Recent Progress in MXene-Based Materials for Metal-Sulfur and Metal-Air Batteries: Potential High-Performance Electrodes

High quality bifunctional cathode for rechargeable zinc-air batteries using N-doped carbon nanotubes constrained CoFe alloy

Building efficient and stable bifunctional electrocatalysts toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for the advancement of rechargeable zinc-air batteries (ZABs). Here, a convenient in situ strategy is reported to controllably encapsulate CoFe alloy nanoparticles within N-doped carbon nanotubes (CoFe@NCNT). The abundant Co(Fe)-Nx active sites and the synergistic interaction between CoFe alloys and carbon nanotubes facilitate mass transfer and interfacial charge transfer, resulting in excellent dual functional electrocatalytic activity of OER/ORR with minor potential difference (ΔE = 0.73 V). Thus, the corresponding rechargeable ZAB displays high power density (194 mW cm-2), excellent specific capacity (795 mAh gZn-1), and favorable stability (900 cycles@5 mA cm-2). This work provides an approach for establishing low-cost bultifunctional electrocatalysts with excellent performance of non-noble metal nanoalloys.

Bidirectional enhancement of Li2S redox reaction by NiSe2/CoSe2-rGO heterostructured bi-functional catalysts

The high activity barriers of Li2S nucleation and deposition limit the redox reaction kinetics of lithium polysulfides (LiPSs), meanwhile, the significant shuttle effect of LiPSs hampers the advancement of Li-S batteries (LSBs). In this work, a NiSe2/CoSe2-rGO (NiSe2/CoSe2-G) sulfur host with bifunctional catalytic activity was prepared through a hard template method. Electrochemical experiment results confirm that the combination of NiSe2 and CoSe2 not only facilitates the bidirectional catalytic function during charge and discharge processes, but also increases the active sites toward LiPSs adsorption. Simultaneously, the highly conductive rGO network enhances the electronic conductivity of NiSe2/CoSe2-G/S and provides convenience for loading NiSe2/CoSe2 catalysts. Benefitting from the exceptional catalytic-adsorption capability of NiSe2/CoSe2 and the presence of rGO, the NiSe2/CoSe2-G/S electrode exhibits excellent electrochemical properties. At 1C, it demonstrates a low capacity attenuation of 0.087 % per cycle during 500 cycles. The electrode can maintain a discharge capacity of 927 mAh/g at a sulfur loading of 3.3 mg cm-2. The bidirectional catalytic activity of NiSe2/CoSe2-G offers a prospective approach to expedite the redox reactions of active S, meanwhile, this work also offers an ideal approach for designing efficient S hosts for LSBs.

Topological Engineering Electrodes with Ultrafast Oxygen Transport for Super-Power Sodium-Oxygen Batteries

Sodium-oxygen battery has attracted tremendous interest due to its extraordinary theoretical specific energy (1605 Wh kg-1 NaO2) and appealing element abundance. However, definite mechanistic factors governing efficient oxygen diffusion and consumption inside electrolyte-flooded air cathodes remain elusive thus precluding a true gas diffusion electrode capable of high discharge current (i.e., several mA cm-2) and superior output power. Herein, 3D-printing technology is adopted to create gas channels with tailored channel size and structure to demystify the diffusion-limited oxygen delivery process. It is revealed that as the clogging discharging products increase, large channel size, and interconnected channel structure are essential to guaranteeing fast O2 diffusion. Moreover, to further encourage O2 diffusion, a bio-inspired breathable cathode with progressively branching channels that balances between O2 passage and reaction is 3D printed. This elaborated 3D electrode allows a sodium-oxygen cell to deliver an impressive discharging current density of up to 4 mA cm-2 and an output power of 8.4 mW cm-2, giving rise to an outstanding capacity of 18.4 mAh cm-2. The unraveled mystery of oxygen delivery enabled by 3D printing points to a valuable roadmap for the rational design of metal-air batteries toward practical applications.

