From Michael Kraft and Coretecs VP of Technology article yesterday !!! The Future is very bright for Coretec !!!
Turning Potential to Reality
The development of silicon anodes for lithium ion batteries has also been hampered by commercially scalable methods to produce nanostructured materials with well-defined size and morphology, with characteristic sizes below 150 nm. Traditional top-down methods, including ball milling, are inexpensive and yield silicon materials with high degrees of agglomeration, relatively large particle sizes, and poorly defined morphologies and surfaces. Metal assisted chemical etching is an alternative method that has been explored to synthesize silicon nanomaterials. Control over the morphology, etching direction, mass transfer issues, and the requirement for highly toxic reagents such as hydrofluoric acid limit the commercialization of that method. Meanwhile, bottom-up methods such as chemical vapor deposition (CVD) methods have also been the subject of intense exploration. CVD-based synthesis yields well-defined particle sizes and a diverse array of nanostructured architectures including nanoparticles (NPs), nanowires (NWs), and thin films. A major hindrance to using CVD methods has been high capital cost, low yields, and the use of hazardous and pyrophoric gaseous silicon feedstocks such as silane, SiH4.
The solution may lie in a silicon-carbon hybrid anode, made with nanostructures that store more lithium ions, while reducing the potential for damage as the silicon expands. These hybrid nanostructures include silicon-coated carbon nanotubes, core-shell nanostructures, and carbon coated silicon nanowires grown by electrospinning or by the vapor-liquid-process. Cyclohexasilane, CHS, enables commercially viable approaches to manufacture these nanostructures due to its ability to be readily functionalized, more ideal handling conditions, and more favorable reaction conditions. All of these merits could result in single-step processing and roll-to-roll manufacturing. This “drop-in” replacement to existing manufacturing processes would offer a means to reduce costs and avoid using CVD methods that have high capital costs.
The figure below highlights the merits of this approach, illustrating that with relatively low silicon incorporation into the anode structure, an increase in the energy density by roughly 3x is readily achieved, while maintaining good cycle life.2
Moreover, the resulting silicon nanostructured morphology can be readily tailored to deliver nanofibers or nanoparticles with a desired size and conductive carbon additive. Silicon thin films are also a possibility, and we envision deposition mechanisms that alleviate some of the delamination issues that have plagued previous efforts.
