Your editor used to teach a class on technical writing. One of its premises was that good technical writing should be so clear it helps us see the error of our ways. If the knights in Monty Python and the Holy Grail had done a brief description and a few simple drawings before catapulting cows over their enemy’s walls, they might have realized that they had supplied bovine bombs for the enemy to catapult back.
To avoid similar defeats on the stored energy front, engineers at Washington University in St. Louis have cooked up a Cliff’s Notes of how different battery chemistries will behave when being charged. This “back of the envelope calculation,” as Venkat Subramanian, PhD, associate professor of energy, environmental & chemical engineering and his team think of it, is an early predictor of success.
Best of all, “The team developed a freely available code that battery developers can use as a model to determine the optimal profile needed to charge a lithium-ion battery as well as any stresses that might be put on the materials used,” Beth Miller reports in the University’s Newsroom article.
Subramiamaniam notes the same effects of charging batteries that Drs. Cui and Cho have explained in their works, that in lithium-ion batteries, the lithium is stored in metallic form inside particles. As the battery charges and discharges, the lithium metal moves into and out of openings between the particles (intercalation), eventually stressing, cracking, and causing failure of the battery’s electrodes.
“With this model and algorithm, we can use materials that are newly developed and those currently thought of as bad materials because of significant stress generation,” Subramanian says. “Combining stress effects with optimization algorithms can help derive smart charging profiles that take advantage of stress dynamics in such a way that it ensures faster charging of a battery.”
The code, designed for a Windows platform, and covering many of the chemical, electrical and physical elements in charging batteries, is available for free download.
Subramanian explains the importance of early software development along with the physical research on batteries. “When newer materials and systems are being developed for batteries, for solar and for storage, simultaneous development of software, algorithms and hardware are going to be important. We’re not going to wait 10 years and find the best material and the best battery, and then start developing the software. You want to be able to start the software development as we develop the new model and algorithms and then adapt it to newer things as they come along.”
The research, also free to view, was recently published in Physical Chemistry Chemical Physics and includes this abstract:
“The cost and safety related issues of lithium-ion batteries require intelligent charging profiles that can efficiently utilize the battery. This paper illustrates the application of dynamic optimization in obtaining the optimal current profile for charging a lithium-ion battery using a single-particle model while incorporating intercalation-induced stress generation. In this paper, we focus on the problem of maximizing the charge stored in a given time while restricting the development of stresses inside the particle. Conventional charging profiles for lithium-ion batteries (e.g., constant current followed by constant voltage) were not derived by considering capacity fade mechanisms. These charging profiles are not only inefficient in terms of lifetime usage of the batteries but are also slower since they do not exploit the changing dynamics of the system. Dynamic optimization based approaches have been used to derive optimal charging and discharging profiles with different objective functions. The progress made in understanding the capacity fade mechanisms has paved the way for inclusion of that knowledge in deriving optimal controls. While past efforts included thermal constraints, this paper for the first time presents strategies for optimally charging batteries by guaranteeing minimal mechanical damage to the electrode particles during intercalation. In addition, an executable form of the code has been developed and provided. This code can be used to identify optimal charging profiles for any material and design parameters.”
The paper was co-written by Bharatkumar Suthar, Venkatasailanathan Ramadesigan, Sumitava De, Richard D. Braatzc and Venkat R. Subramanian.
Funding for this work was provided by the U.S. Department of Energy Advanced Research Projects Agency – Energy (ARPA-E) and the McDonnell International Scholar Academy at Washington University in St. Louis.
Such openness, and open source software, may become an important part of bringing the next great leap in clean energy development. Thanks to Dr. Subramanian and his colleagues, that next step may be an easier one.