Magnetite (Fe3O4) was used as a model high capacity metal oxide active material to demonstrate advantages derived from consideration of both electron and ion transport in the design of composite battery electrodes. The conjugated polymer, poly[3-(potassium-4-butanoate) thiophene] (PPBT), was introduced as a binder component, while polyethylene glycol (PEG) was coated onto the surface of Fe3O4 nanoparticles. The introduction of PEG reduced aggregate size, enabled effective dispersion of the active materials and facilitated ionic conduction. As a binder for the composite electrode, PPBT underwent electrochemical doping which enabled the formation of effective electrical bridges between the carbon and Fe3O4 components, allowing for more efficient electron transport. Additionally, the PPBT carboxylic moieties effect a porous structure, and stable electrode performance. The methodical consideration of both enhanced electron and ion transport by introducing a carboxylated PPBT binder and PEG surface treatment leads to effectively reduced electrode resistance, which improved cycle life performance and rate capabilities.
Designing and controlling the anode–electrolyte interfacial chemistry of a micron Sn-Ni/graphite composite battery anode led to the formation of a stable solid electrolyte interphase (SEI) layer. We utilized fluoroethylene carbonate (FEC)-based electrolyte that is more interfacially compatible than an EC-based electrolyte, trimethyl phosphite electrolyte additive that reduces the attack of LiPF6-derived acidic species in the electrolyte, and the addition of a low fraction of SnF2 to anode for capturing the F anions of HF present in the electrolyte. Mechanistic surface chemistry studies using ATR FTIR and X-ray photoelectron spectroscopy revealed that the SnF2 transforms to SnF4 by capturing F anions, while FEC and phosphite provide a surface protective and robust SEI. The interfacially controlled composite anode with a tuned content of graphite exhibits good cycling stability (90% retention at the 50th cycle) with high discharge capacity of ∼800 mAhg−1 of tin, in contrast to a rapid capacity fade in the conventional electrolyte.
Although stretchable polymer-based devices with promising electrical performance have been produced through the polymer blend strategy, the interplay between the blend film microstructure and macroscopic device performance under deformation has yet to be unambiguously articulated. Here, we discuss the formation of robust semiconducting networks in blended films through a thermodynamic perspective. Thermodynamic behavior along with the linear absorption and photoluminescence measurements predict the competition between polymer phase separation and semiconductor crystallization processes during film formation. Semiconducting films comprised of different pi-conjugated semiconductors were prepared and shown to have mechanical and electronic properties similar to those of films comprised of a model P3HT and PDMS blend. These results suggest that a film's microstructure and therefore robustness can be refined by controlling the phase separation and crystallization behavior during film solidification. Fine-tuning a film's electrical, mechanical, and optical properties during fabrication will allow for advanced next-generation of optoelectronic devices.
Carboxylated polythiophenes, such as poly[3-(potassium-4-butanoate) thiophene] (PPBT), play a critical role in securely connecting single-walled carbon nanotube (SWNT) electrical networks onto the surface of carbon-coated silicon monoxide (c-SiOx). These connections are a function of the materials' surface chemistries and resultant physical/chemical bonding through favorable molecular interactions. Specifically, the PPBT π-conjugated backbone and alkyl side chain carboxylate moieties (COO−), respectively, physically interact with the SWNT and c-SiOx carbon layer π-electron-rich surfaces, and chemically bind to surface hydroxyl (−OH) species of the c-SiOx electroactive materials to form a carboxylate bond. This approach effectively captured pulverized particles that form during battery operation and beneficially suppressed the thickness change that electrodes typically undergo. The resultant electrodes exhibited superior electrochemical performance, which was ascribed to stable SEI layer formation, reduced electrode resistance, and improved electrode kinetics. Moreover, electrodes fabricated by blending 30 wt % of c-SiOx with graphite using <3 wt % binder exhibited remarkable performance in both coin-type half-cell and pouch-type full-cell systems. The concept that introduces robust SWNT electrical networks with PPBT carboxylate linkages suggests a feasible approach for the design of practical, high-performance, and high-capacity anodes for battery applications.
