Revealing the Magnesium-Storage Mechanism in Mesoporous Bismuth via Spectroscopy and Ab-Initio Simulations

Enhancing Proton Co-Intercalation in Iron Ion Batteries Cathodes for Increased Capacity

Recently, aqueous iron ion batteries (AIIBs) using iron metal anodes have gained traction in the battery community as low-cost and sustainable solutions for green energy storage. However, the development of AIIBs is significantly hindered by the limited capacity of existing cathode materials and the poor intercalation kinetic of Fe2+. Herein, we propose a H+ and Fe2+ co-intercalation electrochemistry in AIIBs to boost the capacity and rate capability of cathode materials such as iron hexacyanoferrate (FeHCF) and Na4Fe3(PO4)2(P2O7) (NFPP). This is achieved through an electrochemical activation step during which a FeOOH nanowire layer is formed in situ on the cathode. This layer facilitates H+ co-intercalation in AIIBs, resulting in a high specific capacity of 151 mAh g-1 and 93% capacity retention over 500 cycles for activated FeHCF cathodes. We found that this activation process can also be applied to other cathode chemistries, such as NFPP, where we found that the cathode capacity is doubled as a result of this process. Overall, the proposed H+/Fe2+ co-insertion electrochemistry expands the range of applications for AIBBs, in particular as a sustainable solution for storing renewable energy.

Advances in Electrochemical Energy Storage over Metallic Bismuth-Based Materials

Bismuth (Bi) has been prompted many investigations into the development of next-generation energy storage systems on account of its unique physicochemical properties. Although there are still some challenges, the application of metallic Bi-based materials in the field of energy storage still has good prospects. Herein, we systematically review the application and development of metallic Bi-based anode in lithium ion batteries and beyond-lithium ion batteries. The reaction mechanism, modification methodologies and their relationship with electrochemical performance are discussed in detail. Additionally, owing to the unique physicochemical properties of Bi and Bi-based alloys, some innovative investigations of metallic Bi-based materials in alkali metal anode modification and sulfur cathodes are systematically summarized for the first time. Following the obtained insights, the main unsolved challenges and research directions are pointed out on the research trend and potential applications of the Bi-based materials in various energy storage fields in the future.

Unusual Hybrid Magnesium Storage Mechanism in a New Type of Bi2O2CO3 Anode

Bismuth and bismuth-based compounds have been extensively studied as anodes as prospective candidates for rechargeable magnesium batteries (rMBs). However, the unsatisfactory magnesium-storage capability caused by the typical alloying reaction mechanism severely restricts the practical option for anodes in rMBs. Herein, polyaniline intercalated Bi2O2CO3 nanosheets are prepared by an effective interlayer engineering strategy to fine-tune the layer structure of Bi2O2CO3, achieving enhanced magnesium-storage capacity, rate performance, as well as long cycle life. Excitedly, a stepwise insertion-conversion-alloying reaction is aroused to stabilize the performance, which is elucidated by in/ex situ investigations. Moreover, first-principles calculations confirm that the coupling of Bi2O2CO3 and polyaniline not only increases the conductivity induced by the strong density of states and the interior self-built-in electric field but also significantly reduces the energy barrier of Mg shuttles. Our findings shed light on exploring new electrode materials with an appropriate working mechanism toward high-performance rechargeable batteries.

Bismuth oxyformate microspheres assembled by ultrathin nanosheets as an efficient negative material for aqueous alkali battery

A negative electrode with high capacity and rate capability is essential to match the capacity of a positive electrode and maximize the overall charge storage performance of an aqueous alkali battery (AAB). Due to the 3-electron redox reactions within a wide negative potential range, bismuth (Bi)-based compounds are recognized as efficient negative electrode materials. Herein, hierarchically structured bismuth oxyformate (BiOCOOH) assembled by ultrathin nanosheets was prepared by a solvothermal reaction for application as negative material for AAB. Given the efficient ion diffusion channels and sufficient exposure of the inner surface area, as well as the pronounced 3-electron redox activity of Bi species, the BiOCOOH electrode offered a high specific capacity (C_s, 229 ± 4 mAh g^-1 at 1 A g^-1) and superior rate capability (198 ± 6 mAh g^-1 at 10 A g^-1) within 0 ∼ -1 V. When pairing with the Ni₃S₂-MoS₂ battery electrode, the AAB delivered a high energy density (E_cell, 217 mWh cm^-2 at a power density (P_cell) of 661 mW cm^-2), showing the potential of such a novel BiOCOOH negative material in battery-type charge storage.