Encapsulating Sulfur into a Gel-Derived Nitrogen-Doped Mesoporous and Microporous Carbon Sponge for High-Performance Lithium-Sulfur Batteries

The practical application of Li-S batteries (LSBs) has long been impeded by the inefficient utilization of sulfur and slow kinetics. Utilizing conductive carbonaceous frameworks as a host scaffold presents an efficient and cost-effective approach to enhance sulfur utilization for redox reactions in LSBs. However, the interaction of pure carbon materials with lithium polysulfide intermediates (LiPSs) is limited to weak van der Waals forces. Hence, the development of an economical method for synthesizing heteroatom-doped carbon materials for sulfur fixation is of paramount importance. In this study, we introduce a hierarchical porous nitrogen-doped carbon sponge (NPCS) with an exceptionally high BET surface area of 3182.2 m2 g-1, achieved through a facile template-assisted polymerization method. The incorporation of inorganic salts, free radical polymerization, and deuteric freeze-drying techniques facilitates the formation of hierarchical pores within the NPCS. After sulfur fixation, the resulting S/NPCS electrode demonstrates remarkable electrochemical performance in LSBs. Specifically, it achieves an 80% sulfur utilization rate, maintains a high reversible specific capacity of 400 mA h g-1 even after 600 cycles at a demanding current density of 5.0 A g-1, and exhibits superior rate capability. It is believed that this work will inspire the rational design of cost-effective carbon-based electrodes for high-performance LSBs.

Hybrid Ascharite/Reduced Graphene Oxide with Polysulfide Adsorption Host for Advanced Lithium-Sulfur Batteries

Balancing the adsorption of lithium-polysulfide intermediates on polar host material surfaces and the effect of their electronic conductivity in the subsequent oxidation and reduction kinetics of electrochemical reactions is necessary and remains a challenge. Herein, we have evaluated the role of polarity and conductivity in preparing a series of ascharite/reduced graphene oxide (RGO) aerogels by dispersing strong polar ascharite nanowires of varying mass into the conductive RGO matrix. When severed as Li-S battery cathodes, the optimized S@ascharite/RGO cathode with a sulfur content of 73.8 wt % demonstrates excellent rate performance and cycle stability accompanied by a high-capacity retention for 500 cycles at 1.0 C. Interesting advantages including the enhanced adsorption ability by the formation of the Mg-S and Li bonds, the continuous and quick electron/ion transportations assembled conductive RGO framework, and the effective deposition of Li2S are combined in the ascharite/RGO aerogel hosts. The electrochemical results further demonstrate that the polarity of ascharite components for the S cathode plays a dominant role in the improvement of electrochemical performance, but the absence of a conductive substrate leads to serious capacity attenuation, especially the rate performance. The balanced design protocol provides a universal method for the synthesis of multiple S hosts for high-performance LSBs.

Recent advances and promise of MXene-based composites as electrode materials for sodium-ion and potassium-ion batteries

With the increasing demand for sustainable energy and concerns about the scarcity of lithium resources, sodium and potassium ion batteries have emerged as promising alternative energy storage technologies. MXene, as a novel two-dimensional material, possesses exceptional electrical conductivity, high surface area, and tunable structural features that make it an ideal candidate for high-performance electrode materials. However, its limited theoretical capacity hinders its widespread application. To overcome this limitation, MXene has been combined with other materials through synergistic effects between different components to enhance the overall electrochemical performance and expand its application in sodium/potassium ion batteries. Recently, substantial advancements have been realized in the exploration of MXene-based composites as energy storage materials, encompassing their synthesis, design, and the comprehension of charge storage mechanisms. This paper aims to propose a comprehensive summary of the latest developments in MXene-based composites as electrode materials for sodium ion batteries and potassium ion batteries, with a particular emphasis on the enhanced physicochemical properties resulting from composite formation. Moreover, the challenges faced by MXene materials in sodium ion batteries and potassium ion batteries are thoroughly discussed, and future research directions to further advance this field are proposed.

Facile one-pot synthesis of biomass-derived activated carbon as an interlayer material for a BAC/PE/Al2O3 dual coated separator in Li-S batteries

Lithium-sulfur batteries (LSB) are an attractive alternative electrochemical energy storage device compared to conventional lithium-ion batteries due to their higher theoretical capacity and energy density. Despite these advantages, it is still difficult to commercialize LSB because of poor electrochemical performance caused by the dissolution of soluble lithium polysulfides (LiPS). To solve these critical issues, a multi-functional separator was prepared using biomass-derived activated carbon (BAC) and a ceramic layer on the polyethylene (PE) separator. For this purpose, BAC was synthesized by a facile one-pot synthesis method by a specifically designed furnace using various forms of milk waste. The multi-functional separator suppresses the effect of LiPS dissolution and increases the Li+ diffusion kinetics. BAC was able to absorb the LiPS shuttle, as confirmed by UV-vis measurements and X-ray photoelectron spectroscopy (XPS). LSB cells assembled using this multi-functional separator show a higher discharge capacity of 1092.5 mA h g-1 at 0.1 C-rate, while commercial PE separators deliver a specific capacity of 811.8 mA h g-1. These novel separators were also able to suppress lithium dendrites during cycling. This work offers a novel and simple approach for streamlining the synthesis process of BAC and applying it to LSB, aiding in the development of sustainable energy sources.

