With its abundance of natural resources, Australia is committed to its transition to greener energy production, with solar and wind leading the charge. While this transition is a great step towards achieving the country’s net zero emissions goals, these greener energy solutions are not without their own problems, including large amounts of material waste associated with end-of-life solar panels. A team of researchers from Deakin University’s Institute for Frontier Materials are tackling this problem head-on, and have developed a sustainable and highly lucrative way to extract silicon from end-of-life solar panels and reconfigure it to build better batteries.
In an effort to embrace its abundant natural resources and power towards a greener future, Australia continues to invest in large-scale solar projects across the country. Whilst in the short term it may be difficult to see the associated risks of this kind of investment, with more than 100,000 tonnes of end-of-life solar panels estimated to enter Australia’s waste stream by 2035, it’s becoming increasingly clear that a longer term approach is needed.
Solar PV panels have a maximum period of operation, in most cases 25 to 30 years. It is estimated that worldwide PV waste will increase between four per cent and 14 per cent by 2030, and 80 per cent (around 78 million tons) by 2050, creating a serious waste problem.
This, in turn, may result in unsafe disposal of end-of-life PV, which will produce environmental hazards in the near future.
In an attempt to mitigate this waste stream and potential for unsafe disposal, a team of scientists at Deakin University’s Institute for Frontier Materials (IFM) managed to successfully develop and test a new process that can safely and effectively extract silicon from old solar panels.
The research leading to the discovery
The new method did not come about overnight. Alfred Deakin Professor Ying (Ian) Chen said his nanotechnology team had been working on nanostructured electrodes for lithium-ion, lithium sulfur (Li-S), and potassium ion batteries for the past 15 years.
Nanomaterials such as silicon (Si), germanium (Ge) and other nanoparticles have been used in anodes and cathodes to improve battery energy density and cycling performance in the past.
The team’s world-leading research led to the establishment of the ARC Research Hub for Safe and Reliable Energy Storage and Conversion with six universities and a total budget of $12 million.
The nanotechnology team’s research in Li-S batteries has been under commercialisation by LiS Energy Ltd which is listed on the ASX.
The team has extensive research experience in both nanomaterials and battery development, which led to this discovery of repurposing recycled silicon into battery anodes.
In 2018, Deakin University started to promote a circular economy campaign by recycling various waste materials.
“We proposed a circular economy project of recycling silicon from end-of-life solar panels and repurpose it into anodes for Li-ion batteries,” Professor Chen said. This is because end-of-life solar panels have high-quality silicon films.
Dr Mokhles Rahman, a key researcher of the team, led the project – which was supported by Deakin University’s circular economy fund – and conducted a proof of concept project, with the promising results winning a grant from Sustainability Victoria.
Extracting silicon from end-of-life solar panels
According to Professor Chen, there are several ways to delaminate solar panel modules such as mechanical, physical, and thermal processes.
“We use a thermal process to delaminate the module and extract silicon from the panel.”
The extraction process and subsequent purification, nano silicon production and final anode preparation is illustrated in Figure 1.
“The process delivers a complete package – including recycling of PV panels, recovery and purification of silicon and conversion to nano silicon. Then a subsequent integration of PV nano silicon and graphite into a single system of PV nano silicon/graphite for battery application.
This process has the following advantages compared with any reported results so far:
- Only potassium hydroxide (KOH) is used as an etching agent for the purification process, which offers lower cost and is less dangerous
- A high yield purification process (80 per cent recovery), which delivers high quality and high purity silicon
- An industry-adopted, scalable ball-milling technique is developed to produce large-quantities of nano silicon (<100nm), allowing for diverse applications. Most importantly, the properties of the obtained PV nano silicon are comparable with highly expensive, commercially available Sigma nano silicon in the market (US$ 36 000.00/kg-Product code: 633097 nanopowder <100 nm, SigmaAldrich)
- The ball milling process is further optimised for the production of high-performance battery electrodes of PV nano silicon/graphite hybrids by integration of recovered PV nano silicon and commercial graphite
- An overall process that is faster, with a low cost, and higher yield
Revitalising silicon
The silicon that is extracted from the solar panels is not immediately ready for reuse and must undergo a purification process. Without this purification, the silicon cannot be reused.
According to Professor Chen, the reason for this process is because the silicon extracted from solar panels often contains some heavy metals such as cadmium (Cd), lead (Pb), and selenium (Se) which are used as dopants during the manufacturing process to increase energy efficiency of the panels.
