High-Capacity Mg-Organic Batteries Based on Nanostructured Rhodizonate Salts Activated by Mg-Li Dual-Salt Electrolyte

Carbonyl Chemistry for Advanced Electrochemical Energy Storage Systems

On the basis of the sustainable concept, organic compounds and carbon materials both mainly composed of light C element have been regarded as powerful candidates for advanced electrochemical energy storage (EES) systems, due to theie merits of low cost, eco-friendliness, renewability, and structural versatility. It is investigated that the carbonyl functionality as the most common constituent part serves a crucial role, which manifests respective different mechanisms in the various aspects of EES systems. Notably, a systematical review about the concept and progress for carbonyl chemistry is beneficial for ensuring in-depth comprehending of carbonyl functionality. Hence, a comprehensive review about carbonyl chemistry has been summarized based on state-of-the-art developments. Moreover, the working principles and fundamental properties of the carbonyl unit have been discussed, which has been generalized in three aspects, including redox activity, the interaction effect, and compensation characteristic. Meanwhile, the pivotal characterization technologies have also been illustrated for purposefully studying the related structure, redox mechanism, and electrochemical performance to profitably understand the carbonyl chemistry. Finally, the current challenges and promising directions are concluded, aiming to afford significant guidance for the optimal utilization of carbonyl moiety and propel practicality in EES systems.

In-situ dynamic catalysis electrode electrolyte interphase enabling Mg2+ insertion in 2D metal-organic polymer for high-capacity and long-lifespan magnesium batteries

Rechargeable magnesium battery is regarded as the promising candidate for the next generation of high-specific-energy storage systems. Nevertheless, issues related to severe Mg-Cl dissociation at the electrolyte-electrode interface impede the insertion of Mg2+ into most materials, leading to severe polarization and low utilization of Mg-storage electrodes. In this study, a metal-organic polymer (MOP) Ni-TABQ (Ni-coordinated tetramino-benzoquinone) with superior surface catalytic activity is proposed to achieve the high-capacity Mg-MOP battery. The layered Ni-TABQ cathode, featuring a unique 2D π-d linear conjugated structure, effectively reduces the dissociation energy of MgxCly clusters at the Janus interface, thereby facilitating Mg2+ insertion. Due to the high utilization of active sites, Ni-TABQ achieves high capacities of 410 mAh/g at 200 mA g-1, attributable to a four-electron redox process involving two redox centers, benzoid carbonyls, and imines. This research highlights the importance of surface electrochemical processes in rechargeable magnesium batteries and paves the way for future development in multivalent metal-ion batteries.

Ball-in-ball NiS2@CoS2 heterojunction driven by Kirkendall effect for high-performance Mg2+/Li+ hybrid batteries

Mg2+/Li+ hybrid batteries (MLHBs), which support the rapid insertion and removal of Mg2+/Li+ bimetallic ions, are promising energy storage systems. Inspired by the Kirkendall effect, ball-in-ball bimetallic sulfides with heterostructures were prepared as cathode materials for the MLHBs. First, a nickel-cobalt precursor (NiCo-X precursor) with three-dimensional (3D) nanosheets on its surface was prepared using a solvothermal method based on the association reaction between alkoxide molecules. Subsequently, the NiCo-X precursor was vulcanized at high temperature using the potential energy difference as the driving force to successfully prepare NiS2@CoS2 core-shell hollow spheres. When used as the positive electrode material for the MLHBs, the NiS2@CoS2 hollow spheres exhibited excellent Mg2+/Li+ ion storage capacity, high specific capacity, good rate performance, and stable cyclic stability owing to their tough hierarchical structure. At a current density of 500 mA g-1, a specific capacity of 536 mAh g-1 was maintained after 200 cycles. By explaining the transformation mechanism of Mg2+/Li+ in bimetallic sulfides, it was proven that Mg2+ and Li+ worked cooperatively. This study provides a new approach for developing MLHBs with good electrochemical properties.

Oxocarbon Acids and their Derivatives in Biological and Medicinal Chemistry

The biological and medicinal chemistry of the oxocarbon acids 2,3- dihydroxycycloprop-2-en-1-one (deltic acid), 3,4-dihydroxycyclobut-3-ene-1,2-dione (squaric acid), 4,5-dihydroxy-4-cyclopentene-1,2,3-trione (croconic acid), 5,6-dihydroxycyclohex- 5-ene-1,2,3,4-tetrone (rhodizonic acid) and their derivatives is reviewed and their key chemical properties and reactions are discussed. Applications of these compounds as potential bioisosteres in biological and medicinal chemistry are examined. Reviewed areas include cell imaging, bioconjugation reactions, antiviral, antibacterial, anticancer, enzyme inhibition, and receptor pharmacology.

A High-Rate and Long-Life Aqueous Rechargeable Mg-Ion Battery Based on an Organic Anode Integrating Diimide and Triazine

Aqueous Mg-ion batteries (MIBs) lack reliable anode materials. This study concerns the design and synthesis of a new anode material - a π-conjugate of 3D-poly(3,4,9,10-perylenetracarboxylic diimide-1,3,5-triazine-2,4,6-triamine) [3D-P(PDI-T)] - for aqueous MIBs. The increased aromatic structure inhibits solubility in aqueous electrolytes, enhancing its structural stability. The 3D-P(PDI-T) anode exhibits several notable characteristics, including an extremely high rate capacity of 358 mAh g^-1 at 0.05 A g^-1 , A 3D-P(PDI-T)‖Mg₂ MnO₄ full cell exhibits a reversible capacity of 148 mAh g^-1 and a long cycle life of 5000 cycles at 0.5 A g^-1 . The charge storage mechanism reveals a synergistic interaction of Mg²⁺ and H⁺ cations with C-N/C=O groups. The assembled 3D-P(PDI-T)‖Mg₂ MnO₄ full cell exhibits a capacity retention of around 95 % after 5000 cycles at 0.5 A g^-1 . This 3D-P(PDI-T) anode sustained its framework structure during the charge-discharge cycling of Mg-ion batteries. The reported results provide a strong basis for a cutting-edge molecular engineering technique to afford improved organic materials that facilitate efficient charge-storage behavior of aqueous Mg-ion batteries.

