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NREL - National Renewable Energy Laboratory
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Thermal Management

Battery and ultracapacitor thermal management is important in optimizing the performance and reducing the life-cycle costs of advanced fuel cell, hybrid electric, and electric vehicles (FCVs, HEVs, and EVs). Temperature and temperature uniformity both significantly affect the performance and life of energy storage (ES) devices and vehicles. That's why NREL's energy storage team conducts research and development in the thermal management of batteries and ultracapacitors to optimize performance and extend life.

Our energy storage team works with developers, manufacturers, DOE, and the U.S. Advanced Battery Consortium (USABC) to improve advanced vehicles by developing, evaluating, and validating ES components. Our expertise in thermal characterization and analysis of batteries and ultracapacitors is important in developing and designing advanced thermal management systems for energy storage.

Thermal Characterization

NREL experts analyze fluid flow (liquid or air) through different types of battery packs to determine how this flow affects the pack's performance and life-cycle costs. Researchers measure and analyze the heat generation, efficiency, and specific heat of battery modules under specified charge/discharge cycles using the state-of-the-art calorimeter in NREL's energy storage laboratory.

Using thermal imaging (still and time-lapse video), researchers determine temperature distributions and identify potential trouble spots in ES modules and packs. Temperature distribution is dictated by module and cell chemistry type, aspect ratio, number of cells, geometry, thermal conductivity, location of terminals, and current density. The information from thermal imaging is used in model validation and in developing an optimal ES thermal design and management system.

Photos of a lead-acid battery and a lead-acid battery thermal image.

Photos of a lithium-ion battery and a lithium-ion battery thermal image.

Thermal imaging of a lead-acid and a lithium-ion battery shows their different temperature distributions.

Thermal Analysis

Finite Element Analysis

Photo of a prismatic module.

Simulation of a six-cell prismatic module.

We also use finite element analysis and other computer-aided design tools to improve the design of ultracapacitor stacks, battery modules, and thermal management systems. And, to address temperature issues associated with high-power batteries—such as cold-cranking—we research innovative methods of heating batteries at very cold temperatures.

Electrothermal Approach

Illustration of the thermoelectrical analysis showing current density through cells and cell-interconnects.

Current density through cells and cell-interconnects.

Recently, we developed the first-ever process for analyzing thermal performance of batteries and cells using an electrothermal approach. In this process, physical details of a cell or battery are captured in a finite element modeling software program that can analyze electrical and thermal behavior of components and materials. NREL used knowledge of geometry and material properties and resistances to calculate heat generated and temperature distributions.

To aid in the research and development of energy storage components, NREL researchers also work on vehicle simulation and modeling interactions for trade-off and target analysis.

Thermoelectrical illustration of the temperature distribution in module based on an applied voltage drop.

Temperature distribution in module based on an applied voltage drop.