ICMCTF2012 Session A3-2/F8-2: Coatings for Fuel Cells & Batteries

In this study, Al element was added into Si matrix as the buffer (Si-10Al, Si-25Al, Si-45Al) by co-sputtering to prevent the drastic volumetric expansion of pure Si thin film anode during lithiation and delithiation at high temperature (55°C). Increasing Al content, the electrochemical reaction of Si-xAl anodes would transfer from Si-Al co-dominated to Al dominated and decreased the capacity of first cycle. After the first cycle testing, the anode with lower Al content showed the capacity fading result from impendence increased and electrochemical reaction degraded. In addition, the higher diffusion velocity of lithium ions raised the total capacity and decreased the initial reaction voltage and cycle stability. After annealing, Si-25Al anodes had excellent electrochemical performance at high temperature then as-deposited.

In this talk, we will cover recent advancements in electrified vehicles. In addition, we will look at the critical role surface coatings take on in terms of making current lithium ion batteries function, and we will discuss associated open questions.

Compared to graphite and composite plates, metallic bipolar plates (BPPs) for polymer electrolytic membrane fuel cells (PEMFCs) have many advantages due to their high strength, mechanical durability and electrical conductivity, even for the minimum thickness required to achieve weight and space savings essential for transport applications. However a protective, electrically conductive coating is required to inhibit corrosion, ensure continued electrical functionality and adequate longevity in the aggressive electrochemical environment of the fuel cell.

Maximising system efficiency requires the minimisation of electrical impedance, decreasing parasitic losses. Combined with the reduced plate thickness, this supports an overall reduction in stack size. Power density [kW/kg] is enhanced as the mass of the coated plates is minimised, combined with easier thermal management and reduced packaging requirements, both especially attractive for automotive applications of PEM fuel cells. End of life considerations are also addressed by the potential for conventional re-use and ultimate recyclability of coated metallic plates. Coatings also play a role in the management of water within the cell, however the requirements are complex: hydrophilicity of the coated plate may offer advantages at start up, under low RH conditions, whereas when a stack is operating at high power and approaching 100% RH a hydrophobic surface may assist in the clearance of the water from the cells.

Closed field unbalanced magnetron sputter ion plating (CFUBMSIP) produces dense, well adhered coatings, and both transition metal nitrides and graded, nano-composite, non-hydrogenated amorphous carbon, demonstrating the combination of properties required in this application. The quality of the coatings allows coating thickness to be minimised (typically <1micron) while still providing adequate functionality and longevity, and of course this is also critical to the minimisation of production costs. Ultimately this technology is compatible with low-cost manufacturing techniques similar to those already employed for many automotive parts.