Recent progress in organosulfur cathode materials containing heteroatoms

The rapid development of aqueous zinc-ion batteries poses a challenge for the exploration of cathode materials with high capacity and long cycle life. Organic materials are considered an appropriate choice owing to their structural flexibility and tunable surface chemistry. However, most organic cathode materials still have some shortcomings, such as low electrical conductivity, high cost, and limited cycling durability. Here, a facile synthesis of a novel organic composite cathode composed of cross-conjugated polycatechol (PC) combined with graphene (PC/G) is reported. The PC/G cathode is used for aqueous zinc-ion storage, wherein many hydroxy groups in the PC/G composite cathode can be converted into redox-active carbonyl groups at the initial discharge-charge. This composite cathode can deliver a high specific capacity of 355 mAh g-1 at 0.1 C and a specific capacity of 171 mAh g-1 at 10 C. Moreover, the composite cathode can retain 74.4 % of its initial capacity after 3000 discharge-charge cycles at 2 C. This coordination route to zinc ions within the PC/G composite cathode can avoid the destruction of the cathode material during discharge-charge. This organic cathode shows great promise for reversible zinc-ion storage, bringing aqueous zinc-ion batteries a step closer to future practical applications.

Recent progress in organic Polymers-Composited sulfur materials as cathodes for Lithium-Sulfur battery

Organic cathode materials (OCMs) are promising sustainable alternatives to inorganic counterparts for next-generation batteries, yet their widespread application is largely hindered by intrinsically low electrical conductivity (below 10-6 S cm-1) and material dissolution. The vast chemical space for exploration complicates the discovery of optimal OCMs. In this work, we utilized a machine learning (ML)-based discovery process with a pretrained transformer model in ZINC organic molecules database, yielding a couple of potential high-performance OCMs candidates, including isoindigo-type redox units. The output of such efficient screening inspires the design of poly-benzodifurandione (PBFO) as a free-standing cathode material for high-performance Li-ion and Na-ion storage. The flexible PBFO film exhibits a breakthrough conductivity of 5.9×102 S cm-1, setting a new benchmark for additive-free organic cathodes. The neat PBFO cathodes achieve a reversible capacity of 262 mAh g-1 averaging at 2.5V versus Li+/Li at 25mA g-1, delivering a high electrode-level energy density of 655Wh kg-1, among the highest reported for OCMs. This work provides the first flexible, high-conductivity organic cathodes without conductive additives and binders, opening a new direction toward viable organic batteries.

π-Conjugated N-heterocyclic compound with redox-active quinone and pyrazine moieties as a high-capacity organic cathode for aqueous zinc-ion batteries

Na-ion batteries (NIBs) are promising alternatives to Li-ion batteries (LIBs) due to the low cost, abundance, and high sustainability of sodium resources. However, the high performance of inorganic electrode materials in LIBs does not extend to NIBs because of larger ion size of Na+ than Li+ and more complicated electrochemistry. Therefore, it is vital to search for high-performance electrode materials for NIBs. To this end, organic electrode materials (OEMs) with the advantages of high structural tunability and abundant structural diversity show great promise in developing high-performance NIBs. To achieve advanced OEMs for NIBs, a fundamental understanding of the structure–performance correlation is desired for rational structure design and performance optimization. Tailoring molecular structures of OEMs can enhance their performance in Na-ion batteries, however, the substitution rules and the consequent effect on the specific capacity and working potential remain elusive. Herein, we explored the electrochemical performances and reaction mechanisms of various carboxylate-based anode materials, including halogenated sodium carboxylates, N-doped sodium carboxylates, etc. By examining sodium carboxylates with different functional groups, selective N substitution, and extended conjugation structure, we exploited the correlation between structure and performance to establish substitution rules for high-capacity OEMs. Our results show that substitution position and types of functional groups are essential to create active centers for uptake/removal of Na+ and thermodynamically stabilize organic structures. Furthermore, rational host design and electrolytes modulation were performed to extend the cycle life. In addition to sodium carboxylate-based anode materials, we also designed and synthesized novel organic cathode materials based on azo and carbonyl groups for NIBs. The electrochemical performance of the organic cathode materials with an extended conjugated structure such as a naphthalene backbone structure is better than that with benzene and biphenyl structures due to faster kinetics and lower solubility in the electrolyte. It unravels the rational design principle of extending π-conjugation aromatic structures in redox-active polymers to enhance the electrochemical performance. To further optimize the organic cathodes, nitrogen-doped or single layer graphene is employed to increase the conductivity and mitigate the dissolution of organic materials in the electrolytes. The resulting organic cathodes deliver high specific capacity, long cycle life, and fast-charging capability. Post-cycling characterizations were employed to study the chemical structure and morphology evolution upon cycling, demonstrating that the active centers (azo and carbonyl groups) in the organic cathode materials can undergo reversible redox reactions with Na+ for sustainable NIBs. Our work provides a valuable guideline for the design principle of high-capacity and stable OEMs for sustainable energy storage.

