Yunhong Zhou

Polyimides: Promising Energy‐Storage Materials

Based on this redox mechanism, we developed a series of polyamides with different structures and investigated their electrochemical activity as cathode materials for rechargeable lithium batteries. The results show that the polymer framework endows these samples with excellent cycling stability. Additionally, their capacity and rate capability are also satisfactory. The five polyimides were obtained through a simple polycondensation between commonly used dianhydrides and diamines. Coin cells consisting of the cathode (polyimide: conductive carbon: PTFE= 6:3:1), lithium anode and electrolyte (1 M LiTFSI/DOL+DME) were used for cycling tests, with the cutoff voltage of 1.5~3.5 V. FTIR characterization confirms the obtaining of our target products. In the charge/discharge measurements, all the samples show efficiency close to 100%. The Table below summarizes the results of five typical products. The theoretical capacity is calculated based on a four-electron mechanism shown above. The strong resemblance in the average discharge voltage and voltage profile between the sample PI-1 and PI-2, PI-3 and PI-4 seems to imply that the average discharging voltage are mainly determined by the functional group adjacent to the carbonyl group rather than that attached to the nitrogen atom. Comparing the theoretical capacity and experimental value, it can be generalized that almost half of the active site is available to be attached by Li, which possibly suggests that two electrons have been transferred during the charge/discharge process. Considering the importance of cyclabilty and rate performance, polyimide containing NTCDA(1,4,5,8-naphthalenetetracarboxylic dianhydride) unit seems to be a promising energy-storage material. Authors would express their sincere thanks to the Nature Science Foundation of China (No. 20873094) for the financial support.

Influence of surfactants on electrochemical behavior of zinc electrodes in alkaline solution

The effects of different ionic types of perfluorosurfactants (including hydrocarbon chain surfactant CTAB) on the electrochemistry behavior of zinc have been examined using voltammetric and potentiostatic polarization techniques. The results show that these surfactants can be used as substitute of mercury for decreasing the corrosion in zinc batteries. It is also shown that the deposition of zinc from zincate electrolyte in the presence of these surfactants can be improved to some extent. The morphology of the electrodeposited zinc shows that these surfactants can bring about more uniform and compact deposits and, thereby, reduce dendritic growth. FC-170C and CTAB are found to be the most effective inhibitors.

Electrochemical reduction of oxygen on small palladium particles supported on carbon in alkaline solution

The electrocatalytic behaviour of highly dispersed Pd/carbon catalyst prepared by ion pre-adsorption method for oxygen reduction in alkaline solution was investigated with soft-embedded rotating disk electrode and soft-embedded microelectrode method. The results showed that this catalyst has high catalytic activity both for oxygen and for HO2− reduction in alkaline solution. The occurrence of the peak current on the polarization curves of oxygen reduction on the catalyst when potential was scanned negatively, and the occurrence of the negative slope of IDNIR vs. ω−12 relation were analyzed. It is proved that the competition of Pd and support surface for oxygen molecules during oxygen reduction was the main cause for this new phenomenon.

Effects of lanthanum and neodymium hydroxides on secondary alkaline zinc electrode

Lanthanum and neodymium hydroxides coated on planar zinc electrodes, which are prepared by electrolysis, are found to lower the amount of zinc discharge products that are dissolved in an alkaline electrolyte. This reduces the dendritic growth and shape change of the zinc electrodes. The performance of these hydroxides has been assessed by cyclic voltammetry. Scanning electron microscopy is also applied to examine the morphology of the surface of the zinc electrodes before and after 50 charge/discharge cycles.

Effects of ionomer films on secondary alkaline zinc electrodes

Abstract Three low cost zinc-ionomers that are directly in contact with zinc electrodes are found to greatly impede the dissolution of zinc discharge products into electrolyte. This reduces the dendritic growth and shape change of the zinc electrodes. Discharge experiments with constant current, anodic polarization experiments and charge–discharge studies are carried out to assess the performance of these ionomers. Scanning electron microscopy is also applied to examine the morphology of the surface of the zinc electrodes before and after 50 charge–discharge cycles.

