High-Performance Sulfurized Polyacrylonitrile Cathode by Using MXene as a Conductive and Catalytic Binder for Room-Temperature Na/S Batteries

Sulfurized polyacrylonitrile (PAN@S) is a promising cathode material for room-temperature Na/S batteries but suffers from low conductivity and insufficient electrochemical activity, resulting in unsatisfactory actual capacity and rate performance. Herein, Ti3C2Tx MXene nanosheets are used as a conductive and catalytic binder to establish the PAN@S electrode, wherein MXene constructs a highly conductive framework for fast charge transport and provides high catalytic effect to improve the active material utilization and accelerate the redox kinetics significantly. Therefore, the PAN@S electrode bonded by MXene shows an electronic conductivity of 5.05 S cm-1, 4 orders of magnitude higher than the conventional electrodes bonded by the insulative polymer binders, and much decreased activation energy barrier and resistance. Consequently, the PAN@S electrode displays superior performance in terms of high capacity (697.3 mAh g-1 at 200 mA g-1), unparalleled rate capability (189.0 mAh g-1 at 20 A g-1), and excellent high-rate cycling performance (a capacity decay rate of ∼0.04% per cycle during 1000 cycles at 5 A g-1). This work provides a high-performance electrode for room-temperature Na/S batteries and shows the promising potential of conductive and catalytic MXene binders in boosting the performance of active materials.

Fabrication of Flexible Poly(m-aminophenol)/Vanadium Pentoxide/Graphene Ternary Nanocomposite Film as a Positive Electrode for Solid-State Asymmetric Supercapacitors

In this study, poly(m-aminophenol) (PmAP) has been investigated as a multi-functional conductive supercapacitor binder to replace the conventional non-conductive binder, namely, poly(vinylene difluoride) (PVDF). The kye benefits of using PmAP are that it is easily soluble in common organic solvent and has good film-forming properties, and also its chemical functionalities can be involved in pseudocapacitive reactions to boost the capacitance performance of the electrode. A new ternary nanocomposite film based on vanadium pentoxide (V₂O₅), amino-functionalized graphene (amino-FG) and PmAP was fabricated via hydrothermal growth of V₂O₅ nanoparticles on graphene surfaces and then blending with PmAP/DMSO and solution casting. The electrochemical performances of V₂O₅/amino-FG/PmAP nanocomposite were evaluated in two different electrolytes, such as KCl and Li₂SO₄, and compared with those of V₂O₅/amino-FG nanocomposite with PVDF binder. The cyclic voltametric (CV) results of the V₂O₅/amino-FG/PmAP nanocomposite exhibited strong pseudocapacitive responses from the V₂O₅ and PmAP phases, while the faradaic redox reactions on the V₂O₅/amino-FG/PVDF electrode were suppressed by the inferior conductivity of the PVDF. The V₂O₅/amino-FG/PmAP electrode delivered a 5-fold greater specific capacitance than the V₂O₅/amino-FG/PVDF electrode. Solid-state asymmetric supercapacitors (ASCs) were assembled with V₂O₅/amino-FG/PmAP film as a positive electrode, and their electrochemical properties were examined in both KCl and Li₂SO₄ electrolytes. Although the KCl electrolyte-based ASC has greater specific capacitance, the Li₂SO₄ electrolyte-based ASC delivers a higher energy density of 51.6 Wh/kg and superior cycling stability.

Constructing a Resilient Hierarchical Conductive Network to Promote Cycling Stability of SiOx Anode via Binder Design

Despite exhibiting high specific capacities, Si-based anode materials suffer from poor cycle life as their volume change leads to the collapse of conductive network within the electrode. For this reason, the challenge lies in retaining the conductive network during electrochemical processes. Herein, to address this prominent issue, a cross-linked conductive binder (CCB) is designed for commercially available silicon oxides (SiO_x ) anode to construct a resilient hierarchical conductive network from two aspects: on the one hand, exhibiting high electronic conductivity, CCB serves as an adaptive secondary conductive network in addition to the stiff primary conductive network (e.g., conductive carbon), facilitating faster interfacial charge transfer processes for SiO_x in molecular level; on the other hand, the cross-linked structure of CCB shows resilient mechanical properties, which maintains the integrity of the primary conductive network by preventing electrode deformation during prolonged cycling. With the aid of CCB, untreated micro-sized SiO_x anode material delivers an areal capacity of 2.1 mAh cm^-2 after 250 cycles at 0.8 A g^-1 . The binder design strategy, as well as, the relevant concepts proposed herein, provide a new perspective toward promoting the cycling stability of high-capacity Si-based anodes.

