球磨辅助高温固相法制备Li1.0Na0.2Ni0.13Co0.13Mn0.54O2正极材料及其性能

以乙酸盐(乙酸锂、乙酸钠、乙酸钴、乙酸镍、乙酸锰等)为原材料,采用球磨辅助高温固相法制备Li_(1.0)Na_(0.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_2正极材料。借助XRD、SEM等表征材料的结构和形貌,利用循环伏安、恒流充放电、交流阻抗等方法研究材料的电化学性能。结果表明,钠的掺杂导致颗粒表面光滑度降低,形成Na_(0.77)Mn O_(2.05)新相。0.05C活化过程中,掺钠样品和未掺钠样品首次放电比容量分别为258.4 m Ah·g~(-1)和215.8 m Ah·g~(-1),库伦效率分别为75.2%和72.8%;2C放电比容量分别为116.3 m Ah·g~(-1)和106.2 m Ah·g~(-1)。研究发现,掺钠可减小首次充放电过程的不可逆容量,提高容量保持率;改善倍率性能与容量恢复特性;降低SEI膜阻抗和电荷转移阻抗;掺钠后样品首次循环就可以基本完成Li_2Mn O_3组分向稳定结构的转化,而未掺杂的样品需要两次循环才能逐步完成该过程;XPS结果表明,掺钠样品中Ni~(2+)、Co~(3+)、Mn~(4+)所占比例明显提高,改善了样品的稳定性和电化学性能;循环200次后的XRD结果表明掺钠与未掺钠材料在脱嵌锂反应中的相变化过程基本一致,良好有序的层状结构遭到破坏是循环过程中容量衰减的主要原因。     

球磨辅助高温固相法制备Li1.0Na0.2Ni0.13Co0.13Mn0.54O2正极材料及其性能

以乙酸盐(乙酸锂、乙酸钠、乙酸钴、乙酸镍、乙酸锰等)为原材料,采用球磨辅助高温固相法制备Li_1.0Na_0.2Ni_0.13Co_0.13Mn_0.54O₂正极材料。借助XRD、SEM等表征材料的结构和形貌,利用循环伏安、恒流充放电、交流阻抗等方法研究材料的电化学性能。结果表明,钠的掺杂导致颗粒表面光滑度降低,形成Na_0.77MnO_2.05新相。0.05C活化过程中,掺钠样品和未掺钠样品首次放电比容量分别为258.4 mAh·g^-1和215.8 mAh·g^-1,库伦效率分别为75.2%和72.8%;2C放电比容量分别为116.3 mAh·g^-1和106.2 mAh·g^-1。研究发现,掺钠可减小首次充放电过程的不可逆容量,提高容量保持率;改善倍率性能与容量恢复特性;降低SEI膜阻抗和电荷转移阻抗;掺钠后样品首次循环就可以基本完成Li₂MnO₃组分向稳定结构的转化,而未掺杂的样品需要两次循环才能逐步完成该过程;XPS结果表明,掺钠样品中Ni²⁺、Co³⁺、Mn⁴⁺所占比例明显提高,改善了样品的稳定性和电化学性能;循环200次后的XRD结果表明掺钠与未掺钠材料在脱嵌锂反应中的相变化过程基本一致,良好有序的层状结构遭到破坏是循环过程中容量衰减的主要原因。     

Synthesis and characterization of a reduced heteropoly-tungstovanadate: (NH4)7[VvO4W 10IV V 2IV O36].ca. 22H2O

The compound (NH₄)₇[ V^vO₄W ₁₀ ^VI V ₂ ^VI O₃₆]·ca.22H₂O (1) has been synthesized from an aqueous ammonium acetate buffer (pH 4) containing sodium vanadate, sodium rungstate_and sodium dithionite. Compound (1) crystallizes in a cubic space groupFm — 3, witha = 22.2001(6) ? and Z = 8. The anion [V^vO₄W ₁₀ ^VI V ₂ ^IV O₃₆]^7- is a typical Keggin type structure with V^VO₄ as the central tetrahedron. (1) has further been characterized by elemental analyses, redox titration, IR, EPR, and electronic spectroscopy and room temperature magnetic moment measurement.     

A synthesis of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates from diethyl dixanthogenate using different oxidants

Abstract  

A novel synthesis of N-alkyl and N,N-dialkyl O-ethyl thiocarbamates from diethyl dixanthogenate and primary and secondary amines, using three oxidizing systems, has been developed on the laboratory scale, and the method using sodium hypochlorite has been applied on a semi-industrial scale. The effect of the oxidizing agents, sodium hypochlorite, in-situ-generated peracetic acid, and the manganese(II) acetate/oxygen system on product purity and yield was studied. The results obtained by use of these three methods were compared with those obtained by reaction of sodium ethyl xanthogenacetate and amines, and of sodium ethyl xanthate with amines in the presence of sulfated nickel zeolite catalyst. The reaction mechanism of sodium hypochlorite oxidation has been established on the basis of isolation of reaction intermediates and determination of their structure by use of Fourier-transform infrared, ¹H and ¹³C NMR, and mass spectrometric methods. The suggested sodium hypochlorite and manganese(II) acetate/oxygen systems have many advantages in comparison with commercial and catalytically promoted synthetic methods, because they are new ecologically friendly syntheses.     

