Charge-discharge Process Research Articles

Ultrafast Tailoring Amorphous Zn0.25V2O5 with Precision‐Engineered Artificial Atomic‐Layer 1T′‐MoS2 Cathode Electrolyte Interphase for Advanced Aqueous Zinc‐Ion Batteries

AbstractVanadium (V)‐based oxides as cathode materials for aqueous zinc‐ion batteries (AZIBs) still encounter challenges such as sluggish Zn2+ diffusion kinetics and V‐dissolution, thus leading to severe capacity fading and limited life span. Here, we designed an ultrafast and facile colloidal chemical synthesis strategy based on crystalline Zn0.25V2O5 (c‐ZVO) to successfully prepare a‐ZVO@MoS2 core@shell heterostructures, where atomic‐layer MoS2 uniformly coats on the surface of amorphous a‐ZVO. The tailored amorphous structure of a‐ZVO provides more isotropic pathways and active sites for Zn2+, thus significantly enhancing the Zn2+ diffusion kinetics during charge–discharge processes. Meanwhile, as an efficient artificial cathode electrolyte interphase, the precision‐engineered atomic‐layer MoS2 with semi‐metallic 1T′ phase not only contributes to improved electron transport but also effectively inhibits the V‐dissolution of a‐ZVO. Therefore, the prepared a‐ZVO@MoS2 and conceptually validated a‐V2O5@MoS2 derived from commercial c‐V2O5 exhibit excellent cycling stability at an ultralow current density (0.05 A g−1) while maintaining good rate capability and capacity retention. This research achievement provides a new effective strategy for various amorphous cathode designs for AZIBs with superior performance.

Understanding of a Ni-Rich O3-Layered Cathode for Sodium-Ion Batteries: Synthesis Mechanism and Al-Gradient Doping.

O3-type NaNi0.8Mn0.1Co0.1O2 (NaNMC811) cathode active materials for sodium-ion batteries (SIBs), with a theoretical high specific capacity (∼187mAhg-1), are in the preliminary exploration stage. This study comprehensively investigates NaNMC811 from multiple perspectives. For the first time, the phase evolution ( - - ) during the solid-state synthesis is systemically investigated, which elucidates in-depth the mechanisms of the thermal sodiation process. Furthermore, an Al-gradient doping of NaNMC811 wassuccessfully implemented through Al2O3 coating on the cathode active material (CAM) precursor. The modified Al-NaNi0.8Mn0.1Co0.1O2 (Al-NaNMC811) exhibits excellent electrochemical dynamics and performance, maintaining a specific capacity above 100mAhg-1 after 100 cycles at 0.1 C (1.5-4.1 V) while providing a promising capacity retention of 63%. Additionally, the material demonstrates excellent rate capabilities, retaining a specific capacity of 107 mAh g-1 at 5 C. Compared to pristine NaNMC811, the modified Al-NaNMC811 is proven to have improved electrochemical kinetics with a higher Na+ diffusion coefficient due to dilated (003) interplanar spacing, and a more stable structure during the electrochemical charge-discharge processes, which is attributed to stronger Al-O bond energy. Understanding phase formations during the synthesis and comprehensive insight in the gradient doping for O3-type NaNMC811 CAMs guides further development of next-generation SIBsmaterials.

Origin of the High Catalytic Activity of MoS2 in Na-S Batteries: Electrochemically Reconstructed Mo Single Atoms.

Room-temperature sodium-sulfur (RT Na-S) batteries with high energy density and low cost are considered promising next-generation electrochemical energy storage systems. However, their practical feasibility is seriously impeded by the shuttle effect of sodium polysulfide (NaPSs) resulting from the sluggish reaction kinetics. Introducing a suitable catalyst to accelerate conversion of NaPSs is the most used strategy to inhibit the shuttle effect. Traditional catalytic approaches often want to avoid the irreversible phase transition of the catalyst at a deep discharge. On the contrary, here, we leverage the intrinsic structural tunability of the MoS2 catalyst in the opposite direction and innovatively propose a voltage modulation strategy for in situ generation of trace Mo single atoms (MoSAC) during the first charge-discharge process, leading to the formation of highly active catalytic phases (MoS2/MoSAC) through the self-reconstruction. Theoretical calculations reveal that the incorporation of MoSAC modulates the electronic structure of the Mo d-band center, which not only effectively promotes the d-p orbital hybridization but also accelerates the catalytic intermediate desorption by the bonding transition, the dynamic single-atom synergistic catalytic mechanism enhances the adsorption response between the metal active site and NaPSs, which significantly improves the sulfur redox reaction (SRR), and the initial capacity of the MoS2/MoSAC/CF@S cell at 0.2 A g-1 is increased by 46.58% compared to that of the MoS2/CF@S cell. The discovery of the MoS2/MoSAC/CF catalyst provides new insights into adjusting the structure and function of transition metal disulfide catalysts at the atomic scale, offering hope for the development of high-specific-energy RT Na-S batteries.

