Pillar-beam structures prevent layered cathode materials from destructive phase transitions

Dual-Site Doping in Transition Metal Oxide Cathode Enables High-Voltage Stability of Na-Ion Batteries

Designing cathode materials that effectively enhancing structural stability under high voltage is paramount for rationally enhancing energy density and safety of Na-ion batteries. This study introduces a novel P2-Na0.73K0.03Ni0.23Li0.1Mn0.67O2 (KLi-NaNMO) cathode through dual-site synergistic doping of K and Li in Na and transition metal (TM) layers. Combining theoretical and experimental studies, this study discovers that Li doping significantly strengthens the orbital overlap of Ni (3d) and O (2p) near the Fermi level, thereby regulates the phase transition and charge compensation processes with synchronized Ni and O redox. The introduction of K further adjusts the ratio of Nae and Naf sites at Na layer with enhanced structural stability and extended lattice space distance, enabling the suppression of TM dissolution, achieving a single-phase transition reaction even at a high voltage of 4.4 V, and improving reaction kinetics. Consequently, KLi-NaNMO exhibits a high capacity (105 and 120 mAh g-1 in the voltage of 2-4.2 V and 2-4.4 V at 0.1 C, respectively) and outstanding cycling performance over 300 cycles under 4.2 and 4.4 V. This work provides a dual-site doping strategy to employ synchronized TM and O redox with improved capacity and high structural stability via electronic and crystal structure modulation.

Modulating Valence Electrons and Na Occupancy in Layered Cathodes for High-Performance Na-Ion Batteries

Na-ion batteries (NIBs) hold promise as a leading option for large-scale energy storage. However, their development faces challenges due to the lack of high-performance cathode materials. P2-type layered oxides are seen as potential cathode materials for NIBs due to higher structure stability, yet their commercialization is hindered by limited capacity and subpar phase transitions during Na extraction and insertion at high voltages. In this study, we introduce a new P2-type cathode material, Na0.76Ni0.23Li0.1Ti0.02Mn0.65O1.998F0.02 (NLTMOF), synthesized with ternary Li/Ti/F substitution. This modification of ternary Li/Ti/F substitution significantly tailors the electronic structures, increasing the number of valence electrons near the Fermi energy level. This facilitates the electronic conductivity and their involvement in charge compensation, thereby enhancing reversible capacity. Additionally, ternary doping synergistically adjusts the Na occupancy at the Na layer for favorable Na extraction without P2-O2 phase transitions even under a high voltage of 4.4 V, boosting cycling stability. As a result, NLTMOF demonstrates a reversible capacity of 110.0 and 132.2 mAh g-1 at 2-4.2 and 2-4.4 V, respectively, and maintains greatly enhanced cycling stability over long cycles. This study sheds light on the design of transition metal oxides for advanced cathode materials through the modulation of electronic structure and Na occupancy in cathode materials, thus promoting the development of NIBs.

5G NB-IoT System Integrated with High-Performance Fiber Sensor Inspired by Cirrus and Spider Structures

Real-time telemedicine detection can solve the problem of the shortage of public medical resources caused by the coming aging society. However, the development of such an integrated monitoring system is hampered by the need for high-performance sensors and the strict-requirement of long-distance signal transmission and reproduction. Here, a bionic crack-spring fiber sensor (CSFS) inspired by spider leg and cirrus whiskers for stretchable and weavable electronics is reported. Trans-scale conductive percolation networks of multilayer graphene around the surface of outer spring-like Polyethylene terephthalate (PET) fibers and printing Ag enable a high sensitivity of 28475.6 and broad sensing range over 250%. The electromechanical changes in different stretching stages are simulated by Comsol to explain the response mechanism. The CSFS is incorporated into the fabric and realized the human-machine interactions (HMIs) for robot control. Furthermore, the 5G Narrowband Internet of Things (NB-IoT) system is developed for human healthcare data collection, transmission, and reproduction together with the integration of the CSFS, illustrating the huge potential of the approach in human-machine communication interfaces and intelligent telemedicine rehabilitation and diagnosis monitoring.

