Influences of melt spinning on electrochemical hydrogen storage performance of nanocrystalline and amorphous Mg2Ni-type alloys

In order to improve the electrochemical hydrogen storage performance of the Mg₂Ni-type electrode alloys, Mg in the alloy was partially substituted by La, and the nanocrystalline and amorphous Mg₂Ni-type Mg_20−x La _x Ni₁₀ (x=0, 2) alloys were synthesized by melt-spinning technique. The microstructures of the as-spun alloys were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical hydrogen storage properties of the experimental alloys were tested. The results show that no amorphous phase is detected in the as-spun Mg₂₀Ni₁₀ alloy, but the as-spun Mg₁₈La₂Ni₁₀ alloy holds a major amorphous phase. As La content increases from 0 to 2, the maximum discharge capacity of the as-spun (20 m/s) alloys rises from 96.5 to 387.1 mA·h/g, and the capacity retaining rate (S ₂₀) at the 20th cycle grows from 31.3% to 71.7%. Melt-spinning engenders an impactful effect on the electrochemical hydrogen storage performances of the alloys. With the increase in the spinning rate from 0 to 30 m/s, the maximum discharge capacity increases from 30.3 to 135.5 mA·h/g for the Mg₂₀Ni₁₀ alloy, and from 197.2 to 406.5 mA·h/g for the Mg₁₈La₂Ni₁₀ alloy. The capacity retaining rate (S ₂₀) of the Mg₂₀Ni₁₀ alloy at the 20th cycle slightly falls from 36.7% to 27.1%, but it markedly mounts up from 37.3% to 78.3% for the Mg₁₈La₂Ni₁₀ alloy.     

Electrochemical performance of LiFePO4/（C＋Fe2P） composite cathode material synthesized by sol-gel method

A LiFePO4/(C+Fe2P) composite cathode material was prepared by a sol-gel method using Fe(NO3)3·9H2O,LiAc·H2O,NH4H2PO4 and citric acid as raw materials,and the physical properties and electrochemical performance of the composite cathode material were investigated by X-ray diffractometry(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM) and electrochemical tests.The Fe2P content,morphology and electrochemical performance of LiFePO4/(C+Fe2P) composite depend on the calcination tempera...     

尖晶石型锰酸锂的复合掺杂改性

以固相烧结法制备的尖晶石型锰酸锂为基础,对其结构中掺杂复合非金属元素B和F,合成了B、F掺杂的尖晶石。通过X射线衍射、扫描电镜、电化学分析方法对试样的晶体结构、表面形貌及电化学性能进行表征。结果表明,采用B、F包覆的锰酸锂与纯锰酸锂的X射线衍射结果相似,波峰尖锐且峰值高;随着B的掺入,尖晶石作为正极材料充放电的循环性能得到了提高,但是其初始容量较低,仅为102.3mA·h/g。随着加入复合非金属元素B和F,样品的初始容量提高到了110.9mA·h/g,50次循环后的容量保持率为83.14%。实验结果表明,复合掺杂有效提高了锰酸锂的电化学性能。     

Modification of natural graphite using pitch through dynamical melt-carbonization

The graphite was modified using pitch through dynamical melt-carbonization, and the effects of modification temperature and the amount of pitch on the characteristics of graphite were investigated. The structure and characteristics of the graphite were determined by X-ray diffractometry(XRD), scanning electron microscopy(SEM), particle size analysis and electrochemical measurements. The results show that the modified graphite has a disordered carbon/graphite composite structure, larger average particle diameter, greater tap density, and better electrochemical characteristics than the untreated graphite. The sample coated with 10% pitch dynamical melt-carbonized at 400 ℃ for 3 h and heat-treated at 850 ℃ for 2 h has better electrochemical performances with a reversible capacity of 360.5 mA·h/g, a irreversible capacity of 41.0 mA·h/g, and an initial coulombic efficiency of 89.8% compared with natural graphite and disordered carbon. The cycling stability of the Li/C cell with modified graphite as anodes is improved, and its capacity retention ratio at the 30th cycle is up to 94.37%.     

