By Hariharan B, Research Analyst
Lead acid batteries are the preferred choice for powering automobiles due to certain advantages they carry and also because they are economically viable. Batteries that currently power automobiles are 12-volt (V) starting, lighting and ignition (SLI) batteries that are either of flooded construction or of the valve regulated construction.
Today's lead acid batteries used for powering the automobiles have a limited power range and with the demand for power increasing among the automobiles, automotive vendors and battery manufacturers have been on the lookout for an efficient power device that provides the perfect solution in addition to being cost effective!
With the advent of hybrid electric vehicles and battery powered vehicles, the demand for batteries has been on the upswing. Also, the fact that batteries are environmentally friendlier in comparison to the existing petroleum products that are used to power the automobiles make them much more valuable as a product for use in transportation.
The SLI batteries used today are typically the 2V cells connected in series to provide 12V as a whole. The SLI battery comes into force when the automobile is being started and this current given out by the battery is called the cranking current which could vary from anywhere between 200 – 300 Amps up to 800 – 1000 Amps within a fraction of a few milliseconds. The batteries also come into play for powering certain other electrical and electronic equipments within the automobile.
The automotive segment is the biggest market for lead acid batteries while the stationary and motive applications come a close second in terms of demand for lead acid batteries. The automotive segment offers enormous opportunities as the market is widespread across geographical regions and with the demand coming in from each and every automobile thats manufactured, the growth is likley to be positive with a demand that is likely to be sustained for years to come.
The current battery demand in the automobile segment is being met by lead acid batteries mainly from the SLI segment, while the deep cycle batteries cater to certain specific requirements especially among the electric and hybrid vehicle category. The electrical power needs of a battery / hybrid powered vehicle are much more in comparison to the power needs of typical petroleum fuel powered vehicles.
Future Power Needs
Hybrid electric vehicles (HEV’s) combine the internal combustion (IC) engine of conventional vehicles with the energy storage device and electric motor of electric vehicles. The part of energy storage is normally the batteries, ultracapacitors and flywheels, while batteries are by far the most preferred energy storage choice. Alternatively, in a pure battery powered vehicle, the entire power is being generated by the batteries and this in effect needs larger amount of power as the output from the battery.
On the other hand, gas powered vehicles are increasing their power needs due to increased dependence on electronics and automation. The 42V electrical system demands a 36V battery that can power the demands of the automobile. The challenge is to have a single 36 V battery with a slight increase in size and weight in comparison to the 12V battery and double or triple the electrical performance.
Desirable characteristics in a battery for HEV applications are high peak and pulse specific power, high specific energy at pulse power, a high charge acceptance to maximize regenerative braking utilization with a long cycle life and the fact that they are abuse resistant. All these requirements call for certain improvements in the existing lead acid batteries as they are not designed for pulse power, have low specific energy and short cycle life.
The aforementioned attributes of a battery required by HEV’s are being met by certain other chemistries like nickel metal hydride (Ni-Mh), lithium ion (Li-ion) and lithium ion polymer which meet some of the attributes successfully. Though the above three chemistries are suitable to an extent, aspects like recycling, performance at high temperatures and economic viability limit the acceptance and commercial production of the same.
One of the key reasons for the slow pace in implementation of either the 42V batteries or the acceptance and wide commercial production of complete battery powered / hybrid electric vehicles is the fact that they are prohibitively expensive due to the high cost of the batteries involved, the technology gap to meet the desired expectations and the aspect of compatibility to be met to make a successful transition from gas powered 12V automobiles.
Bipolar Lead Acid Batteries: A Suitable Option
Bipolar lead acid batteries are suitable for pulse power applications (very high power during milliseconds). The bipolar lead acid batteries in comparison to conventional lead acid batteries deliver higher power levels. They offer increased energy density while quadrupling power density in comparison to conventional lead acid batteries.
This is made possible due to the fact that they have more cells spaced closer together. The bipolar plates that connect adjacent cells have a shorter current path and a larger surface area than the connections in conventional cells. This construction reduces the power loss that is normally caused due to the internal resistance of the cells.
A number of advantages are offered by bipolar lead acid batteries as an energy storage device that it makes this technology suitable for use in battery electric / hybrid vehicles. Some of them are:
- In a bipolar construction, much less material weight is needed for electronic conduction of the current in the grid and in the cell connections in comparison to conventional lead acid batteries.
- A well established supply chain and manufacturing methodologies for lead acid batteries make it all the more reliable and provide an attractive cost equation.
- Lead as a raw material is less expensive than the other metals used in certain other battery chemistries and is recyclable to a very large extent.
- Lead acid batteries are abuse resistant to a large extent and the nominal voltage of 2V per cell reduces the number of cells needed for the entire battery string.
Though they carry a lot of advantages, some aspects that leave a lot to be desired before successful commercialization and acceptance include:
- A corrosion resistant, light weight, less expensive bipolar plate material is required.
- The state of charge (SOC) during cycling is often in the range of 30-70 percent which increases the risk of sulfation and hence reduces the life of the battery.
These aspects of the bipolar lead acid battery make it an attractive option for commercializing and implementation of the same for the existing automobiles with the 12V batteries and for the upcoming 42V electrical systems.
With the implementation of 42V systems gaining ground and with the acceptance and implementation of hybrid / battery electric vehicles across the world, the demand for batteries is going to be on the rise and this gives an explosive opportunity to any new battery technology that is economically viable and technically feasible.
Lead acid batteries have proven their performance levels for years together and the bipolar lead acid batteries in addition to the features of conventional lead acid batteries offer some additional features like delivering more power with significant reduction in weight in comparison to a conventional lead acid battery making it an exciting and attractive option for powering the hybrid / battery electric vehicles over other existing chemistries.
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Stay tuned for new Frost & Sullivan Lead Acid Battery research! World Stationary, Motive, and Starting, Lighting, and Ignition Market studies are set to publish by the end of Quarter 2 2004.