PSI were recently part of an initiative to enhance the performance of rechargeable lithium-ion batteries by improving the silicon anode materials required for the Electric Vehicle industry.

The project focused on enhancing the conductivity of silicon anodes, resulting in faster charge rates and sustained battery capacity during charge and discharge cycles. PSI utilised a wealth of engineering expertise and drew on experiences from previous projects to develop a successful nanocoating procedure in a fluidised bed reactor.

Fluidised bed reactors (FBRs) are the ideal tool for applying specialised coatings on to metal and ceramic powders because the fluid-like state of the bed provides a very uniform environment in terms of temperature and exposure to reactant gases when the FBR is used for Chemical Vapour Deposition (CVD).

This application was concerned with the coatings of anode powders used in lithium-ion batteries. The fluidised bed technology was pivotal to this project to provide the uniform coating by means of efficient heat and mass transfer.

Conventionally graphite has been used as the anode material. It can store 372mAhrg^-1 of charge and has a volume charge, when absorbing lithium ions, of only 12% (ref).

HRTEM Images of CVD coating on carbon silicon material

However, the prize is to store as much lithium-ion as possible in the charging cycle because this determines the battery capacity. When applied to Li-Ion batteries used in electric vehicles this is massively important in terms of vehicle range.

Other materials have a much greater potential. For example, silicon has a specific capacity of 4,200mAhrg^-1.

For this reason, composite graphite-silicon anode powders are much researched.

In this case PSI was tasked with applying a range of allotropes of carbon, of which several feature, in the form of coatings, to composite carbon-silicon particles.

Although silicon has a very high absorption capability for lithium-ions, this comes at the expense of physical expansion and contraction of the anode particles during the charging and discharging cycles. This leads to mechanical fracturing of the particles.

Application by the CVD process of carbon layers by decomposition of hydrocarbon gases in PSI’s in-house FBR supported this research.

Electron microscopy performed by a world-leading university using the latest equipment confirmed the range of carbon allotropes that were available in hydrocarbon pyrolysis in an FBR. The images showed the appearance of well-ordered layers about 20-30nm in thickness.

PSI are equipment manufacturers and offer various scale plant equipment for purchase, from 2.5kg to 100kg+. In addition to this, we also offer our services for research and development purposes, where our pre-production scale plant equipment can be contract-hired by organisations involved in similar developments.