TEST: The Winston LiFePO4 cell 160AH short-circuit at 1000Amp for 13 minutes
This test proves the safety of the LiFePO4 technology: no fire, no uncontrolled explosion into in fire, no sparking, no burning, no fire smoke (black).
The short circuit on an over-charged cell. This video shows the extremely high speed discharge (nearing the short circuit) of the Winston 160AH cell. To intensify the abuse conditions, the Winston cell was overcharged and become swollen before the short circuit discharge.
The over charged cell has already damaged internal structure (higher internal resistance). Thus the cell will release more heat than a healthy, regular cell with no overcharge.
After 3 minutes of short circuit the temperature of the terminal connectors increases. Due to the high temperature of the terminals, there is a small smoke coming from the plastics case around the terminals.
After 10 minutes the internal temperature of the cell has increased too high. The high temperature causes the gassing of the chemical substances inside the cell and as a result the cell has become severely swollen. More and more gasses start to be released from the safety valve on the top of the cell.
After 12:30 minutes the internal gassing is so high that the gasses start to be released from the safety valve. At this moment the temperature of the cells is around 180 *C and the internal structure if the cell is collapsing. The cell is no more releasing any energy, but most of the energy is burnt inside as a heat.
At 12:40 the release of the gasses from the cell is so high than the cell makes a „trumpet like sound“. At this moment the internal pressure increases to the maximum.
At 12:56 plastic case will no longer withstand the internal pressure and the plastic case breaks out making an „explosion like sound“, with a lot of smoke. At this moment all gasses inside the cell are released at one moment. The cell continues to generate the smoke.
During the short circuit test there was not any smoke with heat and fire (black color smoke). The cell did not set itself on fire, the cell did not burn, the cell did not explode because of fire.
The „explosion“, or rather burst opening, of the cell was because the case (outside shell) of the cell did not withstand the internal pressure. If the cell was in a battery pack, or tightly located in a proper battery case, the cell would keep the shape, as the neighboring cell would not allow the cell to become swollen. In a battery case, the cell would not most likely „burst open“: it would continue to resale the gasses thru the safety vent much longer.
The regular capacity of the cell is 160 Ah at 3.2V. The charging capacity is 160AH at 4V. This makes 640Wh of energy. With some overcharge, it can be estimated that the cell was holding of 700Wh of energy. This energy was released at some 13 minutes of short-circuit discharge. This corresponds of 3250W of immediate power. At 3.2V the short circuit current was about 1000Amp.
The photo shows the results of an unattended charging from a regulated charger that had a failure. The cells were kept charging up to 4.8V per cell.
The result is obvious: due to the overcharge the cells start swelling and the housing expands.
On the other hand, this accident proved that LiFePO4 cells are a quite safe battery technology. In this hazardous situation, there was no significant temperature increase, no gas leak, no explosion, no fire. (With lithium polymer cells - so called „lipoly“ cells - such kind of over charge would result in an uncontrolled fire.)
The lesson taken from this accident:
Never left batteries charged unattended.
Always install multiple protections to have a backup protection in case of failure of the primary device.
Operate batteries in places where there is a proper fire safety (not on a wooden table in a closed room).
Even professionals can make a mistake or meet with a failure that can lead to an accident.
The lithium iron cells do swell by overcharging. One of the solvents used in the electrolyte has a boiling point of 77C. If you overcharge enough to reach this temperature (internally) it will gas and cause the swelling. It will also cause the cell to vent in most cases.
The example of a large-scale cell damage caused by overcharge
The damage was caused by using a high-speed charger (30A) designed for charging 16 cells with a pack of just 15 cells without proper balancing and management. The voltage of some of the cells reached high above the max voltage level. The result was the swelling of the cells and partial damage of the cells.
First: Analyze the reason for the swelling. Is the battery used properly? Is the BMS working correctly? Note: Do not use the cell any longer, if the cell has become swollen.
Second: Remove the cell, unscrew the safety valve to allow the internal pressure to be released. (Be careful not to spil the electrolyte from the cell).
Third: Put the cell under the pressure to renew its original shape. You may need to increase the pressure gradually as the cell returns to its correct shape. Please allow for many hours or even days to pass to renew the shape.
Fourth: Charge the battery correctly and check its parameters: What is the voltage? What is the capacity? Perform several cycles to get consistent results and to see if the cell can be used again.
Finally: Avoid the same situation to happen again. Remember there is no way to repair a cell that was damaged by improper use.
In order to prevent the swelling of the prismatic cells, it is recommended to mount the cells with “jigs and straps”. The swelling of the cells usually occurs when: 1) the cells are overcharged, 2) there is a repeated high speed charging and discharging, 3) there is some fault of the cells.
Lithium-iron-phosphate batteries from Thunder-Sky …. as they heat up, they can swell and crack the casing if they’re not squeezed together.
Solid casing for the LFP battery packs needed: Lithium-iron-phosphate batteries from Thunder-Sky. They aren’t as sensitive to temperature, but they do need to be kept under pressure. This bracket is part of a vice I’m building for the batteries. As they heat up, they can swell and crack the casing if they’re not squeezed together. (source)
It is necessary to observe the recommendations of the manufacturer concerning the initial charging of the cells. (See the instruction here). If the cells are initially charged too fast or overcharged, the internal structure of the cells may be damaged and the cell may start swelling. That is why it is important to charge the cells individually during the initial charge and to monitor the cells to avoid the permanent change of the shape of the cells.
GWL/Power - Product Information and Technical Support Blog
The top innovative products with high power battery solutions and solar energy strorage. High capacity Lithium Iron LiFePO4 cells and packs for industry and mobility: No toxic acids, no evaporation of gases, charge up to 10000 times, great power performance. Super speed charging. No lead-related ecological issues.
Solar panels, micro-inverters, battery chargers and all kinds of related products.
The most requested topics:
Wish to build your EV right now? The EVTraxer, an open project electric vehicle platform is a way for you. Available now! Homologated for public roads in EU. Just finish your kit and Go! http://www.evtraxer.eu EV-POWER.EU (GWL/Power group)
i4wifi a.s., Prumyslova 11, Praha 10
CZ-10219 Czech Republic, European Union evtech(at)i4wifi.cz
EU VAT ID: CZ27651851