The unending demand for portable, flexible, and even wearable electronic devices that have an aesthetic appeal and unique functionality stimulates the development of advanced power sources that have excellent electrochemical performance and, more importantly, shape versatility. The challenges in the fabrication of next-generation flexible power sources mainly arise from their limited form factors, which prevent their facile integration into differently shaped electronic devices, and from the lack of reliable electrochemical materials that exhibit optimized attributes and suitable processability. This review describes the technological innovations and challenges associated with flexible energy storage and conversion systems such as lithium-ion batteries and supercapacitors, along with an overview of the progress in flexible proton exchange membrane fuel cells (PEMFCs) and solar cells. In particular, recently highlighted cable-type flexible batteries with extreme omni-directional flexibility are comprehensively discussed.
A new class of highly thin, deformable, and safety‐reinforced plastic crystal polymer electrolytes (N‐PCPEs) is demonstrated as an innovative solid electrolyte for potential use in high‐performance flexible lithium‐ion batteries with aesthetic versatility and robust safety. The unusual N‐PCPEs are fabricated by combining a plastic crystal polymer electrolyte with a porous polyethylene terephthalate (PET) nonwoven. Herein, the three‐dimensional reticulated plastic crystal polymer electrolyte matrix is formed directly inside the PET nonwoven skeleton via in‐situ UV‐crosslinking of ethoxylated trimethylolpropane triacrylate (ETPTA) monomer, under co‐presence of plastic crystal electrolyte. The PET nonwoven is incorporated as a compliant skeleton to enhance mechanical/dimensional strength of N‐PCPE. Owing to this structural uniqueness, the N‐PCPE shows significant improvements in the film thickness and deformability with maintaining advantageous features (such as high ionic conductivity and thermal stability) of the PCE. Based on structural/physicochemical characterization of N‐PCPE, its potential application as a solid electrolyte for flexible lithium‐ion batteries is explored by scrutinizing the electrochemical performance of cells. The high ionic conductance of N‐PCPE, along with its excellent deformability, plays a viable role in improving cell performance (particularly at high current densities and also mechanically deformed states). Notably, the cell assembled with N‐PCPE exhibits stable electrochemical performance even under a severely wrinkled state, without suffering from internal short‐circuit failures between electrodes.
While the focus of research related to the design of robust, high-performance Li-ion batteries relates primarily to the synthesis of active particles, the binder plays a crucial role in stability and ensures electrode integrity during volume changes that occur with cycling. Conventional polymeric binders such as poly(vinylidene difluoride) generally do not interact with active particle surfaces and fail to accommodate large changes in particle spacing during cycling. Thus, attention is now turning toward the exploration of interfacial interactions between composite electrode constituents as a key element in ensuring electrode stability. Recently, a poly[3-(potassium-4-butanoate)thiophene] (PPBT) binder component, coupled with a polyethylene glycol (PEG) surface coating for the active material was demonstrated to enhance both electron and ion transport in magnetite-based anodes, and it was established that the PEG/PPBT approach aids in overall battery electrode performance. Herein, the PEG/PPBT system is used as a model polymeric binder for understanding cation effects in anode systems. As such, the potassium ion was replaced with sodium, lithium, hydrogen, and ammonium through ion exchange. The potassium salt exhibited the most stable electrochemical performance, which is attributed to the cation size and resultant electrode morphology that facilitates ion transport. The lithium analogue demonstrated an initial increase in capacity but was unable to maintain this performance over 100 cycles; while the sodium-based system exhibited initially lower capacity as a result of slow reaction kinetics, which increased as cycling progressed. The parent carboxylic acid polymer and its ammonium salt were notably inferior. The results exploring the effect of ion exchange creates a framework for understanding how cations associated directly with the polymer impact electrochemical performance and aid in the overall design of binders for composite Li-ion battery anodes.
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