Charging lithium-ion batteries at different speeds increases the life of electric vehicle battery packs

Stanford University researchers have invented a new method to make lithium-ion batteries last longer and be less prone to damage when fast charging.

The study, published November 5 in IEEE Transactions on Control System Technology, which shows how proactively managing the amount of current flowing to each cell in a package, rather than distributing the charge uniformly, can minimize wear and tear. This method allows each cell to live its best and longest – efficiently.

According to Stanford professor and senior study author Simona Onori, early simulations show that batteries managed with the new technology can handle at least 20% more charge-discharge cycles, even with fast charging. often, this puts extra stress on the battery.

Most previous efforts to extend electric vehicle battery life have focused on improving the design, materials, and manufacturing of single cells, based on the premise that, like links in a Chain, battery only as good as its weakest cell. The new research begins with the understanding that while weak bonds are inevitable – due to manufacturing imperfections and because some cells degrade faster than others when they are exposed. exposed to stresses such as heat – they don’t necessarily damage the entire cell. It is important to tailor the charging rate to the unique capacity of each cell to prevent errors.

“If not handled properly, cell-to-cell heterogeneity can affect longevity, health and safety of the battery pack and cause premature battery failure”. The School of Sustainability. “Our approach balances the energy in each cell in the pack, bringing all cells to the final target state of charge in a balanced manner and improving the life of the pack.”

Get inspired to build batteries millions of miles away

Part of the impetus for the new research stems from Tesla’s 2020 announcement of working on a “million-mile battery.” This would be a battery capable of powering a car for 1 million miles or more (with regular charging) before reaching a point, like lithium-ion battery In an old phone or laptop, the EV’s battery charges too little to function.

Such a battery would exceed automakers’ usual warranties for electric vehicle batteries of eight years or 100,000 miles. While battery packs typically outlast warranties, consumer confidence in electric vehicles could be bolstered if expensive battery pack replacements become rarer. A battery that can still be charged after thousands of charges could also easily electrify long-haul trucks and adopt a so-called vehicle-to-grid system, in which EV batteries will store store and supply renewable energy to the grid.

“It was later explained that the million-mile battery concept was not really a new chemical, but just a way to operate the battery by not making it use up its full charge range,” said Onori. Onori said. Related research has focused on single lithium-ion cells, which typically don’t lose the ability to charge as quickly as full battery packs.

Fascinating, Onori and two researchers in her lab — postdoctoral scholar Vahid Azimi and Ph.D. student Anirudh Allam — decided to investigate how innovative management of existing batteries could improve the performance and lifespan of a full battery pack, which can hold hundreds or thousands of cells.

High-fidelity battery model

As a first step, the researchers created a high-fidelity computer model of the battery’s behavior that accurately represented the physics and chemical change takes place inside the battery during its lifetime. Some of these changes happen in seconds or minutes — others over months or even years.

“To the best of our knowledge, no previous studies have used the high-fidelity, multiple-repeating battery that we have created,” said Onori, director of the Stanford Energy Control Laboratory. “.

Running simulations with the model shows that a modern battery pack can be optimized and controlled by capturing the differences between its constituent cells. Onori and colleagues envision their model being used to guide the development of battery management systems in the coming years that can be easily implemented in existing vehicle designs.

It’s not just electric cars that benefit. Almost any application “emphasis the battery Pack a lot, Onori says, “could be a good candidate for better management informed by new results. An example? Drone-like aircraft capable of take-off and landing electric uprights, sometimes called eVTOLs, which some entrepreneurs expect to act as air taxis and provide other urban air mobility services over the next decade. give lithium-ion battery beckons, including general aviation and large-scale storage of renewable energy.

“Lithium-ion batteries have changed the world in many ways,” said Onori. “It’s important that we get as much as we can from this transformative technology and its successors.”