Block ip Trap

Preventing Thermal Runaway Before It Begins

15 Jan 2021

By Steve Cummings

Utility, industrial, commercial, and government facilities are increasingly turning to Battery Energy Storage Systems (BESSs) - in a variety of sizes and power outputs - for reliable back-up power. This market is expected to exceed more than US $9 billion by 2024, at a compound annual growth rate of 34 percent.

Given the expected growth in this sector, coupled with the fact that most BESSs are designed by interconnecting a series of Lithium-ion (Li-ion) batteries, the industry is continuing to focus attention on measures designed to practically eliminate any potential for dangerous thermal runaway conditions.  

Thermal runaway occurs when excess heat (caused by defects, mechanical failures from damage, or improper operation of the system) creates a reaction that further increases the temperature. If left unchecked by built-in system protections or a Battery Management System (BMS), this process continues to drive up temperature and pressure until the battery cell ruptures, which can spark fires in affected and adjacent cells.  

Fortunately, early detection systems have been developed that can now detect a unique pre-cursor event to thermal runaway: off-gassing in the battery cell that occurs up to 30 minutes prior to a cascading failure. This distinctive and recognizable early warning sign enables the problem to be mitigated - or the system shut down - before thermal runaway can even begin.  

Although virtually all quality BMS equipment monitors temperature and other variables to prevent thermal runaway by triggering protections, the early detection of off-gassing provides a critical additional layer of protection for the entire system, the facility, and even personnel.

Early detection

The early detection of thermal runaway relies on four sequential stages of Li-ion battery failure:

  1. A Li-ion battery cell first begins to fail when it is subjected to an abuse factor like heat, overvoltage, etc.,
  2. The second stage is off-gassing  
  3. The third stage is smoke; 
  4. And the fourth stage is fire. But smoke and fire often occur simultaneously. In other words, by the time smoke is detected, thermal runaway has already begun.

Off-gassing usually occurs due to a breakdown of a Li-ion battery cell electrolyte due to pressure buildup. Later, as temperature increases, smoke is emitted and fire breaks out.

To enable off-gassing detection at the earliest stage of a battery event after the initial abuse, an early detection system offers a battery off-gas monitor and sensor network designed specifically for lithium ion batteries.

Because the system can detect off-gassing at the ppm-level concentration range, it can recognize individual cell failures without contacting the cells; as soon as a single battery cell begins to fail, the system can prevent thermal runaway and its spread to adjacent cells.

The benefits of both Li-ion BESSs and Li-ion specific off-gas detection systems have prompted a growing number of facilities to install them together.

Microgrids are small electrical systems that can operate both independently and together with the larger local electrical grid. They are being increasingly deployed at critical, nonmilitary facilities such as hospitals, fire stations, and airports to provide uninterrupted power during local electric utility outages.

Last year, the U.S. Navy contracted out for the design and building of two transportable microgrid BESSs. The project was funded in part through the California Energy Commission’s Electric Program Investment Charge (EPIC) program, and the Department of Defense’s Environmental Security Technology Certification.

In the Navy’s case, the microgrid will use solar energy. The BESS, along with Navy site generation, will provide emergency backup for blackout recovery, disaster recovery, and weather/fire storm response.

Each BESS is lithium-ion based and can deliver 250kW of power on demand. Both will go through testing at the Port Hueneme Naval Base in Ventura County, CA. Afterwards, they will then go through testing and operational use at a Naval Surface Warfare Center-Port Hueneme division data center in Southern California. 

Taking advantage of the latest in safety technology, a Navy-approved off-gas detection system will be built into the unit’s system supervisory controller as both a redundant safety solution and on-board fire protection/suppression system.

A growing number of facilities are recognizing that, although a BMS can provide data and shut the BESS down, there are times when the BMS can miss critical indicators or malfunction. As a result, there is the need for a separate, redundant system that can indicate the potential for thermal runaway before it occurs so the BESS can be shut down to prevent it.  

 

Steve Cummings is director of the sensors business unit at Nexceris, a developer of gas sensors and monitors. The company worked with the U.S. Navy a decade ago to develop an off-gassing detection technology for Li-ion BESSs that is compatible with all Li-ion chemistries.  

Nexceris | nexceris.com


Author: Steve Cummings
Volume: 2021 January/February