Stability Of Cathode Materials Research Articles

An active and Cr-tolerant high-entropy La0.7Sr0.3FeO3-δ based cathode for solid oxide fuel cells

The development of high active and stable cathode materials is one of the main challenges of intermediate temperature solid oxide fuel cells (SOFCs). Herein, a high-entropy Fe-based perovskite oxide La0.7Sr0.3Fe0.3Ni0.3Co0.3Mo0.1O3-δ (LSFNCM) is synthesized by self-propagation combustion based on La0.7Sr0.3FeO3-δ (LSF) and the electrochemical properties are systematically tested. The symmetric half-cell with the LSFNCM cathode has a high catalytic activity with a polarization impedance of 0.12 Ω·cm2 at 800 °C, and also shows outstanding CO2 resistance and chromium resistance owing to the entropy stabilization strategy. After 50h of treatment in a 10% CO2 environment, the polarization impedance of the LSF electrode increases by 8.89 Ω·cm2, while that of the LSFNCM electrode only increases by 1.81 Ω·cm2. Additionally, after being treated for 24h in a chromium vapor environment, the polarization impedance of the LSF electrode increases by 5.95 Ω·cm2, whereas that of the LSFNCM electrode only increases by 0.44 Ω·cm2. Moreover, the single cell with LSFNCM cathode exhibits the maximum power density of 932.82 mW/cm2 and the polarization impedance of 0.34 Ω·cm2 at 800 °C with humidify hydrogen as fuel. Our results indicate that high-entropy perovskite oxide LSFNCM is an active and Cr-tolerant promising cathode for SOFCs.

Correction to “Air Stable O3-Type Cathode Material with Nanometer Size for Durable Low-Temperature Sodium-Ion Batteries”

Correction to “Air Stable O3-Type Cathode Material with Nanometer Size for Durable Low-Temperature Sodium-Ion Batteries”

Constructing electrochemically stable single crystal Ni-rich cathode material via modification with high valence metal oxides

Single crystal Ni-rich cathode materials (SCNCM) are a good supplement in the market of nickel-based materials due to their safety and excellent electrochemical performance. However, the challenges of cation mixing, phase change during charge/discharge, and low thermal stability remain unresolved in single crystal particles. To address these issues, SCNCM are rationally modified by incorporating transition metal (TM) oxides, and the influence of metal ions with different valence states on the electrochemical properties of SCNCM is methodically explored through experimental results and theoretical calculations. Enhanced structural stability is demonstrated in SCNCM after the modifications, and the degree of improvement in the matrix materials varies depending on the valence state of doped TM ions. The highest structural stability is found in WO3-modified SCNCM, due to the smaller effective ion radii, higher electro-negativity, stronger W–O bond, and efficient suppression of oxygen vacancy generation. As a result, WO3-modified SCNCM have outstanding cycle performance, with a capacity retention rate of 90.2% after 200 cycles. This study provides an insight into the design of advanced SCNCM with enhanced reversibility and cyclability.

Structural and Electrochemical Characterisation of NBZFO Cobalt-Free Cathode Material for Intermediate-Temperature Solid Oxide Fuel Cells: An Experimental Investigation

Compared to other energy-generating technologies and energy conversion devices, intermediate-temperature solid oxide fuel cells (IT-SOFCs) have gained significant attention from energy experts due to its high energy density, moderate operating temperature (600–800°C), low emissions and reliability. Enhancing the performance of IT-SOFCs requires suitable and excellent cathode materials. Thus, a perovskite-type Nd0.5Ba0.5Zr0.8Fe0.2O3+δ (NBZFO) material was synthesised via traditional solid-state reaction technique and analysed as a potential cathode material for IT-SOFCs. Analysis of X-ray diffraction data (XRD) revealed a single-phase perovskite material that crystallises in cubic space group (pm-3m). The thermal and electrochemical properties were analysed with the aid of thermogravimetric analysis (TGA) and electrochemical impedance spectroscopy (EIS). NBZFO has an electrical conductivity in air of 80 S cm−1 at 400°C and a polarisation resistance (Rp) of 0.106 Ω cm2 at 800°C. TGA reveals a slight loss in weight of about 0.58%, thereby suggesting a highly stable cathode material for IT-SOFC. Electrochemical investigation shows that NBZFO has good electronic and ionic conductivity and excellent oxygen stichometry. Further studies are required to understand the effects of varying B-site composition of the cathode material.

