Unveiling the Electrochemical Reversibility of Multielectron Redox in s-Tetrazine Derivatives for Large-Capacity Electrode Materials.

Alkali-ion batteries, including potassium-ion batteries, lithium-ion batteries, and sodium-ion batteries are important energy storage devices; however, with the cation size increased, there exists ...

Recently, Organodisulfide compounds have attracted extensive research interests as cathode materials due to the advantages of higher theoretical capacity, environmental friendness, lightweight and abundant resources for high specific energy lithium secondary batteries. The key moiety of high specific capacity in organodisulfide compounds is the reversible two-electron redox reaction of the disulfide bond (S-S). However, the exiting problem of organodisulfide compounds as electrodes materials in LIBs is the large capacity fading caused by the high solubility of polysulfides in liquid electrolytes. An Important strategy to solve this problem is to polymerize the small molecules into insoluble polymeric chains in order to improve the cyclic stability of the electrodes. Based on this strategy, the electrochemical performance and energy storage mechanism of Poly [1, 2-dithiole-3-thion-4(5)-thio] (PDTT) and Poly [2-(1, 2-ethylenediamino)-1, 6, 6a, Δ4-trithia-1, 6-diaza-pentalen-5-yl] (PETDP) were designed, synthesized, and investigated. As shown in figure 1, based on the two-electron reaction, PDTT can provide theoretical capacity of 326 mAh g-1, and the theoretical capacity of PETDP is calculated to be as high as 371 mAh g-1 based on the three-electron reaction. Electrochemical performances of PDTT and PETDP were evaluated by cyclic voltammogram and galvanostatic discharge/charge measurements. CV results indicated that PDTT electrode has two pairs of redox peaks at 2.09/2.38 and 2.29/2.63 V. PETDP cathode also presents two pairs of well-defined redox peaks at 2.11/2.26 and 2.37/2.42 V, respectively. Cyclic performance of PDTT and PETDP was compared using two type of electrolytes, the ether based (1M LiTFSI in DME/DOL) and carbonate based (1M LiPF6 in EC/DMC) electrolytes. Results show that both of them deliver best cyclic stability in ether based electrolyte. In addition, the discharge and charge profiles of PDTT electrode are consistent with its CV curves and having specific capacity of 321 mAh g-1 at a current density of 0.1 C (1C=33 mA g-1), this value is as high as 98.4% of the theoretical capacity. Even at 0.5C rate, high initial capacity of 318 mAh g-1 (97.5% of theoretical value) was obtained, confirming the almost fully utilization of active materials. When cycled over 50 cycles, PDTT electrodes can still deliver high capacities of 291 mAh g-1with capacity retentions of 90.6%, showing a high potential to be used as organodisulfide cathode materials for high capacity Li-S batteries.More details about the charge storage mechanism studies using synchrotron based X-ray absorption spectroscopy will also be presented at the meeting. Acknowledgement The work at Brookhaven National Lab. was supported by the U.S. Department of Energy, the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies (BMR and VTO Battery500 projects) under Contract Number DE-AC02-98CH10886. Figure 1