Routes to high-performance layered oxide cathodes for sodium-ion batteries

Sodium-ion batteries (SIBs) are experiencing a large-scale renaissance to supplement or replace expensive lithium-ion batteries (LIBs) and low energy density lead-acid batteries in electrical energy storage systems and other applications. In this case, layered oxide materials have become one of the most popular cathode candidates for SIBs because of their low cost and comparatively facile synthesis method. However, the intrinsic shortcomings of layered oxide cathodes, which severely limit their commercialization process, urgently need to be addressed. In this review, inherent challenges associated with layered oxide cathodes for SIBs, such as their irreversible multiphase transition, poor air stability, and low energy density, are systematically summarized and discussed, together with strategies to overcome these dilemmas through bulk phase modulation, surface/interface modification, functional structure manipulation, and cationic and anionic redox optimization. Emphasis is placed on investigating variations in the chemical composition and structural configuration of layered oxide cathodes and how they affect the electrochemical behavior of the cathodes to illustrate how these issues can be addressed. The summary of failure mechanisms and corresponding modification strategies of layered oxide cathodes presented herein provides a valuable reference for scientific and practical issues related to the development of SIBs.

Review on Layered Manganese-Based Metal Oxides Cathode Materials for Potassium-Ion Batteries: From Preparation to Modification

Potassium-ion battery is rich in resources and cheap in price, in the era of lithium-ion battery commercialization, potassium-ion battery is the most likely to replace it. Based on the classification and summary of electrode materials for potassium-ion batteries, this paper focuses on the introduction of manganese-based oxide KxMnO2. The layered KxMnO2 has a large layer spacing and can be embedded with large size potassium-ions. This paper focuses on the preparation and doping of manganese-based cathode materials for potassium-ion batteries, summarizes the main challenges of KxMnO2-based cathode materials in the current stage of research and further looks into its future development direction.

Toward the High-Voltage Stability of Layered Oxide Cathodes for Sodium-Ion Batteries: Challenges, Progress, and Perspectives

Sodium-ion batteries (SIBs) have garnered significant attention as ideal candidates for large-scale energy storage due to their notable advantages in terms of resource availability and cost-effectiveness. However, there remains a substantial energy density gap between SIBs and commercially available lithium-ion batteries (LIBs), posing challenges to meeting the requirements of practical applications. The fabrication of high-energy cathodes has emerged as an efficient approach to enhancing the energy density of SIBs, which commonly requires cathodes operating in high-voltage regions. Layered oxide cathodes (LOCs), with low cost, facile synthesis, and high theoretical specific capacity, have emerged as one of the most promising candidates for commercial applications. However, LOCs encounter significant challenges when operated in high-voltage regions such as irreversible phase transitions, migration and dissolution of metal cations, loss of reactive oxygen, and the occurrence of serious interfacial parasitic reactions. These issues ultimately result in severe degradation in battery performance. This review aims to shed light on the key challenges and failure mechanisms encountered by LOCs when operated in high-voltage regions. Additionally, the corresponding strategies for improving the high-voltage stability of LOCs are comprehensively summarized. By providing fundamental insights and valuable perspectives, this review aims to contribute to the advancement of high-energy SIBs.

Synergistic Effect of Co-Mo Pinning in Lay-Structured Oxide Cathode for Enhancing Stability toward Potassium-Ion Batteries

Owing to the high economic efficiency and energy density potential, manganese-based layer-structured oxides have attracted great interests as cathode materials for potassium ion batteries. In order to alleviate the continuous phase transition and K+ re-embedding from Jahn-Teller distortion, the [Mn-Co-Mo]O6 octahedra are introduced into P3-K0.45 MnO2 herein to optimize the local electron structure. Based on the experimental and computational results, the octahedral center metal molybdenum in [MoO6 ] octahedra proposes a smaller ionic radius and higher oxidation state to induce second-order JTE (pseudo-JTE) distortion in the adjacent [MnO6 ] octahedra. This distortion compresses the [MnO6 ] octahedra along the c-axis, leading to an increased interlayer spacing in the K+ layer. Meanwhile, the Mn3+ /Mn4+ is balanced by [CoO6 ] octahedra and the K+ diffusion pathway is optimized as well. The proposed P3-K0.45 Mn0.9 Co0.05 Mo0.05 O2 cathode material shows an enhanced cycling stability and rate performance. It demonstrates a high capacity of 80.2 mAh g-1 at 100 mAh g-1 and 77.3 mAh g-1 at 500 mAh g-1 . Furthermore, it showcases a 2000 cycles stability with a 59.6% capacity retention. This work presents a promising solution to the challenges faced by manganese-based layered oxide cathodes and offers a deep mechanism understanding and improved electrochemical performance.

