Meaning
Crystallographic divergence between adjacent phases or layers generates interfacial shear and tensile forces when atomic planes attempt to maintain structural continuity across a domain boundary. In secondary battery cathodes, lattice mismatch stress arises as lithium extraction alters unit cell dimensions unevenly across phase boundaries. The magnitude of this internal stress scales with the difference in lattice constants and the elastic modulus of the host material.
This mechanical stress governs interfacial coherence, stopping when microcracking or dislocation networks relieve strain through structural failure.
Interface Movement
Phase boundaries moving through cathode particles generate localized mechanical force fields. When lithium ions depart, the lattice shrinks unequally along distinct crystallographic axes. High strain localized at these moving fronts drives mechanical degradation and alters intercalation kinetics.
Structural Fracture
Repeated volume shifts during cycling cause internal stress accumulation beyond the material yield limit. Microcracks initiate at primary grain boundaries, breaking electrical contact between adjacent crystallites. Secondary particle disintegration accelerates electrolyte penetration into particle cores, increasing side reactions and impedance growth.
Material Mitigation
Compositional grading reduces localized mechanical strain by smoothing lattice parameter transitions across active particles. Core-shell cathode architectures utilize gradual concentration gradients of nickel and cobalt to buffer crystallographic mismatch. Surface coatings offer mechanical reinforcement that suppresses interfacial delamination.
Elemental doping alters unit cell dimensions, lowering the peak stress developed during complete lithium extraction.
