Technology Transfer Department

Application sectors

Problem to solve

The installed photovoltaic power in the world is growing and, since the lifetime of a photovoltaic panel is about 25-30 years, about 60-78 million tons of photovoltaic panels are expected to be disposed of in 2050. Dismantled panels are a resource of useful and valuable materials. Some of them, such as silicon, are classified by the European Union as strategic materials, i.e. materials of high importance for strategic areas but at risk of supply. It is therefore extremely useful to recover silicon from photovoltaic panels at the end of their life in order to be able to re-introduce it into different supply chains such as that of lithium-ion batteries. It is important that recovery technologies have the minimum environmental impact to offer a sustainable way of sourcing this precious material.

Description

The process addresses the fabrication of lithium ion battery (LIBs) anodes from end-of-life or defective photovoltaic panels (PVs). The panels are shredded after removing the frame, the cables and the junction box. Fragments containing silicon are separated from polymeric (EVA) and glass fractions and finally thermally treated. The obtained powder is repeatedly sieved and ground until a material suitable to be used as anode material in LiBs is obtained without any chemical treatment and purification. Nanometric carbon and a polymeric binder are added to the recovered silicon powder. The slurry is deposited and dried on a copper sheet to obtain the LIBs anode. The search for new anode materials as an alternative to the graphite currently used in commercial lithium ion batteries is driven not only by the fact that graphite is a strategic materialfor Europe, but also (and perhaps more so) by the continuous demand for batteries with ever higher energy density and, therefore, by the growing demand for anodes with higher specific capacity than graphite. In particular, silicon offers a theoretical specific capacity of 4200 mAh g-1, which is considerably higher than the theoretical specific capacity of graphite (372 mAh g-1). The innovative process developed, which consists of a suitably studied sequence of grinding and sieving steps, aims to eliminate oxidized components with low electrical conductivity, as well as metallic components with lithiation capability lower than silicon. Meanwhile, the silicon powder is progressively reduced to sub-micrometric dimension in order to obtain, in the electrode construction phase, a high specific surface and a low volumetric expansion of the anode material during operation in the cell. The silicon powder recovered by the process protected by the invention is capable of forming alloys with lithium and can therefore potentially be used as an anode material as a substitute for graphite.

Research group involved