Current Collector Preparation

Fig. 12.3 Fabrication of the nanocomposite paper units for battery, (a) Schematic of the battery assembled by using nanocomposite film units. The nanocomposite unit comprises LiPF6 electrolyte and multiwalled carbon nanotube (MWNT) embedded inside cellulose paper. A thin extra layer of cellulose covers the top of the MWNT array. Ti/Au thin film deposited on the exposed MWNT acts as a current collector. In the battery, a thin Li electrode film is added onto the nanocomposite, (b) Cross-sectional SEM image of the nanocomposite paper showing MWNT protruding from the cel-lulose-RTIL ([bmlm] [Cl]) thin films (scale bar, 2pm). The schematic displays the partial exposure of MWNT. A supercapacitor is prepared by putting two sheets of nanocomposite paper together at the cellulose exposed side and using the MWNTs on the external surfaces as electrodes, (c) Photographs of the nanocomposite units demonstrating mechanical flexibility. Flat sheet (top), partially rolled (middle), and completely rolled up inside a capillary (bottom) are shown (See Color Plates)...

Given the importance of particle size to rate capabilities in Li+ batteries, preparation of nanostructures of Li+ insertion material for possible use as electrodes in Li+ batteries seemed like an obvious extension of our work on nanomaterials. The fact that these nanostructures can be prepared as high-density ensembles that protrude from a surface like the bristles of a brush (Fig, 2A) seemed particularly useful for this proposed application because the substrate surface could then act as a current collector for the nanostructured battery electrode material. 

This work was done in collaboration with Professor Hiroshi Yoneyama of Osaka University [124], The procedure used to prepare the LiMu204 tubules is shown schematically in Fig. 21. A commercially available alumina filtration membrane (Anopore, Whatman) was used as the template. Alumina is especially suited for this application because of its high porosity, monodispersity of pore size, and the fact that it can be heated to high temperature without degradation. This membrane contains 200-nm-diameter pores, is 60 p,m thick, and has a porosity of 0.6. A 1.5 cm X 1.5 cm piece of this membrane was mounted on a Pt plate (2 cm X 2 cm) by applying a strip of plastic adhesive tape (also 2 cm X 2 cm NICHIBAN VT-19) across the upper face of the membrane. The Pt plate will serve as the current collector for the LiMn204 battery electrode material. The strip of tape, which will be subsequently removed, had a 1.0 cm circular hole punched in it, which defined the area of the membrane used for the template synthesis of the LiMn204. 

Fuel cells incorporating lithographic methods and masking/deposition/etching protocols have been fabricated on Si wafers and thereby satisfy two critical needs in a standard fuel cell collection of electrons (current collectors) and controlling the flow field of fuel and oxidant. Kelley et al. produced a miniature direct methanol fuel cell (DMFC) with a current— voltage and fuel utilization performance that matched standard-sized DMFCs prepared in-lab.A working volume for the miniature DMFC of 12 mm was reported, with an operational performance of 822 W h kg at 70 °C. ... 

To prepare the standardized dispersion electrode, a mixture of 100 mg soot, 100 g 97% sulfuric acid and 100 mg pigment was stirred direct into the dilute sulfuric acid of the measuring vessel, so that the concentration of sulfuric acid in the electrolyte after stirring in was about 4.5 N. The current collector electrode was a gold-platinum mesh (90/10) of about 4.5 cm2 area. The current/voltage characteristics shown in Fig. 12 make it possible to compare CoTAA with various phthalocyanines. 

To prepare a working electrode, carbon powder (PFA-P7-H or PFA-AN8-H) was mixed with polytetrafluoroethylene (PTFE) (5 wt%) to form a pellet and it was sandwiched in Ni mesh as a current collector. The EDL capacitance properties were measured by CV and galvanostatic charge/ discharge in a three-electrode cell vs. Ag/AgCl reference electrode. 1 M-(C2H5)4NBF4 in PC was used as a nonaqueous electrolyte. 

Many applications require the preparation of composite electrodes in which the active materials are in a powder form which may be nonconductive. Hence, the electrode must include a rigid current collector, a binder and some electrically conducting additive, in addition to the active substance. Such electrodes are important for electrocatalysis and as cathodes for batteries. For instance, many cathode materials for rechargeable Li and Li ion batteries are lithiated transition metal oxides, which appear as a nonconductive powder. 

Many practical electrodes are prepared from powdered active mass and some conductive additive, such as carbonaceous materials, that are bonded to a metallic current collector with a polymeric binder such as PVDF (described in the previous section). Such electrodes can be measured directly. Is it very useful to measure such electrodes in their pristine from, before any electrochemical treatment, and then as a function of their electrochemical history. For quantitative analysis (phase composition, evaluation of concentration of constituents in mixtures, etc.) it is important to use internal standards in the sample. Fortunately, several components of composite electrodes, which are, in any event, contained in the sample measured, can be used as internal standards. These include the current collector (Cu, Al), the conductive additive, such as graphite, or the binder, such as Teflon. 

In Section 3, the slow rate of the ORR at the Pt/ionomer interface was described as a central performance limitation in PEFCs. The most effective solution to this limitation is to employ dispersed platinum catalysts and to maximize catalyst utilization by an effective design of the cathode catalyst layer and by the effective mode of incorporation of the catalyst layer between the polymeric membrane electrolyte and the gas distributor/current collector. The combination of catalyst layer and polymeric membrane has been referred to as the membrane/electrode (M E) assembly. However, in several recent modes of preparation of the catalyst layer in PEFCs, the catalyst layer is deposited onto the carbon cloth, or paper, in much the same way as in phosphoric acid fuel cell electrodes, and this catalyzed carbon paper is hot-pressed, in turn, to the polymeric membrane. Thus, two modes of application of the catalyst layer - to the polymeric membrane or to a carbon support - can be distinguished and the specific mode of preparation of the catalyst layer could further vary within these two general application approaches, as summarized in Table 4. 

In laboratory-prepared devices (such as oxygen pumps), porous platinum layers that function as both the electrode and current collector are generally deposited on both surfaces of the membrane. 

The General Electric SPE (17) consists of two porous particulate electrodes which are bondecTcohesively with polytetrafluoro-ethylene dispersion particles and connected electrically to the outside of the cell hardware by means of metallic current collectors which are pressed against the SPE by mechanical methods. Such an SPE can be prepared via perfluoroionomer solution techniques. One method is to apply a paste consisting of the electrolyte powder and the perfluoroionomer solution to the membrane and evaporate the solvent. Alternately, the paste can be applied to a sacrificial substrate such as aluminum foil, dried, and subsequently pressed into the membrane as a decal. 

---