Structural characterization and electrochemical intercalation of Li+ in layered Na0.65Ni0.5Mn0.5O2 obtained by freeze-drying method

New data on the structure and reversible lithium intercalation properties of sodium-deficient nickel–manganese oxides are provided. Novel properties of oxides determine their potential for direct use as cathode materials in lithium-ion batteries. The studies are focused on Na _x Ni_0.5Mn_0.5O₂ with x?=?2/3. Between 500 and 700 °C, new layered oxides Na_0.65Ni_0.5Mn_0.5O₂ with P3-type structure are obtained by a simple precursor method that consists in thermal decomposition of mixed sodium–nickel–manganese acetate salts obtained by freeze-drying. The structure, morphology, and oxidation state of nickel and manganese ions of Na_0.65Ni_0.5Mn_0.5O₂ are determined by powder X-ray diffraction, SEM and TEM analysis, and X-ray photoelectron spectroscopy (XPS). The lithium intercalation in Na_0.65Ni_0.5Mn_0.5O₂ is carried out in model two-electrode lithium cells of the type Li|LiPF₆(EC:DMC)|Na_0.65Ni_0.5Mn_0.5O₂. A new structural feature of Na_0.65Ni_0.5Mn_0.5O₂ as compared with well-known O3–NaNi_0.5Mn_0.5O₂ and P2–Na_2/3Ni_1/3Mn_2/3O₂ is the development of layer stacking ensuring prismatic site occupancy for Na⁺ ions with shared face on one side and shared edges on the other side with surrounding Ni/MnO₆ octahedra. The reversible lithium intercalation in Na_0.65Ni_0.5Mn_0.5O₂ is demonstrated and discussed.     

Ion-exchange properties of P2-NaxMnO2: evidence of the retention of the layer structure based on chemical reactivity data and electrochemical measurements of lithium cells

The ion-exchange properties of two P2-type layered Na_xMnO₂ bronzes (x=0.6, 0.75) with a differential microstructure were studied in LiCF₃SO₃ solutions in acetonitrile under ambient conditions. Na⁺ ions are readily exchanged with Li⁺, but the reaction causes a significant loss of crystallinity that results in some amorphization. The feasibility of the process increases with increasing structural disorder in the parent compound; conversion, however, is incomplete. The ability of the exchanged material to intercalate water in the air is consistent with the formation of an Li-Mn-O compound that retains the layered framework. Also, the electrochemical data obtained for this material as cathode in lithium cells are consistent with retention of the layer structure and exclude a potential spinel transition due to the ion-exchange reaction. However, the cycling properties of cells made from these layered compounds are quite modest, probably because of the strong structural disorder induced by the lithium reaction.     

Flexibility of Na,K-ATPase secondary structure upon drug-protein interaction

The enzyme Na⁺, K⁺-ATPase is an integral membrane protein which transports sodium and potassium cations against an electrochemical gradient. The transport of Na⁺ and K⁺ ions is connected to an oscillation of the enzyme between the two conformational states, the E₁ (Na⁺) and the E₂ (K⁺) conformations. The enzymatic activity of ATPase is largley affected by different ligands complexation. This review reports the effects of several drugs such as AZT (anti-AIDS), cis-Pt (antitumor), aspirin (anti-inflammatory) and vitamin C (antioxidant) on the stability and secondary structure of Na,K-ATPase in vitro. Drug-enzyme binding is mainly through H-bonding to the polypeptide C=O and C-N groups with two binding constants K_1(AZT) = 5.30 × 10⁵ M^?1 and K_2(AZT) = 9.80 × 10³ M^?1 for AZT and one binding constant for K_cis-Pt = 1.93 × 10⁴ M^?1, K_aspirin = 6.45 × 10³ M^?1 and K_ascorbate = 1.04 × 10⁴ M^?1 for cis-Pt, aspirin and ascorbic acid. The enzyme secondary structure was altered from that of α-helix 19.8% (free protein) to almost 22–26% and the β-sheet from 25.6% to 18–22%, upon drug complexation with the order of induced stability AZT > cis-Pt > ascorbate > aspirin.     

