Scientists Devise Method to Upcycle Lithium-ion Batteries from Expired Solar Panels

Scientists at Nanyang Technological University, Singapore (NTU Singapore) have unveiled an innovative method for repurposing high-purity silicon from retired solar panels, potentially revolutionizing lithium-ion battery production for the surging electric vehicle market.

Extracting High-Purity Silicon

Typically, the majority of solar cells are constructed from high-purity silicon, yet these cells are often discarded after 25 to 30 years of service. Separating the silicon from other components like aluminum, copper, silver, lead, and plastic has proven to be a complex task, according to the research team.

Furthermore, recycled silicon often contains impurities and defects, rendering it unsuitable for other applications.

The team said that current techniques for reclaiming high-purity silicon are not only energy-intensive but also entail the use of highly toxic chemicals.

In response to these challenges, the NTU team devised a novel extraction process utilizing phosphoric acid, a substance that is often employed in the food and beverage sector.

This method demonstrated superior recovery rates and purity compared to existing silicon retrieval technologies. Notably, the team said it is more efficient, relying on a single reagent (phosphoric acid), whereas traditional methods involve at least two different types of chemicals.

Principal investigator Associate Professor Nripan Mathews stated, "Our approach to silicon recovery is both efficient and effective. We do not have to use multiple chemicals, reducing the time spent on post-treatment of the chemical wastes. At the same time, we achieved a high recovery rate of pure silicon comparable to those produced by energy-intensive extraction techniques."

The method developed by the NTU research team is seen as a sustainable remedy for the growing problem of solar panel waste, ensuring a continuous recycling loop for vital resources.

Silicon holds paramount importance as a key component for the upcoming wave of lithium-ion batteries propelling electric vehicles (EVs), thanks to its ability to deliver extended range and swift charging capabilities.

The NTU research team contends that their newly devised silicon recovery technique could be instrumental in meeting the projected surge in demand for high-purity silicon.

The NTU Approach

The NTU approach entails submerging expired solar cells in hot, diluted phosphoric acid for half an hour to remove surface metals. This procedure is then duplicated with fresh phosphoric acid to ensure comprehensive metal extraction, ultimately yielding a pristine silicon wafer within an additional half-hour.

The team also claimed that advanced spectroscopic analyses confirmed that their sample achieved a recovery rate of 98.9 percent with a purity of 99.2 percent.

Dr. Sim Ying, the lead author, claimed that the similar performance levels exhibited by their upcycled silicon-based lithium-ion battery and freshly procured ones provide evidence for the viability of the NTU approach.

They anticipate that their silicon recovery technique will significantly propel the advancement of EV battery technology. Furthermore, beyond electric vehicles, there are promising prospects for applications like thermoelectric devices, according to Ying.

The study's findings were published in the journal Solar Energy Materials and Solar Cells.