Rechargeable lithium battery safety issues -Lithium - Ion Battery Equipment

Rechargeable lithium battery safety issues -Lithium - Ion Battery Equipment

In recent years, the exposure of many electric vehicle fire incidents has made people pay more and more attention to the safety of electric vehicles, especially lithium-ion batteries. Of course, this does not mean that the safety of electric vehicles is poor. Ordinary gasoline vehicles are also prone to fire incidents. Especially in summer, as long as you pay attention, you will find that spontaneous combustion incidents of gasoline vehicles are not rare. In terms of safety design, similar accidents are prevented. After all, human safety is above everything else, just like the saying "people are the measure of all things".

At present, our evaluation of the safety of lithium-ion batteries is still in a relatively preliminary stage. The judgment standards are relatively vague, and we can only judge a few obvious points of the degree of danger of the battery. But in fact, the lithium-ion battery has changed from a completely safe state to a complete The dangerous state is a continuously changing curve, which means that the current evaluation system cannot judge the battery safety state between the two states, which forms a blind area of ​​the battery safety state. Therefore, the safety evaluation function for lithium-ion batteries is It is particularly important to digitize and digitize, especially the application of power lithium batteries in electric vehicles is of great significance.(Lithium - Ion Battery Equipment)

At present, the commonly used standard for the safety of lithium-ion batteries is the hazard class classification developed by the European Automobile Research and Development Council. The danger level classification table divides the battery risk level into eight levels from 0 to 7. The higher the level, the more dangerous the battery is.

For example, a level 6 indicates that the battery caught fire but did not explode, while a maximum level of 7 indicates that the battery not only caught fire but dangerously exploded. In order to ensure the safety of operators, the danger level should be controlled within 4, which means that the battery will not rupture, catch fire and explode.

First of all, we have to establish a concept that safety and abuse are opposites. Adding abuse intensity will inevitably reduce the safety of the battery system. At present, most of the safety descriptions for lithium-ion batteries are based on the summary of relevant experience, and there is a lack of accurate descriptions of numerical properties.

In order to digitize the battery risk, Ashtiani invented the Risk Model and Risk Analysis (HMRMA) model, which mainly consists of two key parameters, the risk severity Hs and the risk probability HL.

The Hs value of 0-7 represents the severity of the risk, and the HL value of 1-10 represents the likelihood of the risk occurring, representing the number of risks that occur per 1 million samples. In order to reduce the value of risk HR, we can choose to reduce Hs or HL, or we can also introduce a new variable risk control Hc, so the above formula can be transformed into, where the value of Hc is in the range of 0-1, and Hc is not controlled at all is 1, and Hc is 0 for full control.

The risk of the battery is constantly changing with the use state of the battery. In order to reflect this change, Lu et al. discussed the safety of the battery based on the battery voltage and operating temperature, and introduced the functional state function SOF, which is an important function. There are battery state of charge SOC and battery safety state SOH, as well as the output power of the battery.

Where p(t) is the instantaneous power output by the battery, pd is the instantaneous demand power, and pmax is the maximum output power when the battery is in a new state. in


Among them, SOH(t) can be determined according to the value of the voltage, as shown in the following formula, where V(t) is the instantaneous output voltage, Vd is the minimum demand voltage of the load, and Vlim is the minimum output voltage of the load when the battery is in a new state.

The good operation of the system on the lead-acid battery mainly depends on the good linear relationship between the SOC and the voltage of the lead-acid battery, but the relationship between the SOC and the voltage of the lithium-ion battery is not completely linear, so appropriate corrections should be made.

The content of the first part of this article mainly introduces some current scholars' research results on the safety model of lithium-ion batteries.



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