Bismuth Nanoparticle-Embedded Carbon Microrod for High-Rate Electrochemical Magnesium Storage

Bismuth metal is regarded as a promising magnesium storage anode material for magnesium-ion batteries due to its high theoretical volumetric capacity and a low alloying potential versus magnesium metal. However, the design of highly dispersed bismuth-based composite nanoparticles is always used to achieve efficient magnesium storage, which is adverse to the development of high-density storage. Herein, a bismuth nanoparticle-embedded carbon microrod (Bi⊂CM), which is prepared via annealing of the bismuth metal-organic framework (Bi-MOF), is developed for high-rate magnesium storage. The use of the Bi-MOF precursor synthesized at an optimized solvothermal temperature of 120 °C benefits the formation of the Bi⊂CM-120 composite with a robust structure and a high carbon content. As a result, the as-prepared Bi⊂CM-120 anode compared to pure Bi and other Bi⊂CM anodes exhibits the best rate performance of magnesium storage at various current densities from 0.05 to 3 A g^-1. For example, the reversible capacity of the Bi⊂CM-120 anode at 3 A g^-1 is ∼17 times higher than that of the pure Bi anode. This performance is also competitive among those of the previously reported Bi-based anodes. Importantly, the microrod structure of the Bi⊂CM-120 anode material remained upon cycling, indicative of good cycling stability.

Inspired by Wood: Thick Electrodes for Supercapacitors

The emergence and development of thick electrodes provide an efficient way for the high-energy-density supercapacitor design. Wood is a kind of biomass material with porous hierarchical structure, which has the characteristics of a straight channel, uniform pore structure, good mechanical strength, and easy processing. The wood-inspired low-tortuosity and vertically aligned channel architecture are highly suitable for the construction of thick electrochemical supcapacitor electrodes with high energy densities. This review summarizes the design concepts and processing parameters of thick electrode supercapacitors inspired by natural woods, including wood-based pore structural design regulation, electric double layer capacitances (EDLCs)/pseudocapacitance construction, and electrical conductivity optimization. In addition, the optimization strategies for preparing thick electrodes with wood-like structures (e.g., 3D printing, freeze-drying, and aligned-low tortuosity channels) are also discussed in detail. Further, this review presents current challenges and future trends in the design of thick electrodes for supercapacitors with wood-inspired pore structures. As a guideline, the brilliant blueprint optimization will promote sustainable development of wood-inspired structure design for thick electrodes and broaden the application scopes.

Dimethyl sulfoxide as a function additive on halogen-free electrolyte for magnesium battery application

Practical Mg batteries still face significant challenges in their development, like the lack of simple compatible electrolytes, self-discharge, the rapid passivation of the Mg anode, and the slow conversion reaction pathway. Here, we propose a simple halogen-free electrolyte (HFE) based on magnesium nitrate (Mg(NO₃)₂), magnesium triflate Mg(CF₃SO₃)₂, and succinonitrile (SN) dissolved in acetonitrile (ACN)/tetraethylene glycol dimethyl ether (G4) cosolvents, with dimethyl sulfoxide as a functional additive. The addition of DMSO to the HFE changes the interfacial structure at the magnesium anode surface and facilitates the transport of magnesium ions. The as-prepared electrolyte shows high conductivity (σ _b = 4.48 × 10^-5, 6.52 × 10^-5 and 9.41 × 10^-5 S cm^-1 at 303, 323, and 343 K, respectively) and a high ionic transference number (tmg ^₊₂ = 0.91/0.94 at room temperature/55 °C) for the matrix containing 0.75 ml of DMSO. Also, the cell with 0.75 ml of DMSO shows high oxidation stability, a very low overpotential, and steady Mg stripping/plating up to 100 h. Postmortem analysis of pristine Mg and Mg anodes extracted from disassembled Mg/HFE/Mg and Mg/HFE_0.75 ml DMSO/Mg cells after stripping/plating reveals the role of DMSO in improving Mg-ion passage through HFE by evolving the anode/electrolyte interface at the Mg surface. Further optimization of this electrolyte is expected to achieve excellent performance and good cycle stability when applied to the magnesium battery in future work.

