Thin, deformable, and safety-reinforced plastic crystal polymer electrolytes for use in high-performance flexible lithium-ion batteries with aesthetic versatility and robust safety features is reported on page 44 by S.-Y. Lee and co-workers. The combination of a plastic crystal polymer electrolyte matrix with a compliant nonwoven skeleton enables the fabrication of the innovative polymer electrolyte with optimized attributes. The cell assembled with the polymer electrolyte exhibits stable electrochemical performance under severely deformed states (even a wrinkled state), without suffering from internal short-circuit failures.
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 (ProDOT)-based copolymer (WS-PE2) 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-PE2 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.
A carbon nanotube (CNT) web electrode comprising magnetite spheres and few-walled carbon nanotubes (FWNTs) linked by the carboxylated conjugated polymer, poly[3-(potassium-4-butanoate) thiophene] (PPBT), was designed to demonstrate benefits derived from the rational consideration of electron/ion transport coupled with the surface chemistry of the electrode materials components. To maximize transport properties, the approach introduces monodispersed spherical Fe3O4 (sFe3O4) for uniform Li+ diffusion and a FWNT web electrode frame that affords characteristics of long-ranged electronic pathways and porous networks. The sFe3O4 particles were used as a model high-capacity energy active material, owing to their well-defined chemistry with surface hydroxyl (−OH) functionalities that provide for facile detection of molecular interactions. PPBT, having a π-conjugated backbone and alkyl side chains substituted with carboxylate moieties, interacted with the FWNT π-electron-rich and hydroxylated sFe3O4 surfaces, which enabled the formation of effective electrical bridges between the respective components, contributing to efficient electron transport and electrode stability. To further induce interactions between PPBT and the metal hydroxide surface, polyethylene glycol was coated onto the sFe3O4 particles, allowing for facile materials dispersion and connectivity. Additionally, the introduction of carbon particles into the web electrode minimized sFe3O4 aggregation and afforded more porous FWNT networks. As a consequence, the design of composite electrodes with rigorous consideration of specific molecular interactions induced by the surface chemistries favorably influenced electrochemical kinetics and electrode resistance, which afforded high-performance electrodes for battery applications.
The high energy/power density of Li-ion batteries elicits intensive research efforts related to high capacity anode materials. The main obstacles which retard the practical employment of high-capacity electrochemically active particles including Si, Sn, metal oxide and their derivatives, stem from large volume changes associated with Li insertion/extraction and the resultant electrical contact loss, thereby leading to poor cycling performance. Efforts have been made to circumvent the breakdown of electron pathways through the introduction of electrical conducting functionalities to the surface of active materials, such as carbon coatings and conductive polymeric binders, or the fabrication of a stable battery anode with electrically inactive polymeric binders that enable the system to maintain its integrity. These approaches are reasonably effective, however, incorporation of a porous entity which helps ion transport, into a composite electrode is also essential for improved performance. In principle, electrochemical reactions that occur within the electrode, reveal the intrinsic energy capacity when a Li ion encounters an electron inside an active site. Electron and ion transport are both critical factors to determine the internal resistance of the electrodes, which in turn influences their electrochemical performance. Here we present how to improve both electronic and ionic transport in Li-ion battery electrodes using conjugated polymers. The approach includes poly[3-(potassium-4-butanoate)thiophene] (PPBT) — a water-soluble, carboxylate substituted polythiophene — as a binder component, and polyethylene glycol (PEG) as a surface coating on active material, namely, Fe 3 O 4 nanoparticles. Additionally, carbon nanotubes (CNTs) are considered for use as the conducting networks to facilitate design of a light-weight, flexible web electrode. To enhance the electronic conduction in the electrodes, connection between active materials (PEG- Fe 3 O 4 ) and conducting agents (or CNTs) through binding components is of importance. PEG coating and carboxylated polythiophenes play an important role in dispersing the Fe 3 O 4 nanoparticles and conducting agents (or CNTs), respectively, in a water medium, which allow for well-developed and interconnected electrode structures. Furthermore, carboxylated polythiophenes (e.g. PPBT) can boost electronic conduction, based on their high conducting properties and through electrochemical doping during electrochemical testing. The presence of carboxylic moieties on the side chain of polythiophenes such as PPBT could facilitate the formation of stable electrodes via chemical interactions between PPBT moieties (COO-) and the Fe 3 O 4 surface (–OH). The results will show that this methodical consideration of both ion and electron transport through introduction of a carboxylated PPBT component, can remarkably enhance the performance of Fe 3 O 4 based high-capacity anodes.
