Reversible Conversion Reaction Research Articles

CoS2 confined into N-doped coal-based carbon fiber as flexible anode for high performance potassium-ion capacitor

Potassium-ion capacitors (PICs), skillfully combining the features of batteries and capacitors, hold promise in energy conversion and storage. Cobalt sulfide (CoS2) anode are promising alternatives due to its high theoretical capacity and excellent potassium storage capacity. However, severe volume changes of CoS2 anode leads to capacity decline and poor cycle stability, hindering its application in PICs. Herein, we successfully confine CoS2 nanoparticles in N-doped coal-based carbon fibers (CoS2/CF). Coal-based carbon fibers with flexible characteristic elevate the conductivity and relieve the volume expansion of CoS2. Moreover, the high content of edge nitrogen as active sites further enhances the electrochemical properties. The PICs with flexible CoS2/CF-0.8 as anode exhibits superior specific capacity (331.1 mA h g−1 after 150 cycles at 0.1 A g−1) and long cycling (214.1 mA h g−1 after 900 cycles at 1.0 A g−1). Ex-situ X-ray powder diffraction (XRD) reveal that the mechanism of CoS2/CF-0.8 anode is based on reversible intercalation and conversion reaction. Importantly, CoS2/CF-0.8||activated carbon (AC) devices shows excellent energy density (101.9 W h kg−1) and long cycling (82.23% capacity maintenance rate after 1000 cycles). This work offers insights for other materials with high theoretical capacity but volume expansion problem.

Candle soot-metal-organic framework-based hierarchical electrode as high-performance anode for Li-ion batteries

Recently, cobalt oxide-based materials have been considered high-performance anode materials. However, cobalt oxide materials display drawbacks such as capacity fade, poor cycle life, and substantial structural strain. In this work, we report a facile synthesis of carbon-cobalt oxide composite to improve the electrode's storage capabilities and cycle life. First, metal–organic framework-based cobalt oxide nano leaves are synthesized by simple coprecipitation followed by calcination. After that, candle soot-derived carbon nanoparticles are uniformly deposited on the cobalt oxide nano leaves by a simple flame synthesis method to form a composite electrode. The fractal-like interconnected carbon nanoparticles improve the electron conducting pathways. In contrast, metal–organic framework-derived porous cobalt oxide nano leaves enhance energy storage abilities through reversible conversion reactions. The superior performance of the composite electrode is established from the galvanostatic charge–discharge experiments. Also, the composite electrode has delivered outstanding specific capacities of 811 and 503 mAh g−1 at 50 and 1000 mA g−1 current densities, respectively. Furthermore, the composite electrode exhibited good cyclic stability at 1000 mA g−1 current density by delivering an excellent specific charge capacity of 490 mAh g−1 even after 400 cycles. Therefore, these superior electrochemical properties confirm the potential applicability in high-performance and stable Li-ion batteries.

A preparation strategy for highly reversible conversion reaction Tin dioxide/ Carbon anode: Simple, ultrafast and scalable

Combining nanoscale engineering and physical confinement approach to prevent aggregation is a reliable strategy to achieve fully reversible conversion reaction SnO2-based anode. However, the synthesis of such nanostructures relies on complex self-sacrificing template preparation and time-consuming thermal treatment processes, which limit the practical application of high-performance SnO2 anodes for lithium-ion batteries. Herein, we present a simple strategy for the in situ preparation of SnO2 quantum dots embedded in carbon martix using an inherently advantageous MOF template and ultrafast microwave-assisted treatment in a few seconds. (denoted as SnO2 QDs@C). The dispersed SnO2 quantum dots with precise size control (≈5 nm) in the nanostructure shorten the lithium ion transport distance and enhance the reaction kinetics. Meanwhile, the carbon matrix promotes electron transport and suppresses Sn coarsening, thus achieving a highly reversible conversion reaction. Consequently, the SnO2 QDs@C anode achieves a reversible capacity of 1337 mAh g-1 after 200 cycles at 0.2 A g-1 with a capacity retention rate of more than 80%. This preparation method can be extended to prepare other metal oxide quantum dots/ Carbon composites and is expected to be applied in a wide range of fields.

