Industrial scale silicon-carbon composites adapted to battery grade anode material

Energy storage is a bottleneck towards mass adaption of renewable technologies and electrical vehicles. Electrochemical systems in form of Li-ion batteries are the most established and effective energy storage solutions found today. The performance of Li- ion batteries is fundamentally linked to the properties of its constituent materials. As the demand for better and cheaper batteries increases so does our quest to improve the properties of these materials. Todays anode material is graphite with a specific charge capacity of close to 400 mAh/g. Silicon has a theoretical charge capacity of 10x graphite, that is 4000 mAh/g. However, due to an enormous mass expansion during charging, silicone anodes disintegrate. A Si/C composite has shown good results and promising charge capacities have been obtained in half cell testings. Full battery cell testings with commercial cathode materials have started and show optimistic results. The further work is concentrated on optimization of the silicon and graphite material, and testing of different binder- and electrolyte solutions. Prodction of silicon with different particle size and morhology have also been focused. A selection of silicon-based alloys have also been tested. Finally full cell testing of the different qualities with a selection of cathodes have been focused.

Prosjektet har vært essensielt for forståelsen av silisium som anodemateriale i Li-ion batterier. Forståelsen og den økte kompetansen internt og eksternt har igjen vært essensiell for optimaliseringen av Elkems battery grade silisium. Prosjektet har også dradd stor nytte av samarbeid med internasjonale batteriprodusenter og forskningsmiljøer innen Li-ion batterier. Resultater fra prosjektet har vært presentert ved flere internasjonale konferanser; som poster og som foredrag. En velfungerende silisiumbasert anode i Li-ion batterier vil bidra til økning av batteriets lagringskapasitet.

A composite of silicon and carbon as anode material in Li-ion batteries is accepted as one of the most promising short term routes towards higher battery capacities. Elkem is a world leading producer of silicon with a low carbon emission footprint. Together with IFE and Sintef they want to develop an environmentally friendly, high capacity anode for Li-ion batteries. Varta Microbatteries will contribute with verification that the anode material is compatible with industrial processes and demands. Battery silicon is a main strategic research area for IFE, with several ongoing projects. The project aims to establish Elkem as a vendor of silicon for the battery industry. Through the BiA IPN SiNode, Elkem, in collaboration with IFE and SINTEF, has demonstrated that the material shows good cyclability in half cells, but that Li trapping mechanisms related to excessive surface electrolyte interface (SEI) formation are still observed. The SiCAnode project aims to reduce these mechanisms to a level where a full cell, not just half cell, can be cycled for >2000 cycles. The extreme expansion of silicon, as well as the unstable SEI formed on the silicon surface has proven to make cycling of the silicon extremely challenging. Three main approaches will be followed to reduce these problems. First, the right choices of electrolyte additives and binders have been demonstrated to have good effects on cyclability. Second, carbon composites can partially buffer the expansion and protect surfaces. Third, using alloys or suboxides rather than pure Si can stabilize the particles, giving less expansion and more stable SEI. The project will include industrial material synthesis and characterization methods, electrode slurry mixing and deposition as well as electrochemical testing, in order to find an optimal recipe for the use of Elkem silicon in a Li-ion battery.