Influence of Temperature on Electrochemical Performances of Rare Earth Based Hydrogen Storage Material

1 IntroductionRare earth-based hydrogenstorage alloys ofAB5typehave beenthe most major electrode material for small-sizeNi/MHbatteries because of their high discharge capacity,superior highrate capability andfavorable ratio of pricetoperformance. But their electrochemical performances be-come worse when the alloys are applied to large-size Ni/MHbatteries of electric vehicles .Thisfact may be due tothe rising of temperature inside the large batteries causedbythe high electric current of char…     

Nanostructure and formation mechanism of Pt-WO<Subscript>3</Subscript>/C nanocatalyst by ethylene glycol method

Pt-WO3 nanoparticles uniformly dispersed on Vulcan XC-72R carbon black were prepared by an ethylene glycol method.The morphology,composition,nanostructure,electrochemical characteristics and electrocatalytic activity were characterized,and the formation mechanism was investigated.The average particle size was 2.3 nm,the same as that of Pt/C catalyst.The W/Pt atomic ratio was 1/20,much lower than the design of 1/3.The deposition of WO3·xH2O nanoparticles on Vulcan XC-72R carbon black was found to be very difficult by TEM.From XPS and XRD,the Pt nanoparticles were formed in the colloidal solution of Na2WO4,the EG insoluble Na2WO4 resulted in the decreased relative crystallinity and increased crystalline lattice constant compared with those of Pt/C catalyst and,subsequently,the higher specific electrocatalytic activity as determined by CV.The Pt-mass and Pt-electrochemically-active-specific-surface-area based anodic peak current densities for ethanol oxidation were 422.2 mA·mg-1Pt and 0.43 mA·cm-2Pt,1.2 and 1.1 times higher than those of Pt/C catalyst,respectively.     

Synthesis and characterization of triclinic structural LiVPO4F as possible 4.2 V cathode materials for lithium ion batteries

A potential 4.2 V cathode material LiVPO4F for lithium batteries was prepared by two-step reaction method based on a carbon-thermal reduction （CTR） process. Firstly, V2O5, NH4H2PO4 and acetylene black are reacted under an Ar atmosphere to yield VPO4. The transition-metal reduction is facilitated by the CTR based on C→CO transition. These CTR conditions favor stabilization of the vanadium as V^3＋ as well as leaving residual carbon, which is useful in the subsequent electrode processing. Secondly, VPO4 reacts with ElF to yield LiVPO4F product. The property of the LiVPO4F was investigated by X-ray diffractometry （XRD）, scanning electron microscopy （SEM） and electrochemical measurement. XRD studies show that LiVPO4F synthesized has triclinic structure（space group p I ）, isostructural with the naturally occurring mineral tavorite, EiFePO4-OH. SEM image exhibits that the particle size is about 2μm together with homogenous distribution. Electrochemical test shows that the initial discharge capacity of LiVPO4F powder is 119 mA·h/g at the rate of 0.2C with an average discharge voltage of 4.2V （vs Ei/Li^＋）, and the capacity retains 89 mA·h/g after 30 cycles.     

多孔五氧化二铌球的合成及其电化学性能研究

以表面活性剂CTAB为模板,通过水热法及煅烧过程合成了多孔Nb_2O_5微球。对所得产品的表征和电化学性能测试结果表明:合成了正交结构的Nb_2O_5球,且其单分散性能较好,直径为900 nm左右,球上分布有很多孔径为2~70 nm的小孔,形成了独特的多孔结构,该结构增加了材料的比表面积,其比表面积为340 m~2/g。独特的多孔结构和较大的比表面积使得其作为锂离子电池负极材料时表现出优异的电化学性能:首次容量较高,多孔Nb_2O_5球的首次充放电容量分别为297.8和395.9 m A·h·g~(-1);循环性能稳定,在电流密度为20 m A/g下充放电时,第3次循环后的库伦效率几乎达到100%;倍率性能优异,在50,100 m A/g电流密度下,经过20次循环后的容量分别为139.6,117.1 m A·h·g~(-1),容量保持率都为90%以上。     

Synthesis and electrochemical properties of Cr-doped Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> cathode materials for lithium-ion batteries