Unraveling Energy Storage Performance and Mechanism of Metal-Organic Framework-Derived Copper Vanadium Oxides with Tunable Composition for Aqueous Zinc-Ion Batteries.

Achieving high-performance aqueous zinc (Zn)-ion batteries (AZIBs) requires stable and efficient cathode materials capable of reversible Zn-ion intercalation. Although layered vanadium oxides possess high Zn-ion storage capacity, their sluggish kinetics and poor conductivity present significant hurdles for further enhancing the performance of AZIBs. In response to this challenge, a dissolution-regrowth and conversion approach is formulated using metal-organic frameworks (MOFs) as a sacrificial template, which enables the in situ creation of copper vanadium oxides (CuVOx) with porous 1D channels and distinctive nanoarchitectures. Owing to their distinctive structure, the optimized CuVOx cathode experiences a reaction involving the synergistic insertion/extraction of Zn2+, resulting in rapid Zn2+ diffusion kinetics and enhanced electrochemical activity postactivation. Specifically, the activated electrode delivers a reversible capacity of 519mAhg-1 at 0.5Ag-1 for AZIBs. It is noteworthy that the electrode exhibits a remarkable reversible rate capacity of 220mAhg-1 at 5Ag-1 with excellent durable cycleability, retaining 88% of its capacity even after 3000 cycles. Various ex situ testing methods endorse the reversible insertion/extraction of Zn2+ in the CuVOx cathode. This study provides a novel insight into high-performance MOF-derived unique structure designs for AZIB electrodes.

Strong Covalent Metal-Ligand Interaction Enables a Fast Kinetic and Structurally Stable Na-Ion Layered Cathode.

Anionic redox chemistry has attracted increasing attention for the improvement in the reversible capacity and energy density of cathode materials in Li/Na-ion batteries. However, adverse electrochemical behaviors, such as voltage hysteresis and sluggish kinetics resulting from weak metal-ligand interactions, commonly occur with anionic redox reactions. Currently, the mechanistic investigation driving these issues still remains foggy. Here, we chemically designed Na0.8Fe0.4Ti0.6S2 and Na0.8Fe0.4Ti0.6O2 as model cathodes to explore the covalency effects on metal-ligand interactions during anionic redox process. Na0.8Fe0.4Ti0.6S2 with strengthened covalent interaction of metal-ligand bonds exhibits smaller voltage hysteresis and faster kinetics than Na0.8Fe0.4Ti0.6O2 during (de)sodiation process. Theoretical calculations suggest that Fe is the dominant redox-active center in Na0.8Fe0.4Ti0.6S2, whereas the redox-active center moves from Fe to O with the removal of Na+ in Na0.8Fe0.4Ti0.6O2. We attribute the above different redox behaviors between Na0.8Fe0.4Ti0.6S2 and Na0.8Fe0.4Ti0.6O2 to the charge transfer kinetics from ligand to metal. Moreover, the structural stability of Na0.8Fe0.4Ti0.6S2 is enhanced by increasing the cation migration barriers through strong metal-ligand bonds during desodiation. These insights into the originality of metal-ligand interactions provide guidance for the design of high-capacity and structurally stable cathode materials for Li/Na-ion batteries.