Simultaneously promoting the surface/bulk structural stability of Fe/Mn-based layered cathode for sodium ion batteries

Layered sodium iron manganese oxide cathodes have attracted great interest owing to their high specific capacity and cost-effective metal resources, while the detrimental phase transitions and surface structural degradation severely limit their commercial applications. In this work, the bulk and surface structure stability of a P2-Na0.67Fe0.5Mn0.5O2 cathode can be synergically enhanced by a one-step Li/Nb co-doping strategy. Structural characterizations reveal that Li doping promotes the formation of P2/O3 biphasic structure and makes the unfavorable P2-OP4 phase transition convert into a smooth solid-solution reaction. Nb doping enhances the mobility of sodium ions and forms strong Nb-O bonds, thereby enhancing the stability of the TMO2 layer structure. In particular, the Nb element induces the surface reorganization of an atomic-scale NaNbO3 coating layer, which could effectively prevent the dissolution of metals and surface side reactions. The synergistic mechanism of enhanced electrochemical performance is proved by multiple characterizations during cycling. As a result, the as-prepared Na0.67Li0.1Fe0.5Mn0.38Nb0.02O2 exhibits improved capacity retention of 85.4 % than raw material (45.7 %) after 100 cycles at 0.5C (1C = 174 mA g-1) within 2.0-4.0 V. This co-regulating strategy provides a promising approach to designing highly stable sodium-ion battery cathodes. Furthermore, a full cell of Na0.67Li0.1Fe0.5Mn0.38Nb0.02O2 with hard carbon displays excellent cycling stability (85.1 % capacity retention after 100 cycles), making its commercial operation possible. This synergistic strategy of biphasic structure and surface reorganization is a critical route to accelerate the application of layer oxide cathodes.

Comparative Analysis of Differentially Expressed Genes in Chondrocytes from Rats Exposed to Low Selenium and T-2 Toxin

The aim of this study was to construct rat models of environmental risk factors for Kashin-Beck disease (KBD) with low selenium and T-2 toxin levels and to screen the differentially expressed genes (DEGs) between the rat models exposed to environmental risk factors. The Se-deficient (SD) group and T-2 toxin exposure (T-2) group were constructed. Knee joint samples were stained with hematoxylin-eosin, and cartilage tissue damage was observed. Illumina high-throughput sequencing technology was used to detect the gene expression profiles of the rat models in each group. Gene Ontology (GO) functional enrichment analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) signaling pathway enrichment analysis were performed and five differential gene expression results were verified by quantitative real-time polymerase chain reaction (qRT‒PCR). A total of 124 DEGs were identified from the SD group, including 56 upregulated genes and 68 downregulated genes. A total of 135 DEGs were identified in the T-2 group, including 68 upregulated genes and 67 downregulated genes. The DEGs were significantly enriched in 4 KEGG pathways in the SD group and 9 KEGG pathways in the T-2 group. The expression levels of Dbp, Pc, Selenow, Rpl30, and Mt2A were consistent with the results of transcriptome sequencing by qRT‒PCR. The results of this study confirmed that there were some differences in DEGs between the SD group and the T-2 group and provided new evidence for further exploration of the etiology and pathogenesis of KBD.

Investigation into white matter microstructure differences in visual training by using an automated fiber tract subclassification segmentation quantification method

Visual training has emerged as a useful framework for investigating training-related brain plasticity, a highly complex task involving the interaction of visual orientation, attention, reasoning, and cognitive functions. However, the effects of long-term visual training on microstructural changes within white matter (WM) is poorly understood. Therefore, a set of visual training programs was designed, and automated fiber tract subclassification segmentation quantification based on diffusion magnetic resonance imaging was performed to obtain the anatomical changes in the brains of visual trainees. First, 40 healthy matched participants were randomly assigned to the training group or the control group. The training group underwent 10 consecutive weeks of visual training. Then, the fiber tracts of the subjects were automatically identified and further classified into fiber clusters to determine the differences between the two groups on a detailed scale. Next, each fiber cluster was divided into segments that can analyze specific areas of a fiber cluster. Lastly, the diffusion metrics of the two groups were comparatively analyzed to delineate the effects of visual training on WM microstructure. Our results showed that there were significant differences in the fiber clusters of the cingulate bundle, thalamus frontal, uncinate fasciculus, and corpus callosum between the training group compared and the control group. In addition, the training group exhibited lower mean fractional anisotropy, higher mean diffusivity and radial diffusivity than the control group. Therefore, the long-term cognitive activities, such as visual training, may systematically influence the WM properties of cognition, attention, memory, and processing speed.