Bifunctional Single Atom Catalysts for Rechargeable Zinc-Air Batteries: From Dynamic Mechanism to Rational Design

Ever-growing demands for rechargeable zinc-air batteries (ZABs) call for efficient bifunctional electrocatalysts. Among various electrocatalysts, single atom catalysts (SACs) have received increasing attention due to the merits of high atom utilization, structural tunability, and remarkable activity. Rational design of bifunctional SACs relies heavily on an in-depth understanding of reaction mechanisms, especially dynamic evolution under electrochemical conditions. This requires a systematic study in dynamic mechanisms to replace current trial and error modes. Herein, fundamental understanding of dynamic oxygen reduction reaction and oxygen evolution reaction mechanisms for SACs is first presented combining in situ and/or operando characterizations and theoretical calculations. By highlighting structure-performance relationships, rational regulation strategies are particularly proposed to facilitate the design of efficient bifunctional SACs. Furthermore, future perspectives and challenges are discussed. This review provides a thorough understanding of dynamic mechanisms and regulation strategies for bifunctional SACs, which are expected to pave the avenue for exploring optimum single atom bifunctional oxygen catalysts and effective ZABs.

Metal-organic framework derived FeNi alloy nanoparticles embedded in N-doped porous carbon as high-performance bifunctional air-cathode catalysts for rechargeable zinc-air battery

Developing efficient and durable bifunctional air-cathode catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the key efforts promoting the practical rechargeable zinc-air batteries (ZABs). In this paper, high-performance bifunctional air-cathode catalysts by a two-step strategy: atomically dispersed Ni on N-doped carbon is first derived from MOF to form uniformly dispersed NiNC, which are pyrolyzed together with Fe source at different high-temperatures to form FeNi@NC-T (T = 800, 900, and 1000 °C) catalysts. The as-synthesized non-noble metal FeNi@NC-900 catalyst exhibits a considerably small potential gap (ΔE) of 0.72 V between ORR and OER, which is as the same as commercial noble metal Pt/C + Ir black mixed catalyst. The performance of the ZABs using FeNi@NC-900 as the air-cathode catalyst displays a power density of 119 mW·cm^-2 and a specific capacity of 830.1 mAh·g^-1, which is superior to that of Pt/C + Ir black mixed catalyst. This work provides a guideline for designing alloy electrocatalysts with uniform size and nanoparticle distribution for metal-air batteries with bifunctional air-cathodes.

Nucleophilic ring-opening of thiocyclic carbonates: A scheme to prepare sulfhydryl-rich binders for high-performance lithium-sulfur batteries

Problems such as cathode collapse caused by volume change and shuttle effect of lithium polysulfides (LiPSs) limit the commercialization of Lithium-Sulfur (Li-S). Herein, we developed a sulfhydryl-containing multifunctional binder prepared by the nucleophilic ring-opening reaction of thiocyclic carbonates with amino groups. The binders (CNP-T and CNP-F) form sulfur-containing polymers with sulfur through the wet-slurry process, thereby effectively suppressing the shuttle effect. The abundant polar functional groups (e.g., -NH₂, -CS(NH)-) in CNP-T and CNP-F can effectively adsorb LiPSs to weaken the shuttle effect, which is confirmed by both density functional theory (DFT) and experimental results. At the same time, their own hyperbranched network structure can also limit the volume change of the sulfur cathode. Therefore, the Li-S battery exhibits an initial specific capacity of 924.02 mAh/g and a decay rate of 0.033% when cycled at 1C for 500 cycles.