Dual-Ion Intercalation Chemistry Enabling Hybrid Metal-Ion Batteries

To outline the role of dual-ion intercalation chemistry to reach sustainable energy storage, the present Review aimed to compare two types of batteries: widely accepted dual-ion batteries based on cationic and anionic co-intercalation versus newly emerged hybrid metal-ion batteries using the co-intercalation of cations only. Among different charge carrier cations, the focus was on the materials able to co-intercalate monovalent ions (such Li⁺ and Na⁺ , Li⁺ and K⁺ , Na⁺ and K⁺ , etc.) or couples of mono- and multivalent ions (Li⁺ and Mg²⁺ , Na⁺ and Mg²⁺ , Na⁺ and Zn²⁺ , H⁺ and Zn²⁺ , etc.). Furthermore, the Review was directed on co-intercalation materials composed of environmentally benign and low-cost transition metals (e. g., Mn, Fe, etc.). The effect of the electrolyte on the co-intercalation properties was also discussed. The summarized knowledge on dual-ion energy storage could stimulate further research so that the hybrid metal-ion batteries become feasible in near future.

Electrolytes in Organic Batteries

Organic batteries using redox-active polymers and small organic compounds have become promising candidates for next-generation energy storage devices due to the abundance, environmental benignity, and diverse nature of organic resources. To date, tremendous research efforts have been devoted to developing advanced organic electrode materials and understanding the material structure-performance correlation in organic batteries. In contrast, less attention was paid to the correlation between electrolyte structure and battery performance, despite the critical roles of electrolytes for the dissolution of organic electrode materials, the formation of the electrode-electrolyte interphase, and the solvation/desolvation of charge carriers. In this review, we discuss the prospects and challenges of organic batteries with an emphasis on electrolytes. The differences between organic and inorganic batteries in terms of electrolyte property requirements and charge storage mechanisms are elucidated. To provide a comprehensive and thorough overview of the electrolyte development in organic batteries, the electrolytes are divided into four categories including organic liquid electrolytes, aqueous electrolytes, inorganic solid electrolytes, and polymer-based electrolytes, to introduce different components, concentrations, additives, and applications in various organic batteries with different charge carriers, interphases, and separators. The perspectives and outlook for the future development of advanced electrolytes are also discussed to provide a guidance for the electrolyte design and optimization in organic batteries. We believe that this review will stimulate an in-depth study of electrolytes and accelerate the commercialization of organic batteries.

Dual fluorination of polymer electrolyte and conversion-type cathode for high-capacity all-solid-state lithium metal batteries

All-solid-state batteries are appealing electrochemical energy storage devices because of their high energy content and safety. However, their practical development is hindered by inadequate cycling performances due to poor reaction reversibility, electrolyte thickening and electrode passivation. Here, to circumvent these issues, we propose a fluorination strategy for the positive electrode and solid polymeric electrolyte. We develop thin laminated all-solid-state Li||FeF3 lab-scale cells capable of delivering an initial specific discharge capacity of about 600 mAh/g at 700 mA/g and a final capacity of about 200 mAh/g after 900 cycles at 60 °C. We demonstrate that the polymer electrolyte containing AlF3 particles enables a Li-ion transference number of 0.67 at 60 °C. The fluorinated polymeric solid electrolyte favours the formation of ionically conductive components in the Li metal electrode's solid electrolyte interphase, also hindering dendritic growth. Furthermore, the F-rich solid electrolyte facilitates the Li-ion storage reversibility of the FeF3-based positive electrode and decreases the interfacial resistances and polarizations at both electrodes.

Challenges and Perspectives of Organic Multivalent Metal-Ion Batteries

Rechargeable organic multivalent metal-ion batteries (MMIBs) have attracted a surge of interest as promising alternatives for large-scale energy storage applications because they can combine the advantages of both organic electrodes and multivalent metal-ion batteries. However, the development of organic MMIBs is hampered by many factors, which mean they lag far behind organic alkali-metal- (e.g., Li-, Na-, and K-) ion batteries. Herein, the challenges that are specifically faced by organic MMIBs are analyzed and the strategies that can probably solve such challenges are then discussed. As a special challenge that organic MMIBs are facing, the charge-storage mechanism is particularly underlined to deeply understand the structure-property relationships for guiding the future design of high-performance organic electrodes for MMIBs. The perspectives are thereby elaborated in this review with the outlook of practical applications of organic MMIBs.

