|Plot of current performance data in the lab for Si/graphene anodes. Source: XG Sciences. Click to enlarge.|
As part of the FY 2012 Phase I Release 3 SBIR/STTR Award program, the US Department of Energy (DOE) has awarded Michigan-based XG Sciences, a manufacturer of graphene nanoplatelets (earlier post), a contract to develop low-cost, high-energy Si/graphene anodes for Li-ion batteries for use in extended range electric vehicle applications. XG Sciences will lead a team that includes battery maker LG Chem Power, Inc. and the Georgia Institute of Technology.
XG Sciences’ Silicon-graphene nanocomposite anode materials have demonstrated significant increases in energy storage capacity over traditional graphite and are manufactured with a commercially-proven, low-cost process using widely-available and economical starting materials. Current performance data from the company shows demonstrated specific capacity of 900 – 2000 mAh/g, with a 1st cycle efficiency of 80+ %.
This DOE contract will accelerate product commercialization by targeting 600 mAh/g reversible anode capacity and 1000 cycle life in 250 mAh cells. Our Silicon-graphene energy storage materials deliver significant improvements in battery cycle life over traditional Silicon-based materials due to a unique and highly-conductive graphene support network. We believe this research will help enable customers to benefit from extended battery run-time in automotive, portable electronics and grid-scale energy storage applications.—Rob Privette, VP Energy Markets
Although they offer very attractive high theoretical energy capacities, silicon electrode materials experience significant volume changes (up to 400%) upon Li ion insertion, leading to electrode pulverization and the loss of the electrical contact, resulting in poor cycle life and rapid capacity fade.
|XGS Si/xGnP nanocomposite: Si particles (white specs) covered by graphene nanoplatelets in agglomerations. Source: XG Sciences. Click to enlarge.|
Nanostructures are widely being explored as a possible solution to this problem, which has retarded the commercialization for silicon-based electrode materials—especially for applications requiring long cycle life, such as EVs or PHEVs.
In a poster presentation at the AABC 2012 conference, XG Sciences noted that its low-cost process for Si/graphene nanocomposite anode material uses the existing xGnP platelet production. Cost is much lower than other methods for Si- containing composite due to the use of low cost micron-size Si and short processing times, according to the company.
XG Sciences’ energy storage materials are based on the company’s xGnP exfoliated graphite nanoplatelets and XG Leaf graphene sheet products that can be formulated into electrodes, with high charge storage and superior current carrying characteristics for batteries, ultracapacitors and fuel cells. Each particle consists of several sheets of graphene with an overall thickness ranging from an average of about 5 nm to about 15 nm, depending on grade. Particle diameters can range from sub-micron to 50+ microns.
The company recently scaled up its production capacity to 80 tons per year.
Earlier this year, the Air Force Research Laboratory (AFRL) selected XG Sciences, which is a spin-out company from Michigan State University, to develop ultrahigh-energy ultracapacitors for use in space energy storage systems. XG Sciences’ technologies were developed in large part at the Composite Materials and Structures Center in the Michigan State University College of Engineering.
Separately, another SBIR/STTR award went to California-based Farasis Energy, for the development of a new, high capacity, high rate cathode material for Li-ion batteries. Farasis Energy’s core technology is based on its manganese rich (MnR) cathode systems. Farasis says that its Gen 1 MnR products offer almost 40% higher energy density to comparable LiFePO4 based systems, with similar cycle life and excellent safety. Farasis Energy’s Gen 2 MnR technology, which is currently under development, will offer its customers as much as 100% greater energy density in the same large cell format.