Fabrication negative electrodes

Materials obtained by pyrolysis of pitch-polysilane blends have been extensively studied as carbon materials containing Si [157-161], For some of these materials, ca. 600mAh/g of Crev for Li insertion, as well as small irreversible capacities and small hysteresis effects, were reported. It has been shown that the materials contain nanodispersion of Si-O-C and Si-O-S-C instead of nanodispersed Si particles [162-165], Furthermore, the oxygen and sulfur contents are proved to be correlated to the irreversible capacity. There is a report about the fabrication of porous Si negative electrodes with 1-D channels, where the usefulness of the fabricated negative electrodes for rechargeable microbatteries is also suggested [166],... 

Separators in lithium ion batteries must separate positive electrodes and negative electrodes to prevent short circuits, and must allow passage of electrolytes or ions. Porous films and nonwoven fabrics of resins are known separators. The lithium ion battery separators are also required to exhibit stable properties at high temperatures such as in charging, and therefore high heat resistance is desired (21). 

Negative electrodes are fabricated of zinc oxide by any of die methods (pasting, pressing, etc) described. Binders, usually TFE, are used to reduce the solubility of the electrode in KOH. 

The lift-off process is usually employed to fabricate metal electrodes. This method, as opposed to the wet-etch process, allows the dual-composition electrode to be patterned in a single step [747]. In order to achieve well-defined metal electrodes in a channel recess using the lift-off technique, the metal (Pt/Ta) will not be deposited onto the sidewalls of the photoresist structure (see Figure 2.32). This discontinuity of the deposited metal layer around the sidewalls allows metal on the resist to be removed cleanly from the surface without tearing away from the metal on the surface. Thus negative resists were used because they can be easily processed to produce negatively inclined sidewalls. To achieve this, the photoresist is subjected to underexposure, followed by overdevelopment [141]. 

The necessary porosity for thicker layers was introduced by appropriate current densities [321-323], by co-deposition of composites with carbon black [28, 324] (cf. Fig. 27), by electrodeposition into carbon felt [28], and by fabrication of pellets from chemically synthesized PPy powders with added carbon black [325]. Practical capacities of 90-100 Ah/kg could be achieved in this way even for thicker layers. Self-discharge of PPy was low, as mentioned. However, in lithium cells with solid polymer electrolytes (PEO), high values were reported also [326]. This was attributed to reduction products at the negative electrode to yield a shuttle transport to the positive electrode. The kinetics of the doping/undoping process based on Eq. (59) is normally fast, but complications due to the combined insertion/release of both ions [327-330] or the presence of a large and a small anion [331] may arise. Techniques such as QMB/CV(Quartz Micro Balance/Cyclic Voltammetry) [331] or resistometry [332] have been employed to elucidate the various mechanisms. 

One of the battery prototypes for electric vehicles had a volume of 3201 and mass of 820 kg. The positive electrode is manufactured from FeS with the addition of C0S2. A few layers of the active material alternating with graphitized fabric are placed into a basket of molybdenum mesh welded to the central molybdenum current collector. The positive electrode is wrapped into a two-layer separator. The inner layer consists of Zr02 fabric and the outer layer of BN fabric. The negative electrode consists of a lithium-silicon alloy in the porous nickel matrix. The container and the cover are manufactured from stainless steel and electrically connected to the negative electrode. The prototype was drained with current up to 50 A, and the specific power was as high as 53 W/kg (Martino FJ et al, 1978). 

Ortiz, G. F, Lavela, R, Knauth, R, DJenizian, T, Alcantara, R, and Tirado, J. L. (2011]. Tin-based composite materials fabricated by anodic oxidation for the negative electrode of Li-ion batteries,/ Electrochem. Soc., 158, pp. A1094-A1099. 

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