Cheap new alloy may double the anode capacity of lithium batteries

Cheap new alloy may double the anode capacity of lithium batteries
Researchers in Texas have developed a new battery anode (right) that is one quarter the thickness and half the weight of traditional anode (left)
Researchers in Texas have developed a new battery anode (right) that is one quarter the thickness and half the weight of traditional anode (left)
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Researchers in Texas have developed a new battery anode (right) that is one quarter the thickness and half the weight of traditional anode (left)
Researchers in Texas have developed a new battery anode (right) that is one quarter the thickness and half the weight of traditional anode (left)

Lithium-ion batteries are at the heart of all kinds of devices, from smartphones and laptops to the ever-growing contingent of electric cars. So there is interest from many quarters in boosting their performance with advanced materials that make them lighter, more compact and able to hold more energy. A new tin-aluminum alloy developed by engineers in Texas might deliver on all three aspects, and it might even make them faster and cheaper to produce at the same time.

For years, mass-produced lithium-ion batteries have relied on graphite and copper for their anodes, the component that stores the energy as the battery charges. And for years, researchers have sought out alternative materials that could overcome the limitations of those materials, which include a high cost of production and limited storage capacity (silicon, for example, could store 10 times as much energy, although it poses another set of problems).

Creating current-day anodes is a laborious, multi-step process where graphite is powder-coated onto copper foil. But as Karl Kreder, a material scientist at the University of Texas at Austin and lead author of the new study explains, this is kind of inefficient in terms of both the manufacturing process and the battery itself.

"So the active material (graphite) is coated on top of the inactive current collector (copper)," he tells New Atlas. "This adds volume and inactive material mass to the system. By combining the current collector and active material together, a higher capacity active material can be used while simultaneously using less inactive current collecting material."

Kreder and his team achieved this with a simplified manufacturing approach that skips a complicated step, the fastidious coating process. The tin is able to be added directly into the aluminum as it is cast into blocks, creating an alloy that can then be mechanically rolled (a relatively cheap and common metallurgcal alloying process) into nanostructured metal foils. And this last step, where the particles within the material are reduced, is critically important.

"Tin is known to alloy with lithium," Kreder explains. "Unfortunately, if tin foil is used or even micrometer-sized tin particles are used, the tin will break apart when cycled due to volume expansion when it alloys with lithium. This means that if you make a battery with large tin particles it will only last for tens of charge-discharge cycles. However, if you make nanometer-sized tin particles the particles will not break apart during alloying."

The researchers call the resulting material an interdigitated eutectic alloy (IdEA) anode, which they say is one quarter the thickness and half the weight of traditional anode material. They tested it by working it into complete smaller versions of lithium-ion batteries, and then charging and discharging them to measure performance. They found that it demonstrated twice the charge storage capacity of a typical copper-graphite anode.

"The reason that this works so well is that one of the elements is active, tin, and the other one is inactive, aluminum," says Kreder. "The aluminum creates a conductive matrix in which the tin is held. The aluminum provides the structure and electrical conduction, while the tin is alloyed and de-alloyed with lithium when the battery is cycled."

A more compact anode, and in effect battery, could mean big things for manufacturers of smartphones, cars, laptops and myriad other devices. And that's to say nothing of the improved performance and cheaper manufacturing process. In their material, the researchers believe they have an early proof-of-concept for new and improved lithium-ion batteries.

"It is exciting to have developed an inexpensive, scalable process for making electrode nanomaterials," says Arumugam Manthiram, a professor and the director of the Texas Materials Institute, who led the team. "Our results show that the material succeeds very well on the performance metrics needed to make a commercially viable advance in lithium-ion batteries."

The research was published in the journal ACS Energy Letters.

Source: University of Texas

Elon, are you listening?
Martin Winlow
And the downsides??
Martin Winlow
@guzmanchinky - Probably not as he's a bit busy at the moment and he probably gets a new-fangled twist on battery tech arrive on this desk every single day.
Discharge rate? Doesn't current passing through aluminum cause more resistive heating than the same current passing through copper of the same dimensions?
Interesting. At least they are bragging about an incremental improvement, unlike the "stop the presses" announcements on battery tech we are so used to hearing.
And let's face it... cheaper is better...
Tom Lee Mullins
I think that could be good news for anything that runs on a battery.
@kpar A 2X increase with implied cost reduction is a pretty big increment.
Sounds great, until you put the "large molecule/10s of cycle life" with the fact that they aren't stating apparent lifetime yet. 10x the power but 1/300th of the lifetime? OK for some uses (like seldom-used flashlights), but not for most (electric cars) unless the cost of manufacture is so low it makes throwaway lithium packs (recycled, of course) feasible. Incorporate that into the mass production cycle at the NanoFactory and you have a real winner. I'm sure Elon will say something when the time is right. Carry on, researchers. We need all the ideas you can come up with to make everything in our lives (which runs on electricity) to be more efficient, portable, and self-charging.
Li-Ion energy density since '91 has improved a consistant 2-3% per year, up to 2002 the chemisty improved after that the gains have mostly been from packaging improvements, reducing the packaging overhead. At 259 watt/hours per KG. In the last 10 years Combustion has improved dramatically exceeding 50% in Mercedes and Ferrari Formula One engines with improvements every year, 58% with Jet Assisted Compression Ignition.
Ausralian company Nano Nouvelle have developed a polymer Anode that reduces heat and improves power density reducing weight and thickness already tested in production. It's the heat that is the real issue, heat is lost energy. Why the high power density cells have a large reduction in energy density is the thickness of the current carrier. The never above temperature of cells is not that much above ambient temperature in Australia, the temperature where you get Galaxy S7 results. They flash off like a 8000 hp drag engine in self sustaining heat release, keeping the FAA amused in aircraft.