|Used in conjunction with a molybdenum-vanadium-nitride coating, metal foam can deliver a two- to three-fold increase in the energy density in super capacitors.
Image source: IFAM
When it comes to the development and optimization of alternative drive concepts, the open-pored, easily shaped, electrically conductive metal foam produced by Alantum Europe GmbH is providing new opportunities. Whether used as a gas diffusion layer in metal-air batteries or fuel cells, or as a current collector in super capacitors, the innovative material can be adapted ideally to any application, in turn facilitating increased energy densities or longer service lives.
The versatility of the metal foam is the result of a manufacturing process developed specifically by Alantum. Within this process is the production of open porous nickel foam sheets with hollow struts. Definition of pore size is to 450µm, 580µm, 800µm, and 1,200µm. Subsequent annealing keeps the material flexible and easily shaped. Use of the electrically conductive metal foam, in significant quantities, is as a cathode in nickel-metal hybrid (NiMH) batteries, which are state of the art in devices such as electric and hybrid vehicles. In this application, nickel-metal foam also offers optimization potential for increasing energy density; namely by applying a coating of graphite or other powdered materials suitable for energy storage to the open-pored structure in a special sintering process.
|Metal foam offers the potential for increased energy density and improved performance in both nickel-metal hybrid batteries and metal-air batteries. Image source: Alantum|
To achieve improvements in range and acceleration of vehicles, a great deal of research is occurring around the world into battery technology. A promising approach is the use of metal-air batteries, whose performance can enhance through use of the porous material. As a gas diffusion layer, the foam optimizes the flow rate of the metal electrode, such as zinc, with oxygen. This results in more even energy production and power output.
The material is available as pure nickel foam and as metal alloy foam for this purpose. Following production, the latter is coated with a high-alloy, application-optimized metal powder in a patented, stable process. This helps to promote resistance against aggressive atmospheres and corrosion as well as stability when exposed to temperatures of up to 1,000°C.
Super capacitors, as well, are capable of delivering significant improvements to electromobility. This is thanks to their ability to compensate voltage peaks that occur during acceleration and braking, which in turn helps lengthen the durability of batteries and fuel cells. As the so-called supercaps release and absorb energy more quickly than batteries, they do not have such a high energy density.
Whether or not this is an area for improvement, with the use of foam material, was one of the themes of the Alternative Energy Technologies for Transportation (AETT) research project carried. This project was through the Fraunhofer Society in collaboration with the University of Michigan and the Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM) and Alantum Europe as the foam supplier.
Used as a current collector was the metal alloy foam. In contrast to conventional methods, whereby carbon applies to a film, infiltration of the foam was with molybdenum- and vanadium-nitride as an active material. In comparison to carbon, these materials have an energy density that is two, to three, times higher. Thanks to the special structure and large surface of the foam, it is possible to apply sufficient active material to achieve a two- to three-fold increase in the energy density of the super capacitor.
|Used as a gas diffusion layer in fuel cells, metal alloy foam provides optimized equal distribution of the gas, which allows increasing the power density across the entire membrane surface. Image source: Alantum|
Gas Diffusion Layer
Metal alloy foam can also offer a number of advantages when used as a gas diffusion layer in fuel cells. On the one hand, it provides optimized equal distribution of the gas and the resulting increase in power density across the entire membrane surface. On the other hand, sintering of the material to the bipolar plates is possible, in order to achieve a direct electrical connection. An additional advantage is the ability of the metal alloy foam to resist the very aggressive atmospheres that typically exist in fuel cells.
For use as a gas diffusion layer, coating of the material can be with conventional alloys such as stainless steel alloy 316L and CroFer as well as with new, application-optimized metal powders.
Alantum currently produces around four million square meters of nickel foam in China annually. This is in addition to 500,000m2 of metal alloy foam produced in Korea. In order to optimize, further, the material for applications in electromobility, the Munich, Germany-based company is working closely with IFAM in Dresden, Germany. Here, a research laboratory is also available for conducting tests and for the production of samples.
Alantum Europe GmbH