Electronic States Tailoring and Pinning Effect Boost High-Power Sodium-Ion Storage of Oriented Hollow P2-Type Cathode Materials

Fierce phase transformation and limited sodium ion diffusion dynamics are critical obstacles that hinder the practical energy storage applications of P2-type layered sodium transition metal oxides (NaxTMO2). Herein, a synergistic strategy of electronic state tailoring and pillar effect was carefully implemented by substituting divalent Mg2+ into Na0.67Ni0.33Mn0.67O2 material with unique oriented hollow rodlike structures. Mg2+substitution can not only facilitate the anionic oxygen redox reactions and electronic conductivity through increasing the electronic states at Femi energy but also act as pillars within TMO2 layers to alleviate the severe phase transformation to improve structure stability. Moreover, the oriented hollow structure incorporating sufficient buffer spaces and rationally exposed electrochemically active facets effectively alleviates the stresses induced by low volume changes of 8% and provides more open channels for Na+ ion diffusion without crossing multiple grain boundaries. Hence, the Na0.67Mg0.08Ni0.25Mn0.67O2 cathode showed a superior rate capability with high energy density and cycling stability for sodium-ion storage. The underlying mechanisms of these achievements were deciphered through diversified dynamic analysis and the first principle calculations, providing new insights into P2-type NaxTMO2 cathodes for the infinite prospect as an alternative to lithium-ion batteries.

Organic Species-Intercalated Vanadium Oxide for Sodium-Ion Battery: Mixed-Anion Coordination Effect, Enhanced d-p Orbital Hybridization, and Topotactic Phase Conversion Induced by N-Substitution

Sodium-ion battery (SIB) is a reasonable alternative to lithium-ion battery (LIB) in the field of grid-scale energy storage systems. Unfortunately, the development of appropriate cathode material is a bottleneck in the field of SIB. In the present work, (p-TQ)-VO, formulated as (p-TQ)0.2V2O5·0.38H2O, was synthesized based on a facile hydrothermal reaction of V2O5 and methylhydroquinone (p-HTQ). And when V2O5 was replaced by VN, (p-TQ)-VN, formulated as (p-TQ)0.22V2(O/N)5, was prepared instead. The (p-TQ)-VO sample displays good electrochemical performance as the SIB cathode. And (p-TQ)-VN shows a much higher capacity at a small current density, and it can maintain structural integrity with partial topotactic phase transformation into NaxV2O5 during the discharge/charge process. A series of characterizations of (p-TQ)-VO and (p-TQ)-VN reveals the successful intercalation of p-TQ into the layered V2O5 with a (001) lattice spacing of 13.7 and 10.7 Å, respectively. In (p-TQ)-VN, partial terminal oxygen (Ot) atoms from the V-O-V layer have been substituted by N atoms, which can boost the orbital hybridization of V 3d and Ot 2p, shorten the V-Ot bonds in the c-axial direction, and elongate the V-O bonds in the ab plane with compressed {VO4N2} octahedra, giving rise to mixed-anion coordination effect. As a result, the enhanced electron densities around the Ot atoms of the V-O-V layer can facilitate the affinity toward the inserted Na+ ions, leading to partial phase conversion into NaNO2/NaNO3. Moreover, density functional density (DFT) calculations reveal that the N-incorporation can improve electron conductivity with richer molecular orbital energy levels, resulting in multistep redox reactions and enhanced capacity.

