Surpassing the Redox Potential Limit of Organic Cathode Materials via Extended p-π Conjugation of Dioxin

Degradable Radical Polymer Cathode for Lithium Battery with Long-Term Cycling Capability

Polymer-based organic electrodes for rechargeable batteries are attractive due to their design flexibility, sustainability, and environmental compatibility. Unfortunately, waste management of conventional polymer materials typically involves incineration, which emits greenhouse gases. Consequently, degradable polymers should be ideal candidates for future green batteries. However, to date, degradable polymer electrodes have been rarely reported. The few that have been developed exhibit very low capacities (<40 mAh g-1) and poor cycle stability (<100 cycles). Herein, we synthesize a degradable polymer cathode for lithium batteries by copolymerizing 2,3-dihydrofuran with TEMPO-containing norbornene derivatives. This polymer cathode demonstrates a two-electron redox reaction charge storage mechanism, exhibiting a high reversible capacity of 100.4 mAh g-1 and a long cycle life of over 1000 cycles. Furthermore, under a mild acidic environment, this polymer electrode material undergoes complete decomposition via the hydrolysis of enol ethers, confirmed by gel permeation chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. These encouraging results shed light on the design of degradable polymer electrodes.

A High-Voltage n-type Organic Cathode Materials Enabled by Tetraalkylammonium Complexing Agents for Aqueous Zinc-Ion Batteries

Tetrabutylammonium (TBA) salt of hexacyano-substituted cyclopropane dianion (Cp(CN)6 2 -) is prepared through a facile two-step synthetic protocol from commercially available materials and fully characterized as a high-voltage n-type organic cathode in rechargeable aqueous zinc-ion batteries (AZIBs). The addition of tetrabutylammonium triflate (TBAOTf) to the electrolyte mitigates dissolution issues, leading to enhanced cycling stability. Remarkably, the Cp(CN)6 2 - cathode demonstrates a high discharge voltage of 1.43 V in AZIBs and retains 85% of its capacity after 1000 cycles at a high loading of 10 mg cm- 2 and a cycling rate of 10C. These results, combined with spectroscopic analyses, elucidate a reversible two-electron redox process of Cp(CN)6 2 - facilitated by the insertion/de-insertion of TBA cation. These findings underscore the potential of Cp(CN)6 2 - as a conversion-based n-type cathode in energy storage applications.

A Nile red dye cathode with an asymmetric redox unit for lithium organic batteries

A Nile red (NR) dye cathode with an asymmetric redox structure of para CN and CO bonds was developed for use in an efficient lithium organic battery with a good capacity of 125 mA h g-1 and two visible discharge/charge voltage plateaus (≈2.0 V and ≈1.7 V). The NR cathode demonstrated the advantages of employing cost-effective dyes to achieve multigradient voltage platform regulation.

Principles and Design of Biphasic Self-Stratifying Batteries Toward Next-Generation Energy Storage

Large-scale energy storage devices play pivotal roles in effectively harvesting and utilizing green renewable energies (such as solar and wind energy) with capricious nature. Biphasic self-stratifying batteries (BSBs) have emerged as a promising alternative for grid energy storage owing to their membraneless architecture and innovative battery design philosophy, which holds promise for enhancing the overall performance of the energy storage system and reducing operation and maintenance costs. This minireview aims to provide a timely review of such emerging energy storage technology, including its fundamental design principles, existing categories, and prototype architectures. The challenges and opportunities of this undergoing research topic will also be systematically highlighted and discussed to provide guidance for the subsequent R&D of superior BSBs while conducive to bridging the gap for their future practical application.

Modulation of Radical Intermediates in Rechargeable Organic Batteries

Organic materials have been considered as promising electrodes for next-generation rechargeable batteries in view of their sustainability, structural flexibility, and potential recyclability. The radical intermediates generated during the redox process of organic electrodes have profound effect on the reversible capacity, operation voltage, rate performance, and cycling stability. However, the radicals are highly reactive and have very short lifetime during the redox of organic materials. Great efforts have been devoted to capturing and investigating the radical intermediates in organic electrodes. Herein, this review summarizes the importance, history, structures, and working principles of organic radicals in rechargeable batteries. More importantly, challenges and strategies to track and regulate the radicals in organic batteries are highlighted. Finally, further perspectives of organic radicals are proposed for the development of next-generation high-performance rechargeable organic batteries.

Carbonyl-Based Redox-Active Compounds as Organic Electrodes for Batteries: Escape from Middle-High Redox Potentials and Further Improvement?

Extracting─from the vast space of organic compounds─the best electrode candidates for achieving energy material breakthrough requires the identification of the microscopic causes and origins of various macroscopic features, including notably electrochemical and conduction properties. As a first guess of their capabilities, molecular DFT calculations and quantum theory of atoms in molecules (QTAIM)-derived indicators were applied to explore the family of pyrano[3,2-b]pyran-2,6-dione (PPD, i.e., A0) compounds, expanded to A0 fused with various kinds of rings (benzene, fluorinated benzene, thiophene, and merged thiophene/benzene). A glimpse of up-to-now elusive key incidences of introducing oxygen in vicinity to the carbonyl redox center within 6MRs─as embedded in the A0 core central unit common to all A-type compounds─has been gained. Furthermore, the main driving force toward achieving modulated low redox potential/band gaps thanks to fusing the aromatic rings for the A compound series was discovered.

TiO2@COF Nanowire Arrays: A "Filter Amplifier" Heterojunction Strategy to Reverse the Redox Nature

Surface modification is a promising method to change the surface properties of nanomaterials, but it is limited in enhancing their intrinsic redox nature. In this work, a "filter amplifier" strategy is proposed for the first time to reverse the intrinsic redox nature of materials. This is demonstrated by coating a COF-316 layer with controlled thickness on TiO₂ to form core-sheath nanowire arrays. This unique structure forms a Z-scheme heterojunction to function as "a filter amplifier" which can conceal the intrinsic oxidative sites and increase the extrinsic reductive sites. Consequently, the selective response of TiO₂ is dramatically reversed from reductive ethanol and methanol to oxidative NO₂. Moreover, TiO₂@COF-316 provides remarkably improved sensitivity, response, and recovery speed, as well as unusual anti-humidity properties as compared with TiO₂. This work not only provides a new strategy to rationally modulate the surface chemistry properties of nanomaterials but also opens an avenue to design high-performance electronic devices with a Z-scheme heterojunction.