Development of design strategies for conjugated polymer binders in lithium-ion batteries

Abstract

Lithium-ion batteries (LIBs) are complex electrochemical systems whose performance is determined by the proper design and optimization of its individual components, such as active materials, separators, polymer binders, electrolytes and conductive additives. In the quest for high-energy and high-power density batteries and next-generation ultrahigh-capacity battery electrodes, industry and academia have worked hand-in-hand over the last few decades, developing strategies for improving the performance of each component in an LIB. However, only recently has the development of multifunctional polymer binders become a focus, with the goal of providing additional functionality beyond simple mechanical adhesion. Polymer binders, exemplified by poly(vinylidene fluoride) (PVDF), are typically an inactive component in a composite electrode that does not contribute to capacity. Moreover, limited binding strength, poor mechanical properties and the absence of electronic and ionic conductivity make PVDF inadequate for application in emerging high-capacity and highpower density batteries. In this regard, conjugated polymers have gained attention as conductive polymer binders and/or coatings for the cathodes and anodes in LIBs. The ability of conjugated polymers to transport both electronic and ionic charge carriers endows them with mixed electron and Li + ion transporting properties in an LIB. Based on the enormous potential of conjugated polymer binders to enhance the performance of LIBs, in this review, we present an overview of conducting polymer binders/coatings and their chemical design strategies, developed in the last decade, for use in LIBs.

Polymer design for solid-state batteries and wearable electronics

“…LiNi 0.8 Co 0.15 Al 0.05 O 2 , NCA) when cycling at high rates, meaning these binders could have an impact on fast-charging battery technology. 177 Most electronically conductive polymers are semiconductors with extended conjugated pi systems; their conductivity is low (10 −10 to 10 −5 S cm −1 ) in the neutral state but improves signicantly on doping (up to 10 5 S cm −1 ). As conjugated polymers tend to be hydrophobic, their ionic conductivities and adhesion with polar electrode active materials are usually poor; however, decorating them with polar or charged side chains can improve both properties.…”

“…LiNi 0.8 Co 0.15 Al 0.05 O 2 , NCA) when cycling at high rates, meaning these binders could have an impact on fast-charging battery technology. 177 …”

“…As conjugated polymers tend to be hydrophobic, their ionic conductivities and adhesion with polar electrode active materials are usually poor; however, decorating them with polar or charged side chains can improve both properties. 177 It has been proposed that polymers with electronic and ionic conductivity exhibit a synergistic effect that enhances both transport mechanisms. 178 Accessing mixed ionic-electronic conductors in polymer binders is clearly a useful target where optimisation of both conductivity pathways in composite electrodes is essential.…”

Measuring Heat Dissipation and Entropic Potential in Battery Cathodes Made with Conjugated and Conventional Polymer Binders Using Operando Calorimetry

“…To increase the overall conductivity of the electrode, conjugated polymers can be used as battery binders in place of traditional insulating polymers, and in fact, conjugated polymers have been widely investigated as both cathode and anode binders. − While semiconducting polymers have wide band gaps and are insulating in their neutral forms, during battery cycling, the binder can be electrochemically oxidized (cathode, p -type) or reduced (anode, n -type) so that it becomes electrochemically doped and conducting. When an electron is removed from the highest occupied molecular orbital (HOMO) by oxidation, the conjugated polymer becomes p -doped.…”

Unlocking sustainable power: advances in aqueous processing and water-soluble binders for NMC cathodes in high-voltage Li-ion batteries

“…8,9 Recently, there has been a surge in attention towards the binder, despite its relatively modest mass contribution (2–5 wt%) in the electrode preparation. 10,11 The binder serves a dual function in facilitating adhesion between active materials and conductive additivies, 12 binding them onto metal current collectors, and fostering cohesion within the electrode structure, thus enabling efficient electrochemical reactions. 13 Current battery electrode processing technologies employ polyvinylidene fluoride (PVDF) as binder, 10 which requires the use of the toxic N -methyl-2-pyrrolidone (NMP) as a solvent.…”