Porous Polyimide Separator for Lithium-Ion Battery Dendrite Suppression

The patent uses porous polyimide film as separator with controlled pore structure. The film is formed by dissolving polyimide in a solvent to create a casting solution, which is then cast and dried to form a membrane with inherent porosity. This porous structure allows ion transport while maintaining the heat resistance and safety benefits of polyimide material.

The patent optimizes multiple parameters including polyimide molecular weight (intrinsic viscosity 0.5-2.0 dL/g), solvent type and amount, casting temperature, and drying conditions to achieve uniform pore distribution. By controlling these parameters, the film attains both the desired pore uniformity (30-80 nm pore size) and the thermal stability characteristic of polyimide.

The patent creates a separator with non-uniform pore distribution where the pore size and density vary through the film thickness. The surface near the electrode interface has optimized pore characteristics (30-80 nm) that promote uniform lithium ion flux, preventing localized concentration gradients that lead to dendrite formation, while the bulk structure maintains high ionic conductance.

The patent uses polyimide as the base material combined with a porous structure formed through controlled solvent evaporation. This composite approach combines the excellent electrochemical stability and thermal resistance of polyimide with a tailored porous architecture that enhances ionic conductance while suppressing dendrite growth through uniform pore distribution.

The patent divides the separator into functional zones with different pore characteristics. The film is constructed with a skin layer having smaller pores (30-80 nm) for dendrite suppression and a bulk layer with larger pores for high ionic conductance. This segmentation is achieved in a single casting process by controlling solvent evaporation gradients, avoiding the need for multiple lamination steps.

The patent creates pore size gradients through the film thickness dimension rather than using multiple discrete layers. By controlling the casting and drying conditions, a continuous transition in pore size from the surface to the bulk is achieved, providing functional differentiation without the manufacturing complexity of assembling multiple layers.