Charging lithium-ion cells at different rates increases battery life

Charging lithium-ion cells at different rates increases battery life for electric vehicles, a Stanford study has found.

Stanford University researchers have developed a new way to extend the life of lithium-ion batteries and reduce their deterioration due to rapid charging.

Stanford researchers have developed a new way to extend the life of lithium-ion batteries and reduce their deterioration from rapid charging.

The research, published Nov. 5 in IEEE Transactions on Control Systems Technology, shows how actively managing the amount of electrical current flowing through each cell in a pack, rather than providing an even charge, can minimize wear. The approach effectively allows each cell to live its best – and longest – life.

According to Stanford professor and lead author of the study, Simona Onori, initial simulations suggest that batteries managed with the new technology could handle at least 20% more charge-discharge cycles, even with frequent fast charges. which puts additional strain on the battery.

Most previous efforts to extend the life of electric car batteries have focused on improving the design, materials, and manufacturing of individual cells, based on the premise that, like links in a chain , a battery is only as good as its weakest cell. The new study begins with understanding that while weak links are unavoidable – due to manufacturing imperfections and because some cells degrade faster than others when exposed to stresses such as heat – they don’t don’t need to drop the whole package. The key is to match charge rates to each cell’s unique capacity to avoid outages.

“If not properly addressed, cell-to-cell heterogeneities can compromise a battery’s longevity, health, and safety and induce early battery failure,” said Onori, assistant professor of engineering science. energy at Stanford Doerr. School of Sustainability. “Our approach equalizes the energy of each cell in the pack, bringing all cells to the targeted end state of charge in a balanced manner and improving the longevity of the pack.”

Inspired to build a million mile battery

Some of the impetus for the new research dates back to a 2020 announcement by Tesla, the electric car company, of work on a “million mile battery.” This would be a battery capable of powering a car for 1 million miles or more (on a regular charge) before reaching the point where, like the lithium-ion battery in an old phone or laptop, the battery of the electric vehicle contains too little charge to be functional. .

Such a battery would exceed the typical automaker warranty for electric vehicle batteries by eight years or 100,000 miles. Although batteries generally last longer than their warranties, consumer confidence in electric vehicles could be boosted if expensive battery replacements become even rarer. A battery that can still hold a charge after thousands of recharges could also facilitate the electrification of long-haul trucks and the adoption of so-called vehicle-to-grid systems, in which EV batteries would store and distribute renewable energy for the electrical network.

“It was later explained that the million mile battery concept wasn’t really new chemistry, just a way to run the battery by not making it use the full charge range,” he said. Onori said. Related research has focused on single lithium-ion cells, which generally do not lose their charge capacity as quickly as full batteries.

Intrigued, Onori and two researchers in his lab – postdoctoral researcher Vahid Azimi and doctoral student Anirudh Allam – decided to study how inventive management of existing battery types could improve the performance and lifespan of a complete battery, which may contain hundreds or thousands of cells. .

A high-fidelity battery model

First, the researchers designed a high-fidelity computer model of battery behavior that accurately represented the physical and chemical changes that occur inside a battery over its lifetime. Some of these changes take place in seconds or minutes, others over months or even years.

“To our knowledge, no previous study has used the type of high-fidelity, multi-timescale battery model that we created,” said Onori, director of the Stanford Energy Control Lab.

Running simulations with the model suggested that a modern battery can be optimized and controlled by taking into account the differences between its constituent cells. Onori and his colleagues plan to use their model to guide the development of battery management systems in the coming years that can be easily deployed in existing vehicle designs.

It’s not just electric vehicles that benefit. Virtually any app that’s “high on battery power” could be a good candidate for better management informed by the new findings, Onori said. An example? Electric vertical take-off and landing drone-like aircraft, sometimes called eVTOL, that some entrepreneurs expect to operate as air taxis and provide other urban air mobility services over the next decade. Yet other applications for rechargeable lithium-ion batteries are available to us, including general aviation and large-scale renewable energy storage.

“Lithium-ion batteries have already changed the world in many ways,” Onori said. “It’s important that we make the most of this transformative technology and its future successors.”

Azimi is now a researcher at Gatik, a B2B short-haul logistics company in Mountain View, California. Allam is now a battery researcher at Archer Aviation, an eVOTL aircraft company based in San Jose, California.

This research was supported by LG Chem (now LG Energy Solution).

By Adam Hadgazy

Courtesy of Stanford News

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