Enhanced interfacial and cycle stability of 4.6 V LiCoO2 cathode achieved by surface modification of KAlF4

Lithium cobalt oxide is one of the most popular cathode materials for lithium-ion batteries. Due to its relatively low capacity, increasing the output voltage is often necessary to release more capacity. However, subjecting cathode materials to high charging potentials inevitably induces surface-side reactions, compromising the integrity of the crystal structure and accelerating capacity degradation. Therefore, the stability of cathode materials at high voltage becomes crucial for lithium-ion batteries. In this study, we employed the ternary compound KAlF4 (KAF) as a surface modification coating for LiCoO2 (LCO). With the optimized ratio (1 wt%) of KAF, coated LCO cathodes exhibited enhanced capacity retention, excellent cycling, and rate stability. In the high voltage range of 3.0–4.6 V, the specific capacity of the initial discharge at a rate of 0.5 C reached 198.30 mA h g−1. Remarkably, the coated LCO retained 91.56 % of its initial capacity after 200 cycles at 0.5 C. Even at a high rate of 5 C, the coated sample retained a discharge capacity of 120.87 mA h g−1, significantly higher than that of bare LCO (80.24 mA h g−1). After a thorough investigation into the structure changes before and after cycling, we elucidated the mechanism of KAF coating in improving the stability of high-voltage LCO cathodes. The results indicated that KAF forms a stable passivation layer on the surface of LCO, which suppresses cracking and corrosion during charging and discharging, eventually stabilizes the crystal structure, and enhances the cycling stability of LCO.

Copper substituted manganese Prussian blue analogue composite nanostructures for efficient aqueous zinc-ion batteries

Aqueous zinc (Zn)-ion batteries (AZIBs) are considered a promising green energy storage alternative due to their large capacity, low cost, and exceptional safety. Prussian blue analogues (PBAs) with a robust three-dimensional structure and extensive ion channels are highly favorable for Zn2+ insertion/extraction, surpassing manganese (Mn) and vanadium oxides. Herein, copper (Cu) substituted Mn PBA (CuMn PBA) composite nanostructures are synthesized via a simple water-based co-precipitation technique using different concentrations of Cu and Mn sources. The partial substitution of Cu and the formation of Mn vacancies prevent Jahn-Teller distortions of MnN6 octahedra, extending the lifespan. The CuMn PBA-2 electrode exhibits a high discharge capacity of 175.14 mA h g−1 at 0.5 A g−1, superior rate capability of 89.08 mA h g−1 at 2.4 A g−1, and robust cycling stability, maintaining 73.15 mA h g−1 over 2000 cycles at 3 A g−1. Furthermore, the distinct structure provides numerous active sites and reduces volume volatility during cycling. The presence of Cu enhances electrode conductivity, thereby promoting a higher rate of Zn-ion diffusion between electrodes. The reversible intercalation and deintercalation of Zn2+ ions in the CuMn PBA-2 cathode are substantiated by ex-situ analysis methods. This work presents a novel approach for producing high-performance and stable PBA cathode materials for AZIBs.

Monoclinic Silver Vanadate (Ag0.33V2O5) as a High-Capacity Stable Cathode Material for Aqueous Manganese Batteries.

Aqueous rechargeable metal batteries have recently garnered considerable attention owing to their low cost, sufficient capacity, and the use of non-flammable water-based electrolytes. Among them, manganese batteries are particularly favored because of their stability, abundance, affordability, and high energy density. Despite their advantages, Mn storage host structures remain underexplored. Therefore, developing innovative host materials is crucial for advancing this field. In this paper, the study reports for the first time, the use of Ag0.33V2O5 as a cathode material in aqueous manganese batteries. The study explains the displacement/intercalation behavior of manganese and silver using electrochemical, structural, and spectroscopic analyses. Additionally, it is shown that cation (Ag+, Mn2+, H+) diffusion pathways can be simulated using diffusion-barrier calculations. Finally, the study demonstrates high-performance manganese batteries that exhibit a remarkable reversible capacity of ≈261.9 mAhg-1 at a current of 0.1 Ag-1 and an excellent cycle retention of 69.1% after 2000 cycles at a current density of 1.5 A/g. The findings of this study contribute to the advancement of aqueous manganese battery technology, offering a promising pathway for developing safer, more cost-effective, and high-performance energy storage systems.

