Concentrated dual-salt electrolytes for improving the cycling stability of lithium metal anodes

Lithium(Li) metal is an ideal anode material for rechargeable Li batteries, due to its high theoretical specific capacity(3860 mAh/g), low density(0.534 g/cm~3), and low negative electrochemical potential(-3.040 V vs. standard hydrogen electrode). In this work, the concentrated electrolytes with dual salts, composed of Li[N(SO_2F)_2](Li FSI) and Li[N(SO_2CF_3)_2](Li TFSI) were studied. In this dual-salt system, the capacity retention can even be maintained at 95.7%after 100 cycles in Li|Li FePO_4 cells. A Li|Li cell can be cycled at 0.5 mA/cm~2 for more than 600 h, and a Li|Cu cell can be cycled at 0.5 m A/cm~2 for more than 200 cycles with a high average Coulombi efficiency of 99%. These results show that the concentrated dual-salt electrolytes exhibit superior electrochemical performance and would be a promising candidate for application in rechargeable Li batteries.     

Enhanced ionic conductivity in LAGP/LATP composite electrolyte

Nasicon materials(sodium superionic conductors) such as Li_(1.5)Al_(0.5)Ge_(1.5)(PO_4)_3(LAGP) and Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3(LATP) have been considered as important solid electrolytes due to their high ionic conductivity and chemical stability.Compared to LAGP, LATP has higher bulk conductivity around 10~(-3) S/cm at room temperature; however, the apparent grain boundary conductivity is almost two orders of magnitude lower than the bulk, while LAGP has similar bulk and grain boundary conductivity around the order of 10~(-4) S/cm. To make full use of the advantages of the two electrolytes, pure phase Li_(1.5)Al_(0.5)Ge_(1.5)(PO_4)_3 and Li_(1.4)Al_(0.4)Ti_(1.6)(PO_4)_3 were synthesized through solid state reaction, a series of composite electrolytes consisting of LAGP and LATP with different weight ratios were designed. XRD and variable temperature AC impedance spectra were carried out to clarify the crystal structure and the ion transport properties of the composite electrolytes. The results indicate that the composite electrolyte with the LATP/LAGP weight ratio of 80:20 achieved the highest bulk conductivity which shall be due to the formation of solid solution phase Li1.42 Al0.42 Ge0.3 Ti1.28(PO4)3, while the highest grain boundary conductivity appeared at the LATP/LAGP weight ratio of 20:80 which may be due to the excellent interfacial phase between Li_(1+x)Al_xGe_yTi_(2-x-y)(PO_4)_3/LATP. All the composite electrolytes demonstrated higher total conductivity than the pure LAGP and LATP, which highlights the importance of heterogeneous interface on regulating the ion transport properties.     

Effect of Fluorine Substitution on the Electrochemical Property and Structural Stability of a Lithium-Excess Cation Disordered Rock-Salt Cathode

Lithium-excess cation disordered rock-salt materials have received much attention because of their high-capacity as a candidate for cathodes for lithium-ion batteries.The ultra-high specific capacity comes from the coordinated charge compensation of both transition metal and lattice oxygen.However,the oxygen redox at high voltage usually leads to irreversible oxygen release,thereby degrading the structure stability and electrochemical performance.Lithium-excess Li_(1.14)Ni_(0.57+0.5 x)Ti_(0.19-0.5 x)Mo_(0.10)O_(2-x)F_x(x=0,0.05,0.10,0.15,and 0.20) with different amounts of fluorine substitution were synthesized.Among them,Li_(1.14)Ni_(0.62 o)Ti_(0.140)Mo_(0.10)O_(1.85)F_(0.15)exhibits a lower capacity decline,better rate performance,and lower structure damage.The effects of fluorine substitution on the electrochemical property and structural stability were systematic studied by x-ray photoelectron spectroscopy and in situ XRD etc.Results show that fluorine substitution reduces the average valence of the anion,allowing a larger proportion of low-valent redox active transition metals,increasing the transition metal redox capacity,inhibiting irreversible oxygen release and side reaction.Fluorine substitution further improves the structural stability and suppresses lattice deformation of the material.     