High-Voltage Potassium Hexacyanoferrate Cathode via High-Entropy and Potassium Incorporation for Stable Sodium-Ion Batteries

Prussian blue analogues (PBAs) used as sodium ion battery (SIB) cathodes are usually the focus of attention due to their three-dimensional open frame and high theoretical capacity. Nonetheless, the disadvantages of a low working voltage and inferior structural stability of PBAs prevent their further applications. Herein, we propose constructing the Kx(MnFeCoNiCu)[Fe(CN)6] (HE-K-PBA) cathode by high-entropy and potassium incorporation strategy to simultaneously realize high working voltage and cycling stability. The reaction mechanism of metal cations in HE-K-PBA are revealed by synchrotron radiation X-ray absorption spectroscopy (XAS), ex situ X-ray photoelectron spectroscopy (XPS), and in situ Raman spectra. We also investigate the entropy stabilization mechanism via finite element simulation, demonstrating that HE-K-PBA with small von Mises stress and weak structure strain can significantly mitigate the structural distortion. Benefit from the stable structure and everlasting K+ (de)intercalation, the HE-K-PBA delivers high output voltage (3.46 V), good reversible capacity (120.5 mAh g-1 at 0.01 A g-1), and capacity retention of 90.4% after 1700 cycles at 1.0 A g-1. Moreover, the assembled full cell and all-solid-state batteries with a stable median voltage of 3.29 V over 3000 cycles further demonstrate the application prospects of the HE-K-PBA cathode.

Biochemical fulvic acid derived amorphous carbon modified microcrystalline graphite as low-cost anode for potassium-ion storage

Graphite anode has great potential toward potassium ion storage for abundant reserves, yet it suffers from the large volume expansion and slow diffusion rate. Herein, the low-cost biochemical fulvic acid-derived amorphous carbon (BFAC) is employed to modify the natural microcrystalline graphite (BFAC@MG) by a simple mixed carbonization strategy. The BFAC smooths the split layer and folds on the surface of microcrystalline graphite and builds the heteroatom-doped composite structure, which effectively alleviates the volume expansion caused by K⁺ electrochemical de-intercalation processes, together with improving electrochemical reaction kinetics. As expected, the optimized BFAC@MG-0.5 exhibits superior potassium-ion storage performance, which delivers a high reversible capacity (623.8 mAh g^-1), excellent rate performance (147.8 mAh g^-1 at 2 A g^-1), and remarkable cycling stability (100.8 mAh g^-1 after 1200 cycles). As a practical device application, the potassium-ion capacitors are assembled using the BFAC@MG-0.5 anode and commercial activated carbon cathode, which exhibits a maximum energy density of 126.48 Wh kg^-1 and superior cycle stability. Significantly, this work demonstrates the potential of microcrystalline graphite as the host anode material for potassium-ion storage.

Transition Metal Vacancy in Layered Cathode Materials for Sodium-Ion Batteries

Anionic redox has been considered as a promising strategy to break the capacity limitation of cathode materials that solely relies on the intrinsic cationic redox in secondary batteries. Vacancy, as a kind of defect, can be introduced into transition metal layer to trigger oxygen redox, thus enhancing the energy density of layer-structured cathode materials for sodium-ion batteries. Herein, the formation process, recent progress in working mechanisms of triggering oxygen redox, as well as advanced characterization techniques for transition metal (TM) vacancy were overviewed and discussed. Strategies applied to stabilize the vacancy contained structures and harness the reversible oxygen redox were summarized. Furthermore, the challenges and prospects for further understanding TM vacancy were particularly emphasized.

A review of medical wearables: materials, power sources, sensors, and manufacturing aspects of human wearable technologies

Wearable technology is a promising and revolutionary technology that is changing some aspects of our standard of living to a great extent, including health monitoring, sport and fitness, performance tracking, education, and entertainment. This article presents a comprehensive literature review of over 160 articles related to state-of-the-art human wearable technologies. We provide a thorough understanding of the materials, power sources, sensors, and manufacturing processes, and the relationships between these to capture opportunities for enhancement and challenges to overcome in wearables. As a result of our review, we have determined the need for the development of a comprehensive, robust manufacturing system alongside specific standards and regulations that take into account wearables' unique characteristics. Seeing the whole picture will provide a frame reference and road map for researchers and industries through the design, manufacturing, and commercialisation of effective, portable, self-powered, multi-sensing ultimate future wearable devices and create opportunities for new innovations and applications.

