By using the material, silicon dioxide, found in the popular children’s toy and in surgical tubing, engineers have developed a way to make lithium batteries last longer. The team created silicon dioxide (SiO2) nanotube anodes for lithium-ion batteries and found they had over three times as much energy storage capacity as the carbon-based anodes currently being used. It is estimated that these new silicon dioxide infused batteries will last up to three times longer between charges compared to the current industry standard. This has significant implications for both industrial industries as well as for consumer projects including personal electronics and electric vehicles, which are always trying to squeeze longer discharges out of batteries.
The UC Riverside engineering team chose silicon dioxide as the material to focus on because of its abundance, and its environmental friendliness; it is also non-toxic and is found in many other products. The key finding was that the silicon dioxide nanotubes are extremely stable in batteries, which is important because it means a longer lifespan. Specifically, SiO2 nanotube anodes were cycled 100 times without any loss in energy storage capability.[ii] Silicon dioxide has previously been used as an anode material in lithium ion batteries, but the ability to synthesize the material into highly uniform exotic nanostructures with high energy density and long cycle life has been limited.
Many other materials have been investigated as possible anodes for Lithium-ion batteries. Carbon-based anodes such as graphite, 3D graphene sheets, carbon nanotubes (CNTs), and CNT pillared graphene have all indicated possible material systems for lithium-ion batteries. However, while the rate capability of carbon-based anodes is far superior to that of silicon-based anodes, the specific capacity is far less.[iii] A carbon nanotube (CNT) is a tubular structure made of carbon atoms, which has a diameter in nanometers and a length in micrometers. Chemical vapor deposition (CVD) is the most popular way of producing CNTs today. In this process, thermal decomposition of a hydrocarbon vapor is achieved in the presence of a metal catalyst. The process involves passing a hydrocarbon vapor through a tubular reactor in which a catalyst material is present at a sufficiently high temperature (around 600-1200 degrees C) to decompose the hydrocarbon. CNTs are then grown on the catalyst in the reactor, cooled to room temperature and collected.[iv]
Silicon dioxide has previously been used as an anode material in lithium ion batteries, but the ability to synthesize the material into uniform nanostructures with high energy density and long cycle life has been limited. Currently, almost every lithium-ion battery uses a graphite (carbon) anode, which has a specific capacity of 400 mAh per gram. This means the anode has to be relatively large to store a decent amount of power. With the use of silicon-based anodes researchers have successfully built a double-walled silicon nanotube anode that has a capacity of around 4,000 mAh per gram. In other words, this anode is an important precursor to lithium-ion batteries with 10 times their current capacity. Researchers are now focused on developing methods to scale up production of the SiO2 nanotubes in hopes they could become a commercially viable product.[v]
[ii] University of California – Riverside. (2014, May 15). Silly Putty material inspires better batteries: Silicon dioxide used to make lithium-ion batteries that last three times longer. ScienceDaily. Retrieved May 16, 2014 from www.sciencedaily.com/releases/2014/05/140515142839.htm
[iii] Scientific Reports (2014.) Stable Cycling of SiO2 Nanotubes as High-Performance Anodes for Lithium-Ion Batteries. Zachary Favors, Wei Wang, Hamed Hosseini Bay, Aaron George, Mihrimah Ozkan, Cengiz S. Ozkan. Retrieved May 16, 2014. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3986728/
[iv] Ando, Y., Mukul, K., (2010, February 1). Chemical Vapor Deposition of Carbon Nanotubes: A Review on Growth Mechanism and Mass Production.