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.     

The short-term cycling properties of Na/PVdF/S battery at ambient temperature

The Na/PVdF/S cells were composed of solid sodium, sulfur, and polyvinylidene fluoride–hexafluoropropene (PVdF) gel polymer electrolyte. The PVdF polymer electrolyte was prepared form tetraglyme plasticizer and NaCF₃SO₃ salt, and its electrochemical properties were studied using CV and impedance analysis. The interfacial resistance between sodium and polymer electrolyte increase with storage time, which might be associated with passivation layer. Solid-state sodium/sulfur cell using a PVdF gel polymer electrolyte has been tested. The Na/PVdF/S cell with 0.288 mA cm^?2 shows a high discharge capacity of 392 mAh g^?1 and 36 mAh g^?1 after 20 cycles. The cycle performance of Na/GPE/S cell operating at 25 °C is worse than Na/S cell at a high temperature.     

Ionic conductivity in Na+, K+, and Ag+ β″-alumina

This paper presents measurements of the ionic conductivity in single crystals of β″-alumina (0.84 M₂O · 0.67 MgO · 5.2 Al₂O₃, M = Na, K, Ag). Single crystals of sodium β″-alumina were grown from a melt of Na₂O, MgO, and Al₂O₃ at 1660 to 1730°C. Selected crystals were converted to the other isomorphs by ion exchange. The conductivity of sodium β″-alumina varies from 0.18 to 0.01 (ohm · cm)^?1 at 25°C depending upon crystal growth conditions. Potassium β″-alumina has the unusually high room temperature conductivity of 0.13 (ohm · cm)^?1. Silver β″-alumina has a slightly lower conductivity, 4 × 10^?3 (ohm · cm)^?1 at 25°C. The activation energies of sodium and potassium β″-alumina decrease with increasing temperature, while that of silver β″-alumina is constant from ?80 to 450°C.     

The flash-photolysis of sodium pyrenide in tetrahydrofuran. On the photo-oxidation process and on the existence of sodium atoms NaO

Evidence is given that the yields of photo-oxidation for free pyrene anions (Π^?) and for anions associated with sodium cations (Π^?Na⁺) in liquid THF and THP are connected to the effective threshold values for the photo- ionization of free and associated pyrene anions. Our experimental results indicate that the phenomena observed by Fisher and Rämme after flash-photolysis of sodium pyrenide in THF which have led to the postulation of transient; sodium atoms Na⁰ may be interpreted as being caused by benzene or toluene negative ions.     

23Na NMR study of ionic mesophases in molten sodium carboxylates

The ²³Na NMR lineshapes are reported for the ionic mesophase and isotropic phase of the melts of sodium n-butyrate and sodium isovalerate. The powder pattern for the central transition typical for the second-order quadrupole effect observed in the mesophase melts is of particular interest. Some analogies to ²³Na behavior in sodium β-alumina are pointed out.     

Solid-state Na and C NMR characterization of Na3C60

Two separate samples of Na₃C₆₀ were prepared by direct reaction of C₆₀ with sodium metal vapor, and subjected to different annealing times of 10 days and 16 days. Solid-state ¹³C and ²³Na NMR, along with elemental analysis, powder X-ray diffraction (XRD) and Raman spectroscopy, were used to characterize both samples. The Raman spectra of both materials have a single peak at 1447 cm⁻¹ which correspond to the A_g peak of C₆₀³⁻, consistent with the stoichiometry of Na_xC₆₀ with x=3. The powder XRD patterns are also virtually identical for both samples. However, solid-state ²³Na and ¹³C NMR spectra of the two samples are significantly different, suggesting a relationship between annealing times and the final structure of the alkali fulleride. Variable-temperature ²³Na magic-angle spinning (MAS) NMR experiments reveal the existence of two or three distinct sodium species and reversible temperature-dependent diffusion of sodium ions between octahedral and tetrahedral interstitial sites. ¹³C MAS NMR experiments are used to identify resonances corresponding to free C₆₀ and fulleride species, implying that the samples are segregated-phase materials composed of C₆₀ and non-stoichiometric Na₃C₆₀. Variable-temperature ¹³C MAS NMR experiments reveal temperature-dependent motion of the fullerides.     

