Lithium ion batteries

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Lithium ion (or Li-Ion) batteries are most often found in electronics such as laptops and PDAs. They are useful due to their high power density and ability to sustain repeated charges without suffering from the "memory effect" that plagues nickel-cadmium and other types of rechargeable batteries. Lithium ion batteries were first devised in the early 1900s, with the technology reaching commercial maturity in 1991. The technology is perpetually undergoing further development to increase battery life, as well as to decrease battery size and weight. Recently, there has been an increase in documented cases of lithium ion batteries failing and catching fire.

Technology

Lithium ion batteries work like most other batteries by chemically storing up energy that can be released at the needed power level for as long as they can sustain the chemical reaction. They have largely replaced nickel-cadmium batteries as the ideal standard for mobile device power applications since nickel-cadmium batteries, in addition to being heavier than Li-Ion batteries, suffer from the "memory effect" in which the batteries tend to retain less and less charge over time if they are not allowed to discharge completely. Since lithium ion technology allows for approximately twice the energy density of nickel-cadmium, it is the most obvious choice currently for devices such as laptops.

Advantages

Lithium ion batteries have a much lower self-discharge than other batteries: Lithium ion batteries tend to discharge at a rate of 5% per month, as compared to other batteries which are often closer to 15-30% per month. This means that between charge and use, Li-Ion batteries are more capable of retaining a useful charge. The 5% discharge is due to a small but constant drain from the self-monitoring circuit that prevents the battery from being recharged once the power level has dipped below a certain point. Additionally, Li-Ion batteries have no "memory effect". Li-Ion batteries can be partially discharged and then re-charged repeatedly, with no ill effect. The technology itself is very compact in comparison to other batteries, allowing for denser construction and more weight being used for power as opposed to overhead. This also allows the batteries to be very flexible in shape and distribution, enabling placement in the most efficient use of space for the given application.

 

Disadvantages

Although lithium ion batteries do not suffer from the "memory effect", they do indeed lose capacity over time. Li-Ion batteries decrease in capacity continuously from the moment they are constructed, due to internal cell oxidation. This permanent degradation in capacity is about 20% per year. Degradation is, however, highly dependent on the temperature at which the battery is stored, as well as how fully the battery is charged during the storage period. The colder the temperature at which the battery is kept, the less charge is lost. The ideal charge level for storing a Li-Ion battery is 40%, which will have an average degradation of only 4% per year.

 

Permanent Capacity Loss versus Storage Conditions

Storage Temperature 40% Charge  100% Charge
32°F (0°C)  2% loss after 1 year 6% loss after 1 year
77°F (25°C)   4% loss after 1 year 20% loss after 1 year
104°F (40°C) 15% loss after 1 year 35% loss after 1 year
140°F (60°C)  25% loss after 1 year 40% loss after 3 months

Source: BatteryUniversity.com

The cell oxidation process is exacerbated by high power devices such as laptops and video cameras, and is less in devices such as digital cameras and cell phones that have a lower power draw. To avoid permanent damage, lithium ion batteries must never be discharged past a certain point. To avoid this damage, the batteries are equipped with a circuit monitor that will shut down the system using the battery once a predefined threshold is reached. When the monitor is embedded within the battery as opposed to being a part of the utilizing system, the circuit will draw a continuous charge. If the battery is left for too long, it will completely discharge and be irrevocably damaged.

Dangers

The failure of Li-Ion batteries has been receiving more and more attention lately. Research indicates that this sort of failure is not as uncommon as manufacturers had originally led people to believe. There are a number of different reasons that a Li-Ion battery can fail, but the most common is exposure to extreme heat. If a battery is allowed to sit in extreme heat, such as a hot car, or in a computer under heavy use on an insulating surface, the likelihood of failure is increased, especially if the battery is used before it has an opportunity to cool off.

Occasionally, the built in monitors may fail, allowing the internal temperature of the battery to exceed the safety thresholds. Once this happens, individual cells may catch fire, likely igniting other cells. Due to the cobalt oxide in lithium ion batteries, they are also somewhat susceptible to a process called "thermal runaway", in which the cobalt oxide reaches a certain, high temperature at which it begins to self-heat, causing a dramatic rapid rise in temperature which culminates in explosion to releive the pressure built up inside the battery. Additionally, if a battery is allowed to erode or be ruptured in some other manner, the electrolyte fluid inside the battery can cause short circuits, which will ignite the electrolyte causing what has been described as a "flame thrower". The Sony-built batteries causing failures in Dell laptops in the Summer of 2006 were this type of failure. A number of metal fragments are left floating in the electrolyte fluid inside individual cells as a result of the manufacturing process. Unfortunately, in these batteries manufactured by Sony, the barriers between the anodes and cathodes were more susceptible to being breached. As the battery gets hotter and hotter due to charging or use, the metal fragments move around more, increasing the likelihood of a breach. The breach leads to one of the scenarios above.

Recent Recalls

 

Notable Incidents

  • At a Japanese conference in June of 2006, a Dell laptop "exploded" and caught fire, with smaller explosions continuing for about 5 minutes afterward until the fire was put out. This was one of the incidents that motivated Dell to initiate the recall.
  • A Dell Inspiron not covered under Dell's recalls was left on the floor of the passenger side seat of 1966 Ford F-250 as the owner and his friend prepared to head home from a hunting trip in July of 2006. The flames from the laptop were sufficient to ignite the ammunition in the glove box above, which subsequently detonated the fuel tank, resulting in the demolition of the truck and all contents. Fortunately, the two hunters had managed to take cover just before the bullets began firing out of the truck, and were not harmed by the following explosion.
  • In an engineering office, a Dell laptop plugged into power and turned on caught fire in July of 2006. The battery burned a hole through the laptop and caused some damage to the table below. The fire extinguishers used to put out the fire caused some amount of damage as well. This incident was well documented by someone with a 7.1MP camera. This is one of the incidents that motivated Dell to initiate the recall.
  • A 15-inch PowerBook plugged into a wall socket was left in Standby mode over night in August of 2006. At six AM, the owners were awoken by acrid smell and smoke. The battery had overheated and ignited. This battery had been covered under the Apple recall noted above. 

 

Battery Saving Tips   

  • If the battery is not going to be used for a long time, consider discharging it and storing it in a cool, dry place. See chart above for capacity loss time-frames. Storage in a refrigerator will dramatically prolong life, however, make sure to allow the battery to warm to room temperature before use.
  • If you will be using your computer for a prolonged period of time while plugged into an outlet, removing the battery can both improve long-term battery performance, as well as reduce the likelihood of battery failure in the future, due to the isolation from a heat source, i.e., the laptop.
  • If the battery is discharged to within a few percent of available capacity, and then is left for a prolonged period of time without being recharged, the battery may discharge to below the safety threshold. If this threshold is passed, the battery is effectively dead at this point and will no longer allow itself to charge.
  • Tweak your power settings and turn off unused devices. Most modern laptops will allow for in-depth tweaking of fan settings, monitor brightness, and optical drives. Proper configuration of these settings, especially screen brightness, can dramatically improve battery life.
  • Do not bother with "Suspend"; use "Hibernate" or "Suspend to Disk" instead. The power drain needed to make the laptop power on more quickly usually isn't sufficient to compensate for the battery drain. The Hibernate function will move all of the contents of the machine's memory to disk, and then actually shut down the computer. Upon powering on the computer again, your session will be restored precisely as you left it, with no battery power having been drained while the computer was in hibernation.

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Date Posted: April 17, 2013 Tags: Technical Info, Provider Resource, Battery, Notebook

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