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Energy Harvesting Widens Opportunities for Microbatteries

Harvesting tiny amounts of charge requires tiny storage devices. Thin film, miniature and microbatteries supply a range of solutions for RFID, wireless sensor networks and other portable applications.

Linnea Brush, Senior Research Analyst, Darnell, Inc.

Currently, most energy harvesting technologies are using battery back-up and are likely to for several years to come. Companies are trying to find appropriate energy storage alternatives to traditional batteries, however. Batteries are problematic for large-scale wireless applications. Today’s cost premium is typically below what it costs to swap the battery one at a time, including battery cost, labor and so on. Over an expected lifetime of 15 years, a self-powered sensor could provide “significant” cost savings.

Because of the generally low duty cycles of wireless sensor networks, energy density and cycle life requirements take precedence over power density. Thin-film batteries show promise, but low capacities per area and high processing temperatures are still creating obstacles. Thick-film approaches improve capacity, but a compatible, effective solid-polymer electrolyte has yet to be deployed commercially. Although liquid-phase electrolytes are an option for wireless sensor nodes, the packaging costs and environmental constraints required are generally prohibitive, according to a 2008 report from UC Berkeley and LV Sensors.

Still, thin-film cells offer advantages. They can be stored for decades yet retain almost all their charge, according to developers, and they deliver powerful bursts of energy if needed. In many applications, they can be actively used for decades, since they can be charged and discharged tens of thousands of times. This makes them appropriate for “hard to access” places that make traditional batteries problematic – the applications targeted by energy harvesting technologies.

The Market for Microbatteries

Thin film, miniature and microbatteries are not necessarily new. Despite the challenges, these products are facing an expanding market, with new competitors vying with established companies. As the problems with existing batteries become more publicized, companies are coming out with new battery choices, both primary and secondary, for wireless sensor networks.

NanoMarkets projects that the value of the thin-film and printed battery market will reach $5.6 billion by 2015. Of this, about $2.5 billion will be non-lithium batteries. Volume sales are critical. For technologies such as RFID, sensors, smart cards and medical devices that are also high volume and cost-sensitive, the ability of manufacturers to add cheap power sources is crucial. The NanoMarkets report says that thin-film and printed batteries will be driven primarily by active and battery-assisted RFID.

A report from Innovative Research and Products (iRAP) says that, from 2006 to 2011, medical implantables will show the highest annual average growth rate for thin-film batteries (58.4%), followed by MEMS devices, flexible papers, cosmetics and E-papers (46.1%), smart cards (37.9%), and RFID tags (35%). Regionally, North America captured about 61% of the market in 2006, followed by Japan at 19% and Europe at 17%. iRAP projects that the market for flexible, thin-film batteries will reach $230 million by 2011, with an average annual growth rate of 41.1%.

Air Products, Dow Chemical, Intel and NEC have invested in thin-film and printed batteries. Companies like Power Paper, Solicore, Thin Battery Technology (now Blue Spark Technologies) and Enfucell are currently using printing processes to manufacture them that are expected to improve costs. Low-cost versions are usually carbon zinc, and the higher cost, better performance versions are usually based on lithium. In general, Europe is leading in printed and thin-film PV development. Energy-conscious politicians are driving development through large subsidies of both manufacturing and installation.

RFID Leads the Way

According to NanoMarkets, active and semi-active RFID tags, both of which use batteries, represent a sizeable market for thin-film battery makers. RFID is an attractive market because it is one of the few markets with the product volume that will enable battery manufacturers to achieve manufacturing efficiencies and significantly reduce product costs. A three- to five-year lifespan is normal, and 10 years have been required in some cases. Semi-active technology is more cost-effective. Thin-film/printable battery firms are targeting the RFID market because of the ability to increase range, power, data transfer speed, useful lifetime and operating temperature range. Thinner/flexible product packaging and rechargeability are also seen as important factors, as is the ability to print the battery onto a range of substrates.

Blue Spark Technologies introduced two disposable battery products for RFID tags; the carbon-zinc batteries can be used in both passive and active RFID applications. The 1.5V TBT UT Series delivers about 12 mAH of energy to tags and can be made as little as 0.02 inches thick. They are intended for use on RFID transit tickets, loyalty cards and smart labels, among other applications. The TBT HD Series delivers 8mAh and was developed for more power-intensive applications, from real-time locating systems to singing greeting cards.

