vanadium in the high-concentration NaClO4 electrolyte can be effectively suppressed. An asymmetric sodium-ion capacitor with a wide voltage window of 3.2 V was successfully assembled, and it delivered a high energy density of 53.1 Wh kg-1 at a power density of 3.2 kW kg-1.

A New Strategy of Using Cation Intercalation Electrodes for Water Desalination

Water desalination is a promising technological solution to water scarcity. While several technologies are currently utilized to produce freshwater from saline water sources, there are remaining challenges including intensive energy usage (e.g., thermal distillation), fouling (e.g., reverse osmosis), and high material costs (e.g., electrodialysis). The use of cation intercalation electrodes allows for electrochemically driven capture and release of ions, thus effectively desalinating water using inexpensive electrode materials that require low voltage without producing byproducts. To date, previous approaches using cation intercalation electrodes have focused on intercalation and deintercalation of Na+ in order to directly capture Na+ that is abundant in saline water. This approach has limited the choice of electrode materials and electrochemical properties, which are crucial for efficient water desalination. To overcome this challenge, we demonstrated a new strategy for water desalination using cation intercalation electrodes that interact with K+. Water desalination was achieved in a 4-channel electrochemical flow cell separated by an alternative array of anion and cation exchange membranes with copper hexacyanoferrate (CuHCF) as a model electrode material. Deintercalation of K+ upon oxidation of CuHCF enabled the transport of Cl− through an anion exchange membrane from the adjacent channel that produces desalinated water. Intercalation of K+ upon reduction of CuHCF enabled the transport of Cl− through an anion exchange membrane to the adjacent channel that produces concentrated water. A cation exchange membrane located between desalinated and concentrated water channels allowed for separating Na+. Using the new concept of utilizing K+, several performance parameters were evaluated including electrochemical properties, salt separation, and energy consumption. Collectively, we show that the use of K+ as an intercalant for cation intercalation electrodes can represent a new strategy for electrochemical water desalination.

Hard Carbon Nanosheets with Uniform Ultramicropores and Accessible Functional Groups Showing High Realistic Capacity and Superior Rate Performance for Sodium-Ion Storage.

Hard carbon attracts considerable attention as an anode material for sodium-ion batteries; however, their poor rate capability and low realistic capacity have motivated intense research effort toward exploiting nanostructured carbons in order to boost their comprehensive performance. Ultramicropores are considered essential for attaining high-rate capacity as well as initial Coulombic efficiency by allowing the rapid diffusion of Na+ and inhibiting the contact of the electrolyte with the inner carbon surfaces. Herein, hard carbon nanosheets with centralized ultramicropores (≈0.5 nm) and easily accessible carbonyl groups (CO)/hydroxy groups (OH) are synthesized via interfacial assembly and carbonization strategies, delivering a large capacity (318 mA h g-1 at 0.02 A g-1 ), superior rate capability (145 mA h g-1 at 5.00 A g-1 ), and approximately 95% of reversible capacity below 1.00 V. Notably, a new charge model favoring fast capacitive sodium storage with dual potential plateaus is proposed. That is, the deintercalation of Na+ from graphitic layers is manifested as the low-potential plateau region (0.01-0.10 V), contributing to stable insertion capacity; meanwhile, the surface desodiation process of the CO and OH groups corresponds to the high-potential plateau region (0.40-0.70 V), contributing to a fast capacitive storage.

Highly Crystalline Ni-Co Layered Double Hydroxide Fabricated via Topochemical Transformation with a High Adsorption Capacity for Nitrate Ions.