KOH activated carbon fabrics as supercapacitor material

Carbon fabrics from viscose fibers activated with KOH have been investigated as possible electrode materials for electrochemical capacitors. The fibers were first pyrolysed at 400 or 600 °C, then saturated with KOH at C/KOH ratios from 1:3.5 to 1:5 and treated in the temperature range from 700 to 800 °C. The carbon fibers saturated with KOH were analysed by thermogravimetric and differential thermal analysis in order to get information on the temperature dependence of the KOH reaction with carbon. The electrochemical properties of the activated carbons were determined using three-electrode Swagelok^® type capacitors both in 4 M H₂SO₄ and 7 M KOH aqueous electrolytes. Specific capacities of ca. 340 and 270 F/g were determined in acidic and alkaline medium, respectively. We demonstrate that the electrical capacity for both negative and positive electrodes depends on the treatment method. The capacitance values are discussed taking into account the porous texture, the elemental composition and the surface functionality of the activated carbon fibers.     

Effect of the surface treatment of the TiO2 fillers on the properties of hexanoyl chitosan/polystyrene blend-based composite polymer electrolytes

Surface treatment of TiO₂ was done by immersing filler particles in 2 and 4 % sulphuric acid (H₂SO₄) aqueous solutions. Untreated, 2 and 4 % H₂SO₄-treated TiO₂ were referred as neutral, weakly acidic, and acidic TiO₂, respectively. Composite polymer electrolytes (CPEs) based on hexanoyl chitosan–polystyrene blend were prepared by using lithium trifluromethanesulfonate (LiCF₃SO₃) as the doping salt and three different types of the TiO₂ fillers. X-ray diffraction (XRD) results showed that the addition of TiO₂ reduced the crystalline fraction of the electrolytes. The conductivity performance of the CPEs varied in the order: acidic?<?weakly acidic?<?TiO₂ free?<?neutral TiO₂. A model based on the interaction between Lewis acid–base sites of TiO₂ with ionic species of LiCF₃SO₃ has been proposed to understand the conductivity mechanism brought about by the different types of fillers. The conductivity enhancement by neutral TiO₂ is attributed to the increase in the mobility of Li⁺ cations. Acidic TiO₂ decreased the conductivity by decreasing the anionic contribution. The conductivity variation with filler content was discussed on the basis of the number of free ions.     

Capacitance properties of poly(3,4-ethylenedioxythiophene)/carbon nanotubes composites

The electrochemical properties of composites prepared from an electrically conducting polymer poly(3,4-ethylenedioxythiophene), i.e. PEDOT and multiwalled carbon nanotubes (CNTs) have been investigated for supercapacitor application. The novel composite material was prepared by chemical or electrochemical polymerization of EDOT directly on the nanotubes or from a homogenous mixture of PEDOT and CNTs. Acetylene black (AB) has been also used as a composite component in order to evaluate whether nanotubes are giving improved properties or not. Electrodes prepared from such composites were used in supercapacitors operating in acidic (1 M H₂SO₄), alkaline (6M KOH) and organic (1 M TEABF₄ in AN) electrolytic solutions. The capacitance values were estimated by galvanostatic, voltammetry and impedance spectroscopy techniques with two- or three-electrode cell configuration. Due to the open mesoporous network of nanotubes, the easily accessible electrode/electrolyte interface allows quick charge propagation in the composite material and an efficient reversible storage of energy in PEDOT during subsequent charging/discharging cycles. The composites with AB supply quite good capacitance results, however, nanotubes as electrode component gave definitively a more homogenous dispersion of PEDOT that should give a better charge propagation. The values of capacitance for PEDOT/carbon composites ranged from 60 to 160 F/g and such material has a good cycling performance with a high stability in all the electrolytes. Organic medium is especially interesting because of higher energy stored. Another quite important advantage of this composite is its significant volumetric energy because of the high density of PEDOT.     

