Battery Designs

The performance of a battery is often designed to be limited by one electrode ia order to achieve special performance characteristics, such as overcharge protection and safety. The coulombic efficiency of the active mass is of particular iaterest ia battery design and performance. 

Some battery designs have a one-way valve for pressure rehef and operate on an oxygen cycle. In these systems the oxygen gas formed at the positive electrode is transported to the negative electrode where it reacts to reform water. Hydrogen evolution at the negative electrode is normally suppressed by this reaction. The extent to which this process occurs in these valve regulated lead —acid batteries is called the recombination-efficiency. These processes are reviewed in the Hterature (50—52). 

Covers for the battery designs in Figures 1 and 2 are typically molded from materials identical to that of the respective case, and vent plugs are frequentiy made of molded polypropylene. Other combinations are possible, eg, containers molded of polyethylene or polypropylene may be mated with covers of high impact mbber for use in industrial batteries. After the cover is fitted over the terminal post, it is sealed onto the case. The cover is heat bonded to the case, if it is plastic it is sealed with an epoxy resin or other adhesive, if it is vulcanized mbber. Vent caps are usually inserted into the cover s acid fiU holes to faciHtate water addition and safety vent gasses, except for nonaccessible maintenance-free or recombinant batteries. In nonaccessible batteries, the vent is fabricated as part of the cover. 

Whereas automotive batteries have the majority of the market, other types of lead—acid batteries, such as sealed and small maintenance-free varieties, are making inroads into various appHcations. The automotive battery s operating environment has changed substantially in the last 10 years. Underhood temperature has risen and electrical loads have increased. This trend is expected to continue as car manufacturers reevaluate thek design strategies and objectives. Battery design is changing to meet these needs. 

The network of lead wires must provide optimum mechanical support to the pellets of active material that fill the void space. Sufficient conductivity has also to be provided by the grid. Grids for positive and negative electrodes are usually similar. In batteries designed for extended service life, the positive grid is made heavier to provide a corrosion reserve. For very thin electrodes, a lead foil is used as the substrate and current conductor. 

The small-cell approach has been described as having many advantages in battery design [13] ... 

Wilson, B., Battery Design for Cleaner Production, The International Lead Management Centre (ILMC), NC, January 2001. 

The investigations of various types of carbon-based catalysts allow suitable air electrodes to be developed for use in the large variety of metalair cells and batteries designed in this laboratory. 

It is clear that no single separator satisfies all the needs of battery designers, and compromises have to be made. It is ultimately the application that decides which separator is most suitable. We hope that this paper will be a useful tool and will help the battery manufacturers in selecting the most appropriate separators for their batteries and respective applications. The information provided is purely technical and does not include other very important parameters, such as cost of production, availability, and long-term stability. 

Navy Primary and Secondary Batteries, Design and Manufacturing Guidelines, Department of the Navy, Sept 1991 p 85. 

As noted in section 3.1. the fabrication of cells in which the cathode and anode are separated by a conformal thin-film electrolyte, perhaps a few tens of nanometers in thickness, is on the near horizon. Thus, it is interesting to consider potential phenomena. not normally considered in battery design, that... 

The importance of developing pinhole-free, electrolyte films of nanometer thickness is potentially useful for all 3-D battery designs. For this reason, most of this section reviews the synthesis and characterization of this ultrathin polymer electrolyte with an emphasis on topics such as leakage currents and dielectric strength, which become critically important at the nanoscale. A few comments concerning the packaging of 3-D batteries are made at the end. 

Raes, F., and A. Reineking, A New Diffusion Battery Design for the Measurement of Sub-20 nm Aerosol Particles The Diffusion Carrousel, Atmos. Environ., 19, 385-388 (1985). 

It is common in many practical battery designs to immobilize a liquid electrolyte phase within a porous solid insulator. The electrolyte conductivity and ohmic loss in such a system are determined by the number of pores, their size, shape and tortuosity. The tortuosity coefficient, /3, is defined as the ratio of the mean distance covered by an ion traversing a porous matrix, to the direct distance of one side of the matrix to the other. The relative reduction in the conductivity of an electrolyte solution caused by confining it in a porous solid is called the conductivity attenuation, 0. For a matrix of uniform cylindrical pores it is given by... 

The primary objective of miniature battery design is to maximize the energy density in a small container. A compromise must be reached, however, since volumetric energy density decreases as cell volume decreases and the dead volume due to containers, seals, etc. becomes increasingly significant. A plot of energy density as a function of total volume is given in Fig. 3.28 for the zinc-mercuric oxide and zinc-silver oxide systems. 

The number of VRLA batteries used in stationary applications is increasing rapidly. They account for more than 5.2% of the total US standby power production and more than 60% of Japanese and European production. Fig. 5.15 shows a VRLA battery design for telecommunications standby power. Over the past decade, VRLA batteries have been scaled to sizes up to 3000 Ah for industrial applications. Although the original... 

A prototype battery of about 8 mm thickness and a total area of 1 cm2 had a rated capacity of 150 mAh over the full voltage range, which extends from 3.6 to 1.5 V. The battery design is suitable for circuit integration as a standby power source for low current electronic devices. 

---