Cathode Structure Research Articles

Unlocking the potential of cation vacancy-enriched ZnMn1.75O4 cathode for advanced aqueous aluminum-ion batteries

Manganese oxides are widely utilized in aqueous aluminum-ion batteries (AIBs) due to their high voltage and diverse crystal structures. However, the Jahn-Teller effect induced by Mn-O6 units results in irreversible structural damage. Here, we synthesized ZnMn1.75O4 (ZMO) cathodes loaded onto a carbon framework with manganese vacancies (VMn) for AIBs through ion substitution, manganese extraction, and carbonization on Mn-MIL. VMn stabilizes the ZMO structure by damping Mn-O bond vibrations and fosters Mn-O-C bonds between oxide particles and the carbon framework, effectively suppressing irreversible Mn2+ dissolution. Vacancy-modified cathodes provide more ion insertion sites, promoting ion diffusion. Ex-situ characterization revealed dominant H+ and Al3+ insertion behavior during different voltage regimes. Upon initial discharge, ion insertion into vacant lattice sites causes lattice distortions in adjacent unit cells, prompting ZMO to undergo a crystal structure transition and partial zinc deintercalation, resulting in a more stable cathode structure. Therefore, Al/ZMO batteries exhibit enhanced electrochemical performance.

Minireview: Design of Cathode Structures for Solid-State Lithium–Air Batteries─Learning from Solid Oxide Fuel Cells

Minireview: Design of Cathode Structures for Solid-State Lithium–Air Batteries─Learning from Solid Oxide Fuel Cells

Spin Symmetry Breaking-Induced Hubbard Gap Near-Closure in N-Coordinated MnO2 for Enhanced Aqueous Zinc-Ion Battery Performance.

Transition metal oxides (TMOs) are promising cathode materials for aqueous zinc ion batteries (ZIBs), however, their performance is hindered by a substantial Hubbard gap, which limits electron transfer and battery cyclability. Addressing this, we introduce a heteroatom coordination approach, using triethanolamine to induce axial N coordination on Mn centers in MnO2, yielding N-coordinated MnO2 (TEAMO). This approach leverages the change of electronegativity disparity between Mn and ligands (O and N) to disrupt spin symmetry and augment spin polarization. This enhancement leads to the closure of the Hubbard gap, primarily driven by the intensified occupancy of the Mn eg orbitals. The resultant TEAMO exhibit a significant increase in storage capacity, reaching 351 mAh g-1 at 0.1 A g-1. Our findings suggest a viable strategy for optimizing the electronic structure of TMO cathodes, enhancing the potential of ZIBs in energy storage technology.

Spin Symmetry Breaking‐Induced Hubbard Gap Near‐Closure in N‐Coordinated MnO2 for Enhanced Aqueous Zinc‐Ion Battery Performance

AbstractTransition metal oxides (TMOs) are promising cathode materials for aqueous zinc ion batteries (ZIBs), however, their performance is hindered by a substantial Hubbard gap, which limits electron transfer and battery cyclability. Addressing this, we introduce a heteroatom coordination approach, using triethanolamine to induce axial N coordination on Mn centers in MnO2, yielding N‐coordinated MnO2 (TEAMO). This approach leverages the change of electronegativity disparity between Mn and ligands (O and N) to disrupt spin symmetry and augment spin polarization. This enhancement leads to the closure of the Hubbard gap, primarily driven by the intensified occupancy of the Mn eg orbitals. The resultant TEAMO exhibit a significant increase in storage capacity, reaching 351 mAh g−1 at 0.1 A g−1. Our findings suggest a viable strategy for optimizing the electronic structure of TMO cathodes, enhancing the potential of ZIBs in energy storage technology.

A strategy of high entropy enabling advanced NASICON sodium-ion cathodes with high stabilization and multicationic redox

The sodium superionic conductor (NASICON) suffer from irreversible phase transition and insufficient cycle life above 4 V. Innovations in high-performance NASICON cathodes, alongside the comprehension of their corresponding structural and chemical aspects, remain a challenge. Inspired by the high-entropy alloys, this work proposes a NASICON cathode structure, Na4Cr0.7Fe0.4Mn0.3V0.3Al0.2(PO4)3 (HE-NASICON). HE-NASICON exhibits a reversible capacity of 165.0 mAh g−1 at 0.1 C. It undergoes successive oxidation–reduction reactions, enabling high-voltage multi-electron reactions. Furthermore, HE-NASICON maintains a capacity retention of 70.5 % after 2,000 cycles at 10 C (1.2 A g−1). In-situ X-ray diffraction analysis revealed minimal volume variation of HE-NASICON cathode crystals (1.45 %), indicating excellent stability, with the effective resistance of adverse crystal evolution by the high-entropy stabilization effect (ΔSconf >1.5R). Forming a full cell with hard carbon as the anode, it delivers a cathode-based specific capacity of 131.09 mAh g−1 at 12 mA g−1, achieving an energy density of 307.06 Wh kg−1. Considering the commercialization of NASICON-type cathodes necessitates higher energy density and lower costs. HE-NASICON not only significantly reduces the use of vanadium, thus lowering battery costs, but also anticipates widespread application of this strategy for enhancing positive electrode configuration entropy in the development of polyanion electrode materials.

