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Application of Fluid Immersion for Increased Safety and Efficiency of Lithium-Ion Battery and Electronic Devices

IP.com Disclosure Number: IPCOM000236511D
Publication Date: 2014-Apr-30
Document File: 7 page(s) / 730K

Publishing Venue

The IP.com Prior Art Database

Abstract

Lithium-ion batteries are in widespread use worldwide in a vast array of electronic and electric devices ranging from hybrid and electric vehicles to power tools, portable computers and mobile devices. While generally safe and reliable energy storage devices, lithium-ion batteries are subject to a catastrophic failure mode known as thermal runaway1 under certain conditions. The focus of the work described herein is on mitigating the danger caused by thermal runaway resulting from mechanical damage and external heat. Lithium-ion batteries present a significant fire hazard. The wide-spread adoption and use of lithium-ion batteries, coupled with the potentially catastrophic failure mode of thermal runaway, has created a fire safety issue that requires a solution. Mechanical damage and internal shorts cannot always be avoided and the resulting energy release must be contained or lessened. Testing was performed on 6-cell lithium-ion battery packs assembled with fully charged 18650 type cells. A nail puncture was used to create an internal short in a single lithium-ion cell in a battery pack. A baseline, unprotected test was performed in a standard air atmosphere. The internal short caused nearly instant thermal runaway within the cell and a subsequent explosion that vented high temperature materials. The high energy release triggered by the puncture dramatically increased the temperature of the pierced cell. This high temperature heat source along with the freely burning electrolyte solution caused a cell-to-cell cascading thermal runaway event that was significantly more energetic than the initial event. This work reports on a new approach to mitigate this risk. Experiments showed that immersion of the battery packs in a dielectric fluid greatly reduced the maximum surface temperature of the initial cell with the internal short, no external combustion was observed, and the cell-to-cell cascading thermal runaway event was completely eliminated. This paper will further describe the experimental approach, results, and implications of this work.

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Application of Fluid Immersion for Increased Safety and Efficiency of Lithium-Ion Battery and Electronic Devices

INTRODUCTION

Lithium-ion batteries are in widespread use worldwide in a vast array of electronic and electric devices ranging from hybrid and electric vehicles to power tools, portable computers and mobile devices. The worldwide market of $28 billion in 2013 is growing rapidly and could reach $41 billion by 20181. While generally safe and reliable energy storage devices, lithium-ion batteries are subject to catastrophic failure known as thermal runaway2 under certain conditions. Thermal runaway is a series of internal exothermic reactions that are triggered by heat. The creation of excessive heat can be from electrical over-charge, thermal over-heat, or from an internal electrical short. Internal shorts are typically caused by manufacturing defects or impurities, dendritic lithium formation3 and mechanical damage. While there is typically protective circuitry in the charging devices and in the battery packs that will disable the battery in the event of overcharging or overheating, it cannot protect the battery from internal shorts caused by internal defects or mechanical damage.

The focus of the work described herein is on mitigating the danger caused by thermal runaway resulting from mechanical damage and external heat. However, it is important to note that the energy released in a thermal runaway event is determined primarily from the electro-chemical composition and charge level of the battery2 and for a given lithium battery, is essentially the same regardless of the trigger. While this study focused on mechanically induced shorts to initiate the event, the immersion technology would be equally effective with internal shorts resulting from other thermal runaway triggers such as internal defects or dendritic lithium formation.

Testing was performed on various battery pack configurations containing six 18650 type lithium-ion cells. A nail puncture of a single cell caused an instantaneous thermal runaway event in the initiating cell. In an unprotected standard air atmosphere this high energy event has been found to increase the temperature of adjacent cells and to cause them to subsequently enter thermal runaway creating a cell-to-cell cascading thermal runaway event significantly more energetic than the initial event. Immersing the battery packs in a dielectric fluid and performing the same nail puncture test, it has been observed that the maximum temperature caused by the thermal runaway event of the initiating cell was reduced by half and the more significant cell-to-cell cascading thermal runaway event was completely avoided.

This has significant potential to provide fire and thermal runaway protection for devices that utilize lithium-ion battery packs, bulk transportation and storage of new and recycled lithium-ion batteries. Transportation vehicles that derive primary or auxiliary electrical energy from lithium-...