Study On Thermal Runaway And Safety Warning Via Gas Detection Of LiFePO₄ Energy Storage Battery Under Overcharge Condition

Li-ion battery?LIB?has become one of the most competitive electrochemical energy storage technologies due to its advantages of long serving time and environmental friendly.And lithium iron phosphate?Li Fe PO₄?battery has been widely used in large-scale energy storage field because of its high energy density and low cost.However,the inherent thermal producing property of lithium-ion batteries,and the operating characteristics of the battery energy storage system?constant temperature,static energy storage?,make overcharge become the biggest threat to the thermal runaway disaster of grid scale application.At present,the fire protection system of LIB energy storage power station mainly relies on temperature or smoke detection.Actually,this widely used system sends an alarm signal only after the fire accident occurs.In this paper,overcharge experiments on cell,pack and cluster are carried out to study the thermal runaway process and electrochemical reaction mechanism in Li Fe PO₄ battery,and a new method of lithium dendrites growth perception for super-early safety warning of Li Fe PO₄ battery energy storage system based on hydrogen detection is proposed.Firstly,lithium dendrite was experimentally found growing on graphite anode with hydrogen bubbles generation in the early overcharge stage via in situ observation and gas chromatograph?GC?analysis on an assembled LIB.Theoretical calculation indicates that even micron-scale lithium dendrites metal(about 2.86×10^-4mg,equal to a Li-metal particle which the radius is?50?m)can generate enough hydrogen gas to be detected by GC,which provides a theoretical basis for super-early safety warning via hydrogen detection.Besides,an overcharge experiment on Li Fe PO₄ energy storage single cell was carried out to verify the effectiveness of hydrogen online detection.An overcharge experiment on Li Fe PO₄ battery pack was conducted in a real energy storage cabin environment,where six kinds of gases?hydrogen,carbon monoxide,carbon dioxide,hydrogen chloride,hydrogen fluoride and sulphur dioxide?were online detected.Results demonstrate that compared with the other gases,hydrogen is the first to be detected to achieve early warning of Li Fe PO₄ battery thermal runaway,even 13 minutes before catching fire.Surface temperature of the battery pack increased only 20 ^oC when hydrogen was detected.At last,to prove the reliability and practicability of hydrogen detection on early safety warning of Li Fe PO₄ battery system in field application,an overcharge experiment involving nine fully charged Li Fe PO₄ battery packs?25.6 V/2752 Ah and consists of 32 single cells per pack?in the real energy storage cabin was carried out,which is closer to the real operating conditions compared with previous studies.Results demonstrate that by cutting off the charge process as soon as hydrogen is detected,heat accumulation inside battery can be immediately suppressed without any smoke nor fire.Hydrogen detection ensures fast and accurate forecast of the safety state of Li Fe PO₄battery,which will greatly improve the safety level of grid scale energy storage.