Battery Gurus

[uninformed]

Ok battery heads,

If one lithium battery cell is 3.6v or there abouts, how can companies make a 9v lithium battery?

cheers
Serg

[bee utey]

Yeah, but, what kind of lithium 9V battery?

wikipedia to the rescue

[ame="http://en.wikipedia.org/wiki/Lithium_battery"]Lithium battery - Wikipedia, the free encyclopedia[/ame]

lithium cells can produce voltages from 1.5 V to about 3.7 V.

[Ferret]

Multiple cells, just like a car battery.

[uninformed]

rechargeable not primary. Think the little 9v rectangle type that goes in cheap smoke detectors and some alarm clocks.

he is one thing I grabbed of the net, Lithium-based Batteries Information

"The specific energy of Li‑ion is twice that of NiCd, and the high nominal cell voltage of 3.60V as compared to 1.20V for nickel systems contributes to this gain. Improvements in the active materials of the electrode have the potential of further increases in energy density. The load characteristics are good, and the flat discharge curve offers effective utilization of the stored energy in a desirable voltage spectrum of 3.70 to 2.80V/cell. Nickel-based batteries also have a flat discharge curve that ranges from 1.25 to 1.0V/cell."

Here is another from Wiki, from this page: Lithium-ion battery - Wikipedia, the free encyclopedia

Safety requirements
If overheated or overcharged, Li-ion batteries may suffer [ame="http://en.wikipedia.org/wiki/Thermal_runaway"]Thermal runaway - Wikipedia, the free encyclopedia[/ame] and cell rupture.[52] In extreme cases this can lead to combustion. Deep discharge may short-circuit the cell, in which case recharging would be unsafe.[[ame="http://en.wikipedia.org/wiki/Wikipedia:Citation_needed"]Wikipedia:Citation needed - Wikipedia, the free encyclopedia[/ame]] To reduce these risks, Lithium-ion battery packs contain fail-safe circuitry that shuts down the battery when its voltage is outside the safe range of 3–4.2 V per cell.[35][44] When stored for long periods the small current draw of the protection circuitry itself may drain the battery below its shut down voltage; normal chargers are then ineffective. Many types of lithium-ion cell cannot be charged safely below 0 °C.[53]
Other safety features are required in each cell:[35]

• Shut-down separator (for overtemperature)
• Tear-away tab (for internal pressure)
• Vent (pressure relief)
• Thermal interrupt (overcurrent/overcharging)

These devices occupy useful space inside the cells, add additional points of failure and irreversibly disable the cell when activated. They are required because the anode produces heat during use, while the cathode may produce oxygen. These devices and improved electrode designs reduce/eliminate the risk of fire or explosion. Further, these features increase costs compared to nickel metal hydride batteries, which require only a hydrogen/oxygen recombination device (preventing damage due to mild overcharging) and a back-up pressure valve.[44]
These safety issues present a problem for large scale application of such cells in Electric Vehicles; A dramatic decrease in the failure rate is necessary.
[edit] Market

• Costs more[[ame="http://en.wikipedia.org/wiki/Wikipedia:Please_clarify"]Wikipedia:Please clarify - Wikipedia, the free encyclopedia[/ame]] per watt-hour than other chemistries
• Not suitable for AAA, AA, C or D form factors due to voltage per cell being more than 2 volts (i.e. 3.7 volts), though most devices designed for a voltage that is a multiple of 1.5 can run safely on a voltage that is 30% higher.[[ame="http://en.wikipedia.org/wiki/Wikipedia:Citation_needed"]Wikipedia:Citation needed - Wikipedia, the free encyclopedia[/ame]]

The way im reading it, and probably wrong, is that an idividual cell is approx 3.6v. Now if you use multiple cells, you can have either 7.2v or 10.8v. Im looking for very good quality 9v rechargeable batteries to power a portable headphone amplifier. I can get Ni-MH or Li-ion or even Lithium polymar. They are generally labelled as 9v or 8.4v. I can understand Ni-MH making these volts as there nominal cell size is 1.2v, just very confused about Li-ion in this application.

cheers
Serg

[Hoges]

You are correct: The voltage of a battery is a nominal value only. The actual measured voltage of a new battery should always exceed the nominal value. There are many posts on this forum for example, regarding the state of charge of "12v" deep cell and starting batteries : a fully charged battery will register anywhere between 12.8 and 13.x volts. Thus a reading of 12.5v some would consider to represent around 50%-60% of full charge. So it is also with the "9v" alkaline or Li ion batteries. A fully charged example probably registers 9.6v or more on a meter. If a device requires "exactly" 9 volts, then it generally has some sort of regulated power input device which compensates accordingly... hope this helps clarify..