Molecular and Morphological Engineering of Organic Electrode Materials for Electrochemical Energy Storage

Organic electrode materials (OEMs) can deliver remarkable battery performance for metal-ion batteries (MIBs) due to their unique molecular versatility, high flexibility, versatile structures, sustainable organic resources, and low environmental costs. Therefore, OEMs are promising, green alternatives to the traditional inorganic electrode materials used in state-of-the-art lithium-ion batteries. Before OEMs can be widely applied, some inherent issues, such as their low intrinsic electronic conductivity, significant solubility in electrolytes, and large volume change, must be addressed. In this review, the potential roles, energy storage mechanisms, existing challenges, and possible solutions to address these challenges by using molecular and morphological engineering are thoroughly summarized and discussed. Molecular engineering, such as grafting electron-withdrawing or electron-donating functional groups, increasing various redox-active sites, extending conductive networks, and increasing the degree of polymerization, can enhance the electrochemical performance, including its specific capacity (such as the voltage output and the charge transfer number), rate capability, and cycling stability. Morphological engineering facilitates the preparation of different dimensional OEMs (including 0D, 1D, 2D, and 3D OEMs) via bottom-up and top-down methods to enhance their electron/ion diffusion kinetics and stabilize their electrode structure. In summary, molecular and morphological engineering can offer practical paths for developing advanced OEMs that can be applied in next-generation rechargeable MIBs.

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A Magnesium/Lithium Hybrid-Ion Battery with Modified All-Phenyl-Complex-Based Electrolyte Displaying Ultralong Cycle Life and Ultrahigh Energy Density

Magnesium/lithium hybrid-ion batteries (MLHBs) combine the advantages of high safety and fast ionic kinetics, which enable them to be promising emerging energy-storage systems. Here, a high-performance MLHB using a modified all-phenyl complex with a lithium bis(trifluoromethanesulfonyl)imide electrolyte and a NiCo₂S₄ cathode on a copper current collector is developed. A reversible conversion involving a copper collector with NiCo₂S₄ efficiently avoids the electrolyte dissociation and diffusion difficulties of Mg²⁺ ions, enabling low polarization and fast redox, which is verified by X-ray absorption near edge structure analysis. Such combination affords the best MLHB among all those ever reported, with a reversible capacity of 204.7 mAh g^-1 after 2600 cycles at 2.0 A g^-1, and delivers an ultrahigh full electrode-basis energy density of 708 Wh kg^-1. The developed MLHB also achieves good rate performance and temperature tolerance at -10 and 50 °C with a low electrolyte consumption. The hybrid-ion battery system presented here could inspire a broad set of engineering potentials for high-safety battery technologies and beyond.

Triple Conductive Wiring by Electron Doping, Chelation Coating and Electrochemical Conversion in Fluffy Nb2 O5 Anodes for Fast-Charging Li-Ion Batteries

High-rate anode material is the kernel of developing fast-charging lithium ion batteries (LIBs). T-Nb2 O5 , well-known for its "room and pillar" structure and bulk pseudocapacitive effect, is expected to enable the fast lithium (de)intercalation. But this property is still limited by the low electronic conductivity or insufficient wiring manner. Herein, a strategy of triple conductive wiring through electron doping, chelation coating, and electrochemical conversion inside the microsized porous spheres consisting of dendrite-like T-Nb2 O5 primary particles is proposed to achieve the fast-charging and durable anodes for LIBs. The penetrative implanting of conformal carbon coating (derivative from polydopamine chelate) and NbO domains (induced by excess discharging) reinforces the global supply of electronically conductive wires, apart from those from Co/Mn heteroatom or O vacancy doping. The polydopamine etching on T-Nb2 O5 spheres promotes their evolution into fluffy morphology with better electrolyte infiltration. The synergic electron and ion wiring at different scales endow the modified T-Nb2 O5 anode with ultralong cycling life (143 mAh g-1 at 1 A g-1 after 8500 cycles) and high-rate performance (144.1 mAh g-1 at 10.0 A g-1 ). The permeation of multiple electron wires also enables a high mass loading of T-Nb2 O5 (4.5 mg cm-2 ) with a high areal capacity of 0.668 mAh cm-2 even after 150 cycles.

Size-Controllable Nickel Sulfide Nanoparticles Embedded in Carbon Nanofibers as High-Rate Conversion Cathodes for Hybrid Mg-Based Battery

The integration of highly-safe Mg anode and fast Li+ kinetics endows hybrid Mg2+ /Li+ batteries (MLIBs) a promising future, but the practical application is circumvented by the lack of appropriate cathodes that enable the realization of an enough participation of Mg2+ in the reactions, resulting in a high dependence on Li+ . Herein, the authors develop a series of size-controllable nickel sulfide nanoparticles embedded in carbon nanofibers (NiS@C) with synergistic effect of particle diameter and carbon content as the cathode material for MLIBs. The optimized particle size is designed to maximize the utilization of the active material and remit internal stress, and appropriate carbon encapsulation efficiently inhibiting the pulverization of particles and accelerates the ability of conducting ions and electrons. In consequence, the representative NiS@C delivers superior electrochemical performance with a highest discharge capacity of 435 mAh g-1 at 50 mA g-1 . Such conversion cathode also exhibits excellent rate performance and remarkable cycle life. Significantly, the conversion mechanism of NiS in MLIBs is unambiguously demonstrated for the first time, affirming the corporate involvement of both Mg2+ and Li+ at the cathodic side. This work underlines a guide for developing conversion-type materials with high rate capability and cyclic performance for energy storage applications.