Battery Performance Amelioration by Introducing a Conducive Mixed Electrolyte in Rechargeable Mg-O2 Batteries

With magnesium being a cost-effective anode metal compared to the other conventional Li-based anodes in the energy market, it could be a capable source of energy storage. However, Mg-O2 batteries have struggled its way to overcome the poor cycling stability and sluggish reaction kinetics. Therefore, Ru metallic nanoparticles on carbon nanotubes (CNTs) were introduced as a cathode for Mg-O2 batteries, which are known for their inherent electronic properties, large surface area, and increased crystallinity to favor remarkable oxygen reduction reactions and oxygen evolution reactions (ORR and OER). Also, we deployed a first-of-its-kind, conducive mixed electrolyte (CME) (2 M Mg(NO3)2:1 M Mg(TFSI)2/diglyme). Hence, this synergistic incorporation of CME-based Ru/CNT Mg-O2 batteries could unleash long cycle life with low overpotential, excellent reversibility, and high ionic conductivity and also reduces the intrinsic corrosion behavior of Mg anodes. Correspondingly, this novel amalgamation of CME with Ru/CNT cathode has displayed superior cyclic stability of 65 cycles and a maximum discharge potential of 25 793 mAh g-1 with a small overvoltage plateau of 1.4 V, noticeably subjugating the findings of conventional single electrolyte (CSE) (1 M Mg(TFSI)2/diglyme). This CME-based Ru/CNT Mg-O2 battery design could have a significant outcome as a future battery technology.

Reacquainting the Sudden-Death and Reaction Routes of Li-O2 Batteries by Ex Situ Observation of Li2O2 Distribution Inside a Highly Ordered Air Electrode

The unclear Li₂O₂ distribution inside an air electrode stems from the difficulty of conducting observation techniques inside a porous electrode. In this work, an integrated air electrode is prepared with highly ordered channels. The morphological composition and distribution of Li₂O₂ inside the real air electrode are clearly observed for the first time. The results show that the toroidal Li₂O₂ is constrained by the channel size and exhibits a larger diameter on the separator side at high currents. In contrast to the reported single-factor experiments, the coupling effects of charge transfer impedance and concentration polarization on sudden death are analyzed in-depth at low and high currents. The growth model suggests that toroidal Li₂O₂ exhibits a high dependence on the electrode surface structure. A new route is proposed in which the Li₂O₂/electrode interface of a toroid is controlled partially by the second single-electron reduction.

Tailoring electronic-ionic local environment for solid-state Li-O2 battery by engineering crystal structure

Solid-state Li-O2 batteries (SSLOBs) have attracted considerable attention because of their high energy density and superior safety. However, their sluggish kinetics have severely impeded their practical application. Despite efforts to design highly efficient catalysts, efficient oxygen reaction evolution at gas-solid interfaces and fast transport pathways in solid-state electrodes remain challenging. Here, we develop a dual electronic-ionic microenvironment to substantially enhance oxygen electrolysis in solid-state batteries. By designing a lithium-decorative catalyst with an engineering crystal structure, the coordinatively unsaturated sites and high concentration of defects alleviate the limitations of electronic-ionic transport in solid interfaces and create a balanced gas-solid microenvironment for solid-state oxygen electrolysis. This strategy facilitates oxygen reduction reaction, mediates the transport of reaction species, and promotes the decomposition of the discharge products, contributing to a high specific capacity with a stable cycling life. Our work provides previously unknown insight into structure-property relationships in solid-state electrolysis for SSLOBs.

Plasma Surface Engineering of NiCo2S4@rGO Electrocatalysts Enables High-Performance Li-O2 Batteries

The sluggish redox reaction kinetics for aprotic Li-O₂ batteries (LOBs) caused by the insulating discharge product of Li₂O₂ could result in the poor round-trip efficiency, low rate capability, and cyclic stability. To address these challenges, we herein fabricated NiCo₂S₄ supported on reduced graphene oxide (NiCo₂S₄@rGO), the surface of which is further modified via a unique low-pressure capacitive-coupled nitrogen plasma (CCPN-NiCo₂S₄@rGO). The high ionization environment of the plasma could etch the surface of NiCo₂S₄@rGO, introducing effective nitrogen doping. The as-prepared CCPN-NiCo₂S₄@rGO has been employed as an efficient catalyst for advanced LOBs. The electrochemical analysis, combined with theoretical calculations, reveals that the N-doping can effectively improve the thermodynamics and kinetics for LiO₂ adsorption, giving rise to a well-knit Li₂O₂ formation on CCPN-NiCo₂S₄@rGO. The LOBs based on the CCPN-NiCo₂S₄@rGO oxygen electrode deliver a low overpotential of 0.75 V, a high discharge capacity of 10,490 mA h g^-1, and an improved cyclic stability (more than 110 cycles). This contribution may pave a promising avenue for facile surface engineering of the electrocatalyst in LOBs and other energy storage systems.

