Chia-Chen Li

An efficient approach to derive hydroxyl groups on the surface of barium titanate nanoparticles to improve its chemical modification ability.

Highly hydroxylated barium titanate (BaTiO(3)) nanoparticles have been prepared via an easy and gentle approach which oxidizes BaTiO(3) nanoparticles using an aqueous solution of hydrogen peroxide (H(2)O(2)). The hydroxylated BaTiO(3) surface reacts with sodium oleate (SOA) to form oleophilic layers that greatly enhance the dispersion of BaTiO(3) nanoparticles in organic solvents such as tetrahydrofuran, toluene, and n-octane. The results of Fourier transform infrared spectroscopy confirmed that the major functional groups on the surface of H(2)O(2)-treated BaTiO(3) nanoparticles are hydroxyl groups which are chemically active, favoring chemical bonding with SOA. The results of transmission electron microscopy of SOA-modified BaTiO(3) nanoparticles suggested that the oleate molecules were bonded to the surfaces of nanoparticles and formed a homogeneous layer having a thickness of about 2 nm. Furthermore, the improved dispersion capability of the modified BaTiO(3) nanoparticles in organic solvents was verified through analytic results of its settling and rheological behaviors.

Improvements of Dispersion Homogeneity and Cell Performance of Aqueous-Processed LiCoO2 Cathodes by Using Dispersant of PAA – NH4

The dispersion property of aqueous lithium cobalt oxide (LiCoO 2 ) slurries and their corresponding cell performance with and without addition of dispersant, ammonium polyacrylic acid (PAA-NH 4 ), were investigated. The surface chemical properties of LiCoO 2 and graphite powders were characterized by diffuse reflectance using infrared Fourier transform spectrometry. The adsorption effects of PAA-NH 4 and latex binder (LA132), respectively, on the dispersion behaviors of LiCoO 2 and graphite powders in aqueous suspensions were analyzed by measurements of adsorption behavior, ζ potential, sedimentation property, and rheology. The results showed that the PAA-NH 4 can adsorb onto both the LiCoO 2 and graphite powders to stabilize them in aqueous suspensions, but LA132 binder only adsorbs onto graphite and showed a competitive adsorption with PAA-NH 4 on the graphite surface. By observation of scanning electron microscope, it was shown that the as-prepared LiCoO 2 sheet without PAA-NH 4 addition had significant agglomeration of powders and accumulation of binder around the powder. These undesired coagulations of powder and binder can be diminished by increasing the PAA-NH 4 content. Although the dispersion property of powders was increased with increasing PAA-NH 4 content, too much addition of PAA-NH 4 is detrimental to the electronic conduction, adhesion strength, and electrochemical properties of LiCoO 2 electrode. To simultaneously obtain a well-dispersed and a better electrochemical property of LiCoO 2 electrode sheet, the appropriate amount of PAA-NH 4 was found to be on the order of 0.01 wt % based upon LiCoO 2 .

Effects of PAA-NH4 Addition on the Dispersion Property of Aqueous LiCoO2 Slurries and the Cell Performance of As-Prepared LiCoO2 Cathodes

The dispersion property of aqueous lithium cobalt oxide slurries and the corresponding cell performance of electrodes with and without dispersant additions were investigated. The influence of dispersant, ammonium polyacrylic acid , and polyacrylic latex binder (LA132) on the dispersion behaviors of in aqueous suspensions is characterized by zeta potential and rheology measurements. The results show that the can adsorb onto the powder to provide an electrosteric stabilization in aqueous suspensions, but LA132 does not show such function. For the as-prepared electrode without addition, the powder agglomerates and the binder accumulates around the powder. This unfavorable phenomenon can be diminished by increasing content. However, it is found that too much addition of is detrimental to the electrochemical properties of . To simultaneously obtain a well-dispersed and a electrode with a better electrochemical property, the appropriate amount of is about based upon weight.

Using Poly(4-Styrene Sulfonic Acid) to Improve the Dispersion Homogeneity of Aqueous-Processed LiFePO4 Cathodes

The dispersion properties of aqueous lithium iron phosphate (LiFePO 4 ) slurries and the electrochemical properties of the corresponding as-prepared cathodes with the addition of a dispersant, poly(4-styrene sulfonic acid) (PSSA), have been investigated. The influence of PSSA on the dispersion behaviors of LiFePO 4 and conductive agents, graphite and carbon black, in aqueous suspensions are explored by the analyses of zeta-potential and rheology. The results show that the PSSA adsorbs onto the LiFePO 4 and conductive agents so that they can be electrosterically stabilized in aqueous suspensions. Through the observation using a scanning electron microscope, it is shown that the homogeneity and dispersion of the composition distributed in the LiFePO 4 electrode sheet are significantly improved with increasing content of PSSA. However, an excess addition of PSSA is detrimental to the electronic conduction and the electrical capacity of the cathode. To obtain a homogeneous electrode with a good cell performance, the optima content of PSSA is suggested to be 2.0 wt % based on the LiFePO 4 weight.

