Introduction: Almost most of the safety accidents caused by lithium batteries are caused by short circuit.
1、Avoid short circuit and overcharge
Almost most of the safety accidents caused by lithium batteries are caused by short circuit. We know that when the positive and negative electrodes of the battery are connected to each other in a non-normal path with very low resistance, that is, when we often say short circuit, the battery will generate a very large current and heat, the heat generated and the release of excessive power will not only lead to serious damage to the battery life, and for the use of hermetically sealed lithium battery, the internal pressure will lead to a sudden increase in pressure inside the battery. And because of the chemical properties of lithium ion is very active, and will eventually produce shell bursting and burning situation.
Due to the chemical properties of lithium-ion batteries, when we overcharge the battery (overcharge) operation, the lithium ion can not embed more lithium ions in the negative electrode, resulting in the precipitation of lithium ions on the negative electrode surface as lithium metal, resulting in the phenomenon of dendrite lithium, when the dendrite lithium growth to a certain extent will pierce the diaphragm, resulting in internal short circuit battery, the isolation film is broken, the same will occur internal short circuit, thus lead to safety accidents.
Therefore, in our daily use of lithium batteries, we should try to avoid a short circuit or overcharge, but for most digital products, the internal charging circuit will be equipped with the corresponding protection IC to avoid the overcharge of lithium batteries, when the protection circuit detects that the lithium battery has reached the full state, will automatically cut off the charging circuit. But here it is still not recommended to connect the phone or other devices for a long time in the energized state of the charger, after all, who do not want to use their cell phones or other devices and even personal safety and a small charging protection chip bet.
2, puncture is also very dangerous
Compared to short circuit and overcharge, the lithium battery puncture is also a very unwise practice. If the lithium battery is pierced by any hard object, its internal lithium ions will directly react with the oxygen in the air chemical reaction, the same phenomenon of violent combustion will occur.
For the lithium battery itself or other electronic products containing lithium batteries inside, we usually see a prominent trash can sign. If you discard lithium batteries will not only cause environmental pollution, but also in the process of garbage disposal is more likely to fire and other situations.
3, avoid high temperature and fire high temperature or fire will also lead to the explosion and burning of lithium batteries
Especially in the hot summer or long exposure to the sun in the car, will lead to the lithium battery in the ambient temperature higher than its normal storage temperature. So when we use the equipment containing lithium-ion batteries, we should try to avoid the use of high temperature environment for a long time, although the lithium battery in the case of direct use of fire, the explosion and burning time is relatively long, but there will still be a sudden increase in its internal pressure, which is often referred to as a bulge.
When our cell phone battery or other lithium-ion battery bulge, you should immediately cut off the power and stop using it to prevent further increase in internal pressure, and replace the battery with a new one.
Summarize the production and use of lithium batteries in some cases of explosion.
1. Overcharge explosion
Protection line out of control or detection cabinet out of control so that the charging voltage is greater than 5V, resulting in electrolyte decomposition, the internal reaction of the battery, the battery pressure rises rapidly, the battery explodes.
2. Overcurrent explosion
Protection circuit out of control or testing cabinet out of control so that the charging current is too large to cause lithium ions too late to embed, and the formation of lithium metal on the surface of the electrode, penetrating the diaphragm, the positive and negative electrodes directly short circuit resulting in an explosion (rarely occur).
3, ultrasonic welding plastic shell when the explosion
ultrasonic welding plastic shell, due to the equipment so that its ultrasonic energy transfer to the battery core, ultrasonic energy is very large so that the battery internal diaphragm melted, the positive and negative electrodes directly short-circuit, resulting in an explosion.
4 spot welding explosion
Spot welding when the current is too large to cause a serious internal short circuit resulting in an explosion, in addition, spot welding when the positive connection piece directly connected to the negative electrode, so that the positive and negative electrodes directly short-circuited explosion.
5. over-discharge explosion
battery over-discharge or over-current discharge (more than 3C) is easy to dissolve the negative copper foil deposited on the diaphragm so that the positive and negative electrodes directly short-circuit the explosion (rarely occur).
6. Explosion during vibration and fall
The core in the violent vibration or drop caused by the internal pole piece dislocation, direct serious short circuit and explosion (rarely occur).
Lithium battery cells overcharge to a voltage higher than 4.2V, will begin to produce side effects. The higher the overcharge voltage, the higher the danger will follow. After the lithium cell voltage is higher than 4.2V, the number of lithium atoms left in the positive electrode material is less than half, and the storage cell will collapse at this time, causing a permanent drop in battery capacity. If charging continues, as the storage compartment of the negative electrode is already filled with lithium atoms, subsequent lithium metal will accumulate on the surface of the negative electrode material. These lithium atoms will grow dendritic crystals from the cathode surface in the direction of the lithium ions.
These lithium metal crystals can pass through the diaphragm paper and short-circuit the positive and negative electrodes. Sometimes the battery explodes before the short circuit occurs, because in the overcharge process, the electrolyte and other materials will be cracked to produce gas, making the battery shell or pressure valve bulge rupture, allowing oxygen to go in and react with the lithium atoms piled up on the surface of the negative electrode, and then explode.
Therefore, when charging lithium batteries, the voltage limit must be set in order to take into account the battery life, capacity, and safety at the same time. The ideal charging voltage limit is 4.2 V. When discharging lithium cells, there should also be a voltage limit. When the cell voltage is below 2.4V, some materials will start to be destroyed. As the battery will self-discharge, the longer you put the voltage will be lower, therefore, it is best not to put it to 2.4V when discharging before stopping. The energy released during the period from 3.0V to 2.4V for Li-ion batteries only accounts for about 3% of the battery capacity. Therefore, 3.0V is an ideal discharge cut-off voltage. When charging and discharging, in addition to the voltage limit, the current limit also has its necessity. When the current is too high, lithium ions do not have time to enter the storage compartment and will collect on the material surface.
These lithium ions gain electrons and crystallize lithium atoms on the surface of the material, which can be just as dangerous as overcharging. In case the battery case breaks, it can explode. Therefore, the protection of lithium-ion batteries should include at least three items: the upper limit of charging voltage, the lower limit of discharging voltage, and the upper limit of current. Generally, in addition to the lithium battery pack, there will be a protection plate, this protection plate is mainly to provide these three protections. However, the protection board of the three protection is obviously not enough, the global lithium battery explosions are still frequent.
The reasons for the battery explosion, a more careful analysis, to list some.
1, a large internal polarization.
2, the pole piece of water absorption, and electrolyte reaction gas drum.
3, the quality of the electrolyte itself, performance problems.
4、Injecting liquid when the amount of liquid does not meet the process requirements.
5, poor sealing performance of laser welding in the assembly process, air leakage when measuring air leakage.
6, dust, pole piece dust first easy to cause micro short circuit.
7, positive and negative pole piece is thicker than the process range, difficult to enter the shell.
8, liquid injection sealing problems, poor sealing performance of steel beads lead to gas drum.
9, shell incoming material exists shell wall thick, shell deformation affects the thickness.
10, outside the ambient temperature is too high is also the main reason for the explosion.
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