Precautions for the operation of marine lithium iron phosphate batteries

　　As for the discharge test items, the requirements for individual batteries vary depending on their usage environment. The intended use of single cell batteries that comply with GB/T 36276 is for energy storage. This type of battery system is usually online, connected to the power grid, and can timely replenish the discharged electricity from the grid. It is mainly used for peak shaving and valley filling of the power grid, as well as as serving as a backup power source for important places and equipment. As a power source for peak shaving and valley filling in the power grid, its output requirements are fully determined at the beginning of design, and the output power requirements are determined during use; As a backup power source for important equipment and places, the electrical load and duration that the battery system needs to bear can also be fully determined during design. Meanwhile, due to the above two situations, the battery system is fixedly installed indoors with controllable environmental conditions, and the impact of environmental conditions on the battery cells can be ignored. The consistency of the battery cells themselves will not be significantly affected during use. As a battery cell used for energy storage, it requires a low discharge rate during use and is not prone to over discharge. Therefore, in GB/T 36276, the requirements for the over discharge test of batteries are relatively low in terms of discharge current and discharge depth.

　　When used as a power source for automobiles, the requirements for battery performance characteristics under its application conditions mainly include high specific energy, high output power, and long cycle life. In this case, the requirements for the battery include both high energy density and high discharge rate. In the actual use of electric vehicles, various factors such as the driver's usage habits and the distribution of charging stations can have an impact on the battery system. Considering the significant changes in environmental factors such as temperature, humidity, vibration, and impact during use, the consistency of battery cells may undergo significant changes compared to when they were manufactured. In terms of over discharge, electric vehicle batteries are more prone to experiencing a certain depth of over discharge under high rate discharge conditions. So GB/T 31485 has higher requirements for discharge current than GB/T 36276, while IEC 62660-2 and IEC 62619 have higher requirements for discharge current and depth than GB/T 36276.

　　When batteries are used as a power source for ship propulsion, the sensitivity of ships to battery weight is much lower than that of cars, and their endurance is a key consideration in battery capacity design. This leads to the fact that ship lithium batteries do not require high power output, so the requirements for discharge rate are not high. But the usage environment on board is slightly better than that of electric vehicles, but it is also worse than the usage environment of electric energy storage batteries, so the consistency guarantee of battery cells during use is not as good as that of electric energy storage batteries. At the same time, due to the influence of wind and waves on speed and propulsion load, the larger the wind and waves, the greater the propulsion resistance of the ship. Due to the fact that pure battery powered ships can only use shore power for charging after arriving at the port, this may result in a deeper discharge depth of the battery cells under harsh sea conditions. Overall, when lithium iron phosphate batteries are used as power sources for ship propulsion, the discharge rate of the battery cells may not be high during the process of over discharge, but the discharge depth may be relatively large. The requirements for its over discharge test should be adapted to the over discharge conditions that may occur during its use.

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