Cr-doped Li₃V₂(PO₄)₃ cathode materials Li₃V_2−x Cr _x (PO₄)₃ were prepared by a carbothermal reduction(CTR) process. The properties of the Cr-doped Li₃V₂(PO₄)₃ were investigated by X-ray diffraction (XRD), scanning electron microscopic (SEM), and electrochemical measurements. Results show that the Cr-doped Li₃V₂(PO₄)₃ has the same monoclinic structure as the undoped Li₃V₂(PO₄)₃, and the particle size of Cr-doped Li₃V₂(PO₄)₃ is smaller than that of the undoped Li₃V₂(PO₄)₃ and the smallest particle size is only about 1 μm. The Cr-doped Li₃V₂(PO₄)₃ samples were investigated on the Li extraction/insertion performances through charge/discharge, cyclic voltammogram (CV), and electrochemical impedance spectra(EIS). The optimal doping content of Cr was that x=0.04 in the Li₃V_2−x Cr _x (PO₄)₃ samples to achieve high discharge capacity and good cyclic stability. The electrode reaction reversibility was enhanced, and the charge transfer resistance was decreased through the Cr-doping. The improved electrochemical performances of the Cr-doped Li₃V₂(PO₄)₃ cathode materials are attributed to the addition of Cr³⁺ ion by stabilizing the monoclinic structure. Funded by the Guangxi Natural Science Foundation(No. 0832259) and the National Basic Research Program of China (No. 2007CB613607)     

Graphene as a high-capacity anode material for lithium ion batteries

Graphene was produced via a soft chemistry synthetic route for lithium ion battery applications. The sample was characterized by X-ray diffraction, nitrogen adsorption-desorption, field emission scanning electron microscopy and transmission electron microscopy, respectively. The electrochemical performances of graphene as anode material were measured by cyclic voltammetry and galvanostatic charge/discharge cycling. The experimental results showed that the graphene possessed a thin wrinkled paper-like morphology and large specific surface area (342 m²·g^?1). The first reversible specific capacity of the graphene was as high as 905 mA·h·g^?1 at a current density of 100 mA·g^?1. Even at a high current density of 1000 or 2000 mA·g^?1, the graphene maintained good cycling stability, indicating that it is a promising anode material for high-performance lithium ion batteries.     

锂离子电池负极材料多孔硅/硅铁合金的制备及性能

为改善锂离子电池硅负极材料的电化学性能,利用镁热还原法制备了不同铁掺杂量的多孔硅/硅铁合金复合材料,并对其结构以及在锂离子电池中的充放电性能进行了研究.材料均呈现多孔结构,硅铁合金均匀分布在孔道内部.多孔硅/硅铁合金复合材料具有较好的循环稳定性,在0.1C倍率下循环100圈后可逆容量为1 133.5 m A·h/g,容量保持率为66%;在1C倍率下可逆容量仍可以达到776.9 m A·h/g.     

Optimizing pyrolysis of resin carbon for anode of lithium ion batteries

1INTRODUCTION Lithiumionbatterieshaveattractedworldwide attentionandbeendevelopedrapidlyduetotheirhighenergydensity,goodcharge dischargeper formancesandlongcyclelife[14].Theseoutstand ingpropertiesresultfromtheuseofcarbonmateri alsasanodeinsteadoflithiummetal.However,thespecificcapacityofcarbonmaterialsisfar smallerthanthatoflithiummetal(3670mA·h/g).Muchefforthasbeenfocusedonimprovingca pacityofcarbonanodesduringthepastfew years[57].Recentworkindicatedthatdisorderedcar bons,obtainedbypy…     

Theoretical calculation and experimental study of influence of oxygen vacancy on the electronic structure and hemocompatibility of rutile TiO2

In this work, the relationship between electronic structure and hemocompatibility of oxygen deficient rutile TiO_2?x was studied by both theoretical calculation and experimental study. Based on the local density functional theory, first-principals method was performed to calculate the electronic structure of rutile TiO₂ with different oxygen vacancy concentration. In the range of less than 10% of (or equal) physically realistic O vacancy concentration, the band gap of rutile TiO₂ increases with increasing O vacancy concentration, leading the TiO₂ changes from a p-type to an n-type semiconductor. The valance band of TiO₂ is predominated by O 2p orbital, while the conduction band is occupied by Ti 3d orbital for different O vacancy concentration. The O vacancy results in the occupation of electrons at the bottom of conduction band of TiO₂, and the donor density increases with increasing O vacancy concentration. When materials come in contact with blood, the n-type semiconductor feature of oxygen deficient TiO_2?x with the bottom of conduction band occupied by electrons would prevent charge transfer from fibrinogen into the surface of materials, thus inhibiting the aggregation and activation of platelets, therefore improving the hemocompatibility of rutile TiO_2-x .

