By Jim Kerr
With the introduction of hybrid and electric cars, battery technology is creating a lot of discussion with consumers, the repair industry and the manufacturers. Battery technology and performance is rapidly improving but it is still the limiting factor in determining vehicle range, performance and fuel economy. Let’s take a look at what is currently or very shortly to be on the market.
The big news has to be the introduction of lithium ion batteries in automotive applications. Mercedes, General Motors and others are working with this technology and the advantages it provides. We already use Lithium Ion batteries in devices such as laptop computers and cell phones. Lithium is the world’s lightest metal and it is good at holding an electrical charge. These characteristics make it great for portable devices, where low weight is important.
Another important feature of lithium ion batteries is that they have no memory effect. Unlike other rechargeable batteries, lithium ion batteries can be recharged at any time and state of charge. Do this with other types and the battery materials will form crystals that limit how much energy the battery can store. This decreased ability to generate power is referred to as the memory effect.
Inside the lithium ion battery, you will find a positive electrode typically made of lithium cobalt oxide, lithium iron phosphate or lithium manganese oxide. There are many variations on the exact composition and General Motors tested more than 100 different combinations for use in electric cars. A thin plastic membrane separates the lithium from the graphite negative electrode. Copper layers on the outside of both the positive and negative electrodes hold it all together. As the ions pass through the plastic layer between the electrodes, power is produced. These batteries can be formed into a variety of shapes, which make them ideal for packaging where space is at a premium. However, a big disadvantage is that they are also more expensive to produce than other battery types.
Nickel Metal Hydride (NiMH) batteries have been the mainstay for hybrid vehicles so far and we will continue to see their use in the future. NiMH rechargeable batteries have become commonplace consumer items and it is hard to believe the first ones only appeared on the market in 1989. As automotive batteries they work well. Although heavier than lithium ion batteries, they are still lighter than lead acid batteries and in automotive applications they are charged by sophisticated computer-controlled regulators that extend the battery life long beyond that of a conventional lead acid type. Ask any of the auto manufacturers how long their NiMH battery will last and you won’t get an answer. However, an eight-year warranty is provided currently by all of them on the batteries and there are already hybrids running around with batteries that are much older. When these batteries are charged, they are typically only charged up to about an 80 per cent level maximum. This extends the life of the chemical reactions inside the battery and prevents them from overheating.
Most of our vehicles still use a lead-acid battery to start the engine and these batteries use liquid sulphuric acid solution as an electrolyte. Eventually the lead on the battery plates break down or hardens (sulphates). This can happen over several years, or it can happen in a few weeks if the battery is left in a discharged state. A battery will last longer is used regularly and recharged properly. Vehicle charging systems are now mostly electronically controlled and this has helped prolong the life of automotive lead-acid batteries.
You may find glass mat batteries or gel batteries on the shelf at your automotive outlet. These are a little more expensive than lead-acid batteries so they are not used as original equipment, but they have advantages in some applications. These batteries are “sealed” so they can be mounted in a variety of manners. Although the batteries are sealed, they do have a safety vent valve that can open if the battery becomes overheated. In glass mat batteries, the electrolyte is absorbed into a mat of fine glass fibers. In the gel batteries, the electrolyte is a gel. Also, the construction of the plates is different in these batteries from conventional lead-acid batteries to take advantage of the different type of electrolyte. Gel batteries and glass mat batteries work well where there is a lot of vibration, or the battery needs to be mounted in a restricted space.
In the future, we may see zinc-air batteries or even molten salt batteries. With all the time and money currently being spent on battery development, you can expect battery technology to change rapidly over the next few years, but expect conventional lead-acid batteries to still be around for a long time.