Do you know the little knowledge about charging and discharging lithium batteries
Lithium-ion battery discharge
Discharge termination voltage: The rated voltage of lithium-ion batteries is 3.6V (some products are 3.7V), and the termination discharge voltage is 2.5-2.75V (the battery factory gives the operating voltage range or the termination discharge voltage, each parameter is slightly different ). The discharge termination voltage of the battery should not be less than 2.5 (n is the number of batteries connected in series). Continuing to discharge below the termination discharge voltage is called overdischarge. Overdischarge will shorten the battery life and cause battery failure in severe cases. When the battery is not in use, charge the battery to 20% of its capacity, and store it in moisture-proof packaging. Check the voltage once every 3 to 6 months and charge it to ensure that the battery voltage is within the safe voltage value (above 3V).
Discharge current: Lithium-ion batteries are not suitable for high-current discharge. When discharged with excessive current, higher temperatures will be generated internally and energy will be lost, reducing the discharge time. If there is no protective element in the battery, it will overheat and damage the battery. Therefore, the battery production factory gives the maximum discharge current, which cannot exceed the maximum discharge current given in the product characteristics table during use.
Discharge temperature: The discharge curve at different temperatures is different. At different temperatures, the discharge voltage and discharge time of lithium-ion batteries are also different. The battery should be discharged (working) within the temperature range of -20°C to +60°C.
Lithium-ion battery charging
In the use of lithium batteries, it should be noted that after the battery is left for a period of time, it will enter the dormant state. At this time, the capacity is lower than the normal value, and the use time is also shortened. But the lithium battery is easy to activate, as long as 3-5 normal charge and discharge cycles can activate the battery and restore normal capacity. Due to the characteristics of the lithium battery itself, it is determined that it has almost no memory effect. Therefore, the new lithium battery in the user's mobile phone does not require special methods and equipment during the activation process.
To charge the lithium-ion battery, a dedicated lithium-ion battery charger should be used. Lithium-ion battery charging adopts the "constant current/constant voltage" method. The first is constant current charging, and when it is close to the end voltage, it is changed to constant voltage charging. For example, a battery with a capacity of 800mA.h has a final charging voltage of 4.2V. The battery is charged with a constant current of 800mA (charging rate of 1C). At the beginning, the battery voltage rises with a large slope. When the battery voltage is close to 4.2V, it is changed to 4.2V constant voltage charging. The current of the lithium battery gradually decreases, and the voltage changes little. When the charging current drops to 1/10C (approximately 80mA), it is considered to be nearly full and the charging can be terminated (some chargers start a timer after 10C, and the charging ends after a certain period of time). It is not possible to use a nickel-cadmium battery charger (for three nickel-cadmium batteries) to charge a lithium-ion battery (although the rated voltage is the same, both are 3.6V), due to different charging methods, it is easy to cause overcharging.
Charging voltage: The final charging voltage when fully charged is related to the negative electrode material of the battery. Coke is 4.1V, while graphite is 4.2V. It is generally called 4.1V lithium ion battery and 4.2V lithium ion battery. When charging, it should be noted that 4.1V batteries cannot be charged with 4.2V chargers, otherwise there will be a risk of overcharging (the charger IC used by 4.1V and 4.2V chargers is different). Lithium-ion batteries have very high requirements for charging, and they require sophisticated charging circuits to ensure the safety of charging. The tolerance of the final charging voltage accuracy is ±1% of the rated value (for example, charging a 4.2V lithium-ion battery has a tolerance of ±0.042V). Overvoltage charging will cause permanent damage to the lithium-ion battery.
Charging current: The charging current of lithium-ion batteries should be based on the recommendations of the battery manufacturer, and a current-limiting circuit should be required to avoid overcurrent (overheating). Generally, the commonly used charging rate is 0.25~1C, and the recommended charging current is 0.5C (C is the capacity of the battery, such as a battery with a nominal capacity of 1500mA.h, and the charging current is 0.5*1500=750mA). It is often necessary to detect the temperature of the battery during high-current charging to prevent damage to the battery or explosion due to overheating.
Charging temperature: When charging the battery, the ambient temperature cannot exceed the temperature range listed in the product characteristics table. The battery should be charged in the temperature range of 0～45℃, away from high temperature (above 60℃) and low temperature (-20℃) environment.
Overcharge, overdischarge, or overcurrent of lithium-ion batteries during charging or discharging will cause damage to the battery or reduce its service life. To this end, various protection components and protection circuits composed of protection ICs have been developed, which are installed in batteries or battery packs to provide complete protection for the batteries. However, in use, overcharge and overdischarge should be prevented as much as possible. For example, during the charging process of a mobile phone battery, it should be separated from the charger in time when it is almost full. When the depth of discharge is shallow, the cycle life will be significantly improved. Therefore, when using it, don't wait until the low battery signal appears on the phone before charging, let alone continue using it when this signal appears, although there is still a part of the remaining capacity available when this signal appears.
