Negative active materials properties

NEGATIVE ACTIVE MATERIALS AND THEIR PROPERTIES 2.3.1 Composition of Negative Active Materiaes... 

Comparative Evaluation of the Traction Battery Separators Which separator properties are important for use in traction batteries For this aspect primarily the highly predominant application, namely forklift traction batteries, is to be considered chemical resistance against attacks by acid and oxidation, mechanical stability for problem-free assembly, stiffness to counteract overexpansion of the negative active material, and low acid displacement are particularly desirable. Delay in antimony poisoning, absence or near-absence of oily deposits in the cells, and - last but not least - a low electrical resistance complete the requirement profile. 

These requirements hold for the films at both the positive and negative electrode surfaces. Thus, these surface films frequently comprise quite complex mixtures of reaction products and their presence affects the kinetic properties of charge transfer across the interface. It is the deviation of surface film s properties from meeting this set of ideal requirements that is the single most important cause of cell failure in a large fraction of cases. When the decomposition reactions occur, a small amount of active material must also be irreversibly consumed. 

Interactions between the precious metal and support influence the performance of the catalyst. Beil (1987) has defined metal-support interaction as depending on contact between the metal particle and the support which can be a dissolution of the dispersed metal in the lattice. The interaction could also depend on the formation of a mixed metal oxide, or the decoration of the metal particle surface with oxidic moieties derived from the support. It is possible that in this study, the differences in catalytic performance of the same active material supported on different washcoats can be attributed to any of these phenomena. Another explanation could be that the support materials exhibit different acid-base properties. According to the Bronsted and Lewis definitions, a solid acid shows a tendency to donate a proton or to accept an electron pair, whereas a solid base tends to accept a proton or to donate an electron pair. The tendency of an oxide to become positively or negatively charged is thus a function of its composition, which is affected by the preparation method and the precursors used. Refer to the section Catalyst characterization for further discussion on the influence of support material on catalyst performance. To thoroughly examine the influence of the support... 

In a different battery test with a simulated EV load pattern, a SWP-7 cell with an assembly pressure of 60 kPa achieved 450 cycles versus 270 cycles for an AGM cell with 73 kPa. The failure mode was found not to be the expansion of positive plate but, rather, sulfation of the negative plate. This led to the conclusion that the favourable mechanical properties of SWP-type separators suppress degradation of the positive active-material. 

Since BM-500B is a particle dispersion type, it does not increase the viscosity of the solution, and when used exclusively provides insufficient properties for paint. Therefore, it is important to employ a thickener such as the CMC used with BM-400B for negative electrodes. Zeon Corporation has been developing various thickeners for positive electrodes depending on the types of the active material. The details are not described here due to lack of space. 

In conducting polymers, the extra carriers added upon doping are able to drift under an applied electrical field. In semiconducting polymers, no carriers are available except those thermally excited across the gap. However, negative (positive) carriers can be injected into the material by metallic contacts when the barrier between the metal work function and the LUMO (HOMO) molecular levels is overcome. Then, the injected carriers can move inside the semiconductor if a bias field is applied. Injection of carriers and their transport is a fundamental issue for all electronic devices and transistors in particular. In the following, main transport properties of organic semiconductors (both small molecules and polymers-based) used as active materials in transistors will be reviewed. 

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