BU-106a - Choices of The Primary Batteries

Knowing the difference in run-time performance

Alkaline delivers more energy at higher load currents than zinc-carbon. Furthermore, a regular household alkaline provides about 40 percent more energy than the average Li-ion but alkaline is not as strong as Li-ion on loading. Alkaline has very low self-discharge and does not leak electrolyte when depleted as the old zinc-carbon does, but it is not totally leak-proof.

Zinc-carbon, also known as carbon-zinc or the Leclanché battery, is one of the earliest and least expensive primary batteries. It delivers 1.5V and often come with consumer devices. The first zinc-carbon invented by Georges Leclanché in 1859 was wet.

Alkaline. Alkaline-manganese, also known as alkaline, is an improved version of the zinc-carbon battery and delivers 1.5V. Lewis Urry invented alkaline in 1949 while working with the Eveready Battery Company laboratory in, Ohio, USA.

All primary batteries produce a small amount of hydroxide gas on discharge and battery-powered devices must make provision for venting. Pressure buildup in the cell can rupture the seal and cause corrosion. This is visible in form of a feathery crystalline structure that can develop and spread to neighboring parts in the device and cause damage.

Lithium iron disulfide (Li-FeS2) is a newcomer to the primary battery family and offers improved performance compared to alkaline. Lithium batteries normally deliver 3 volts and higher, but Li-FeS2 has 1.5 volts to be compatible with the AA and AAA formats. It has a higher capacity and a lower internal resistance than alkaline. This enables moderate to heavy loads and is ideal for digital cameras. Further advantages are improved low temperature performance, superior leakage resistance and low self-discharge, allowing 15 years of storage at ambient temperatures.

The disadvantages of the Li-FeS2 are a higher price and transportation issues due to the lithium metal content in the anode. In 2004, the US DOT and the Federal Aviation Administration (FAA) banned bulk shipments of primary lithium batteries on passenger flights, but airline passengers can still carry them on board if the allotted lithium content is not exceeded. Each AA-sized Li-FeS2 contains 0.98 grams of lithium; the air limitation of primary lithium batteries is 2 grams (8 grams for rechargeable Li-ion). This restricts each passenger to two cells, but exceptions have been made in which 12 sample batteries can be carried. (See BU-704a: Shipping Lithium-based Batteries by air.)

Figures 1 and 2 compare the discharge voltage and internal resistance of alkaline and Li-FeS2 at a 50mA pulsed load. Of interest is the flat voltage curve and the low internal resistance of lithium; alkaline shows a rapid voltage drop and a permanent increase in resistance with use. This shortens the runtime, especially at an elevated load.

The Li-FeS2 includes safety devices in the form of a positive thermal coefficient (PTC) that limits the current at high temperature and resets when normal. The Li-FeS2 cell cannot be recharged as is possible with NiMH in the AA and AAA formats. Recharging, putting a cell in backwadrs, mixing in a depleted cell or adding a foreign cell could cause a leak or explosion. (See BU-304a: Safety Concerns with Li-ion.)

Figure 1: Voltage and internal resistance of alkaline on discharge.
The voltage drops rapidly and causes the internal resistance to rise.
Source: Energizer


Figure 2: Voltage and internal resistance of lithium on discharge.
The voltage curve is flat and the internal resistance stays low.
Source: Energizer

Lithium-thionyl chloride (LiSOCI2 or LTC) is one of the most rugged lithium-metal batteries. The ability to withstand high heat and strong vibration enables horizontal drilling, also known as fracking. Some LTC are said to operate from 0°C to 200°C (32°F to 392°F). Other uses are in medical and sensor applications.

With a specific energy of over 500Wh/kg, LTC offers twice the capacity of the best Li-ion. The nominal voltage is 3.60V/cell; the end-of-discharge cut-off voltage is 3.00V. The runtime is not based on capacity alone; thermal conditions and load pattern also have an effect. Constant current is more enduring than pulsed load; a phenomenon that applies to most batteries.

LTC is one of the most powerful and potent battery chemistries and should only be used by trained workers. For safety reasons, this battery is not used in consumer devices.
Like alkaline, lithium-thionyl chloride has a relatively high resistance and can only be used for moderate discharge loads. If stored for a time, a passivation layer forms between the lithium anode and the carbon-based cathode that dissipates when applying a load. This layer protects the battery by granting low self-discharge and a long shelf life. (See BU-701: How to Prime Batteries.)

Lithium manganese dioxide (MnO2 or Li-M) is similar to LTC but has a lower specific capacity and is safe for public use. The voltage is 3.0–3.30V and the specific energy is about 280Wh/kg. Li-M is economically priced, has a long life and allows moderate loads but can deliver high pulse currents. Operational temperature ranges from -30°C to 60°C (-22°F to 140°F). Typical uses are meter sensing, medical devices, road toll sensors and cameras.

Lithium sulfur dioxide (LiSo2) is a primary battery with a voltage of 2.8V and an energy density up to 330Wh/kg. It offers a wide temperature range of --54°C to 71°C (-65°F to 160°F) with a projected shelf life of 5–10 years at room temperature. LiSo2 is inexpensive to make and is commonly used by the military. The Iraqi war used tons of these batteries, but it is giving way to the more superior Li-M.

Note: Primary lithium batteries are also known as lithium-metal. The cathode is carbon and the anode holds the active material, the reverse of Li-ion, which features a carbon anode.