Iodine-Ion-Assisted Galvanic Replacement Synthesis of Bismuth Nanotubes for Ultrafast and Ultrastable Sodium Storage

Bismuth (Bi) has emerged as a promising anode material for fast-charging and long-cycling sodium-ion batteries (SIBs). However, its dramatically volumetric variations during cycling will undesirably cause the pulverization of active materials, severely limiting the electrochemical performance of Bi-based electrodes. Constructing hollow nanostructures is recognized as an effective way to resolve the volume expansion issues of alloy-type anodes but remains a great challenge for metallic bismuth. Here, we report a facile iodine-ion-assisted galvanic replacement approach for the synthesis of Bi nanotubes (NTs) for high-rate, long-term and high-capacity sodium storage. The hollow tubular structure effectively alleviates the structural strain during sodiation/desodiation processes, resulting in excellent structural stability; the thin wall and large surface area enable ultrafast sodium ion transport. Benefiting from the structural merits, the Bi NT electrode exhibits extraordinary rate capability (84% capacity retention at 150 A g^-1) and outstanding cycling stability (74% capacity retention for 65,000 cycles at 50 A g^-1), which represent the best rate performance and longest cycle life among all reported anodes for SIBs. Moreover, when coupled with the Na₃(VOPO₄)₂F cathode in full cells, this electrode also demonstrates excellent cycling performance, showing the great promise of Bi NTs for practical application. A combination of advanced research techniques reveals that the excellent performance originates from the structural robustness of the Bi NTs and the fast electrochemical kinetics during cycling.

Recent Progress in Bi-Based Anodes for Magnesium Ion Batteries

Rechargeable magnesium ion batteries (MIBs) have attracted increasing interest due to abundant reserves, high theoretical specific capacities and safety. However, the incompatibility between Mg metal and conventional electrolytes, among the most serious challenges, restrains their development. Replacing Mg metal with alloy-type anodes offers an effective strategy to circumvent the surface passivation issue of Mg metal in conventional electrolytes. Among them, Bi has the most potential in Mg storage owing to its unique characteristics. Herein, the advantages/challenges and progress of Bi-based anodes in MIBs are summarized. The theoretical evaluations, battery configurations, electrode designs, electrochemical properties as well as Mg storage mechanisms are summarized and discussed. Moreover, the key issues and some views on the future development of Bi-based anodes in MIBs are provided.

Phase Separation Induced Binary Core-Shell Alloy Nanoparticles Embedded in Carbon Sheets for Magnesium Storage

Magnesium-ion batteries (MIBs) have aroused widespread interest in large-scale applications due to their low cost, high volumetric capacity, and safety. However, magnesium (Mg) metals are incompatible with conventional electrolytes, making it difficult to plate and strip reversibly. Therefore, developing novel Mg²⁺ host anodes remains a huge challenge. Herein, we present a rational design and fabrication of binary Bi@Sn alloy nanoparticles embedded in carbon sheets (Bi@Sn-C) as a superior anode for MIBs employing phase separation during the annealing of bimetallic MOFs. The Bi@Sn-C simultaneously integrates the nanostructure design and multi-element coordination strategies which is favorable to improve the overall structural stability and Mg²⁺ diffusion kinetics. Benefiting from the aforementioned features, the Bi@Sn-C electrodes deliver good cycling stability of 214 mA h g^-1 at 100 mA g^-1 after 100 cycles and rate capability with 200 mA h g^-1 at 500 mA g^-1. And when using all-phenyl complex with lithium chloride (LiCl-APC) dual-salt electrolyte, the electrochemical performance of Bi@Sn-C is further optimized and shows enhanced rate performance (238 mA h g^-1 at 500 mA g^-1) and reversible capacity (308 mA h g^-1 at 100 mA g^-1 after 100 cycles). This novel strategy holds great promise for designing efficient alloy electrode materials for MIBs.