Layered double hydroxide (LDH) has emerged as promising candidates for removing harmful oxoanions (i.e., SO42-, HPO42-, andNO3- ions) from wastewater because of their intrinsic ability to accommodate anionic species in the interlayer space. Highly crystalline [Ni0.67Co0.33(OH)2]Cl0.29·0.53H2O (Ni-Co LDH) particleswith an exceptionally high anion-exchange capacity of 58.8 mg g-1 and a distribution coefficient (Kd) of 2396 mL g-1 for NO3- ions were successfully prepared by the flux method and a topochemical strategy. Layered Na0.97Ni0.67Co0.33O2 (NNCO) was prepared using a high-temperature flux and used as a starting material for topotactic transformation consisting of oxidative hydrolysis with KOH and NaClO and subsequent reduction with H2O2 and NaCl. During the transformation from NNCO to Ni-Co LDH, a drastic change in the valences of the Ni and Co belonging to the host layer and in the cationic and anionic species occurs in interlayer space; the valences of the Ni and Co in NNCOwereincreased from Ni2+,3+ and Co2+,3+ to Ni3+ and Co2+,3+,4+ by an oxidative hydrolysis reaction with simultaneous intercalation of K+ionsand deintercalation of Na+ions,and subsequentlydecreased from Ni3+ and Co2+,3+,4+ to Ni2+ and Co2+,3+ by a reduction reaction with simultaneous intercalation of anionic species such as CO32- and Cl-ionsand deintercalation of Na+ and K+ions. Through synchrotron powder X-ray diffraction analysis and Rietveld refinement, the resultant Ni-Co LDH was clearly shown to exhibit high crystallinity with less compositional deviation even after topochemical transformation in comparison with the one prepared by traditional coprecipitation and solid-state methods. Furthermore, the adsorption isotherm for NO3- ions elucidated that homogeneous adsorption sites are consistently constructed in the crystal structure, which could be found from the fitting to a Langmuir curve, with the R2 value being 0.98. This work opens up a new route for the fabrication of excellent not only ion-exchangeable but also ion-conductive inorganic materials for direct utilization in environmental and energy-storage processes.

Reaction Mechanisms of Sodium‐Ion Batteries under Various Charge and Discharge Conditions in a Three‐Electrode Setup

AbstractCharge‐discharge reaction mechanisms of sodium‐ion batteries under various condition are studied by using a three‐electrode setup of a pouch‐type sodium‐ion battery. The sodium‐ion battery is constructed by using cost‐effective ternary layered Na0.76Ni0.3Fe0.4Mn0.3O2 and commercial hard carbon as the cathode and anode materials, respectively, and 1.0 M NaPF6 in mixed carbonate solvent as the electrolyte. The electrochemical impedance spectroscopy (EIS) results and transmission electron microscopy (TEM) images show that an apparent solid‐electrolyte interphase (SEI) film is formed on anode material surface during the formation (pre‐charging) process, and the potentials for the SEI film formation of the solvents (ethylene carbonate and ethylene carbonate) and the additive (fluorinated ethylene carbonate) in the electrolyte are 2.04 and 2.79 V, respectively. The X‐ray diffraction (XRD) results demonstrate that, during charge, the crystal structure of cathode material changes significantly with the deintercalation of Na+. When the battery is charged to 5.0 V, the diffraction peak corresponding to the (002) plane disappears, as Na+ is further deintercalated, and the structure changes from the hexagonal phase to the monoclinic phase, causing the rapid degradation of the cycle performance. When the battery is overdischarged to 0 V, the EIS results and TEM images show that the SEI film is destroyed completely, and the cycle life performance is significantly deteriorated.

Synthesis and Characterization of Na3V2(PO4)2F3 Based Cathode Material for Sodium Ion Batteries

Na3V2(PO4)2F3 was synthesized via two-step carbothermal reduction from NaF and VPO4 intermediate precursor and tested as cathode material for aqueous and non-aqueous Na-ion batteries. The synthesized material was characterized using XRD, SEM-EDX, TOF-SIMS. The cyclic voltammetry and charge/discharge measurements for non-aqueous system indicated that the intercalation / deintercalation of Na+ ions is being carried out in two steps: the first one at 3.5/3.7 V and the second one at 4.1/4.3 V, indicative for a structural transformation of the cathode material. Discharge capacity of 55 mA g-1 was measured for the first cycle. However, the capacity decreased nearly 50 %, to 22 − 25 mA g-1 after the second galvanostatic cycle within 3.0 – 4.5 V. Discharge capacity decreases during the first 10 cycles but stabilizes after 50 cycles, maintaining ~ 20 mA g-1 after 3000 cycles. Cycling in aqueous media showed even faster capacity fade.

