Why lithium batteries need a lithium battery management system?

Source: 2020 - 04 - 15 'hits: time why do we need a lithium battery management system? Remote instrument because of its special working environment and working mode, the battery has a high requirement. It needs a long time continuous power supply, battery usually last for a year or longer. Lithium-ion batteries due to its high working voltage, small volume, light weight, large energy density, no memory effect, no pollution, low self-discharge, long cycle life, etc, are widely used in long time standby remote monitoring instruments. Compared with nickel metal hydride batteries, lithium ion battery light weight 30 - 40%, 60% energy than high. Lithium-ion batteries also has serious defects, however, can be summarized as the following two aspects: ( 1) Poor safety lithium battery safety, explosion and other defects. Especially in cobalt acid lithium as the anode material of lithium battery, power in the big flow discharge, poor safety. In addition, almost all of the lithium battery overcharge or overdischarge can cause irreversible damage to the battery. Lithium battery was also sensitive to temperature, if the temperature is too high, may cause the electrolyte decomposition, combustion and explosion; If the temperature is too low, the performance of lithium-ion batteries will be significantly worse, affect the normal use of equipment. Because of the limitation of battery manufacturing process of each battery internal resistance and capacity will be different. When multiple cells in series, each battery charge and discharge rate, lead to battery capacity utilization rate is low. In view of this, in the process of actual use lithium battery needs a special protection system to monitor the health status of the battery, to manage the use of lithium battery. Figure 1 after decomposition of the electrolyte of lithium battery. Figure 1 after decomposition of the electrolyte of lithium battery, 2) Maintainability under low temperature, the attenuation and power capacity can predict, the maintainability of equipment is reduced. Long-term online instrument need regular replacement, and remote monitoring equipment working in scattered locations, and the distance between each location is very long, so change the battery of a lot of work, the cost is high. In order to reduce the maintenance workload, reduce maintenance costs, battery management system needs to have accurate capacity state estimation function, accurately grasp the battery state of charge, work more targeted for battery replacement. At the same time, the battery management system needs to have relatively low power consumption, to reduce maintenance frequency, extend battery life. Therefore, the reasonable design of battery management system, continuous power supply for a long time, remote monitoring instrument maintenance is of great significance. However, due to the working characteristic of remote monitoring instrument and the intrinsic characteristics of lithium battery, it is difficult to develop to meet the application requirements of battery management system. Basically has the following several factors: first, from the remote working characteristics of the measuring instrument, in order to reduce power consumption, remote measuring instruments generally regular sleep and wake up, this is the dynamic changes of the working current, wake up working current phase is far higher than that of static state, but wake up after working time is far less than the dormant phase; Secondly, lithium-ion battery discharge curve is very flat, main power concentrated in the 3. 6 v and over voltage. Then, with the further reduce the voltage, battery began to fell sharply, remote equipment can't according to the battery voltage is low battery alarm. Finally, lithium battery self-discharge rate with large temperature fluctuations. Work in the field of instrument, extremely extreme temperature conditions, further increased the difficulty of the battery power prediction. The existing battery management system is difficult to adapt to these functions and performance requirements.