Solar panels have been making the cheapest electricity in history for several years . And not too surprisingly have been growing like crazy. China (the largest coal consumer) actually produces more energy from solar now . Because solar is growing so fast and eating up fossil fuel’s market share, the fossil fuel industry has focused a lot of recent on solar cell waste. Alberta even mandated taxing solar panels because of it. Although solar panels, make waste, it is a trivial fraction of the pollution from fossil fuels. It does not mean the solar industry cannot do better and find innovative ways to recycle. One new way: silicon has been proposed as a promising alternative to graphite in the anode of lithium-ion batteries as it offers a higher theoretical specific capacity. In a new study , silicon–carbon composite anodes for a battery were fabricated from recycled waste from crystalline silicon solar cells using open source 3D printing.

How Hot to Cook a Battery From Recycled Solar Cells

Specifically, the study investigated the effect of pyrolysis (cooking without oxygen) temperature on structural, electrical, and electrochemical properties of the battery component made from recycled solar cells. The aim of this was to suppress the formation of electrochemically inactive silicon carbide. A previous study had shown you can make a battery out of recycled silicon, but they found silicon carbide at 1400 °C -- the temperature they did their cooking. Here the goal was to avoid the useless silicon carbide, while maintaining high electrical conductivity and stable structure. The materials were first 3D printed using a desktop 3D printer. 3D printed anodes were pyrolyzed at 800 °C, 1100 °C, and 1200 °C. The results showed that pyrolysis temperature influences both the microstructure and electrochemical performance of the 3D printed anodes. Pyrolysis at 1200 °C produced a highly conductive carbon matrix without formation of electrochemically inactive silicon carbide. The scientists confirmed their results with x-ray diffraction analysis: at 1200 °C, no silicon carbide peaks appeared. They then threw some other materials science tests at it to be sure. The enhanced graphitization observed in Raman spectra at this temperature, coupled with the reduced charge-transfer resistance in electrochemical impedance spectroscopy, indicates that the carbon network achieved high electronic conductivity while preserving the active silicon phase.

The Bottom Line: A Phone Battery Can Now Be Made From Recycled Solar Cells

Cooking the recycled silicon solar cell material at the right temperature gave the anode had an initial specific capacity of approximately 771 mAh g -1 , with the Coulombic efficiency of 99.9%, and a capacity retention of 61% over 120 cycles. This is really good. The performance achieved here demonstrates an improvement over the earlier SLA-printed PV-silicon anodes pyrolyzed at 1400 °C, which confirms that tuning pyrolysis temperature is a key strategy to obtain the optimal morphology. The next step will be to scale up the process, test over longer time periods and take a deep dive into the scaled economics. It looks like a good new way to make a higher value product (battery) out of solar cells that has reached the ends of its life.