Electrochemical and structural investigation of NaCrO2 as a positive electrode for sodium secondary battery using inorganic ionic liquid NaFSA–KFSA

The electrochemical performance of NaCrO2 as a positive electrode material for an intermediate-temperature sodium secondary battery was evaluated in an inorganic ionic liquid, NaFSA–KFSA (FSA = bis(fluorosulfonyl)amide), at 363 K. The positive electrode using NaCrO2, acetylene black, and polytetrafluoroethylene exhibited a stable discharge capacity of 113 mA h g−1 at a current density of 125 mA g−1. The Coulombic efficiency and the capacity retention at the 100th cycle were 99.6% and 98.5%, respectively. Even at the very high current density of 2000 mA g−1, the discharge capacity was maintained at 63 mA h g−1. X-ray diffraction analyses revealed that the deintercalation of Na+ ion from NaCrO2 was associated with several phase transitions in the following sequence: rhombohedral O3, monoclinic O′3, and monoclinic P′3.

Investigation of phase transitions for the hydrothermal formation of TiO2 in the presence of F− ions

The hydrothermal phase transition of ammonium titanate into TiO2 in aqueous ammonia media was investigated in the presence of F− ions by adding various kinds of electrolytes such as NaCl, NH4Cl, NaF, and NH4F. The phase composition and the morphologies of the products were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). With the assistance of F− ions, pure brookite TiO2 can be hydrothermally prepared with a wide range of Na+ ion concentrations from 0.25M to 1.5M in just 24h, which has obvious advantages over the previous NaCl scheme [1,2]. Moreover, photocatalytic degradation of MO shows that both anatase and brookite prepared in the presence of F− ions show superior photocatalytic activities than those prepared in the absence of F− ions. The phase transition mechanism from ammonium titanate into TiO2 was also proposed. Besides the introduction of Na+ ions that benefits the phase transition from titanate to brookite, F− ions are suggested to play two key roles during the hydrothermal process: catalyzing the condensation reaction of TiOH to produce TiOTi linkages by forming TiF and regulating the intercalation and the de-intercalation of Na+ ions by counteracting the electrostatic interaction between the Na+ ions and the titanate layers.

Variation of the MnO2 Birnessite Structure upon Charge/Discharge in an Electrochemical Supercapacitor Electrode in Aqueous Na2SO4 Electrolyte

This paper provides new insight on the charge storage mechanism in crystallized Mg-doped sodium birnessite-type manganese dioxide used as active supercapacitor electrode material that involves the intercalation/deintercalation of cations between the sheets during electrochemical reduction/oxidation, respectively. An increase of the interlayer spacing from 0.710 to 0.720 nm upon electrochemical oxidation in the presence of Na+ cations in the electrolyte is associated with the deintercalation of Na+ and the intercalation of H2O between the layers. A progressive crystallinity loss of the material is also observed upon potential cycling between the oxidized and reduced states. Despite these structural changes, the birnessite electrode exhibits a stable capacitance of 145 F/g over 1100 cycles.

Synthesis of superconducting cobalt oxyhydrates using a novel method: Electrolyzed and oxidized water

By deintercalation of Na+ followed by inserting bilayers of water molecules into the host lattice, the layered cobalt oxide of γ-Na0.7CoO2 undergoes a topotactic transformation to a layered cobalt oxyhydrate of Na0.35(H2O)1.3CoO2−δ with the c-axis expanded from c≈10.9Å to c≈19.6Å. In this paper, we demonstrate that the superconducting phase of c≈19.6Å can be directly obtained by simply immersing γ-Na0.7CoO2 powders in electrolyzed/oxidized (EO) water, which is readily available from a commercial electrolyzed water generator. We found that high oxidation–reduction potential of EO water drives the oxidation of the cobalt ions accompanying by the formation of the superconductive c≈19.6Å phase. Our results demonstrate how EO water can be used to oxidize the cobalt ions and hence form superconducting cobalt oxyhydrates in a clean and simple way and may provide an economic and environment-friendly route to oxidize the transition metal of complex metal oxides.