Electrical conductivity and phase transitions of the solid electrolyte system (Cs1−yRby)Cu4Cl3(I2−xClx)

Results of electrical conductivity measurements, thermal analysis, and X-ray diffraction studies indicate the existence of four phases, between 295 K and the melting points, in the system (Cs_1?yRb_y)Cu₄Cl₃I₂. These phases are designated α, á β, γ in order of decreasing temperature. The α phase is isostructural with α-RbAg₄I₅; the á phase is also cubic and very likely belongs to space groupP2₁3, a subgroup ofP4₁32 andP4₃32 to which the α phase belongs. There is a high probability that the á → α transition is continuous. The á → α transition is not discernible in the conductivity measurements or thermal analysis; therefore the line of á-α transitions is presently unknown. The β phase transforms to the á and the γ phase transforms to the β phase wheny ≤ 0.36; the γ phase transforms to the α phase wheny ≥ 0.36. That is, there is a triple point aty = 0.36, T = 399K. The γ-β, β-α′, and γ-α transitions are all hysteretic and are therefore first order. The conductivities of the β phases are relatively low and the enthalpies of activation relatively high. The conductivity of the β phase decreases with increasingy. The β phase probably belongs to space groupR3, in which the Cu⁺ ions can be ordered. The α and á phases are the true solid electrolytes; the conductivities are high, >0.73 Ω^?1cm^?1 at 419 K, and the enthalpies of activation of motion of the Cu⁺ ions low, 0.11 eV.In the system CsCu₄Cl₃(I_2?xCl_x), 0 ≤ x ≤ 0.25, the Cl^? for I^? substitutions affect the transitions to only a small extent relative to the stoichiometric compound. The β phase occurs for allx and transforms to á.     

Iron–Oxalato Framework with One‐Dimensional Open Channels for Electrochemical Sodium‐Ion Intercalation

Discovery of a new class of ion intercalation compounds is highly desirable due to its relevance to various electrochemical devices, such as batteries. Herein, we present a new iron–oxalato open framework, which showed reversible Na⁺ intercalation/extraction. The hydrothermally synthesized K₄Na₂[Fe(C₂O₄)₂]₃ ? 2 H₂O possesses one‐dimensional open channels in the oxalato‐bridged network, providing ion accessibility up to two Na⁺ per the formula unit. The detailed studies on the structural and electronic states revealed that the framework exhibited a solid solution state almost entirely during Na⁺ intercalation/extraction associated with the reversible redox of Fe. The present work demonstrates possibilities of the oxalato frameworks as tunable and robust ion intercalation electrode materials for various device applications.     

Stabilization of over-stoichiometric Mn in layered Na2/3MnO2

Sodium manganates with nominal composition Na_2/3MnO₂ were prepared by solid state reaction between Na₂CO₃ and MnCO₃ at 1000 °C. The composition and structure of Na_xMnO₂ were controlled by the rate of cooling from the temperature of preparation. This is a consequence of the capability of Na_2/3MnO₂ to accommodate over‐stoichiometric Mn⁴⁺ ions up to 12.5%. Structural characterization was carried out by XRD powder diffractions, TEM analysis and Raman spectroscopy. The composition and oxidation state of manganese were determined by chemical analysis and magnetic susceptibility measurements. The manganese distribution in the layers was analysed using electron paramagnetic resonance (EPR) spectroscopy. By quenching from 1000 °C, the orthorhombic distorted modification is stabilized. A phase separation into orthorhombic and hexagonal modifications takes place when Na_2/3MnO₂ is slow cooled. The structure changes are concomitant with an increase in the oxidation state of Mn. The over‐stoichiometric Mn⁴⁺ ions are accommodated in the hexagonal modification by creation of vacancies in the MnO₂‐layers.     

Combustion-synthesized sodium manganese (cobalt) oxides as cathodes for sodium ion batteries

We report on the electrochemical properties of layered manganese oxides, with and without cobalt substituents, as cathodes in sodium ion batteries. We fabricated sub-micrometre-sized particles of Na_0.7MnO_2?+?z and Na_0.7Co_0.11Mn_0.89O_2?+?z via combustion synthesis. X-ray diffraction revealed the same layered hexagonal P2-type bronze structure with high crystallinity for both materials. Potentiostatic and galvanostatic charge/discharge cycles in the range 1.5–3.8 V vs. Na | Na⁺ were performed to identify potential-dependent phase transitions, capacity, and capacity retention. After charging to 3.8 V, both materials had an initial discharge capacity of 138 mA?h?g^?1 at a rate of 0.3 C. For the 20th cycle, those values reduced to 75 and 92 mA?h?g^?1 for Co-free and Co-doped samples, respectively. Our findings indicate that earlier works probably underestimated the potential of (doped) P2-type Na_0.7MnO_2?+?z as cathode material for sodium ion batteries in terms of capacity and cycle stability. Apart from doping, a simple optimization parameter seems to be the particle size of the active material.     

