Process development and industrial scale demonstrator for silicon kerf into powder applications

Process development and industrial scale demonstrator for silicon kerf into powder applications

ReSiTec AS is a Norwegian company, owned by Å Energy, that is specialized in the recycling of industrial waste- and side- stream materials, bringing them back to market and into a circular economy. Services comprise research and development of new processes and products, pilot testing and verification, engineering and recovery services/production. The company was founded in 2012 and has several years of experience from recycling cutting materials and kerf from production of silicon blocks and wafers.

In ICARUS, ReSiTec is responsible for two activities: to make the ingots manufacturing industry circular, to upscale and to demonstrate of economical method for raw materials purification and agglomeration pre-treatment. Consequently, its focus is to develop processes and industrial scale demonstrators for the waste streams, silicon kerf, graphite and silicon, making them suitable for the different applications. This is Pilot A in the project, which has the following objectives:

• Develop industrial routes for collection and pre-treatment of silicon, silica and graphite waste streams from ingot and wafer manufacturing
• Build and operate modular industrial scale demonstrators for the process as shown in figure below
• Improve the initial waste product quality by reducing external contamination sources

 

In the solar value chain, silicon kerf loss is generated during the wafering step. For collection a filter press solution is employed at the supplier to gather the silicon kerf loss. Subsequently the material is collected in the form of a moist filter cake, with typical moisture contents reaching up to 50%. Despite the high moisture contents, the appearance of the filter cake is rather dry, due to the high specific surface area of the silicon kerf particles.

ReSiTec has developed an industrial scale processing route to convert silicon kerf from a moist filter cake material into purified and dry fine powder material with a median particle size of ~700 nm. A continuous drying process has been established during the project, as well as a post treatment step.

The purification process (pre-treatment) efficiently reduces aluminum and nickel levels, achieving a purity of at least 3N (excluding light elements) and with remaining moisture contents below 1 wt%. The processed silicon kerf from ReSiTec has been tested both directly into different applications and into the other three pilots planned in the project.

 

Left – Purified and dried filtercake material	Right – continuous drying

 

Left – fine silicon powder material after post processing	Right – particle size distribution of the powder

 

Elemental contents in purified silicon kerf through pre-treatment step vs. non purified silicon kerf	Effect of secondary treatment step on carbon contents in silicon kerf

For testing in other pilots, a simplified processing route was used. For advanced powder applications such as Li-ion batteries and thermoelectric modules, a full-route, yielding a fine powder material, was employed.

In addition, ReSiTec has developed surface treatments for the Li-ion battery application that improve significantly the cycling stability of the material.

After testing for the two applications, the results obtained are very promising and have been presented in conferences (the Advanced Automotive Battery Conference Europe) and published in peer-review journals.

For the Li-ion batteries application, the most promising sample of silicon kerf processed at ReSiTec will be tested in pilot scale (pouch cell). For the thermoelectric module, a generator will be constructed for on-bench testing and validation.