Binary Metallic CuCo5 S8 Anode for High Volumetric Sodium-Ion Storage.

With the rapid improvement of compact smart devices, fabricating anode materials with high volumetric capacity has gained substantial interest for future sodium-ion batteries (SIBs) applications. Herein, a novel bimetal sulfide CuCo5 S8 material is proposed with enhanced volumetric capacity due to the intrinsic metallic electronic conductivity of the material and multi-electron transfer during electrochemical procedures. Due to the intrinsic metallic behavior, the conducting additive (CA) could be removed from the electrode fabrication without scarifying the high rate capability. The CA-free CuCo5 S8 electrode can achieve a high volumetric capacity of 1436.4 mA h cm-3 at a current density of 0.2 A g-1 and 100 % capacity retention over 2000 cycles in SIBs, outperforming most metal chalcogenides, owing to the enhanced electrode density. Reversible conversion reactions are revealed by combined measurements for sodium systems. The proposed new strategy offers a viable approach for developing innovative anode materials with high-volumetric capacity.

Reversible Electrochemical Conversion Reaction for Selective Ion Removal and Recovery

AbstractCapacitive deionization (CDI) is a green and pollution‐free emerging technology that can be used for ions removal and recovery from water. However, the traditional electro‐adsorption process to achieve ions removal faces the challenges of non‐selectivity, low efficiency and difficult ion recovery. In recent years, the conversion reaction has attracted wide attention due to its high selectivity, reversibility and excellent desalination ability for ions removal and recovery. This concept article will focus on the connotation and representative applications of conversion reactions that can be used for ion‐selective removal and recovery and put forward the perspectives and outlooks of conversion reactions.

Carbon encapsulated FeS nanosheet-nanoribbon interwoven sandwich structure as efficient sodium-ion battery anodes

Carbon encapsulation and optimization of nanoparticle structure are key strategies in the development of battery electrode materials. Herein, we report a simple, one step chemical vapor deposition-like method to synthesize carbon encapsulated sandwich structured nanosheets/nanoribbons of ferrous sulphide (FeS@C NSRs) as a high performance sodium-ion battery anode material. The structurally advantageous FeS@C NSRs arises from heating Fe foam in the presence of a sulphur-containing resin, which supplies both the sulphur and carbon for the reaction. FeS@C NSRs maintains a high capacity of 582.8 mAh g−1 at 0.1 A g−1 for 120 cycles and a high rate capability of 270 mAh g−1 at 10 A g−1 for 2500 cycles. The impressive cycling performance results from fast electron and ion transfer with low structural strain on the bulk material. Furthermore, in situ Raman spectroscopy and XRD also reveal evidence that FeS@C NSRs cycles via a fully reversible conversion reaction pathway facilitated by the C–S–Fe bond. The efficient synthesis method could also be explored to produce other carbon coated transition metal sulphides for electrochemical applications.

Regulating ion-solvent chemistry enables fast conversion reaction of tellurium electrode for potassium-ion storage

Tellurium (Te) has attracted wide interests as the electrode material of potassium-ion batteries (KIBs) due to its high theoretical capacity and good electronic conductivity, but still faces the issues of polytelluride dissolution in electrolyte and the loss of active Te species. Herein, we propose an ion–solvent complex tunning strategy to allow reversible and fast conversion reaction of Te electrode for K+ storage. The electrolyte of potassium hexafluorophosphate (KPF6) dissolved in dimethoxyethane (DME) enables rapid electrochemically-driven conversion of Te in electrode to in-situ construct amorphous CuxTe upon cycling, which benefits from strong oxidation tendency of K+–PF6−–2DME complex to lose electrons. Moreover, the weak solvation facilitates the formation of a thin solid/electrolyte interphase with the KF-rich inner layer on Te electrode, further enhancing K+ diffusion. In addition, the weak interaction between the potassium polytelluride and K+–PF6−–2DME complex largely inhibits the solubility of polytelluride intermediates. Consequently, the Te-based electrode exhibits a high reversible capacity of 272 mAh/g at 0.05 A/g, excellent rate capability (168 mAh/g at 2.0 A/g), and superior cycling stability. This approach could be extended to other alkali metal–chalcogen batteries (Li–S, Li–Se, Na–S, Na–Se, etc.).