Manganese octahedral point-constructed oxygen defects realize highly stable lithium-rich cathode materials

Lithium-rich layered oxides (LLOs) are highly favored by researchers for their high specific capacity and low cost. However, the severe voltage and capacity degradation of the material have become the biggest obstacle to commercial application. In this work, the construction of oxygen vacancies on the surface of Li-rich cathode and SiO44- gradient doping have been used in Li-rich materials to improve its performance. The presence of oxygen defects in MnO6 octahedra stabilizes its structure and enhances the electrochemical activity of TM ions. This also serves to reduce the energy level and intensity of the unhybridized O 2p orbitals, as well as decrease the release of lattice oxygen. The "localization effect" of SiO44− on TM ions also inhibits their irreversible migration. After modification, the electrochemical performance of the material has been significantly improved. The initial Coulombic efficiency increased to 89.46 % (82.68 % for LLO), while the specific capacity discharge at 5C reached 178.8 mAh g−1 (139.2 mAh g−1 for LLO). Additionally, the capacity rate after 500 cycles at 1C was 74.1 % (54.5 % for LLO). Therefore, this work provides valuable insights for designing oxygen-deficient lithium-rich cathode materials.

Functional carbon dots induced defect configuration entropy strengthening polyanion cathode for ultrafast-charging sodium ion batteries in a wide temperature

The development of fast-charging and wide-temperature sodium-ion batteries (SIBs) is of great significance to all-climate energy storage. However, the gigantic challenge lies in achieving super dynamic performance and stability of cathode materials. Herein, the defect configuration entropy (DCE) is conceptualized in Na3V2(PO4)3/carbon composite (NVP/C) cathode by manipulating heteroatoms and vacancies in the surface carbon layer. It is found that the bonding energy between the carbon layer and NVP interface increases with the DCE. Accompanying, the Na+ migration energy barrier is reduced and the electronic conductivity is enhanced, which are pivotal factors underpinning the low-temperature performance. Furthermore, the increase of DCE engenders the formation of a NaF-rich cathode-electrolyte interface, furnishing support for high-temperature stability. As a result, the DCE-strengthened NVP/carbon composite cathode exhibits a high capacity of ∼88 mAh g−1 at an ultrahigh rate of 200 C (13 s per charge process). Moreover, the superior electrochemical performance in the wide temperature range of −30–60 °C is achieved with 0.101 % capacity decay per cycle at −20 ℃, and 0.0047 % capacity decay per cycle at 60 ℃.

MoO3 nanobelts cathode promotes Al3+ insertion in aqueous aluminum-ion batteries

Aqueous aluminium ion batteries (AAIBs) have attracted much attention due to their high theoretical capacity, safety, and environmental friendliness. However, the Research and Development (R&D) of cathode materials has limited its development and application. MoO3 has been proven to be a reliable and stable cathode material, nevertheless, it faces the dilemma of poor cycling performance and low specific capacity in AAIBs due to the irreversible phase transition in its structure. In this paper, MoO3 synthesized by a hydrothermal method has a unique nanobelt structure, which significantly enhances the structural stability of MoO3 and reduces its structural damage during charging/discharging. In addition, the nanobelt structure also gives MoO3 a rougher surface, which provides a large number of active sites and spaces for the insertion and extraction of Al3+ and improves the diffusion rate of Al3+ to a large extent. Experimental results demonstrate that this MoO3 nanobelt cathode exhibits significantly improved cycling stability and high specific capacity in AAIBs. This paper provides a practical solution to the existing challenges of AAIBs and further promotes the development and application of molybdenum-based materials in AAIBs.

