Batteries Raise Li-Ion Peak Power to New Heights

Aug 15, 2007 4:51 PM
By Mark Valentine, Technical Editor, Power Electronics Technology

The VLV series from Saft features the highest-power commercially available Li-ion cells in the world, according to the vendor. The VLV series exhibits a specific power double that of typical high-power cells that are available for defense applications and hybrid-electric military vehicles. The series consists of three sizes of cells, the VL4V, VL8V and VL12V (see the figure) sizes, which promise to advance capabilities in military systems that require high peak power.

Another cell, the VL6A (designed for civil applications such as wind turbine blade pitch control), is slated for introduction later this year. Wind turbine blade-pitch control is a common application for ultracapacitors. However, VLV technology has both higher power and energy density than ultracapacitors, and can serve in this or any other application where ultracapacitors are currently used, according to Saft.

While the higher densities translates into reduced weight for given power and energy design targets, the interest in the VLV technology has been in larger systems, as opposed to portable or wearable power systems, according to Saft. Wearable power tends to be comprised of smaller, or polymer-based cells, which can be made to conform to a favorable form factor, but Saft’s VLV technology is based on larger cell sizes. However, smaller VLV cells (D cells) are available that can be used in smaller packages.

Furthermore, portable power deals mainly with energy density, and Saft’s VLV technology is specifically designed to provide high power. Therefore, the series is best suited for applications with extremely high-power pulsed loads. One range of applications that are the virtual epitome of pulsed loads are high-power lasers.

Saft Li-ion batteries are powering the Lawrence Livermore Solid State Heat Capacity Laser (SSHCL) system, which pre-dates the evolution to VLV technology, according to Saft; currently, there are no fielded airborne directed energy weapons systems. However, Saft batteries do power the ground-based Active Denial System. Saft’s technology is also being considered for use in future laser and high-power-microwave defense systems because of its very-high-power capability.

Apart from these more exotic defense applications, the VLV cells are currently deployed in more conventional military platforms. “Our VLV cells are already being manufactured and are currently in use on military fighter aircraft providing emergency back-up power to operate flight controls and to start the APU,” said Dr. Kamen Nechev, Manager of Advanced Development, Saft Space and Defense Division. “The VL6A is an exciting addition to our portfolio of very high power cells and will satisfy the power demands of many emerging technologies. We are in a unique position because Saft is the only supplier offering cells of this high level of power.”

Saft’s portfolio includes 6-Ah, 8-Ah and 12-Ah cells, with a maximum charge voltage of 4.1 V and an average voltage of 3.6 V. Specific power exceeds 9 kW/kg for two-second pulses, and 12 kW/kg for 100-ms pulses. The cells are capable of continuous discharge of 6 kW/kg, and the very high power cells are used in battery products ranging from 28 V to as high as 600 V.

The VLV cells from Saft are manufactured in Cockeysville, Md., and the full line is available now.

Figure. Saft’s VL12V cell is rated for a capacity of 12 Ah at 25°C, and up to 12,000 W/kg for a 100-ms pulse at 2.5 V. The VL4V and VL8V are smaller cells with smaller capacities, but have the same specific power.