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Like other conventional batteries, Lithium-ion (Li-ion) or cell phone batteries are made up of three primary components: an anode, a cathode, and electrolyte. The anode of the battery is made up of carbon (graphite) and the cathode is made up of metal oxide. The non-aqueous electrolyte is a composite of lithium salts in an organic solvent. Non-aqueous electrolyte is used to safeguard the battery because of the reactive nature of pure lithium, which has a tendency to chemically react with water to generate lithium hydroxide and hydrogen gas. The chemical reaction can be described as
Li + H-OH → LiOH + H2
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Electrodes made of intercalated lithium compound are preferred over metallic lithium electrodes for the manufacturing of cell phone batteries. An air-tight closed container is used to keep water away from the battery. As mentioned earlier, lithium is chemically a very reactive element, which means that energy stored in its atomic bonds is high. Hence, Li-ion batteries have a very high "energy density."
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Lithium-Polymer Cell Phone Battery
Lithium-polymer is technically a lithium-ion polymer battery. These are rechargeable batteries (secondary batteries), and, if used with care, can be recharged hundreds of times and have a lifetime of many years. The major distinction between Li-polymer and Li-Ion batteries is the kind of electrolyte used. Li-Po actually uses an SPE, i.e. Solid Polymer Electrolyte such as polycrylonitrile and plastic anode material, while Li-Ion uses lithium salt in an organic solvent as an electrolyte. Additionally, some Li-Pos use a polymer gel containing the electrolyte solution, which is coated onto the electrode surface. The lithium polymer mitigates the risks of fire as there is no liquid electrolyte in such batteries.
Charging Chemical Reaction
LiCoO2 + 6C → LixC6 + Li1-xCoO2
Discharging Chemical Reaction
Li1-xCoO2 + LixC ↔ Li1-x+dxCoO2 + Lix-dxC
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Output Voltage of Li-ion Battery
This battery provides relatively higher voltage of the range of 3.7 Volts compared to 1.2 Volts provided by other rechargeable batteries like nickel-metal hydride batteries and nickel cadmium batteries. Thus a single cell of this battery is used in cell phones so that cell phones can have a sleek size and lighter body.
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The anode transmits the current through Li+ lithium ions to the cathode during discharging of the battery. A higher voltage external power source is used for charging the battery. This higher voltage is applied to the battery with the same polarity as that of the battery. It pushes the current in the opposite direction, i.e. from cathode to anode. In the process, lithium ions drift from thu cathode to the anode electrode and are pushed into the anode, and this is the process called "intercalation."
Unfortunately, during charging it forms deposits that gradually lessen its life, so a lithium-ion battery won’t last forever. Time and temperature also affect the life of these batteries, which today normally last from two to three years even if they are unused. So do not "avoid using" the lithium-ion battery with the idea in mind that the battery will last forever.
The voltage rating, life, and charging/discharging cycle of this battery may vary due to different materials used during manufacturing of different batteries. Fortunately, recent batteries used for mobile phones are following nanotechnology-based design methodology, making their specification broadly standard for mobile phones.
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Li-ion batteries can handle hundreds of charge/discharge cycles. The discharge rate of these batteries in idle state is relatively lower than other rechargeable batteries. Generally this battery, being inactive, can store their charge for a duration of months, while other rechargeable batteries lose up to 4-5% of their charge per day. So once charged, this battery can keep mobile phones alive for a longer duration.
The discharging rate of these batteries is dependent on their operational and storage temperature. The higher the temperature, the greater the discharging rate. One should always store this battery at lower temperatures to increase its discharging cycle.
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Can You Overcharge Your Lithium-ion Cell Phone Battery?
As has been seen, the regular recharging of a Li-ion or cell phone battery is a basic redox reaction that causes lithium ions to travel from the negative (cathode) to the positive (anode) electrode. Li-ion batteries can be recharged a number of times, but eventually, after a number of charge discharge cycles, this battery will need replacement, too.
It is important not to overcharge the cell phone battery, or to let it drain out completely. If it runs out of charge completely, it will spoil the battery cells, so it is required to plug it in the charger while it still contains some charge. Furthermore, if you overcharge the battery, it creates heat which could be a fire hazard, or even cause a fire itself.
Since lithium-ion (and lithium-polymer) are sensitive to overcharging and over-discharging, the cells that make up the battery pack are charged independently. With NiMH and NiCad packs, the standard charging phenomena is to provide a current and voltage to cells connected in series so all the cells receive the same amount of current. The cell voltages in that case are not necessarily equal, in fact it is almost certain that they are not, but the voltage across the battery pack will be the same. Since NiMH and NiCad relatively show resistance to overcharging, there is usually no danger. It is common for one cell in a NiMH or NiCad battery pack to be dead without an effect on the charging of other cells. What does that mean? Let me explain it with an example.
Let’s suppose that we have a 6-cell battery pack, with the nominal voltage of each cell being 1.2 Volts (7.2 Volts total). If a charging voltage of 5 Volts is present, each cell would ideally receive 0.83 Volts approx. If one cell is dead, the voltage across each cell would be 1 Volt. That means a 20.5% increase after the death of one cell. This percentage increase is catered to by most Nickel-based cells, but a 20.5% overvoltage to lithium cells would ultimately result in a failure, and likely a fire. Li-Ion/Li-Poly batteries cannot tolerate over discharging as well, and tend to die if discharged below around 2.5 V.
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How to Treat Your Cell Phone Battery
During storage, cell phone batteries, i.e. Li-ion batteries, discharge quicker if fully charged initially. So it is recommended to partially charge the battery (50-60% ) prior to storing it. It is generally recommended to recharge this battery after few months if they have to be stored for longer duration.
A cell phone battery comes with the circuitry to protect it from over-charging and under-charging, which makes it best suited for mobile phones and other handheld devices. If this battery is ever discharged below a minimum “threshold” voltage, this protection circuitry does not allow recharging of the battery, making the battery dead for future use.
This battery comes in different sizes with dedicated chargers. Using any other charger for charging this battery may pose serious danger of ignition of the battery.
And a word of caution about disposing of these batteries: they may explode if burned, so try to sell these batteries back to the battery seller as lithium-ion batteries can be recycled.
- Image from Flickr, by Benson Mitchell
- Lithium Ion Batteries, http://www.apple.com/batteries/
- Li-Ion FAQs ,http://www.greenbatteries.com/libafa.html
- Is Lithium-ion the Ideal Battery?, http://batteryuniversity.com/learn/article/is_lithium_ion_the_ideal_battery
- Use Li-Ion Batteries in Your next Mobile Computer, http://electronicdesign.com/print/power/Use-Li-Ion-Batteries-In-Your-Next-Mobile-Computer.aspx