Advances in battery chemistries push the portable market forward

With all the attention and exposure given to the introduction of the latest portable electronic devices, it is easy to overlook the strides and advances being made in the power sources that run these devices. The latest in technological wonders such as iPods, high-speed notebook computers, digital cameras and converged communication devices like BlackBerries are evolving and improving at a phenomenal pace. As a result, they require an increasing amount of power. Today's consumers demand not only greater functionality in their electronic devices, but also aesthetically appealing form factors. This demand has resulted in the emergence of lithium-ion batteries as the power source of choice for portable electronic devices.

Lithium-ion and Lithiumpolymer batteries currently hold 69.4% of the total worldwide rechargeable battery packs market share. Their combined unit totals are expected to increase from 739.1 million units in 2005 to 1.4 billion units in 2010, a compounded annual growth rate of 13.4%. This growth will result in a combined 84.6% unit market share for lithium battery technology by 2010.
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COMPLEX DEVICES
Also, as portable electronic devices become more complex, original equipment manufacturers (OEMs) will be forced to re-evaluate their battery selection carefully. In some cases, these new criteria will influence battery design. For example, OEM demands for physically smaller units are driving developments in battery form factor, while devices with more bells and whistles put a greater strain on battery life span and thus increase efforts in chemistry research. In order to meet all of these demands, manufacturers are not only investing time and money in improved battery chemistries, but also in semiconductor development and better business models.

Increased research also continues to boost the performance of lithium-polymer batteries, which are essentially Li-ion batteries but with two distinctions. The Lipolymer cells use a gelled electrolyte rather than a liquid electrolyte and an aluminum laminate casing instead of the aluminum or steel can associated with Li-ion prismatics. Li-polymer cells have been touted because of their ability to be manufactured in the thinnest form factors (below 4mm).

Valence Technology (www.valence.com) is producing phosphate batteries that "capitalize on the energy density and efficiency of lithium-ion" with the added benefit of low cost. Valence calls these new batteries Saphion lithium-ion polymer batteries. They are packaged in foil, significantly reducing battery weight. Additionally, Valence claims that the phosphate-based chemistry is more thermally stable than traditional lithium-ion, which enables the fabrication of larger cell formats. The batteries can be used for many applications, such as laptops, cellular phones and other portable devices.



HIGH SPECIFIC ENERGY
Traditionally, batteries based on lithium chemistries have always had the highest specific energy and energy density among battery types. As a result, they are expected to take the lead in providing power for portable electronic devices. However, due to the rapid advancement in portable electronic technology, manufacturers are now looking at chemistries whose performance would provide an alternative to traditional lithium-ion and lithiumpolymer batteries. One of these alternatives, lithium thionyl chloride, is a primary battery. It has the highest energy density and the highest open-circuit voltage, 3.6V, of any lithium chemistry, primary or secondary. Thus, in most applications, only one cell is required to maintain sufficient operating voltage, so long as one cell is sufficient to supply the current necessary for the required operating lifetime. The expected service life of this battery is expected to be 15 to 20 years. This holds true for all case types, cylindrical, coin or wafer.

LOW CURRENT
Lithium thionyl chloride cells are best suited for applications that have very low continuous current and moderate pulse current requirements, a description that fits small electronics, computer memory backup power and most RFID tag applications. Their extremely long service life and low self-discharge rate make them ideal for applications where physical access is limited. This long service life is most valuable when circumstances require a very long time to battery replacement or where replacement is not desired during the service life of the device being powered.

Aside from the emergence of lithium technology, there have been very few battery innovations over the last decade that have had much impact on the rechargeable battery market. However, the incorporation of carbon nanotubes into the lithium chemistry could change all of that in the near future. Nanocrystalline materials and nanotubes have been demonstrated to greatly improve both power density, lifetime and charge/discharge rates. However, they are still very expensive and their practical application in the batteries is currently not costeffective.