Uniform Bi-Bi2O3 nanoparticles/reduced graphene oxide composites for high-performance aqueous alkaline batteries

Aqueous alkaline batteries (AABs) with the merits of both high energy density and power density have emerged as one of the most promising candidates for the new generation of energy storage devices, while their practical applications are still limited by the lack of high-performance electrode materials, especially for the anode materials. Herein, metallic bismuth-bismuth oxide nanoparticles (Bi-Bi₂O₃), with numerous heterogeneous interfaces, are successfully anchored and uniformly distributed on reduced graphene oxide (rGO) sheets. When Bi-Bi₂O₃/rGO-20 electrode is used as the anode material for an AAB, it shows a high specific capacity of 288.0 mA h g^-1 (1036.9 F g^-1) at 1 A g^-1 and good rate capability (74.7% of capacity retention ratio at 20 A g^-1). Additionally, in order to match well with a Bi-Bi₂O₃/rGO-20 anode, CoVS_x thin sheets decorated with Ni-Co layered double hydroxide sheets (NiCo-LDH) were successfully constructed via a facile multistep hydrothermal method and a subsequent electrodeposition process. The resulting cathode exhibits a high specific capacity of 306.0 mA h g^-1 (2448 F g^-1) at 1 A g^-1. The assembled CoVS_x@NiCo-LDH//Bi-Bi₂O₃/rGO-20 AAB delivers an outstanding energy density of 106.1 Wh kg^-1 at a power density of 789.6 W kg^-1. Besides, the as-synthesized Bi-based electrode is also used in aqueous Zn alkaline batteries to further extend its application and the assembled Bi-Bi₂O₃/rGO-20//Zn batteries possess an ultralong flat discharge plateau and exhibit a specific capacity of 250.6 mA h g^-1 at 1 A g^-1. The results demonstrate that the as-assembled AAB has huge potential for practical applications and provides an inspiration for the next-generation energy storage devices.

Tellurium: A High-Performance Cathode for Magnesium Ion Batteries Based on a Conversion Mechanism

Magnesium ion batteries (MIBs), due to the low redox potential of Mg, high theoretical capacity, dendrite-free magnesiation, and safe nature, have been recognized as a post-lithium energy storage system. However, an ongoing challenge, sluggish Mg²⁺ kinetics in the small number of available cathode materials of MIBs, restricts its further development. The existing cathodes mostly deliver unsatisfactory capacity with poor cycling life based on the traditional ion-intercalation mechanism. Herein, we fabricated a conversion-type Mg∥Te battery based on a reversible two-step conversion reaction (Te to MgTe₂ to MgTe). High discharge capacities (387 mAh g^-1) and rate capability (165 mAh g^-1 at 5 A g^-1) can be achieved. The diffusivity of Mg²⁺ can reach 3.54 × 10^-8 cm² s^-1, enabled by the high electrical conductivity of Te and increased surface conversion sites. Subsequently, ab initio molecular dynamics simulation was also carried out to further confirm the conversion mechanism and fast Mg²⁺ transportation kinetics.

Synchrotron X-ray Spectroscopic Investigations of In-Situ-Formed Alloy Anodes for Magnesium Batteries

Magnesium batteries present high volumetric energy density and dendrite-free deposition of Mg, drawing wide attention in energy-storage devices. However, their further development remains stagnated due to relevant interfacial issues between the Mg anode and the electrolyte and sluggish solid-state diffusion kinetics of Mg²⁺ ions. Herein, an in situ conversion chemistry to construct a nanostructured Bi anode from bismuth selenide driven by Li⁺ is proposed. Through the combination of operando synchrotron X-ray diffraction, ex situ synchrotron X-ray absorption spectroscopy, and comprehensive electrochemical tests, it is demonstrated that the nanosize of the in-situ-formed Bi crystals contributes to the fast Mg²⁺ diffusion kinetics and highly efficient Mg-Bi alloingy/de-alloying. The resultant Bi anodes exhibit superior long-term cycling stability with over 600 cycles under a high current density of 1.0 A g^-1 . This work provides a new approach to construct alloy anode and paves the way for exploring novel electrode materials for magnesium batteries.