Cross-conjugated oligomeric quinones for high performance organic batteries

Aqueous Zinc-ion batteries are very appealing for massive energy storage applications due to their inherent safety, low cost, and longevity. Nevertheless, the lack of positive electrode material (cathode) caused by the slow diffusion of Zn2+ inside solid inorganic frameworks is impeding their advancement. Organic electrode materials have recently been endorsed as a less-toxic and environment-benign substitute for traditional inorganic electrode materials. Even though, its performance is hampered by the poor rate capability and limited cycle life caused by cathode material deterioration during Zn2+ insertion/de-insertion. An efficient charge-discharge in aqueous zinc ion batteries, even at high current densities with good capacity retention, is made possible by the stability of aromatic organic heterocyclic cathode materials with the necessary intermolecular spacing. Herein, we describe a strategy to utilize a commercially available redox-active organic molecule (ROM), Phenazine (PNZ) derivative, which can offer efficient and reversible Zn2+ storage due to its high molecular symmetry with low molecular weight. The use of a cation exchange membrane and optimization of volume of the electrolyte and conductive carbon enabled the PNZ electrode to provide a better specific capacity value of 247 mAh g-1 (90% of the theoretical capacity of PNZ) at 1 A g-1 with a good capacity retention of 75 % over 300 cycles. These results indicated that exceptional water insolubility in small organic molecules like PNZ would make them a desirable electrode material for AZIBs. In contrast to conventional design ideas for organic electrode materials such as having a larger molecular weight or adding certain polar functional groups to the organic molecular bulk, our research offered fresh and insightful recommendations for the creation of simpler organic electrodes. Fig. 1. Cyclic performance with charge-discharge plots of PNZ/Katjen black carbon Zinc coin cells with Nafion 212 membrane a) capacity vs. voltage plot b) cycle number vs. capacity plot. Figure 1

ConspectusLithium-ion batteries (LIBs) have achieved great success and dominated the market of portable electronics and electric vehicles owing to their high energy density and long-term cyclability. However, if applying LIBs for large-scale energy storage scenarios, such as regulating the output of electricity generated by sustainable energy in the future age of carbon neutrality, the current electrochemistry of LIBs based on Li-ion interaction/deinteraction between a transition-metal oxide cathode and graphite anode will suffer from problems of scarce natural resources (e.g., Li, Co, and Ni) and high energy consumption/CO2 emission involved in the production of electrodes. Similarly, other commercial batteries such as lead-acid batteries and nickel-metal hydride batteries are also plagued by these issues.In contrast, organic electrode materials, especially carbonyl materials, exhibit advantages of abundant resources, renewability, high capacity, environmental friendliness, and structural designability and have shown great promise for various rechargeable batteries in recent years. However, organic carbonyl electrode materials generally exhibit unsatisfactory cycling stability and rate performance, which are highly dependent on the electrolyte and interfacial chemistry. Appropriate electrolytes and a stable electrode/electrolyte interface would be beneficial for preventing the dissolution of organic carbonyl electrode materials and/or their redox intermediates in electrolytes and promoting fast ion transport between the electrode and electrolyte. In this regard, designing an appropriate electrolyte and constructing a stable electrode/electrolyte interface are the keys to enhancing the comprehensive performance of organic carbonyl electrode materials.In this Account, on the basis of our progress and related works from other groups in the past decade, we afford an overview of understanding the effects of electrolyte and interfacial chemistry on the electrochemical performance of organic carbonyl electrode materials. We will start by briefly introducing the basic properties, working mechanisms, and issues of organic carbonyl electrode materials. Then, the implications of electrolyte and electrode/electrolyte interfacial chemistry on electrochemical performance will be summarized and highlighted through discussing the performance of organic carbonyl electrodes in different types of electrolytes (organic liquid and aqueous and solid-state electrolytes). Meanwhile, the design principles of electrolytes and interfacial chemistry for organic carbonyl electrodes are also discussed. A representative example is that organic carbonyl electrode materials often exhibit better electrochemical performance in ether-based electrolytes than in ester-based electrolytes, which could be mainly attributed to the stable and robust solid electrolyte interphase (SEI) formed on carbonyl electrodes in the ether-based electrolyte. This example demonstrates the importance of investigating the electrode/electrolyte interfacial chemistry of organic carbonyl electrode materials. Finally, future perspectives on designing appropriate electrolytes and understanding electrode/electrolyte interfacial chemistry will also be discussed. It is meaningful to thoroughly reveal the dynamic evolution of the electrode/electrolyte interface during discharge/charge processes and evaluate the compatibility between electrolytes and organic carbonyl electrode materials under practical conditions using limited quantities of electrolytes and high areal-specific-capacity electrodes in the future. This Account could attract more attention to electrolytes and the electrode/electrolyte interfacial chemistry of organic carbonyl electrode materials and finally promote their future commercial applications.

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.

