Separator design plays a critical role in battery recycling, particularly in closed-loop systems where materials are recovered and reused with minimal degradation. The choice of separator architecture influences shredding compatibility, pore structure retention, and ease of separation from electrodes—all of which determine the feasibility and efficiency of recycling processes. Two prominent separator designs, polyethylene/polypropylene (PE/PP) trilayer structures and ceramic-coated separators, exhibit distinct behaviors during recycling, each with advantages and limitations in terms of mechanical stability, thermal resistance, and material recovery.

PE/PP trilayer separators are widely used in lithium-ion batteries due to their balanced mechanical strength and thermal shutdown properties. The typical construction consists of a PP layer sandwiched between two PE layers, providing a melt temperature gradient that enhances safety. During shredding, the mechanical properties of PE/PP separators allow them to fracture cleanly without excessive elongation, reducing the risk of fibrous entanglement with other components. However, the low surface energy of polyolefins complicates their separation from electrode materials, often requiring aggressive solvent treatments or thermal processing to dislodge adhered particles. The pore structure of PE/PP separators, typically created through dry or wet stretching processes, can collapse during high-temperature recycling steps, necessitating careful control of processing conditions to preserve porosity for reuse.

Ceramic-coated separators, on the other hand, incorporate inorganic particles such as alumina or silica applied to one or both sides of a polyolefin substrate. The ceramic layer improves thermal stability and wettability but introduces challenges during recycling. Shredding ceramic-coated separators generates fine particulate debris that can contaminate other recycled streams, requiring additional filtration steps. However, the ceramic coating often acts as a sacrificial layer, protecting the underlying polymer substrate from complete degradation during mechanical processing. The pore structure of ceramic-coated separators tends to be more resilient to compression and heat, making them better suited for processes where pore integrity must be maintained for direct reuse. The binder systems used in ceramic coatings—typically aqueous-based acrylics or PVDF—can be selectively dissolved or thermally decomposed, enabling cleaner separation from electrodes compared to uncoated polyolefins.

Binder systems in both separator types significantly impact recycling efficiency. PE/PP separators rely on the inherent properties of the polymers for adhesion control, whereas ceramic-coated separators use polymeric binders to anchor the inorganic particles. Water-soluble binders, such as carboxymethyl cellulose or styrene-butadiene rubber, facilitate easier separation in aqueous recycling processes. In contrast, PVDF-based binders require polar aprotic solvents like N-methyl-2-pyrrolidone for dissolution, increasing process complexity and cost. The choice of binder affects the purity of recovered separator materials, with solvent-based recovery methods generally yielding higher-purity polymers but at the expense of greater energy input and chemical usage.

Solvent-based recovery methods for separators involve selective dissolution of binders or the separator matrix itself. For PE/PP separators, nonpolar solvents like xylene or cyclohexane can dissolve the polymer at elevated temperatures, allowing filtration of undissolved electrode materials. This approach is effective for producing high-purity polyolefins but risks altering the molecular weight distribution of the polymers, potentially compromising their mechanical properties upon reprocessing. Ceramic-coated separators benefit from solvent systems that target the binder without dissolving the ceramic or polyolefin components, enabling stepwise recovery. The challenge lies in solvent recovery and minimizing cross-contamination between material streams.

Melt-processing recovery methods, such as extrusion or hot pressing, are more energy-efficient but often result in lower-purity outputs. PE/PP separators can be melted and filtered to remove electrode debris, but the process degrades the pore structure, limiting the recycled material to non-separator applications unless supplemented with pore-forming additives. Ceramic-coated separators present additional difficulties in melt processing due to the abrasive nature of inorganic particles, which can damage processing equipment. However, melt processing is advantageous for recovering the polymeric fraction of separators in a form suitable for injection molding or other non-battery applications where pore structure is irrelevant.

Purity requirements for reused separator materials depend on the intended application. For direct reuse in new batteries, separator materials must maintain consistent pore size distribution, mechanical strength, and electrochemical stability. Solvent-based methods are more likely to meet these requirements but at higher operational costs. For downgraded applications, such as plastic composites or non-critical components, lower-purity materials from melt processing may be acceptable. The presence of residual electrode materials or binder fragments must be carefully controlled to prevent performance degradation in either case.

Comparative analysis of separator recycling reveals tradeoffs between material recovery efficiency and process sustainability. PE/PP trilayer separators offer simplicity in material composition but require energy-intensive steps for clean separation. Ceramic-coated separators provide better thermal and mechanical resilience during recycling but introduce complexities in handling inorganic residues. Advances in binder chemistry, such as the development of thermally cleavable or enzymatically degradable binders, could further enhance the recyclability of both separator types. Closed-loop recycling systems must balance these factors to achieve economically viable and environmentally sustainable separator recovery. Future separator designs may incorporate reversible crosslinking or modular architectures to facilitate disassembly, further improving compatibility with emerging recycling technologies.