Meaning
Interface between two crystallites of varying orientation within a polycrystalline material. A grain boundary acts as a site for atomic mismatch and structural strain that deviates from the perfect lattice. It greatly influences the mechanical and electrochemical behavior of solid state electrolytes and cathode particles.
Ionic Transport
Disordered regions at the junction of crystals often present a barrier to the movement of ions. In ceramic electrolytes, the grain boundary resistance typically exceeds the resistance of the bulk crystal. Reducing this impedance requires specific sintering profiles to ensure tight contact and minimal secondary phases at the contact points.
Mechanical Integrity
Fracture frequently initiates at the intersection of grains due to concentrated stresses. A strong grain boundary prevents the propagation of cracks during the volume expansion of active materials. If the adhesion between crystals is weak, the electrode will pulverize over many charge cycles.
Impurity Concentration
Segregation of non active elements occurs preferentially at these internal surfaces. Because the grain boundary provides more open space than the lattice, it traps contaminants that may cause side reactions. Controlling the chemical purity at the interface is a primary goal in the production of high performance battery ceramics.
Even small amounts of calcium or silica at the grain boundary can block lithium paths and cause the resistance to rise. High purity precursors are used to minimize these effects and ensure that the conductivity of the final ceramic part meets the specifications required for automotive applications.