Compared with conventional lithium-ion batteries with organic electrolytes, aqueous zinc-ion batteries with low cost, sustainable, and environmentally friendly organic cathodes exhibit promising potential to meet the continuously increasing demand of safe and large-scale energy storage. The representative organic cathodes, including quinoidal polycyclic aromatic hydrocarbons (PAHs) and 2,2,6,6-tetramethylpiperidinyl-N-oxyl (TEMPO) polymers, suffer from challenging synthesis and limited theoretical specific capacity. Herein, different from PAHs and TEMPO polymers, stable 4,4',4″-nitrilotriphenol [TPA-(OH)3] is explored as the organic radical cathode material by extremely low-cost raw materials and two simple reactions. Further, an open-shell TPA-O3 radical is obtained by facile oxidation with air. Interestingly, TPA-O3 showed unexpected higher electron conductivity of 3.35 × 10-4 S cm-1 than the precursor [2.73 × 10-6 S cm-1 for TPA-(OMe)3]. The nitro-like nitroxide resonance structures of TPA-O3 contribute to its high electrochemical stability during the 200-cycle cyclic voltammetry test in air and thus exhibit good reversibility when used as a cathode material. Moreover, TPA-O3 exhibits a reduction voltage of ∼ 1.0 V vs Zn/Zn2+ at 0.5 mV s-1, which is higher than those of most quinone-based cathodes and comparable to TEMPO-type radical cathodes. It also demonstrates a stable capacity of 123.7 mA h g-1 and a high-capacity retention of 95.87% after 2000 stable cycles at 5 A g-1, marking its superiority to those of previously reported organic radical cathodes.

Eliminating the use of critical metals in cathode materials can accelerate global adoption of rechargeable lithium-ion batteries. Organic cathode materials, derived entirely from earth-abundant elements, are in principle ideal alternatives but have not yet challenged inorganic cathodes due to poor conductivity, low practical storage capacity, or poor cyclability. Here, we describe a layered organic electrode material whose high electrical conductivity, high storage capacity, and complete insolubility enable reversible intercalation of Li+ ions, allowing it to compete at the electrode level, in all relevant metrics, with inorganic-based lithium-ion battery cathodes. Our optimized cathode stores 306 mAh g-1cathode, delivers an energy density of 765 Wh kg-1cathode, higher than most cobalt-based cathodes, and can charge-discharge in as little as 6 min. These results demonstrate the operational competitiveness of sustainable organic electrode materials in practical batteries.