Electrochemical energy storage (EES) systems such as battery and capacitor are important because of their short charge/discharge time, high energy storage efficiency, long cycle life, and ease of integration into renewable energy sources. Currently, lithium-ion batteries have become the dominant power sources for portable electronic devices through the utilization of transition metal oxides or metal phosphates as the positive electrode (Cathode) materials. Now organic electrode materials have obtained great amount of attention because organic electrode materials are composed of inexpensive and earth abundant elements such as carbon, oxygen, nitrogen, sulfur, and hydrogen, and additionally the structural change of organic materials associated with redox reactions is very small compared to significant volume change of conventional metal and metal oxide materials. More importantly, their properties can be finely tuned by well-established principles of organic chemistry. To develop more cost-effective and sustainable battery technology, organic electrode materials have received lots of attention since organic electrode materials are composed of earth abundant elements such as carbon, oxygen, nitrogen, sulfur, and hydrogen and their properties can be finely tuned via well-established principles of organic chemistry. In this study, we aim at establishing an integrated design framework to identify high-performance organic electrode materials through the first-principles modeling approach. Thus, various DFT methods are used to obtain the redox potentials of various quinone-derivatives 1) to identify accurate computational method and process; 2) to achieve the structure-property relationship by investigating effect of molecular architectures such as aromaticity and functional groups on electrochemical properties, which can guide the development of new organic materials for battery applications. We compare our computational results with experimental data for validating our approach.

In spite of the recent progress made in organic electrode materials, high-performance candidates are still lacking, especially when taking affordability into account. Herein, we report a novel polymeric lithium salt, namely dilithium salt of poly(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (Li2PDBM), which can be easily synthesized by phenol-formaldehyde condensation, followed by lithiation in LiOH solution to eliminate the negative effect of phenol groups in PDBM. Benefiting from a high theoretical capacity (327 mA h g-1), structure stability, insolubility, and redox reversibility, Li2PDBM exhibits superior electrochemical performance as a cathode for rechargeable lithium batteries, including a high reversible capacity (256 mA h g-1), a high rate capability (79% @ 2000 mA g-1), and a high cycling stability (77% @ 2000th cycle). Besides the cost-effective electrode material synthesis approach, this work also provides an important mechanistic understanding of the structure-performance relationship of carbonyl-based electrode materials, especially those with -OH or -OM (M = Li, Na, and K) substituents.

