Carbon Nanotube Web with Carboxylated Polythiophene "Assist" for High-Performance Battery Electrodes

Achievements, challenges, and perspectives in the design of polymer binders for advanced lithium-ion batteries

Energy storage devices with high power and energy density are in demand owing to the rapidly growing population, and lithium-ion batteries (LIBs) are promising rechargeable energy storage devices. However, there are many issues associated with the development of electrode materials with a high theoretical capacity, which need to be addressed before their commercialization. Extensive research has focused on the modification and structural design of electrode materials, which are usually expensive and sophisticated. Besides, polymer binders are pivotal components for maintaining the structural integrity and stability of electrodes in LIBs. Polyvinylidene difluoride (PVDF) is a commercial binder with superior electrochemical stability, but its poor adhesion, insufficient mechanical properties, and low electronic and ionic conductivity hinder its wide application as a high-capacity electrode material. In this review, we highlight the recent progress in developing different polymeric materials (based on natural polymers and synthetic non-conductive and electronically conductive polymers) as binders for the anodes and cathodes in LIBs. The influence of the mechanical, adhesion, and self-healing properties as well as electronic and ionic conductivity of polymers on the capacity, capacity retention, rate performance and cycling life of batteries is discussed. Firstly, we analyze the failure mechanisms of binders based on the operation principle of lithium-ion batteries, introducing two models of "interface failure" and "degradation failure". More importantly, we propose several binder parameters applicable to most lithium-ion batteries and systematically consider and summarize the relationships between the chemical structure and properties of the binder at the molecular level. Subsequently, we select silicon and sulfur active electrode materials as examples to discuss the design principles of the binder from a molecular structure point of view. Finally, we present our perspectives on the development directions of binders for next-generation high-energy-density lithium-ion batteries. We hope that this review will guide researchers in the further design of novel efficient binders for lithium-ion batteries at the molecular level, especially for high energy density electrode materials.

Microcrystalline Nanofiber Electrode with Adaptive Intrinsic Structure and Microscopic Interface

A strategy of microcrystalline aggregation is proposed to fabricate energy storage electrode with outstanding capacity and stability. Carbon-rich electrode (BDTG) functionalized with benzo[1,2-b:4,5-b']dithiophene units and butadiyne segments are prepared. The linear conjugate chains pack as microcrystalline nanofibers on nanoscale, which further aggregates to form a porous interpenetrating network. The microcrystalline aggregation feature of BDTG exhibit stable structure during long cycling test, revealing the following advantage in structure and property. The stretchable butadiyne linker facilitates reversible adsorption and desorption of Li with the aid of adjacent sulfur heteroatom. The alkyne-alkene transition exhibits intrinsic structural stability of microcrystalline region in BDTG electrodes. Meanwhile, alkynyl groups and sulfur heteroatoms on the surface of BDTG nanofibers participate in the formation of microscopic interface, providing a stable interfacial contact between BDTG electrodes and adjacent electrolyte. As a proof-of-concept, BDTG-based electrode shows high capacity (1430 mAh g-1 at 50 mA g-1) and excellent cycle performance (8000 cycles under 5 A g-1) in half-cell of lithium-ion batteries, and a reversible capacity of 120 mAh g-1 is obtained under the current density of 2 C in full-cell. This work shows microcrystalline aggregation is beneficial to realize adaptive intrinsic structure and interface contact during the charge-discharge process.

Enhancing composite electrode performance: insights into interfacial interactions

Propelled by the widespread adoption of portable electronic devices, electrochemical energy storage systems, particularly lithium-ion batteries (LIBs), have become ubiquitous in modern society. The electrode is the critical battery component, where intricate interactions between the materials govern both the energy output and the overall lifespan of the battery under operational conditions. However, the poor interfacial properties of traditional electrode materials fall short in meeting escalating performance demands. To facilitate the advent of next-generation lithium-ion batteries, attention must be devoted to the interfacial chemistry that dictates and modulates the various dynamic and transport processes across multiple length scales within the composite electrodes. Recent research has concentrated on systematically understanding the properties of distinct electrode components to engineer meticulously tailored electrode formulations. These are geared towards composite electrodes with heightened chemical stability, thermal robustness, enhanced local conductivities, and superior mechanical resilience. This review elucidates the latest advances in understanding the impact of interfacial interactions in achieving high-capacity, high-stability electrodes. Through comprehensive insights into the interfacial interactions between the various electrode components, we can create improved integrated systems that outperform those developed through empirical methods. In light of this, the adoption of a holistic approach to enhance the interactions among electrode materials becomes of paramount importance. This concerted effort ensures the attainment of heightened rate capability, facilitation of lithium-ion transport, and overall system stability throughout the entirety of the cyclic process.

