Battery technology separators

To further reduce weight and improve energy density, several companies are developing thin lead film electrodes in a spiral-wound construction with glass fiber separators. Already on the market for cordless electric tools, this battery technology may eventually be used in electric vehicles. 

Figure 2. Section through a cylindrical AA-size alkaline Mn02-Zn cell. Primary cells and the rechargeable cells discussed later have same construction and differ only in separator type, electrode compositions, and cathode / anode balance. (Reproduced by courtesy of Battery Technologies, Inc.).

Two VRLA battery technologies are currently predominant, i.e., absorptive glass mat (AGM) and gel designs. In the former, the AGM immobilizes the electrolyte and simultaneously functions as a separator. In gel batteries, the acid is immobilized by means of fumed silica, and an additional separator is required to fix the plate distance and to prevent electronic shorts. 

Many advances have been made in battery technology in recent years, both through continued improvement of specific electrochemical systems and through the development and introduction of new battery chemistries. Nevertheless, there still is no one ideal battery that gives optimum performance under all operating conditions. Similarly, there is no one separator that can be considered ideal for all battery chemistries and geometries. 

Imidazolium-based ILs have been increasingly used as green solvents to replace the volatile and relatively toxic oiganic solvents, in homogeneous and heterogeneous catalysis, material science, nanomateiials, lithium-ion batteries, and separation technology. 

Failure Mechanisms. Failure meehanisms for earlier niekel-zine batteries include zinc migration, shape change, dendritie shorting and hydrolysis of the eellulose-based separator. These have been substantially eliminated in modem niekel-zine battery technology. Dendritic shorting and shape change have been virtually eliminated through the use of redueed solu-... 

Battery breaking technologies use wet classification to separate the components of cmshed batteries. Before cmshing, the sulfuric acid is drained from the batteries. The sulfuric acid is collected and stored for use at a later stage in the process, or it may be upgraded by a solvent extraction process for reuse in battery acid. 

The original expanded film membranes were sold ia roUs as flat sheets. These membranes had relatively poor tear strength along the original direction of orientation and were not widely used as microfiltration membranes. They did, however, find use as porous inert separating barriers ia batteries and some medical devices. More recentiy, the technology has been developed to produce these membranes as hoUow fibers, which are used as membrane contactors (12,13). 

Redox flow batteries, under development since the early 1970s, are stUl of interest primarily for utility load leveling applications (77). Such a battery is shown schematically in Figure 5. Unlike other batteries, the active materials are not contained within the battery itself but are stored in separate tanks. The reactants each flow into a half-ceU separated one from the other by a selective membrane. An oxidation and reduction electrochemical reaction occurs in each half-ceU to generate current. Examples of this technology include the iron—chromium, Fe—Cr, battery (79) and the vanadium redox cell (80). 

This section reviews the state-of-the-art in battery separator technology for lithium-ion cells, with a focus on separators for spirally wound batteries in particular, button cells are not considered. 

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