Further demand for higher energy density of lithium-ion batteries (LIBs) is growing, especially for the development of electric vehicles to reduce dependence on fossil fuel. Although Co/Ni ions are used as positive electrode materials, its depletion of material resources is an emerging problem. Among electrode materials with 3d transition metal ions, LiVO2 with a layered rocksalt structure (s.g. R-3m) is known to be electrochemical inactive, associated with phase transition during charge. Nevertheless, our group has reported Li-excess Li3NbO4–LiVO2 binary oxides, and Li1.25Nb0.25V0.5O2 on this binary system with a cation disordered rocksalt structure delivers a large reversible capacity of 250 mA h g-1 with two-electron redox of V3+/V5+ at room temperature. (1) In this study. Instead of Li3NbO4, Li2TiO3–LiVO2 binary oxides are targeted as potential high capacity positive electrode materials. We also discuss the possibility of high capacity and long cycle life batteries without Co/Ni ions in the future. Li2TiO3–LiVO2 binary oxides were prepared by conventional calcination method from stoichiometric amounts of Li2CO3, anatase type TiO2, and V2O3. The precursors were mixed by wet ball milling and dried in air, and then calcined at 900 oC for 12 h in argon atmosphere. Thus obtained oxides were mechanically milled at 600 rpm for 36 h to prepare nanosized oxides. All of synthesized samples were stored in an argon filled glovebox to prevent the contact with oxygen and water. Electrode performance of the oxides was examined after reducing particle sizes by ball milling with 10 wt% acetylene black. Crystal structures and electrochemical properties of the oxides were studied by X-ray/neutron diffraction and galvanostatic charge/discharge measurement in two-electrode cells. XRD patterns and SEM images of LiVO2 (x = 0) and Li8/7Ti2/7V4/7O2 (x = 0.33) in the binary system x Li2TiO3–(1 – x) LiVO2 before and after mechanical milling are shown in Fig. 1. As-prepared LiVO2 and Li8/7Ti2/7V4/7O2 crystallized into the layered rocksalt structure (with partial cation disordering for Li8/7Ti2/7V4/7O2) change into nanosized and cation-disordered rocksalt structure (s.g. Fm-3m) after mechanical milling. The mechanical milled samples consist of nanosized, less than 10 nm, and low crystallinity oxides, which are agglomerated for each other, forming (sub-)micrometer-sized secondary particles. Discharge capacities of LiVO2 and Li8/7Ti2/7V4/7O2 obtained by galvanostatic charge/discharge are plotted in Fig. 2. LiVO2 after mixing with carbon by milling delivers a reversible capacity of 150 mA h g-1 in the Li cell, and a much higher reversible capacity of 270 mA h g-1 is observed for Li8/7Ti2/7V4/7O2. XAS study reveals reversible two-electron vanadium redox reaction (V3+/V5+) is activated for Li8/7Ti2/7V4/7O2. Moreover, the nanosized and rocksalt sample prepared by mechanical milling delivers over 300 mA h g-1 even though capacity deterioration is non-negligible in the Li cell with 1 M LiPF6 used as electrolyte. Nevertheless, electrode reversibility is significantly improved for the Li cell with the concentrated electrolyte, LiFSA:DMC = 1:1.1 in a molar ratio,(2) and excellent capacity retention is achieved for continuous 100 cycle test. From these results, we further discuss the origin of excellent capacity retention as electrode materials and possibility of high capacity LIBs with V3+/V5+ two-electron redox in the future.Reference(1) M. Nakajima and N. Yabuuchi, Chem. Mater., 29, 6927 (2017).(2) A. Yamada, et al, Nat. Commun, 7, 12032 (2016). Figure 1