Advancements in Alumina Ultrathin Coatings for Enhanced Electrochemical Performance of Ni-Rich NMC811 Thick Electrodes

Lithium-ion batteries, renowned for their high energy density, face a significant challenge in the development of stable, high-performing, and cost-effective cathode materials. Ni-rich cathodes, while promising, suffer from instability issues such as microcracking, high surface reactivity, phase transformation, and thermal runaway. This study introduces a breakthrough: the application of an alumina (Al2O3) ultrathin coating to enhance the stability of Ni-rich thick electrodes. The uniform distribution of the Al2O3 coating across the electrode acts as a protective barrier, effectively reducing oxygen lattice release and microcracking. Our findings reveal that this atomic layer deposition (ALD) technique markedly boosts the cycling stability of the electrodes. Coated electrodes maintained high specific capacity after long cycling, significantly outperforming uncoated electrodes, which retained only small capacity. This innovative approach shows great potential for the development of high-performance and stable lithium-ion batteries. Figure 1

High-Performance Lithium-Sulfur Batteries with Atomic V- and Co-Modified Ketjen Black-Sulfur Composite Cathode

Lithium-sulfur (Li-S) batteries are potential alternatives to lithium-ion batteries, which are known to have certain drawbacks. This has drawn special technological attention. Sulfur’s low electrical conductivity, shuttling of the intermediate polysulfides, the slow conversion reaction kinetics of various lithium polysulfides (LiPS), and the major volume change of sulfur in the lithiation reaction are some of the main issues that still need to be resolved before Li-S batteries can be used in practical applications. Additionally, it is likely because there are not enough prognostic models determining energy densities at the cell and pack level based on materials and cell design, most of the articles do not report system-level metrics, specific energy (Wh kg-1), and energy density (Wh L-1).To overcome these problems, atomic vanadium (V) and cobalt (Co) modified ketjen black-sulfur composite (VCKBS) was prepared and used as a cathode in Li-S batteries. The synthesized composite was characterized by various techniques, e.g., XRD, Raman, SEM, HR-TEM, HAADF-STEM, and XPS spectra. The polysulfide adsorption test showed that V had increased the adsorption ability, and cyclic voltammetry displayed the increased catalytic activity resulting from Co, offering a large number of interfacial active sites and ensuring smooth electron transfer. Cycling performance tests showed an initial specific capacity of 1329 mAh g−1, maintained at 1249 mAh g−1 after 100 cycles. Under a higher sulfur loading (2.4 mg cm−2), at 0.2 C, Li-S cells demonstrated an initial specific capacity of 1201 mAh g−1 and retained 985 mAh g−1 after 300 cycles with a low fading rate of 0.059% per cycle. The rate performance tests showed that the prior capacity is nearly recovered, going from 1C back to 0.1C, demonstrating the superiority of the VCKBS material.In addition to the experimental characterization of the Li-S cell performance, energy densities were also predicted by a proposed system-level performance model. The 1st and 100th discharge capacities were used to forecast the system-level specific energies and energy densities. The system-level specific energies and energy densities based on the 100th discharge capacity of VCKBS cathodes had improvements of 1342 and 568%, respectively. This suggests that an easy route to construct the highly stable cathode material may pave the way for the development of highly efficient Li-S batteries. Acknowledgments Hira Fazal acknowledges support from the Türkiye Scholarship/Research Fellowship Program sponsored by the Prime Ministry of Turkey Presidency for Turks Abroad and Related Communities (21PK070917). Damla Eroglu acknowledges support from the Istanbul Development Agency (Award No: TR10/21/YEP/0001). We also thank the National Natural Science Foundation of China (22171180) and the Science and Technology Commission of Shanghai Municipality (20520710400).