Al and/or Ni-doped nanomanganese dioxide with anisotropic expansion and their electrochemical characterisation in primary Li–MnO2 batteries

A variety of MnO₂ nanorods containing one or two transition metals (M) (with M?=?Al and/or Ni) have been successfully synthesised via a facile hydrothermal synthesis route. The physical–chemical properties and electrochemical performance of manganese oxide were analysed by X-ray diffraction (XRD), inductively coupled plasma atomic emission spectrometry (ICP-OES), Fourier transform infrared spectrometer (FT-IR), scanning electron microscopy (SEM), Brunauer–Emmett–Teller method (BET), galvanostatic discharge and cyclic voltammetry (CV). The result indicated that α-type MnO₂ was obtained, and a small quantity of Al and/or Ni were embedded into the crystal lattice of manganese oxide instead of the partial Mn ion, which resulted in anisotropic expansion of the MnO₂ unit cell. The doping of Al can strengthen Mn–O bonds in the [MnO₆] octahedral and increases the specific surface area of the modified material (i.e., Al–MnO₂ is 119 m² g^?1). Interestingly, MnO₂ electrode co-doped with equimolar Al and Ni exhibited the highest specific capacity of 169 mAh g^?1 at 0.05 mA cm^?2. The substantial enhancement of the electrochemical lithium storage capacity was due to the ameliorating of integrative factors, such as high specific surface area, excellent lattice parameters and lower electrical resistance, as well as short Li⁺ and electron transport length. In addition, a more stable host skeleton also guaranteed an endurable Li⁺ intercalation behaviour during the discharge process.     

Electron microscope studies of sodium and lithium intercalation in TiS2

Lithium and sodium intercalation in TiS₂ have been studied by transmission electron microscopy using lattice imaging and diffraction contrast techniques. Na_xTiS₂ samples (0 ≤ x ≤ 0.6) from $\text{Na}\text{NaI}$ in propylene carbonate/TiS₂ batteries were found to contain a complex variety of phases inhomogeneous on a fine scale. Observations showed variable staging and a 2H phase not previously reported for this system at ambient temperatures. Observations on both Na_xTiS₂ and chemically prepared Li_xTiS₂ showed highly dislocated structures. A model is proposed whereby dislocations are introduced to accommodate misfit strains caused by nonuniform intercalation and, in the case of Na_xTiS₂, to initiate phase transformations, leading to potentially irreversible structural changes in cycled material.     

Sodium and Manganese Stoichiometry of P2‐Type Na2/3MnO2

To realize a reversible solid‐state Mn^III/IV redox couple in layered oxides, co‐operative Jahn–Teller distortion (CJTD) of six‐coordinate Mn^III (t_2g³–e_g¹) is a key factor in terms of structural and physical properties. We develop a single‐phase synthesis route for two polymorphs, namely distorted and undistorted P2‐type Na_2/3MnO₂ having different Mn stoichiometry, and investigate how the structural and stoichiometric difference influences electrochemical reaction. The distorted Na_2/3MnO₂ delivers 216 mAh g^?1 as a 3 V class positive electrode, reaching 590 Wh (kg oxide)^?1 with excellent cycle stability in a non‐aqueous Na cell and demonstrates better electrochemical behavior compared to undistorted Na_2/3MnO₂. Furthermore, reversible phase transitions correlated with CJTD are found upon (de)sodiation for distorted Na_2/3MnO₂, providing a new insight into utilization of the Mn^III/IV redox couple for positive electrodes of Na‐ion batteries.     

Structural and electronic properties of transition metal thiophosphates

From the viewpoint of metal coordination we examine the structural characteristics of several new members of transition metal thiophosphates (i.e., MPS phases with M = V, Nb, Ta), in which various ligands such as S²⁻, S²⁻₂, and phosphorus-sulfur polyanions P_nS^x−_m (1 ≤ n ≤ 4; 3 ≤ m ≤ 13; 2 ≤ x ≤ 6) provide either an octahedral or a bicapped prismatic coordination of the metal. Tight-binding band electronic structure calculations show that the low-lying acceptor orbitals responsible for lithium intercalation of thiophosphates are their d-block bands. This prediction is confirmed by our electrochemical lithium intercalation study which reveals that the reduction sites of thiophosphates are their metal cations. Molecular orbital calculations are carried out on vanadium compounds with extremely short interligand S···S contacts. The occurrence of such short contact distances is not caused by covalent bonding in the S···S contacts but by the small size of vanadium cations which forces its surrounding sulfur ligands to squeeze one another.     