     

Preparation and electrochemical properties of Co3O4/graphite composites as anodes of lithium ion batteries

Co₃O₄/graphite composites were synthesized by precipitation of cobalt oxalate on the surface of graphite and pyrolysis of the precipitate, and the effects of graphite content and calcination temperature on the electrochemical properties of the composites were investigated. The samples were characterized by thermogravimetry and differential thermal analysis (TG/DTA), X-ray diffractometry (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and charge/discharge measurements. With increasing the graphite content, the reversible capacity of the Co₃O₄/graphite composites decreases, while cycling stability improves dramatically, and the addition of graphite obviously decreases the average potential of lithium intercalation/deintercalation. The reversible capacity of the composites with 50% graphite rises from 583 to 725 mA·h/g as the calcination temperature increases from 300 to 500 °C, and the Co₃O₄/graphite composites synthesized at 400 °C show the best cycling stability without capacity loss in the initial 20 cycles. The CV profile of the composite presents two couples of redox peaks, corresponding to the lithium intercalaction/deintercalation for graphite and Co₃O₄, respectively. EIS studies indicate that the electrochemical impedance decreases with increasing the graphite content.     

Theoretical calculation and experimental study of influence of oxygen vacancy on the electronic structure and hemocompatibility of rutile TiO2

In this work, the relationship between electronic structure and hemocompatibility of oxygen deficient rutile TiO_2−x was studied by both theoretical calculation and experimental study. Based on the local density functional theory, first-principals method was performed to calculate the electronic structure of rutile TiO₂ with different oxygen vacancy concentration. In the range of less than 10% of (or equal) physically realistic O vacancy concentration, the band gap of rutile TiO₂ increases with increasing O vacancy concentration, leading the TiO₂ changes from a p-type to an n-type semiconductor. The valance band of TiO₂ is predominated by O 2p orbital, while the conduction band is occupied by Ti 3d orbital for different O vacancy concentration. The O vacancy results in the occupation of electrons at the bottom of conduction band of TiO₂, and the donor density increases with increasing O vacancy concentration. When materials come in contact with blood, the n-type semiconductor feature of oxygen deficient TiO_2−x with the bottom of conduction band occupied by electrons would prevent charge transfer from fibrinogen into the surface of materials, thus inhibiting the aggregation and activation of platelets, therefore improving the hemocompatibility of rutile TiO_2-x . Supported by the National Basic Research Program of China (Grant No. 2005CB623904), National High-Tech Research Program of China (Grant No. 2006AA02A139) and National Natural Science Foundation of China (Grant No. 20603027)     

Preparation and microstructure characterization of poly-sialate-disiloxo type of geopolymeric cement

In order to investigate the influence of three key molar ratios (n(SiO₂)/n(Al₂O₃), n(K₂O)/n(Al₂O₃) and n(H₂O)/n(K₂O)), a total of nine potassium poly-sialate-disiloxo (K-PSDS) geopolymeric cement matrices were designed according to orthogonal design principle. Subsequently, XRD, ESEM-EDXA and MAS-NMR techniques were employed to further characterize the microstructure of the most fully reacted geopolymeric cement matrix. The experimental results show that n(K₂O)/n(Al₂O₃) has the most significant effect on compressive strength amongst the three ratios. The highest compressive strength (20.1 MPa) can be achieved when n(SiO₂)/n(Al₂O₃)=6.5, n(K₂O)/n(Al₂O₃)=0.8 and n(H₂O)/n(K₂O)=10.0. The FTIR spectra of nine PSDS geopolymeric cement matrices also indicate that geopolymeric cement matrix with the highest strength is the most fully reacted one and possesses the largest amount of geopolymeric cement products. The microscopic analysis reveals that PSDS geopolymeric cement matrix possesses structural characteristics similar to gel substances in having a wide range of Si endowments, but predominantly the framework molecular chains of Si partially replaced by 4-coordinated Al tetrahedral.     

Electronic band structures of TiO<Subscript>2</Subscript> with heavy nitrogen doping

The first-principles density-functional calculation was conducted to investigate the electronic band structures of titanium dioxide with heavy nitrogen doping （TiO2-xNx）.The calculation results indicate that when x≤0.25,isolated N 2p states appear above the valence-band maximum of TiO2 without a band-gap narrowing between O 2p and Ti 3d states.When x≥0.50,an obvious band gap narrowing between O 2p and Ti 3d states was observed along with the existence of isolated N 2p states above the valence-band of TiO2,indicating that the mechanism proposed by Asahi et al operates under heavy nitrogen doping condition.     

