Principle of lithium battery charging circuit
1、 Lithium batteries and nickel cadmium and nickel hydrogen batteries:
The cathode of lithium ion battery is graphite crystal, usually lithium dioxide. During charging, lithium ions move from positive to negative and embed into the graphite layer. During the discharge, lithium ions are separated from the negative electrode surface of the graphite crystal to the positive electrode. Therefore, in the process of battery charging and discharging, lithium always appears in the form of lithium ion, rather than metal lithium. Therefore, this kind of battery is called lithium ion battery, or lithium battery for short.
Lithium battery has the advantages of small size, large capacity, light weight, no pollution, high single voltage, low self discharge rate, and many battery cycles, but it is expensive. Due to the low capacity of nickel cadmium battery, self discharge is serious and environmental pollution. Is being phased out. NiMH battery has high performance price ratio and does not pollute the environment, but the single voltage is only 1.2V, and the scope of use is limited.
2、 Features of lithium battery:
1. High weight energy ratio and volume energy ratio;
2. High voltage, the voltage of a single lithium battery is 3.6V, which is equal to the series voltage of three nickel cadmium or nickel hydrogen rechargeable batteries;
3. Self discharge can be stored for a long time. This is the most outstanding advantage of the battery;
4. No memory effect. The so-called memory effect of lithium battery does not exist in the nickel cadmium battery, so the lithium battery does not need to be discharged before charging;
5. Long life. Under normal working conditions, the number of charging and discharging cycles of lithium battery is far greater than 500;
6. It can be charged quickly. Lithium battery can be charged with current of 0.5 to 1 time capacity, and the charging time is shortened to 1 to 2 hours;
7. Can be used in parallel;
8. As the battery does not contain heavy metal elements such as cadmium, lead and mercury, it does not pollute the environment and is the most advanced green battery in the contemporary era;
9. High cost. Lithium batteries are more expensive than other batteries.
3、 Internal structure of lithium battery:
There are two types of lithium batteries: cylindrical and rectangular.
The internal battery adopts spiral winding structure and is made of extremely thin and transparent polyethylene film insulation material. The positive electrode comprises a lithium ion collector composed of lithium and cobalt and a current collector composed of aluminum film. The cathode is composed of lithium ion collector and copper film collector made of sheet carbon material. The battery has an organic electrolyte solution. In addition, safety valve and PTC element are also equipped to protect the battery from damage in case of battery abnormality and output short circuit.