Rechargeables: More energy, less cost
By James Carbone -- Purchasing, 12/10/1998
For years, the demise of nickel cadmium cells has been forecast. Nickel metal hydride cells and lithium batteries were to displace NiCd in all applications because they have a higher energy density resulting in longer run times for the electronic equipment they power.To a large degree, that has occurred. It's hard to find a nickel cadmium (NiCd) battery in a cell phone, camcorder, or portable computer. But unit shipments of NiCd cells are increasing, driven by such applications as power tools and interruptible power supplies, according to market researcher Frost and Sullivan. In 1996, about 1.7 billion NiCd cells shipped. By the year 2003, shipments will increase to 2 billion. But during the same time, revenue will fall from $1.5 billion to $1.27 billion. That means NiCd prices will fall over the next five years.
"Ten years ago NiCds were used extensively in cell phones," says Joe Carcone, vice president of marketing for Sanyo Battery. Sanyo manufactures NiCd, nickel metal hydride (NiMH), lithium ion, and is developing lithium polymer cells. "Eight years ago with cell phones it was 50% NiCd and 50% NiMH. Today there is no NiCd, about 70% NiMH, and 30% lithium. In five years, who knows?," he says. The same is also true with portable computers and camcorders.
But NiCd remains the battery of choice in power tools and are being used in UPS systems because they are low cost and have some venerable characteristics. "NiCd can be stored up to 10 years," says Carcone. "No other systems can do that. NiMH and lithium ion are like tomatoes, they last only a few months. They go into self degradation on the shelf. NiCd can also operate at -40 degrees??. Other systems can't operate below zero. Most of the material in NiCd's can be used over and over again if recycled," he says.
Carcone says that over the years, battery manufactures have been able to increase energy density in NiCd cells through improvements in battery chemistry. On average, energy density has increased about 5% per year. However, in January, Sanyo will introduce new NiCd batteries that will have 30%-40% more energy density than current NiCd cells.
"We are going to introduce a brand-new generation of NiCd that will have changes in its electrochemistry," says Carcone. "We have found some new compounds that we are adding which will extend power density." Carcone would not say what the compounds were, but they have been used in other systems.
"In the same volumetric space you will have more run time at higher rates. Duty cycle will be 1,000 cycles. We are going to reinvent NiCd, largely for applications like power tools and UPS and local wireless loop," says Carcone.
The future of NiMH cells is probably more of a question mark than NiCd cells. NiMH sales are used in portable computer camcorders and cell phones. But so are lithium rechargeables.
"NiMH [cells] offer higher energy density almost equivalent to lithium ion, at almost 50% more weight but 50% less cost," says Carcone. "So when cost is the issue, portable equipment manufacturers will use NiMH. When cost is not the driver, for example in a notebook, they use lithium ion because the total cost of the system can absorb the additional cost of the battery. If NiMH can't compete on cost per watt hour and lithium ion can beat or meet it on cost per watt hour, lithium will be used in everything," he says.
There are other disadvantages to NiMH besides cost, according to Derrick Fritsch, engineering manager for sony's lithium-ion division. Nickel metal hydride has memory effect. Memory effect occurs when a battery is recharged before it has been fully discharged. If a battery is recharged after 50% of its run-time capacity, it will "remember" that shorter discharge period and after being recharged, will discharge to only 50% of its run-time capacity.
"You just don't get two years reliable use out of nickel metal hydride batteries," says Fritsch. NiMH also delivers fewer cycles than lithium.
Still, because of the cost advantage, NiMH cells will be used in lower-end portable computers and lithium ion in more expensive equipment costing $500 or more.
In late 1999, battery manufacturers are expected to have lithium polymer batteries in the market. The batteries are similar to lithium ion batteries, but will use a plastic non-liquid electrolyte. The cells will have high-energy density and are stable. Polymers are light, flexible, and can be molded to fit a certain space in a computer. That flexibility will be popular with portable-computer manufacturers because batteries are frequently the last concern for designers.
Lithium polymer cells most likely will be placed on the back of a portable computer screen. "Lithium polymer can be used in a 3 mm thick cell," says Fritsch. They'll be thin but measure about 8.5 x 11 inches. "You don't have to place it in a can so the amount of battery you have in the same area is significantly better," says Fritsch. "And it's only half the weight of lithium ion so you'll get a lot more efficiency."
The cells will also be the most expensive of all the rechargeables and for that reason alone won't replace lithium ion. Instead there will be a hierarchy of applications.
Lithium polymer will be used in high-end portable computers and lithium ion and nickel metal hydride in equipment.
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