“Schematic representation of electrochemical cycling-induced damage in Si particles in Si-Al
Researchers from the University of Windsor in Ontario have discovered a new means of improving silicon anode durability (when in use with lithium-ion batteries) through the utilization of newly observed self-healing behavior of cracks in micron-sized silicon particles dispersed “in a ductile Al matrix cycled using a high lithiation rate of 15.6 C.”
As some of those reading this will be aware, a major issue with the use of high-capacity silicon anodes in rechargeable lithium-ion batteries is lithiation-induced volume changes in silicon — which results in the fracture and fragmentation of the anode material, and thus with a loss of energy storage capacity.
The new findings — which are detailed in a paper published in the Journal of Power Sources — mean that a potential pathway towards the development of more durable silicon battery anodes has been found.
anodes. (1) Prior to cycling, the microstructure of the electrode depicted a uniform distribution of the Si particles in the ductile Al matrix. (2) As lithiation occurred, the near-surface regions in Si transformed to amorphous from crystalline structure. Crevices were formed in the amorphous layer due to propagation of compressive shear cracks. The crevices also acted as stress concentrators to initiate the cracks in the crystalline interior. The crack surfaces provided easy diffusion paths for the electrolyte reduction products (Li and Cl) that were deposited on the crack flanks. However, the surrounding Al matrix acted as an impediment to crack propagation at the Si/Al interface. (3) When the de-lithiation stage initiated, a fraction of the amorphous structure transformed back to crystalline and at the end of de-lithiation, localized amorphization at the Si crack faces promoted crack closure due to volume expansion. Bhattacharya and Alpas (2016).”
The research paper stated: “By electrochemically cycling these electrodes vs. Li/Li+, crack formation and growth in Si particles during the lithiation/de-lithiation cycles were monitored using analytical microscopy and surface characterization techniques. An interesting self-healing process occurred and consisted of arresting of cracks formed in Si particles by the Al matrix, and closure of cracks during de-lithiation.”
The conclusion offered by the researchers was: “In summary, composite electrode materials consisting of uniformly distributed Si embedded in a ductile and inert phase having high fracture toughness could reduce the propensity for electrode fragmentation and improve battery electrode durability.”
As with all battery-related research, a grain of salt is advised — what goes on in a lab may or not be economically viable, or repeatable for that matter.