Rechargeable lithium-ion batteries (LIBs) have emerged as a key technology to meet the demand for electric vehicles, energy storage systems, and portable electronics. In LIBs, a permeable porous membrane (separator) is an essential component located between positive and negative electrodes to prevent physical contact between the two electrodes and transfer lithium ions. Among several types, microporous polyolefin membranes have dominated the commercial separator market for LIBs operated with liquid electrolytes, favored for their chemical and electrochemical stability, high mechanical strength, uniform pore size, and inexpensive manufacturing and materials cost. In this review, we summarize the principles and theoretical background underlying conventional manufacturing processes and newly emerging microporous polyolefin separators. Based on their mechanical and physical properties, as collected from the literature, we introduce a number of processing type-dependent characteristics and universal correlations among their properties. This will provide a macroscopic view on the subject and a guideline for the development of next-generation separators.

Polyolefin separators comprising polyethylene and polypropylene have long been used in commercial Li‐ion batteries because of their electrochemical stability, robust mechanical properties, uniform pore structure, and cost‐effectiveness. However, conventional separators have limitations in withstanding harsh environmental conditions, such as elevated temperatures, owing to their poor mechanical durability. Moreover, with the development of advanced Li rechargeable batteries, these separators are required to overcome new challenges such as preventing the migration of polysulfide intermediates in Li–S batteries and inhibiting the formation of Li dendrites in Li metal batteries. Natural clay minerals have emerged as a viable solution to these issues owing to their porous structure, high mechanical strength, and abundant polysulfide‐capturing Lewis acid sites. However, the manner in which the structural characteristics of minerals influence the separator performance has not been extensively assessed, thereby impeding the development of separators for future high‐performance Li batteries. This review comprehensively outlines various clay minerals and their effects on the parameters and performance metrics of battery separators. Based on this review, a design guide is proposed for mineral‐based separators that could potentially be integrated into next‐generation Li batteries with high energy density and long‐term stability.

To develop highly efficient thermoelectric materials, the generation of homogeneous heterostructures in a matrix is considered to mitigate the interdependency of the thermoelectric compartments. In this study, Cu₂Te nanoparticles were introduced onto Bi₂Te_2.7Se_0.3 n-type materials and their thermoelectric properties were investigated in terms of the amount of Cu₂Te nanoparticles. A homogeneous dispersion of Cu₂Te nanoparticles was obtained up to 0.4 wt.% Cu₂Te, whereas the Cu₂Te nanoparticles tended to agglomerate with each other at greater than 0.6 wt.% Cu₂Te. The highest power factor was obtained under the optimal dispersion conditions (0.4 wt.% Cu₂Te incorporation), which was considered to originate from the potential barrier on the interface between Cu₂Te and Bi₂Te_2.7Se_0.3. The Cu₂Te incorporation also reduced the lattice thermal conductivity, and the dimensionless figure of merit ZT was increased to 0.75 at 374 K for 0.4 wt.% Cu₂Te incorporation compared with that of 0.65 at 425 K for pristine Bi₂Te_2.7Se_0.3. This approach could also be an effective means of controlling the temperature dependence of ZT, which could be modulated against target applications.

In this study, a simple method for quantifying the porous nature based on the permeability of the thin ceramic coating on microporous polyolefin flims used as separators in lithium-ion batteries is demonstrated. The air permeability of the ceramic coating was determined via the ideal laminate theory (ILT), which is widely accepted for multilayered films or well-defined laminates. This study mainly aims at introducing an ILT-based resistors-in-series model with the Gurley method and its potential applications in battery separators. We investigated a few previously reported examples of ceramic-coated separators to compare the air permeability of various ceramic coatings along with their base polyolefin films.

Conductive additives play a crucial role in secondary batteries by providing additional conductive pathways for charge transport, compensating for the inherently low electronic conductivity of active materials. Notably, electronic conductivity is a key factor governing the rate capability of battery cells, as higher conductivity enables more efficient electron transport at fast charge–discharge rates. While lower‐dimensional (0D–2D) additives offer distinct benefits, they often face limitations in maintaining continuous conductive networks and mechanical stability under demanding battery conditions. In contrast, 3D conductive frameworks establish continuous electron‐transport networks that also maintain mechanical stability and interfacial integrity, thereby supporting improved cycle life as well as rate capability. This review highlights the potential of constructing 3D carbon architectures using bio‐derived carbon precursors—a scalable and environmentally favorable approach that produces frameworks with high surface area and hierarchical porosity. The integration of these features positions bio‐derived 3D carbons as promising components for next‐generation batteries, with the potential to improve electrode–electrolyte interface stability while also offering environmental advantages. Overall, bio‐derived 3D carbons are discussed here as a promising design platform for next‐generation batteries, with their practical value depending on how effectively these structural advantages are translated into stable electrode‐level conductive networks.