Constant dripping wears away a stone: Fatigue damage causing particles' cracking

Abstract Once Li+ ions start mobilizing, the crystalline active particles will persistently endure the internal stresses, which originate from the lattice deformation and will remain until reaching a new equilibrium state. While it is still lack of the fundamental understanding on this effect although the particle cracking has been accepted as a failure mode. Here we demonstrate the degradation of particles' mechanical properties and their influence on cathodes' electrochemical performances with a commercial ∼4 μm LiNi1/3Co1/3Mn1/3O2 single-crystals as the sample materials to simplify the model. As Li+ ions reciprocating, the particle strains induce the generation of the line dislocations and accordingly the aggrandization of these bulky defects, and then eventually lacerate the particles mainly along the (110) plane, which is the cleavage plane for the layer oxides. In the selected tested points, the particle cracking is always accompanied with the inflexion of cyclic stability. Obviously, the crystalline’ fracture-strength is gradually fatigued in every cycle, and eventually can't sustain the internal stress to result in the particle cracking and cyclic-stability plummet, similar to ‘constant dripping wears away a stone’. Our approaches demonstrate that the crystalline active materials are suitable to the fracture-damage model, which is another principle for predicting the maximum of LIB's operational life.