Lithium-ion (Li-Ion) is one of the most recent rechargeable battery chemistries. Li-ion batteries are gaining popularity as rechargeable battery for consumer electronics because of their high energy-to-weight ratio. The energy density of a typical Li-ion battery is around two times than that of a standard NiCd battery.

Research on lithium battery began in 1912 and became commercially available in the early 1970s. This was followed by attempts to develop rechargeable batteries in 1980. Initial attempts to develop rechargeable lithium batteries failed due to the instability of lithium metal. This inherent instability was later overcome by replacing lithium metal with lithium-ion. In 1991, the first Li-ion battery became commercially available.

In addition to having a high energy density, Li-ion batteries require very low maintenance. They have no memory, and hence, do not require periodic cycling to prolong battery life. They are light and self-discharge around 50% less than nickel-based batteries. However, Li-ion batteries are very fragile and require a protection circuit for safety. These batteries are also susceptible to aging, whether in use or not.

Examples of Li-ion batteries include two way radio batteries, barcode scanner batteries, and barcode printer batteries and laptop batteries.

Applications
Lithium-ion batteries offer a significant advantage over other rechargeable batteries because of their lightweight and high energy density. They find their application in portable devices like cellular phones, two way radios, barcode scanners, barcode printers, laptop computers, digital cameras, and MP3 players.

Applications of Li-ion batteries in implantable medical devices and in satellites are also emerging.

How Li-ion Battery Works
A typical lithium-ion cell uses an anode made from carbon, the cathode is a metal oxide and the electrolyte is a lithium salt in solution. During the electrolytic reaction, lithium-ions inside the cell do not get oxidized or reduced. They are simply transported to and from the cathode and anode. However, cobalt is oxidized during charge, and reduced during discharge.

Voltage
The operating voltage of Li-ion batteries is 3.6 volts, approximately three times the voltage of NiCd and NiMH batteries. This makes it an ideal choice for sophisticated and compact portable equipments.

The use of a carbon anode creates a relatively flat discharge voltage, allowing the production of stable power throughout the discharge cycle.

Higher terminal voltage, capacity or power density can be obtained by assembling Li-Ion cells in a series, parallel or a mixture of both.

Charging method
There is only one way to charge a lithium-ion battery, i.e. the “constant voltage/constant current” method. Most Li-ion cells can be charged to 4.20V. Full charge is attained when the voltage has reached 4.2 volts and the charge current has dropped to 10% of the initial charge rate. It takes most chargers, at a 1C initial current, around 3 hours to fully charge a lithium-ion battery. An increase in the charge current does not have much affect on the charge time. Even though the voltage peak is reached quicker with higher charge current, it takes longer to top up the battery.

Most lithium-ion batteries contain a protection circuits that limits the peak voltage of each cell at 4.2 volts/cell during charge and prevents cell voltage from dropping below 2.50V/cell during discharge. The safety circuit is designed to cut off the current path if the battery voltage reaches above or below these two limits.

Lithium-ion batteries should not be trickle charged to avoid overcharging. An overcharge could cause plating of lithium metal, which would render the battery unsafe for use.

Advantages
The biggest advantage of Li-ion batteries over other rechargeable batteries is its high energy-to-weight ratio. The energy density of a typical Li-ion battery is around 50% more than that of a standard NiCd battery.

Lithium-ion batteries have an operating voltage of around 3.6 volts. This is three times than that of a standard Ni-based battery. The high operating voltage reduces the number of cells required to generate a higher voltage and contributes to the miniaturization of electronic devices.

Li-ion batteries are low maintenance batteries. Unlike nickel-based batteries, they do not suffer from “memory effect.” This reduces the need for periodic cycling to prolong battery life. Moreover, they have a very low self-discharge.

Another advantage of Li-ion batteries is their environment friendliness. Li-ion does not use restricted pollutants such as cadmium, mercury and lead. It is also profitable to recycle these batteries. The metals in these batteries can be recovered through recycling.

Problems with Li-ion
Lithium-ion batteries are fragile and can be extremely dangerous if mistreated. They do not take overcharge and deep discharge very well, and require a protection circuit, limiting the voltage and current, for safe operation.

Lithium-ion cells have a higher internal resistance than nickel-cadmium cells and consequently discharge a moderate current.

A major drawback of Li-ion batteries is that they are susceptible to aging, even in storage. An older battery will not last as long as a new battery because of its age. These batteries generally fail after two or three years from the date of manufacture.

Li-ion batteries are around 40% more expensive to manufacture than NiCd batteries and are subject to transportation regulations.

Maintenance Tips for Li-ion Batteries:

• Partial discharges with frequent recharges are better for Li-ion batteries instead of full discharge and recharge.


• Full discharges should be avoided as this puts additional strain on the battery.


• Charge in room temperatures between 0°C and 45°C.


• Do not overcharge a Li-ion battery.


• Li-ion batteries should be stored in room temperature, charged to about 40% of capacity.


• Check the manufacturing date before buying a new Li-ion battery. Do not buy old batteries.


• Avoid charging to 4.20 volts to improve cycle life.