Lead traction batteries

Polyethylene separators offer the best balanced property spectrum excellent mechanical and chemical stability as well as good values for acid availability and electrical resistance have established their breakthrough to be the leading traction battery separator. Rubber separators, phenolic resin-resorcinol separators, and mi-croporous PVC separators are more difficult to handle than polyethylene separators their lack of flexibility does not allow folding into sleeves or use in a meandering assembly in addition they are more expensive. 

Figure 4.8 Peripheral devices cooling system for the lead traction battery of an electric bus.

Typical dimensions for the /5-alumina electrolyte tube are 380 mm long, with an outer diameter of 28 mm, and a wall thickness of 1.5 mm. A typical battery for automotive power might contain 980 of such cells (20 modules each of 49 cells) and have an open-circuit voltage of lOOV. Capacity exceeds. 50 kWh. The cells operate at an optimum temperature of 300-350°C (to ensure that the sodium polysulfides remain molten and that the /5-alumina solid electrolyte has an adequate Na" " ion conductivity). This means that the cells must be thermally insulated to reduce wasteful loss of heat atjd to maintain the electrodes molten even when not in operation. Such a system is about one-fifth of the weight of an equivalent lead-acid traction battery and has a similar life ( 1000 cycles). 

The historical development of the separator and of the lead-acid storage battery are inseparably tied together. When referring to lead-acid batteries today one primarily thinks of starter batteries or forklift traction batteries, but the original applications were quite different. 

Table 4. World lead-acid traction battery production 1997 (million Wh, estimate)...

Table 11. Separators for lead-acid traction batteries...

The world market for batteries of all types now exceeds 100 billion. Over half of this sum is accounted for by lead-acid batteries - mainly for vehicle starting, lighting and ignition (SL1), and industrial use including traction and standby power, with about one-third being devoted to primary cells and the remainder to alkaline rechargeable and specialist batteries. 

By far the largest sector of the battery industry worldwide is based on the lead-acid aqueous cell whose dominance is due to a combination of low cost, versatility and the excellent reversibility of the electrochemical system, Lead-acid cells have extensive use both as portable power sources for vehicle service and traction, and in stationary applications ranging from small emergency supplies to load levelling systems. In terms of sales, the lead-acid battery occupies over 50% of the entire primary and secondary market, with an estimated value of 100 billion per annum before retail mark-up. 

Over the past few years a number of studies have been made of the use of lead-acid batteries for load levelling. The service required is very similar to that of traction batteries except that energy density is less important than cycle efficiency. 

Different types of lead-acid batteries have been developed as energy sources for many power applications, like traction and backup or standby power systems. The flooded lead-acid batteries have an excess or flooded electrolyte and they were the largest used at the beginning of the last century for many applications. Valve-regulated lead-acid (VRLA) batteries were developed as an alternative to the flooded lead-acid batteries, in order to maintain levels of distilled water and prevent drying of cells, which means safe operation for battery packs in electric... 

The classical scheme for the manufacture of flat pasted plates for automotive, traction and stationary lead-acid batteries is shown in Fig. 3.1. There is no difference between the technology of plate manufacture for conventional (flooded) and valve-regulated (VRLA) lead acid batteries. The two versions do differ, however, in the method of separation of the plates, the quantity and type (hquid or gel) of electrolyte, and in the design of the battery itself. 

VRLA as an EV battery. The traction battery in EVs has long been identified as the key to commercial success of this product line motors, transmissions, and silicon components can all attain reasonable economies of scale and technology, but the component which is the most resistant to cost-reduction is the battery. This is a critical point since batteries comprise approximately 20% of the total cost of lead-acid-powered vehicles and about 55% of the cost of Ni-MH vehicles (see Fig. 11.28) [2]. Therefore, batteries provide the best opportunity to reduce the overall cost of EVs. With the battery cost of advanced technologies such as Ni-MH greater than the vehicle cost, there is a clear need for a low-priced battery such as lead-acid can offer. 

Lead acid batteries have been used for more than 130 years in many different applications including automotive and various traction duties and also telecommunication systems and uninterruptible power supphes (UPS). The last two groups constitute the major part of the so-called stationary battery sector, and the lead-acid battery has proved to be a very reliable system for these appUcations. 

Sonnenschein was the first company to introduce gel battery technology to the market successfully. They started in 1958 with rather small batteries for flashlights. Since that time, this technology has steadily replaced the conventional, flooded lead-acid battery in various applications [38,71,72]. Phosphoric acid addition for cycling was first introduced in 1965. Larger gel batteries with tubular positive plates were developed for stationary applications in 1978. More recently, gel batteries have been produced for starter and traction applications, and thick, flat positive plates were added for telecommunications applications. 

Lead is used in batteries, inorganic chemicals, pipes, solders, electric wires, etc., but batteries accounted for 72% of the total usage of lead in 1997. Therefore it can be said that batteries play an important role in the recycling of lead. Lead-acid batteries are classified into motor vehicle batteries (for automobiles and motorcycles), industrial batteries (stationary batteries, traction batteries, etc.), small-size sealed batteries (for UPS and consumer products). Table 2.1 shows their shipments. 

As evident from these data, the electrochemically and chemically active components in a lead—acid battery account for about two-thirds of the total battery weight. Mass-produced SLI batteries have typical specific energy values of 34—40 Wh kg , whereas traction EV batteries have a specific energy of between 28 and 34 Wh kg ... 

The classical technological scheme for the manufacture of flat-plate lead—acid batteries is presented in Fig. 2.52. This technological process is basically used for the production of SLI, traction and stationary batteries. The process involves the following main production stages ... 

Table 15.1 presents the value ranges for the specific capacity per kg active mass (weight coefficients (jS) per Ah for the basic types of commercial lead—acid batteries SLI, traction and stationary. The table also gives the respective specific energies (by volume and weight). 

The most important market remains the car battery for starting, lighting and ignition (SLI), with approximately 50 x 10 units per year being sold in the USA. Lead/acid batteries are, however, also used on a very large scale for traction (e.g. delivery vans, milk floats, fork-lift trucks, industrial trucks — there are more than 100 000 such vehicles in the UK) and for stationary back-up or emergency power supplies. More recently, small lead/acid cells to compete with high-quality primary cells and nickel/cadmium cells for instruments, radios, etc., have also become available. 

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