This Small Business Innovation Research Phase I project proposes to develop and commercialize new types of silicon nanowire anodes which may be used to safely store large amounts of lithium for many types of lithium batteries. The key innovation involves unique functionalization and integration methods that enable nanowire anodes to be cycled reversibly for thousands of cycles without mechanical failure, agglomeration, or deleterious side reactions. Silicon nanowires will be fabricated via electroless etching, and chemically or electrochemically functionalized to improve their performance and capacity retention in a lithium-ion battery. The objective of this work is to develop novel silicon composite anodes that may undergo over 200 deep cycles with capacities of at least 1000 mA.hg-1.
The broader impact/commercial potential of this project is to develop high capacity anode rechargeable lithium batteries with capacities of over 1000 mA.hg-1, which represents approximate doubling of cell capacity without a significant change in manufacturing or cost. There is a critical need for high energy density rechargeable batteries for next generation hybrid vehicles and fully electric vehicles. In a recent report, the U.S. Department of Energy pointed out that the primary obstacles to the widespread introduction of lithium-based batteries for electric vehicles are the relatively low specific energy and the relatively high cost per kWh. The proposed integration and surface engineering methods will address these problems allowing the safe storage of lithium in silicon anodes for current and future generations of lithium batteries.
This SBIR Phase I project focused on using surface modification methods to create composite (silicon and graphite) anodes for rechargeable lithium-ion batteries. While silicon has a 10× greater capacity than graphite, its practical use as an anode is prohibited due to mechanical problems (swelling, pulverization) and unwanted chemical reactions at silicon surfaces. This work shows that nanoscale silicon can sustain the volumetric cycling without mechanical failures and surfaces may be controlled to promote adhesion, prevent unwanted side reactions, and facilitate lithium-ion transport. Silicon nanostructures, including nanowires and nanoparticles, were fabricated and native oxide surfaces were removed allowing electrochemical or chemical grafting. These surface-engineered silicon nanostructures were integrated with graphite and binders to create composite anodes. Over 50 types of surface chemistries and methods were evaluated in half cell experiments and over 250 prototype lithium-ion coin cells were prepared and evaluated using factorial experimental design. Our approach relies on wet processes to modify surfaces of silicon nanowires resulting in a significant improvement in charge capacities and improved reversibility over hundreds of cycles. We demonstrate surface-engineered silicon nanoparticles can be used to create composite anodes which show reversible capacities over 1000 mA·hg-1 for over 250 cycles. Furthermore, the surface modified anodes show a 39% increase in full cell specific capacity compared to cells with conventional graphite anodes for more than 500 cycles. The broader impacts of higher capacity lithium-ion batteries will be quickly realized in portable electronics and electric vehicles. Lithium-ion batteries have revolutionized portable communications and electric vehicle power sources, yet their materials of construction have remained essentially unchanged since the mid 1980â€™s. If successful, the commercialization of surface-engineered silicon nanoparticles in lithium-ion anodes would result in 30 to 40% capacity gains along with an approximately 20% drop in cost per watt. Cell phones, tablets, and laptop users (~70% of the world population) could use portable devices for longer periods between charging intervals. Likewise the technology could have a profound effect in displacing the hundreds of millions of gasoline or diesel-powered vehicles that burn more than 200 billion gallons of fuel each year. Electric vehicles with lithium-ion batteries could increase driving ranges by 40% and improve their cost competitiveness with gasoline-powered vehicles. Electrochemical Materials has strong relationships with major specialty chemical manufacturers, battery materials providers and battery manufacturers and intends to leverage NSF funds to commercialize their innovative capacity-enhancing anode material.