Influence of perfluorinated surfactants on the positive active-material of lead/acid batteries

Abstract The influence of perfluorinated anionic (FC-99), cationic (FC-135), and non-ionic (FSN) surfactants on the discharge capacities and cycle live of Plante positive electrodes in sulfuric acid are studied by cyclic voltammetry, charge/discharge cycling, X-ray diffraction, and scanning electron microscopy. The discharge capacities of PbO 2 electrodes, i.e., the utilization of the positive active-material, are increased for the electrolytes with FC-99 or FC-135, but the cycle live both surfactants are reduced. On the other hand, the presence of FSN has negligible influence on the discharge capacity and the cycle life of the PbO 2 electrode. The differences in the effects of the various types of perfluorinated surfactants are discussed with respect to the adsorption of perfluorinated surfactant molecules on the PbO 2 electrode surface during the charge and/or the discharge process.

Facile preparation of Ag2V4O11 nanoparticles via low-temperature molten salt synthesis method

Nanosized Ag2V4O11 powders have been prepared via the low-temperature molten salt method using LiNO3 as a reaction medium. The powders have been characterized by x-ray diffraction and transmission electron microscopy. The discharge properties of the powders have been assessed by the galvanostatic discharge test using CR2016 coin cells. The powder made at 300°C for 2 h is composed of nearly spherical particles about 40 nm in size. The discharge test shows that the powders prepared by the low-temperature molten salt method exhibit high discharge capacities.

Effect of perfluoroalkylsulfonate on the discharge behaviour of PbO2 electrodes in sulfuric acid solution

Abstract Amine perfluoroalkylsulfonate (FC-99) is seen as a prospective additive for lead/acid battery positive plates. Accordingly, its effect on the electrochemical behaviour of PbO 2 electrodes in 5 M H 2 SO 4 is studied by cyclic voltammetry, charge/discharge cycling and scanning electron microscopy. For sulfuric acid solution with FC-99, the discharge capacity of the PbO 2 electrode is increased, but the cycle life is reduced. These effects are attributed to adsorption of FC-99 on the electrode surface. The latter changes the morphology of the PbO 2 crystals to enlarge the electrode surface area, but weakens the contact between the positive active material and the substrate metal.

Influence of perfluorinated surfactants on the electrochemical behaviour of a lead electrode in sulfuric acid solution

Abstract The influence of various types of perfluorinated surfactants and their analogous hydrocarbon chain surfactants on the electrochemical behaviour of a lead electrode in sulfuric acid is studied by linear sweep voltammetry and cyclic voltammetry. The hydrogen evolution reaction is affected mainly by the type of the hydrophobic chain of the added surfactant (perfluorinated or hydrogenated). Nevertheless, these surfactants exert little expander acticn on the negative electrode, or even show an adverse effect on the discharge capacity of the lead electrode. A possible explanation is given in terms of the adsorption properties of different surfactants on the electrode surface during charge and discharge.

Li+-Permeable Film on Lithium Anode for Lithium Sulfur Battery

Lithium-sulfur (Li-S) battery is an important candidate for next-generation energy storage. However, the reaction between polysulfide and lithium (Li) anode brings poor cycling stability, low Coulombic efficiency, and Li corrosion. Herein, we report a Li protection technology. Li metal was treated in crown ether containing electrolyte, and thus, treated Li was further used as the anode in Li-S cell. Due to the coordination between Li+ and crown ether, a Li+-permeable film can be formed on Li, and the film is proved to be able to block the detrimental reaction between Li anode and polysulfide. By using the Li anode pretreated in 2 wt % B15C5-containing electrolyte, Li-S cell exhibits significantly improved cycling stability, such as∼900 mAh g-1 after 100 cycles, and high Coulombic efficiency of>93%. In addition, such effect is also notable when high S loading condition is applied.