Lithium and sodium N,N′-di(2,6-dialkylphenyl)formamidinate complexes

A study has been undertaken of the lithium and sodium metallation of N,N′-di(aryl)formamidines with alkyl groups at the 2- and 6-aryl position. ¹H NMR and X-ray diffraction data indicate an increase in steric bulk from 2,6-dimethylphenyl to 2,6-diethylphenyl to 2,6-diisopropylphenyl incites incremental changes in amidinate binding and nuclearity. In selected instances, this invokes the first lithium and sodium amidinate/guanidinate complexes to exhibit metal-arene contacts.     

Ion transport in Ca2+, Sr2+, Ba2+, and Pb2+ beta″ aluminas

Single crystals of Ca²⁺, Sr²⁺, Ba²⁺, and Pb²⁺ beta″ alumina were prepared from sodium beta″ alumina by ion exchange. The ionic conductivities of Ca²⁺, Sr²⁺, and Ba²⁺ beta″ alumina are comparable, about 3 × 10^?2 (ohm-cm)^?1 at 300°C. Surprisingly, Pb²⁺ beta″ alumina is much more conductive, 1.5 × 10^?1 (ohm-cm)^?1 at 300°C and 4.6 × 10^?3 (ohm-cm)^?1 at 40°C. Its conductivity approaches that of sodium beta″ alumina at temperatures below 25°C. The diffusion coefficient for Sr²⁺ in beta″ alumina at 600°C was estimated from radiotracer experiments. It is consistent with that expected from conductivity measurements.     

A valence-bond diatomics-in-molecules model for the formation of Na+ and Na2+ ions from the interaction of excited sodium atoms with a tungsten surface

Potential energy surfaces for Na(²S, ²P) interacting with a partially covered tungsten surface are computed within the framework of the method of diatomics-in-molecules (DIM). Only two sodium atoms are considered explicitly but the effect of all of the adsorbed sodium is taken into account through its influence on the fragment matrix elements in the DIM formulation. Na₂⁺ wavefunctions are approximated by valence-bond calculations for the ²Σ_g⁺ and ²Σ_u⁺ manifolds. The three lowest potential energy surfaces of the polyatomic system suggest plausible pathways for the production of Na⁺ and Na₂⁺ ions from the interaction of Na(²P) atoms with the metal surface as observed by Auschwitz and Lacmann.     

One pot synthesis from the elements of symmetrical and unsymmetrical triaryl-phospines, -arsines and -stibines by the SRN1 mechanism

The reactions of elemental phosphorus, arsenic and antimony with sodium metal in liquid ammonia form “M^?1“ species that react with haloarenes under irradiation to form symmetrical triaryl derivatives of these metals by the S_RN1 mechanism in fair to good yields. Further reaction with sodium metal gives a derivative nucleophile (diarylphosphide and diarylarsenide ions) that reacts with another haloarene under irradiation to form unsymmetrical phosphines and arsines.     

Pulse radiolysis of pentacyanonitrosylferrate/II/ ions in aqueous solutions

Pulse radiolysis of aqueous solutions of sodium pentacyanonitrosylferrate/II/ Na₂[Fe/CN/₅NO] /sodium nitroprusside/ was studied in the presence of ethylene glycol as an OH radical scavenger. The rate constants of the one-electron reduction of nitroprusside ion were measured with e _q ^– and with radicals derived from some alcohols /ethylene glycol, ethanol, 2-propanol/ as reducing species. The results show that the transition state for the reduction by alcohol radicals is polar. The only observed product of reduction is the Fe/CN/₅NO^3– ion, which then undergoes a slow dissociation to form Fe/CN/₄NO^2–. Only a small isotope effect k_H/k_D=1.08 was observed in D₂O solutions for the dissociation reaction. This suggests an intramolecular electron transfer as rate-determining step for the dissociation reaction.Dedicated to Professor Schulte-Frohlinde on the occasion of his 60th birthday.     

Study on extraction of cobalt(II) by sodium laurate/pentan-1-ol/heptane/NaCl microemulsion system

A microemulsion consisting of sodium laurate, n-pentanol, n-heptane and NaCl solution was investigated for Co(II) extraction. The dilution method and conductivity method were used for the determination of structural parameters of sodium laurate/pentan-1-ol/heptane/NaCl microemulsion system. Co(II) was found to be extracted into the microemulsion phase due to the compound formation of [CoCl]⁺[R₁₁COO]^?, which was confirmed by the continuous variation of R₁₁COONa concentration. Moreover, the effects of cosurfactant, the contact time, the phase ratios, PH and the NaCl concentration in feed solutions on the cobalt extraction yield were investigated. Under the optimum conditions, the extraction percentage of Co(II) could reach 98.9%.     

