Good Cycling Properties Research Articles

Functionalized ionic liquids based on guanidinium cations with two ether groups as new electrolytes for lithium battery

Two new functionalized ionic liquids (ILs) based on guanidinium cation with two ether groups and TFSA − anion are synthesized and characterized. Their physicochemical and electrochemical properties, including melting point, thermal stability, density, viscosity, conductivity, and electrochemical window are determined. Both the ILs are liquids at room temperature, and the viscosities are about 60 mPa s at 25 °C. Behavior of lithium redox, chemical stability against lithium metal and charge–discharge characteristics of lithium battery, are also examined for the two ILs as electrolyte with 0.6 mol kg −1 LiTFSA. Though the cathodic limiting potentials of the two ILs are higher than 0 V versus Li/Li +, the lithium plating and stripping on Ni electrode can be observed in the two IL electrolytes, indicating their good chemical stability against lithium metal. Li/LiFePO 4 cells using the two IL electrolytes without any additive showed good cycle property at the current rate of 0.2 C at 25 °C and 55 °C.

Disasterization: A Simple Way to Fix the Asset Pricing Properties of Macroeconomic Models

A central difficulty in economics is to create a model with both good business cycle properties and asset pricing properties. I show how to solve this difficulty by a simple portable modeling device: the “disasterization” of models. Take an economy with good business cycle properties and create a new, “disasterized” economy, which is essentially identical to the original one except that disasters can destroy part of the capital stock and productivity. In such a disasterized economy, asset prices exhibit high and volatile risk premia, but macro variables remain unchanged. Perturbations of this benchmark allow for feedback from finance to macro.

New functionalized ionic liquids based on pyrrolidinium and piperidinium cations with two ether groups as electrolytes for lithium battery

Four new functionalized ILs based on piperidinium and pyrrolidinium cations with two ether groups and TFSI − anion are synthesized and characterized. Physical and electrochemical properties of these ILs, including melting point, thermal stability, viscosity, conductivity and electrochemical stability, are investigated. All the ILs are liquids at room temperature, and the viscosities of P(2o1) 2-TFSI and P(2o1)(2o2)-TFSI are 55 and 53 mPa s at 25 °C, respectively. Behavior of lithium redox, chemical stability against lithium metal and charge–discharge characteristics of lithium batteries, are also investigated for these IL electrolytes with 0.6 mol kg −1 LiTFSI. Though the cathodic limiting potentials of these ILs are 0.4 V versus Li/Li +, the lithium plating and striping on Ni electrode can be observed for these IL electrolytes, and these IL electrolytes show good chemical stability against lithium metal. Li/LiFePO 4 cells using these IL electrolytes without additives have good capacity and cycle property at the current rate of 0.1 C, and the cell using the P(2o1)(2o2)-TFSI electrolyte owns good rate property.

Functionalized ionic liquids based on quaternary ammonium cations with three or four ether groups as new electrolytes for lithium battery

New functionalized ILs based on quaternary ammonium cations with three or four ether groups and TFSI − anion were synthesized and characterized. Physical and electrochemical properties, including melting point, thermal stability, viscosity, conductivity and electrochemical stability were investigated for these ILs. Five ILs with lower viscosity in these ILs were applied in lithium battery as new electrolytes. Behavior of lithium redox and charge–discharge characteristics of lithium battery were investigated for these IL electrolytes with 0.6 mol kg −1 LiTFSI. Lithium plating and striping on Ni electrode could be observed in these IL electrolytes. Li/LiFePO 4 cells using these IL electrolytes without additives had good capacity and cycle property at the current rate of 0.1 C, and the N(2o1) 3(2o2)TFSI and N2(2o1) 3TFSI electrolytes owned better rate property.

In situ synthesis of high-loading Li4Ti5O12–graphene hybrid nanostructures for high rate lithium ion batteries

Nanocrystalline Li4Ti5O12 grown on conducting graphene nanosheets (GNS) with good crystallinity was investigated as an advanced lithium-ion battery anode material for potential large-scale applications. This hybrid anode nanostructure material showed ultrahigh rate capability and good cycling properties at high rates.

