Porous Separator Polymer Coating for Uniform Lithium Metal Deposition

The separator is constructed as a composite structure combining a porous substrate (providing mechanical strength and porosity) with a polymer coating layer (providing lithium ion conductivity and uniform surface coverage). This composite design resolves the contradiction by achieving improved cycling performance through the functional polymer coating while maintaining the structural integrity and manufacturing feasibility of the porous substrate base.

The polymer coating is applied selectively on the surface of the porous substrate, creating a localized functional layer that provides lithium ion conductivity and promotes uniform lithium deposition. The coating covers the substrate surface but does not completely fill the pores, maintaining local porosity for electrolyte infiltration. This local quality modification addresses the cycling performance issue without requiring complete structural redesign.

The polymer coating is applied in a controlled manner to achieve partial coverage of the porous substrate surface. The coating layer provides sufficient surface coverage to promote uniform lithium deposition, but intentionally leaves the pores partially open to maintain electrolyte infiltration pathways. This partial action approach resolves the contradiction by achieving the minimum necessary surface coverage without excessive filling that would block ion transport.

The separator utilizes a porous substrate structure that maintains open pore channels even with the polymer coating present. The porous architecture allows electrolyte to infiltrate through the coating layer and substrate, preserving lithium ion conductivity. The coating modifies the pore structure rather than completely filling it, balancing surface coverage with ion transport requirements.

The polymer coating on the separator acts as an intermediary layer between the electrolyte and the lithium metal negative electrode. This coating provides a uniform surface that guides lithium ion deposition, preventing direct contact between the electrolyte and electrode surface that would cause uneven deposition. The intermediary coating maintains the high energy density benefit of lithium metal while protecting against deposition-related deterioration.

The polymer coating is pre-applied to the separator before battery assembly, creating a prepared surface that promotes uniform lithium deposition from the first cycle. This preliminary action establishes a favorable surface morphology that guides subsequent lithium deposition, preventing the formation of dendrites and uneven structures that would deteriorate the electrode over time.