Explanation of Battery Charging Test Principle
The basic principle of charging and discharging lithium batteries is achieved through the insertion and extraction of lithium ions between the positive and negative electrodes. During the charging process, electrons on the positive electrode run to the negative electrode through an external circuit, while lithium ions pass through the electrolyte, the separator material, and ultimately reach the negative electrode, where they are reduced to carbon material embedded in the negative electrode. This process is reversible and is known as the “rocking chair theory”
Daily usage specifications for lithium battery charge and discharge testing
1. Many people have a certain degree of accuracy about the charging time of lithium batteries, and many opinions suggest that the charging time must exceed 12 hours and be repeated three times in order to activate the battery. The statement that ‘the first three charges should be charged for more than 12 hours’ is not entirely correct. According to the research results, all serious formal technical materials emphasize that overcharging and overdischarging can cause significant damage to lithium batteries, especially liquid lithium-ion batteries. Therefore, it is best to charge according to standard time and methods, especially not for over 12 hours of ultra long charging.
2. Not suitable for long-term charging or recharging after the battery is completely depleted
Lithium ion battery smartphones or chargers will automatically stop charging after the battery is fully charged. After the lithium battery is fully charged, it will automatically stop charging. Excessive charging time and complete use of empty power can cause overcharging and overdischarging, which will permanently damage the positive and negative electrodes of the lithium-ion battery. From a molecular perspective, overdischarging will cause the negative carbon to release lithium ions excessively, causing its layer structure to collapse. Overcharging will force too many lithium ions into the negative carbon structure, making it impossible for some of them to be released again.
3. Charging method for lithium batteries
Step 1: If the voltage is less than 3V, it is necessary to perform pre charging with a current of 0.05C;
Step 2: Determine if 3V<voltage<4.2V, constant current charging with 0.2C~1C current;
Step 3: Determine if the voltage is greater than 4.2V and charge at a constant voltage of 4.20V. The current decreases with increasing voltage until fully charged.
The correct discharge method for lithium batteries
1. Standard discharge method: discharge at a constant current of 0.2C5 until the battery terminal voltage is 2.75V. Because it is difficult to meet this condition in daily use, it is of little significance. This method is important for calibrating battery capacity.
2. Fast discharge method: Due to the low internal resistance of lithium batteries, high current discharge is allowed. It can be discharged for more than 54 minutes at room temperature with a current of 1C5; 1.5C5 discharge time of more than 30 minutes; 2C5 discharge time of more than 23 minutes; And allow for short-term discharge of larger currents.
3. The discharge process of lithium batteries during operation is balanced. In theory, the discharge rate and depth should be considered when discharging lithium batteries.
4. The depth of discharge is the ratio of the amount of discharge to the nominal capacity, and the best reference indicator in practice is voltage. The general standard for discharging lithium batteries is that a lithium battery can be charged when discharged between 2.75V and 3V, because discharging below 2.75V can easily lead to the taboo of overdischarging in rechargeable batteries. Overdischarging can cause excessive evaporation of the electrolyte, and the negative electrode of the lithium battery can react excessively, causing changes in its dielectric film and a permanent loss of capacity.
Precautions for the use of lithium batteries
1. After discharging at high temperatures outdoors or retrieving the battery at high temperatures, it cannot be charged immediately. The battery can only be charged after the surface temperature has cooled down.
2. When storing, simply place it in a dry and safe indoor environment; Low temperature storage will not damage the battery, but the battery temperature should be increased during use, and it should be placed in the car as much as possible when used outdoors.
3. Pay attention to the “+” and “-” signs on the battery and electrical appliances, and correctly install the battery into the appliance. If the battery is reversed, it may be charged or short circuited, resulting in overheating, leakage, discharge, rupture, explosion, fire, and personal injury.
4. When replacing batteries, it is necessary to use new batteries of the same brand and model to replace all batteries at the same time. When batteries of different brands and models are used, or when new and old batteries are mixed, due to differences in voltage or capacity, some batteries may be over discharged or forcibly discharged, resulting in leakage, discharge, explosion, fire, and personal injury.
5. Maintaining moderate charging and discharging of lithium batteries can extend their lifespan, and keeping the battery level between 10% and 90% is beneficial for protecting the battery. This means that when charging lithium battery products and devices, there is no need to reach the maximum value.
In general, lithium batteries are widely used by consumers due to their advantages of “energy conservation and environmental protection”. In working use, lithium batteries do not need to be charged to 100% full, let alone exhaust the battery. If the situation permits, try to maintain the battery level around half full, and the smaller the charging and discharging amplitude, the better.