Why do lithium-ion batteries need management systems?
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2023/04/01 11:44:16
Because of its special operating environment and mode, remote external devices have very high requirements on batteries. It has a long battery life, usually lasting a year or more. Lithium-ion batteries are widely used in long time standby remote monitoring appearance because of their high working voltage, small size, light weight, high energy density, no recall effect, no pollution, small self-discharge, long cycle life and many other advantages. Compared with nickel-metal hydride batteries, lithium-ion batteries are 30% to 40% lighter and have a 60% higher energy ratio. However, lithium-ion batteries also have serious drawbacks. To sum up, there are the following two aspects:
(1) Security
Lithium-ion battery has some disadvantages such as poor safety and explosion. In particular, lithium cobalt oxide as the cathode material of lithium ion battery can not discharge current, safety is poor. In addition, almost all types of lithium-ion battery overcharge or overdischarge can cause irreversible damage to the battery. Lithium-ion batteries are also very sensitive to temperature: if used at too high a temperature, they can cause electrolytes to differentiate, burn and even explode. Low temperature deteriorates the functions of lithium-ion batteries and affects the normal use of devices.
Due to the limitations of battery manufacturing technology, the internal resistance and capacity of each battery will vary. When multiple batteries are used in series, the charge and discharge rates of each battery are inconsistent, resulting in low battery capacity utilization. In view of this, the actual use of lithium ion batteries generally requires a special protection system to monitor the health of the battery, so as to deal with the use of lithium ion batteries. Figure 1 shows a lithium ion battery after electrolyte differentiation.
(2) Protection
The low temperature capacity of lithium ion batteries decreases and the power cannot be accurately guessed, which reduces the protection of equipment. Batteries need to be replaced regularly when online for long periods of time, and remote monitoring equipment operates at scattered sites that are far apart, so changing batteries is a huge and expensive task. In order to reduce the amount of protection and reduce the cost of protection, the battery processing system is required to accurately judge the charging state of the battery, can accurately grasp the charging state of the battery, and more targeted battery replacement operation; At the same time, the battery processing system is required to have low power consumption to reduce the protection frequency and extend the service life of the battery. Therefore, it is of great significance to design the battery management system reasonably to monitor the state of power from a long distance.
However, monitoring the performance of surfaces over long distances and the inherent characteristics of lithium-ion batteries make it difficult to develop battery handling systems that meet the requirements of such applications. There are several important factors: first, from the working characteristics of long-distance measurement, in order to reduce power consumption, long-distance measurement tends to periodic sleep and wake up, the operation is the dynamic change of current, the current stage operation is much higher than hibernation, but the operation time of the wake up stage is far less than the dormancy stage;
Secondly, the discharge curve of lithium-ion batteries is very smooth, and the main charge is concentrated above 3.6v voltage. Then, as the voltage drops further, the battery begins to drop sharply, and the remote external device cannot send out a low battery alarm based on the battery voltage. Finally, as the temperature changes, the self-discharge rate of lithium-ion batteries will also change greatly. When external devices are working in the field, the temperature conditions are extremely extreme, adding to the difficulty of guessing battery power. It is difficult for existing battery management systems to adapt to these functions and functional requirements.
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