Expanded K0.37Fe0.04Al0.07Mn0.89O2 Layered Material as a High-Performance Cathode in Sodium-Ion Batteries

Due to a high operating voltage and theoretical capacity, P2-type layered Mn-based metal oxides are considered to be promising cathodes in sodium-ion batteries, but their poor structural stability in the process of Na+ insertion/deinsertion severely hinders their practical application. Here, an interesting K+ pre-intercalation is used to expand the interlayer distance and enhance the electrochemical reversibility of KsFexAlyMnzO2. With a suitable K+ content, the optimized electrode shows a high specific capacity of 135 mAh g−1 at 0.1 C, a good rate capability of 80 mAh g−1 at 5 C and an excellent cycling performance of 76.4% capacity retention after 200 cycles at a high rate of 5 C. This work proves the feasibility of a K+ pre-intercalation strategy in a P2-type layered cathode.

A high-capacity self-sacrificial additive based on electroactive sodiated carbonyl groups for sodium-ion batteries

A new type of high-capacity sacrificial additive (Na₄C₆O₆) is proposed to replenish the sodium loss in sodium ion full-cells. The HC//Na₃V₂(PO₄)₂F₃ full-cells demonstrate significantly enhanced energy density after introducing an appropriate amount of additive.

Atomically Dispersed Manganese on Biochar Derived from a Hyperaccumulator for Photocatalysis in Organic Pollution Remediation

Phytoremediation is a potentially cost-effective and environmentally friendly remediation method for environmental pollution. However, the safe treatment and resource utilization of harvested biomass has become a limitation in practical applications. To address this, a novel manganese-carbon-based single-atom catalyst (SAC) method has been developed based on the pyrolysis of a manganese hyperaccumulator, Phytolacca americana. In this method, manganese atoms are dispersed atomically in the carbon matrix and coordinate with N atoms to form a Mn-N₄ structure. The SAC developed exhibited a high photooxidation efficiency and excellent stability during the degradation of a common organic pollutant, rhodamine B. The Mn-N₄ site was the active center in the transformation of photoelectrons via the transfer of photoelectrons between adsorbed O₂ and Mn to produce reactive oxygen species, identified by in situ X-ray absorption fine structure spectroscopy and density functional theory calculations. This work demonstrates an approach that increases potential utilization of biomass during phytoremediation and provides a promising design strategy to synthesize cost-effective SACs for environmental applications.

Dual-Function of Cation-Doping to Activate Cationic and Anionic Redox in a Mn-Based Sodium-Layered Oxide Cathode

Recently, sodium-ion batteries have shown great potential for energy storage owing to their favorable electrochemical properties and intrinsic cost performance, which fuels the research and development of Mn-based layered oxides as promising sodium-ion cathodes. However, the undesirable structural evolution and oxygen redox impose great challenge on the cycling stability and rate capability of such cathodes. In this work, it is reported that Fe and Al can effectively tailor the Na_2/3 Mn_2/3 Fe_1/6 Al_1/6 O₂ to trigger a stable cationic and anionic redox behavior. In situ X-ray diffraction analysis confirms the retention of a stable P2 phase upon cycling, and density functional theory results demonstrate that Al³⁺ doping can strengthen the covalency of MnO bond. The Na_2/3 Mn_2/3 Fe_1/6 Al_1/6 O₂ cathode can retain 90% of its initial capacity within the voltage range of 2.0-4.2 V versus Na⁺ /Na at 200 mA g^-1 after 100 cycles. Moreover, ex situ X-ray photoelectron spectroscopy reveals that the specific capacity can be replenished by the synergistic reactions between Fe³⁺ /Fe⁴⁺ /Fe³⁺ and O^2- /(O₂ )^{n -} pairs within the voltage range of 4.0-4.4 V versus Na⁺ /Na, which is also elucidated by theoretical calculation.