Re-Functionalization of Aged Lithium Iron Phosphate Cathode Materials

As lithium-ion batteries continue to be implemented in everyday technologies, it is imperative to repurpose these battery materials upon their degradation. Carbon-coated lithium iron phosphate (LFP/C) is considered one of the most stable cathode materials for application in lithium-ion batteries. Due to this stability, LFP/C possesses a remarkably long cycle life of greater than 3000 cycles.1 Extended cycling of these cathode materials may result in multiple modes of degradation, including degradation of the carbon coating, and loss of contact between the cathode and the current collector.2,3 In this work, a suitable process and reagents have been selected to isolate and purify the LFP/C from the cathodes of cycled batteries. Isolating and purifying aged LFP/C materials enables the diagnosis of the mode(s) of degradation of these materials and their coatings using a variety of techniques including X-ray diffraction, scanning electron microscopy, and transmission electron microscopy methods.Furthermore, additional work was pursued to give new life to these isolated, spent cathode materials. The addition of a coating with a relatively high lithium conductivity to the aged LFP/C particles was sought to provide a second life to these electrochemically aged materials. Half-cells were fabricated using the coated, aged LFP/C cathode materials to compare their performance to both pristine LFP/C nanoparticles and aged LFP/C nanoparticles without the addition of this custom coating. Electrochemical testing techniques such as galvanostatic cycling, cyclic voltammetry, and electrochemical impendence spectroscopy were used to probe the performance of each type of LFP/C nanoparticle as cathode materials in lithium-ion batteries. The coated, aged LFP/C particles were also characterized using transmission electron microscopy, energy dispersive spectroscopy, and X-ray photoelectron spectroscopy techniques. The techniques developed herein can be used to isolate, purify, and re-functionalize other cathode materials from lithium-ion batteries. Lewerenz, M.; Munnix, J.; Schmalstieg, J.; Kabitz, S.; Knips, M.; Sauer, D. U. Systematic aging of commercial LiFePO4|Graphite cylindrical cells including a theory explaining rise of capacity during aging. Power Sources. 2017, 345, 254-263.Wang, L.; Qiu, J.; Wang, X.; Chen, L.; Cao, G.; Wang, J.; Zhang, H.; He, X. Insights for understanding multiscale degradation of LiFePO4 cathodes. eScience 2022, 2(2), 125-137.

Bilayered Vanadium Oxides Pillared by Strontium Ions and Water Molecules as Stable Cathodes for Rechargeable Zn-Metal Batteries.

Vanadium-based compounds have attracted significant attention as cathodes for aqueous zinc metal batteries (AZMBs) because of their remarkable advantages in specific capacities. However, their low diffusion coefficient for zinc ions and structural collapse problems lead to poor rate capability and cycle stability. In this work, bilayered Sr0.25V2O5·0.8H2O (SVOH) nanowires are first reported as a highly stable cathode material for rechargeable AZMBs. The synergistic pillaring effect of strontium ions and water molecules improves the structural stability and ion transport dynamics of vanadium-based compounds. Consequently, the SVOH cathode exhibits a high capacity of 325.6mAhg-1 at 50mAg-1, with a capacity retention rate of 72.6% relative to the maximum specific capacity at 3.0Ag-1 after 3000 cycles. Significantly, a unique single-nanowire device is utilized to demonstrate the excellent conductivity of the SVOH cathode directly. Additionally, the energy storage mechanism of zinc insertion and extraction is investigated using a variety of advanced in situ and ex situ analysis techniques. This method of ion intercalation to improve electrochemical performance will further promote the development of AZMBs in large-scale applications.

A Unique Wide-Spacing Fence-Type Superstructure for Robust High-Voltage O3-Type Sodium Layered Cathode.

Enhancing the energy density of layered oxide cathode materials is of great significance for realizing high-performance sodium-ion batteries and promoting their commercial application. Lattice oxygen redox at high voltage usually enables a high capacity and energy density. But the structural degradation, severe voltage decay, and the resultant poor cycling performance caused by irreversible oxygen release seriously restrict the practical application. Herein we introduce a novel fence-type superstructure (2a×3a type supercell) into O3-type layered cathode material Na0.9Li0.1Ni0.3Mn0.3Ti0.3O2 and achieve a stable cycling performance at a high voltage of 4.4 V. The fence-type superstructure effectively inhibits the formation of the vacancy clusters resulting from out-of-plane Li migration and in-plane transition metal migration at high voltage due to the wide d-spacing, thereby significantly reducing the irreversible release of lattice oxygen and greatly stabilizing the crystal structure. The cathode exhibits a high energy density of 545 Wh kg-1, a high rate capability (112.8 mAh g-1 at 5 C) and a high cycling stability (85.8 %@200 cycles with a high initial capacity of 148.6 mAh g-1 at 1 C) accompanied by negligible voltage attenuation (98.5 %@200 cycles). This strategy provides a distinct spacing effect of superstructure to design stable high-voltage layered cathode materials for Na-ion batteries.

