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　　Several suggestions for over discharge test of lithium iron phosphate batteries

　　Due to overcharging of lithium-ion batteries, lithium dendrites are easily generated at the positive electrode of the battery, piercing the separator and causing internal short circuits in the positive and negative electrodes of the battery. This further leads to thermal runaway of the battery cells, causing fires or explosions. Therefore, the safety and protection of overcharging of lithium-ion batteries are highly valued. The testing requirements for overcharge safety testing items are consistent across all standards. However, due to the decrease in the direction of battery energy change during over discharge, the possibility of fire or explosion is unlikely. In various standards, especially under the GB and IEC standard systems, there are significant differences in the test requirements for over discharge tests.

　　(1) Due to the good ability of lithium iron phosphate batteries to withstand over discharge, and the possibility of deep discharge depth when used as a power source for ship propulsion, strict requirements should be considered for the discharge depth of the over discharge test. For example, according to the requirements of IEC 62660-2 and IEC 62619, the SOC of the discharged battery should be -150%.

　　(2) Due to the low discharge rate of battery cells in actual marine operating conditions, the discharge current for over discharge tests can be considered to be the smaller of 1C or the maximum discharge current specified by the factory.

　　(3) If the selected discharge current in the experiment is less than 1C, the discharge time needs to be extended to ensure the discharge depth. The discharge time corresponding to the test discharge current should be calculated according to the requirements of IEC 62619. The actual discharge time is equal to the ratio of 1C to the actual discharge current multiplied by 90 minutes.

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