Origin of multiple voltage plateaus in P2-type sodium layered oxides

Although layered transition metal (TM) oxides have attracted considerable attention for cathode materials of sodium-ion batteries, they suffer from uncontrolled multiple voltage plateaus due to local structure transformations such as TM-layer gliding and Na⁺/vacancy ordering upon Na⁺ extraction and insertion. However, the intrinsic origins of these local structure transformations are not fully understood, preventing the rational design of better cathode materials. Here, we concentrate on Na⁺/vacancy ordering in single phase domains to reveal the underlying mechanism of multiple voltage plateaus by tracking desodiation-induced electronic structure evolutions of two typical compounds, P2-Na_0.6[Cr_0.6Ti_0.4]O₂ and P2-NaCrO₂. During desodiation, P2-NaCrO₂ generates obvious multiple voltage plateaus, which are not observed in P2-Na_0.6[Cr_0.6Ti_0.4]O₂ due to TM disordering. A combination of first-principles desodiation calculations and electronic structure analysis reveals that charge localization accompanied by Na⁺ migration is an intrinsic feature of multiple voltage plateaus in P2-NaCrO₂. A correlation between charge localization and multiple voltage plateaus is established by a comparative study in which P2-Na_0.6[Cr_0.6Ti_0.4]O₂ always follows the charge transfer order from high-activity to low-activity sites. This finding reveals that disordering design of active sites to avoid charge localization in redox is of much importance for developing high-performance Na-ion cathode materials.

Iron Catalyzed Cascade Construction of Molybdenum Carbide Heterointerfaces for Understanding Hydrogen Evolution

The intercrystalline interfaces have been proven vital in heterostructure catalysts. However, it is still challenging to generate specified heterointerfaces and to make clear the mechanism of a reaction on the interface. Herein, this work proposes a strategy of Fe-catalyzed cascade formation of heterointerfaces for comprehending the hydrogen evolution reaction (HER). In the pure solid-phase reaction system, Fe catalyzes the in situ conversion of MoO₂ to MoC and then Mo₂ C, and the consecutive formation leaves lavish intercrystalline interfaces of MoO₂ -MoC (in Fe-MoO₂ /MoC@NC) or MoC-Mo₂ C (in Fe-MoC/β-Mo₂ C@NC), which contribute to HER activity. The improved HER activity on the interface leads to further checking of the mechanism with density functional theory calculation. The computation results reveal that the electroreduction (Volmer step) produced H* prefers to be adsorbed on Mo₂ C; then two pathways are proposed for the HER on the interface of MoC-Mo₂ C, including the single-molecular adsorption pathway (Rideal mechanism) and the bimolecular adsorption pathway (Langmuir-Hinshelwood mechanism). The calculation results further show that the former is favorable, and the reaction on the MoC-Mo₂ C heterointerface significantly lowers the energy barriers of the rate-determining steps.

Alternate Storage of Opposite Charges in Multisites for High-Energy-Density Al-MOF Batteries

The limited active sites of cathode materials in aluminum-ion batteries restrict the storage of more large-sized Al-complex ions, leading to a low celling of theoretical capacity. To make the utmost of active sites, an alternate storage mechanism of opposite charges (AlCl₄ ^- anions and AlCl₂ ⁺ cations) in multisites is proposed herein to achieve an ultrahigh capacity in Al-metal-organic framework (MOF) battery. The bipolar ligands (oxidized from 18π to 16π electrons and reduced from 18π to 20π electrons in a planar cyclic conjugated system) can alternately uptake and release AlCl₄ ^- anions and AlCl₂ ⁺ cations in charge/discharge processes, which can double the capacity of unipolar ligands. Moreover, the high-density active Cu sites (Cu nodes) in the 2D Cu-based MOF can also store AlCl₂ ⁺ cations for a higher capacity. The rigid and extended MOF structure can address the problems of high solubility and poor stability of small organic molecules. As a result, three-step redox reactions with two-electron transfer in each step are demonstrated in charge/discharge processes, achieving high reversible capacity (184 mAh g^-1 ) and energy density (177 Wh kg^-1 ) of the optimized cathode in an Al-MOF battery. The findings provide a new insight for the rational design of stable high-energy Al-MOF batteries.

