1.Possible reasons for thermal out of control
Energy capacity batteries for the most part experience thermal out of control under misuse conditions, and normal maltreatment conditions are isolated into three classifications: mechanical maltreatment, electrical maltreatment, and thermal maltreatment.
The most widely recognized event of thermal out of control because of electrical maltreatment. In oppressive working circumstances, lithium-particle batteries not just delivery response heat, ohmic intensity, and polarization heat, yet in addition incorporate intensity delivered by inward shortcircuits and heat delivered by responses. The intensity delivered by inner shortcircuits and side responses (counting SEI layer disintegration, positive and negative cathode electrolyte response, film disintegration, electrolyte decay) is a lot more noteworthy than the intensity created under typical working circumstances, which can prompt a fast expansion in battery temperature and effectively lead to uncontrolled thermaling
(1) Mechanical maltreatment
The principal normal for mechanical maltreatment is the general uprooting of battery cells and modules under outer powers. The primary structures for battery cells (monomers) incorporate impact, pressure, and cut. At the module (battery pack) level, vibration issues additionally should be thought of.
In mechanical maltreatment, the most hazardous is cut, where the guide is embedded into the battery body, causing an immediate short out between the positive and negative shafts. Contrasted with crashes, crushing, and different circumstances where inner shortcircuits just happen with likelihood, the age of intensity during the cut cycle is more extreme, bringing about a higher likelihood of out of control thermaling
(2) Power misuse
Electrical maltreatment by and large incorporates a few structures, for example, cheating, over release, or outer short out, and cheating is the probably going to form into thermal out of control. Because of the great energy content of batteries, cheating is the most unsafe type of electrical maltreatment, and the age of intensity and gas are two normal attributes in the cheating system. thermaling comes from Ohmic intensity and side responses.
First and foremost, because of unnecessary lithium addition, lithium dendrites develop on the anode surface, and the stoichiometric proportion of the cathode to the anode decides when lithium dendrites start to develop. Furthermore, exorbitant separation of lithium prompts the breakdown of the positive cathode structure because of thermaling and oxygen discharge, which speeds up the decay of the electrolyte and produces a lot of gas. Because of the expansion in inner power, the wellbeing valve opens, and the battery opens. After the dynamic substance in the battery cell comes into contact with air, it responds fiercely and discharges a huge sum
(3) Intensity misuse
Heat misuse seldom exists freely and frequently creates from mechanical and electrical maltreatment, and is eventually a piece of contact with heat runaway. Neighborhood energy is a run of the mill thermal maltreatment circumstance that happens in battery packs. As well as overheating brought about by mechanical and electrical maltreatment, it has been affirmed that overheating may likewise be brought about by free association contacts
2.Process of thermal out of control
The thermal out of control cycle of lithium-particle batteries can by and large be summed up as follows: ① SEI disintegration; ② Lithium installed negative terminal responds with electrolyte; ③ Film liquefying; ④ The positive cathode goes through a decay response; ⑤ The electrolyte goes through a deterioration response all alone; ⑥ Electrolyte vaporization and ignition.
1) During the principal phase of typical charging, the surface temperature of the battery is generally low (26-30 ° C). Lithium particles typically segregate from the positive terminal and supplement into the negative cathode, bringing about a sluggish expansion in battery voltage. At the point when the battery voltage is around 3.6V, the negative cathode of the battery will in general soak
2) During the second phase of slight cheating, the surface temperature of the battery fundamentally expanded (39-46 ° C). The positive cathode seriously loses lithium, and the lithium particle will in general immerse from being implanted in the negative terminal. Lithium particles will accelerate on the outer layer of the negative anode and will more often than not store in the edge region of the negative terminal nearer to the positive cathode. Past investigations have shown that lithium dendrites encouraged on the outer layer of the negative cathode will respond with the natural folio of the negative terminal.
Past examinations have shown that lithium dendrites encouraged on the outer layer of the negative cathode will respond with the natural folio of the negative terminal to produce hydrogen lithium metal precipitation and serious lithium expulsion from the positive cathode, bringing about a proceeded with expansion in battery voltage.
3) In the third stage, lithium dendrites go through a side response with the electrolyte to create heat, prompting an expansion in the inner temperature of the battery. At the point when the temperature surpasses 90 ℃, it will set off the decay of the SE film and produce gas
4) In the fourth stage, when the inside temperature of the lithium-particle battery stretches around 130 ℃, the separator liquefies, causing a huge area of short out in the battery and producing heat. The high temperature brought about by heat gathering structures a positive input on the inside response, creating gas, and the battery starts to go through wild self speeding up responses, further making the temperature of the battery rise.
In the scope of 200~300 ℃, the actual electrolyte will go through deterioration responses, creating gas and at last prompting fire and even blast mishaps. The damage brought about by thermal out of control of a solitary battery is for the most part restricted, however in the application situation of energy stockpiling power plants, the quantity of single batteries is enormous and organized firmly. At the point when a solitary battery encounters thermal out of control, the intensity created might be communicated to the encompassing batteries, making the thermal out of control spread and the mischief caused will be extended.
3.Detect trademark boundaries
1) The inside opposition of the battery diminishes with the increment of temperature inside the typical working temperature range. In any case, when the battery encounters thermal out of control and causes unusual temperature climb, there is a critical expansion in its inner obstruction. In any case, the unexpected change in battery inward opposition can likewise be impacted by different elements, for example, outside aggravations or unfortunate contact brought about by certain reasons, which can likewise prompt an abrupt expansion in battery inner obstruction. Consequently, depending entirely on changes in protection from decide if a battery has encountered thermal out of control isn’t precise, and it should be joined with other trademark boundaries to decide.
2) Temperature is a significant boundary of thermal out of control in lithium-particle batteries, as there is a commonly supporting connection among temperature and side responses when the battery encounters thermal out of control, framing a positive criticism. Numerous battery cautioning gadgets and battery the board frameworks are furnished with temperature detecting gadgets to screen battery temperature. When the temperature surpasses the preset edge, an alert sign will be given or relating moves will be made.
A three-level admonition methodology has been proposed for the 18650 lithium-particle battery and battery pack: when the battery temperature surpasses 50 ℃, the limit will rot, and the temperature will climb gradually in the scope of 50-80 ℃, with 70-80 ℃ being the slowest. Consequently, the three-level admonition temperatures are set to 50 ℃, 70 ℃, and 80 ℃ separately. Nonetheless, this technique for observing surface temperature has hysteresis, as the intensity produced inside carves out opportunity to communicate to the surface, and there is likewise heat scattering during the transmission interaction (heat trade between the battery and the climate).
3) When the battery is in the beginning phase of thermal out of control, these trademark gases will slowly increment in fixation without any preparation, showing a massive change in qualities. Along these lines, involving relating gas sensors for early advance notice of battery thermal out of control is additionally a significant way.
