Interview with André Oliveira, Battery Innovation Engineer at Nanomakers
What does the Silicon/Carbon composite anode material selection and development consist of?
Most of the Li-ion batteries (LIB) in the market are produced with graphite as anode active material. It has a working potential close to lithium, a very good stability, and a capacity of around 370 mAh.g-1. For next generation of LIB, more energy density is needed, and it could be achieved by increasing the anode active material capacity. That could be done by adding silicon which has a specific capacity of 3,400 mAh.g-1.
However, the use of silicon leads to several issues for the electrode: high volume variations and surface reactions with the electrolyte during cycling. Both phenomena combined greatly decrease the anode cycle life. Side reactions at the silicon surface consume silicon, electrolyte and lithium but could be then electrochemically stable. The most problematic issue is the silicon large volume expansion (300% volume swelling) which cracks particles and exposes new surface to the electrolyte but also disconnects electrode parts at each cycle.
These issues could be solved by integrating silicon nanoparticles, provided by Nanomakers, into a carbon matrix to prevent volume expansion and silicon surface exposure to electrolyte. Indeed, the use of nanoparticles narrows cracks, and the carbon matrix protects silicon particle surface and prevent disconnections without adding an electrochemically inactive mass.
Which will be the role of Nanomakers in the process upscaling of anodes?
The role of Nanomakers in the project is to optimise the anode material composite to reach a stability of more than 500 cycles before 80% capacity loss at 1C rate (meaning a charge in 1 hour and a discharge in 1 hour too) and more than 1,000 cycles before 80% capacity loss at a lower C-rate of C/2 (charge/discharge in 2 hours).
Moreover, as Gigagreen project is based on water-based or solvent-free electrode formulations, Nanomakers develops the formulation protocol to prevent hydrogen emission which could occurs in water-based slurries due to oxidative surface reaction between silicon and water.