Knowledge of rechargeable lithium batteries
We have learned the knowledge of lithium battery protection boards for so long, and we know that lithium battery protection boards are used for lithium batteries. In fact, this understanding is wrong. There are many kinds of lithium batteries, and there are also different models. Today, the Chinese Chuangfa will take a look at the lithium battery protection board as the core component of the battery in the lithium battery. Today, I mainly learn the knowledge of rechargeable lithium batteries. There are many kinds of rechargeable lithium batteries, such as lithium-vanadium oxide batteries, lithium-ion batteries and newly developed lithium-polymer batteries abroad. Only the first two are introduced here, focusing on lithium-ion batteries.
Li-ion battery charging requirements are very high. To ensure that the termination voltage accuracy is within 1%, major semiconductor device manufacturers have developed a variety of lithium-ion battery charging ICs. , To ensure safe, reliable and fast charging. Nowadays, mobile phones are very common. Some of the mobile phones are Ni-MH batteries, but smart phones are lithium-ion batteries. Proper use of lithium-ion batteries is very important to extend battery life.
1. Lithium-vanadium oxide battery (Li-V6O13)
Lithium-vanadium oxide battery uses lithium as anode, vanadium oxide as cathode, and organic solvent of inorganic salt as Electrolyte composition. Its characteristic is that it can be charged. Taking the No. 2 battery as an example, the comparison of the lithium-vanadium oxide battery with the lithium-manganese dioxide battery and the lithium-thionyl chloride battery is shown in Table 5.
As far as we know, because the rated voltage of the lithium-vanadium oxide battery is only 2.8V, and the rated capacity is also small, compared with the other two kinds of lithium batteries, its specific energy is the smallest. The main parameters of this type of cylindrical battery are shown in Table 6. It can be seen from Table 6 that the number of recharges (cycle life) is not long, so this rechargeable battery will soon be replaced by a lithium ion battery.
2. Lithium ion battery (Li-Ion)
Lithium ion battery is currently the most widely used lithium battery. It can be made into a flat rectangle according to the requirements of different electronic products. Cylindrical, rectangular and button type, and there are battery packs composed of several batteries connected in series.
The rated voltage of lithium-ion batteries is 3.6V (some products are 3.7V). The final charging voltage when fully charged is related to the anode material of the battery: the anode material is 4.2V of graphite; the anode material is 4.1V of coke. The internal resistance of different anode materials is also different, the internal resistance of the coke anode is slightly larger, and the discharge curve is also slightly different, as shown in Figure 1. Generally called 4.1V lithium ion battery and 4.2V lithium ion battery. The termination discharge voltage of lithium-ion batteries is 2.5V～2.75V (the battery factory provides the working voltage range or the termination discharge voltage, each parameter is slightly different). Continue to discharge below the termination discharge voltage is called overdischarge, and overdischarge will damage the battery.
Lithium-ion batteries are not suitable for high-current discharge. Excessive current discharge will reduce the discharge time (higher temperature is generated inside and energy is lost). Therefore, the battery production factory gives the maximum discharge current, which should be less than the maximum discharge current during use. Lithium-ion batteries have certain requirements for temperature. The factory provides the charging temperature range, discharging temperature range and storage temperature range. 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 termination charge voltage accuracy is ±1% of the rated value (for example, for a 4.2V lithium-ion battery, the tolerance is ±0.042V). Overvoltage charging will cause permanent damage to the lithium-ion battery. 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 0.25C～1C (C is the capacity of the battery, such as Cu003d800mAh, the charging rate of 1C means the charging current is 800mA). It is often necessary to detect the battery temperature during high-current charging to prevent overheating from damaging the battery or causing an explosion.
Lithium-ion battery charging is divided into two stages: first, constant current charging, and changing to constant voltage charging when it is close to the termination voltage. The charging characteristics are shown in Figure 2. This is a battery with a capacity of 800mAh, and its final charging voltage is 4.2V. The battery is charged with a constant current of 800mA (charging rate of 1C). At the beginning, the battery voltage is boosted with a larger slope. When the battery voltage is close to 4.2V, it is changed to 4.2V constant voltage charging. The current gradually drops and the voltage changes little. When the charging current drops to 1/10C (approximately 80mA), it is considered that it is close to being fully charged and the charging can be terminated (some chargers start a timer after 1/10C, u200bu200band the charging ends after a certain period of time).
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