One ether-functionalized guanidinium ionic liquid as new electrolyte for lithium battery

One ether-functionalized guanidinium ionic liquid is used as new electrolytes for lithium battery. Viscosity, conductivity, behavior of lithium redox, chemical stability against lithium metal, and charge–discharge characteristics of lithium batteries, are investigated for the IL electrolytes with different concentrations of lithium salt. Though the cathodic limiting potential of the IL are 0.7 V vs. Li/Li +, the lithium plating and striping on Ni electrode can be observed in the IL electrolytes, and the IL electrolytes show good chemical stability against lithium metal. Li/LiCoO 2 cells using the IL electrolytes without additives have good capacity and cycle property at the current rate of 0.2 C when the LiTFSI concentration is higher than 0.3 mol kg −1, and the cell using the IL electrolyte with 0.75 mol kg −1 LiTFSI owns good rate property. The activation energies of the LiCoO 2 electrode for lithium intercalation are estimated, and help to analyze the factors determining the rate property.

Effects of drying control chemical additive on properties of Li 4Ti 5O 12 negative powders prepared by spray pyrolysis

High-density Li 4Ti 5O 12 powders comprising spherical particles are prepared by spray pyrolysis from a solution containing dimethylacetamide (drying control chemical additive) and citric acid and ethylene glycol (organic additives). The prepared powders have high discharge capacities and good cycle properties. The optimum concentration of dimethylacetamide is 0.5 M. The addition of dimethylacetamide to the polymeric spray solutions containing citric acid and ethylene glycol helps in the effective control of the morphology of the Li 4Ti 5O 12 powders. At a constant current density of 0.17 mA g −1, the initial discharge capacities of the powders obtained from the spray solution with and without the organic additives are 171 and 167 mAh g −1, respectively.

Preparation and capacitance property of MnO 2-pillared Ni 2+–Fe 3+ layered double hydroxides nanocomposite

A novel MnO 2-pillared Ni 2+–Fe 3+ layered double hydroxides nanocomposite has been successfully fabricated using an intercalation/reduction reaction followed by heating treatment. The structural evolution of the samples obtained at different stages has been characterized by XRD, TEM, XPS, IR and N 2 adsorption–desorption. The layered structure of MnO 2-pillared Ni 2+–Fe 3+ layered double hydroxides nanocomposite can be maintained at 300 °C, and the obtained material has a large surface area of 202 m 2 g −1. Electrochemical studies indicate that the material obtained by heating at 200 °C exhibits an ideal capacitive behavior and good cycling property in 1 mol L −1 Na 2SO 4 aqueous solution, and the specific capacitance value was 190 F g −1 at a scan rate of 5 mV s −1.

Electrosprayed polyaniline as cathode material for lithium secondary batteries

Doped polyaniline with LiPF 6 is electrosprayed onto aluminum foil using electrospinning technique, and evaluated as cathode active material for application in room-temperature lithium batteries. Doping level is characterized using FTIR and UV–vis spectroscopy. In FTIR Spectra, characteristic peaks of PANI are shifted to lower bands as a result of doping which indicates the effectiveness of doping. Doping level is also confirmed by UV–vis spectra. Surface morphology of the cathode is studied using scanning electron microscope. Electrochemical evaluation of the cell using electrosprayed PANI as cathode show good cycling properties. The cell delivers a high discharge value of 142.5 mAh/g which is about 100% of theoretical capacity, and the capacity is lowered during cycle and reached 61% of theoretical capacity after 50 cycles. The cell delivers a stable but lower discharge capacity at higher C-rates.

Guanidinium-based ionic liquids as new electrolytes for lithium battery

Two ionic liquids based on guanidinium cations and TFSA − anion were prepared, and their electrochemical stabilities were investigated. The cathodic limiting potentials of the two ILs were 0.7 V versus Li/Li +, and their electrochemical windows were 4.2 V. However, the lithium plating and striping on Ni electrode could been observed in the two IL electrolytes containing 0.3 mol kg −1 of LiTFSA without additive. And Li/LiCoO 2 cells using the two IL electrolytes without additive showed good capacity and cycle property at the current rate of 0.2 C.

Reversible Insertion Properties of Zinc Ion into Manganese Dioxide and Its Application for Energy Storage

The reversible intercalation of Zn 2+ ions into manganese dioxide was first reported in an aqueous system and a large capacity (210 mAh g -1 ) was measured. A cycle life test was performed at 1 A g -1 , and after 50 cycles, no capacity fading was found, which indicates the good cycling properties of manganese dioxide toward the insertion of zinc ions. X-ray photoelectron spectrum measurements indicated that Zn 2+ ions in the electrolyte are involved in the charge storage process of manganese dioxide. X-ray diffraction results exhibited the kinetic stability of the host structure in allowing high-capacity, single-phase, and reversible zinc-ion intercalation.

