Meaning
Physical cracking at the grain boundaries of active material particles occurs due to the repeated volume changes of the electrode during charging and discharging. The initiation of micro structural fracture reduces the surface area available for electrochemical reactions and restricts ion pathway continuity. This mechanical damage occurs in both transition metal oxide cathodes and high-capacity anodes over long-term cycling.
Mechanical Stress
Diffusion-induced stresses build up when lithium concentration gradients develop within the active particles during high-rate operation. This pressure exceeds the cohesive strength of the material grains, leading directly to micro structural fracture. The cracking behavior is particularly severe in high-nickel cathode materials, where anisotropic volume changes stress the crystal structure in multiple directions.
Electrical Disconnection
Cracking separates fragments of the active material from the conductive carbon matrix, isolating these regions from the electrical circuit. When micro structural fracture disconnects these grains, they can no longer participate in storing or releasing charge. This isolation directly reduces the overall capacity of the cell and increases its internal resistance.
Electrochemical Acceleration
Freshly exposed surfaces created by fracture interact with the electrolyte, accelerating the formation of secondary passivation layers. This continuous chemical reaction consumes active lithium and electrolyte, leading to rapid performance loss.