Water-Mediated Surface Engineering Enhances High-Voltage Stability of Fast-Charge LiCoO2 Cathodes.

Maintaining the surface structure stability of LiCoO2 (LCO) during rapid charge-discharge processes (>5C) and under high-voltage conditions (>4.2 V) is challenging due to interfacial side reactions, cobalt dissolution, and oxygen redox activity at deeply delithiated states, all of which contribute to performance degradation. Herein, different from traditional surface coating methods, we report a water-mediated strategy that modifies the surface architecture of LCO, creating a passivating layer to inhibit surface degradation and enhance cycling stability under fast charging conditions. The surface etching of LCO by H2O is accompanied by a concurrent Li+/H+ cation exchange, which passivates surface oxygen with H+ ions, thereby enhancing both the hydrophobicity and structural stability. Consequently, the modified LCO exhibits superior capacity retention, which is 2.5 times that of the pristine LCO, after 100 cycles at a current density of 1000 mA g-1 (∼6C at 4.5 V). Even at an elevated temperature of 45 °C, it maintains impressive cycling stability at a current density of 500 mA g-1 (∼3C), as demonstrated in practical full-cell configurations. Investigation with multiple samples confirmed that the water-mediated strategy demonstrated broad applicability. We emphasize that the water-mediated modification of the surface architecture on cathode materials offers significant insights into enhancing the stability of high-energy-density lithium-ion batteries (LIBs).

Intercalation Behavior of a Spiro-bipyrrolidinium Cation into a Graphite Electrode from Dimethyl/Propylene Carbonates.

Quaternary ammonium-graphite intercalation compounds (QA+-GICs) are promising negative electrode materials in dual-carbon batteries by virtue of safety, low cost, and environmental friendliness. However, the intercalation behavior of QA+ into graphite electrodes in mixed solvents has never been reported. Herein, spiro-(1,1')-bipyrrolidinium tetrafluoroborate dissolved in a dimethyl/propylene carbonate (DMC/PC) binary solvent system was employed in graphite/activated carbon (AC) capacitors. The storage behavior of the spiro-(1,1')-bipyrrolidinium cation into graphite is very related to the solvent composition of the electrolyte solutions. In situ X-ray diffraction tests revealed that the graphite electrodes can form different QA+-GICs during cycling, which is a key factor influencing the electrochemical performance of graphite/AC capacitors. Besides, the reversible thickness change of graphite in graphite/AC capacitors with different electrolytes during the charge-discharge process was also addressed. These findings provide sound evidence for the co-intercalation of the solvent with the cation.

Insights into the ternary substitution Na2.96+xK0.04 V2-xNix(PO4)2.98F0.06 with superior rate capability and near-zero strain property