Nanostructured Conducting Polymers and Their Applications in Energy Storage Devices

Due to the energy requirements for various human activities, and the need for a substantial change in the energy matrix, it is important to research and design new materials that allow the availability of appropriate technologies. In this sense, together with proposals that advocate a reduction in the conversion, storage, and feeding of clean energies, such as fuel cells and electrochemical capacitors energy consumption, there is an approach that is based on the development of better applications for and batteries. An alternative to commonly used inorganic materials is conducting polymers (CP). Strategies based on the formation of composite materials and nanostructures allow outstanding performances in electrochemical energy storage devices such as those mentioned. Particularly, the nanostructuring of CP stands out because, in the last two decades, there has been an important evolution in the design of various types of nanostructures, with a strong focus on their synergistic combination with other types of materials. This bibliographic compilation reviews state of the art in this area, with a special focus on how nanostructured CP would contribute to the search for new materials for the development of energy storage devices, based mainly on the morphology they present and on their versatility to be combined with other materials, which allows notable improvements in aspects such as reduction in ionic diffusion trajectories and electronic transport, optimization of spaces for ion penetration, a greater number of electrochemically active sites and better stability in charge/discharge cycles.

Effect of Electrolytic Cations on a 3D Cd-MOF for Supercapacitive Electrodes

A cadmium-based metal-organic framework (Cd-MOF) is synthesized in a facile manner at ambient temperature by an easy slow diffusion process. The three-dimensional (3D) structure of Cd-MOF is authenticated by single-crystal X-ray diffraction studies and exhibits a cuboid-shaped morphology with an average edge length of ∼1.13 μm. The prepared Cd-MOF was found to be electroactive in nature, which resulted in a specific capacitance of 647 F g^-1 at 4 A g^-1 by maintaining a retention of ∼78% over 10,000 successive cycles in the absence of any binder. Further, to distinguish the efficiency of Cd-MOF electrodes, different electrolytes (NaOH, KOH, and LiOH) were explored, wherein NaOH revealed a higher capacitive response due to its combined effect of ionic and hydrated ionic radii. To investigate the practical applicability, an asymmetric supercapacitor (ASC) device is fabricated by employing Cd-MOF as the positive electrode and activated carbon (AC) as the negative electrode, enabling it to light a commercial light-emitting diode (LED) bulb (∼1.8 V). The as-fabricated ASC device delivers comparable energy density and power density.

Mechanically Strong, Thermally Stable Gas Barrier Polyimide Membranes Derived from Carbon Nanotube-Based Nanofluids

Gas barrier membranes with impressive moisture permeability are highly demanded in air or nature gas dehumidification. We report a novel approach using polyetheramine oligomers covalently grafted on the carbon nanotubes (CNTs) to engineer liquid-like CNT nanofluids (CNT NFs), which are incorporated into a polyimide matrix to enhance the gas barrier and moisture permeation properties. Benefiting from the featured liquid-like characteristic of CNT NFs, a strong interfacial compatibility between CNTs and the polyimide matrix is achieved, and thus, the resulting membranes exhibit high heat resistance and desirable mechanical strength as well as remarkable fracture toughness, beneficially to withstanding creep, impact, and stress fatigue in separation applications. Positron annihilation lifetime spectroscopy measurements indicate a significant decrease in fractional free volume within the resulting membranes, leading to greatly enhanced gas barrier properties while almost showing full retention of moisture permeability compared to that of the pristine membrane. For membranes with 10 wt % CNT NFs, the gas transmission rates, respectively, decrease 99.9% for CH₄, 94.4% for CO₂, 99.2% for N₂, and 97.9% for O₂ compared with that of the pristine membrane. Most importantly, with the increasing amount of CNT NFs, the hybrid membranes demonstrate a simultaneous increase of barrier performance and permselectivity for H₂O/CH₄, H₂O/N₂, H₂O/CO₂, and H₂O/O₂. All these results make these membranes potential candidates for high-pressure natural gas or hyperthermal air dehydration.

The Influence of Reaction Time on Non-Covalent Functionalisation of P3HT/MWCNT Nanocomposites

Non-covalent functionalisation of the carbon nanotube (CNT) sidewall through polymer wrapping is the key strategy for improving well-dispersed CNTs without persistent alteration of their electronic properties. In this work, the effect of reaction time on regioregular poly (3-hexylthiophene-2,5-diyl) (P3HT)-wrapped hydroxylated multi-walled CNT (MWCNT-OH) nanocomposites was investigated. Five different reaction times (24, 48, 72, 96, and 120 h) were conducted at room temperature in order to clearly determine the factors that influenced the quality of wrapped MWCNT-OH. Morphological analysis using Field Emission Scanning Electron Microscopic (FESEM) and High-Resolution Transmission Electron Microscope (HRTEM) analysis showed that P3HT successfully wrapped the MWCNT-OH sidewall, evidenced by the changes in the mean diameter size of the nanocomposites. Results obtained from Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS) as well as Thermogravimetric Analysis (TGA) showed a significant effect of the wrapped polymer on the CNT sidewall as the reaction time increased. Overall, the method used during the preparation of P3HT-wrapped MWCNT-OH and the presented results significantly provided a bottom-up approach to determine the effect of different reaction times on polymer wrapping to further expand this material for novel applications, especially chemical sensors.

