Deformation and Stresses During Alkali Metal Alloying/Dealloying of SnBased Electrodes

Abstract

Enhancement of energy density and safety aspects of Liion cells necessitate the usage of “alloying reaction”based anode materials in lieu of the presently used intercalationbased graphitic carbon. This becomes even more important for the upcoming Naion battery system since graphitic carbon does not intercalate sufficient Naions to qualify as an anode material. Among the potential “alloying reaction” based anode materials for Liion batteries and beyond (viz., Naion, Kion battery systems), Si and Sn have received the major focus; with the inherently ductile nature of Sn (as against the brittleness of Si) and the considerably better stability in the context of electrochemical Na/Kstorage, of late, tilting the balance somewhat in favor of Sn. Nevertheless, similar to Si and most other “alloying reaction”based anode materials, Sn also undergoes volume expansion/contraction and phase transformations during alkali metalion insertion/removal. These cause stressinduced cracking, pulverization, delamination from current collector, accrued polarization and, thus, fairly rapid capacity fade upon electrochemical cycling. Unlike Si, the aforementioned loss in mechanical integrity is believed to be primarily caused by some of the deleterious firstorder phase transformations and concomitant formation of brittle intermetallic phases during the alloying/dealloying process. Against this backdrop, this review article focuses on aspects related to deformation, stress development and associated failure mechanisms of Snbased electrodes for alkalimetal ion batteries; eventually establishing correlations between phase assemblage/transformation, stress development, mechanical integrity, electrode composition/architecture and electrochemical behavior.