Meaning
The reduction in the glass transition temperature of a polymer through the addition of low-molecular-weight substances constitutes a major phase modification process in material science. This plasticization increases the flexibility and workability of the polymer by increasing the free volume between molecular chains. In battery technology, the absorption of organic electrolyte solvents into polymer separators or binders often induces this effect.
Polymer Behavior
Softening of the polymer binder can weaken the mechanical cohesion of the composite electrode. For example, when an acrylic or polyvinylidene fluoride binder undergo plasticization, the adhesive force holding the active material to the current collector degrades. This mechanical weakening can lead to the delamination of the active layer under the swelling forces of lithiation.
Separator Response
Polymer separators experience increased ductility and reduced tensile strength when exposed to electrolyte solvents. This change makes the separator more compliant but also more vulnerable to penetration by metallic dendrites.
Processing Benefit
Controlled addition of plasticizing agents during the manufacture of solid polymer electrolytes facilitates the extrusion of thin, uniform membranes. This processing advantage allows manufacturers to scale up the production of solvent-free solid-state cells. The resulting sheets of electrolyte maintain high ionic conductivity at room temperature while remaining sufficiently tough for high-speed assembly lines.