Suppressing Polysulfide Shuttling in Lithium-Sulfur Batteries via a Multifunctional Conductive Binder

Exhibiting high specific energy and low cost, lithium-sulfur batteries are considered promising candidates for the next-generation battery. However, its wide applications are limited by the insulating nature of the sulfur, dissolution of polysulfide species, and large volume change of the sulfur cathode. In this work, a conductive binder, crosslinked polyfluorene (C-PF) is synthesized and employed in Li-S batteries to enhance the overall electrochemical performance from the following three aspects: 1) possessing high electronic conductivity, C-PF facilitates lowered areal resistance for the sulfur electrode and leads to an improved rate capability; 2) owing to the cross-linked polymer structure, favorable mechanical properties of the electrode can be achieved, hence the well-preserved electrode integrity; 3) forming strong binding with various polysulfide species, C-PF manages to trap them from diffusing to the Li anode, which greatly improves the cycling stability of Li-S cells. Through designing a multifunctional binder to comprehensively enhance the Li-S cathode, this proposed approach could be broadly applied to fully harness the energy from S redox in addition to cathode material modifications.

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.

Conductive Binder for Si Anode with Boosted Charge Transfer Capability via n-Type Doping

Employing conductive binders in silicon (Si) anode has been considered as a fundamental solution to the pulverization of Si particles. Therefore, it is still a great challenge to improve the charge transfer capability of the conductive binder. Herein, a copolymer (PFPQ-COONa) is synthesized, characterized, and electrochemically tested as conductive binder for Si anode. It is found that PFPQ-COONa exhibits not only excellent cycling stability, but also satisfactory rate performance with relatively high areal loading, which outperforms currently reported single-component conductive binders. The superior electrochemical performance can be attributed to the molecular-level contact between binder and Si particles and to the enhanced intrinsic conductivity of PFPQ-COONa at reductive potential. This method provides a fresh perspective to design and develop conductive binder for high-capacity battery anode.

Secondary-Phase Stochastics in Lithium-Ion Battery Electrodes

Lithium-ion battery electrodes exhibit complex interplay among multiple electrochemically coupled transport processes, which rely on the underlying functionality and relative arrangement of different constituent phases. The electrochemically inactive solid phases (e.g., conductive additive and binder, referred to as the secondary phase), while beneficial for improved electronic conductivity and mechanical integrity, may partially block the electrochemically active sites and introduce additional transport resistances in the pore (electrolyte) phase. In this work, the role of mesoscale interactions and inherent stochasticity in porous electrodes is elucidated in the context of short-range (interface) and long-range (transport) characteristics. The electrode microstructure significantly affects kinetically and transport-limiting scenarios and thereby the cell performance. The secondary-phase morphology is also found to strongly influence the microstructure-transport-kinetics interactions. Apropos, strategies have been proposed for performance improvement via electrode microstructural modifications.

A Conductive Binder for High-Performance Sn Electrodes in Lithium-Ion Batteries

Tin (Sn) has been widely studied as a promising anode material for high-energy and high-power-density Li-ion batteries owing to its high specific capacity. In this work, a water-soluble conductive polymer is studied as a binder for nanosized Sn anodes. Unlike conventional binders, this conductive polymer formed a conductive network, which maintained the mechanical integrity during the repeated charge and discharge processes despite the inevitable Sn particle pulverization. The resultant Sn anode without conductive additives showed a specific capacity of 593 mA h g^-1 after 600 cycles at the current density of 500 mA g^-1, exhibiting better cycling stability as well as rate performance compared to Sn anodes with conventional binders. Furthermore, it was also found that the conductive binder enhanced the formation of stable solid electrolyte interphase (SEI) layers.