Effect of electrodeposition modes on ruthenium oxide electrodes for supercapacitors

With developments in energy storage devices, supercapacitors are gaining more attraction because of their potential to excel batteries shortly. In this work, ruthenium oxide (RuO₂) has been deposited on stainless steel and studied the influence of surface modification of solid electrodes on capacitance properties. Hydrous ruthenium oxide was plated by different modes such as potential sweep method (cyclic voltammetric), constant potential method (chronoamperometry) and optimised potential pulse method using a recently reported precursor material namely ruthenium nitrosylsulfate (RuNS). The structural information and morphology of electrodeposits were characterised by X-ray diffractometer and scanning electron microscope respectively. The XRD studies indicate a poor crystalline state for RuO₂ in all the modes of deposition but can contribute to a higher surface area when compared to a highly crystalline form. The SEM analysis revealed the formation of surface modification concerning the change of potential mode. Mud-cracked morphology, spherical particles and dendrimeric morphology observed on chronoamperometry, potential pulse and cyclic voltammetry respectively. Electrochemical studies were also conducted on the samples to assess their performance for supercapacitor applications. The spherical particles of hydrous RuO₂ show high performance of capacitance behaviour 1180 F/g in 0.5 M H₂SO₄ at the scan rate of 5 mV/s. Dendrimeric morphology and mud-cracked morphology shows 573 F/g and 546 F/g respectively in same 0.5 M H₂SO₄ at the scan rate of 5 mV/s. The studies reveal that RuO₂ electrodes can be exploited for their outstanding capacitive behaviour by properly controlling the morphology of the deposits.     

Electrochemical behavior of nanostructured LiV3O8 in aqueous LiNO3 solution

Despite the large number of studies on the electrochemical behavior of LiV₃O₈ as a cathode material in nonaqueous lithium ion batteries, little information is available about the electrochemical behavior of LiV₃O₈ as an anode material in aqueous rechargeable lithium batteries. In this work, nanostructured LiV₃O₈ is successfully prepared using a low-temperature solid-state method. The electrochemical properties of the LiV₃O₈ electrode in 1 M, 5 M, and saturated LiNO₃ aqueous electrolytes have been characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge experiments. The results show that LiV₃O₈ electrode in saturated LiNO₃ electrolyte exhibits good electrochemical performance in terms of specific capacity and electrochemical cycling performance. LiV₃O₈ electrode can be reversibly cycled in saturated LiNO₃ aqueous electrolyte for 300 cycles at a rate of 0.5 C (300 mA g⁻¹ is assumed to be 1 C rate) with impressive specific capacities.     

Investigation of electrochemical performance of MgNiO2 prepared by sol-gel synthesis route for aqueous-based supercapacitor application

In this work, we have successfully synthesized MgNiO₂ using a sol-gel wet chemical synthesis technique named MNO - 3. Electrochemical measurements in the presence of aqueous 1 M Li₂SO₄ electrolyte indicate that MNO - 3 samples exhibit a capacitance value of about 30 F/g and an energy density of about 20 Wh/kg. Subsequently, in the experiment involving aqueous 0.5 M Na₂SO₄ electrolyte system, it has been found that the capacitance for MNO - 3 sample is about 34 F/g and the energy density is about 23 Wh/kg for MNO - 3 sample. Finally, in the presence of aqueous-based 1 M Mg(ClO₄)₂ electrolyte, MNO - 3 sample is found to exhibit a capacitance of about 26 F/g and an energy density of about 17 Wh/kg, respectively. In all three electrolyte systems, the MNO -3 sample exhibit a long cycle capacitance retention of greater than 85% for 1000 charge-discharge cycles.     

