When Sony introduced the first lithium-ion battery in 1991, they knew of the potential safety risks. A recall of the previously released rechargeable metallic lithium battery was a bleak reminder of the discipline one must exercise when dealing with this high energy-dense battery system.
Pioneering work for the lithium battery began in 1912 by G. N. Lewis. It was not until the early 1970s when the first non-rechargeable lithium batteries became commercially available. Attempts to develop rechargeable lithium batteries followed in the eighties. These early models were based on metallic lithium and offered very high energy density. However, inherent instabilities of lithium metal, especially during charging, put a damper on the development. The cell had the potential of a thermal run-away. The temperature would quickly rise to the melting point of the metallic lithium and cause a violent reaction. A large quantity of rechargeable lithium batteries sent to Japan had to be recalled in 1991 after the pack in a cellular phone released hot gases and inflicted burns to a mans face.
Because of the inherent instability of lithium metal, research shifted to a non-metallic lithium
sony vaio vgn-ar590e battery using lithium ions. Although slightly lower in energy density, the lithium-ion system is safe, providing certain precautions are met when charging and discharging. Today, lithium-ion is one of the most successful and safe battery chemistries available. Two billion cells are produced every year.
Lithium-ion holds twice the energy of a nickel-based battery and four-times that of lead acid. Lithium-ion is a low maintenance system, an advantage that most other chemistries cannot claim. There is no memory and the battery does not require scheduled cycling to prolong its life. Nor does lithium-ion have the sulfation problem of lead acid that occurs when the battery is stored without periodic topping charge. Lithium-ion has a low self-discharge and is environmentally friendly. Disposal causes minimal harm.
With the high usage of lithium-ion in cell phones, digital cameras and laptops, there are bound to be issues. A one-in-200,000 failure rate triggered a recall of almost six million lithium-ion packs used in laptops manufactured by Dell and Apple. Heat related battery failures are taken very seriously and manufacturers chose a conservative approach. The decision to replace the batteries puts the consumer at ease and lawyers at bay. Lets now take a look at whats behind the recall.
Sony Energy Devices (Sony), the maker of the lithium-ion cells in question, says that on rare occasions microscopic metal particles may come into contact with other parts of the battery cell, leading to a short circuit within the cell. Although
dell latitude d830 battery manufacturers strive to minimize the presence of metallic particles, complex assembly techniques make the elimination of all metallic dust nearly impossible. Energy dense cells with ultra-thin separators are more susceptible to impurities than older designs with lower Ah ratings.
A mild short will only cause an elevated self-discharge. Little heat is generated because the discharging energy is very low. If, however, enough microscopic metal particles converge on one spot, a major electrical short can develop and a sizable current will flow between the positive and negative plates. This causes the temperature to rise, leading to a thermal runaway, also referred to venting with flame.
Lithium-ion cells with cobalt cathodes (same as the recalled laptop batteries) should never rise above 130C (265F). At 150C (302F) the cell becomes thermally unstable, a condition that can lead to a thermal runaway in which flaming gases are vented.
During a thermal runaway, the high heat of the failing cell can propagate to the next cell, causing it to become thermally unstable as well. In some cases, a chain reaction occurs in which each cell disintegrates at its own timetable. A pack can get destroyed within a few short seconds or linger on for several hours as each cell is consumed one-by-one. To increase safety, packs are fitted with dividers to protect the failing cell from spreading to neighboring cells.
Safety level of lithium-ion systems
There are two basic types of lithium-ion
hp pavilion dm4 battery chemistries: cobalt and manganese (spinel). To achieve maximum runtime, cell phones, digital cameras and laptops use cobalt-based lithium-ion. Manganese is the newer of the two chemistries and offers superior thermal stability. It can sustain temperatures of up to 250C (482F) before becoming unstable. In addition, manganese has a very low internal resistance and can deliver high current on demand. Increasingly, these batteries are used for power tools and medical devices. Hybrid and electric vehicles will be next.
The drawback of spinel is lower energy density. Typically, a cell made of a pure manganese cathode provides only about half the capacity of cobalt. Cell phone and laptop users would not be happy if their batteries quit halfway through the expected runtime. Rather than less, the consumer wants more stored energy to support new features that chew up extra battery power.
To find a workable compromise between high energy density, operational safety and good current delivery, manufacturers of lithium-ion batteries use different cathode metals. Typical mixes are cobalt, nickel, manganese and iron phosphate. Lithium-ion acer travelmate 4000 battery systems are not yet mature and have the potential of increasing the energy density further. Looking back in history, lithium-ion has achieved a notable energy improvement of 8-10% per annum.
Packing more energy into a cell increases safety concerns and appropriate measures will need to be taken to achieve the mandated safety standard set forth by UL 1642. Whereas a nail penetration test could be tolerated on the older 1.35Ah 18650 cell, a high-density 2.4Ah would become a bomb when performing the same test. UL 1642 does not require nail penetration.