Excellatron Solid State is also developing high-power-density thin-film batteries for RFID tags, using two patented substrates: metal foil and polymer. Both are flexible and compatible with web coating for large-scale, low-cost manufacturing. The company has developed high-rate deposition methods for the battery layers, along with low-cost hermetic packaging solutions.

Nanobatteries

AlwaysReady Inc. has an “electronically activated” Smart NanoBattery. The device exploits the phenomenon of electrowetting – the ability to electronically manipulate the way liquids behave when in contact with a solid or porous surface. Water will bead up on a surface that is superhydrophobic, but can be made to move or spread out by electrowetting. The same is true for an organic liquid if the surface is superlyophobic. The Smart NanoBattery operates by manipulating the liquid electrolyte via a proprietary silicon structure, a porous membrane, combined with a unique battery architecture. This technology can be used with various primary and secondary battery chemistries and produces batteries with virtually unlimited shelf life.

In April, 2008, AlwaysReady announced that it had successfully demonstrated the remote activation of its Smart NanoBattery. Building on the electrical activation mechanism, the remote mechanism is said to offer another way to obtain power on command from the NanoBattery. Remote activation is especially relevant for applications involving RFID tags for inventory control and asset tracking, unmanned ground sensors, and wireless sensor networks.

Infinite Power Solutions (IPS) has the LITE*STAR battery technology, which can be incorporated into semi-active RFID tags. The 0.13 mm battery has “virtually unlimited charge cycles,” according to the company, and can endure extreme temperatures. This makes it suitable for applications or environments such as industrial processing, where devices or components are subjected to some very high temperature processes. The battery has a wide power band, with ~100 mW peak.

Medical Applications

Indeed, medical devices are an application where thin-film technologies could provide value. Key factors in this market include flexibility, long periods between charges, and small form factor. Thin-film batteries could provide improved power for implants, limiting the need for battery replacement and patient surgeries, and offering smaller, thinner devices, which could be charged throughout the body.

In December, 2008, IPS announced the completion of its Series B round of financing – raising $13 million in new capital to fund the ramp to volume production of its new THINERGY™ (Figure 1) micro-energy cell (MEC™) product family. This recent financing augments the $35.7 million IPS raised in 2006 during its Series A round, which was used for the construction and build-out of what is described as the world’s first facility for volume manufacturing of solid-state, rechargeable thin-film batteries.

Figure 1: Infinite Power Solutions LITE*STAR battery

IPS’ THINERGY MECs are said to represent a new class of electronic components that are ultra-thin and flexible – said to provide nearly lossless energy storage along with “unrivaled” rechargeability, cycle life and power performance. IPS’ MECs are well suited for harvesting and storing all forms of ambient energy such as solar, thermal, RF, magnetic and vibration energy – which the company says provide a safe, reusable and clean energy source that can deliver a lifetime of power to electronic devices and systems.

Integrated Battery Management

In October, 2008, Cymbet Corp. developed what it describes as a “breakthrough” in battery technology with the introduction of the EnerChip CC CBC3112 and CBC3150 thin-film batteries with integrated battery management (Figure 2). The EnerChip CC combines the Cymbet EnerChip with a sophisticated battery control logic in a single surface-mount technology package.

Figure 2: Cymbet’s CC CBC3112 and CBC3150 thin-film batteries with integrated battery management

The EnerChip CC internally combines several power system features: thin-film battery, charge pump with integrated dc-dc converter, supply supervisor, low-ripple charger, configurable switchover to battery when input power fails, supply voltage status signals, and operation from 2.5 to 5.5V. The EnerChip CC CBC3112 is a 12 µAh device and the CBC3150 is a 50 µAh device. The EnerChip CC devices are packaged in either 7 x 7mm or 9 x 9mm DFN surface mount, reflow tolerant packages.

The EnerChip CC is described as a cost-effective solution in many applications: standby supply for microcontrollers, real-time clocks and SRAMs, wireless sensors and RFID tags, power bridging during exchange of main batteries, and energy harvesting with transducers such as inductive coils and piezoelectric beams. The device is a suitable replacement for supercapacitors and coin cells in applications such as thermostats, hand-held devices, medical diagnostic equipment and embedded computing systems. A single EnerChip CC can manage multiple external EnerChips for high-capacity applications up to 500 µAh. It can also power low-voltage systems at 2.5 and 3.3V.

Darnell Group Inc.
Corona, CA
(951) 279-6684
www.darnell.com

This article first appeared in the March/April, 2009 issue of Portable Design. Reprinted with permission.

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