3.7V LiPo Battery Guideline

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This guide is intended to give people a better understanding of the 3.7V LiPo battery.

In daily life, we use lithium ion polymer battery in animal food device, car alarm, vehicle tracking, Bluetooth headset, mobile phones, laptop, personal digital assistant, blood pressure devices, body fat monitors……and more new applications of lithium polymer battery is also continually expanding.

Therefore, learning a 3.7v rechargeable LiPo battery is very necessary, we hope you can gain something from this guide.

1. High Energy Density
2. Stardard size well compatibility
3. More safer
4. Completely discharged

1. Much heavier, and limited on size.
2. High self discharge rate
3. Low voltage output
4. Long charging time
5. Unreliable foe low load devices

After analysis the loss capacity of 3.7v lipo battery, we got the main reason is overcharge that charging voltage is over the prescriptive voltage (4.2V) and then keep charging. In this process of overcharge will result in loss capacity of 3.7v lipo battery. The main points are as follow

1. The overcharge of graphite anode of 3.7v lipo battery
2. The overcharge of positive reaction of 3.7v lipo battery
3. The oxidizing of electrolyte when overcharging

Lithium ion will be easy deposited on the cathode and stop lithium ion implanted. The efficiency of discharge and capacity of 3.7v lipo battery will be lost.

1. The circulatory lithium ion will be reduced.
2. The deposit lithium ion of metal will be reacted with electrolyte to Li2CO3 and LiF.
3. The lithium ion of metal will happen between negative and septum, and it may increase the internal resistance of 3.7v lipo battery.

Rapid charging is another way to lose the capacity of 3.7v lipo battery. When we doing rapid charging 3.7v lipo battery, the discharge current is high, polarization will happen on the cathode, lithium ion will deposit obviously. The main reason for loss capacity of 3.7v lipo battery when we rapid charging is the matter of electronic chemical inertness, such as Co3O4, Mn2O3 and so on. They break the balance of capacity between cathode and anode. But the losing capacity of 3.7v lipo battery is irreversible.

Self-discharge of 3.7v lipo battery is the losing capacity when the battery is not using. It have two conditions when self-discharge happened. No.1 is reversible losing capacity and No.2 is irreversible losing capacity. Reversible losing capacity is the capacity of lithium polymer battery will be recovered in next charging. Irreversible losing capacity is that the capacity of 3.7v lipo battery can’t be recovered in next charging. The influencing factor has the material of cathode/anode, technology, temperature and so on.

These batteries may also power the next generation of battery electric vehicles. The cost of an electric car of this type is prohibitive, but proponents argue that with increased production, the cost of 3.7V Rechargeable LiPo batteries will go down.

Hyundai Motor Company plans to use this battery type in its hybrid electric vehicles. A LiPo powered Audi A2 covered the record distance of 600 km without recharging on October 26, 2010.

There are currently two commercialized technologies, both lithium-ion-polymer (where “polymer” stands for “polymer electrolyte/separator”) cells. These are collectively referred to as “polymer electrolyte batteries”.
The battery is constructed as:
Cathode: LiCoO2 or LiMn2O4
Separator: Conducting polymer electrolyte
Anode: Li or carbon-Li intercalation compound
Typical reaction:
Anode: carbon–Lix → C + xLi+ + xe−
Separator: Li+ conduction
Cathode: Li1−xCoO2 + xLi+ + xe− → LiCoO2

Polymer electrolytes/separators can be solid polymers (e.g., polyethylene oxide, PEO) plus LiPF6, or other conducting salts plus SiO2, or other fillers for better mechanical properties (such systems are not available commercially yet). Some manufacturers like Avestor (since merged with Batscap) are using metallic Li as the anode (these are the lithium-metal-polymer batteries), whereas others wish to go with the proven safe carbon intercalation anode.

Both currently commercialized technologies use PVdF (a polymer) gelled with conventional solvents and salts, like EC/DMC/DEC. The difference between the two technologies is that one (Bellcore/Telcordia technology) uses LiMn2O4 as the cathode, and the other the more conventional LiCoO2.

Other, more exotic (although not yet commercially available) LiPo batteries use a polymer cathode. For example, Moltech is developing a battery with a plastic conducting carbon-sulfur cathode. However, as of 2005 this technology seems to have had problems with self-discharge and manufacturing cost.

Yet another proposal is to use organic sulfur-containing compounds for the cathode in combination with an electrically conductive polymer such as polyaniline. This approach promises high power capability (i.e., low internal resistance) and high discharge capacity, but has problems with cyclability and cost.