Na3V2(PO4)3 (NVP) is considered the most favorable cathode for sodium-ion batteries due to its solid NASICON skeleton. Nevertheless, poor intrinsic conductivity is insufficient for its further commercialization. In this paper, we present a promising K/Ni/F co-doped and carbon nanotubes (CNTs) encapsulated Na2.96+xK0.04 V2-xNix(PO4)2.98F0.06 (KNF@CNTsx) cathode materials. The synthesis of KNF@CNTsx is achieved using a facile sol-gel method. The replacement of Na+ with K+ broadens the migratory pathway and supports the crystal skeleton, while F− substitution reduces the average grain dimension, thereby increasing the diffusion rate of Na+. Furthermore, the reduction of resistance by Ni2+ doping enables optimization of the transport of electrical charge, while also facilitating the optimization of chemically-defined properties. Concurrently, the optimal quantity of carbon capping and wrapping of CNTs facilitate the formation of efficacious conductive network, which diminishes the size of grains and shortens the pathway for the diffusion of Na+. This network could also serve as a buffer against crystal deformation. In conclusion, the modified KNF@CNTsx samples exhibit notable enhancements in their conductivity, ion diffusion capacity, and structural stability. Among them, the KNF@CNTs0.04 sample exhibits a capacity for reversibility of 93.3 mAh g−1 at 50C, with a remaining capacity of 68.5 mAh g−1 after 4000 successive long charge-discharge cycles. Ex-situ electrochemical XRD demonstrates the V3+/V4+ redox reaction occurs accompanied by the phase transfer reaction, during which Na+ prefers to diffuse along c-axial in the crustal structure. Moreover, volume alteration of this KNF@CNTs0.04 cellular entity is miniscule and reversible during the charge-discharge process, further confirming the stabilized construction and near-zero strain property. The after-cycled XRD/SEM/XPS certify the improved chemical and structural stability of KNF@CNTs0.04, indicating the constructive effects of K/Ni/F ternary substitution.

Nano ZnO modified amorphous carbon materials enabling long-cycle performance and high-capacity for lithium/sodium-ion batteries

Zinc-modified carbon materials exhibit high specific capacity, good safety, and low self-discharge, making them promising anode materials for lithium-ion and sodium-ion batteries. However, the high cost of raw materials, complex fabrication processes, and limited cycle life remain significant challenges to their further development. In this study, we elucidated a two-step process, simple in technique and suitable for large-scale production, for in-situ zinc modification of amorphous carbon. The synthesized carbon material exhibited superior reversible specific capacity (maintaining 780.27 mAh·g−1 capacity after 80 cycles at 50 mA·g−1 current density), high cycling stability (maintaining Coulombic efficiency at 100.06 % after 15,000 cycles at 10 A·g−1 current density), and good application value (achieving a capacity of 89.67 mAh·g−1 after 1000 cycles at 200 mA·g−1 current density for the assembled MFAC-Zn||NVP full cell). Through our investigation, we discovered that Nano ZnO not only directly participate in electrochemical reactions but also effectively improve the microstructure of amorphous carbon, increasing its three-dimensional axial stacking and providing more reaction sites. The enrichment of open pores significantly enhances the diffusion efficiency of ions within the carbon-based matrix. The superior diffusion ability of alkali metal-ion in the electrode is the reason for the excellent electrochemical performance of Zinc-modified amorphous carbon. Moreover, the incorporation of Nano ZnO aids in the formation of a robust and thin SEI layer. This significantly enhances the stability of the electrode materials during cycling and improves charge transfer efficiency during the charge-discharge process. Our study provides a new strategy for adjusting the internal microstructure of amorphous carbon materials to achieve high-performance lithium/sodium storage.

Enhanced bifunctional electrocatalysis of Co5.47N nanocrystals in porous carbon nanofibers for high-efficiency zinc-air batteries

As a promising energy conversion and storage device, recently, rechargeable zinc-air batteries (ZABs) have developed rapidly, and the exploitation of excellent electrode catalysts to improve the energy efficiency and long-term performance of ZABs has become a focus of current research. Herein, the Co5.47N nanocrystals embedded in porous carbon nanofibers (Co5.47N PCNFs) were designed to act as a bifunctional electrocatalyst for the oxygen reduction reaction (ORR) and iodide oxidation reaction (IOR), which occur on the electrode in the charging-discharging process of ZABs. The electrochemistry results showed that the ORR activity of Co5.47N PCNFs is comparable to the commercial Pt/C electrocatalyst, and the IOR activity and stability are higher than those of the Pt/C electrocatalyst. Importantly, Co5.47N PCNFs electrocatalyst endows ZABs with a low charge–discharge voltage difference (0.49 V), a high round-trip energy efficiency (72.1 %), as well as a large specific capacity (791.5 mAh gZn−1), surpassing the performance of Pt/C electrocatalyst. Density functional theory calculation demonstrates that Co5.47N PCNFs have lower Gibbs free energy for the formation of IOR intermediate species, thereby displaying outstanding IOR catalytic performance compared to that of Pt/C electrocatalyst. These findings offer crucial insights into the rational design of cobalt nitride-based electrocatalysts for application in ZABs with high energy efficiency.

