Deformation and stress in electrode materials for Li-ion batteries

Structural stability and mechanical integrity of electrode materials during lithiation/delithiation influence the performance of Li-ion batteries. Significant dimensional and volume changes are associated with variations in lattice parameters and transformations of crystalline/amorphous phases that occur during electrochemical cycling. These phenomena, which occur during Li-intercalation/deintercalation, Li-alloying/dealloying and conversion reactions, result in deformations and stress generation in the active cathode and anode materials. Such stresses can cause fragmentation, disintegration, fracturing, and loss in contact between current collectors and the active electrode materials, all of which can also expose fresh surfaces to the electrolyte. These degradation processes ultimately lead to capacity fade with electrochemical cycling for nearly all electrode materials, and are some of the major causes for the eventual failure of a Li-ion cell. Furthermore, severe stresses have made it nearly impossible to use higher capacity anode materials (e.g., Si, Sn) in practical batteries and also limit the ‘usable’ capacity of the present cathode materials (e.g., LiCoO2, LiMn2O4) to nearly half the theoretical capacity. Against this backdrop, this review presents an overview of the causes and the relative magnitudes of stresses in the various electrode materials, highlights some of the more recent discoveries concerning the causes (such as stress development due to passivation layer formation), introduces the recently developed techniques for in situ observations of lithiation induced deformations and measurement of stresses, analyses the strategies adopted for addressing the stress-related issues, and raises various issues that still need to be addressed to overcome the stress related problems that are some of the major bottlenecks towards the development of new high-capacity electrode materials for Li-ion batteries.