Researchers at the Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT) have successfully recycled silicon from solar panels and repurposed it to make superior-performance lithium-ion batteries. This approach is not only sustainable but also low-cost and paves the way for repurposing solar panel components at the end of their life. 

The recent surge in solar panel installations is a great move away from fossil fuels. Still, it is also the beginning of a worrying trend – the colossal amount of waste generated at the end of three decades when the panels reach the end of their product life. 

Researchers around the world are, therefore, working on identifying suitable roles for individual components. Metals like copper and silver used in solar panels are likely to have high demand three decades from now, but repurposing easily available silicon has been a challenge so far. 

A team led by CUI Guanglei, a professor at QIBEBT and the director of the institute’s Applied Energy Technology Division, has now found a sustainable and low-cost solution: using it in lithium-ion batteries. 

Lithium batteries with silicon anodes

Conventionally, lithium-ion batteries use graphite anodes. Research has shown that silicon anodes help lithium batteries deliver a better energy density. However, the challenge with silicon anodes is that the material is prone to significant expansion and reduction in volume during the charge-discharge cycle. 

This results in mechanical fractures in the anode and degraded battery performance. Under CUI’s guidance, the research team used micrometre-sized silicon (uM-Si) particles to make the anode. Instead of working to build micrometre-sized particles, the team repurposed silicon from used solar cells, making the approach more sustainable in the long run. 

“The sustainable sourcing of silicon from discarded solar panels mitigates both the economic and environmental impacts of photovoltaic waste,” said Dong Tiantian, a researcher at QIBEBT, who was involved in the work. “Converting waste into valuable battery components significantly reduces the cost of lithium-ion batteries and increases their accessibility.”

When tested for performance, these batteries with uM-Si had better electrochemical stability and maintained a coulombic efficiency of 99.94% even after 200 charge-discharge cycles.  

a) mixed inorganic-organic SEI in traditional electrolyte; b) Rigid-flexible coupling SEI in our electrolyte. Image: QIBEBT. 

Secret sauce: The electrolyte

The size of the silicon anodes did not make all the difference. The researchers also tweaked the electrolyte’s constituents, which helped deliver this superior performance. 

The team used a 3M solution of LiPF6 electrolyte dissolved in a 1,3-dioxane and dimethoxyethane solution mixed with a volumetric ratio of 1:3. The unique chemical formulation helps form a solid-electrolyte interphase (SEI) that holds together silicon particles, even when they are fractured during charge-discharge cycles. This aids in maintaining the ionic conduction and keeping unnecessary reactions to a minimum. 

The team tested the cell pouches with uM-Si and a new electrolyte for 80 cycles to test whether the battery would also maintain its performance in harsh conditions. The cells delivered an energy density of 340.7 Wh per kg, which is impressive for a lithium-ion battery. 

Batteries developed using this technology can work in harsh conditions and be deployed for a wide range of functions, from powering electric vehicles to storing energy for the grid. 

“By using recycled materials and advanced chemical engineering, we have demonstrated that high-performance and environmentally sustainable lithium-ion batteries are not only possible but also within reach,” said Cui in a press release. 

The research findings were published recently in the journal Nature Sustainability.