Study on Fire Behaviors of Primary Lithium Batteries and Lithium-ion Batteries under Normal and Low Pressures

常壓和低壓下鋰原電池和鋰離子電池火災行為研究

Student thesis: Doctoral Thesis

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Award date28 Aug 2017

Abstract

With the widespread applications of lithium batteries in consumer electronics, many lithium batteries’ fire and explosion accidents have been reported. Applications of lithium batteries require precise appraisal about their fire and explosion hazards problems. The work of this thesis is summarized as following:

An experimental study of the combustion characteristics of primary lithium batteries is conducted. Burning tests of single and bundles of primary lithium batteries were conducted in a calorimeter to measure their heat release rates. In these tests the batteries were exposed to an irradiance of 20 kWm-2. Several parameters including time to ignition, mass loss, heat release rate and the centerline fire plume temperature distribution were measured to evaluate the ignition and combustion characteristics. The burning primary lithium batteries were observed to have flame temperatures in excess of 1200 oC and release hot and corrosive solid compounds. The experimental results show that the combustion efficiency, carbon dioxide yield and mass loss are proportional to the number of batteries in the bundle. The total heat release by battery bundles was deduced to be empirically proportional to the number of batteries with a power of 1.26. The results provide scientific basis for the development of fire protection measures during the usage, storage and distribution of primary lithium batteries.

A fire calorimeter is utilized to test the combustion performance of two commercial 18650 lithium ion batteries (LiCoO2 and LiFePO4) at different state of charge (SOC). Characteristics on thermal hazards of lithium ion batteries including surface temperature, time to ejection, mass loss and heat release rate (HRR) are measured and evaluated. In case of thermal runaway all the lithium ion batteries will rupture the can and catch fire even explode automatically. The solid electrolyte interface (SEI) layer decomposition and the polymer separator shrinking are direct causes of the lithium ion battery fire. The experimental results show that the HRR and total heat generally rise as the SOC increases, whereas the time to first ejection and the time gap between first and second ejection decrease. LiCoO2 18650 battery shows higher explosion risk than LiFePO4 18650, as the former has released much more oxygen. The experimental combustion heats calculated and modified in the oxygen consumption method reveal that the internally generated oxygen have significant effect on the estimate of the heat, where the largest modified rate is 29.9 % for 100 % SOC LiCoO2 18650 battery. The results can provide scientific basis for fire protection during the storage and distribution of lithium ion batteries. An experimental study of different arrangements: horizontal 41, horizontal 22 and vertical 22 lithium-ion batteries fire behaviors was conducted. The photographs of fire processes and the batteries before and after the fire tests were directly shown to describe the fire hazard. The mass loss rate, heat release rate and heat flux were used to analyze the combustion behavior more detailed. Based on the results, lithium-ion batteries are volatile and burning with potentially deadly explosions. The arrangements can affect the ignition time, heat release rate, released heat and the heat flux, while the way of mass loss and the total mass loss are similar. The results indicate that batteries with bigger heating area have more risky and fierce fires compared with others.

Fire hazard performs a serious threat to personal and property safety, while the decreasing pressure affects the physical and chemical reaction in the process of combustion, and changes the fuel combustion characteristics which are significantly different from those in the ordinary ambient pressure. The fire behavior of lithium-ion battery is affected by the environment conditions. The experimental results of lithium battery fires was provided, expecting to offer guidance to facilitate the safe handling of battery packs and cells under normal and high altitude conditions. Single and bundles of primary lithium batteries experiments were performed to study the fire behaviors of primary lithium batteries. The same configured calorimeter was built in a sea-level city Hefei (100.8 kPa/ 24m) and a high altitude city Lhasa (64.3 kPa/ 3650m), respectively, to investigate the effect of altitude on the fire behaviors. From the results, the mass loss exhibits as a linear function of cell numbers in both Hefei and Lhasa. The mass loss also increases as altitude decreases for the same number of cells. The study also shows that the heat release rate, effective heat of combustion and heat flux decrease at higher altitude. The combustion efficiency in Lhasa is lower than that in Hefei. The fire hazards of lithium-ion batteries at low pressure were characterized by measuring the ignition time, mass loss, heat release rate, and released heat. From the results, the ignition time of single battery decreased with the ascending of the state of charge, whiles the mass loss, and ejection energy increased with that at two pressures. The increment of pressure caused the battery to ignite faster, while the mass loss, heat release rate and released heat both for single battery and bundle batteries decreased at low pressure. The released heat in the bundle increases with the battery numbers in a power function. The coefficient of the proportionality is pressure dependent.

    Research areas

  • primary lithium battery, lithium-ion battery, fire behavior, state of charge, heat release rate, high altitude, low air pressure, arrangements