Discover what a battery needs to get going and attain a long life.
In many ways, a battery behaves like a human being; it senses the kindness offered and delivers on the care and attention given. Looking after the battery well will return the benevolence bestowed and deliver good performance over a long life. There are exceptions, however, as any parent raising a large family will know, and the generosity conferred may not always deliver the anticipated returns.
To become a good custodian, the battery keeper must understand the basic needs of a battery, a subject that is not taught in school. This section teaches what to do when the battery is new, how to feed the right “food” and what to do when putting the pack aside for a while. Chapter 7 also looks into restrictions when traveling with batteries by air and how to dispose of them when their useful life has passed.
Just as we cannot predict a person’s life expectancy at birth, neither can we date-stamp a battery. Some packs live to a great old age while others die young. Incorrect charging, harsh discharge loads and exposure to heat are the battery’s worst enemies. Although we have ways to protect a battery, the ideal situation is not always attainable. This chapter discusses how we can get the most from our batteries.
Not all rechargeable batteries deliver the fully rated capacity when new and require formatting. While this applies to most battery systems, manufacturers of lithium-ion batteries disagree. They say that Li-ion is ready at birth and does not need priming. Although this may be true, users have reported some capacity gains by cycling after a long storage.
What’s the difference between formatting and priming? Both address capacities that are not optimized and can be corrected with cycling. Formatting completes the manufacturing process and occurs naturally during early usage when the battery is being cycled. Priming, on the other hand, is a conditioning cycle that is applied as a service tool to improve battery performance during usage or after prolonged storage. Priming relates mainly to nickel-based batteries.
Formatting a lead acid battery occurs by applying a charge, followed by a discharge. This is done at the factory and is completed in the field as part of regular use. A new battery may be sensitive and if possible, do not strain a new battery by giving it heavy duty when new but gradually work it in with moderate discharges like an athlete trains for weight lifting or long-distance running. This, however, may not be possible with a starter battery in a vehicle and other uses. Lead acid typically reaches the full capacity potential after 50 to 100 cycles. Figure 1 illustrates the cycle lire of lead acid.
Figure 1: Cycle life of Lead Acid
A new lead acid battery may not by fully formatted and only attains full performance after 50 or more cycles. Formatting occurs during use; deliberate cycling is not recommended as this would wear down the battery unnecessarily.
Deep-cycle batteries are at about 85 percent when new and will increase to 100 percent, or close to full capacity, when fully formatted. There are some outliers that are as low as 65 percent when tested with a battery analyzer. The question is asked, “Will these low-performers recover and stand up to the stronger brothers when formatted?” A seasoned battery experts replied, “These batteries will improve somewhat but they are the first to fail.” An analogy is the weak kitten in a kitty litter.
The function of a starter battery lies in delivering high load currents to crank the engine and this attribute is present from the beginning without the need to format. In addition, the capacity of a starter can fade to 20 percent without a noticeable effect in the ability to crank the engine. This phenomenon has stranded many drivers when the vehicle won’t start one morning due to insufficient capacity. (See also BU-904: How to Measure Capacity)
Manufacturers advise to trickle charge a nickel-based battery for 16 to 24 hours when new and after a long storage. This allows the cells to adjust to each other and bring them to an equal charge level. A slow charge also helps redistribute the electrolyte to eliminate dry spots on the separator that might have developed by gravitation.
Nickel-based batteries are not always fully formatted when leaving the factory. Applying several charge/discharge cycles through normal use or with a battery analyzer completes the formatting process. The number of cycles required to attain full capacity differs between cell manufacturers. Quality cells perform to specification after 5 to 7 cycles, while others may need 50 or more cycles to reach acceptable capacity levels. Lack of formatting causes a problem when the user expects a new battery to work to specification right out of the box. Organizations using batteries for mission critical applications verify performance through a discharge/charge cycle as part of quality control. The “prime” program of automated battery analyzers (Cadex) apply as many cycles as needed to attain full capacity.
Cycling also restores lost capacity when a nickel-based battery has been stored for a few months. Storage time, state-of-charge and temperature under which the battery was stored govern ease of recovery. The longer the storage and warmer the temperature, the more cycles will be required to regain full capacity. Battery analyzers help in the priming functions and assure that the desired capacity has been achieved.
Some battery users insist that a passivation layer develops on the cathode of a lithium-ion cell after storage. Also known as interfacial protective film (IPF), this layer is said to restrict ion flow, cause an increase the internal resistance, and in the worst case lead to lithium plating. Charging, and more effectively cycling, is known to dissolve the layer and some battery users claim to have gained extra runtime after the second third cycle on a smartphone.
Scientists do not fully understand the nature of this layer, and the few published resources on this subject only speculate that performance restoration with cycling is connected to the removal of the passivation layer. Some scientists deny outright the existence of the IPF, saying that the idea is highly speculative and inconsistent with existing studies.