Chemical synthesis of nano-porous ruthenium oxide (RuO2) thin films for supercapacitor application

Ruthenium oxide (RuO₂) thin films have been prepared using single step chemical method containing Ru(III) Cl₃ solution in an aqueous medium at low temperature. The structural, morphological and optical properties have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and optical absorption technique. The XRD study revealed the formation of amorphous RuO₂ thin film. The surface examination by SEM showed formation of nano-porous material on the substrate. The TEM study revealed the formation of nanostructured material. The optical absorption studies showed the presence of direct band transition with band gap equal to 2.2 eV. The RuO₂ has proved its applicability in supercapacitor showing 50 F/g specific capacitance in 0.5 M H₂SO₄ at 20 mV/s scan rate.     

Solubility and Critical Phenomena in Ternary Aqueous Solutions Containing Type-2 Salt and Alkali

Supercritical phase equilibria in the ternary system K₂SO₄–KOH–H₂O at 420–500°C and up to 130 MPa pressure with binary boundary subsystems of different types are studied. The binary subsystem of type 1 features no critical phenomena in saturated (l = g) aqueous solution and no phase separation (l1–l2) (KOH–H₂O); the binary subsystem of type 2 is characterized by immiscibility of the liquid phase and has two critical end-points \(p(g = l-_{S_{K_{2}SO_{4}}})\) and \(Q(l_{1} = l_{2}-_{S_{K_{2}SO_{4}}})\) in saturated aqueous solution (K₂SO₄–H₂O). The ternary system has two three-phase equilibria (g–l–s) and (l1–l2–s), separated by a two-phase supercritical fluid region \((fl-_{S_{K_{2}SO_{4}}})\), and two types of monovariant critical curves \((g=l-_{S_{K_{2}SO_{4}}})\) and \((l_{1}=l_{2}-_{S_{K_{2}SO_{4}}})\). The three-phase regions approach each other upon temperature increase up to the point where the two-phase supercritical equilibrium disappears, and the two mentioned monovariant critical curves are joined into a double homogeneous critical point \((g=l-_{S_{K_{2}SO_{4}}} \leftrightarrow l_{1} = l_{2}-_{S_{K_{2}SO_{4}}})\) at maximum temperature ~445°C and 51–52 MPa.     

Effect of nickel catalyst on physicochemical properties of carbon xerogels as electrode materials for supercapacitor

Carbon xerogels and Ni-doped carbon xerogels prepared by the sol-gel polymerization were examined to reveal the effect of metallic nickel incorporated in carbon matrix on the physicochemical properties of carbon xerogels and their electrochemical performance for supercapacitor electrode in aqueous 6 M KOH solution. As shown by XRD and XPS measurements, the decomposition of nickel precursor in carbon matrix led to the creation of well-crystalline particles of metallic nickel which gave rise to the changes in the morphology, chemical and porous structure of carbon xerogels. Due to the modification of porous structure the surface area increased from 595 m²/g via 632 m²/g up to 660 m²/g for carbon xerogel, 7 wt% and 10 wt% Ni-doped composites, respectively. The enhancement of the surface area occurred along with diminishing the BJH average pore diameter. The value for nickel free xerogel amounted to 11.35 nm, whereas the value of 5.71 nm was measured for 10 wt% Ni xerogel. The changes in the porous and chemical structure created during the formation of carbon-nickel composites as well as the pseudo-capacitive effects arising from the redox reaction of nickel particles present in carbon matrix brought about a significant improvement of electrode capacitance. Electrochemical measurements showed that in comparison with capacitances measured for nickel free electrode (82.1 F/g calculated using the cyclic voltammetry and 88.8 F/g calculated using the galvanostatic charge/discharge method), the respective capacitances for 10 wt% Ni-doped carbon xerogel increased up to 103.0 F/g and 103.4 F/g. These values correspond to 25 and 16% improvement, respectively.     

