Until recently, single-use high energy devices were typically powered by reserve/thermal batteries using decades-old technology. Recognizing that battery performance limitations could hinder new product development, the U.S. DoD identified a “critical need” for a new generation of high-power, long life batteries.
In response to this challenge, high energy lithium metal oxide batteries have been developed that outperform legacy batteries on many fronts: extended shelf life, system readiness testing, instantaneous activation, and cost. These batteries compete directly with reserve/thermal batteries and spin-activated batteries, and less frequently with silver zinc, LiSO2, and rechargeable batteries.
Reserve/thermal batteries encompass a broad range of chemistries, including lead-acid, silver-zinc, and lithium thionyl chloride. The most popular version is the thermal battery, which utilizes a metallic salt electrolyte that is solid, inert, and non-conducting at ambient temperatures. A squib is used to deliver a pyrotechnic charge, causing the electrolyte to become molten at 400°C to 700°C, delivering continuous power ranging from a few watts to several kilowatts depending upon battery size and chemistry.
The advantages of reserve/thermal batteries include ruggedness, safety, and long shelf life, but these cells also have limitations. System readiness cannot be tested without fully depleting the cell. Battery activation is also delayed until the chemical reaction occurs. Layers of bulky insulation are required for heat retention so the electrolyte can remain molten, and to protect surrounding components from heat-related damage. Spin-activated batteries store electrolyte inside an ampoule or bladder, which is cut open when a projectile is fired, with the spinning action distributing the electrolyte throughout the cell stack. Spin-activated batteries made with lithium thionyl chloride chemistry are powering minelets and communication jammers that are launched into the battlefield by artillery shells that are equipped with parachutes to ensure a soft landing.
Lithium metal oxide batteries, developed by Tadiran as the TLM Series, are constructed with a carbon-based anode, multi-metal oxide cathode, organic electrolyte, and shut-down separator. Lithium metal oxide batteries can deliver high current pulses and high rate energy, with up to 20 years of storage life due to a self-discharge rate of less than 1% per year. An enhanced version, the TLM-HE Series, now available in an AAsize, provides an open circuit voltage of 4V, with a discharge capacity of 1,100 mAh for an AA-size cell (20 mA at 2.8V RT), capable of handling 5A continuous current and 15A pulses.
TLM batteries feature a wide operating temperature range (-40°C to +85°C), and comply with MIL-STD 810G specs for vibration, shock, temperature shock, salt fog, altitude, acceleration (50,000 gn), and spinning (30,000 rpm). They also conform to UN 1642 and IEC 60086 standards for crush, impact, nail penetration, heat, overcharge and short circuit, and can be shipped as non-hazardous goods. Standard cells come in cylindrical configurations (AA-size, CR-2 size, and 20mm length) and a AAA-size (10mm), and can be easily configured into custom battery packs.
Unlike thermal/reserve and spin-activated batteries, TLM batteries permit instantaneous activation without the need for squibs or gas generators. They can also be periodically tested to ensure system readiness, thus reducing the number of “duds” in missile guidance systems. Power can also be drawn intermittently, so their use is not restricted to single-use applications. In addition, these cells do not generate the high internal temperatures required by thermal batteries, thus eliminating the need for bulky insulation.
Some real-life military applications for lithium metal oxide batteries are:
• ODAM 60 mm mortar guidance systems: Under DARPA’s Optically Directed Attack Munitions (ODAM) project, BAE Systems conducted feasibility studies for a low-cost, laser-guided, 60mm mortar round. BAE Systems selected TLM-1530-HP lithium batteries to power the laser-guided optical seekers. TLM-1530-HP batteries were chosen over CR-2 consumer type batteries because they could withstand extremely cold temperatures (-40°C) and offered four times longer shelf life (20 years versus 5 years).
• Unmanned Aerial Vehicles: Lithium metal oxide batteries power the emergency recovery system of an unmanned air reconnaissance aircraft. To create a weight- and space-saving solution, a 32V/480W battery pack was developed using 96 AA-size lithium metal oxide batteries, delivering up to 120W per hour at -30ºC, and weighing approximately 2 Kg including a metal enclosure. This battery pack can be quickly reconfigured for other UAV applications.
• Powering missile systems: The guidance system of an air-to-ground missile previously powered by 19 silverzinc cells can be converted to a battery pack consisting of 24 high-power lithium metal oxide cells, resulting in 3.5 times greater energy density, as well as reducing size by 30% and weight by 75% (2.2 Kg vs. 0.5 Kg). The squib, gas generator, and heater required by silver-zinc batteries are also eliminated.
Choice of battery is influenced by performance criteria such as voltage, capacity, size, weight, special packaging, service life, temperature, and environmental requirements. Other design considerations can include the need for instant activation, system readiness testing, and multiple use requirements, where applicable.
Recently the U.S. DoD decided to require oxhalide batteries instead of lead-acid or thermal batteries to power the latest generation of spin-activated Multi-Option Fuses for Artillery (MOFA), including 105mm and 155mm bursting artillery projectiles. Had lithium metal oxide been chosen over lithium oxhalide chemistry, significant performance advantages could have been realized, including seven times greater capacity (200 mAh vs. 30 mAh), over ten times greater current (3.5A vs. 325 mA), more stable voltage, and faster activation (instantaneous vs. a 100 ms delay).
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