Cause Analysis of Thermal Runaway of LiFePo4 Powerwall battery



Time of issue:2022-04-24 18:15


The safety problem of LiFePo4 Powerwall battery can be summed up as "thermal runaway", that is, after reaching a certain temperature, it is uncontrollable, the temperature rises in a straight line, and then it will burn and explode. Overheating, overcharge, internal short circuit, and collision are several key factors that cause thermal runaway of power batteries.

48V 200Ah LifePO4 Powerwall Battery
(1) Overheating triggers thermal runaway
The reason for the overheating of the LiFePo4 Powerwall battery comes from the unreasonable selection and thermal design of the battery, or the external short circuit causes the temperature of the battery to rise, the connector of the cable becomes loose, etc. It should be solved from the aspects of battery design and battery management.
From the perspective of battery material design, materials can be developed to prevent thermal runaway and block the reaction of thermal runaway; from the perspective of battery management, different temperature ranges can be predicted to define different safety levels, so as to perform hierarchical alarms.
(2) Overcharge triggers thermal runaway
The thermal runaway triggered by overcharging is specifically caused by the lack of circuit safety function of the battery management system for overcharging, which causes the BMS of the LiFePo4 Powerwall battery to be out of control but still charging. For the cause of this type of overcharging, the first solution is to find the fault of the charger, which can be solved by the complete redundancy of the charger; the second is to see whether the battery management is reasonable, for example, the voltage of each battery is not monitored. It is worth noting that as the battery ages, the consistency between the individual batteries will become worse and worse, and overcharging is more likely to occur at this time. This requires equalization of the entire battery pack to maintain battery pack consistency.We have done more than 20% over design in the current, including the overcurrent capacity of BMS of 48V 200Ah powerwall. The over-current capability of the input and output cables, etc., while the circuit part (BMS, etc.) and the battery part are completely isolated and designed to ensure that the heat generated by each does not interfere with each other.
(3) Internal short circuit triggers thermal runaway
Impurities in battery manufacturing, metal particles, shrinkage due to charge and discharge expansion, and lithium precipitation may all cause internal short circuits. This internal short occurs slowly, for a very long time, and it is unknown when it will thermally runaway. If the test is carried out, the verification cannot be repeated. At present, experts around the world have not found a process that can repeat the internal short circuit caused by impurities, and they are all under study. To solve the problem of internal short circuit, we must first find a LiFePo4 Powerwall battery manufacturer with good product quality, select the battery and battery cell capacity; secondly, make a safe prediction of internal short circuit, and before thermal runaway occurs, we must find the internal short circuit. Our 48V 200Ah powerwall is a perfect option for heat dissipation and safety.
(4) Mechanically triggered thermal runaway
A crash is typically one way of mechanically triggering a thermal runaway. The solution to thermal runaway triggered by collision is to do a good job in the safety protection design of the 48V 200Ah Powerwall. This requires researchers to first understand the process of thermal runaway.
In short, in terms of thermal runaway expansion and suppression of 48V 200Ah Powerwall, R&D personnel should start from two aspects: safety protection design and battery management.


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