Laptop battery chemistries and technologies have evolved over the years in the same way that electronic devices in general have evolved, and more specifically the way that laptop computers developed. This article provides information regarding the developmental progression of this battery class.
Laptop computers and electronic devices have progressed substantially. Battery technology today remains one of the areas of great research and application of that research and development is a very practical application to theoretical development. Enormous amounts of time, energy and money are being expended to squeeze more power into lighter and smaller storage devices and to make them safer more cost effective.
The chemistries that have been used in laptop computer batteries are nickel-cadmiun (NiCD or NiCad); nickel metal hydride (NiMH) and Lithium Ion (Li-ion).
NiCd battery chemistry is the oldest battery technology used to power laptop computers and they have been produced in the US since 1946. Since this was a readily (and only) available technology at the time, most early suppliers of laptop computers resorted to NiCd batteries as the remote power source. These batteries are heavier than the newer battery technologies, provide a lower voltage and amp-hour rating and present disposal problems due to the heavy metals inherent in their design. Another disadvantage to NiCd batteries, particularly in mobile computer use, is the "memory effect" condition that effects them if they are recharged before being fully discharged. Most manufacturers have discontinued production of this battery type but they remain in use in cordless telephones, emergency lighting, radio-controlled cars and planes, camera flash units and power tools due to their ability to supply a high surge current.
NiMH batteries have been commercially available since 1989 and are a variation of the nickel hydrogen cell from the 70s. This battery technology is less susceptible to "memory effect" and have a better power to weight ratio than NiCd batteries. NiMH batteries currently use high energy-energy paste and high-energy hybrid alloys and provide a much more friendly alternative. NiMH batteries are relatively inexpensive to produce and are able to meet the demands of high current drain devices. Consequently, NiMH batteries are used by consumers, particularly in the AA and AAA battery sized, to replace alkaline batteries and power their portable media devices. NiMH batteries are also being used in the development and manufacture of electric and hybrid vehicles. However, these batteries have been discontinued by most laptop manufacturers since lithium-ion batteries are compatible and a more viable alternative.
Li-ion batteries have become the main battery chemistry type used in laptop computer batteries due to their excellent power to weight ratio. They also display little or no "memory effect and are characterized by a slow charge loss when not in use. For these reasons, they are gaining popularity in other consumer electronic products in addition to notebook batteries. In addition to consumer application, they are also being utilized in the defense, aerospace and automotive industries because of their high energy density. Lithium ion batteries were first theorized in the 70s and researched in the 80s, but their mainstream consumer use did not become realized until the late 90s when lithium iron phosphate was used in the cells and balanced the batteries' cost, safety, stability and performance. However, disadvantages to Li-ion batteries are their high internal resistance and their durability (compared to the other chemistries considered). For these reasons, protection circuits are incorporated into the design of the battery to protect against under and over voltage situations.
Currently Li-ion batteries are being supplanted by Li-ion polymer batteries, or more commonly Lithium-polymer (Li-poly or LiPo), that replace the organic solvent with a solid polymer. The advantages of Li-poly over the lithium-ion design include a lower production cost and a greater resistance to physical damage.