Late last year, Sandia received funding for its “Mechanistic Modeling Framework for Predicting Extreme Battery Response: Coupled Hierarchical Models for Thermal, Mechanical, Electrical and (Electro)chemical Processes” project under the Computer Aided Engineering (CAE) for Electric Drive Batteries area in the DOE “EV Everywhere” program.
Vehicle electrification is widely seen as a method to reduce U.S. dependence on foreign oil as well as carbon emissions related to transportation. Lithium-ion batteries are increasingly important in electrification because of their higher energy density compared to other battery chemistries. However, Li-ion batteries have safety issues: driven to high enough temperatures, Li-ion batteries can undergo “thermal abuse,” generating large amounts of heat and catching fire. The Sandia Battery Abuse Testing Laboratory (BATLab) has played an important role in assessing the risks and understanding the processes that lead to thermal abuse in a variety of battery chemistries, among them Li-ion.
Battery chemistry is anticipated to change substantially over the next 5–10 years to increase capacity, lower cost, and reduce weight—to become more practical for transportation applications. To gain broad acceptance with consumers, safety margins for all Li-ion chemistries must be assessed, for those that exist today as well as for those that have only been conceived. Moreover, a mechanistic understanding of why a battery failed is often much harder to obtain than is the mere observation that it failed. This team will develop a predictive simulation capability to understand battery abuse.
The first goal is to advance the state of the art in modeling chemical processes, using open software standards. Because the battery community lacks such an infrastructure, significant fundamental quantitative comparisons of chemistry have not occurred. The team hopes to emulate what has occurred within the combustion community with programs such as Chemkin, which brought together experimentalists and computational scientists to create an infrastructure which was then used to elucidate mechanistic details.
The project’s second goal is to demonstrate this infrastructure with models of various levels of fidelity that will address the thermal runaway process observed to occur within Li-ion batteries. Ideally, this would involve understanding solid-electrolyte interface layer formation and its evolution as a function of temperature. This process’s mechanistic details, as well as inputs for constitutive models that would make a model for this, are not available for engineering-level capabilities. This research team will start with models proposed in the literature and then couple suggested mechanisms with correct thermodynamic and transport parameters.
An indirect project goal is to facilitate developing cell materials and components that are more resistant to abusive environments. The team will not develop the materials, but integrate materials-development knowledge into a CAE framework to predict abuse response. Incorporating materials-development knowledge into the CAEBAT computational framework will also facilitate comparisons between proposed physics-based models and experimental observations.
By the end of the project, the team will have created infrastructure for including detailed mechanistic models for thermochemical processes that are important to battery performance and safety and advance the mechanistic understanding of thermal runaway processes in Li-ion batteries. This capability can be linked to existing cell, module, and pack-level capabilities being developed under the CAEBAT-I model.
The 10-member Sandia-led research team working on this two-year project includes two members from ORNL and an ME professor from the Colorado School of Mines.