Thermal Diagnostics and Management of Batteries

Thermal Diagnostics and Management of Batteries

Electrochemical batteries have become a ubiquitous form of small-scale energy storage for sensors and personal electronics. But in order to fully electrify transportation, which could reduce the U.S.’s total oil consumption by 70%, batteries need to be rechargeable in under 10 minutes. Furthermore, they need to be safe from catastrophic thermal failure, and able to operate in a wide range of temperatures. We are developing techniques to enable previously impossible measurements of the thermal and electrochemical properties of lithium-ion and solid state batteries, to make them safer, better performing, and capable of extreme fast charging.

Projects

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Operando battery thermal transport diagnostics for extreme fast charging

Effective heat dissipation in batteries is important for a variety of reasons, including performance, reliability, safety, and fast charging. Currently, the thermal management of battery cells is provided at the system level using external cooling equipment, resulting in complex system level designs and reduced effective energy densities. A sensor measuring properties of a battery using a thermal wave. Our research is focused on providing battery cell materials-level thermal solutions by enhancing thermal transport material properties. Our approach is to: 1) Develop an embedded 3ω sensor for operando thermal characterization of batteries; 2) Identify thermal bottlenecks in Li-ion batteries during operation; 3) Explore various techniques to minimize the identified thermal bottlenecks without compromising electrical performance; 4) Understand thermal and electrochemical transport in buried interfaces in solid state cells from thermal signatures; and 5) Detect electrochemical phenomena using thermal signals. This project is funded by the Department of Energy Vehicle Technology Office.

Heat generation and battery thermodynamics

Our group is working on studying the mechanisms of heat generation and battery thermodynamics during extreme fast charge (XFC). Specifically, we are working to improve mathematical modeling of heat generation physics in fast charge by incorporating enthalpy of mixing due to lithium diffusion in electrode particles. This method is based on an overall enthalpy change analysis and is an extension to the modeling of heat generation with Newman's P2D formulation. This project is funded by the Department of Energy Vehicle Technology Office.

Plot showing what percentage of a battery’s total heat generation comes from entropic heat of mixing as a function of increasing battery charge rate. The amount increases from 10% to 22% at charge rates of 1C to 6C

Non-Invasive Detection and Mapping of Internal Electrochemical and Entropic Processes

We are working on developing a non-invasive frequency lock-in detection technique to measure and distinguish the different electrochemical processes in a cell. Each type of electrochemical process is separated based on its unique thermal signatures at different harmonics of the frequency of the electrical current passing through the battery. The spatial resolution of the information is acquired from the frequency-dependent thermal penetration depth and temperature rise of each subsurface heat source.

Left: A serpentine-shaped thin metal sensor. Right: AC electrical charging current produces battery heat generation at different harmonic frequencies, such as the second and fourth harmonic of the charging current.

This technique provides unique capabilities to directly distinguish the relative magnitudes of various electrochemical processes within the cell and spatially map their corresponding internal heat generation, even though our sensors live on the outside of the cell. This project is funded by the Department of Energy Vehicle Technology Office.