Feature ArticleOceanographic Applications Of Lithium Battery Technology
By Lee Gordon
As remote sensors include more capabilities in ever-shrinking packages, engineers are looking to power management solutions that use advanced lithium batteries, which deliver enhanced performance and longer service life. While there are many different lithium chemistries, remote sensing applications mainly use lithium-thionyl chloride (Li-SOCl2) batteries because they offer the highest specific energy (energy per unit weight) and energy density (energy per unit volume) of existing battery chemistries. One reason for the high-energy density is lithium's large electric potential, which exceeds that of other metals and produces high voltages (typically 2.7 to 3.9 volts DC). The nonaqueous electrolyte used in lithium batteries can enable operation in extreme temperatures (-55° C to 125° C).
A CORK device, which measures temperature and pressure at the seafloor and deep in boreholes, uses a battery pack with six DD-sized primary cells, delivering 750 watt-hours over a service life of up to seven years. (Photo courtesy of the Woods Hole Research Center)
Li-SOCl2 cells are constructed two ways: bobbin-type and spiral-wound. Bobbin cells are best suited for long-term ocean deployments because they combine the highest energy density, the highest voltage, a wide temperature range and an exceedingly low self-discharge. Bobbin cells consist of an outer cylinder made of lithium metal and an inner electrode that is similar to a bobbin of thread. Spiral cells use flat sheets of metal wound around a core, providing a large surface area that can create high currents. The insulation between these layers reduces the volume of electrolyte the spiral cells can hold. Bobbin cells can hold more lithium, enabling them to deliver about 30 percent more energy than spiral cells of equivalent size.
Development of PulsesPlus Battery Technology
Approximately 10 years ago, Tadiran Batteries Ltd. (Lake Success, New York) developed PulsesPlus, a patented technology that combines a hybrid layer capacitor (HLC) with bobbin cells to combine the benefits of both technologies into a single battery pack. The HLC receives a trickle charge from the primary cell, storing a small amount of energy that then supplies short-duration, high-current pulses. HLC technology has evolved so that newer applications can now use fewer of them or smaller sizes.
PulsesPlus produces important advantages for long-term deployments. By using various combinations of bobbin cells and HLCs, battery packs can be optimized for each instrument. Because the primary cells charge the HLCs with a small current, the battery pack loses less energy to the primary cell's internal resistance. HLCs therefore make the battery packs even more efficient. And while lithium cells are known for voltage delays (i.e., a temporary reduction in voltage when starting to supply current, known as passivation), HLCs eliminate this problem. When the instrumentation draws a current, the HLCs supply the current with a minimal voltage drop. These features make PulsesPlus technology ideal for applications requiring high capacities, low average current and periodic high-current pulses.
Doppler Ltd. develops PulsesPlus battery packs for marine applications. Its design work gives Doppler Ltd. insight into how PulsesPlus battery packs actually work in the field, as well as the performance advantages of this battery technology.
A VEMCO VR2W monitoring receiver being secured to the seafloor to provide continuous listening for tagged fish and sea mammals. Data are extracted on site via a Bluetooth connection. (Photo copyright Matthew D. Potenski)
Remote Monitoring of Fish Telemetry
Underwater receivers and ultrasonic transmitters provide data that scientists use to track the migratory patterns of aquatic animals. This technology is also used in early warning systems that provide alerts when sharks or other predatory fish approach beaches. PulsesPlus battery packs are ideal for these applications, which call for exceptionally long deployment durations (five to 10 years). While most battery packs lose much of their energy to self-discharge in long-term deployments, PulsesPlus batteries retain 93 percent of their original capacity after 10 years.
This year VEMCO (Halifax, Canada) will introduce the VR4-UWM, an upgraded acoustic receiver for remote monitoring of aquatic species tagged with 69-kilohertz transmitters, 180-kilohertz transmitters or both. Designed for long-term deployments exceeding nine years at depths up to 500 meters, the VR4-UWM communicates with an acoustic modem at the surface that 'wakes up' the unit, transfers data, then returns the VR4-UWM to a standby mode to minimize power consumption.
Seeking to optimize product performance, engineers at VEMCO worked with Tadiran to design a battery pack that combines 24 D-sized primary cells and 12 HLCs. The primary cells deliver 1,600 watt-hours (152 amp-hours at 10.8 volts) over a 9.5-year design life for single-channel listening or 5.5-year design life for dual-channel listening. The HLCs deliver the high current required for the periodic communications via the acoustic modem. VEMCO also offers a version of the VR4-UWM powered by alkaline battery packs, but these packs can only provide power for one year.
The performance requirements of the VR4-UWM demanded a more robust and intelligent power management solution that could provide such features as dual-frequency listening capability at 69 and 180 kilohertz. The additional power and capacity provided by the PulsesPlus battery also supports design features such as omnidirectional listening and fast acoustic 'wake up' that enables the modem to communicate in less than 20 seconds. To continue this article please click here.
Lee Gordon (firstname.lastname@example.org) is president of Doppler Ltd., which he founded with Kent Deines in 2005. The company consults on oceanographic and electronic projects and also designs and develops electronic products.