Hierarchical Flower Array NiCoOOH@CoLa‐LDH Nanosheets for High‐Performance Supercapacitor and Alkaline Zn Battery

AbstractNickel oxyhydroxide based energy storage materials have been largely confined by insufficient exposure of active sites which results in low energy efficiency and poor stability. In order to resolve the problems, hierarchical flower array heterostructure NiCoOOH@CoLa‐LDH (denoted as NC@CL) nanosheets are designed with NiCo oxyhydroxide (NiCoOOH, denoted as NC) being tightly covered on CoLa layered double hydroxide (CoLa‐LDH, denoted as CL) nanosheet. This rational design creates more active sites, enlarges the electrode‐electrolyte contact area, improves electron conductivity, and prevents agglomeration during the cycling charge–discharge processes. Density functional theory calculations and differential charges concurrently illustrate that heterostructure formation optimizes the reaction kinetics and promotes electron redistribution. Benefiting from the heterogeneous structure and rich electro‐active sites caused by NC, NC@CL displays outstanding reversible specific capacitance (3228 F g−1 at 1 A g−1). The aqueous rechargeable alkaline Zn battery NC@CL//Zn exhibits a high capacity of 381.1 mA h g−1 at 0.5 A g−1 and cycling durability (98% capacity retention after cycling at 5 A g−1 for 2000 cycles). The excellent electrochemical performances indicate that NC@CL has great application potential as electrode material for aqueous energy storage device.

Heterostructure Engineering of Biphase‐Coupled Ternary Transition Metal Phosphoselenide by Topological Transformation Enabling High Performance for Supercapacitors

AbstractThe exploration of promising electrode materials with structural stability and rapid interfacial reaction kinetics is highly desirable for supercapacitors toward large‐scale applications. Herein, the synthesis of biphase‐coupled CoPSe/NiP0.24Se1.76 with multiple in‐plane heterointerfaces using the in situ topological transformation approach is presented. As a novel ternary metal phosphoselenide (TMPSe) for supercapacitor cathode that is fabricated by synchronous phosphoselenization strategy, it realizes a superior lifespan with cycling compared to conventional transition metal selenides. The depleted anti‐bonding eg* orbitals of transition metal ions (Co/Ni) in the CoPSe/NiP0.24Se1.76, as proved by preliminary theoretical calculations, strengthens the chemical bonding between Co/Ni and coordinating atoms, thereby enhancing the chemical stability. Simultaneously, the CoPSe/NiP0.24Se1.76 in‐plane multi‐heterostructures can not only alleviate the volume change during the charge–discharge process but also expose more active sites, promoting the adsorption of OH− ions, which is conducive to the rapid redox reaction kinetics of the CoPSe/NiP0.24Se1.76, and consequently, it delivers a remarkable reversible capacity and excellent long‐term cycle stability with 97.7% initial capacitance retention over 16 000 cycles. Moreover, the asymmetric supercapacitors with this cathode demonstrate outstanding rate capability and high energy density. This strategy of constructing biphase‐coupled CoPSe/NiP0.24Se1.76 by topological transformation is of great potential application for the high‐performance electrode material.

Zn-doped hollow cubic MnO2 as a high-performance cathode material for Zn ion batteries.

Manganese-based compounds have the characteristics of high theoretical capacity, low cost and stable performance, thus become a research hotspot for cathode materials of zinc-ion batteries (ZIBs). However, in the process of charging and discharging, it is accompanied by problems such as structural collapse and low conductivity, which resulted in severe capacity degration during cycles. In this paper, a kind of Zn2+ doped MnO2 hollow cube cathode material (Zn-MnO2) was prepared by self-sacrificing template method. The Zn2+ doped in MnO2 crystals can induce oxygen vacancies in the structure, thereby improving the structural stability ion diffusion coefficient and electrical conductivity of the material. After 100 cycles at 0.3 A g-1, the high specific capacity of 281.2 mA h g-1 is still maintained. Through ex-situ XPS and ex-situ XRD tests, the mechanism of charge-discharge process was discussed. The results show that the storage mechanism of Zn-MnO2 is H+ and Zn2+ insertion/removal and Mn3+/Mn2+ two-electron reaction pathway. The total state density (TDOS) and partial state density (PDOS) of Zn-MnO2 and MnO2 further demonstrated that the doping of Zn2+ enhanced the electron conductivity and is beneficial to the electron transfer during the electrochemical reaction.

