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The world is a big place, but the advent of mobile technology has brought us all closer together. Laptops, smartphones and tablets have revolutionised the way we communicate – and a battery lies in each of them.
With the forecast boom in electric cars and rapid growth in renewable energy, batteries’ role in our modern lives will grow even bigger. In the coming years, we will also expect – and demand – much faster charging from electronic devices.
My group has worked on nanomaterials – materials with features measuring 1-100nm, or billionths of a metre – since I joined Cornell University, with the goal of generating novel properties not available with macroscale materials. This work ranges from studies of how nanomaterials are formed, to exploring entirely novel material architectures – how the materials arrange and join together on the nanoscopic scale – to using nanomaterials in human clinical trials.
The main focus of our latest work is an entirely new architecture for batteries, with the aim of reducing charging times. The result is what we call a three-dimensional battery.
Shrinking architecture
Instead of the conventional architecture, where 10-20 micron thick layers of anode, separator and cathode are sandwiched in a layer-like fashion between charge collectors, this revolutionary architecture has completely interpenetrating and intertwined anodes and cathodes, with the separator in-between. All three components have a thickness of only 10-20nm, rather than 10-20 micron each – 1,000 times smaller.
These small dimensions lead to fast diffusion between anode and cathode, which substantially reduces charging times compared to conventional batteries.
There were lots of challenges in the work, including building a carbon anode with periodic 40nm pores weaving through the entire material in a three-dimensional way. We also had to create a 10nm separation layer that was free of ‘pinholes’ and was fully electronically insulating, but still let lithium ions diffuse through. We then filled the 20nm pores left behind after these processes with cathode and current-collector materials.
We had to carefully do each of these steps in a tiny carbon ‘monolith’ – only 50 microns thick – and in such a way that each step left the material fully functioning.
Exciting advance
In the end, the thing that surprised us the most was that it actually worked. Quite a number of experts in the field had told us that it would never happen. It is simply incredibly difficult, which is why the community has discussed 3D batteries for more than 15 years but – to the best of our knowledge – nobody had ever got one to work with all components having a thickness below 50nm, and delivering the subsequent reduction in charging times.
This is a fundamentally new battery architecture, which in principle could revolutionise all areas where batteries are used. It minimises dead volume of the battery, maximises charge density, and – because of the short diffusion distances between electrodes – it also substantially enhances power density.
This work showed only proof-of-principle. It demonstrated that such a design, with all components having a thickness of only about 20nm, is actually possible, and can lead to a functioning battery. But there is a long way to go to convert this concept demonstration into a commercial product. We still have to overcome substantial challenges.
On the other hand, it is very exciting that after so many years the first step has been taken. It will be fascinating to see if others pick this up and find improvements on our design and material choices.
Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.