Industry Market Trends
Graphene: Tiny Particles are Making a Big Impact on Batteries
May 3, 2013
Roadmap, speculating as to what the next generation of lithium-ion batteries might look like, they suggested silicon anodes. It has been well known for some time that silicon can store a great deal of lithium, an attribute that could provide a lithium battery with unprecedented storage capacity. The problem was that no one knew how to make one of those that wouldn't self-destruct after a few dozen cycles. Technically speaking, the term is self-pulverization, which comes about as the result of the silicon swelling in size when loading up with lithium, and then shrinking back down when unloaded. Not long after, a team of researchers at Northwestern University, led by Professor Harold H. Kung, published a paper in the journal Advanced Energy Materials, which said that by supporting silicon in a nano-composite graphene matrix, a high-performance battery could be produced using a silicon anode that could theoretically achieve a dramatic improvement in capacity as well as in charging time. They predicted that this technology could be expected to hit the market in three to five years. They were wrong. Eighteen months later, XG Sciences of Lansing, Mich., a company that spun off from Michigan State University, made an announcement. They had been producing graphene platelets for a variety of applications since 2010. Graphene is the basic building block of graphite which consists of a single layer of atoms. It has incredible properties. Besides being the strongest material known to man, it is also quite flexible and highly conductive both thermally and electrically. No surprise then, that the two scientists, Andre Geim and Konstantin Novoselov, from the University of Manchester who first extracted it, in tiny quantities, using adhesive tape, won the 2010 Nobel Prize for doing so. XG Sciences developed an efficient and economically viable production process, capable of producing 80 tons of graphene per year, the world's largest output. It's been used for everything from structurally reinforcing plastic materials, to thermally conductive paper used as lightweight heat sinks for electronics (XG Leaf), to anti-wear additives for lubricants, to additives used to improve electrical conductivity in batteries. Most of their product is distributed in powder form to over 600 customers in 32 countries, who then incorporate it into their various products. They have, by now, licensed the manufacturing process to two manufacturers: Cabot and POSCO. XG then brought in Rob Privette to expand their line of energy-related applications for the material I spoke with Rob about their latest announcement, which appears to fulfill the expectation of that DoE roadmap for electric vehicles as well as some of the claims made by the Northwestern team. Starting with their existing production process, and taking advantage of the unique combination of properties that graphene has to offer -- namely its strength, flexibility and electrical conductivity -- XGS was able to produce a nano-composite anode that involves silicon particles, wrapped with graphene platelets. The silicon still swells in size when it absorbs lithium, only with this super-strong and flexible structure holding it together, it does not break up as it did before. Instead, it exhibits impressively durable cycle life. The result is an active battery material with a specific storage capacity that is four times greater than the current state of the art, based on ordinary graphite. The powdered material is moistened to form a slurry, which is then used to coat a foil electrode. According to the company announcement:When the U.S. Dept. of Energy (DoE) first put together their Electric Vehicle
"Our new Silicon-graphene anode material, when used in combination with our existing xGnP® graphene products as conductive additives, provides significantly higher energy storage than conventional battery materials. This is great news for applications like smartphones, tablet computers, stationary power, and vehicle electrification that use rechargeable lithium-ion batteries. We are working with battery makers to translate this exciting new material into batteries with longer run-time, faster charging and smaller sizes than today's batteries."The exact performance achieved will depend on the specific formulations used by the battery makers. Batteries made using this anode exhibit several characteristics that have long been considered "holy grails" of battery makers. These include:
- high capacity - 1500 mA-hr/g as opposed to 372 for graphite.
- stable performance over its cycle life,
- 85 percent first cycle efficiency.