Preparation of high strength and rigidity carbon layer on SiO material surface by dynamic CVD method using gas carbon source C2H2

The main issue in the application of silicon-based negative electrode materials is the inevitable volume expansion, leading to negative electrode material fracture, which severely impacts the performance of batteries. This study employed Chemical Vapor Deposition (CVD) (C2H2@SiO), solid-phase coating method (Pitch@SiO), and liquid-phase coating method (RGFQ@SiO) to coat the surface of SiO materials with a dense amorphous carbon structure. Material property analysis revealed that C2H2@SiO has a relatively small specific surface area (1.8 m2 g−1) and surface carbon increment (2.4 %). It exhibited high reversible specific capacity (1563.4 mAh g−1), high initial Coulombic efficiency (81.45 %), and low volume expansion rate (9.3 %). Mechanical performance testing indicated that the surface carbon layer Young's modulus of C2H2@SiO was the highest (35 GPa), suggesting that using the CVD method to obtain a dense carbon layer can enhance the structural strength of the material. Based on the electrochemical-mechanical coupling theory simulation analysis of the stress during the charge-discharge process of electrode materials, the evolution of concentration and stress field during lithium insertion process was obtained, showing that the coating can further improve the electrochemical and mechanical performance of the negative electrode materials effectively. Additionally, the negative electrode sheets fabricated using sample C2H2@SiO were assembled into 18650 cylindrical batteries, exhibiting excellent cycling performance in 1000 cycles at 25 °C with a capacity retention rate of 85.7 %, along with good rate capability and high/low-temperature performance. The conclusions of this study provide certain guidance for the design and optimization of negative electrode materials for battery electrodes.

Tailoring eco-friendly siloxane-based electrolytes for high-performance lithium–sulfur batteries

Lithium–sulfur batteries (LSBs), with their ultra-high theoretical energy density (2600 Wh kg−1), are considered one of the most attractive high-energy batteries. However, the “shuttling effect” of polysulfides and the uncontrolled growth of lithium (Li) dendrites pose significant challenges to the practical implementation of LSBs. Herein, a lightweight and eco-friendly diethoxydimethylsilane (DEMS) is chosen as a multi-functional solvent for LSBs. The low polarity of DEMS promotes the “solid–solid” conversion of sulfurized polyacrylonitrile (SPAN) during charge–discharge processes, eliminating the shuttle effect of polysulfides. Moreover, the DEMS-based electrolyte enables highly reversible Li plating/stripping processes across a wide temperature range spanning from −20 to 60 °C. As a result, the Li/SPAN batteries using the DEMS electrolyte exhibit excellent cyclic stability at 0.2 C with retainable capacities of 524.4 mAh/g after 200 cycles, 598.8 mAh/g after 100 cycles, and 318.6 mAh/g after 50 cycles at 26, 60 and −20 °C, respectively. This study aims to identify low-cost and highly stable electrolytes through solvent screening to enhance the electrochemical performance of LSBs.

Stabilizing zinc anodes by a solvation sheath modification with toluenesulfonate additive

As an advanced electrochemical energy storage device, aqueous zinc-ion batteries offer high theoretical capacity and energy density, employing water-based electrolytes to reduce fire and explosion risks. However, zinc tends to form dendrites during charge-discharge processes, leading to reduced electrode surface area and shortened cycling lifespan. In this study, we propose the use of a commonly used and cost-effective additive, sodium p-toluenesulfonate (OTM), to stabilize zinc anodes. Experimental and theoretical simulations demonstrate that OTM can enter the solvation sheath of Zn2+, reduce the activity of nearby H2O molecules, facilitate uniform Zn2+ deposition, and suppress zinc dendrite formation. Therefore, Zn//Zn symmetric batteries utilizing ZnSO4 (ZSO) electrolytes containing OTM achieved outstanding long-term performance exceeding 1700 h at 1 mA cm−2, significantly surpassing those employing ZSO electrolytes. Additionally, Zn//VO2 full batteries with OTM additives exhibited enhanced cycling stability and an initial discharge capacity of 180 mAh g−1 at 3 A g−1, demonstrating its superior application potential.