Interface Behavior of Electrolyte/Quinone Organic Active Material in Battery Operation by Operando Surface-Enhanced Raman Spectroscopy

To elucidate the microscopic charge/discharge (delithiation/lithiation) mechanism at the interface of the electrolyte and organic cathode active material in the lithium-ion battery, we prepared a self-assembled monolayer (SAM) electrode of 1,4-benzoquinone terminated dihexyl disulfide (BQ-C6) on Au(111). An electrochemical setup with the BQ-C6 SAM as a working electrode and 1 M lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI)/triethyleneglycol dimethylether (G3) as the electrolyte was used. We adopted the shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS) method to obtain sufficient Raman signal of SAM for operando Raman spectroscopy measurements by the enhancement with ∼100 nm diameter Au particles coated with SiO₂ shell (average thickness = 2 nm). By this method, we succeeded in acquiring the Raman signal of the molecular monolayer on the model electrode simulating the interface between the electrolyte and the organic active material. In the cyclic voltammogram, two peaks were observed during the reduction reaction (lithiation), whereas only one peak was detected in the course of the oxidation process (delithiation). Simultaneous operando SHINERS showed a two-step spectral shape change in lithiation and coinciding (or simultaneous) one-step recovery during delithiation to match cyclic voltammetry behavior. The results indicate an asymmetric lithiation/delithiation mechanism.

Red Phosphorus Anchored on Nitrogen-Doped Carbon Bubble-Carbon Nanotube Network for Highly Stable and Fast-Charging Lithium-Ion Batteries

A nitrogen-doped carbon bubble-carbon nanotube@red phosphorus (N-CBCNT@rP) network composite is fabricated, featuring an rP film embedded in a highly N-doped CBCNT network with hierarchical pores of different sizes and interior void spaces. Highly N-doped CBCNT with an optimized structure is utilized to achieve an ultrahigh rP content of 53 wt% in the N-CBCNT@rP composite by the NP bond, which shows a record rP content for rP-carbon composites by the vaporization-condensation process. When tested as an anode for lithium-ion batteries, the N-CBCNT@rP composite exhibits an ultrahigh initial Coulombic efficiency of 87.5%, high specific capacity, outstanding rate performance, and superior cycling stability at a high current density (capacity decay of 0.011% per cycle over 1500 cycles at 5 A g^-1 ), which is the lowest capacity fading rate of those previously reported for rP-based electrodes. The superior lithium-ion storage performance of the N-CBCNT@rP composite electrode is primarily attributed to its structure. The 3D hierarchical conducting network of the N-CBCNT@rP composite with abundant N-P bonds endows the entire electrode with maximized conductivity for superior ion and electron transfer kinetics. Moreover, N-CBCNT networks with hierarchical pores of different sizes can fix the location of rP, prevent agglomeration, and avoid volume expansion of rP.

Solvation Effect on the Improved Sodium Storage Performance of N-Heteropentacenequinone for Sodium-Ion Batteries

The performance of electrode material is correlated with the choice of electrolyte, however, how the solvation has significant impact on electrochemical behavior is underdeveloped. Herein, N-heteropentacenequinone (TAPQ) is investigated to reveal the solvation effect on the performance of sodium-ion batteries in different electrolyte environment. TAPQ cycled in diglyme-based electrolyte exhibits superior electrochemical performance, but experiences a rapid capacity fading in carbonate-based electrolyte. The function of solvation effect is mainly embodied in two aspects: one is the stabilization of anion intermediate via the compatibility of electrode and electrolyte, the other is the interfacial electrochemical characteristics influenced by solvation sheath structure. By revealing the failure mechanism, this work presents an avenue for better understanding electrochemical behavior and enhancing performance from the angle of solvation effect.

Advancing towards a Practical Magnesium Ion Battery

A post-lithium battery era is envisaged, and it is urgent to find new and sustainable systems for energy storage. Multivalent metals, such as magnesium, are very promising to replace lithium, but the low mobility of magnesium ion and the lack of suitable electrolytes are serious concerns. This review mainly discusses the advantages and shortcomings of the new rechargeable magnesium batteries, the future directions and the possibility of using solid electrolytes. Special emphasis is put on the diversity of structures, and on the theoretical calculations about voltage and structures. A critical issue is to select the combination of the positive and negative electrode materials to achieve an optimum battery voltage. The theoretical calculations of the structure, intercalation voltage and diffusion path can be very useful for evaluating the materials and for comparison with the experimental results of the magnesium batteries which are not hassle-free.

Hierarchical 3D Cuprous Sulfide Nanoporous Cluster Arrays Self-Assembled on Copper Foam as a Binder-Free Cathode for Hybrid Magnesium-Based Batteries

On account of easy accessibility, high theoretical volumetric capacity and dendrite-free magnesium (Mg) anode, Mg battery has a great promise to be next generation rechargeable batteries, yet still remains a challenging task in acquiring fast Mg²⁺ kinetics and effective cathode materials. Herein, hierarchical 3D cuprous sulfide porous nanosheet decorated nanowire cluster arrays with robust adhesion on copper foam (Cu₂ S HP/CF), which is employed as a binder-free conversion cathode material for magnesium/lithium hybrid battery, delivering impressively initial and reversible specific capacity of 383 and 311 mAh g^-1 at 100 mA g^-1 , respectively, which are obviously outperformed corresponding powder cathode in a traditional method by using polymer binder, is reported. Intriguingly, benefiting from the hierarchical nanoporous array architecture and self-assembly feature, Cu₂ S HP/CF cathode shows a remarkable cycling stability with a high capacity of 129 mAh g^-1 at 300 mA g^-1 over 500 cycles. This work not only highlights a guide for designing hierarchical nanoporous materials derived from metal-organic frameworks, but also provides a novel strategy of in situ formation to fabricate binder-free cathodes.

