Are Redox-Active Organic Small Molecules Applicable for High-Voltage (>4 V) Lithium-Ion Battery Cathodes?

A Porphyrin-Phenylalkynyl-Based Conjugated Organic Polymer as a High-Performance Cathode for Rechargeable Organic Batteries

Organic electrode materials (OEMs) have attracted much attention for rechargeable batteries due to their low cost, environment friendliness, flexibility, and structural versatility. Despite the above advantages, high solubility in electrolyte and low electronic conductivity remain critical limitations for the application of OEMs. In this work, the conjugated organic polymer (COP) poly([5,10,15,20-tetrakis(4-phenylalkynyl)porphyrin]Cu(II)) (PCuTPEP) is proposed as a cathode for high performance in organic lithium batteries. The polymerization inhibits the dissolution of the organic electrodes in the electrolyte, and the porphyrin and ethynyl-phenyl groups greatly expand the conjugated system and result in a high average discharge plateau at 4.0 V (vs Li+/Li). The PCuTPEP cathode exhibits a reversible discharge capacity of 119 mAh g-1 at a current of 50 mA g-1. Even at a high current density of 2.0 A g-1, excellent cycling stability up to 1000 cycles is achieved with capacity retentions of 88.5 and 90.4% at operating temperatures of 25 and 50 °C in organic lithium batteries, respectively. This study provides the approach for the development of organic cathodes for electrochemical energy storage.

Charging the Future: Harnessing Nature's Designs for Bioinspired Molecular Electrodes

The transition toward electric-powered devices is anticipated to play a pivotal role in advancing the global net-zero carbon emission agenda aimed at mitigating greenhouse effects. This shift necessitates a parallel focus on the development of energy storage materials capable of supporting intermittent renewable energy sources. While lithium-ion batteries, featuring inorganic electrode materials, exhibit desirable electrochemical characteristics for energy storage and transport, concerns about the toxicity and ethical implications associated with mining transition metals in their electrodes have prompted a search for environmentally safe alternatives. Organic electrodes have emerged as promising and sustainable alternatives for batteries. This review paper will delve into the recent advancements in nature-inspired electrode design aimed at addressing critical challenges such as capacity degradation due to dissolution, low operating voltages, and the intricate molecular-level processes governing macroscopic electrochemical properties.

Insoluble low-impedance organic battery cathode enabled by graphite grafting towards potassium storage

Organic electrode materials are extensively applied for potassium storage as their sustainability and low cost. However, the organic electrodes' (i) solubility (such as naphthalene-1,4,5,8-tetracarboxylic dianhydride, NTCDA; 2,6-diaminoanthanthraquinone, DAQ, which are easily soluble in organic solvents) and (ii) intrinsic poor conductivity often result in high impedance and inferior electrochemical performance. Herein, the monomers of NTCDA and DAQ were polymerized (PND) to obtain an insoluble organic cathode, and a 5 wt% graphite (G) was also used to graft the PND sheet and increase its conductivity. Consequently, the as-prepared organic cathode (PND-G) achieved a long-life cycling performance of over 1500 cycles at 100 mA g-1. This work may provide guidelines for designing and developing insoluble and high conductive organic electrode materials.

MXene-Based Current Collectors for Advanced Rechargeable Batteries

As an indispensable component of rechargeable batteries, the current collector plays a crucial role in supporting the electrode materials and collecting the accumulated electrical energy. However, some key issues, like uneven resources, high weight percentage, electrolytic corrosion, and high-voltage instability, cannot meet the growing need for rechargeable batteries. In recent years, MXene-based current collectors have achieved considerable achievements due to its unique structure, large surface area, and high conductivity. The related research has increased significantly. Nonetheless, a comprehensive review of this area is seldom. Herein the applications and progress of MXene in current collector are systematically summarized and discussed. Meanwhile, some challenges and future directions are presented.

Impact of Structural Flexibility of Amine Moieties as Bridges for Redox-Active Sites on Secondary Battery Performance

Although environmentally benign organic cathode materials for secondary batteries are in demand, their high solubility in electrolyte solvents hinders broad applicability. In this study, a bridging fragment to link redox-active sites is incorporated into organic complexes with the aim of preventing dissolution in electrolyte systems with no significant performance loss. Evaluation of these complexes using an advanced computational approach reveals that the type of redox-active site (i. e., dicyanide, quinone, or dithione) is a key parameter for determining the intrinsic redox activity of the complexes, with the redox activity decreasing in the order of dithione>quinone>dicyanide. In contrast, the structural integrity is strongly reliant on the bridging style (i. e., amine-based single linkage or diamine-based double linkage). In particular, owing to their rigid anchoring effect, diamine-based double linkages incorporated at dithione sites allow structural integrity to be maintained with no significant decrease in the high thermodynamic performance of dithione sites. These findings provide insights into design directions for insoluble organic cathode materials that can sustain high performance and structural durability during repeated cycling.

A 3D-Printed, Freestanding Carbon Lattice for Sodium Ion Batteries

Increasing mass loadings of battery electrodes critically enhances the energy density of an overall battery by eliminating much of the inactive components, while compacting the battery size and lowering the costs of the ingredients. A hard carbon microlattice, digitally designed and fabricated by stereolithography 3D-printing and pyrolysis, offers enormous potential for high-mass-loading electrodes. In this work, sodium-ion batteries using hard carbon microlattices produced by an inexpensive 3D printer are demonstrated. Controlled periodic carbon microlattices are created with enhanced ion transport through microchannels. Carbon microlattices with a beam width of 32.8 µm reach a record-high areal capacity of 21.3 mAh cm^-2 at a loading of 98 mg cm^-2 without degrading performance, which is much higher than the conventional monolithic electrodes (≈5.2 mAh cm^-2 at 92 mg cm^-2 ). Furthermore, binder-free, pure-carbon elements of microlattices enable the tracking of structural changes in hard carbon that support the hypothesized intercalation of ions at plateau regions by temporal ex situ X-ray diffraction measurements. These results will advance the development of high-performance and low-cost anodes for sodium-ion batteries as well as help with understanding the mechanisms of ion intercalations in hard carbon, expanding the utilities of 3D-printed carbon architectures in both applications and fundamental studies.

Series module of quinone-based organic supercapacitor (> 6 V) with practical cell structure

Inexpensive, high-performing, and environmentally friendly energy storage devices are required for smart grids that efficiently utilize renewable energy. Energy storage devices consisting of organic active materials are promising because organic materials, especially quinones, are ubiquitous and usually do not require harsh conditions for synthesis, releasing less CO2 during mass production. Although fundamental research-scale aqueous quinone-based organic supercapacitors have shown excellent energy storage performance, no practical research has been conducted. In this study, we aimed to develop a practical-scale aqueous-quinone-based organic supercapacitor. By connecting 12 cells of size 10 cm × 10 cm × 0.5 cm each in series, we fabricated a high-voltage (> 6 V) aqueous organic supercapacitor that can charge a smartphone at a 1 C rate. This is the first step in commercializing aqueous organic supercapacitors that could solve environmental problems, such as high CO2 emissions, air pollution by toxic metals, and limited electricity generation by renewable resources.