Bioinspired Hierarchical Porous Architecture for Enhanced Kinetics and Mechanical Integrity in Thick Cathode.

Increasing the thickness of the electrodes is considered the primary strategy to elevate battery energy density. However, as the thickness increases, rate performance, cycling performance, and mechanical stability are affected due to the sluggish ion transfer kinetics and compromised structural integrity. Inspired by the natural hierarchical porous structure of trees, electrodes with bioinspired architecture are fabricated to address these challenges. Specifically, electrodes with aligned columns consist of tree-inspired vertical channels, and hierarchical pores are constructed by screen printing and ice-templating, imparting enhanced electrochemical and mechanical performance. Employing an aqueous-based binder, the LiNi0.8Mn0.1Co0.1O2 cathode achieves a high areal energy density of 15.1 mWh cm-2 at a rate of 1C at mass loading of 26.0mg cm-2,benefitting from the multiscale pores that elevated charge transfer kinetics in the thick electrode. The electrodes demonstrate capacity retention of 90% at the 100th cycle at a high current density of 5.2mA cm-2. To understand the mechanisms that promote electrode performance, simplified electro-chemo-mechanical models are developed,the drying process and the charge-discharge process are simulated. The simulation results suggested that the improved performance of the designed electrode benefits from the lower ohmic overpotential and less strain gradient and stress concentration due to the hierarchical porous architecture.

Infiltration-driven performance enhancement of poly-crystalline cathodes in all-solid-state batteries

All-solid-state batteries (ASSBs) with adequately selected cathode materials exhibit a higher energy density and better safety than conventional lithium-ion batteries (LIBs). Ni-rich layered cathodes are benchmark materials for traditional LIBs owing to their high energy density. Recent studies have highlighted the advantages of using crack-free, single-crystalline cathode materials in ASSBs. In this study, a scalable infiltration sheet-type process was used to fabricate composite electrodes with different cathode-material morphologies for ASSBs. Typically, crack-free single-crystalline materials exhibit better retention performance and lower rate capability (i.e., slower kinetics in charge‒discharge processes) than polycrystalline cathode materials. Li6PS5Cl-infiltrated polycrystalline electrodes showed excellent retention performance and rate capability. Galvanostatic intermittent titration technique analysis and transmission electron microscopy of the single-crystalline electrode confirmed severe polarization and the presence of a rock-salt-structure layer in the cathode particles; these results indicated side reactions within the layered structure of the material. In contrast, composite electrodes consisting of polycrystalline cathode materials infiltrated with the solid electrolyte Li6PS5Cl showed excellent electrochemical performance owing to intimate electrode–electrolyte interfacial contact. The result from this study confirmed the critical influence of interface engineering and material morphology on the overall performance and stability of ASSBs and could facilitate the development of high-performance ASSBs in the future.

Accelerating sulfur redox kinetics by rare earth single-atom electrocatalysts toward efficient lithium–sulfur batteries

Toward practical lithium−sulfur (Li−S) batteries, there is a pressing need to improve the rate performance and longevity of cells. Herein, we report developing a cathode electrocatalyst Lu SA/NC, capable of accelerating sulfur redox kinetics with a high specific capacity of 1391.8 mAh g−1 at 0.1 C, and a low-capacity fading rate of 0.049 % per cycle over 1000 cycles even with a high sulfur loading (5.96 mg cm−2). The unparalleled cathodes are built upon the unique structure in which single-atoms of rare earth metals are doped in nitrogen-doped porous carbon (RM SAs/NC). The theoretical and experimental studies reveal that the rare earth Lu atom has an unrivaled adsorption capacity for polysulfides and can promote facile deposition and dissolution reactions in charge-discharge processes. The in-situ Raman experiments provide direct evidence for its promotion of polysulfide transformation to eliminate the shuttle effect. The theoretical calculations suggest that the presence of f-d-p hybridization enables accelerating sulfur reduction kinetics and enhancing lithium−sulfur battery performance. The strategic paradigm introduced in this study underscores significant practical potential in the exploration of rare earth single-atom catalysts for high performance Li−S batteries.