Synchrotron radiation studies on the growth of TSe 2 (T=Ta, Ti) thin films on Ta substrates: intercalation and de-intercalation of Na

In this paper, we study the formation of TSe 2 (T=Ta, Ti)-layered compound thin films, grown on polycrystalline Ta substrates. The experiments were performed in UHV by means of photoemission spectroscopy with synchrotron radiation measurements. The adsorption of elemental Se on Ta substrate at RT produces a film of Se multilayers. With subsequent heating up to 450°C, the deposited Se interacts with Ta, leading to the formation of a TaSe 2 thin film. The simultaneous co-adsorption of Se and TiCl 4 on clean polycrystalline Ta at 250°C produces a TiSe 2 film of ∼5 molecular layers. The production of TiSe 2 film has been confirmed by Na intercalation and following de-intercalation of Na by exposure of the Na/TiSe 2 film to TiCl 4.

Na and Cl2 Interaction on it and 2H–TaSe2(0001) Surfaces

In this paper we study the interaction of Cl 2 and Na on 1T– TaSe 2 and 2H– TaSe 2(0001) surfaces in the temperature range of 100–300 K. The experiments are performed in UHV with the use of LEED and SXPS by synchrotron radiation measurements. Deposition of Na on Cl 2-covered 1T– TaSe 2 at 100 K forms initially a [Formula: see text], which with increasing temperature to 300 K leads to NaCl formation. Adsorption of Cl 2 on Na-intercalated 1T and 2H– TaSe 2 surfaces at 100 K forms Cl 2 multilayers. The first Cl 2 layer, in contact with the substrate, interacts with the Na near the surface and forms [Formula: see text]. Warming up to 300 K leads to partial desorption of Cl 2, while the remaining chlorine interacts strongly with Na, causing the deintercalation of Na to the surface in the tendency to form NaCl. The intercalation–deintercalation process takes place across the van der Waals planes and it is much faster on 2H than on 1T– TaSe 2, which is attributed to the different crystal structure of 2H and 1T of TaSe 2.

Alkali displacements in intercalated 1T-TaSe2

Single crystals of 1T-TaSe2 have been intercalated with different alkali metals by deposition in ultra-high vacuum onto in situ-cleaved (0001) surfaces. In a second step a different alkali metal, or Cl2, has been deposited on top. The interactions among the deposited species and the substrate have been investigated using soft x-ray photoelectron spectroscopy (SXPS). Li and Na appear to compete in the intercalation process. Li replaces Na, by pushing it deeper into the crystal. Cs on Li:TaSe2 does not intercalate, but stays on top, repelling intercalated Li+ deeper inside. For Li on Cs:TaSe2 an exchange reaction takes place, and Cs is deintercalated. The same effect is induced by Na deposited on intercalated Cs. 1T→2H phase transition for TaSe2 has been observed only for Li deposition. Cl2 deposition on Na intercalated substrate induced deintercalation of Na. The experimental results are discussed in relation to thermodynamic, electronic and electrostatic effects.

ADSORPTION OF Br2 ON Na-INTERCALATED LAYERED COMPOUNDS: BROMINE-INDUCED DEINTERCALATION

This work refers to a study of the behavior of Br2 adsorbed on Na-intercalated 1T-TaSe2(0001) and TiSe2(0001) surfaces at 100 K and during subsequent warming up to 300 K. The investigation was performed in UHV with LEED and photoemission with synchrotron radiation measurements. At 100 K, the bromine forms molecular multilayers on Na/TaSe2 . The Br2 layer, close to the substrate, interacts weakly with Na near the surface, forming [Formula: see text]. At 300 K, part of the Br 2 overlayer desorbs while the remainder on both 1T-TaSe2 and Tise2 surfaces interacts strongly with Na, leading to deintercalation of Na to the surface in the tendency to form NaBr. The formation of NaBr overlayers causes the transition of the incommensurate [Formula: see text] surface structure of 1T-TaSe2 (0001) to 1×1. ESD from the Br/Na/1T-TaSe2 surface causes the restoration of the [Formula: see text].