Capacitive Behavior and Charge Storage Mechanism of Manganese Dioxide in Aqueous Solution Containing Bivalent Cations

Manganese dioxide shows an ideal capacitive behavior in the aqueous solution containing bivalent cations . A specific capacitance value as high as in electrolyte was measured at a sweep rate of . A cycle life test was also performed and no capacity loss of electrode was found after , which indicates the electrode possesses a good cycling property in the aqueous electrolyte containing bivalent cations . X-ray photoelectron spectroscopy data reveal that the ions in the electrolyte are involved in the charge storage process of manganese dioxide in an aqueous system and correspondingly a part of ions will become to ion to balance the charge.

Effects of preparation conditions on the electrochemical and morphological characteristics of Li 4Ti 5O 12 powders prepared by spray pyrolysis

Li 4Ti 5O 12 anode powders were prepared by post-treatment of the precursor powders obtained by spray pyrolysis at various preparation conditions. The precursor powders had fine size, narrow size distribution, dense inner structure and homogeneous composition when the flow rate of the carrier gas and the preparation temperature were 10 l min −1 and 800 °C. The spherical shapes of the precursor powders obtained at the optimum preparation conditions maintained after post-treatment at a temperature of 800 °C. The mean sizes of the Li 4Ti 5O 12 powders were controlled by changing the concentrations of the spray solution. The initial discharge capacities and cycle properties of the Li 4Ti 5O 12 powders were strongly affected by the preparation temperatures of the precursor powders. The optimum preparation temperature of the precursor powders was 800 °C when the flow rate of the carrier gas was 10 l min −1. The discharge capacities and cycle properties of the Li 4Ti 5O 12 powders were not affected by flow rates of the carrier gas. The Li 4Ti 5O 12 powders had good cycle properties irrespective of the concentrations of the spray solution. However, the Li 4Ti 5O 12 powders obtained from the spray solutions with high concentration above 0.5 M had high discharge capacities than those obtained from the spray solutions with low concentration below 0.1 M.

Fine-sized LiNi 0.8Co 0.15Mn 0.05O 2 cathode particles prepared by spray pyrolysis from the polymeric precursor solutions

Fine-sized LiNi 0.8Co 0.15Mn 0.05O 2 cathode particles with high discharge capacities and good cycle properties were prepared by spray pyrolysis from the polymeric precursor solutions. The cathode particles obtained from the spray solution without polymeric precursors had irregular morphology and hardly aggregated morphology. On the other hand, the cathode particles obtained from the spray solution with citric acid and ethylene glycol had fine size and regular morphologies. The cathode particles obtained from the spray solution containing adequate amounts of citric acid and ethylene glycol had several hundreds nanometer and narrow size distribution. The maximum discharge capacity of the cathode particles was 218 mAh/g when the excess of lithium component added to the spray solution was 6 mol% of the stoichiometric amount to obtain the LiNi 0.8Co 0.15Mn 0.05O 2 particles. The discharge capacities of the fine-sized LiNi 0.8Co 0.15Mn 0.05O 2 particles dropped from 218 to 213 mAh/g by the 50th cycle at a current density of 0.1 C.

Characteristics of spherical-shaped Li 4Ti 5O 12 anode powders prepared by spray pyrolysis

Spherical-shaped Li 4Ti 5O 12 anode powders with a mean size of 1.5 μm were prepared by spray pyrolysis. The precursor powders obtained by spray pyrolysis had no peaks of crystal structure of Li 4Ti 5O 12. The powders post-treated at temperatures of 800 and 900 °C had the single phase of spinel Li 4Ti 5O 12. The powders post-treated at a temperature of 1000 °C had main peaks of the Li 4Ti 5O 12 phase and small impurity peaks of Li 2Ti 3O 7. The spherical shape of the precursor powders was maintained after post-treatment at temperatures below 800 °C. The Brunauer–Emmett–Teller (BET) surface areas of the Li 4Ti 5O 12 anode powders post-treated at temperatures of 700, 800 and 900 °C were 4.9, 1.6 and 1.5 m 2/g, respectively. The initial discharge capacities of Li 4Ti 5O 12 powders were changed from 108 to 175 mAh/g when the post-treatment temperatures were changed from 700 to 1000 °C. The maximum initial discharge capacity of the Li 4Ti 5O 12 powders was obtained at a post-treatment temperature of 800 °C, which had good cycle properties below current densities of 0.7 C.