Evaluation of Sn0.9Fe0.1O2‐δ as Potential Anode Material for Sodium‐Ion Batteries

AbstractThe introduction of transition metals such as iron in oxides of alloying elements as, for instance, SnO2 has been proven to enable higher capacities and superior charge storage performance when used as lithium‐ion electrode materials. Herein, we report the evaluation of such electrode materials, precisely (carbon‐coated) Sn0.9Fe0.1O2−δ(−C), for sodium‐ion battery applications. The comparison with SnO2 as reference material reveals the beneficial impact of the presence of iron in the tin oxide lattice, enabling higher specific capacities and a greater reversibility of the de‐/sodiation process – just like for lithium‐ion battery applications. The overall achievable capacity, however, remains relatively low with about 300 mAh g−1 and up to more than 400 mAh g−1 for Sn0.9Fe0.1O2‐δ and Sn0.9Fe0.1O2−δ‐C, respectively, compared to the theoretical specific capacity of more than 1,300 mAh g−1 when assuming a completely reversible alloying and conversion reaction. The subsequently performed ex situ/operando XRD and ex situ TEM/EDX analysis unveils that this limited capacity results from an incomplete de‐/sodiation reaction, thus, providing valuable insights towards an enhanced understanding of alternative reaction mechanisms for sodium‐ion anode material candidates.

Engineering the interfacial doping of 2D heterostructures with good bidirectional reaction kinetics for durably reversible sodium-ion batteries

Interfacial doping engineering has been considered a promising strategy to improve the reaction kinetics of 2D heterostructures in sodium-ion batteries (SIBs). Much attention has been paid to the enhancement mechanism of reaction kinetics of pristine heterostructures during discharge, whereas less attention has been given to the optimization of reaction kinetics of discharged products during charge. Therefore, there is an urgent need for systematic understanding and design guide for interfacial doping engineering of 2D heterostructures to achieve good bidirectional reaction kinetics. In this paper, interfacial doping engineering is designed by the guidance of theoretical calculation, a new interface composed of Co-doped MoS2 (Co-MoS2) and N-doped graphene (NG) has excellent electrical conductivity and Na+ adsorption ability during discharge. Moreover, the revealed Na2S-Mo(Co)/NG interface is greatly beneficial to the dispersion, adsorption, and decomposition of Na2S and the overall electrical conductivity during charge. The good bidirectional reaction kinetics of Co-MoS2/NG interfaces in cobalt-doped MoS2 anchored on three-dimensional nitrogen-doped carbon (Co-MoS2/3DNC) composites have been systematically demonstrated by electrochemical characterization technologies. Therefore, an efficient reversible conversion reaction is enabled by the Co-MoS2/NG interfaces. The Co-MoS2/3DNC shows good rate performance and excellent long-term cycling stability of 1500 cycles at the current density of 1 A g−1. This work provides new insight into designing interfacial doping engineering for highly reversible and durable conversion-type composite anodes.

Pressure-Stabilized High-Entropy (FeCoNiCuRu)S2 Sulfide Anode toward Simultaneously Fast and Durable Lithium/Sodium Ion Storage.

Pressure-stabilized high-entropy sulfide (FeCoNiCuRu)S2 (HES) is proposed as an anode material for fast and long-term stable lithium/sodium storage performance (over 85% retention after 15000 cycles @10 A g-1 ). Its superior electrochemical performance is strongly related to the increased electrical conductivity and slow diffusion characteristics of entropy-stabilized HES. The reversible conversion reaction mechanism, investigated by ex-situ XRD, XPS, TEM, and NMR, further confirms the stability of the host matrix of HES after the completion of the whole conversion process. A practical demonstration of assembled lithium/sodium capacitors also confirms the high energy/power density and long-term stability (retention of 92% over 15000 cycles @5 A g-1 ) of this material. The findings point to a feasible high-pressure route to realize new high-entropy materials for optimized energy storage performance.

