Jyh-Tsung Lee

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 .

Formation of nano-scaled crevices and spacers in NiO-attached graphene oxide nanosheets for supercapacitors

Graphene oxide nanosheets were deposited directly onto the stainless steel substrate using electrophoretic deposition (EPD). The nickel ions adsorbed at the graphene oxide surface were reduced electrochemically to form nickel nanoparticles during the EPD process in the presence of a nickel nitrate additive. The attached Ni nanoparticles converted to NiO nanoparticles after annealing at 300 °C. The NiO nanoparticles functioned as nanospacers to improve the face-to-face aggregation of the graphene oxide sheets. The nano-scaled crevices could be formed in the NiO-attached graphene oxide electrode after heat treatment due to different shrinkage or expansion rates between the graphene oxide and NiO nanoparticles. The wettability of electrode might be improved by the deposition of hydrophilic NiO nanoparticles at the surface of graphene sheets. Therefore, the specific capacitance of the NiO-attached graphene oxide reached as high as 569 F g−1, which is 40 times higher than that of the bare graphene oxide electrode (13 F g−1) at a discharge current density of 5 A g−1.

Synthesis and electrochemical behaviour of nitroxide polymer brush thin-film electrodes for organic radical batteries

Nitroxide polymer brushes for thin-film electrodes for organic radical batteries are synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP). Patterned nitroxide polymer brush thin-film electrodes are fabricated by microcontact printing. The thickness of the polymer brushes is proportional to the polymerization time of SI-ATRP. The results of cyclic voltammetry and AC impedance indicate that when the polymer brush is thicker than 55 nm, the poly(2,2,6,6-tetramethylpiperidin-4-yl methacrylate) (PTMPM) segment at the bottom of the brush is not sufficiently oxidized to yield a nitroxide polymer brush during a 10 min oxidation time. Electrochemical and X-ray photoelectron spectroscopy results also show that an increase in the oxidation time could oxidize the PTMPM segment at the bottom of the brush but results in over-oxidation of the brush at the top, which decreases the energy capacity of the polymer brush. Moreover, the energy capacity of the polymer brush electrode for organic radical batteries is determined to be approximately 94.0 mA h g−1 at a discharge rate of 20 C; its cycle-life performance exhibits 97.3% retention after 100 cycles. Atomic force microscopy results also confirm that after 100 cycles the surface morphology of the polymer brush electrodes does not show obvious changes, indicating that the polymer brush resists dissolution of polymers into electrolytes.

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 Aromatic Esters as Propylene Carbonate-Based Electrolyte Additives in Lithium-Ion Batteries

The role of aromatic esters as additives in propylene carbonate (PC) based electrolytes used in lithium-ion batteries has been investigated. The addition of aromatic esters into the 1.0 M LiPF 6 -PC:DEC (3:2 in volume) suppresses the co-intercalation of PC and solvated Li + ions and inhibits the further decomposition of electrolytes during the first lithium intercalation process. A graphitic anode (MCMB-2528, mesocarbon microbeads) in a PC-based electrolyte with the aromatic esters exhibits a high reversible capacity. Scanning electron microscopy and the first discharge curve results show that the aromatic esters decompose and form a proper solid electrolyte interphase (SEI) film on the MCMB surface to not only prevent exfoliation of the graphite electrode but also stabilize the electrolyte. Both cyclic voltammogram and the lowest unoccupied molecular orbital energy level show that the aromatic esters have higher reduction potentials than that of the electrolyte solvents. An increase in reverse capacity may be achieved by increasing the addition. However, when the addition exceeds a certain critical value, the SEI film inhibits the intercalation of lithium ions and lowers the capacity. Furthermore, the percentage of the aromatic esters in electrolytes directly influences the low-temperature performance and the rate capability of the cells. An optimal result may be obtained when the addition is approximately 2-4%.

Nitroxide radical polymer/carbon-nanotube-array electrodes with improved C-rate performance in organic radical batteries

A poly(2,2,6,6-tetramethylpiperidin-1-oxy-4-yl methacrylate)/carbon-nanotube-array (PTMA/CNT-array) electrode was used as a cathode to improve the high-rate charge/discharge performance in organic radical batteries. Scanning electron microscopy observations showed that the PTMA/CNT-array electrode provides continuous conduction paths for electrons, and its electrochemical behaviours were investigated using cyclic voltammetry, charge/discharge tests, and AC impedance measurements. The results indicated that the PTMA/CNT-array electrode exhibits a lower electron-transfer resistance between CNTs and either the current collector or CNTs compared with conventional PTMA/suspended-CNT composite electrodes, enhancing the C-rate performance of batteries.

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.