1 What’s the normal way of charging

Since in the 1970 the coming of primary lithium battery and 1990 SONY launched lithium ion  battery (usually referred to for lithium ion battery or rechargeable lithium battery ) first generation. Because of its high of energy density,  high of battery voltage,  less discharge voltage,  long cycle life ,  environmental friendly, and simple charging and li-ion battery packmaintenance , it has became most welcomed high-energy battery; in addition, lithium battery also has relative high of voltage (3.0V to 4.3V ) And the number of portable products are able to work with a single lithium-ion battery. All along, people‘s focus remains on increasing the capacity of the lithium-ion battery pack, longer battery life, more charge cycles or more security more important than battery capacity battery.

In this paper several methods can significantly extend the battery life of the lithium-ion battery charging and discharging.

2 lithium batteries Components

Cathode material for lithium-ion batteries are usually composed of active compounds from lithium, carbon anode is a special molecular structure. Common cathode material mainly composed of LiCoO2, charging, plus potential forced the positive poles of the battery release lithium-ion compounds, embedded in negative molecular arrangement of lamellar structure of carbon. When discharging, lithium-ion is precipitated from the lamellar structure of carbon, and compound of the cathode back. Lithium-ion mobile produces an electric current. Lithium batteries can also be divided into nonrechargeable and rechargeable two broad categories. Do not charge batteries disposable batteries, it can only convert chemical energy into electricity once, can’t restore the power back to the chemical energy (or very poor restore performance). Rechargeable battery called the secondary battery, also known as the battery. It can turn transforming electrical energy into chemical energy stored, used and convert chemical energy into electrical energy, which is reversible, which is the main characteristics of lithium-ion batteries.

3  lithium battery charging principle

Lithium-ion batteries are designed to provide a voltage of approximately 3.0V to4.3V. Always keep the lithium-ion battery voltage within its design limits is important, otherwise the battery will suffer irreparable damage. If the battery voltage is below 3.0 Volts, lithium battery deep discharge, once in this State, it can take hours or even days to recover. In fact, deep discharge may cause short circuit the battery,and the battery cannot be restored. If the charging voltage is higher than the other side 4.3V may be worse, because doing so will damage the battery and cause overheating or other disastrous consequences. Figure 1 is a typical lithium battery charge curve diagram shows the charging current, battery voltage and battery capacity changes with time.

Better lithium-ion batteries to the battery charging method is to provide a constant current of ± 1% pressure limiting, until the battery is fully charged and stop charging. Charging voltage should be less than the maximum voltage can usually be set to 4.1V; the charge current ranges from c/2 to 1C for 2.5 to 3 hours. You can also use a lower charging current, but will take longer. Monitor the charging currentand charging. With the battery charging voltage rise, and when the charging 3.7v lithium battery cellvoltage is reached the battery voltage, charging current began to decline. Current startfalling, about charging to the battery capacity of 50% to 60%. Charging voltage continued until the charging current down to a low enough level, usually selected to terminate current between the c10 to C/20, then about charging to the battery capacity of 92% to 99%, terminate the charging cycle.

4 the correct lithium-ion battery charging method

On the correct method of charging lithium battery, the most important thing is to make sure a good charging voltage and charging termination of current size. Main factors determining battery charge voltage battery cathode active material for use in electrochemical potential, lithium is concerned about 4V. Other compounds will raise or lower the voltage. A second factor is the battery capacity, cycle life, achieve a balance between battery life and security.

Current lithium batteries usually have a misunderstanding, and one-sided pursuit of batteries work longer hours, so that the batteries close to 100%. This approach in the long term without maximize the use of lithium-ion batteries. Most of the lithium-ion battery manufacturer set a 4.2V charge voltage, use this as the optimal balance between capacity and cycle life. 4.2V as constant charging voltage, the battery provides about 500 charge/discharge cycles, and battery capacity to 80%. Figure shows the recommended charge voltage and decreasing charge voltage comparisons.

You can see from Figure 2, in order to avoid 100% of lithium batteries to capacity can be extended lithium-ion battery life to a great extent. Reduce the charging voltage will increase cycle life and service life, at the cost of reduced battery capacity.Studies have shown that the charging voltage from 100mV to 300mV cycles life expectancy can be 2 to 5 times or more. Select the appropriate charge termination current. Select a minimum charging current termination (C/10 or C/x) charger, not charged to capacity through 100%, or you can extend battery life. Many Chargers have to be able to function for extended battery life, and sometimes you can extend battery life significantly. Battery charger for extended battery life is mainly determined by the charger the charging voltage and charging termination of current decisions. C/10 terminates the charging current is only about charging the battery to its volume of 92%, but will increase cycle life of lithium batteries. Not recommended for continuous voltage after the battery is fully charged and the battery still because it will speed up

Permanent capacity loss, and may cause internal lithium metal plating. This plating may develop into internal short circuit path, causing overheating and makes them unstable.

Some lithium-ion battery charger allows you to use thermistor monitoring the battery temperature. The main purpose of doing so is, if the battery temperature is outside the recommended range from 0 to 40 window, that prohibit charging to prevent damage caused by battery overheating.

In short, wants people to concern about the capacity of the lithium-ion battery, into the lithium-ion battery life concerns. Although many factors influence the lithium-ion battery life, but with the suitable charging mode to extended lithium-ion battery life plays a big role. The right way is to use a lower charge voltage, the appropriate charging termination current.

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