Tremendous efforts have been devoted to the development of electrode materials, electrolytes, and separators of energy-storage devices to address the fundamental needs of emerging technologies such as electric vehicles, artificial intelligence, and virtual reality. However, binders, as an important component of energy-storage devices, are yet to receive similar attention. Polyvinylidene fluoride (PVDF) has been the dominant binder in the battery industry for decades despite several well-recognized drawbacks, i.e., limited binding strength due to the lack of chemical bonds with electroactive materials, insufficient mechanical properties, and low electronic and lithium-ion conductivities. The limited binding function cannot meet inherent demands of emerging electrode materials with high capacities such as silicon anodes and sulfur cathodes. To address these concerns, in this review we divide the binding between active materials and binders into two major mechanisms: mechanical interlocking and interfacial binding forces. We review existing and emerging binders, binding technology used in energy-storage devices (including lithium-ion batteries, lithium-sulfur batteries, sodium-ion batteries, and supercapacitors), and state-of-the-art mechanical characterization and computational methods for binder research. Finally, we propose prospective next-generation binders for energy-storage devices from the molecular level to the macro level. Functional binders will play crucial roles in future high-performance energy-storage devices.

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HIGHLIGHTS• The roles of binders in both sulfur host-based and sulfur host-free systems are considered for polymer composite frameworks in lithium-sulfur batteries.• The applications of the existing and potential multifunctional polymer composite frameworks are summarized for manufacturing lithium-sulfur batteries.ABSTRACT Extensive efforts have been devoted to the design of micro-, nano-, and/or molecular structures of sulfur hosts to address the challenges of lithium-sulfur (Li-S) batteries, yet comparatively little research has been carried out on the binders in Li-S batteries. Herein, we systematically review the polymer composite frameworks that confine the sulfur within the sulfur electrode, taking the roles of sulfur hosts and functions of binders into consideration. In particular, we investigate the binding mechanism between the binder and sulfur host (such as mechanical interlocking and interfacial interactions), the chemical interactions between the polymer binder and sulfur (such as covalent bonding, electrostatic bonding, etc.), as well as the beneficial functions that polymer binders can impart on Li-S cathodes, such as conductive binders, electrolyte intake, adhesion strength etc. This work could provide a more comprehensive strategy in designing sulfur electrodes for long-life, large-capacity and high-rate Li-S battery.

Polyurethane nanocomposites incorporated with polydopamine (PDA)-coated graphene sheets (D-Graphene) were fabricated by solution blending. It is found that the interfacial PDA layers not only facilitate the dispersion of the graphene sheets in the polymer matrix, but also strengthen the stress transfer from the polymer matrix to the filler, enhancing tensile and thermo-mechanical properties of the nanocomposites and decreasing the electrical conductivity percolation threshold of the nanocomposites. Furthermore, due to the free-radical scavenger ability of PDA, the nanocomposites also show impressive ultraviolet resistance. Electromagnetic interference (EMI) shielding performance study shows that the PU/ D-Graphene nanocomposite is a promising candidate for light-weight high-performance EMI shielding materials with improved microwave absorption as the dominant EMI shielding mechanism.