Enhanced conversion reaction of Na-Cu-PO3 via amorpholization and carbon-coating for large Na storage

Conversion-type cathodes have a higher theoretical capacity compared to intercalation-type cathodes due to the use of more transition metal cations. However, their sluggish kinetics and low operation voltage hinder their practical application in the industry, resulting in low specific capacity. To address these issues, we prepare an amorphous carbon-coated Cu(PO3)2 nanocomposite, and evaluate its electrochemical performance under rechargeable Na-ion battery system. At a current density of 24 mA/g, it achieves a large specific capacity of ∼232 mAh/g with an average operation voltage of ∼2.0 V (vs. Na+/Na). Furthermore, the amorphous carbon-coated Cu(PO3)2 nanocomposite exhibits a cycle retention of ∼90% compared to the initial capacity after 100 cycles. In contrast, bare Cu(PO3)2 shows poor electrochemical performance under the same conditions. Various experimental measurements have demonstrated that the amorphous carbon-coated Cu(PO3)2 nanocomposite exhibits a reversible and smooth conversion reaction of Cu(PO3)2 phase in the rechargeable Na-ion battery system.

In Situ Synthesis of Amorphous GeSe/CNT Composite via Defective-carbon-mediated Chemical Bonding for Ultrastable Na Ion Storage.

Herein, we report the in-situ synthesis of amorphous GeSe/CNT composite via defective-carbon-mediated chemical bonding for ultrastable Na-ion storage. Structural defects in CNTs play a crucial role in the chemical bonding and bonding strength in GeSe/CNTs composites. Specifically, the bonding strength tends to increase with increasing defect concentrations of CNTs. Remarkably, the strong chemical bonding between GeSe and CNTs significantly weakens Ge-Se bonds and promotes amorphization of GeSe, thus facilitating a reversible conversion reaction and enhancing Na-ion diffusion. Consequently, GeSe/CNTs composite exhibits outstanding cyclability of 87.9% even after 1000 cycles at 1 A g-1 and a high-rate capability of 288.3 mA h g-1 at 10 A g-1 . Our work presents a promising approach for the amorphization of electrode materials enabled by the defective-carbon-mediated strong chemical bonding for Li-, Na-, and K-ion batteries.

Rationally incorporated SnO2/SnS2 nanoparticles on sulfur-doped graphene aerogels for high-performance lithium/sodium-ion batteries

Tin-based anode materials, such as tin oxide and tin sulfide, have received increased attention due to their high theoretical capacity, natural abundance, and adequate operating voltage. But the large volume variation and sluggish reaction kinetics lead to severe structural deterioration and capacity fading during the charge-discharge process, hindering their practical application. Herein, we synthesized a unique ternary hybrid structure to grow SnS2 nanosheets and SnO2 particles on graphene aerogels by hydrothermal method (denoted as SnO2/SnS2/SGA). The SnO2/SnS2/SGA exhibited better cycling stability than SnS2/GA and SnO2/GA. The tight adhesion of SnO2/SnS2 helps to alleviate the undesired electrode materials destruction due to volume expansion. Furthermore, SnO2 and SnS2 quantum dots anchored on graphene aerogels can undergo reversible conversion reaction that profit by synergistic effect. The reversibility of the SnO2/SnS2/SGA material during the transition was also proved by ex-situ high-resolution transmission electron microscopy. The SnO2/SnS2/SGA hybrid was endowed with enhanced electrochemical capability.

Enhanced reversible conversion of Cu2S anodes for Na-ion batteries enabled by carbon nanotubes

Sodium-ion batteries (SIBs) with copper(I) sulfide (Cu2S) anodes has been gaining significant attention because of their relatively high capacity and inherent safety. The highly reversible conversion of Cu/Na2S in charging process to pristine Cu2S is essential for its electrochemical properties. Here, we have prepared Cu2S/carbon nanotube (CNT) anode for SIBs, in which highly-conductive CNTs are employed as a catalyst to promote the reversible reaction kinetics of Cu2S anode. By using a combination of electrochemical and ex-situ X-ray diffraction analysis, we demonstrate that Cu2S/CNT anodes can be converted efficiently and reversibly in comparison with a pure Cu2S anode. CNTs have superior electron conductivity and high surface area, and are therefore used for balancing the poor electronic conductivity of Cu2S and discharged products, as well as physically inhibition of the dissolution of sodium polysulfide. Consequently, a partially reversible conversion reaction is enabled during the charging process. In this study, we are contributing to the design of conversion-type materials that feature reversible mechanisms, opening up new possibilities for materials design.