Effects of Surface-coated Carbon on the Chemical Selectivity for Water-Soluble Dispersants of LiFePO4

The effects of additions of dispersants, poly(4-styrene sulfonic acid) (PSSA), poly(ammonium acrylate) (PAA-NH 4 ) and poly(acrylic acid-co-maleic acid) (PAMA), on the dispersion and electrochemical properties of carbon-coated lithium iron phosphate (LiFeP0 4 ) cathodes are studied. The influence of the addition of dispersants on the dispersion behaviors of carbon-coated LiFeP0 4 and conductive agents in aqueous suspensions is explored by analyses of zeta-potential and rheology. The homogeneity of the composition in the LiFePO 4 cathode is assessed by scanning electron microscopy observation. The result shows that both PSSA and PAMA can interact with the carbon-coated LiFeP0 4 and they are efficient dispersants for LiFeP0 4 cathodes. PAA-NH 4 , however, is unfavorable to interact with carbon materials, and thus has a restricted efficiency for the dispersion of carbon-coated LiFeP0 4 cathodes. In addition to the dispersion property, the effect of the addition of dispersants on the rate capability of LiFeP0 4 cathodes is also examined. Although PSSA improves the dispersion homogeneity of the LiFeP0 4 electrodes, it is detrimental to the electrochemical property due to its high average molecular weight (M n ) of 70,000 g/mol. On the contrary, the PAMA used has a low M n of 3,000 g/mol, and hence only the positive influence of the improved dispersion of the cathode in terms of an increase in rate capability is observed.

Synthesis of non-oxidative copper nanoparticles

A novel aqueous reduction method for the efficient synthesis of non-oxidative copper (Cu) nanopowders without using a protecting agent or introducing of an inert gas is presented. By this new method, high purity Cu nanopowders can be produced that exhibit good electrical conductivity with an electrical resistivity on the order of 10−4 Ω cm.

Conductive microcapsules for self-healing electric circuits

Conductive microcapsules that are compatible with inorganic-based materials such as Ag conductive paste for casting electric circuits are prepared. These conductive microcapsules show high efficiency, more than 80% within 30 s, for the restoration of an interrupted circuit that presented a cracking width of about 150 μm.

Gel Polymer Electrolytes Prepared by In Situ Atom Transfer Radical Polymerization at Ambient Temperature

The preparation of gel polymer electrolytes using atom-transfer radical polymerization (ATRP) has been investigated. A liquid electrolyte with poly(ethylene glycol) methyl ether methacrylate and poly(ethylene glycol) dimethacrylate was successfully polymerized by ATRP at ambient temperature to form a gel polymer electrolyte. Infrared spectroscopy confirms that the polymerization of gel polymer electrolytes can take place at room temperature. The concentration of salt and the percentage of either polymer in electrolytes directly influence the ionic conductivity. An optimal ionic conductivity of the gel polymer electrolyte is obtained to be 2.1 X 10 -3 S cm -1 at 30°C. Furthermore, the lithium transference number is found to be about 0.32. Cyclic voltammogram and cell performance show that the gel polymer electrolyte has good electrochemical stability and good cyclability.

Newly designed diblock dispersant for powder stabilization in water-based suspensions

A newly designed dispersant for water-based suspensions, ammonium poly(methacrylate)-block-poly(2-phenoxyethyl acrylate) (PMA-b-PBEA), is proposed in this study. According to the results of rheological analysis, the dispersion efficiency of this new dispersant is superior to that of the commercially available ammonium polyacrylate (PAA-NH4). The diblock structure of PMA-b-PBEA, which simultaneously contains a low-polar anchoring head group and a water-dissociable stabilizing moiety, is the main cause for its extremely high efficiency for powder dispersion. The unique structure not only results in effective adsorption approximately double that of PAA-NH4, but also produces a low number of counter-ions that compress the electrical double layer and ruin powder stabilization. Based on Derjaquin-Landau-Verwey-Overbeek calculations, the large adsorbance of PMA-b-PBEA gives the powder, titania (TiO2) in this study, a high steric stabilization energy. In addition, PMA-b-PBEA provides TiO2 with a remarkably high electrostatic energy because it generates fewer counter-ions. This energy provides excellent dispersity of powder in the suspensions with a high solid content of 60wt% without showing any rheological hysteresis.

Superparamagnetic core–shell radical polymer brush as efficient catalyst for oxidation of alcohols to aldehydes and ketones

Nitroxide polymer brush grafted on superparamagnetic nanoparticles has been synthesized. Using the brush as a catalyst, the conversion by catalytic oxidation of alcohols to aldehydes and ketones is more than 99%. The catalyst can be easily recovered by applying a magnetic field. Furthermore, the reused catalyst still maintain high performance in catalytic oxidation.