Subnitride chemistry: A first-principles study of the NaBa3N, Na5Ba3N, and Na16Ba6N phases

An ab initio study on the electronic structure of the subnitrides NaBa₃N, Na₅Ba₃N, and Na₁₆Ba₆N is performed for the first time. The NaBa₃N and Na₅Ba₃N phases consist of infinite ¹_∞[NBa_6/2] strands composed of face-sharing NBa₆ octahedra surrounded by a “sea” of sodium atoms. The Na₁₆Ba₆N phase consist of discrete [NBa₆] octahedra arranged in a body-cubic fashion, surrounded by a “sea” of sodium atoms. Our calculations suggest that the title subnitrides are metals. Analysis of the electronic structure shows partial interaction of N(2s) with Ba(5p) electrons in the lower energy region for NaBa₃N and Na₅Ba₃N. However, no dispersion is observed for the N(2s) and Ba(5p) bands in the cubic phase Na₁₆Ba₆N. The metallic band below the Fermi level shows a strong mixing of N(2p), Ba(6s), Ba(5d), Ba(6p), Na(3s) and Na(3p) orbitals. The metallic character in these nitrides stems from delocalized electrons corresponding to hybridized 5d^l6s^m6pⁿ barium orbitals which interact with hybridized 3sⁿ3p^m sodium orbitals. Analysis of the electron density and electronic structure in these nitrides shows two different regions: a metallic matrix corresponding to the sodium atoms and the regions around them and heteropolar bonding between nitrogen and barium within the infinite ¹_∞[NBa_6/2] strands of the NaBa₃N and Na₅Ba₃N phases, and within the isolated [NBa₆] octahedra of the Na₁₆Ba₆N phase. The nitrogen atoms inside the strands and octahedra are negatively charged, the anionic character of nitrogens being larger in the isolated octahedra of the cubic phase Na₁₆Ba₆N, due to the lack of electron delocalization along one direction as opposed to the other phases. The sodium and barium atoms appear to be slightly negatively and positively charged, the latter to a larger extent. From the computed Ba-N overlap populations as well as the analysis of the contour maps of differences between total density and superposition of atomic densities, we suggest partial covalent bonding between nitrogen and barium atoms along the infinite ¹_∞[NBa_6/2] strands and within isolated [NBa₆] octahedra.     

长循环高电压钠离子电池正极材料P2-Na2/3Mn1/3Bi1/3Ni1/3O2的合成及性能

镍基层状氧化物NaNiO₂钠离子电池材料具有高电压和高容量的特性,且制备方法较为简单,但姜-泰勒(Jahn-Teller)效应使其在高倍率循环下容量较低以及在高电压(4.5 V)下无法稳定循环。通过调节溶胶-凝胶工艺的条件,设计、合成了Na_2/3Mn_1/3Bi_1/3Ni_1/3O₂片层状金属氧化物,并将其作为正极活性材料,在空气环境中组装成钠离子电池,进行电化学测试,考察Bi、Mn掺入量对电池电化学影响。研究结果表明：当金属Mn和Bi共掺时,在1.2~4.5 V宽电压范围内,电池在循环50周后容量为90.39 mAh·g^-1。在2.0~4.0 V电压范围内1.0C (115 mA·g^-1)倍率下恒流充放电50周后的容量保持率为96.96%,循环850周后的保持率为80.15%,具有良好的循环稳定性和安全性。     

长循环高电压钠离子电池正极材料P2-Na2/3Mn1/3Bi1/3Ni1/3O2的合成及性能

镍基层状氧化物NaNiO₂钠离子电池材料具有高电压和高容量的特性,且制备方法较为简单,但姜-泰勒(Jahn-Teller)效应使其在高倍率循环下容量较低以及在高电压(4.5 V)下无法稳定循环。通过调节溶胶-凝胶工艺的条件,设计、合成了Na_2/3Mn_1/3Bi_1/3Ni_1/3O₂片层状金属氧化物,并将其作为正极活性材料,在空气环境中组装成钠离子电池,进行电化学测试,考察Bi、Mn掺入量对电池电化学影响。研究结果表明：当金属Mn和Bi共掺时,在1.2~4.5 V宽电压范围内,电池在循环50周后容量为90.39 mAh·g^-1。在2.0~4.0 V电压范围内1.0C (115 mA·g^-1)倍率下恒流充放电50周后的容量保持率为96.96%,循环850周后的保持率为80.15%,具有良好的循环稳定性和安全性。     

N-(Trifluoromethylsulfonyl)trifluoromethanesulfinimidic acid and its salts

Lithium, sodium and potassium N-(trifluoromethylsulfonyl)trifluoromethanesulfinimidates were obtained by the reaction of the corresponding sulfinimidoyl chloride with alkali metal trimethylsilanolates. The potassium and sodium salts were converted to the free acid, having predominantly the amidic tautomeric structure, CF₃S(O)NHSO₂CF₃, by treatment with concentrated H₂SO₄ or with H⁺-cationite.