Mn-Based Transition Metal Oxide Positive Electrode for K-Ion Battery Using an FSA-based Ionic Liquid Electrolyte

Layered Mn-based transition metal oxides have gained interest as positive electrode materials for K-ion batteries due to their high capacity, excellent structural stability, and abundant resources. However, their practical utility is significantly hindered by insufficient electrochemical performances during operations. This study reports the successful synthesis of P3-K0.46MnO2 via the solid-state method and investigates its charge–discharge behavior as a positive electrode working in an FSA-based (FSA= bis(fluorosulfonyl)amide) ionic liquid electrolyte at 298 K. The K0.46MnO2 electrode demonstrates superior performance compared to previously reported K x MnO2 counterparts, delivering a reversible discharge capacity of about 100 mAh g−1 at a current density of 20 mA g−1 and a capacity retention of 68.3% over 400 cycles at 100 mA g−1. Ex situ X-ray diffraction analyses confirm the occurrence of reversible structural changes during the charge–discharge process. Further, we explore potassium storage mechanisms through ex situ synchrotron soft X-ray absorption spectroscopy. Spectra obtained in Mn L-edge region suggest that Mn is reversibly oxidized and reduced during K+ deintercalation and intercalation processes. Remarkably, discharging the electrode below 2.3 V induces reversible formation of Mn2+ from Mn3+/4+ on the electrode surface. The study demonstrates superior electrochemical performance of K0.46MnO2 positive electrode for K-ion battery using ionic liquid electrolyte.

Local electronic structure modulation via S substitution enables fast-discharging capability for Li-rich Mn-based oxides cathodes

Anionic and cationic redox reaction contribute to the ultrahigh specific capacities of Li-rich Mn-based oxides cathodes (LMNC). However, the irreversible oxygen evolution and sluggish kinetics result in the continuous capacity decay and poor rate performance, which limited its application as cathode material in lithium-ion batteries. Herein, the local electronic structure of LMNC is appropriately modulated via S2− doping to alleviate oxygen release, stabilize the crystal structure stability, and facilitate Li+ diffusion via facile surface defect engineering. The effect of S2− doping site on the systematically energy is investigated by DFT. Under the guidance of this result, LNMC-S is prepared by co-precipitation and high-temperature solid-phase reaction method. The effect of doping concentration on electrochemical property of LMNC was systematically investigated. The results exhibit that S2− doping can effectively suppress the electronic insulation of Li2MnO3, enhance the transport dynamics of lithium ion and inhibit the phase transition of LMNC sample during charge-discharge process. Thereby, the modified sample exhibits superior electrochemical property, such as the 200th discharge capacity is 184.3 mAh·g−1 under 1C, with a capacity retention rate of 87.6 %. This paper is beneficial for enriching the existing theoretical findings and discoveries, providing theoretical guidance for the preparation of high-performance material.

High-capacity and long-life Fe2O3/MOFs composite anodes: Preparation, characterization, morphology regulation and electrochemical performance

Among the various transition metal oxides used in lithium-ion battery anodes, iron oxide (Fe2O3) has received extensive attention due to its low cost, good environmental compatibility and high theoretical capacity. However, the volume expansion and structural collapse during the charging-discharging cycling process significantly limited the practical application of Fe2O3. Herein, we demonstrate enhanced electrochemical properties and stability of Fe2O3 by anchoring it on metal-organic frameworks (MOFs). Through adjusting the MOF ligands and introducing humic acid (HA), we reached rational control of the morphology for the Fe2O3/MOF composites. The optimized sample, namely Fe2O3@HA-Fe-ATA, shows 3D cauliflower-like structure with abundant pores, which are beneficial to the active sites exposure, electrolyte penetration, as well as the tolerance toward volume expansion. Consequently, high reversible capacity of 1442.7 mAh g−1 (at 0.1 A g−1), excellent rate performance (<11 % capacity decrease when current density increases from 0.1 A g−1 to 1 A g−1), and satisfactory cycle stability (91 % capacity retention after 500 cycles at 1 A g−1) are obtained. This work demonstrates that the rational design of MOF by introduction of appropriate ligand is a very efficient approach to optimize the electrochemical properties of the resultant electrode material.