Tin‐based anode materials are promising candidates for high‐energy density Li‐ion batteries. Unstable anode–electrolyte interface is a critical problem that needs to be resolved for these materials. The improvement of solid electrolyte interphase (SEI) stability and cycling stability of fluorine‐doped Sn–Ni film electrode is observed by the use of fluoroethylene carbonate (FEC)‐based electrolyte with respect to ethylene carbonate (EC)‐based conventional electrolyte. Mechanisms of FEC‐derived SEI formation and stabilization are investigated using state of charge‐dependent ex situ attenuated total reflection FTIR combined with X‐ray photoelectron spectroscopy. The data reveal that enriched fluorinated compounds of SnF 4 , SnF 2 , and LiF form in FEC‐based electrolyte as the earliest SEI compounds, and those inorganic species together with Li 2 CO 3 and organic/polymeric compounds effectively passivate the electrode surface at a limited SEI thickness and inhibit further electrolyte decomposition, in contrast to continuous electrolyte decomposition with cycling in EC‐based electrolyte. The stable FEC‐derived SEI layer limits cracks but improves particles connectivity, leading to improved cycling stability of the battery. The SEI formation mechanism by FEC reduction at the surface of the electrode is proposed. The approach of SEI control for the performance improvement gives an insight into the importance of SEI composition and stability in achieving improved battery performance.
Unprecedented improvement in the selectivity (the ratio of proton conductivity to methanol permeability) of DMFC (direct methanol fuel cell) membranes has been demonstrated with a value roughly 16 times higher than that of Nafion117 having been achieved. The novel morphology of semi-interpenetrating polymer network (semi-IPN) membranes characterized by nanometer-sized domains as well as well-developed phase cocontinuity is a key factor in enabling such notable progress, which has not been seen in conventional microscale phase separation. The semi-IPN membranes (sIPN-100) consisted of a hydrophilic component acting as a proton conductor, that is, acrylate-terminated fully sulfonated poly(arylene ether sulfone) oligomers (acSPAES-100, degree of sulfonation = 100%), and a hydrophobic component functioning as a methanol barrier, that is, poly(ether sulfone) copolymers (RH-2000). We determined the nanoscale phase separation of sIPN-100 by deliberately controlling the kinetics (the change of solvent-evaporation conditions) as well as the thermodynamics (shift of the phase separation boundary to the lower concentration of solvent in the phase diagram, mostly driven by the low molecular weight and the low hydrophilicity of acSPAES-100). Finally, the influence of this unique morphology on the membrane transport properties including the proton conductivity, the methanol permeability, and, more notably, the selectivity, was systematically investigated.
Conjugated polymers possessing polar functionalities were shown to effectively anchor single-walled carbon nanotubes (SWNTs) to the surface of high-capacity anode materials and enable the formation of electrical networks. Specifically, poly[3-(potassium-4-butanoate) thiophene] (PPBT) served as a bridge between SWNT networks and various anode materials, including monodispersed Fe3O4 spheres (sFe3O4) and silicon nanoparticles (Si NPs). The PPBT π-conjugated backbone and carboxylate (COO−) substituted alkyl side chains, respectively, attracted the SWNT π-electron surface and chemically interacted with active material surface hydroxyl (−OH) species to form a carboxylate bond. Beneficially, this architecture effectively captured cracked/pulverized particles that typically form as a result of repeated active material volume changes that occur during charging and discharging. Thus, changes in electrode thickness were suppressed substantially, stable SEI layers were formed, electrode resistance was reduced, and enhanced electrode kinetics was observed. Together, these factors led to excellent electrochemical performance.
The mechanical flexibility of a cable-type battery reaches levels far beyond what is possible with conventional designs. The hollow-spiral (helical) multi-helix anode architecture is critical to the robustness under mechanical stress and facilitates electrolyte wetting of the battery components. This design enables the battery to reliably power an LED screen or an MP3 player even under severe mechanical twisting and bending. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
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