In Situ Anchoring Anion-Rich and Multi-Cavity NiS2 Nanoparticles on NCNTs for Advanced Magnesium-Ion Batteries

Magnesium (Mg)-ion batteries with low cost and good safety characteristics has attracted a great deal of attention recently. However, the high polarity and the slow diffusion of Mg²⁺ in the cathode material limit the development of practical Mg cathode materials. In this paper, an anion-rich electrode material, NiS₂ , and its composite with Ni-based carbon nanotubes (NiS₂ /NCNTs) are explored as the cathode materials for Mg-ion batteries. These NiS₂ /NCNTs with excellent Mg²⁺ storage property is synthesized by a simple in situ growth of NiS₂ nanoparticles on NCNTs. NiS₂ with both a large regular cavity structure and abundant sulfur-sulfur (SS) bonds with high electronegativity can provide a large number of active sites and unobstructed transport paths for the insertion-disinsertion of Mg²⁺ . With the aid of 3D NCNTs skeleton as the transport channel of the electron, the NiS₂ /NCNTs exhibit a high capacity of 244.5 mAh g^-1 at 50 mA g^-1 and an outstanding rate performance (94.7 mAh g^-1 at 1000 mA g^-1 ). It achieves capacitance retention of 58% after 2000 cycles at 200 mA g^-1 . Through theoretical density functional theory (DFT) calculations and a series of systematic ex situ characterizations, the magnesiation/demagnesiation mechanisms of NiS₂ and NiS₂ /NCNTs and are elucidated for fundamental understanding.

Mesoporous Ti4O7 nanosheets with high polar surface area for catalyzing separator to reduce the shuttle effect of soluble polysulfides in lithium-sulfur batteries

In the effort to accelerate adsorption and catalytic conversion of lithium polysulfides (Li-PSs) and suppress the shuttle effect of lithium-sulfur batteries (LSBs), the Ti 4 O 7 nanosheets/carbon material-modified separator is successfully fabricated to reducing soluble Li-PSs' crossover from cathode to anode. The catalyst of mesoporous Ti 4 O 7 nanosheets with O-Ti-O units synthesized at low temperature shows both excellent conductivity and high surface area. The modified separator can serve as a diffusion barrier of Li-PSs and catalyst for converting soluble low-chain sulfides into insoluble ones and then remarkably enhance the sulfur utilization and electrochemical performance of the LSB. This work provides a feasible avenue in both design and synthesis of mesoporous catalyst materials for suppressing the shuttle effect of lithium-sulfur batteries.

One-Dimensional Co-Carbonate Hydroxide@Ni-MOFs Composite with Super Uniform Core-Shell Heterostructure for Ultrahigh Rate Performance Supercapacitor Electrode

The insufficient contact between two phases in the heterostructure weakens the coupling interaction effect, which makes it difficult to effectively improve the electrochemical performance. Herein, a Co-carbonate hydroxide@ Ni-metal organic frameworks (Co-CH@Ni-MOFs) composite with super uniform core-shell heterostructure is fabricated by adopting 1D Co-CH nanowires as structuredirecting agents to induce the coating of Ni-MOFs. Both experimental and theoretical calculation results demonstrate that the heterostructure plays a vital role in the high performance of the as-prepared materials. On the one hand, the construction of super uniform core-shell heterostructure can create a large number of interfacial active sites and take advantages of the electrochemical characteristics of each component. On the other hand, the heterostructure can increase the adsorption energy of OH^- ions and promote the electrochemical activity for improving the reversible redox reaction kinetics. Based on the aforementioned advantages, the as-fabricated Co-CH@Ni-MOFs electrode exhibits a high specific capacity of 173.1 mAh g^-1 (1246 F g^-1 ) at 1 A g^-1 , an ultrahigh rate capability of 70.3% at 150 A g^-1 and excellent cycling stability with 90.1% capacity retention after 10 000 cycles at 10 A g^-1 . This study may offer a versatile design for fabricating a MOFs-based heterostructure as energy storage electrodes.