A comprehensive analysis of two decades-worth of research on how nanomaterials are being used to improve energy storage technology, published in the latest edition of Science, suggests that they will play an important role in the wide-ranging plans for sustainability.
Yury Gogotsi, PhD, Distinguished University and Bach professor in the College of Engineering one of the lead authors explains what will need to happen for this invisibly small technology to make its impact.
When batteries were being developed some of the biggest hurdles to market were reliability, safety, sourcing materials, scalability of manufacturing, after just 40 years or so of modern nanomaterials research, which hurdles would you say they have already cleared en route to this application?
The rechargeable batteries live much longer and are much more reliable compared to the beginning of their era. This is partially due to use of nanotubes in lithium-ion battery cathodes. Control of pore size in electrodes of supercapacitors (ultracapacitors) also improved — almost doubling — their capacitance over the past decade. However, the impact of nanomaterials on evolution of energy storage devices has been limited so far.
Batteries are manufactured in huge volumes and they have penetrated all aspects of our life. The price of lithium-ion batteries has dropped by about an order of magnitude since the beginning of the century. And every person in developed countries has multiple battery-powered devices and most of those use rechargeable (secondary) batteries, such as lithium-ion. It is really a dominant technology today.
Many people drive electric cars or scooters and batteries store energy from renewable sources. However, our devices need more energy and need much faster charging — who wants to wait for hours to charge a car or cell phone. Nanomaterials can help to solve the problem of faster charging, as ions that store energy in batteries won’t have to slowly move through dense solid particles, which is what makes charging of current batteries a slow process.
What are the primary challenges facing manufacturers who are trying to use nanomaterials?
The cost of nanomaterials compared to conventional materials is a major obstacle and low-cost, large-scale manufacturing techniques are needed. This has already been accomplished for carbon nanotubes, with hundreds of tons manufactured to fill the needs of the battery industry in China. This should be done for other nanomaterials built of abundant and environmentally friendly elements, such as carbon, nitrogen, titanium, aluminum, zinc and others.
Nanomaterials may also require the use of different kind equipment and a different assembly processes in battery manufacturing. The most successful introduction of nanomaterials to energy storage technology happened when they were preprocessed, which allowed the use of current battery manufacturing equipment.
A good example is silicon-based nanocomposites for batteries – a technology developed by Gogotsi’s former post-doc Gleb Yushin, who created a billion-dollar company, Sila Nanotechnologies
The challenge with many conductive materials is that they are not stable for long periods of time – they oxidize or lose their conductive properties – this problem has only just been addressed in MXenes in the last year, how long do you predict that it will take for similar discoveries to be made with regards to stabilizing other nanomaterials?
Smaller particle size and larger surface area always equals to higher reactivity. This may be good for energy storage, as the entire particle is available for quick reversible electrochemical reaction, allowing much faster charging or high-power discharging. However, it may also lead to faster degradation during storage/processing of materials and later in devices during their cycling or even storage.
Reactivity of nanoparticles is a challenge, but it’s possible to overcome it and our Science paper describes some of the ways of doing it, for example by assembling nanoparticles into clusters and then protecting each cluster with, for example, a carbon coating. This makes larger particles with nanoparticles hidden inside and protected from reaction with the battery electrolyte.
What is the environmental impact of the growth in nanomaterial manufacturing?
It should not be larger than that from manufacturing of other materials, as long as environmentally friendly elements, such as carbon, nitrogen, titanium, aluminum, iron, or manganese are used. Moreover, modern manufacturing techniques are typically more environmentally friendly compared to manufacturing processes developed in the beginning or middle of the 20th century.
How are researchers addressing concerns about the toxicity of some nanomaterials being examined for use in energy storage?
Actually, majority of nanomaterials, such as carbon (graphene, nanoporous carbons and majority of nanotubes), carbon nitride, sulfur, silicon, tin, titania, or titanium carbide MXene, are non-toxic. I’m always skeptical when I read in scientific literature about testing compounds containing tellurium or arsenic that may produce toxic fumes when burned or toxic compounds when exposed to environment.
Lithium-ion batteries have already pushed nickel-cadmium batteries from the market. They are replacing lead-acid batteries in many applications — powering scooters and electric bikes in China and elsewhere — decreasing the use of toxic cadmium and lead.
Whenever scientists consider new materials for energy storage, they should always take into account toxicity to humans and environment, also in case of accidental fire, incineration or dumping into waste.
How might the success of nanomaterials in energy storage benefit the push toward a green energy future that includes ubiquitous use of renewable energy sources?
The more devices are powered by long-lasting batteries or supercapacitors, the more use we have for renewable energy sources like sun and wind. Also, integration of energy storage devices with solar panels and other energy harvesting devices will allow wider use of renewable energy sources, which are intermittent in nature.
Gogotsi is an authority on the development of nanomaterials for energy storage. His research on carbon nanomaterials and layered two-dimensional materials has paved the way for many developments in the field. An article he authored for Nature Materials in 2018 is recognized as a seminal work in this area and has already been cited more than 12,000 times. With fellow College of Engineering professor Michel Barsoum, PhD, and collaborators, Gogotsi is credited with the discovery MXenes, a family of two-dimensional materials that are showing great promise for a number of applications, including energy storage.
For more information about this research visit: https://drexel.edu/engineering/research-design/centers-institutes-labs/drexel-nanomaterials-institute/
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