The crystal structure of Na7Mg4.5(P2O7)4

The crystal structure of Na₇Mg_4.5(P₂O₇)₄ has been solved by direct methods from the three-dimensional X-ray data. The space group is $\text{P}\text{1}$. The crystal structure consists of Mg²⁺, Na⁺, and P₂O^4?₇ ions. One magnesium atom at symmetry center (0,0,0) and two sodium atoms at ±(?0.0421, ?0.0596, 0.2230) display occupation factors 0.5 each. A short interatomic distance between these Na⁺ and Mg²⁺ ions (1.80 ± 0.01 Å) excludes the occupation of both sites in the same unit cell. The crystal structure of Na₇Mg_4.5(P₂O₇)₄ consists of unit cells containing Na₈Mg₄(P₂O₇)₄ or Na₆Mg₅(P₂O₇)₄ with a statistical occurrence 1:1.Each Mg²⁺ ion is octahedrally coordinated by six O^2? ions at distances 1.979 – 2.270 Å. The coordination polyhedra around the Na⁺ ions are ill-defined. The bond angles POP in the P₂O^4?₇ groups are 126.6 and 133.6° (±0.3°). The final reliability factor R is 7.1%.     

Ti3C2Tx/MnO2正极在水系锌电池中的电化学性能

二氧化锰(MnO₂)材料具有比容量大、电极电位高、储量丰富以及价格低廉等优势,成为水系锌电池正极最受关注的一类材料,然而其仍然存在着结构稳定性差和电化学储存机理复杂的问题。因此,我们通过两步合成法制备了一种花苞状结构的MnO₂负载在Ti₃C₂T_x表面形成Ti₃C₂T_x/MnO₂复合材料,通过X射线粉末衍射(XRD)、X射线光电子能谱(XPS)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)对复合样品的结构、成分和形貌进行表征。通过将Ti₃C₂T_x/MnO₂复合材料作为正极,与锌负极匹配组装成水系锌电池,研究了其分别在2 mol·L^-1 ZnSO₄、2 mol·L^-1 ZnSO₄+0.1 mol·L^-1 MnSO₄、30 mol·L^-1三氟甲基磺酸四乙基铵(TEAOTf)+1 mol·L^-1三氟甲烷磺酸锌(ZnOTf)和3 mol·L^-1 ZnOTf四种电解液中的电化学性能。结果表明,Ti₃C₂T_x/MnO₂在2 mol·L^-1 ZnSO₄中的比容量较高,但循环稳定性很差。将TEAOTf盐和ZnOTf盐共溶于水中,设计了一种新型的含惰性阳离子的超高浓度盐包水电解液(30 mol·L^-1 TEAOTf+1 mol·L^-1 ZnOTf),不仅提高了Ti₃C₂T_x/MnO₂材料的可逆性,而且有效抑制了电极材料在循环过程中的溶解。     

Esr spectra and magnetic constants of α-Al2O3:Co,H

ESR spectra of the defect α-Al₂O₃:Co²⁺, H⁺ are reported and used to derive the magnetic tensors g and A. This defect is shown to exist in several types, and models in the framework of the α-Al₂O₃ structures are proposed.     

Experimental determination of repulsive potentials between alkali ions (Li+, Na+, and K+) and N2 and CO molecules

Integral scattering cross sections have been measured for alkali ions (Li⁺, Na⁺ and K⁺) in the energy range 500–4000 eV scattered by room temperature N₂ and CO molecules through effective laboratory angles greater than 5 × 10^?3 rad. The repulsive potentials deduced from the cross sections are represented bya practically identical formula for the Na⁺N₂ and Na⁺CO systems, and for the K⁺CO systems, respectively, while the repulsive potentials of the Li⁺N₂ system are somewhat smaller than those of the Li⁺CO system at larger intermolecular distances.     