A well-known layer that builds up on the anode is the solid electrolyte interphase (SEI). SEI is an electric insulation that has sufficient ionic conductivity to allow the battery to function normally. While the SEI layer lowers the capacity, it also protects the battery, without which Li-ion might not get the accustomed longevity. (See also BU-307: Electrolyte).
Another film that builds up is the electrolyte oxidation on the cathode. This causes a permanent capacity loss and increases the internal resistance. Keeping Li-ion at a voltage above 4.10V/cell while at an elevated temperature promotes electrolyte oxidation. No remedy exists to remove the layer once there but electrolyte additives in modern Li-ion minimize the effect of forming it. Field use revealed that the combination of heat and high voltage can cause more stress to Li-ion than harsh cycling.
Whatever the outcome on the passivation of Li-ion may be, there is no parallel to the “memory” effect with NiCd batteries that require periodic cycling to prevent capacity loss. The symptoms may appear similar but the mechanics are different. Nor can the effect be compared to sulfation of lead acid batteries.
Lithium-ion is a very clean system that does not need additional once it leaves the factory, nor does it require the level of maintenance that nickel-based batteries do. Additional formatting makes little difference because the maximum capacity is available right from the beginning, (the exception may be a small capacity gain after a long storage). Nor does a full discharge improve the capacity once the battery has faded. A low capacity signals the end of life. A discharge/charge may only be beneficial to calibrate a “digital” battery; it does nothing to improve the “chemical battery.” (See BU-601: Inner Working of a Smart Battery) Instructions recommending charging a new battery for eight hours do not cause harm but this is “old school,” a left-over from the old nickel battery days.
Primary lithium batteries, such as lithium-thionyl chloride, suffer from passivation in storage. The passivation is a thin layer that forms as part of a reaction between the electrolyte with the lithium anode and the carbon-based cathode. (Note that the anode of a primary lithium battery is lithium and the cathode is graphite, the reverse of Li-ion.) Without this layer forming, most lithium batteries could not function because the lithium would cause a rapid self-discharge and degrade the battery quickly. The layer protects the battery and allows a10-year storage.
Temperature and state-of-charge promote the build-up of the passivation layer. A partially discharged lithium thionyl chloride is subject to more passivation than a new one, and warm storage contributes to the cause.
The passivation layer causes a voltage delay when first applying a load to the battery. Figure 2 illustrates the voltage recovery when applying a load to three batteries with different passivation levels. Battery A demonstrates a minimal voltage drop while battery C needs time to recover.
Figure 2: Voltage behavior when applying a load to a passivated battery
Voltage A has mild passivation, B takes longer to restore, and C is affected the most.
Courtesy EE Times
Devices with very low current consumption, such as a scanner for toll roads, may develop a passivation layer as part of usage caused by the heat in the vehicle. As prevention, some lithium batteries are shipped with a 36KOhm resistor. A stead low discharge current or a periodic pulse during storage prevents the layer from growing too thick but this will reduce the storage life. After a two year storage with the 36kOhm resistor, the battery are said to still have 90% capacity.
Not all primary lithium batteries recover by simply installing in a device; the current may be too low to reverse the effect. It is also possible that the device rejects a passivated battery as low state-of-charge or defective. These batteries can be prepared with a battery analyzer (Cadex) by applying a controlled load and verifying proper function before engaging the battery in the field.
The required discharge current for de-passivation is a C-rate of 1C to 3C (1 to 3 times of the rated capacity). The cell voltage must recover to 3.2V when applying the load; the service time is typically 20 seconds. The process can be repeated but it should take no longer than 5 minutes. With a load of 1C, the voltage of a correctly functioning cell should stay above 3.0V. A drop to below 2.7V means end-of-life.
The three most common primary lithium batteries are lithium thionyl chloride (3.6V highest energy density), lithium sulfur dioxide (3.9V) and lithium manganese dioxide. Lithium thionyl chloride is found in oil drilling, medical devices, military weapons and sensors. These batteries have an exceptionally high energy density and perform well under high temperature. Relatively high internal resistance limits the loading capabilities. (See BU-106: Primary Batteries)
Please also note that these lithium-metal batteries have high lithium content and have more stringent shipping requirements to Li-ion of same Ah. (See BU-704a: Shipping Lithium-based Batteries by air) Because of the high specific energy, special care must be taken in handling these cells.
When charging an SLA with over-voltage, current limiting must be applied to protect the battery. Always set the current limit to the lowest practical setting and observe the battery voltage and temperature during charge.
In case of rupture, leaking electrolyte or any other cause of exposure to the electrolyte, flush with water immediately. If eye exposure occurs, flush with water for 15 minutes and consult a physician immediately.
Wear approved gloves when touching electrolyte, lead and cadmium. On exposure to skin, flush with water immediately.
Last Updated 2015-04-07
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