Rechargeable Mg-Na and Mg-K hybrid batteries based on a low-defect Co3[Co(CN)6]2 nanocube cathode

Rechargeable Mg-Li hybrid batteries have the merits of a Mg metal anode and a Li⁺ intercalation cathode, but the limited availability of Li resources hinders their large-scale application. Herein, rechargeable Mg-Na and Mg-K hybrid batteries are constructed with a low-defect Co₃[Co(CN)₆]₂ nanocube cathode. The large redox active cavities of Co₃[Co(CN)₆]₂ are highly favorable for reversible Na⁺ and K⁺ intercalations. The Mg-Na and Mg-K hybrid batteries provide reversible capacities of 123 and 126 mA h g^-1, respectively, and a stable long-term cycling over 600 cycles. By contrast, the Mg-Li hybrid battery delivers a much lower capacity of 55 mA h g^-1. It is also demonstrated that controlled crystallization of well-defined nanocubes with few lattice defects is important for these high-capacity Mg-Na and Mg-K hybrid battery cathodes. The low-defect Co₃[Co(CN)₆]₂ nanocube cathode shows good rate capability, providing specific capacities of 45 and 53 mA h g^-1 at 1000 mA g^-1 in Mg-Na and Mg-K hybrid batteries, respectively. This study illustrates that low-defect Prussian blue analogs of Co₃[Co(CN)₆]₂ are highly compatible and promising cathodes for Mg-Na and Mg-K hybrid batteries. The present study also provides a new method for the development of low-cost and high-performance batteries based on Mg metal anodes.

A Chlorine-Free Electrolyte Based on Non-nucleophilic Magnesium Bis(diisopropyl)amide and Ionic Liquid for Rechargeable Magnesium Batteries

The electrolyte based on magnesium bis(diisopropyl)amide (MBA), a low-cost and non-nucleophilic organic magnesium salt, is proposed to be an admirable alternative for rechargeable magnesium batteries but suffers from limited ionic conductivity and an inferior electrochemical window in the commonly used ether solvents. In this work, the 1-butyl-1-methylpiperidinium bis(trifluoromethyl sulfonyl)imide (PP₁₄TFSI) ionic liquid as the cosolvent of tetrahydrofuran (THF) in chlorine-free MBA-based electrolytes has been first demonstrated to remarkably improve the ionic conductivity and broaden the oxidative stable potential (2.2 V vs Mg/Mg²⁺) on stainless steel. Reversible Mg electrochemical plating/stripping with a low overpotential below 200 mV and ca. 90% Coulombic efficiency are obtained. The current density of Mg plating/stripping is increased 238 times after the addition of PP₁₄TFSI, where the mechanism of competitive coordination of TFSI^- making an easier Mg plating/stripping is proposed theoretically. The MBA-2AlF₃ electrolyte with a ratio-optimized THF/PP₁₄TFSI cosolvent exhibits good compatibility with the Mo₆S₈ cathode. Furthermore, the Se@pPAN|Mg full cell exhibits an initial capacity of 447.8 mAh g^-1 and as low as ∼0.66% capacity decay per cycle for more than 70 cycles at 0.2 C with the synergy of LiTFSI additives. The facile modification strategy of ionic liquid in the MBA-based electrolyte sheds inspiring light on exploring non-nucleophilic and chlorine-free electrolytes for practical rechargeable magnesium batteries.

Maximizing Magnesiation Capacity of Nanowire Cluster Oxides by Conductive Macromolecule Pillaring and Multication Intercalation

Magnesium metal batteries (MMBs) have obtained the reputation owing to the high volumetric capacity, low reduction potential, and dendrite-free deposition behavior of the Mg metal anode. However, the bivalent nature of the Mg²⁺ causes its strong coulombic interaction with the cathode host, which limits the reaction kinetics and reversibility of MMBs, especially based on oxide cathodes. Herein, a synergetic modulation of host pillaring and electrolyte formulation is proposed to activate the layered V₂ O₅ cathode with expanded interlayers via sequential intercalations of poly(3,4-ethylenedioxythiophene) (PEDOT) and cetyltrimethylammonium bromide (CTAB). The preservation of bundled nanowire texture, copillaring behavior of PEDOT and CTA⁺ , dual-insertion mode of Mg²⁺ and MgCl⁺ at cathode side enable the better charge transfers in both the bulk and interface paths as well as the interaction mitigation effect between Mg-species cations and host lattices. The introduction of CTA⁺ as electrolyte additive can also lower the interface resistance and smoothen the Mg anode morphology. These modifications endow the full cells coupled with metallic Mg anode with the maximized reversible capacity (288.7 mAh g^-1 ) and superior cyclability (over 500 cycles at 500 mA g^-1 ), superior to most already reported Mg-ion shuttle batteries even based on passivation-resistant non-Mg anodes or operated at higher temperatures.

Unlocking solid-state conversion batteries reinforced by hierarchical microsphere stacked polymer electrolyte

