Why do lithium-ion batteries need management systems?
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2023/08/31 15:33:01
Remote external devices have very high battery requirements due to their special operating environment and operation mode. It has a long battery life, usually lasting a year or more. Lithium-ion batteries are widely used in long standby remote monitoring appearance because of their high operating 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 in weight and 60% higher in energy ratio. However, lithium-ion batteries also have serious drawbacks. To sum up, there are the following two aspects:
(1) Safety
Lithium-ion batteries have disadvantages such as poor safety and explosion. In particular, lithium cobalt oxide as a positive electrode material of lithium-ion batteries can not discharge large current, poor safety. In addition, almost all types of lithium-ion batteries overcharge or overdischarge will 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 the electrolyte to divide, burn and even explode. Low temperature will lead to deterioration of lithium-ion battery function, affecting the normal use of equipment.
Due to the limitations of battery manufacturing technology, the internal resistance and capacity of each battery will be different. When multiple batteries are used in series, the charge and discharge rate of each battery is inconsistent, resulting in low battery capacity utilization. In view of this, lithium-ion batteries in actual use generally require 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 the lithium-ion battery after electrolyte differentiation.
(2) Protection
The low-temperature capacity attenuation of lithium-ion batteries and the inability to accurately guess the power make the device less protective. The battery needs to be replaced regularly for long periods of time online, and the remote monitoring equipment operates at scattered sites with long distances between sites, so replacing the battery 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 battery charging state, which can accurately grasp the battery charging state and more targeted battery replacement operation. At the same time, the battery handling system is required to have a low power consumption to reduce the protection frequency and extend the service life of the battery. Therefore, the rational design of battery management system is of great significance for long-term remote monitoring of power supply status.
However, monitoring the operating characteristics of surfaces over long distances and the inherent nature of lithium-ion batteries make it difficult to develop battery handling systems that meet the needs 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 a dynamic change of current, the current stage operation is much higher than hibernation, but the operation time of the post-wake stage is much less than the hibernation stage;
Secondly, the discharge curve of lithium-ion batteries is very gentle, and the main charge is concentrated above 3.6v voltage. Then, as the voltage drops further, the battery power begins to drop sharply, and the remote external device cannot issue a low battery alarm based on the battery voltage. Finally, with the change of temperature, the self-discharge rate of lithium-ion batteries will also change greatly. When external devices work in the field, the temperature conditions are extremely extreme, further 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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