Electrochemomechanical Fatigue: Decoupling Mechanisms of Fracture-Induced Performance Degradation in Li_XMn₂O₄

Abstract

Decades of Li-ion battery (LIB) research have identified mechanical and chemical culprits that limit operational lifetime of LIB electrodes. For example, severe capacity fade of unmodified Li X Mn 2 O 4 electrodes has been linked historically with Mn dissolution and, more recently, fracture of the electrochemically active particles. Mitigation approaches targeting both effects have prolonged cycle and calendar life, but the fundamental mechanistic sequences linking fracture to capacity fade in Li X Mn 2 O 4 and many other cathode materials remain ambiguous. Here, we investigate specifically the temporal correlations of fracture, capacity fade, and impedance growth to gain understanding of the interplay between these phenomena and the time scales over which they occur. By conducting controlled excursions into the cubic-tetragonal phase transformation regime of Li X Mn 2 O 4 , we find that fracture contributes to impedance growth and capacity fade by two distinct mechanisms occurring over different time scales: (1) poorly conducting crack surfaces immediately hinder electronic conduction through the bulk of the electrode, and ( The deconvolution of these effects in a well-studied cathode material such as Li X Mn 2 O 4 facilitates understanding of the complex relationship between mechanics and electrochemistry in LIB electrodes.