Unlocking the Mysteries of Rechargeable Batteries

Stanford University researchers are seeking a new fundamental understanding of how particles charge and discharge at the nanoscale level. Their work could lead to a new generation of lithium-ion battery design.

Kristopher Sturgis

It is actually possible to observe the electrochemical reactions that fuel lithium-ion batteries, the most commonly used rechargeable cell, providing a better understanding of battery technology building blocks, says Yiyang Li, a doctoral candidate at Stanford and one of the lead authors of a new study out of the university.

Such an understanding is crucial in the medical device field, where batteries provide a major technological challenge for designers of miniaturized and connected health devices.

"Usually batteries are [studied] on the macro scale where the information is averaged over a highly heterogeneous, nonuniform system," Li says. "Our approach is to study the building block of batteries, which is to understand them on the level of individual particles. This way, we not only identify how batteries fundamentally work, but we can also detect minority features that do not show up on an average measurement."

The tiny particles Li was talking about measure less than 1/100th the size of a human hair--a size that has prevented scientists from developing an effective way to measure and study the electrochemical reactions that occur at the nanoscale level. Li and his colleagues turned used an x-ray microscope to drill down to the needed level of detail.

As it turns out, these reactions are far more complex than previously imagined, and this new method not only provides the ability to observe these reactions in real time, but can also provide new insights on lithium-ion battery design and management.

"This method could be used to design battery management protocols that can be recharged more often before failing," Li says. "The most interesting result is that the material charges more uniformly at higher rates of charge and discharge. Typically, materials are more uniform when they change slowly, but in contrast, this material is more uniform when it quickly goes from charged to a discharged state. In many cases, the uniformity of charge and discharge directly affects how fast the battery degrades."

Battery technologies have been progressing at a steady rate these past few years as devices continue to get smaller, and manufacturers look to power flexible devices in wearable technologies. Earlier this year scientists from the University of Illinois developed a new flexible power system that aims to take advantage of solar cell technologies that could stretch and bend without any detectable loss in power.

Similarly, Li and his colleagues are looking for ways to enhance battery technologies through their own method, which involves using x-rays to see exactly where lithium goes inside the battery as it charges.

"We use the synchrotron at Berkeley National Laboratory to generate a high quantity of x-rays, and use these high-energy x-rays to see exactly where the lithium goes inside a battery as it charges and discharges," Li says. "The key challenge is developing a battery cell that is only one micrometer thick, in order to image particles that are only 100 nm thick. This way, we can see exactly how a battery particle charges (gives up lithium) and discharges (receives lithium) on the nanoscale."

The x-ray microscope has proven to be another advancement that the group is hoping to explore  as they move forward with their research. The aim is to explore and enhance energy research across the board by observing the dynamics of nanoscale chemical reactions.

"We are broadly using this approach to study how materials change dynamically during chemical reaction at the nanoscale," Li says. "Here, we study what happens when a battery charges and discharges --but we are also investigating topics such as what happens when a fuel cell converts hydrogen to water."

Kristopher Sturgis is a contributor to Qmed.

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