Researchers funded by a South Korean solar panel recycling program have produced silica nanoparticles averaging 109 nanometers (nm) in diameter from sodium silicate derived from end-of-life solar cell powder. They found that blending the particles into graphite anodes raised battery capacity.

The team reacted silicon-containing cell powder from end-of-life panels with sodium hydroxide and water to make a sodium silicate solution. They then used that solution as the starting material in a modified Stöber process, a method that grows silica particles in an alkaline mix of ammonia and alcohol.

Earlier studies that made silica from solar panel-derived sodium silicate mostly used acid precipitation, which the researchers said tends to produce clumped particles. Their alkaline route yielded spherical particles with limited clumping, without surfactants or polymer additives.

Particles made from the solar waste averaged 109 nm, compared with 97 nm for particles made from commercial sodium silicate under the same conditions.

The researchers tested the material in laboratory coin half-cells, which pair the test anode with a lithium-metal counter electrode. An anode of 95% graphite and 5% silica by weight delivered 370.34 mAh/g after 100 cycles at 0.1 A/g, compared with 308.24 mAh/g for pure graphite. The blended anode’s first-cycle Coulombic efficiency, the share of charge recovered in the first cycle, was 86.17%, against 79.14% for graphite alone. At a higher current of 1.0 A/g, the blended anode kept 24.6% of its capacity, about double the 12.5% retained by graphite.

Elemental analysis found sodium at about 4% and aluminum at less than 1% of the atoms measured in the silica.

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