Superlithiation Performance of Covalent Triazine Frameworks as Anodes in Lithium-Ion Batteries

Recent developments in covalent Triazine frameworks for Lithium-ion and Lithium-sulfur batteries

The escalating demand for sustainable energy storage solutions has spurred significant research into materials that can efficiently store and convert energy. Among these, Covalent Triazine Frameworks (CTFs) have emerged as a promising class of two-dimensional nanomaterials due to their unique properties which includes permanent porosity, abundant active sites, exceptional stability and structural diversity. This review examines the role of CTFs in enhancing the performance of electrochemical energy storage devices, particularly in LIBs and LSBs as electrode materials. Despite the advantages of CTFs based electrode materials, such as their lightweight nature, design flexibility, and sustainability, they often suffer from low ionic conductivity and durability issues. This review examines recent advancements and design approaches focused on enhancing the electrochemical performance of CTF-based electrodes for lithium-ion (LIBs) and lithium‑sulfur (LSBs) batteries. It also addresses the major challenges that limit the effectiveness of CTFs in energy storage applications and suggests potential strategies for overcoming these obstacles. The primary aim of this review is to offer a thorough and detailed overview of the current state of research on CTFs. By critically analyzing existing work and highlighting future research directions, this review intends to support the advancement of CTF-based technologies in pursuit of more efficient and sustainable energy storage solutions.

Unveiling Covalent Triazine Frameworks for Lithium Metal Anodes: Recent Developments and Prospective Advances

Lithium metal batteries (LMBs) are distinguished by their elevated energy densities which represent themselves as the formidable contenders for the forthcoming generation of energy storage technologies. Nonetheless, their cycling efficiency is hindered owing to unregulated growth of lithium dendrites and unstable solid electrolyte interphase (SEI). This raises serious safety concerns while rendering LMBs unfeasible for real-world implementation. Covalent Triazine Frameworks (CTFs) have emerged as a promising class of 2D nanomaterials due to their unique properties such as high surface area, chemical stability, tailorable properties, porosity and high N-containing groups. These groups serve as an efficient acceptor for Li. Consequently, the problem of lithium dendrite formation is significantly reduced. This review offers an extensive examination of CTF based anode materials utilized to address the challenges associated with lithium dendrites in LMBs. It is outline future prospects and provide recommendations for the design and engineering of lithium metal anodes (LMAs) and architectures that can make LMBs viable for practical use. This review also highlights promising strategies for surmounting challenges to ensure the safety and efficiency of LMBs.

Naphthalene Diimide-Based Cyanovinylene-Containing Conjugated Organic Polymers for Efficient Lithium-Ion Battery Electrodes

The pursuit of innovative organic materials and the examination of the "structure-function" correlation in lithium-ion batteries (LIBs) are crucial and highly desirable. Current research focuses on the creation of novel conjugated organic polymers with polycarbonyl groups and examining the impact of electrode structure on the function of lithium-ion batteries. In this paper, two novel cyanovinylene-based conjugated organic polymers, NBA-TFB and NBA-TFPB, are synthesized using a Knoevenagel condensation reaction with naphthalene diimide as the integral unit. The performance of NBA-TFB and NBA-TFPB as cathodes in lithium-ion batteries is investigated. Improved conductivity and increased active site density in NBA-TFPB resulted in superior electrochemistry compared to NBA-TFB. Specifically, NBA-TFPB exhibited a larger reversible capacity (87.58 mAh g-1 at 0.2C and 88.34% retention after 100 cycles), exceptional rate capability (66.13 mAh g-1 at 5C), and robust cycling stability (99.58% coulombic efficiency at 1C and 60.71% retention after 2000 cycles). This study expands the family of diimide-based naphthalene polymers and provides a strategy for enhancing the performance of organic electrode materials containing polycarbonyl structure.

Ultra-Long Lifespan Aqueous Zinc-Iodine Batteries Enabled by a Defect-Rich Covalent Triazine Framework

