In the heart of all kinds of devices, there are Lithium-ion batteries, from smartphones and laptops to the ever-growing contingent of electric cars. So, the interest to boost their performance is an ever-growing one – with advanced materials to make them lighter, more compact and able to hold more energy. A new tin-aluminium alloy, developed by engineers in Texas, might deliver on all three aspects, and it might even make them faster and cheaper to produce for the consumer.
For years now, many mass-produced lithium-ion batteries have relied on graphite and copper for their anodes, the component that stores the energy as the battery charges. During this time, 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.
Creating current-day anodes is a laborious, multi-step process where the graphite is power-coated onto the copper foil. A material scientist at the University of Texas in Austin, and lead author of the new study, Karl Kreder, 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)," Kreder explains. "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 simple approach that skips a complicated step, the fastidious coat process. The tin is able to be added directly into the aluminium as it is cast into blocks, creating an alloy that can be mechanically rolled – a relatively cheap and common metallurgical alloying process – into nanostructured metal foils. The 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 micrometre-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 research team 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 worked it into a smaller version of the 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 this works so well is that one of the elements is active, tin, and the other one is inactive aluminium," says Kreder. "The aluminium creates a conductive matrix in which the tin is held. The aluminium 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 could mean big things for manufacturers of smartphones, cars, laptops and myriad other devices. 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."
You can read the full research paper here.