The necessity of lithium battery life factors and protection

Source: 2020 - 04 - 11 18:59 hits: the necessity of protecting the first lithium battery life factor and abstract: this paper studies the charge and discharge and temperature conditions affect ordinary rechargeable lithium battery life. Through the summary of experimental data, discussed the necessity of lithium battery protection and the reasonable range of parameters. Key words: lithium-ion batteries, electric tools, lithium protection 0 introduction current charge discharge, electric tool development presents the trend of miniaturization, lightweight, cordless. In portable electric tools used in the nickel cadmium battery is more and more limited. At the same time, non-ferrous metals such as nickel and cobalt prices doubled, as well as the application of new type lithium ion battery materials and large-scale production, greatly narrowed the lithium ion battery and nickel cadmium, nickel metal hydride batteries cost gap between. These factors effectively promote the lithium ion battery application and development in portable power tools. 1 overview of lithium ion battery must consider the security and consistency of cells, charge and discharge, in order to prevent the battery deterioration. Lithium battery energy density is high, difficult to guarantee the safety of the battery. In overcharge state, after the battery temperature excess energy, electrolyte decomposition to produce gas, easy to cause the internal pressure, cause spontaneous combustion or fracture. On the contrary, in the condition of excessive discharge, the electrolyte decomposition leads to the deterioration of the battery characteristics and durability, reduced the number of rechargeable. The change in temperature, especially at low temperature, make the two cases are more likely to happen. Therefore, lithium battery overcharge, over discharge, over current, short circuit and temperature protection is very important, so usually the battery protection circuit design to protect lithium battery. Analysis 2. 1 the battery voltage is too high and the corresponding overcharge protection under normal circumstances, lithium batteries to 4. 2v; At the same time, when the charging current is less than 0. 1 or 0 c. 5 c, a full charge. Will be 3000 ma battery from 3. 0 v charging, get capacity curve is shown in figure 1: the battery can be divided into three groups, to study the effect of charging voltage of the battery life. Charge cut-off voltage set to 4, respectively. 200 v, 4。 275 v, 4。 As the voltage 350 v, discharge unified set to 3. 0 v, realizes the battery charge and discharge cycle, record the change of the battery capacity. See figure 2. As is shown above, due to the increase of charging voltage, the initial discharge capacity of the no. 3. The battery is larger than 1. I don't have. 2. However, after about 20 cycles, battery capacity began to fell sharply; No. 2 batteries have similar properties, but slightly lower cutoff point, charging charging capacity began to decline after about 130 times. As a result, the battery voltage is higher, the life fall ( Or decrement) The faster. According to the 300 cell cycle after the remaining 80% of electricity demand 2, no. 3 can't meet. Can be accurate to 1, that is, under normal circumstances, the lithium battery charging voltage should not be greater than 4. 2v。 Accordingly, the overcharge protection limit battery voltage over this range. More than this range, battery life is bound to decline. The battery voltage is higher, the greater the risk. In general, when the battery voltage is more than 4. 25 v, should be particularly vigilant to avoid explosion danger. Therefore, combined with the charging termination voltage, discharge depth and the capacity of the battery. 3. Battery 100%, namely the battery capacity every time. After a 250 - cycle, rapid attenuation of battery capacity, the discharge the deeper, the faster battery attenuation. Under normal circumstances, the terminal voltage should not be less than 2. 5 v or 2. 4v。 When the battery voltage is lower than 2. 4 v, the battery into the depth of discharge. Lithium battery discharge depth is deep, the shorter the life of charging, lead to shorter battery life. In practice, usually by setting the discharge protection termination voltage to control the deep discharge. The termination voltage setting of over discharge protection should consult discharge current for the equipment and the application environment, but should be higher than 2. 4v。