Pursuing all-solid-state lithium metal batteries with dual upgrading of safety and energy density is of great significance. However, searching compatible solid electrolyte and reversible conversion cathode is still a big challenge. The phase transformation at cathode and Li deformation at anode would usually deactivate the electrode-electrolyte interfaces. Herein, we propose an all-solid-state Li-FeF₃ conversion battery reinforced by hierarchical microsphere stacked polymer electrolyte for the first time. This g-C₃N₄ stuffed polyethylene oxide (PEO)-based electrolyte is lightweight due to the absence of metal element doping, and it enables the spatial confinement and dissolution suppression of conversion products at soft cathode-polymer interface, as well as Li dendrite inhibition at filler-reinforced anode-polymer interface. Two-dimensional (2D)-nanosheet-built porous g-C₃N₄ as three-dimensional (3D) textured filler can strongly cross-link with PEO matrix and LiTFSI (TFSI: bistrifluoromethanesulfonimide) anion, leading to a more conductive and salt-dissociated interface and therefore improved conductivity (2.5 × 10^-4 S/cm at 60 °C) and Li⁺ transference number (0.69). The compact stacking of highly regular robust microspheres in polymer electrolyte enables a successful stabilization and smoothening of Li metal with ultra-long plating/striping cycling for at least 10,000 h. The corresponding Li/LiFePO₄ solid cells can endure an extremely high rate of 12 C. All-solid-state Li/FeF₃ cells show highly stabilized capacity as high as 300 mAh/g even after 200 cycles and of ~200 mAh/g at extremely high rate of 5 C, as well as ultra-long cycling for at least 1200 cycles at 1 C. High pseudocapacitance contribution (>55%) and diffusion coefficient (as high as 10^-12 cm²/s) are responsible for this high-rate fluoride conversion. This result provides a promising solution to conversion-type Li metal batteries of high energy and safety beyond Li-S batteries, which are difficult to realize true "all-solid-state" due to the indispensable step of polysulfide solid-liquid conversion.

Molecular Regulation on Carbonyl-Based Organic Cathodes: Toward High-Rate and Long-Lifespan Potassium-Organic Batteries

Organic redox-active molecules have been identified as promising cathodes for practical usage of potassium-ion batteries (PIBs) but still struggle with serious dissolution problems and sluggish kinetic properties. Herein, we propose a pseudocapacitance-dominated novel insoluble carbonyl-based cathode, [2,6-di[1-(perylene-3,4,9,10-tetracarboxydiimide)]anthraquinone, AQ-diPTCDI], which possesses high reversible capacities of 150 mAh g^-1, excellent cycle stability with capacity retention of 88% over 2000 cycles, and fast kinetic properties. The strong intermolecular interactions of AQ-diPTCDI and in situ formed cathode electrolyte interphase films support it against the dissolution problem. The high capacitive-like contribution in capacities and fast potassium-ion diffusion enhance its reaction kinetics. Moreover, a symmetric organic potassium-ion battery (OPIB) based on AQ-diPTCDI electrodes also exhibits outstanding K-storage capability. These results suggest that AQ-diPTCDI is a promising organic cathode for OPIBs and provide a practicable route to realize high-performance K storage.

Oxygen-Functionalized Polyacrylonitrile Nanofibers with Enhanced Performance for Lithium-Ion Storage

Functionalization and morphological construction can promote lithium-ion storage performance of organic polymers. In this contribution, exceptional lithium ion storage performance is empowered to porous polyacrylonitrile (PAN) nanofibers via the integration of template-assisted electrospinning technology and thermal treatment. It is found that the atmosphere adopted during the annealing process controls the storage behaviors of Li⁺. Impressively, the samples annealed in air present competitive capacities, rate capabilities, and a stable lifetime, compared with other counterparts (PAN powders and PAN fibers treated in N₂). Such enhancement in performance is attributed to the enriched oxygen-based functionalities (mainly C=O group) which guarantee a high specific capacity and the porous structure which facilitates the transportation of Li⁺ and electrons to improve the rate capability. It is envisioned that such morphology control and surface functionalization open up new horizons in the development of organic electrode materials with enhanced lithium-ion storage performances.

Efficient Na+-storage in a Li4Ti5O12 anode to expand the voltage-window for full SIBs of high energy density

The stable storage of sodium ions always presents some difficulties for sodium-based dual-ion batteries (S-DIBs), such as the irreversibility of guest-storage and kinetic hindrance in the anode. Based on the low strain volume and stable phase structure, herein, lithium titanate (LTO, Li₄Ti₅O₁₂) was developed to store sodium ions between the working potential (∼0.8 V), which expands the lower plateau over than that of lithium ion storage (∼1.55 V) to obtain a high energy density of full batteries. The spinel lithium titanate shows negligible volume change and extremely stable structure under Na⁺-storage, which completely overcomes the shortage problems of the Na⁺-host. Additionally, by the detection of the transfer state of anions and cations in dual-ion batteries, the diffusion coefficient of the sodium ion in the LTO electrode is higher than that of the cathode, which shows that the transport process of sodium ions can meet the kinetic demands of full batteries. Such S-DIBs exhibit a large working voltage of 2.0–4.6 V and stable electrochemical performance over 1280 cycles, which is superior to conventional sodium-based systems, and further exhibit many advantages such as high energy density, environmental friendliness, and low cost.

The stable storage of sodium ions always presents some difficulties for sodium-based dual-ion batteries (S-DIBs), such as the irreversibility of guest-storage and kinetic hindrance in the anode.

Three-Dimensional Magnesiophilic Scaffolds for Reduced Passivation toward High-Rate Mg Metal Anodes in a Noncorrosive Electrolyte

Magnesium ion batteries are a promising alternative of the lithium counterpart; however, the poorly ion-conductive passivation layer on Mg metal makes plating/stripping difficult. In addition to the generally recognized chemical passivation, the interphase is dynamically degraded by electrochemical side reactions. Especially under high current densities, the interphase thickens, exacerbating the electrode degradation. Herein, we adopt 3D Mg₃Bi₂ scaffolds for Mg metal, of which the high surface area reduces the effective current density to avoid continuous electrolyte decomposition and the good Mg affinity homogenizes nucleation. The greatly alleviated passivation layer could serve as a stable solid/electrolyte interface instead. The symmetric cell delivers a low overpotential of 0.21 and 0.50 V at a current density of 0.1 and 4 mA cm^-2, respectively, and a superior cycling performance over 300 cycles at 0.5 mA cm^-2 in a noncorrosive conventional electrolyte. This work proves that the control of dynamic passivation can enable high-power density Mg metal anodes.