Aqueous Zinc-iodine batteries (ZIBs) are widely viewed as promising energy storage devices due to their high energy density and intrinsic safety. However, they encounter great challenges such as grievous polyiodides shuttle and sluggish iodine (I2) redox reaction kinetics, thus undesirable cycling performance. Here a high-performance ZIB with an ultra-long lifespan is reported through the rational I2 cathode catalyst design. Specifically, a covalent triazine framework with defect-rich sites and micro-mesoporous structure (i.e., CTF500) is developed as an effective I2 cathode catalyst. Benefiting from the synergistic effect of micro-mesoporous structure and defect-rich sites for the confinement and conversion of I2 species, the resulting ZIBs with I2 loaded CTF500 (I2@CTF500) cathode show an ultra-long lifespan over 75,000 cycles at 5 A g-1, and an impressive cyclic performance over 15,000 cycles at high I2 loading of 3.59 mg cm-2, highlighting its commercial application prospect. In/ex situ spectral characterizations combined with theoretical calculations clearly reveal the reversible reaction mechanism of I2 species in I2@CTF500 cathode and the essential role of defect-rich sites in boosting the performance of ZIBs. This work not only guides the design of advanced I2 cathodes for metal-iodine batteries but also expands the range of possible applications for defect-rich CTFs.

Polar Covalent Triazine Frameworks as High-Performance Potassium Metal Battery Cathodes

The exploration of potassium metal batteries (PMBs) has been intensified, leveraging potassium's abundant availability, low redox potential, and small Stokes radius. Covalent triazine frameworks (CTFs) stand out for their accessible nitrogen sites and customizable structures, making them attractive electrode materials. Nonetheless, there is a lack of established design principles to guide the development of high-performance PMBs using CTFs. In this work, CTFs consisting of different monomers are used as PMB cathodes to investigate the structure-performance correlation. The electronic structure analysis reveals the polar characteristic of a CTF derived from the tetracyanoquinodimethane monomer, setting it apart with superior capacity (161 mAh g-1 at 0.1 A g-1), rate performance (85 mAh g-1 at 5 A g-1), and stability (capacity retention of 81% after 1000 cycles) over three non-polar counterparts in PMBs. Calculations based on density functional theory support the exceptional performance with increased K+ adsorption energy. Ultimately, among multifaceted factors, the polarity of CTF is the leading element that determines the K+ storage capability. These findings pave the way for the development of prudent CTF electrodes for high-performance PMBs.

Fully Conjugated Covalent Triazine Framework Integrating Hexaazatrinaphthylene Unit as Anode Material for High-Performance Hybrid Lithium-Ion Capacitors

As a high-performance energy storage device consisting of a battery-type anode and a capacitor-type cathode, hybrid lithium-ion capacitors (HLICs) combine the advantages of high energy density of batteries and high power density of capacitors. However, the imbalance in electrochemical kinetics between the battery-type anode and the capacitor-type cathode hinders the further development of HLICs. Fully conjugated covalent organic frameworks have great potential as electrode materials for HLICs due to the designability of their structure. Herein, a fully conjugated covalent triazine framework (PT-CTF) integrating the hexaazatrinaphthylene unit was constructed, which provides abundant active sites (C═N and C═C groups) as the pseudocapacitive anode material for HLICs. And the connection of the triazine unit of PT-CTF improves the molecular conjugate degree, facilitating the transport of electrons. The fabricated PT-CTF||AC HLICs exhibit a high energy density (164.9 Wh kg-1 at 100 mA g-1), large power density (13.1 kW kg-1 at 4 A g-1), and excellent cycling capability (72% after 10 000 cycles at 2 A g-1).

Construction of High-Performance Anode of Potassium-Ion Batteries by Stripping Covalent Triazine Frameworks with Molten Salt

Covalent triazine frameworks (CTFs) are promising battery electrodes owing to their designable functional groups, tunable pore sizes, and exceptional stability. However, their practical use is limited because of the difficulty in establishing stable ion adsorption/desorption sites. In this study, a melt-salt-stripping process utilizing molten trichloro iron (FeCl3) is used to delaminate the layer-stacked structure of fluorinated covalent triazine framework (FCTF) and generate iron-based ion storage active sites. This process increases the interlayer spacing and uniformly deposits iron-containing materials, enhancing electron and ion transport. The resultant melt-FeCl3-stripped FCTF (Fe@FCTF) shows excellent performance as a potassium ion battery with a high capacity of 447 mAh g-1 at 0.1 A g-1 and 257 mAh g-1 at 1.6 A g-1 and good cycling stability. Notably, molten-salt stripping is also effective in improving the CTF's Na+ and Li+ storage properties. A stepwise reaction mechanism of K/Na/Li chelation with C═N functional groups is proposed and verified by in situ X-ray diffraction testing (XRD), ex-situ X-ray photoelectron spectroscopy (XPS), and theoretical calculations, illustrating that pyrazines and iron coordination groups play the main roles in reacting with K+/Na+/Li+ cations. These results conclude that the Fe@FCTF is a suitable anode material for potassium-ion batteries (PIBs), sodium-ion batteries (SIBs), and lithium-ion batteries (LIBs).