Enhanced lithium-ion intercalation and conduction of transparent tantalum oxide films by lithium addition with an atmospheric pressure plasma jet

An investigation is conducted on enhancing lithium-ion intercalation and conduction performance of transparent organo tantalum oxide (TaO _y C _z ) films, by addition of lithium via a fast co-synthesis onto 40 Ω/□ flexible polyethylene terephthalate/indium tin oxide substrates at the short exposed durations of 33–34 s, using an atmospheric pressure plasma jet (APPJ) at various mixed concentrations of tantalum ethoxide [Ta(OC₂H₅)₅] and lithium tert-butoxide [(CH₃)₃COLi] precursors. Transparent organo-lithiated tantalum oxide (Li _x TaO _y C _z ) films expose noteworthy Li⁺ ion intercalation and conduction performance for 200 cycles of reversible Li⁺ ion intercalation and deintercalation in a 1 M LiClO₄-propylene carbonate electrolyte, by switching measurements with a potential sweep from ?1.25 to 1.25 V at a scan rate of 50 mV/s and a potential step at ?1.25 and 1.25 V, even after being bent 360° around a 2.5-cm diameter rod for 1000 cycles. The Li⁺ ionic diffusion coefficient and conductivity of 6.2?×?10^?10 cm²/s and 6.0?×?10^?11 S/cm for TaO _y C _z films are greatly progressed of up to 9.6?×?10^?10 cm²/s and 7.8?×?10^?9 S/cm for Li _x TaO _y C _z films by co-synthesis with an APPJ.     

Regulating Cation Interactions for Zero-Strain and High-Voltage P2-type Na2/3Li1/6Co1/6Mn2/3O2 Layered Oxide Cathodes of Sodium-Ion Batteries

Deep sodium extraction/insertion of sodium cathodes usually causes undesired Jahn–Teller distortion and phase transition, both of which will reduce structural stability and lead to poor long-cycle reliability. Here we report a zero-strain P2- Na_2/3Li_1/6Co_1/6Mn_2/3O₂ cathode, in which the lithium/cobalt substitution contributes to reinforcing the host structure by reducing the Mn³⁺/Mn⁴⁺ redox, mitigating the Jahn–Teller distortion, and minimizing the lattice change. 94.5 % of Na⁺ in the unit structure can be reversibly cycled with a charge cut-off voltage of 4.5 V (vs. Na⁺/Na). Impressively, a solid-solution reaction without phase transitions is realized upon deep sodium (de)intercalation, which poses a minimal volume deviation of 0.53 %. It attains a high discharge capacity of 178 mAh g⁻¹, a high energy density of 534 Wh kg⁻¹, and excellent capacity retention of 95.8 % at 1 C after 250 cycles.     

Charge carriers and dc polarization phenomena in solid Na2WO4

Ionic transport measurements based on the Tubandt method have been performed in all three solid phases of Na₂WO₄ at temperatures between 550 and 600°C in air. It is shown that t_Na⁺ = 1.00 in all cases. Ag is oxidized anodically to Ag⁺ at Ag/Na₂WO₄ interfaces. Cathodically only (air) oxygen reduction occurs, resulting in the formation of a poorly conducting layer of Na₂O and Na₂CO₃ at the cathode.     

The crystal structure of eulytite Na3Bi5(PO4)6

The crystal structure of Na₃Bi₅(PO₄)₆ was solved using the single-crystal X-ray diffraction technique. The structural refinement has led to a reliability factor of R₁=0.0257 (wR₂=0.0533) for 428 independent reflections. This compound was found to crystallize in the cubic system (space group I4̄3d) with eulytite structure and the lattice parameters: a=10.097 (4) Å, V=1029.38 ų, Z=2, D_calc.=5.43 g cm⁻³ (D_exp.=5.32(5) g cm⁻³). The structure is characterized by the existence of one single general position (48a) for oxygen anions and two distinguished positions (16c) occupied by Na⁺ and Bi³⁺ cations, respectively. The site occupation factors are equal to 3/8 and 5/8 for sodium and bismuth, respectively. Although all PO distances are identical (1.529(4) Å), the OPO angles ranging from 108.06 (15) to 112.32 (31)°, show that [PO₄]³⁻ are rather distorted. Both sodium and bismuth cations are located in octahedral sites with corresponding mean distances of NaO and BiO equal to 2.428 and 2.386 Å, respectively. As expected from the close values of the ionic radii of Na⁺ and Bi³⁺, these distances lie in the same range.