Bi2S3/rGO nanocomposites with covalent heterojunctions as a high-performance aqueous zinc ion battery material

Bismuth(III) sulfide (Bi2S3) is a promising cathode material for aqueous zinc ion batteries (ZIBs), yet suffers from serious capacity issues due to its poor electrical conductivity and microstructural degradations. In this work, Bi2S3 anchored on reduced graphene oxide (rGO) is prepared through hydrothermal reaction and is used as cathode material for aqueous ZIBs. Raman and XPS characterizations confirmed that the oxygen bridge in Bi–O–C heterostructures is successfully created during the hydrothermal synthesis. These oxygen bridges are energy favourable in the Bi2S3/rGO composite materials and serve as the electron transfer channels for rapid charge compensation during Zn2+ incorporation/extraction. Rotating ring–disc electrode (RRDE) measurements demonstrate improved electrochemical stability of the Bi2S3/rGO composite material compared to pristine Bi2S3. As a result of these improved characteristics, Bi2S3/rGO composite shows notably better rate performance and cycling stability than unsupported Bi2S3. Ex-situ X-ray diffraction and XPS characterizations indicate that Zn2+ undergoes a reversible conversion reaction with Bi2S3 to form ZnS/Bi0, rather than being intercalated into Bi2S3 crystal interlayers. The rGO substrate forms chemical bonds with bismuth in the composite material, and the strongly anchored bismuth on the rGO through a Bi–O–C bridge enables a highly reversible conversion reaction. As a result, the Bi2S3/rGO composite with 8 wt% rGO can deliver a reversible capacity of ∼186 mAh g−1 at the current density of 500 mA g−1 after 150 cycles, showing high promise as Zn-ion battery material.

Current collectors based on multiwalled carbon-nanotubes and few-layer graphene for enhancing the conversion process in scalable lithium-sulfur battery

We investigated herein the morphological, structural, and electrochemical features of electrodes using a sulfur (S)-super P carbon (SPC) composite (i.e., S@SPC-73), and including few-layer graphene (FLG), multiwalled carbon nanotubes (MWCNTs), or a mixture of them within the current collector design. Furthermore, we studied the effect of two different electron-conducting agents, that is, SPC and FLG, used in the slurry for the electrode preparation. The supports have high structural crystallinity, while their morphologies are dependent on the type of material used. Cyclic voltammetry (CV) shows a reversible and stable conversion reaction between Li and S with an activation process upon the first cycle leading to the decrease of cell polarization. This activation process is verified by electrochemical impedance spectroscopy (EIS) with a decrease of the resistance after the first CV scan. Furthermore, CV at increasing scan rates indicates a Li+ diffusion coefficient (D) ranging between 10−9 and 10−7 cm2·s−1 in the various states of charge of the cell, and the highest D value for the electrodes using FLG as electron-conducting agent. Galvanostatic tests performed at constant current of C/5 (1 C = 1675 mA·gS−1) show high initial specific capacity values, which decrease during the initial cycles due to a partial loss of the active material, and subsequently increase due to the activation process. All the electrodes show a Coulombic efficiency higher than 97% upon the initial cycles, and a retention strongly dependent on the electrode formulation. Therefore, this study suggests a careful control of the electrode in terms of current collector design and slurry composition to achieve good electrode morphology, mechanical stability, and promising electrochemical performance in practical Li-S cells.

Interfacial coupling metallic MoS2 nanosheets with wrinkled Ti3C2TX MXene for reversible and stable sodium storage

Owing to high electronic conductivity and large interlayer spacing, 1T–MoS2 has attracted remarkable attention as one of the most potential anode materials for sodium-ion batteries. However, the electrochemical instability seriously hinders its wide application. The high reversible regeneration of Mo–S bonds to pristine 1T–MoS2 inevitably determines electrochemical reversibility of 1T–MoS2. Herein, hierarchical 1T–MoS2/MXene architectures demonstrate impressive Na–storage performance with stable reversibility. The theoretical simulation results reveal that the favorable structure of Na–S bonding at Mo/MXene heterointerfaces weakens Na–S bond and thereby decreases the recombination energies of Mo–S bond upon desodiation, greatly promoting reversible Na–storage. Moreover, the ex operando X-ray diffraction and Raman spectra further demonstrate an efficient reversible conversion reaction in 1T–MoS2/MXene anode. Therefore, the heterogenous 1T–MoS2/MXene achieves a considerable performance as a sodium-ion battery anode material.