Sustainable Battery Materials from Biomass

Sustainable sources of energy have been identified as a possible way out of today's oil dependency and are being rapidly developed. In contrast, storage of energy to a large extent still relies on heavy metals in batteries. Especially when built from biomass-derived organics, organic batteries are promising alternatives and pave the way towards truly sustainable energy storage. First described in 2008, research on biomass-derived electrodes has been taken up by a multitude of researchers worldwide. Nowadays, in principle, electrodes in batteries could be composed of all kinds of carbonized and noncarbonized biomass: On one hand, all kinds of (waste) biomass may be carbonized and used in anodes of lithium- or sodium-ion batteries, cathodes in metal-sulfur or metal-oxygen batteries, or as conductive additives. On the other hand, a plethora of biomolecules, such as quinones, flavins, or carboxylates, contain redox-active groups that can be used as redox-active components in electrodes with very little chemical modification. Biomass-based binders can replace toxic halogenated commercial binders to enable a truly sustainable future of energy storage devices. Besides the electrodes, electrolytes and separators may also be synthesized from biomass. In this Review, recent research progress in this rapidly emerging field is summarized with a focus on potentially fully biowaste-derived batteries.

Rechargeable Zn-MnO2 batteries: advances, challenges and perspectives

As one type of advanced alternative batteries, zinc-ion batteries (ZIBs) have attracted increasing attention because of their advantages of cost-effectiveness, high safety and environmentally benign features. However, the performance of cathode materials has become a bottleneck for the future application of ZIBs. In recent years, manganese dioxide (MnO₂)-based materials as cathodes for ZIBs have been intensively explored. In this review, recent advances in MnO₂-based cathode materials for ZIBs are comprehensively reviewed with a discussion about the reaction mechanisms for the fundamental understanding of the electrochemical processes. Furthermore, several challenges hindering the technology maturity are also analyzed with corresponding strategies to further improve the electrochemical performance of such Zn-MnO₂ batteries.

Challenges and benefits of post-lithium-ion batteries

Post-Li-ion batteries based on Na, Mg, and Al offer substantial electrochemical and economic advantages in comparison with Li-ion batteries.

A quasi-solid composite electrolyte with dual salts for dendrite-free lithium metal batteries

The cycle stability of the Li|HSE|Li battery can be greatly improved by adding magnesium salt to the electrolyte membrane.

Two-dimensional Nb2O5 holey nanosheets prepared by a graphene sacrificial template method for high performance Mg2+/Li+ hybrid ion batteries

Mg²⁺/Li⁺ hybrid ion batteries (MLIBs) are regarded as promising candidates for electrical energy devices due to their combination of a fast lithium intercalation cathode and a safe magnesium anode. Herein, two-dimensional Nb₂O₅ holey nanosheets are synthesized using a graphene oxide sacrificial template method and these are then used as the cathode of a MLIB for the first time. It exhibits a high discharge capacity (195.9 mA h g^-1 at 100 mA g^-1), excellent rate performance (72.1 mA h g^-1 at 2000 mA g^-1) and a long cycling life (exhibiting a capacity fading rate of 0.032% per cycle at 2000 mA g^-1 over 1000 cycles). The remarkable electrochemical performance can be attributed to the unique two-dimensional holey nanosheet structure, which is beneficial for improving electronic conductivity and lithium ion conductivity.

Molecular Design Strategies for Electrochemical Behavior of Aromatic Carbonyl Compounds in Organic and Aqueous Electrolytes

To sustainably satisfy the growing demand for energy, organic carbonyl compounds (OCCs) are being widely studied as electrode active materials for batteries owing to their high capacity, flexible structure, low cost, environmental friendliness, renewability, and universal applicability. However, their high solubility in electrolytes, limited active sites, and low conductivity are obstacles in increasing their usage. Here, the nucleophilic addition reaction of aromatic carbonyl compounds (ACCs) is first used to explain the electrochemical behavior of carbonyl compounds during charge-discharge, and the relationship of the molecular structure and electrochemical properties of ACCs are discussed. Strategies for molecular structure modifications to improve the performance of ACCs, i.e., the capacity density, cycle life, rate performance, and voltage of the discharge platform, are also elaborated. ACCs, as electrode active materials in aqueous solutions, will become a future research hotspot. ACCs will inevitably become sustainable green materials for batteries with high capacity density and high power density.

Anatase TiO2 as a Na+-Storage Anode Active Material for Dual-Ion Batteries

Anatase TiO₂ used as the sodium-storage anode is coupled with a graphite cathode to construct dual-ion batteries. The batteries display wide voltage window (1.0-4.7 V), long cycling stability (98 mAh g^-1 after 1400 cycles at 500 mA g^-1), and considerable rate performance (102 mAh g^-1 at 1500 mA g^-1). Furthermore, the kinetic behaviors of Na⁺ and PF₆^- ions are investigated through electrochemical impedance spectroscopy, the galvanostatic intermittent titration technique, and the potentiostatic intermittent titration technique. The corresponding apparent ion diffusion coefficient is calculated, and the results indicate that the transport of PF₆^- anions in the graphite cathode is swift.