The mechanism of ground granulated blastfurnace slag preventing alkali aggregate reaction

Three different methods were applied to study the alkali content of gelpores in cement. In the closed system, the concentration of K⁺, Na⁺ and OH⁻ have not reduced with the increase of age. In the open system, the diffusion and transferring of K⁺ and Na⁺ towards free space leads to the decrease of total alkali content. In the micro-analysis system, the contents of K⁺ and Na⁺ in the first hydrated layer of ground granulated blastfurnace slag (GBFS) are very low, while the contents of calcium and magnesium are relatively high. This phenomenon shows that the mechanism of GBFS preventing alkali aggregate reaction (AAR) is: when GBFS is dissolved by alkali medium, SiO₂ and Al₂O₃ are dissolved into the cement matrix, then around GBFS particles form reaction rings rich in Ca²⁺ and Mg²⁺, and the C-S-H gel of positive charges formed in the area repulses K⁺ and Na⁺, which are forced to transfer to the mortar’s matrix, pore or mortar sample surface. The transferred K⁺ and Na⁺ form alkali gel products with other dissolved ions, then become evenly distributed in the mortar sample and react with Ca(OH)₂ in pore solutions to form (Na,K) _x−2z ·zCa·(SiO₂)_y·(OH)_x gel products; and thus changes the AAR gel products’ structure. The gel products will not expand, and so they can delay expansion destruction.     

Electroless copper plating process of N, N, N′, N′-tetrakis (2-hydroxypropyl) ethylenediamine system with high plating rate

Electroless copper plating process of N, N, N′, N′-tetrakis (2-hydroxypropyl) ethylenediamine (THPED) chelating agent was researched comprehensively. The results indicate that plating rate decreases with the increase of concentration for THPED, CuSO₄ · 5H₂O and HCHO, pH value and bath temperature. The additive of K₄[Fe(CN)₆] · 3H₂O, 2, 2′-dipyridyl and polyethylene glycol(PEG) decrease plating rate and K₄[Fe(CN)₆] · 3H₂O has a bad effect on deposits quality, but 2, 2′-dipyridyl and PEG make deposits quality improve greatly. Low concentration of 2-mercaptobenzothiozole (2-MBT) increases plating rate and improves deposits quality, but decreases plating rate and worsens deposits quality when 2-MBT reaches 5 mg/L. The optimal conditions of this electroless copper plating process are that the concentration of THPED, HCHO, CuSO₄ · 5H₂O, PEG, 2, 2′-dipyridyl and 2-MBT are 16.8 g/L, 16.0 mL/L, 13.3 g/L, 0.5 g/L, 5.0 mg/L and 2.0 mg/L, respectively, pH value is 12.75, bath temperature is 30 °C. Plating rate reaches 9.54 μm/h plating for 30 min in the bath. The SEM images demonstrate that the surface of copper film is smooth and the crystal is fine. Foundation item: Project supported by Hubei Daye Nonferrous Metal Corporation of China     

Microstructures and Electrical Properties of Bi_(0.5)-(Na_(1-x-y)K_xLi_y)_(0.5)TiO_3 Lead-free Piezoelectric Ceramics

The microstructures and electrical properties of Bi0.5(Na1-x-yKxLiy)0.5TiO3 lead-free piezoelectric ceramics were studied.These ceramics were prepared by conventional ceramic technique.XRD analysis reveals that the ceramics possess almost pure perovskite phase when y≤0.2.The SEM results show that,with more amounts of Li+,the crystalline grain growing speed is accelerated,and the sintering temperature can effectively be decreased.The measurements of piezoelectric properties indicate that the ceramics with relatively low amount of Li+ and high amount of K+ have comparatively large piezoelectricity.The dielectric measurements show that the ceramics have properties like relaxor ferroelectrics and diffuse phase transition(DPT) at Td and Tc,respectively.The results of ferroelectric measurements reveal the system has relatively higher remanent polarization Pr(27.6 μC/cm2) and lower coercive field Ec(37.5 kV/cm).