A fundamental and persistent problem in the study of carbonbased electrode materials for lithium ion batteries is the question of how many lithium ions can be inserted onto a C6 aromatic ring. Although different empirical models of Lix/C6 (x< 3) have been proposed, the question remains unresolved. Herein we employ 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), an aromatic compound containing a naphthalene ring system (fused C6 aromatic rings), to demonstrate that each carbon in a C6 ring can accept a Li ion to form a Li6/C6 additive complex through a reversible electrochemical lithium addition reaction. This process results in Li ion insertion capacities of up to nearly 2000 mAhg , depending on the exact molecular structure. This value is several times higher than any other organic electrode material previously reported and can be fully released under certain conditions. Our experiments and theoretical calculations indicate that the anhydride groups on the sides of the aromatic system are crucial for this process, which provides a promising strategy for the design of novel high-performance organic electrode materials. Organic molecules are intriguing candidates for electrode materials for use in rechargeable Li ion batteries. The application of such species has aroused much interest recently, owing to the obvious advantages of such a system: no need for rare metals, low safety risks compared to transition metal oxides, and design flexibility at the molecular level. However, organic molecules are usually considered to possess relatively poor specific energies and cycling properties, as compared to those of inorganic materials, and these factors greatly limit their practical application. Recently, studies on aromatic carbonyl derivatives showed that organic materials can possess outstanding electrochemical performance comparable to, or even superior to, inorganic materials. Furthermore, the wide diversity of organic redox systems, as well as the excellent flexibility in their molecular design, suggest even greater prospects for these materials, and this has inspired the exploration of new organic Li ion insertion systems with improved performance. Aromatic C6 rings are the basic structural units of graphite and other carbon-based electrode materials, which are the most commonly used anodes in commercial Li ion batteries owing to their high electric conductivity and low cost. It has traditionally been believed that each C6 ring can accept one Li ion to form an intercalated Li/C6 complex, giving a relatively low theoretical capacity of 372 mAhg . Recently, studies on graphene, nanographene, and their derivatives reveal that, through the reduction of size and dimensionality, these materials exhibit unique electric and electrochemical properties superior to those of conventional graphitic materials; thus, these materials are currently a hot research topic. In studies of electrode materials for Li ion batteries, these derivatives also exhibit high reversible capacities of up to almost twice the theoretical value of graphite, although the detailed mechanism is still unclear. This leads to a fundamental question in the study of carbonbased electrode materials: How many Li ions can actually be inserted onto each C6 aromatic ring? Multi-ring aromatics (for example, naphthalene, NTCDA, perylene, etc.) and their derivatives have planar C6 ring structures similar to graphene or nanographene. NTCDA is a typical example; it has a naphthalene-like ring structure consisting of two C6 rings fused together along with two cyclic anhydride groups (Figure 1a). NTCDA is a well-known organic semiconductor with good crystallinity and has been extensively studied for use in molecular electric devices. It provides an ideal model to study Li ion insertion onto C6 rings owing to the minimal number of C6 rings it possesses, which guarantees the necessary insolubility of the electrode materials in the commonly used electrolyte solution (ethylene carbonate/dimethyl carbonate/LiPF6) for Li ion batteries. NTCDA also possesses the necessary degree of conductivity for electron transport among molecules. We investigated the electrochemical Li ion insertion/deinsertion properties of NTCDA using model test cells with Li metal as the counter electrode. The working electrode consisted of NTCDA, acetylene black (AB), and polytetrafluoroethylene binders in a weight ratio of about 60:35:5. The cells were initially cycled by discharging (Li ion insertion) and charging (Li ion deinsertion) repeatedly in a potential range of 0.001–3.0 V vs. Li/Li at a moderate current rate of 100 mAg . Figure 1b shows selected discharge/charge curves (the 1st, 2nd, 3rd, and 8th cycles) for NTCDA. Figure 1c shows the corresponding discharge and charge capacities of NTCDA versus the cycle number. The first discharge and charge capacities are 1273 and 724 mAhg , respectively, showing a coulombic efficiency [*] X. Han, G. Qing, T. Sun State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology Wuhan, 430070 (China) E-mail: suntaolei@iccas.ac.cn

Alkali metal storage mechanism in organic semiconductor of perylene-3,4,9,10-tetracarboxylicdianhydride

Approaching the theoretical capacity limit of Na2FeSiO4-based cathodes with fully reversible two-electron redox reaction for sodium-ion battery

Tailoring π-Conjugated Systems: From π-π Stacking to High-Rate-Performance Organic Cathodes

Taming Active Material-Solid Electrolyte Interfaces with Organic Cathode for All-Solid-State Batteries

Lithium-ion battery has received intensive attention as a candidate for efficient and portable electrochemical energy storage systems (EES) to be used in many applications ranging from cell phones to electric vehicles. Lithium-ion batteries not only have the high performance but also cyclic stability making them the optimal choice for recharging-discharging process. Despite the high potential, the slow diffusivity of lithium ions, which is mainly due to the intrinsic properties of the conventional cathode materials, which are mainly transition metal oxides, resulting in poor power density. Organic electrode materials have been considered as promising substitute for metallic oxide cathodes due to safety, low cost, and low density. Among various organic materials, the ones with the carbonyl functional group have been recognized to achieve high-performance redox couples with stable and reversible redox reactions. Finding cathode materials with high redox potentials is critical for organic molecules as they exhibit lower potential compared to the conventional electrode materials. The lower potential exhibited by the organic molecules compared to the metallic oxides are believed to be due to the low ionic conductivity of organic materials, despite having good electron conductivity. In this study, we characterize the electrochemical potentials of quinone-based structures in as a function of molecular structures. Quinone-based organic materials have well-defined active sites and fast electron and ionic transfer kinetics compared to other organic molecules, which is suitable for battery application. We also investigate what factors may contribute to the electrochemical properties using machine learning technique, especially artificial neural network.