Also intriguing, but still in the development stage is a process to develop a new class of lithium batteries. Polyplus Battery Company (www.polyplus.com) claims to have made a "revolutionary" break-hrough in lithium metal battery chemistry based on glass-coated Lithium metal electrodes that can be reversibly cycled in extremely aggressive liquid electrolytes, including both aqueous and non-aqueous systems. This method coats the electrodes in a lithium-ion battery with an ultra-thin glass layer that can improve the battery's performance and life span. The technology can potentially be used to make smaller, lighter batteries for portable electronic devices.

Also fueling the portable power market is research into alternative battery chemistries such as zinc-air and manganese silicon batteries. Zinc-air cells work like conventional batteries in that they generate electrical power from chemical reactions. However, instead of packing the necessary ingredients inside the cell, zinc-air batteries get one of their main reactants oxygen from the outside air. This chemistry may offer consumers a new choice of power for handheld electronics. Also available is the manganese silicon lithium rechargeable battery. This battery uses silicon oxide as anode and lithium manganese composite oxide as cathode. As a result, it offers twenty times the capacity of conventionally available batteries, in addition to longer cycle-life and highly stable overdischarge characteristics. It is best suited for use in back up power supplies for memory or clocks in various small and thin equipment like cellular phones, cordless phones, PDAs and personal computers.



BUSINESS CHANGES
Two noteworthy business model changes are underway that will greatly affect the portable power packs industry. The first and clearly most pervasive trend affecting this industry is the commoditization of lithium-ion and lithium-polymer batteries and the resulting shift of production of these batteries to contract manufacturers in China. Secondly, Intel (www.intel.com) has initiated the Mobile Value-Added Distributor (MVAD) program, which is designed to increase the market share of "clone" notebooks. Both of these business model shifts place additional downward price pressure on lithium-based batteries, and hence on the portable power market overall.

There are a variety of power semiconductor advances that have helped to maximize battery life and meet the demand for portable power electronics. New low dropout regulators (LDOs) have come to market that improve energy efficiency. Better "fuel gauge" devices have been developed by a variety of companies. These technologies provide a more accurate and more precise measure of usable battery life, which helps users maximize the time they can run their portable devices.

SYSTEM-CHIP TECHNOLOGY
Also, Hitachi Ltd, (www.hitachi.com) a major electrical machinery manufacturer, and Renesas Technology Corp. (www.renesas.com), a microcontroller producer equally owned by Hitachi and Mitsubishi Electric Corp (www.mitsubishielectric.com), have developed a systemchip technology that can reduce the power consumption of cellular phones during standby time by 90%. This technological breakthrough concerns a CMOS transistor used in mobile phones and other small terminals. The successful application of this technology is expected to enable mobile phone batteries to last ten times longer with a single recharge.

In addition, large semiconductor manufacturers such as Texas Instruments (www.ti. com), Linear Technology (www. linear.com), Fairchild Semiconductor (www.fairchildsemi.com), Phillips Semiconductors (www.semiconductors.phillips.com) International Rectifier (www.irf. com), Semtech (www.semtech.com) and others have introduced a variety of products designed to extend battery life, or at least better a battery's ability to provide necessary power for portable electronic devices. For example, Texas Instruments recently announced digital RF processor (DRP) architecture. Similar designs anticipated from other suppliers combine RF analog functions with low-power, digital complimentary metal-oxide silicon (CMOS) logic on a single chip. The new architecture minimizes the analog portion of the circuit by "immediately" digitizing all analog RF signals. Since large blocks of CMOS logic can now operate at multi-gigahertz frequencies, sampled-data processing techniques, switchedcapacitor filters, over-sampling converters and digital signal processors can take over the role of analog amplifiers, filters and mixers. The resulting integrated solution consumes half the power of today's equivalent mixed-process solutions. Innovations like this extend battery runtime by reducing power requirements, hence enabling batteries to meet today's and possibly tomorrow's power requirements.