Tuning Conjugated Polymers for Binder Applications in High-Capacity Magnetite Anodes

Abstract

Battery electrodes are complex mesoscale systems comprising an active material, conductive agent, current collector, and polymeric binder. Although significant research on composite electrode materials for Li-ion batteries focuses on the design, synthesis, and characterization of the active particles, the binder component has been shown to critically impact stability and ensure electrode integrity during volume changes induced upon cycling. Herein, we explore the ability of water-soluble, carboxylated conjugated polymer binders to aid in electron and ion transport in magnetite-based anodes. Specifically, poly[3-(potassium-4-butanoate)thiophene] (PPBT) and a potassium carboxylate functionalized 3,4-propylenedioxythiophene (Pro-DOT)-based copolymer (WS-PE 2 ) were investigated and evaluated against the control, potassium salt form of poly(acrylic acid) (PAA-K). When used in conjunction with a polyethylene glycol (PEG) surface coating for the magnetite active material, PPBT provided for overall improved electrode performance as a result of more favorable intermolecular interactions between the composite constituents. The ProDOT-based copolymer WS-PE 2 exhibited comparable cycling performance to PPBT, whereas PAA-K and PPBT were similar with respect to rate capability. This investigation compares and contrasts a series of carboxylated polymers to elucidate the roles of different functional groups and identify materials chemistry-based structural parameters that can be manipulated to assist overall electrochemical performance of composite Li-ion battery anodes.

Active Material Interfacial Chemistry and Its Impact on Composite Magnetite Electrodes

“…Figure schematically illustrates the attachment strategies, whereby each synthetic route was designed to probe the role of distinct chemical characteristics that could be integral to creating high performing Fe 3 O 4 anodes. On the basis of prior studies, PEG aids in the dispersion of magnetite, providing for more uniform composites and possibly creating a highly ion conductive network at the electroactive material surface. − Thus, the PEG coated material served as a control. Benzoic acid functionalization has been shown to mitigate electrode pulverization due to volume expansion, and the aromatic acid may be expected to facilitate π–π stacking interactions with PPBT creating an electronically conductive network. , Alternatively, PPBT could be directly attached to the particle surface to create a flexible electronically conductive network that links with other particles in the electrode.…”

“…The PEG-Fe 3 O 4 approach (Figure A) was shown previously to afford composite electrodes with high capacity retention and improved kinetics that were attributed to the presence of an ionic conductor, leading to formation of nanoparticle agglomerates that create stable mesoparticle structures. − Synthesis of PPBT-APTES-Fe 3 O 4 (Figure D) employs EDC/NHS chemistry using APTES as a linker enabling attachment of PPBT to the particle: use of APTES to graft polymers onto a hydroxyl-containing surface is a known method to attach polymers onto the surface of silicon, cellulose nanocrystals, − magnetite, , and other nanomaterials. , Direct attachment of PPBT carboxylic acid moieties onto the hydroxyl-containing magnetite surface to generate PPBT-Fe 3 O 4 (Figure C) was achieved using Fisher esterification, which is a more direct and greener functionalization technique. One-step Fischer esterification has previously been used to modify the surface of nanocellulose structures and their derivatives. − For PPBT-Fe 3 O 4 , the end product is favored as a result of the difference in hydrophilicity of the magnetite and magnetite-PPBT complex in solution.…”

“…PPBT was chosen as the binder for its water processability, beneficial ionic/electronic conductivity in a composite electrode, and good affinity to the active materials. Hansen solubility parameter analysis demonstrated that PPBT has high physical affinity for PEG, enabling fabrication of homogeneous magnetite electrodes exhibiting low aggregation, low phase segregation, and low delamination. , Polyacrylic acid (PAA) on the other hand, possesses low physical affinity to PEG and magnetite electrodes fabricated using PAA as the binder exhibited poor electrochemical performance. As a result, PPBT was selected as the binder over more conventional, commodity carboxylic-acid containing polymers, such as PAA and carboxymethylcellulose to ensure good affinity to the active materials and limit energetic mismatches that can create phase segregation and delamination in the electrode …”

“…As a result, PPBT was selected as the binder over more conventional, commodity carboxylic-acid containing polymers, such as PAA and carboxymethylcellulose to ensure good affinity to the active materials and limit energetic mismatches that can create phase segregation and delamination in the electrode. 29 In addition to having good affinity to the active material, the mixed conduction characteristics 47 of PPBT allow exploration of the impact of binders that are capable of both ion and electron conduction on electrochemical performance. As battery demands increase in favor of fast charging and discharging applications, 48 the advantages associated with multifunctional binders exhibiting high electronic and ionic conductivity could become significant.…”

Multiscale Understanding and Architecture Design of High Energy/Power Lithium‐Ion Battery Electrodes

“…Using Fe 3 O 4 particles as active materials, Minnici et al studied the influence of the conjugated polymers, i.e., poly[3‐(potassium‐4‐butanoate) thiophene] (PPBT) and potassium carboxylate functionalized 3,4‐propylenedioxythiophene (ProDOT)‐based copolymer (WS‐PE 2 ), both on electrode architecture and electrochemical performance. [ 103 ] Polyethylene glycol (PEG) is used in conjunction with the conjugated polymers to avoid the aggregation of active materials. PEG/PPBT electrode exhibits overall improved rate and cycling performance as a result of more favorable intermolecular interactions between the active material and polymer binders, which in turn promotes the electron and ion transport.…”