Graphene-Supported Naphthalene-Based Polyimide Composite as a High-Performance Sodium Storage Cathode

Electroactive acid anhydride with multicarbonyl is highly promising for electrochemical energy storage because of its high specific capacity and environmental benignity. Its low electrical conductivity and high dissolution in organic electrolyte, however, result in poor cycling and rate capabilities. Here, we report a naphthalene polyimide derivative (NPI) synthesized by using anhydride under condensation polymerization conditions, along with its composite with graphene (NPI-G) fabricated via in situ polymerization. The composite delivers a high reversible capacity and outstanding cycling stability and rate capability as a cathode for sodium-ion batteries (SIBs) owing to the formation of a polymer, the improvement in the electrical conductivity brought about by the highly dispersed graphene sheets, and the enhancement of structural stability resulting from the π-π stacking interaction between the phenyl groups of NPI and the six-member carbon rings of graphene. This investigation sheds light on the development, design, and screening of next-generation organic electrode materials with high performance for SIBs.

Native lattice strain induced structural earthquake in sodium layered oxide cathodes

High-voltage operation is essential for the energy and power densities of battery cathode materials, but its stabilization remains a universal challenge. To date, the degradation origin has been mostly attributed to cycling-initiated structural deformation while the effect of native crystallographic defects induced during the sophisticated synthesis process has been significantly overlooked. Here, using in situ synchrotron X-ray probes and advanced transmission electron microscopy to probe the solid-state synthesis and charge/discharge process of sodium layered oxide cathodes, we reveal that quenching-induced native lattice strain plays an overwhelming role in the catastrophic capacity degradation of sodium layered cathodes, which runs counter to conventional perception—phase transition and cathode interfacial reactions. We observe that the spontaneous relaxation of native lattice strain is responsible for the structural earthquake (e.g., dislocation, stacking faults and fragmentation) of sodium layered cathodes during cycling, which is unexpectedly not regulated by the voltage window but is strongly coupled with charge/discharge temperature and rate. Our findings resolve the controversial understanding on the degradation origin of cathode materials and highlight the importance of eliminating intrinsic crystallographic defects to guarantee superior cycling stability at high voltages.

Native crystallographic defects are often introduced during synthesis of battery materials, but has been overlooked. Here, using in situ synchrotron X-ray probes and electron microscopy, the authors have revealed their adverse effect during battery operation.

Structural Origins of Voltage Hysteresis in the Na-Ion Cathode P2-Na0.67[Mg0.28Mn0.72]O2: A Combined Spectroscopic and Density Functional Theory Study

P2-layered sodium-ion battery (NIB) cathodes are a promising class of Na-ion electrode materials with high Na+ mobility and relatively high capacities. In this work, we report the structural changes that take place in P2-Na0.67[Mg0.28Mn0.72]O2. Using ex situ X-ray diffraction, Mn K-edge extended X-ray absorption fine structure, and 23Na NMR spectroscopy, we identify the bulk phase changes along the first electrochemical charge-discharge cycle-including the formation of a high-voltage "Z phase", an intergrowth of the OP4 and O2 phases. Our ab initio transition state searches reveal that reversible Mg2+ migration in the Z phase is both kinetically and thermodynamically favorable at high voltages. We propose that Mg2+ migration is a significant contributor to the observed voltage hysteresis in Na0.67[Mg0.28Mn0.72]O2 and identify qualitative changes in the Na+ ion mobility.

A Comparative Review of Metal Oxide Surface Coatings on Three Families of Cathode Materials for Lithium Ion Batteries

In the recent years, lithium-ion batteries have prevailed and dominated as the primary power sources for mobile electronic applications. Equally, their use in electric resources of transportation and other high-level applications is hindered to some certain extent. As a result, innovative fabrication of lithium-ion batteries based on best performing cathode materials should be developed as electrochemical performances of batteries depends largely on the electrode materials. Elemental doping and coating of cathode materials as a way of upgrading Li-ion batteries have gained interest and have modified most of the commonly used cathode materials. This has resulted in enhanced penetration of Li-ions, ionic mobility, electric conductivity and cyclability, with lesser capacity fading compared to traditional parent materials. The current paper reviews the role and effect of metal oxides as coatings for improvement of cathode materials in Li-ion batteries. For layered cathode materials, a clear evaluation of how metal oxide coatings sweep of metal ion dissolution, phase transitions and hydrofluoric acid attacks is detailed. Whereas the effective ways in which metal oxides suppress metal ion dissolution and capacity fading related to spinel cathode materials are explained. Lastly, challenges faced by olivine-type cathode materials, namely; low electronic conductivity and diffusion coefficient of Li+ ion, are discussed and recent findings on how metal oxide coatings could curb such limitations are outlined.