Encapsulation of Cu2S with a nitrogen-doped carbon boosts Na+ storage with a reversible Na2S conversion reaction

The high reversibility of a conversion-anode material enables high reversible capacity and maintains its cyclability. In this work, we report copper sulfide microspheres encapsulated by nitrogen-doped carbon (Cu2S@NC) prepared via a conventional polyol process and demonstrate their potential use as anode materials for sodium-ion batteries. Nitrogen-doped carbon stimulates a reversible conversion reaction of Cu2S + Na ↔ Na2S + Cu while corroborating the phase stability, leading to excellent Na + storage properties of the Cu2S@NC. Thus, the Cu2S@NC anode demonstrates an excellent cyclability of 284.99 mA/h/g at a higher current at 5000 mA/g. Operando X-ray diffraction and density functional theory calculations are combined to verify the electrochemical Na + storage mechanism of the Cu2S@NC.

A General Route for Encapsulating Monodispersed Transition Metal Phosphides into Carbon Multi‐Chambers toward High‐Efficient Lithium‐Ion Storage with Underlying Mechanism Exploration

AbstractTransition metal phosphides (MPx) with high theoretical capacities and low cost are regarded as the most promising anodes for lithium‐ion batteries (LIBs), but the large volume variations and sluggish kinetics largely restrict their development. To solve the above challenges, herein a generic but effective method is proposed to encapsulate various monodispersed MPx into flexible carbon multi‐chambers (MPx@NC, MNi, Fe, Co, and Cu, etc.) with pre‐reserved voids, working as anodes for LIBs and markedly boosting the Li+ storage performance. Ni2P@NC, one representative example of MPx@NC anode, shows high reversible capacity (613 mAh g−1, 200 cycles at 0.2 A g−1), and superior cycle stability (475 mAh g−1, 800 cycles at 2 A g−1). Full cell coupled with LiFePO4 displays a high reversible capacity (150.1 mAh g−1 at 0.1 A g−1) with stable cycling performance. In situ X‐ray diffraction and transmission electron microscope techniques confirm the reversible conversion reaction mechanism and robust structural integrity, accounting for enhanced rate and cycling performance. Theoretical calculations reveal the synergistic effect between MPx and carbon shells, which can significantly promote electron transfer and reduce diffusion energy barriers, paving ways to design high‐energy‐density materials for energy storage systems.

Insight into the Substrate Specificity of Lactobacillus paracasei Aspartate Ammonia-Lyase

Aspartate ammonia-lyase (AAL) catalyzes the reversible conversion reactions of aspartate to fumaric acid and ammonia. In this work, Lactobacillus paracasei LpAAL gene was heterologously expressed in Escherichia coli. As well as a recombinant His-tagged LpAAL protein, a maltose-binding protein (MBP) fused LpAAL protein was used to enhance its protein solubility and expression level. Both recombinant proteins showed broad substrate specificity, catalyzing aspartic acid, fumaric acid, phenylalanine, and tyrosine to produce fumaric acid, aspartic acid, trans-cinnamic acid, and p-coumaric acid, respectively. The optimum reaction pH and temperature of LpAAL protein for four substrates were measured at 8.0 and 40 °C, respectively. The Km values of LpAAL protein for aspartic acid, fumaric acid, phenylalanine, and tyrosine as substrates were 5.7, 8.5, 4.4, and 1.2 mM, respectively. The kcat values of LpAAL protein for aspartic acid, fumaric acid, phenylalanine, and tyrosine as substrates were 6.7, 0.45, 4.96, and 0.02 s−1, respectively. Therefore, aspartic acid, fumaric acid, phenylalanine, and tyrosine are bona fide substrates for LpAAL enzyme.