Organic radical batteries (ORBs) comprise a relatively new technology that uses cathodes based on stable polymeric organic radical-based polymers. These materials show great promise as cathodes in batteries because the neutral, radical species (at left, Figure 1) is remarkably stable and the one-electron oxidation depicted is fully reversible. The rate at which charge can be pushed into or extracted from an electrode is determined by the timescales on which charges are able to move within an electrode and across an electrode-electrolyte, electrode-current collector interface. This work focused on various test-cell pressures to determine how the charge/discharge processes based on the radical polymer’s redox interfacial and intramolecular mass-transfer processes would be influenced by the external pressure on the organic radical polymer electrode matrix. For the Redox process, reversible oxidation/reduction process for a stablized nitroxide radical PTMA, poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidine-N-oxyl, the expansion-contraction of the polymer by the inclusion-exclusion of the solvated anions during charge-discharge can have a direct affect on the mass transfer mechanism with the electrode matrix. Therefore, we have observed that the rate of the interfacial charge transfer may be affected by; nitroxide radical concentration, cathode capacity, pendant group chain length, cathode thickness and the current collector surface.AC impedance measurement of the composite electrodes at pressure from 25 to 85 inch-lbs revealed a correlation between the overall electron transfer resistance of the composite electrode and the composition of the current collector surface; capacity of nitroxide polymer; and the charge-discharge rate limits. These data suggest that the ionic conduction pathways both across the solvent-electrode interface and within the electrode matrix can be altered by pressure.Specifically, we have observed a gradual decrease in charge transfer resistance with an increase in pressure to 65 in-lbs. It is postulated that due to compression of the porous polymer structure variations possible in mass transfer process, i.e., anionic interfacial migration/diffusion, and intra-electrode diffusion pathways. Then as we continue to increase pressure, that the inability for the polymer matrix to swell, causes an increase in charge transfer resistance, possible due minimal pathways for anion mass-transfer.Overall, our results indicate that the interfacial electron transfer processes both within the electrode matrix, and across the electrolyte-electrode interface can dominate the charge/discharge performance of an organic radical battery system. Therefore, the performance of organic cathode materials could be improved by suitably designing the interfacial structure for specific charge-discharge rate requirements to maximize interfacial charge transfer through distinct composition for maximal pressure, correct polymer expansion and maximized redox sites.The detailed electrochemical investigation including cyclic voltammetry, AC impedance and spectroelectrochemical studies will be presented.Acknowledgements: This work is supported by a grant from the US Department of Energy Basic Energy Sciences Materials Division. Alliance for Sustainable Energy, LLC, managing and operating contractor for the National Renewable Energy Laboratory under U.S. Department of Energy M&O Contract No., DE-AC36-08GO28308

Two organic cathode materials based on the poly(anthraquinonyl sulfide) structure with different substitution positions were synthesized and their electrochemical behavior and battery performance were investigated. The substitution positions on the anthraquinone structure, the type of binders for electrode preparation, and electrolyte formulations have been found to have significant effects on the performance of batteries containing these organic cathode materials. The polymer with less steric hindrance at the substitution positions has higher capacity, longer cycle life and better high-rate capability. Polyvinylidene fluoride binder and ether-based electrolytes are favorable for the high capacity and long cycle life of the anthraquinonyl organic cathodes.

Among various organic cathode materials, C═O group-enriched structures have attracted wide attention worldwide. However, small organic molecules have long suffered from dissolving in electrolytes during charge-discharge cycles. π-Conjugated microporous polymers (CMPs) become one solution to address this issue. However, the synthesis strategy for CMPs with rich C═O groups and stable backbones remains a challenge. In this study, a novel CMP enriched with C═O units was synthesized through a highly efficient Diels-Alder reaction. The as-prepared CMP exhibited a fused carbon backbone and a semiconductive characteristic with a band gap of 1.4 eV. When used as an organic electrode material in LIBs, the insoluble and robust fused structure caused such CMPs to exhibit remarkable cycling stability (a 96.1% capacity retention at 0.2 A g-1 after 200 cycles and a 94.8% capacity retention at 1 A g-1 after 1500 cycles), superior lithium-ion diffusion coefficient (5.30 × 10-11 cm2 s-1), and excellent rate capability (95.8 mAh g-1 at 1 A g-1). This study provided a novel synthetic method for fabricating quinone-enriched fused CMPs, which can be used as LIB cathode materials.

High-performance Mg–organic batteries based on hybrid MgCl2–LiCl/THF electrolytes

Agricultural biomass-based carbon cathode materials for lithium-sulfur batteries: A systematic review

A 2D covalent organic framework as a high-performance cathode material for lithium-ion batteries

Surface Stabilization of O3-type Layered Oxide Cathode to Protect the Anode of Sodium Ion Batteries for Superior Lifespan.

Dual redox groups enable organic cathode material with a high capacity for aqueous zinc-organic batteries