Effects of impurities containing phosphorus on the surface properties and catalytic activity of TiO2 nanotube arrays

TiO₂ nanotube arrays were prepared by titanium anodic oxidation with either HF or H₃PO₄/NH₄F aqueous electrolyte solutions. The samples were characterized by means of X-ray diffraction (XRD), infrared spectroscopy (IR), Raman spectroscope, photoluminescence spectra (PL) and photocurrent response. Aqueous solutions of methylene blue or Cr(VI) ions were used as the target pollutants to compare catalytic activities of the two nanotube array types. The amorphous impurities containing phosphorus were confirmed by XRD and IR, for the sample synthesized with H₃PO₄/NH₄F electrolytes. They closed a portion of the active sites, acted as recombination centers of photo-generated charges, and were also involved in the negative reactions of competing photo-generated holes or OH radicals. The TiO₂ nanotube arrays formed in the H₃PO₄/NH₄F electrolytes exhibited a stronger fluorescence spectrum, a weaker photocurrent and a lower catalytic activity than the sample fabricated with HF electrolyte without phosphorus impurities.     

常压干燥法制备碳气凝胶及其电极性能研究北大核心CSCD

以间苯二酚-甲醛为前驱体,通过加入P123以增强有机气骨架的方法,采用常压干燥技术制备碳气凝胶电极材料,有机凝胶在干燥过程中收缩率极大降低。通过二氧化碳活化法对常压干燥获得的碳气凝胶孔结构进行了调控。研究了不同温度对其结构的影响,获得了最高比表面积达3544m2/g的碳气凝胶。6mol/L的KOH电解液中测试表明,常压干燥碳气凝胶具有稳定的充放电性能,随着活化温度的升高,比容量逐渐增加,最高比电容可达261F/g。常压干燥技术制备的碳气凝胶电极材料在降低生产成本的同时,仍具有理想的电化学性能。     

Electrochemical synthesis of flower like Mn-Co mixed metal oxides as electrode material for supercapacitor application

In the present work flower like Mn-Co mixed metal oxide electrode materials were successfully synthesized by simple, low cost electrodeposition method on stainless steel substrates. Different volume ratio of Mn-Co was used to attempt enhancement in the supercapacitive properties of electrode material. Structural, morphological and wettability properties of synthesized electrodes were carried out using XRD, RAMAN, FE-SEM and Contact Angle Measurement techniques. Electrochemical properties of electrodeposited Mn-Co mixed metal oxide at three different volume variation such as 50-50, 60-40 and 70-30 electrodes were analyzed by using cyclic voltammetry, galvonostatic charge discharge and electrochemical impedance spectroscopy in 1 M NaOH aqueous electrolyte. The Mn-Co:60-40 composition shows maximum specific capacitance which is 679 F/g at scan rate 5 mV/sec. Charge discharge studies gives 95% columbic efficiency. Impedance spectroscopy reveals capacitive behavior and gives series resistance ∼0.19 ohm and combined internal resistance ∼0.89 ohm. The 80% retention of specific capacitance after the 1000 cycles. The synergistic effect of Mn-Co mixed metal oxide electrode having good conductivity, large surface area and improved charge transportation than individual electrode material leads to enhancing supercapacitor performance of electrode material for its practical application.     

Synthesis of carbon-coated Fe3O4 nanorods as electrode material for supercapacitor

Carbon-coated Fe₃O₄ and pure Fe₃O₄ nanorods are synthesized via hydrothermal reaction and subsequent sintering procedure. The as-prepared products characterized by X-ray diffraction and scanning electron microscopy analysis indicate that carbon coating does not affect the structure and morphology of Fe₃O₄. Transmission electron microscope shows that Fe₃O₄ nanorods are homogeneously coated by carbon layer with a thickness of approximately 2 nm. The electrochemical properties measured by cyclic voltammetry, galvanostatic charge–discharge cycling and electrochemical impedance spectroscopy tests show that carbon-coated Fe₃O₄ (Fe₃O₄/C) nanorods present improved electrochemical performance due to the carbon layer. A specific capacitance of 275.9 F?g^?1 is achieved at a current density of 0.5 A g^?1 in 1 M Na₂SO₃ aqueous solution for the Fe₃O₄/C nanorods in comparison to that of 208.6 F?g^?1 for pure Fe₃O₄.     

