Can Lab-on-Fiber Combat Thermal Runaway in Li-Ion Batteries?

As batteries become more predominant in daily life, concerns over their safety are becoming increasingly important. One of the most pressing safety issues is thermal runaway, a well-known but largely unsolved challenge.

 

Fire in a battery storage system at a solar farm near Chaumont, N.Y. Image used courtesy of CTIF

 

To gain better insight into the nature of thermal runaway, researchers from the University of Science and Technology of China (USTC) have proposed a new battery monitoring method. 

 

What Is Thermal Runaway?

Thermal runaway is hazardous in lithium-ion batteries when some internal or external trigger sets off an uncontrolled exothermic reaction. 

 

Thermal runaway poses a significant safety concern in lithium-ion batteries. Image used courtesy of Mitsubishi Electric 

 

In simpler terms, it's a snowball effect where an initial increase in temperature leads to conditions that further boost the temperature, creating a feedback loop that spirals out of control. This temperature rise can accelerate various electrochemical reactions inside the battery, causing rapid temperature and internal pressure increases. This culmination of events can lead to catastrophic outcomes, including explosions, fires, or even the release of toxic gases.

The complexity of thermal runaway arises from the intricate electrochemical processes within the battery. As lithium-ion cells function through the movement of lithium ions between the anode and cathode, any disturbance in this process can lead to thermal instability. Factors like manufacturing defects, physical damage, overcharging, or overheating can act as triggers. Once initiated, thermal runaway is almost impossible to halt because of the self-sustaining nature of the exothermic reactions involved.

 

Research Tackles Thermal Runaway

In many ways, thermal runaway is exacerbated by the limitations of current monitoring technologies. Traditional methods of battery monitoring often rely on external sensors that can't provide real-time, internal data. To address these issues, researchers from USTC proposed a new means of monitoring thermal runaway in lithium-ion cells.

To this end, the team developed an optical fiber sensor that can be implanted directly into the battery based on lab-on-fiber technology. In lab-on-fiber technology, an external light source injects light into an optical fiber with a specially engineered tip. This tip interacts with the condition or material being monitored, altering the light's properties like intensity, wavelength, or polarization. The modified light returns through the fiber to a detector, which forwards the data to an analysis unit. By examining these changes, the system infers the state of the monitored condition. 

 

The research team developed specialized fiber optical sensors to monitor thermal runaway inside lithium-ion cells. Image used courtesy of Mei et al.

 

By integrating specialized sensors directly into commercial lithium-ion cells, the system can simultaneously track variables such as temperature, pressure, and gas composition inside the battery. The sensors then continuously feed data to a monitoring system, capturing dynamic changes in the battery's state. This enables the research team to observe the complex sequence of events that lead to thermal runaway, including exothermic reactions and the evolution of gases.

Because of this, the researchers can monitor multiple parameters inside a lithium-ion battery during thermal runaway in real-time. 

 

A Milestone for Battery Monitoring

While the USTC team's research hasn't conclusively unraveled the complete nature of thermal runaway, their research offers a newfound ability to gain insights into the nature of the phenomenon. With that, the research team hopes to provide a path forward for ultimately solving the thermal runaway issue in lithium-ion batteries.