These impurities can negatively affect the performance of silicon if they are used in batteries or other applications.
“In addition, during the operation of a solar panel, the silicon material is exposed to various environmental factors such as heat, moisture, and ultraviolet radiation. These factors can also cause the formation of impurities in the silicon, such as oxygen, carbon, and metals.
“These impurities can lead to a decrease in the efficiency of the solar panel, as they can reduce the ability of the silicon to absorb light and generate electricity.” As well as this, over a solar panel’s 25 to 30 years of life, several other factors can cause the silicon to become contaminated and not fit for reuse. These include:
- Degradation: the silicon used in solar panels can degrade over time due to exposure to sunlight, moisture, and temperature fluctuations. This degradation can lead to a decrease in the panel’s efficiency and can also cause impurities to form in the silicon
- Surface contamination: the surface of a solar panel can become contaminated over time due to exposure to dust, dirt, and other environmental pollutants. This contamination can make it difficult to reuse the silicon in new panels without extensive cleaning and processing.
- Manufacturing defects: during the manufacturing process, defects can occur in the silicon that can make it unsuitable for reuse in new panels
- Cost-effectiveness: even if the silicon from old solar panels is still technically usable, it may not be cost-effective to reuse it in new panels due to the high cost of processing and cleaning the silicon
Overall, the degradation, contamination, and defects that can occur in silicon over the 25 to 30-year lifespan of a solar panel can make it unsuitable for reuse in new panels without extensive processing and cleaning. As a result, most silicon from old solar panels is typically recycled or disposed of rather than being reused in new panels.
The silicon purification process involves removing these impurities from the silicon material to restore its high-purity level.
This process typically involves several steps, such as melting the silicon and then applying various refining techniques, such as zone refining or distillation.
These techniques can help remove impurities such as oxygen, carbon, and metals from the silicon material.
“Once the silicon material has been purified, it can then be used in the production of new solar panels or other applications, where it can help maximise the efficiency and lifespan of the resulting products.
“The purification process is necessary to remove impurities from the extracted silicon and restore its high-purity level, which is essential for the performance and longevity of the resulting solar panels or other products.”
The next step: integration into new battery technology
“Among various battery raw materials, silicon (Si) is the most emerging and safe anode materials proposed for lithium-ion batteries (LIBs) with a high theoretical capacity of 4200 mAh g-1, which is ten times higher than the commercial graphite anodes (372 mAh g-1),” Professor Chen said.
“However, pure silicon alone cannot be used as an anode, because silicone anode in LIBs undergoes extraordinarily high volume expansion by up to 300 per cent during full lithiation.”
This large volume change leads to repeated cracking and pulverisation of the silicon and facilitates disintegration and fracturing of the silicon electrode, accompanied by electrical isolation.
“In addition to this, repeated cracking and pulverisation of the silicon electrode leads to continual breaking up of the solid electrolyte interphase (SEI) layer and the explosion of a new surface, which quickly consumes electrolyte and lithium ions.
“Hence, the use of sole silicone anode suffers from extremely fast capacity decay and low coulombic efficiency (CE) as a result of the severe volume changes and unstable SEI.”
Hybridisation/co-utilisation of silicon and graphite has recently been found to be one of the practical strategies for commercialisation of a silicon/graphite anode in the near future.
The incorporation of graphite into nano silicon can combat against the volume alteration, increase the electric conductivity, and achieve high specific, areal, and volumetric capacities at the same time.
“Most importantly, the co-utilisation of silicon and graphite can use the same commercial production lines – translating into high manufacturability and minimal investment.
“On the other hand, the hybridisation of silicon and graphite in a single electrode is capable of delivering advantages by avoiding individual disadvantages of both electrodes and can secure its success in the anode market.”
To replace the existing commercial graphite anode, the commercial goal of the current anode market is set to achieve any materials with a specific capacity of 500 mAh g-1 or higher with a capacity retention of 80 per cent after 500 cycles.
Whereas the initial CE and average CE should exceed 90 per cent and 99.8 per cent, respectively, it is, however, still a challenge to integrate the silicon and graphite into a single system or composite to obtain such desired performance, because both of these materials are significantly different in terms of their physical and chemical properties.
The results obtained by the group of researchers, however, are very close to the commercial value.
