Conducting Block Copolymer Binders for Carbon-Free Hybrid Vanadium Pentoxide Cathodes with Enhanced Performance

Structural Lithium-Ion Battery Cathodes and Anodes Based on Branched Aramid Nanofibers

Structural batteries and supercapacitors combine energy storage and structural functionalities in a single unit, leading to lighter and more efficient electric vehicles. However, conventional electrodes for batteries and supercapacitors are optimized for high energy storage and suffer from poor mechanical properties. More specifically, commercial lithium-ion battery anodes and cathodes demonstrate tensile strength values <4 MPa and Young's modulus of <1 GPa. Here, we show that using branched aramid nanofibers (BANFs) or nanoscale Kevlar fibers as a binder leads to mechanically stronger lithium-ion battery electrodes. BANFs are combined with lithium iron phosphate (LFP, cathode) or silicon (Si, anode) particles and reduced graphene oxide (rGO). Hydrogen-bonding interactions between rGO and BANFs are harnessed to accommodate load transfer within the nanocomposite electrodes. Overall, we obtained up to 2 orders of magnitude improvements in Young's modulus and tensile strength compared to commercial battery electrodes while maintaining good energy storage capabilities. This work demonstrates an efficient route for designing structural lithium-ion battery cathodes and anodes with enhanced mechanical properties using BANFs as a binder.

CoS nanowires grown on Ti3C2Tx are promising electrodes for supercapacitors: High capacitance and remarkable cycle capability

Benefitting from the large interlayer spacing, ultrahigh conductivity and abundant surface chemistry, Ti₃C₂T_x has been a promising electrode material for supercapacitors (SCs). CoS has attracted much attention due to its low cost, weak Co-S bond and relatively high theoretical capacity. Herein, CoS nanowires were grown on few-layered Ti₃C₂T_x by one-step solvothermal method as a SC electrode. Within the composite, Ti₃C₂T_x could function as conductive network and buffer matrix to provide ultra-fast electronic transport and relieve volume expansion of CoS nanowires. Simultaneously, the active CoS nanowires with high capacitance act as interlayer spacer to restrain the restacking of Ti₃C₂T_x nanosheets. As a result, CoS/Ti₃C₂T_x-5 electrode exhibits a remarkable improvement specific capacitance of 528 F g^-1 at a current density of 1 A g^-1 and ultrahigh capacitance retention of 99.3% after 20 000 cycles at a current density of 10 A g^-1. The attempts and efforts made in this work provide a prototype for achieving excellent electrochemical properties.

100th Anniversary of Macromolecular Science Viewpoint: Solid Polymer Electrolytes in Cathode Electrodes for Lithium Batteries. Current Challenges and Future Opportunities

Solid polymer electrolytes (SPEs) are an important class of ion-transporting materials for enabling safe and high-energy-density all-solid lithium batteries. Within the composite cathode electrode (CCE), an SPE plays a critical role as both binder material for mechanical integrity and electrolyte to facilitate ion transport. The inclusion of an SPE within the CCE leads to the formation of distinctive heterogeneous SPE/solid interfaces that are not present in traditional liquid electrolyte-containing CCE. Here, the viewpoint emphasizes the importance of understanding the interfacial behavior of SPEs in all-solid CCEs. Challenges and opportunities are highlighted in achieving and maintaining good interfacial contact, and the role of interfacial dynamics and nanoconfinement on ion transport. Additionally, routes to achieving high-voltage electrochemical stability through stabilization of interfaces and the development of SPEs with inherently higher oxidative stability are discussed. SPEs with high-voltage stability will provide a pathway to using cathode active materials operating at 4.5 V versus Li/Li⁺ and beyond, which are essential to attaining next-generation higher-energy batteries. Overall, the viewpoint clarifies the importance of targeted research and development of SPEs for enabling all-solid CCEs for lithium batteries.

Branched aramid nanofiber-polyaniline electrodes for structural energy storage

Strong electrodes with good energy storage capabilities are necessary to accommodate the current needs for structural and flexible electronics. To this end, conjugated polymers such as polyaniline (PANI) have attracted much attention due to their exceptional energy storage performance. However, PANI is typically brittle and requires the use of substrates for structural support. Here, we report a strategy for developing free-standing structural supercapacitor and battery electrodes based on PANI. More specifically, aniline is polymerized in the presence of branched aramid nanofibers (BANFs) and single walled carbon nanotubes (SWCNTs). This results in a network morphology that allows for efficient load transfer and electron transport, leading to electrodes with capacity values up to 128 ± 5 mA h g-1 (vs. a theoretical capacity of 147 mA h g-1), Young's modulus of 4 ± 0.5 GPa, and tensile strength of 40 ± 4 MPa. Furthermore, the charge storage mechanism is investigated, in which both Faradaic and non-Faradaic contributions are observed. This work demonstrates an efficient strategy for designing structural electrodes based on conjugated polymers.