Dual metal oxides interconnected by carbon nanotubes for high-capacity Li- and Na-ion batteries

Sb₂O₃ and Co₃O₄ as potential anode materials for Li- and Na-ion batteries exhibit high theoretical capacities and excellent electrochemical stability; however, volume expansion, exfoliation and poor electronic conductivity affect the electrochemical performance to some extent. Here, we design dual metal oxide hybrid composites by one- and two-step solvothermal processes, in which Co₃O₄ with Sb₂O₃ traps Li⁺ ions and carbon nanotubes (CNTs) as a network guarantee for electron transport. Sb₂O₃/CNTs/Co₃O₄ and Sb₂O₃/Co₃O₄/CNTs composites exhibit different morphologies, particles sizes and Li⁺/Na⁺ storage performance. The Sb₂O₃/CNTs/Co₃O₄ composite showes initial capacities of 1790 and 1450 mAh g^-1 after 100 cycles as the anode for a Li-ion battery. The capacity retention of the Sb₂O₃/Co₃O₄/CNTs composite is better than the Sb₂O₃/CNTs/Co₃O₄ composite for Na-ion storage. With charge/discharge cycles, the transition reaction of Sb₂O₃ and Co₃O₄ to Sb and Co repeats, leading to a homogenous distribution in CNTs and further growth of the nanoparticles. This work provides new insights into the design of high-capacity anodes for Li- and Na-ion storage by adjusting their composition and morphology.

Electrically Conductive Shell-Protective Layer Capping on the Silicon Surface as the Anode Material for High-Performance Lithium-Ion Batteries

Rational design and construction of effective silicon (Si) electrode structures to relieve large volumetric changes that occur during the charge/discharge process remain significant challenges for the development of robust lithium-ion batteries (LIBs). Herein, we propose an electrically conductive poly[3-(potassium-4-butanoate)thiophene] (PPBT) capping layer on the Si surface (Si@PPBT) to serve as the active material and be used in conjunction with a common polymer binder as an approach to tackle issues emanating from volumetric changes. The PPBT protective shell layer provides the system with tolerance toward variations in active material volume during cycling, improves the dispersion of Si nanoparticles in the binder, enhances the electrolyte uptake rate, and provides a strong adhesion force between the Si/carbon additives/current collector, thereby helping to maintain electrode integrity during the charge/discharge process. The π-conjugated polythiophene backbone structure also allows the Si core to maintain electrical contact with carbon additives and/or polymer binder, enabling the formation of effective electrical transport bridges and stabilizing solid electrolyte interphase layer growth. The integrated Si@PPBT/carboxymethyl cellulose (CMC) anode exhibited high initial Coulombic efficiency (84.9%), enhanced rate capability performance, and long cycling stability with a reversible capacity of 1793 mA h g^-1 after 200 cycles, 3.4 times higher than that of pristine Si anodes with the same CMC binder (528 mA h g^-1). The results suggest that the Si@PPBT design presents a promising approach to promote the practical use of Si anodes in LIBs, which could be extended to other anode materials exhibiting large volume changes during lithiation/delithiation.

Design of a Zn-MOF biosensor via a ligand “lock” for the recognition and distinction of S-containing amino acids

A new method of introducing a ‘lock’ ligand into the frame of MOFs is described to achieve the first example of a MOF-based biosensor for the recognition and distinction of S-containing amino acids.

Deterministic Design of Chemistry and Mesostructure in Li-Ion Battery Electrodes

All battery electrodes have complex internal three-dimensional architectures that have traditionally been formed through the random packing of the electrode components. What is now emerging is a new concept in battery electrode design, where the important electronic and ionic pathways, as well as the chemical interactions between the components of the electrode, are deterministically designed. Deterministic design enables far better properties than are possible through random packing, including dramatic improvements in both power and energy. Such a design approach is particularly attractive for emerging high-energy-density materials, which require available free volume as they swell during cycling. In addition to controlled structure, another important facet of the design of such systems is the stable chemical linkages between the active material and the conductive network that survive the lithiation and delithiation processes. In this Perspective, we discuss and provide our views on deterministically designed battery electrodes.