That’s another great question, and also a very broad one.  Let’s look at the two most talked about advanced battery technologies individually.

Nickel-Based Battery Technology
In this section, we’re going to take a quick overview of the nickel-cadmium battery and its direct descendent, the nickel-metal-hydride battery.

The sealed nickel-cadmium (or Ni-Cad) battery was developed in the mid 20th century to meet the need for a rechargeable battery that was compact and robust.  The technology was successful enough to be incorporated into a wide range of applications.  Today, consumers can still find a wide array of cordless power tools that utilize nickel-cadmium batteries.  They are solid and dependable and can endure high rates of discharge.  Unlike classic lead acid batteries, they can be left in a discharged state and re-charged without damaging the battery.  Despite these virtues and their popularity, Ni-Cad batteries have some pretty serious limitations.

• They are quite heavy, meaning that their energy density is relatively low.
• They are subject to “memory effect” if not completely discharged before recharge.
• They self-discharge relatively quickly if stored
• The cost to manufacturer these batteries has risen because of the dramatic increase in nickel (from $10K/ton in 2003 to well over $25K/ton in 2006)
• Cadmium is a toxic metal that is coming under increasing scrutiny due to environmental issues.

The nickel-metal-hydride (NiMH) battery is a new technology that was developed in the 1970s.  This chemistry has better energy density characteristics than Ni-Cad and is not nearly as prone to memory effect.  NiMH batteries have very good cycle life characteristics.  That is, they have the ability to be recharged a high number of times after deep discharges.  The technology also has a much lower level of toxic components than Ni-Cad batteries.  Again, though, the chemistry has its limitations:

• Require tightly controlled voltage and current parameters during charging.
• A limited cycle life if deeply discharged.
• Limited shelf life, especially if stored at high temperatures.
• Elevated self-discharge rates.  (Even higher than Ni-Cad.)
• Subject to crystalline formation (analogous to sulfation in lead acid batteries) if not used regularly.

Furthermore, there are cost concerns stemming from the limited availability of nickel.  Since steep nickel prices have been primarily driven by rapid growth in the Chinese economy and its use of nickel in stainless steel, batteries based on nickel will continue to increase in price.  As these batteries become more popular, increased demand for nickel could drive prices sharply upward.

Lithium-Ion Technology
Lithium-ion (abbreviated Li-ion) is probably the most talked-about battery technology in the world today.  The idea behind lithium batteries has been around for many years, but only relatively recently in the last 10 years has the technology been developed to mass-produce these batteries for practical applications.  Rechargeable Li-ion batteries are commonly found in devices where their virtues of light weight and compact size (energy density) are most valued.  In the consumer market, these batteries are commonly found in laptop computers, cell phones, and digital cameras and camcorders.  (In the past, as we have seen, consumer devices that required rechargeable batteries always used nickel-cadmium technology, but this has fallen from favor for a variety of reasons, including weight, usage constraints, and toxic components.)

Lithium-ion batteries are solid state.  That is, they contain no liquid electrolyte.  This makes them attractive for uses in the types of consumer products mentioned above.  As we’ve seen, they have good energy density.  Their self-discharge rate is much lower than Ni-Cad and NiMH batteries.  All of these characteristics have led to vastly increased use of Li-ion batteries in the past few years.  With this increased use, some problems have surfaced.

Lithium ion batteries have received some negative publicity recently. Several prominent laptop computer manufacturers recently recalled a total of nearly six million lithium-ion batteries due to concerns that they could overheat and catch fire. If this can occur in the relatively small batteries powering laptop computers, the potential for this to occur is magnified if the chemistry is up-sized, say, for use in a vehicle. Although performance of small single Lithium-ion cells can be very high, manufacturers must put a lot of controls on it to throttle its performance when these cells are placed into a multi-cell application, because with Lithium-ion, one must worry about such issues as thermal runaway.

• As promising as the technology is in many ways, the industry must confront the combustibility issue.
• A key component of lithium ion batteries is cobalt.  Cobalt is also an alloying element in certain types of steel.  Current high demand for steel has caused cobalt prices to increase dramatically (to well over $70K/ton).  Widespread use of Li-ion batteries could drive prices even higher, upsetting the delicate cost / benefit ratio of this technology.