Interfacial Assembly and Applications of Functional Mesoporous Materials

Functional mesoporous materials have gained tremendous attention due to their distinctive properties and potential applications. In recent decades, the self-assembly of micelles and framework precursors into mesostructures on the liquid-solid, liquid-liquid, and gas-liquid interface has been explored in the construction of functional mesoporous materials with diverse compositions, morphologies, mesostructures, and pore sizes. Compared with the one-phase solution synthetic approach, the introduction of a two-phase interface in the synthetic system changes self-assembly behaviors between micelles and framework species, leading to the possibility for the on-demand fabrication of unique mesoporous architectures. In addition, controlling the interfacial tension is critical to manipulate the self-assembly process for precise synthesis. In particular, recent breakthroughs based on the concept of the "monomicelles" assembly mechanism are very promising and interesting for the synthesis of functional mesoporous materials with the precise control. In this review, we highlight the synthetic strategies, principles, and interface engineering at the macroscale, microscale, and nanoscale for oriented interfacial assembly of functional mesoporous materials over the past 10 years. The potential applications in various fields, including adsorption, separation, sensors, catalysis, energy storage, solar cells, and biomedicine, are discussed. Finally, we also propose the remaining challenges, possible directions, and opportunities in this field for the future outlook.

Influence of Electrolyte on the Electrode/Electrolyte Interface Formation on InSb Electrode in Mg-Ion Batteries

Achieving the full potential of magnesium-ion batteries (MIBs) is still a challenge due to the lack of adequate electrodes or electrolytes. Grignard-based electrolytes show excellent Mg plating/stripping, but their incompatibility with oxide cathodes restricts their use. Conventional electrolytes like bis(trifluoromethanesulfonyl)imide ((Mg(TFSI)₂) solutions are incompatible with Mg metal, which hinders their application in high-energy Mg batteries. In this regard, alloys can be game changers. The insertion/extraction of Mg²⁺ in alloys is possible in conventional electrolytes, suggesting the absence of a passivation layer or the formation of a conductive surface layer. Yet, the role and influence of this layer on the alloys performance have been studied only scarcely. To evaluate the reactivity of alloys, we studied InSb as a model material. Ex situ X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy were used to investigate the surface behavior of InSb in both Grignard and conventional Mg(TFSI)₂/DME electrolytes. For the Grignard electrolyte, we discovered an intrinsic instability of both solvent and salt against InSb. XPS showed the formation of a thick surface layer consisting of hydrocarbon species and degradation products from the solvent (THF) and salt (C₂H₅MgCl-(C₂H₅)₂AlCl). On the contrary, this study highlighted the stability of InSb in Mg(TFSI)₂ electrolyte.

Surface Engineering of a Mg Electrode via a New Additive to Reduce Overpotential

In nonaqueous Mg batteries, inactive adsorbed species and the passivation layer formed from the reactive Mg with impurities in the electrolyte seriously affect the Mg metal/electrolyte interface. These adlayers can impede the passage of Mg²⁺ ions, leading to a high Mg plating/stripping overpotential. Herein, we report the properties of a new additive, bismuth triflate (Bi(OTf)₃), for synthesizing a chlorine-free Mg electrolyte to enhance Mg plating/stripping from initial cycles. The beneficial effect of Bi(OTf)₃ can be ascribed to Bi/Mg₃Bi₂ formed in situ on the Mg metal surface, which increases the charge transfer during the on-off transition by reducing the adsorption of inactive species on the Mg surface and enhancing the resistance of the reactive surface to passivation. This simple method provides a new avenue to improve the compatibility between the Cl-free Mg electrolyte and the Mg metal anode.