Boosting lithium storage in covalent triazine framework for symmetric all-organic lithium-ion batteries by regulating the degree of spatial distortion

Covalent triazine frameworks (CTFs) with tunable structure, fine molecular design and low cost have been regarded as a class of ideal electrode materials for lithium-ion batteries (LIBs). However, the tightly layered structure possessed by the CTFs leads to partial hiding of the redox active site, resulting in their unsatisfactory electrochemical performance. Herein, two CTFs (BDMI-CTF and TCNQ-CTF) with higher degree of structural distortion, more active sites exposed, and large lattice pores were prepared by dynamic trimerization reaction of cyano. As a result, BDMI-CTF as a cathode material for LIBs exhibits high initial capacity of 186.5 mAh/g at 50 mA g-1 and superior cycling stability without capacity loss after 2000 cycles at 1000 mA g-1 compared with TCNQ-CTF counterparts. Furthermore, based on their bipolar functionality, BDMI-CTF can be used as both cathode and anode materials for symmetric all-organic batteries (SAOBs), and this work will open a new window for the rational design of high performance CTF-based LIBs.

Superlithiation Performance of Pyridinium Polymerized Ionic Liquids with Fast Li+ Diffusion Kinetics as Anode Materials for Lithium-Ion Battery

Polymerized ionic liquids (PILs) with super ion diffusion kinetics have aroused considerable attention in rechargeable batteries, which are very promising to solve the problem of the slow ion diffusion kinetics in organic electrode materials. Theoretically, PILs incorporated redox groups are very suitable as anode materials to realize "superlithiation" performance, achieving high lithium storage capacity. In this study, redox pyridinium-based PILs (PILs-Py-400) have been synthesized through trimerization reactions by pyridinium ionic liquids with cyano groups under an appropriate temperature (400 °C). The positively charged skeleton, extended conjugated system, abundant micropores, and amorphous structure for PILs-Py-400 can boost the utilization efficiency of redox sites. A high capacity of 1643 mAh g-1 at 0.1 A g-1 (96.7% of the theoretical capacity) has been obtained, indicating intriguing 13 Li+ redox reactions in per repeating unit of one pyridinium ring, one triazine ring, and one methylene. Moreover, PILs-Py-400 exhibit excellent cycling stability with a capacity of around 1100 mAh g-1 at 1.0 A g-1 after 500 cycles, and the capacity retention is 92.2%.

Hexaazatrinaphthalene-Based Covalent Triazine Framework-Supported Rhodium(III) Complex: A Recyclable Heterogeneous Catalyst for the Reductive Amination of Ketones to Primary Amines

The development of efficient and recyclable heterogeneous catalysts is an important topic. Herein, a rhodium(III) complex Cp*Rh@HATN-CTF was synthesized by the coordinative immobilization of [Cp*RhCl₂]₂ on a hexaazatrinaphthalene-based covalent triazine framework. In the presence of Cp*Rh@HATN-CTF (1 mo l% Rh), a series of primary amines could be obtained via the reductive amination of ketones in high yields. Moreover, catalytic activity of Cp*Rh@HATN-CTF is well maintained during six runs. The present catalytic system was also applied for the large scale preparation of a biologically active compound. It would facilitate the development of CTF-supported transition metal catalysts for sustainable chemistry.

Cross-linked polyaniline for production of long lifespan aqueous iron||organic batteries with electrochromic properties

Aqueous iron batteries are appealing candidates for large-scale energy storage due to their safety and low-cost aspects. However, the development of aqueous Fe batteries is hindered by their inadequate long-term cycling stability. Here, we propose the synthesis and application as positive electrode active material of cross-linked polyaniline (C-PANI). We use melamine as the crosslinker to improve the electronical conductivity and electrochemical stability of the C-PANI. Indeed, when the C-PANI is tested in combination with a Fe metal negative electrode and 1 M iron trifluoromethanesulfonate (Fe(TOF)₂) electrolyte solution, the coin cell can deliver a specific capacity of about 110 mAh g^-1 and an average discharge voltage of 0.55 V after 39,000 cycles at 25 A g^-1 with a test temperature of 28 °C ± 1 °C. Furthermore, mechanistic studies suggest that Fe²⁺ ions are bonded to TOF^- anions to form positively charged complexes Fe(TOF)⁺, which are stored with protons in the C-PANI electrode structures. Finally, we also demonstrate the use of C-PANI in combination with a polymeric hydrogel electrolyte to produce a flexible reflective electrochromic lab-scale iron battery prototype.