Applications of nano silicon
The uses for nano silicon are not, however, limited to battery technology. There are currently a multitude of applications for nano silicon beyond just battery technology, including:
- Electronics: nano silicon can be used in the production of high-performance electronics, including transistors, memory devices, and solar cells. Nano silicon-based electronics have the potential to be faster, smaller, and more efficient than traditional silicon-based devices
- Biotechnology: nano silicon can be used in biotechnology research, including as a platform for drug delivery and as a biosensor for detecting biomolecules. Nano silicon-based biosensors have the potential to be more sensitive and specific than traditional biosensors
- Energy: nano silicon can be used in the production of more efficient solar cells, as well as in the development of new types of energy storage devices
- Catalysis: nano silicon can be used as a catalyst in chemical reactions, including in the production of fine chemicals and pharmaceuticals. Nano silicon-based catalysts have the potential to be more efficient and selective than traditional catalysts
- Advanced materials: Nano silicon can be used to produce advanced materials, including nanocomposites and nanofilms. These materials have potential applications in areas such as aerospace, automotive, and construction
“Overall, nano silicon has the potential to impact a wide range of industries and applications, and ongoing research is likely to uncover even more potential uses for this versatile material,” Professor Chen said.
Nano silicon market value
The current market price for nano silicon is about $45,000 per kilo, compared to about $650 for regular silicon. It is also in even higher demand – not just for new battery materials, but also for use in the development of nano-fertilisers, innovative new methods for carbon capture, and on demand hydrogen gas generation.
Nano silicon, also known as ‘nanosized silicon’ can be expensive for several reasons:
- Manufacturing costs: the process of producing nano silicon involves specialised equipment and techniques, which can be costly to set up and maintain. The production of nano silicon also requires high-purity silicon, which can be expensive to obtain
- Limited supply: the production of nano silicon is still relatively new and not yet fully optimised, which means that the supply is limited. As a result, the cost of nano silicon can be higher due to the low supply and high demand
- Research and development costs: the development of nano silicon technologies requires extensive research and development, which can be expensive. These costs may be reflected in the final price of the product
- Specialty applications: nano silicon is often used in specialty applications, such as in the production of high-performance electronics or in biotechnology research. These applications require high-quality nano silicon, which can also drive up the price
The discovery’s ripple effects for the industry
The Deakin University team’s discovery of this new, more efficient method for extracting silicon from discarded solar panels is expected to have a significant impact on both the resources sector and Australia’s renewable industry.
“Firstly, the discovery could reduce the amount of waste generated by the solar panel industry and provide a new source of raw material for the production of new panels,” Professor Chen said.
“This could help reduce the environmental impact of the solar panel industry and promote more sustainable practices.
“Secondly, the more efficient extraction method could help increase the supply of high-purity silicon, which is a critical component in the production of solar panels, microchips, and other high-tech products.
“This could help reduce the cost of producing these products, making them more affordable and accessible to consumers.”
Professor Chen said that Australia’s renewable industry could also benefit from this discovery.
“The country has abundant solar resources, and solar energy is a rapidly growing sector of the economy. By reducing the cost of producing solar panels, this discovery could help accelerate the adoption of solar energy in Australia and increase the country’s energy security.”
Another potential benefit is that with this discovery, Australia could also become a leader in the recycling and reuse of silicon materials from discarded solar panels, providing a new source of revenue and job opportunities in this emerging sector.
“Overall, this discovery has the potential to reduce waste, increase the supply of critical raw materials, and promote the growth of Australia’s renewable industry, making it an important development for both the resources sector and the broader economy.”
The next step for the team is commercialisation of the process in collaboration with industry partners.
The team estimates that their technique could generate US$15 billion in material recovery if extrapolated to the 78 million tonnes of solar panel waste expected to be generated globally by 2050.
“We want to scale up the process from laboratory scale to industry scale to reuse the recycled silicon into various areas.
“Recycling is critically important to prevent environmental damage caused by the industry.”
In order to reach energy security and independence, Australia must develop its own fully integrated domestic solar supply chains.
This method of extracting silicon from end-of-life solar panels is just one way that allows the country to mitigate the damage of the 100,000 tonnes of end-of-life solar panels predicted to enter Australia’s waste stream by 2035, while also working towards a fully-fledged supply chain for silicon and solar cells.
Featured image: Akhil Nelson, Dr Md Mokhlesur Rahman and Professor Ying Chen. Image credit. Deakin University.
