PNNL Researchers Developing High-Capacity Silicon Anode Material Using Micrometer-sized Particles with Nanopore Structure; 1600 mAh/g After 40 Cycles
|transmission electron microscopic (TEM) images of silicon anode morphologies: a) original porous silicon and b) porous silicon coated with nano layer of carbon. Source: PNNL. Click to enlarge.|
Scientists at the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) have developed a silicon-based anode material for Li-ion batteries using micrometer-sized silicon particles with a nanopore structure. The material shows reversible capacity of more than 1,600 mAh/g after 40 charging/discharging cycles.
With a theoretical capacity some 10 times that of graphite, silicon anodes could contribute to a doubling of the capacity of graphite-anode Li-ion batteries. However, a silicon anode experiences a large volume expansion during lithium-ion insertion and a consequent shrinkage during extraction; this leads to severe particle pulverization, resulting in quick failure of the electrode structure and resulting capacity fade with cycling. Accordingly, a numerous efforts are underway to devise a structure and a material resistant to those changes.
Dr. Jason Zhang and the PNNL research team are addressing that challenge by designing a silicon particle architecture that would maintain structural integrity. The porous structure of the Si helps accommodate the large volume variations that occur during the Li insertion/extraction processes.
Chemical vapor deposition (CVD) of carbon coatings and highly elastic Ketjen Black (KB) carbon were used to improve the electrical conductivity throughout all cycling stages. The team placed these anodes between graphene—planar sheets of bonded carbon atoms—to maintain strong electrical contact between silicon particles.
The combination of the nanopore structure, CVD-coated carbon on the Si surface, and the elastic carbon (KB) among the silicon particles provides a cost-effective approach to utilize the large micrometer-sized Si particles in Li-ion batteries.—Xiao et al.
The PNNL research team continues to improve the performance and long-term stability of the silicon anodes from 40 to 50 charging/discharging cycles today to a goal of about 500 cycles in the future. One solution may be the development of a better binder that can maintain improved mechanical and electrical contact. This method has potential for much greater cyclability while maintaining high energy density.
Xiao J, W Xu, D Wang, D Choi, W Wang, X Li, GL Graff, J Liu, and J Zhang (2010) Stabilization of Silicon Anode for Li-Ion Batteries. Journal of The Electrochemical Society, doi: 10.1149/1.3464767