Symmetric All-Organic Battery Containing a Dual Redox-Active Polymer as Cathode and Anode Material

All-organic batteries are a promising sustainable energy storage technology owing to the wide availability, flexibility, and recyclability of organic/polymeric compounds. The development of all-organic or polymer batteries is still a challenge, as both electrode materials need to be carefully optimized to have a wide difference of redox potential and compatibility with the electrolyte. Herein, dual redox-active polyimides based on phenothiazine and naphthalene tetracarboxylic dianhydride units are presented. After only one optimization step, the electrodes based on these dual redox polymers can be applied simultaneously as anode and cathode in a symmetric all-organic battery. The phenothiazine functional polyimide shows two redox active voltages at around 2.5 and 3.7 V (vs. Li/Li⁺ ) with high discharge capacities of 160 mAh g^-1 . Moreover, the symmetric full battery delivers high power density up to 1542 W kg^-1 with stable cyclability for 1000 cycles. This work demonstrates an efficient strategy to develop dual redox active polymer electrodes for next generation all-polymer batteries.

Block copolymers for supercapacitors, dielectric capacitors and batteries

Block copolymer-based energy storage emerges as an active interdisciplinary research field. This topical review presents a survey of the recent advances in block copolymers for energy storage. In the first section, we introduce the background of electrochemical energy storage and block copolymer thermodynamics. In the second section, we discuss the current understandings of block copolymer chemistry, processing, pore size, and ionic conductivity. In the third section, we summarize the design principles and state-of-the-art applications of block copolymers in three energy storage devices, namely, supercapacitors, dielectric capacitors, and batteries. Lastly, we present our perspectives on future possible breakthroughs and associated challenges that are essential to propel the development of advanced block copolymers for energy storage. We expect the review to encourage innovative studies on integrating block copolymers into energy storage applications.

Self-Doped Conjugated Polymeric Binders Improve the Capacity and Mechanical Properties of V₂O₅ Cathodes

Polymeric binders serve to stabilize the morphology of electrodes by providing adhesion and binding between the various components. Successful binders must serve multiple functions simultaneously, including providing strong adhesion, improving conductivity, and providing electrochemical stability. A tradeoff between mechanical integrity and electrochemical performance in binders for lithium-ion batteries is one of the many challenges of improving capacity and performance. In this paper, we demonstrate a self-doped conjugated polymer, poly(9,9-bis(4′-sulfonatobutyl)fluorene-alt-co-1,4-phenylene) (PFP), which not only provides mechanical robustness but also improves electrode stability at temperatures as high as 450 °C. The self-doped PFP polymer is comprised of a conjugated polyfluorene backbone with sulfonate terminated side-chains that serve to dope the conjugated polymer backbone, resulting in stable conductivity. Composite electrodes are prepared by blending PFP with V₂O₅ in water, followed by casting and drying. Structural characterization with X-ray diffraction and wide-angle X-ray scattering shows that PFP suppresses the crystallization of V₂O₅ at high temperatures (up to 450 °C), resulting in improved electrode stability during cycling and improved rate performance. This study demonstrates the potential of self-doped conjugated polymers for use as polymeric binders to enhance mechanical, structural, and electrochemical properties.

Fabrication and Electrochemical Performance of Structured Mesoscale Open Shell V2O5 Networks

Crystalline vanadium pentoxide (V₂O₅) has attracted significant interest as a potential cathode material for energy storage applications due to its high theoretical capacity. Unfortunately, the material suffers from low conductivity as well as slow lithium ion diffusion, both of which affect how fast the electrode can be charged/discharged and how many times it can be cycled. Colloidal crystal templating (CCT) provides a simple approach to create well-organized 3-D nanostructures of materials, resulting in a significant increase in surface area that can lead to marked improvements in electrochemical performance. Here, a single layer of open shell V₂O₅ architectures ca. 1 μm in height with ca. 100 nm wall thickness was fabricated using CCT, and the electrochemical properties of these assemblies were evaluated. A decrease in polarization effects, resulting from the higher surface area mesostructured features, was found to produce significantly enhanced electrochemical performance. The discharge capacity of an unpatterned thin film of V₂O₅ (∼8.1 μAh/cm²) was found to increase to ∼10.2 μAh/cm² when the material was patterned by CCT, affording enhanced charge storage capabilities as well as a decrease in the irreversible degradation during charge-discharge cycling. This work demonstrates the importance of creating mesoscale electrode surfaces for improving the performance of energy storage devices and provides fundamental understanding of the means to improve device performance.