Microstructure Characteristics of Cathode Materials for Rechargeable Magnesium Batteries

Rechargeable magnesium batteries (RMBs) that use pure Mg or Mg alloy as anode and materials allowing Mg ions to insert/extract as cathode have many advantages such as high energy density, environmental friendliness, low cost, and safety of handling. RMBs are regarded as a promising candidate for portable power sources and heavy load energy devices. However, there are still some technological issues impeding their commercial application. The most important issue is the absence of applicable cathode materials because of the high charge density, strong polarization effect, and very slow insertion/extraction speed of Mg²⁺ ions. In recent years, the research reports on the cathode materials of RMBs have increased significantly. Here, an extensive number of research papers are reviewed in terms of the microstructure characteristics of cathode materials for RMBs. The status and issues of cathode materials are analyzed and discussed in detail. The future development directions and perspectives are prospected for providing an understanding of the related research activities on RMBs.

Recent Progress in Multivalent Metal (Mg, Zn, Ca, and Al) and Metal-Ion Rechargeable Batteries with Organic Materials as Promising Electrodes

The emerging demand for electronic and transportation technologies has driven the development of rechargeable batteries with enhanced capacity storage. Especially, multivalent metal (Mg, Zn, Ca, and Al) and metal-ion batteries have recently attracted considerable interests as promising substitutes for future large-scale energy storage devices, due to their natural abundance and multielectron redox capability. These metals are compatible with nonflammable aqueous electrolytes and are less reactive when exposed in ambient atmosphere as compared with Li metals, hence enabling potential safer battery systems. Luckily, green and sustainable organic compounds could be designed and tailored as universal host materials to accommodate multivalent metal ions. Considering these advantages, effective approaches toward achieving organic multivalent metal and metal-ion rechargeable batteries are highlighted in this Review. Moreover, organic structures, cell configurations, and key relevant electrochemical parameters are presented. Hopefully, this Review will provide a fundamental guidance for future development of organic-based multivalent metal and metal-ion rechargeable batteries.

Stacking of Tailored Chalcogenide Nanosheets around MoO2-C Conductive Stakes Modulated by a Hybrid POM⊂MOF Precursor Template: Composite Conversion-Insertion Cathodes for Rechargeable Mg-Li Dual-Salt Batteries

Mg anode has pronounced advantages in terms of high volumetric capacity, resource abundance, and dendrite-free electrochemical plating, which make rechargeable Mg-based batteries stand out as a representative next-generation energy storage system utilized in the field of large-scale stationary electric grid. However, sluggish Mg²⁺ diffusion in cathode lattices and facile passivation on the Mg anode hinder the commercialization of Mg batteries. Exploring a highly electroactive cathode prototype with hierarchical nanostructure and compatible electrolyte system with the capability of activating both an anode and a cathode is still a challenge. Here, we propose a POM⊂MOF (NENU-5) core-shell architecture as a hybrid precursor template to achieve the stacking of tailored chalcogenide nanosheets around MoO₂-C conductive stakes, which can be employed as conversion-insertion cathodes (Cu_1.96S-MoS₂-MoO₂ and Cu₂Se-MoO₂) for Mg-Li dual-salt batteries. Li-salt modulation further activates the capacity and rate performance at the cathode side by preferential Li-driven displacement reaction in Cu⁺ extrusible lattices. The heterogeneous conductive network and conformal dual-doped carbon coating enable a reversible capacity as high as 200 mAh/g with a coulombic efficiency close to 100%. The composite cathode can endure a long-term cycling up to 400 cycles and a high current density up to 2 A/g. The diversity of MOF-based materials infused by functional molecules or clusters would enrich the nanoengineering of electrodes to meet the performance demand for future multivalent batteries.

s-Tetrazines as a New Electrode-Active Material for Secondary Batteries

Because of the limitations of conventional metal-oxide-based electrodes, studies on organic redox-active materials as alternative electrodes for secondary batteries are emerging. However, reported organic electrode materials are still limited to a few kinds of organic redox groups. Therefore, the development of new redox-active groups for high-performance electrode materials is indispensable. Here, we evaluate s-tetrazine derivatives as a new electrode material in Li-ion batteries and study their charge/discharge mechanisms by ex situ XPS measurements. The porous carbon CMK-3 was introduced to encapsulate the s-tetrazines, which allowed 100 % utilization of the theoretical capacity and stable cycle performance of the s-tetrazines by preventing dissolution of the molecules into the electrolytes. This new class of redox-active group can pave the way for the next-generation of energy storage systems.

High-Rate Nanostructured Pyrite Cathodes Enabled by Fluorinated Surface and Compact Grain Stacking via Sulfuration of Ionic Liquid Coated Fluorides

Metal-polysulfide batteries are attracting broad attention as conversion reaction systems of high theoretical energy density and low cost. However, their further applications are hindered by the low loading of active species, excess conductive additive, and loose (nanostructured) electrode networkss. Herein, we propose that compact grain stacking and surface fluorination are two crucial factors for achieving high-rate and long-life pyrite (FeS₂) cathodes enabled by sulfurating ionic liquid wrapped open-framework fluorides. Both of the factors can accelerate the Li- and Na-driven transport across the pyrite-electrolyte interface and conversion propagation between adjacent grains. Such an electrode design enables a highly reversible capacity of 425 mAh/g after 1000 cycles at 1 C for Li storage and 450 mAh/g after 1200 cycles at 2 C for Na storage, even under a high loading of pyrite grains and ultrathin carbon coating (<2 nm). Its cathode energy density can reach to 800 and 350 Wh/kg for Li and Na cells, respectively, under a high power density of 10000 W/kg. The cross-linkage between ionic liquid and fluoride precursors appears to be a solution to the reinforcement of surface fluorination.