Off-Stoichiometry of Sodium Iron Pyrophosphate as Cathode Materials for Sodium-Ion Batteries with Superior Cycling Stability.

As one of the important devices for large-scale electrochemical energy storage, sodium-ion batteries have received much attention due to the abundant resources of raw materials. However, whether it is a base station power source, an energy storage power station, or a start-stop power supply, long energy cycle life (more than 5000 cycles), high stability, and safety performance are application prerequisites. Regrettably, currently, few sodium-ion batteries can meet this requirement, mainly due to shortcomings in positive electrode performance. We report a sufficiently stable sodium-ion battery cathode material, Na2Fe0.95P2O7, that retains 97.5% capacity after 5000 charge/discharge cycles. The use of nonstoichiometry in the lattice enables simultaneous modification of the crystal and electronic structure, promoting Na2Fe0.95P2O7 to be extremely stable while still being able to achieve a capacity of 92 mAh g-1 and stable cycling at high temperatures up to 60 °C. Our results confirm the positive effect of nonstoichiometric ratios on the performance of Na2Fe0.95P2O7 and provide a reliable idea to promote the practical application of sodium-ion batteries.

High‐entropy configuration strategy boosts excellent rate performance of layered oxide for sodium‐ion batteries

AbstractLayered oxides are considered to be potential cathodes for sodium‐ion batteries based on high theoretical capacity and ease of synthesis. However, the complex phase transition caused by interlayer sliding in layered oxides leads to poor cycling stability, which will hinder their further application. Here, we designed a newly O3‐type layered cathode NaNi0.3Co0.2Cu0.1Mn0.2Ti0.2O2 based on high‐entropy to achieve highly reversible phase transition behavior. It reveals 132 mAh g−1 at 0.2 C within 2–4 V increasing the energy density to 408 Wh kg−1 and it shows an outstanding rate capability of 90 mAh g−1 at 80 C (84.90% capacity retention after 1,500 cycles at 80 C). In‐situ XRD shows that reasonable design of high‐entropy components in layered material can achieve the purpose of delaying the occurrence of phase transition and DFT calculations show that the introduction of Co in transition metal layers can effectively improve the rate performance of the material. This work is of great significance in guiding the design and synthesis of highly stable layered cathode materials for sodium‐ion batteries.

Mesoporous copper-doped δ-MnO2 superstructures to enable high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are competitive alternatives for large-scale energy-storage devices owing to the abundance of zinc and low cost, high theoretical specific capacity, and high safety of these batteries. High-performance and stable cathode materials in AZIBs are the key to storing Zn2+. Manganese-based cathode materials have attracted considerable attention because of their abundance, low toxicity, low cost, and abundant valence states (Mn2+, Mn3+, Mn4+, and Mn7+). However, as a typical cathode material, birnessite-MnO2 (δ-MnO2) has low conductivity and structural instability. The crystal structure may undergo severe distortion, disorder, and structural damage, leading to severe cyclic instability. In addition, its energy-storage mechanism is still unclear, and most of the reported manganese oxide-based materials do not have excellent electrochemical performance. Herein, we propose a copper-doped Cu0.05K0.11Mn0.84O2·0.54H2O (Cu2-KMO) cathode, which exhibits a large interlayer spacing, a stable structure, and accelerated reaction kinetics. This cathode was prepared using a simple hydrothermal method. The AZIB assembled using Cu2-KMO showed high specific capacity (600 mA h g−1 at 0.1 A g−1 after 75 cycles). The dissolution-deposition energy storage mechanism of Cu-KMO in AZIBs with double electron transfer was revealed using ex situ tests. The good electrochemical performance of the Cu2-KMO cathode fabricated by the doping strategy in this study provides ideas for the subsequent preparation of manganese dioxide using other strategies.