Making safer and more powerful lithium-ion batteries requires the right recipe

Making safer and more powerful lithium-ion batteries requires the right recipe
Purdue University engineers, including doctoral degree candidate Daniel Robles (shown here), are discovering more about how lithium ion batteries work – information that should make for safer, and longer-lasting batteries. Credit: Purdue University photo/Jared Pike

A Purdue University team has published research that examines the relationship between the active and inactive elements of lithium-ion batteries, and how the micro- and nano-structure of their respective ingredients reflects on the performance and safety of the batteries.

The study was recently featured on the front cover of the journal ACS Applied Materials & Interfaces.

"Rechargeable batteries are everywhere," said Partha Mukherjee, associate professor of , and principal investigator of the research.  "We probably carry two or three portable electronics with us at all times. But the interactions between the different elements of the battery itself are still not clearly understood. My research hopes to bridge that gap."

In Mukherjee's lab, the Energy and Transport Sciences Laboratory (ETSL), researchers study all forms of energy transport and storage, including batteries and fuel cells. They use computer modeling to propose new configurations of the constituent elements involved and then test different phenomena in the lab.

"It's like baking a cake," said Aashutosh Mistry, a Ph.D. candidate in mechanical engineering. "How much dough should you use? How much cherry should you put in so that it tastes nice? In the same way, we look at the fundamental proportions, or the recipe, of these battery electrodes. Anything you change on the microscale ends up affecting the overall performance."

Credit: Purdue University

"Let's take electric vehicles, for example," said Mukherjee.  "People are interested in three things. Performance: how fast can I drive my car? Life: how long can I drive my car before recharging it? And finally, safety concerns. We've seen these batteries fail publicly, in spectacular ways, exploding in smartphones and electric cars. So, all three of these aspects - performance, life, and safety - are very important. It can be a tricky balance getting everything just right."

ometimes their lab works on recreating the spectacular failures on purpose. In a typical electric car, the batteries are not one massive unit, but thousands of individual cells wired together.  If one fails, what happens to the others nearby? For one test, a sample module of 24 cells (about the size of a brick) was purposely overcharged. One cell exploded, which led to a chain reaction where all the cells caught on fire. 

"The temperature and pressure inside one cell got so high, it melted the metal casing, which caught fire," said Ph.D. candidate Daniel Robles, as he held a plastic bag of the charred remains. "In an electric car, there are several thousand of these , and these are located underneath your seat!  That's why it's important to understand the fundamentals of these phenomena, so we can prevent it from happening."

Rechargeable batteries typically contain a positive electrode and a negative electrode, consisting of "active material" to store lithium. Between the two electrodes is a separator, and there is liquid electrolyte throughout, to transport lithium ions. Finally, a combination of electrochemically inactive materials, such as conductive additives and binders (called the "secondary phase") helps to shape the physical ingredients in the composite porous electrodes and enhance the electrical conductivity. In the published research, Mukherjee and his team examine the relationship between the active material and secondary phase on the micro- and nano-scale - the porosity, the physical shapes, and their interactions with each other. Altering any of these characteristics results in significant changes in the battery's overall performance.

"We're still at a nascent stage in understanding these complex interactions," Mukherjee said.  "But that's the key to our research. We connect what's happening at the micro- and nano-scale to the battery's performance, life, and safety." 

And as become more prevalent, their research becomes even more vital. "Batteries are being used everywhere, from to vehicles, and even in large-scale electrical grids.  This is a great and exciting time to do research in energy storage."

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More information: Aashutosh N. Mistry et al. Secondary-Phase Stochastics in Lithium-Ion Battery Electrodes, ACS Applied Materials & Interfaces (2018). DOI: 10.1021/acsami.7b17771
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Citation: Making safer and more powerful lithium-ion batteries requires the right recipe (2018, May 11) retrieved 15 October 2019 from
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May 12, 2018
The question is like asking "how to make gunpowder not explode".

Batteries are fundamentally dangerous devices. They're chemical systems where all the ingredients needeed to release the energy are present and in close proximity, just waiting for the right conditions to react.

Diluting the reactive materials into an inert matrix or otherwise slowing the reaction rate down by choice of different reagents will result in a safer battery, but also reduce the energy density and power output, making the result useless. Increasing the energy density and power of the battery will increase its tendency to fail in dramatic ways, making it more and more explosive.

The only real solution to the safety problem of batteries is to not use batteries. Don't mix the "oxidizer" with the "fuel" and it can't explode on you.

Fuel cells are the only safe solution for very high energy densities and large amounts of energy, like in automobiles.

May 12, 2018
As for smaller devices like cellphones, batteries will just have to do. Sure, it can explode, but the amount of energy is relatively small and can't do very much damage.

Lithium-air batteries would solve the issue, but they suffer from a number of drawbacks such as poor efficiency, low cycle life, sensitivity to water vapor etc. that they're not really contenders to fuel cells in anything.

May 12, 2018
"Fuel cells are the only safe solution for very high energy densities and large amounts of energy, like in automobiles."?

Beware, Eikka. Prophecies are even more dangerous than gunpowder.

Fuel cells aren't fated to be "that only safe solution" forever, if it is in the first place. Who knows what'll be coming next?
I wouldn't even be surprised to learn that batteries the way we know them will change a lot in the coming decades, and won't be surprised AT ALL if suddenly, we find a way to create battery even YOU would feel safe around.
Because we haven't found it yet doesn't mean it doesn't exist.

May 13, 2018
"Because we haven't found it yet doesn't mean it doesn't exist."

That's religious thinking.

There are safe batteries of course, or at least batteries where the failure modes don't occur until everything is a blazing inferno to begin with, but these have poor performance characteristics otherwise. Solid/dry electrolytes for example have poor ion conductivity at room temperature.

The fundamental issue is that lithium, sodium, sulfur etc. are very reactive materials to begin with which is why they are able to store so much charge. This makes them inherently unstable - you take a piece of plain lithium and it starts to smoulder just from the moisture in the air.

The worst proposal I've heard for stabilizing batteries is by using lithium nitrate, which like ammonium nitrate, potassium nitrate etc. turns it into a high explosive when combined with a combustible fuel - like the hydrocarbons in the electrolyte or the carbon matrix in the electrodes.

May 13, 2018
Now now. I'm not saying i'm certain it exists. I'm saying noone is certain it doesn't exist yet, and we're talking about something that has yet to reveal ALL its secrets and is still evolving.
Don't compare it with religion, where everything is already stone set or so. And, sometimes, explodes too.

May 13, 2018
Don't compare it with religion, where everything is already stone set or so.

The point is, absence of evidence means absence of evidence, not potential of a miracle. I put forth the fundamental point: chemical batteries are inherently prone to dramatic failures because you have very reactive chemicals stuffed tightly together separated only by a thin barrier - if the chemicals are less reactive and/or the barrier made thicker the battery perfomance suffers. This points towards better batteries being also inherently less safe.

What you're searching for is a system where all the chemical components can be put through a blender and subjected to high temperatures without reacting dangerously, yet somehow these same chemicals in the battery need to produce a rapid and energetic reaction at low temperatures - a contradiction in requirements.

That's why fuel cells or air batteries are the answer: only half the chemicals needed for the reaction are present in the device.

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