纳米晶Gd2O3：Eu^3＋的制备及发光性能

采用低温燃烧合成法制备了Gd2O3：Eu^3＋纳米晶。用X射线衍射仪（XRD）、高分辨透射电子显微镜（HRTEM）和荧光光谱仪分别对样品的结构、形貌和发光性能进行了研究。结果表明，改变甘氨酸与稀土离子的比例（G／M）、退火温度可以制备出不同结构和晶粒尺寸的Gd2O3：Eu^3＋纳米晶。在退火温度为800℃，G／M等于0．83和1．0时，均得到了纯立方相的Gd2O3：Eu^3＋纳米晶，随着G／M的增加，Gd2O3：Eu^3＋从立方相逐渐向单斜相转变。粉末的晶粒尺寸随着退火温度的增高而增大，晶粒尺寸在10-30nm之间。立方相的Gd2O3：Eu^3＋纳米晶主发射峰位置在612nm（^5D^0→^7F2跃迁），激发光谱中电荷迁移态发生了红移。     

MnO_2/石墨烯复合电极材料的制备与储能性能

以葡萄糖为还原剂,天然石墨片为原料,采用Hummer法制备了石墨烯粉末(Graphene);并以该产物、KMnO4和HCl为原料,采用水热法制备了MnO2/Graphene复合材料。用扫描电子显微镜和X射线衍射对所制备的复合材料进行了表征,结果表明,水热法制备的MnO2材料为纯的α-MnO2相,且石墨烯粉末的加入并没有影响MnO2的晶体结构。在1mol/L Na2SO4电解液中进行了循环伏安和计时电位扫描测试,电极材料电化学性能稳定,具有较好的可逆性,在1.27mA/cm2电流密度下进行充放电测试时,电极比电容为147.9F/g;再循环1000次后,电极仍能保持稳定的电容,是一种理想的电化学电极材料。     

Ultrafine Mo-Doped Co_2P Nanorods Anchored on Reduced Graphene Oxide as Efficient Electrocatalyst for the Hydrogen Evolution Reaction

One-dimensional(1 D) transition metal phosphides(TMPs) with large specific surface areas,high charge transfer efficiency and excellent electrical conductivity have attracted significant attention in hydrogen evolution reaction(HER) as versatile and active catalysts.Herein,the sub-4 nm Mo-Co_2 P ultrafine nanorods(NRs) anchored on reduced graphene oxide(rGO) were successfully synthesized by a colloidal mesostructured strategy.Electrochemical test results reveal that the Mo-Co_2 P@rGO electrode exhibits superior activity with overpotentials of204 mV and Tafel slope of 88 mV/dec for HER at 10 mA/cm~2,relative to the Co_2 P@rGO electrode in 0.5 M H_2 SO_4 solution.This improvement could be ascribed to the Mo doping,which results in more active sites,higher electrical conductivity and faster electron-transfer rates.This versatile strategy will provide a promising pathway for transition metal-doped compounds as an efficient catalyst.     

ZnO-coated LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> cathode material for lithium-ion batteries synthesized by a combustion method

ZnO-coated LiMn₂O₄ cathode materials were prepared by a combustion method using glucose as fuel. The phase structures, size of particles, morphology, and electrochemical performance of pristine and ZnO-coated LiMn₂O₄ powders are studied in detail by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge test, and X-ray photoelectron spectroscopy (XPS). XRD patterns indicated that surface-modified ZnO have no obvious effect on the bulk structure of the LiMn₂O₄. TEM and XPS proved ZnO formation on the surface of the LiMn₂O₄ particles. Galvanostatic charge/discharge test and rate performance showed that the ZnO coating could improve the capacity and cycling performance of LiMn₂O₄. The 2 wt% ZnO-coated LiMn₂O₄ sample exhibited an initial discharge capacity of 112.8 mAh g^?1 with a capacity retention of 84.1 % after 500 cycles at 0.5 C. Besides, a good rate capability at different current densities from 0.5 to 5.0 C can be acquired. CV and EIS measurements showed that the ZnO coating effectively reduced the impacts of polarization and charge transfer resistance upon cycling.