Electrochemical properties of nanosized hydrous manganese dioxide synthesized by a self-reacting microemulsion method

Manganese dioxide has been synthesized by a new simple self-reacting microemulsion method. The synthesized MnO 2 has been found to be amorphous structure containing a moderate amount of water by X-ray diffraction, Fourier transform infrared spectroscopy and thermogravimetric analysis. Particles in a spherical shape with about 4 nm in diameter have been observed by transmission electron microscopy. Cyclic voltammetic tests have been performed between −0.5 and 0.5 V versus Hg/Hg 2SO 4 in 1 mol L −1 Na 2SO 4 solution at sweep rates up to 50 mV s −1. A specific capacitance value as high as 246.2 F g −1 was obtained, which was much higher than 146.5 F g −1 of MnO 2 prepared by chemical co-precipitation. After 600 cycles, only 6% decrease of specific capacitance was measured which indicated that such a material possesses good cycling property.

Nano-Si/Cellulose Composites as Anode Materials for Lithium-Ion Batteries

In this work we report an easy method for improving the deficient properties of nanosized Si as an electrode material for lithiumcells. The method involves mixing it with cellulose fibers in appropriate amounts. A composite electrode made in a ratio 34:66%w/w Si/cellulose and containing no other additive was found to exhibit very good cycling properties e.g., specific capacity of ca.1400 mAh/g after 50 cycles, compared to only 400 mAh/g for the electrode made from pure Si . The performance was comparableto, or even better than, that of other Si-based composite electrodes obtained by using more sophisticated and expensive methods.© 2008 The Electrochemical Society. DOI: 10.1149/1.2902305 All rights reserved.Manuscript submitted November 26, 2007; revised manuscript received February 27, 2008. Available electronicallyApril 4, 2008.

Study of lithium/polypyrrole secondary batteries with Lithium as cathode and polypyrrole anode

Lithium/polypyrrole (Li/PPy) batteries were fabricated using lithium sheet as cathode, PPy as anode, microporous membrane polypropylene/polyethylene/polypropylene (PP/PE/PP) composite as separator and LiPF 6/ethylene carbonate-dimethyl carbonate-methyl ethyl carbonate (EC-DMC-EMC) as electrolyte. Polypyrrole was prepared by chemical polymerization. Certain fundamental electrochemical performances were investigated. Properties of the batteries were characterized and tested by SEM, galvanostatic charge/discharge tests, cyclic voltammetry (CV), and a.c. impedance spectroscopy. The influences of separator, morphology, and conductivity of PPy anode, cold-molded pressure, and electric current on the performances of the batteries were studied. Using PP/PE/PP membranes as separator, the battery showed good storage stability and cycling property. The conductivity of materials rather than morphology affected the behavior of the battery. The higher the conductivity, the better performances the cells had. Proper cold-molded pressure 20 MPa of the anode pellet would make the properties of the cells good and the fitted charge/discharge current was 0.1 mA. The cells showed excellent performance with 97%-100% coulombic efficiency. The highest discharge capacity of 95.2 mAh/g was obtained.

Spray-drying process for synthesis of nanosized LiMn2O4 cathode

Nanosized LiMn2O4 cathode material was synthesized by a spray-drying process. The calcined LiMn2O4 powder retained a well-define spinel structure and good crystallization. Electrochemical measurements showed that the nanosized LiMn2O4 reached an initial discharge capacity of 131 mAhċg−1 at 1/5 C rate and exhibited a good cycling property at 1 C rate. The results indicate that spray-drying method is a promising method suitable for mass production of nanosized LiMn2O4 with improved electrochemical performances and low cost.

Fine-sized LiCoO 2 particles prepared by spray pyrolysis from polymeric precursor solution

Fine-sized LiCoO 2 particles with high discharge capacities and good cycle properties were prepared by spray pyrolysis from a spray solution with citric acid and ethylene glycol. The precursor particles obtained from the spray solution with citric acid and ethylene glycol transformed into fine-sized LiCoO 2 particles with regular morphology after post-treatment at temperatures between 700 and 900 °C. The mean size and aggregation degree of the primary particles were affected by the concentrations of polymeric precursors added into spray solutions. The LiCoO 2 particles obtained from the spray solution without polymeric precursors had irregular and aggregated morphology. The discharge capacities of the LiCoO 2 particles changed from 132 to 151 mAh/g when the concentrations of the citric acid and ethylene glycol changed from 0 to 1 M. The particles prepared from the spray solution containing 0.3 M each of citric acid and ethylene glycol had the maximum discharge intensity.