How to prevent lithium-ion batteries from exploding
Lithium is the smallest and most vivid metal on the periodic table. Due to its small size and high capacity density, it is very popular with customers and engineers. However, the chemical reaction is too active and it poses a high risk. When lithium is exposed to air, it undergo a violent oxidation reaction with oxygen. To improve safety and voltage, scientists have made it possible to store lithium atoms in materials such as graphite and lithium-cobalt oxide
The molecular structure of this data forms nanoscale micro-batteries that can be used to store lithium atoms. That way, even if the shell cracks and oxygen gets in, the oxygen molecules are too big to fit inside the tiny battery, so the lithium atoms don't come into contact with the oxygen, preventing it from exploding. This principle of lithium-ion battery makes people achieve high capacity density at the same time can achieve the purpose of safety.
When a lithium-ion battery is charged, lithium atoms lose electrons and oxidize to lithium ions. The lithium ions travel through the electrolyte to the negative electrode, where they enter a storage cell, where they gain electrons, which are reduced to lithium atoms. When unloading, the process is reversed. In order to prevent the short circuit caused by the direct contact between the positive and negative electrodes of the battery, the diaphragm paper with many holes is added to the battery to prevent the short circuit. A good diaphragm paper can also automatically close the fine hole when the battery temperature is too high, so that lithium ions can not pass through, so as not to waste effort and prevent risks.
Safeguard measures
Lithium-ion batteries begin to have side uses when the battery overcharge voltage is above 4.2V. The greater the stress, the greater the risk. At voltages above 4.2V, less than half of the lithium atoms remain in the anode data, and the battery often crashes, permanently reducing the battery's capacity. If the battery continues to charge, subsequent lithium metal will accumulate on the surface of the anode, because the anode storage chamber is already full of lithium atoms. These lithium atoms grow dendritic crystals from the surface of the negative electrode toward the lithium ions. These lithium crystals will pass through the diaphragm paper, short-circuiting the anode and cathode.
Sometimes a short circuit occurs before the battery bursts, because during the process of overcharging, the electrolyte and other information will break down to appear gas, causing the battery shell or pressure valve to expand and break, allowing oxygen to enter and reacting lithium atoms to accumulate on the negative surface, and then explode. Therefore, when the lithium ion battery is charged, a voltage upper limit must be set to take into account the life, capacity and safety of the battery. The maximum charging voltage is 4.2V. Lithium-ion batteries must also discharge at a lower voltage limit. When the battery voltage is below 2.4V, some data will be corrupted at first. And because the battery will self-discharge, the longer the voltage is lower, therefore, it is best not to discharge to 2.4V to stop. Lithium-ion batteries can only release about 3% of their capacity between 3.0V and 2.4V discharges. Therefore, 3.0V is the ideal discharge cutoff voltage.
In charge and discharge, besides voltage constraint, current constraint is also necessary. When the current is too high, the lithium ions don't have time to enter the storage cell and accumulate on the surface of the data. When these lithium ions gain electrons, they crystallize lithium atoms on the surface of the data, which is the same as overcharging and poses a certain risk. If the battery box is broken, it will explode.
Therefore, the maintenance of lithium-ion batteries should include at least three aspects: the upper limit of charging voltage, the lower limit of discharging voltage and the upper limit of current. General lithium ion battery pack, in addition to lithium ion battery, there will also be a maintenance board, maintenance board is important to supply the three maintenance. However, the maintenance of these three maintenance plates is obviously not enough, and lithium ion battery explosions still occur frequently around the world. In order to ensure the safety of battery system, it is necessary to analyze the cause of battery explosion more carefully.