Nickel-doped CNTs composite as cathode by sulfur vapor deposition for high-performance all-solid-state lithium‑sulfur batteries

Shuttle effect of polysulfide in the cathode and the safety issues arising from dendrite formation at Li metal anode are the main challenges of traditional liquid lithium‑sulfur batteries. In order to solve the shuttle effect and prevent short circuit, the all-solid-state lithium‑sulfur battery (ASSLSB) is proposed. However, the huge volume expansion of sulfur and the improvement of sulfur conversion efficiency during charge and discharge, which could lead to the limitation of electrochemical performance. Herein, a homogeneous Ni-doped carbon-nanotubes (H-Ni-SVD@CNT) composite cathode of ASSLSB is prepared by sulfur vapor deposition to confine sulfur and promote the conversion of sulfur and Li2S. In this work, SVD-5-S@CNT composite cathode demonstrates high reversible discharge capacity of 1001.1 mAh g−1 after 127 cycles and capacity retention rate of 78.6 % at the rate of 0.1C and 60 °C. Moreover, H-Ni-SVD@CNT composite cathode exhibits superior electrochemical performance, displaying the discharge specific capacity of 1519.3 mAh g−1 at 0.1C and 60 °C. Meanwhile, the discharge specific capacity of H-Ni-SVD@CNT composite cathode is 1060.9 mAh g−1 at room temperature. The synergistic effect of physical confinement and chemical catalysis improves the electrochemical performance of the all-solid-state lithium‑sulfur battery. This work proposes a new strategy for the cathode structure design of the all-solid-state lithium‑sulfur battery.

The Effect of Oxygen Vacancy Defects on the Structure and Electrochemical Behaviors of LiMn0.65Fe0.35PO4 Cathode

The presence of oxygen vacancy defects significantly impacts the crystal structure and electrochemical attributes of phosphate cathodes. In this investigation, LiMn0.65Fe0.35PO4 materials with varying levels of oxygen vacancy defects were synthesized via hydrogen plasma-induced reduction. It was observed that the content of oxygen vacancy defects on the crystal surface increased proportionately with the rise in hydrogen (H2) flow rate. Notably, the LMFP-3 sample, prepared with an H2 flow rate of 10 ml min−1, demonstrated superior electrochemical performance, characterized by a 159.7 mAh g−1 discharge capacity at 0.1 C and a remarkable 99.8% capacity retention at 5 C after 200 cycles. This enhancement in electrochemical performance is attributed to the improved intrinsic conductivity of the LiMn0.65Fe0.35PO4 material due to the presence of oxygen vacancy defects. However, it is important to note that an excessively high H2 flow rate can lead to the formation of Fe2P impurities, which hinder lithium ion (Li+) diffusion. Furthermore, theoretical calculations conducted using density functional theory provide a rational explanation for the observed improvement in electronic conductivity. The introduction of oxygen vacancy defects results in a significant reduction in the Band gap, which is highly beneficial for enhancing the intrinsic conductivity of the LiMn0.65Fe0.35PO4 materials.

Hollow-structured cobalt sulfoselenide as cathode host to enhance the kinetics and improve the energy density of lithium-sulfur batteries

Lithium-sulfur batteries are a promising next-generation battery system due to their high energy density, low cost, and environmental friendliness. However, the shuttle effect and resulting low redox kinetics are significant issues that currently hinder their development. The addition of catalysts to accelerate the redox process is a common strategy. Metal sulfide catalysts, in particular, have been widely studied due to their good affinity for sulfur and sulfides. Although metal sulfide show good adsorption performance for lithium polysulfides, their low conductivity does not significantly improve the kinetic performance of the battery. Additionally, the high molecular weight of the inactive sulfide leads to the low actual energy density of the battery. Thus, this study constructed the hollow structural cobalt sulfoselenide by replacing partial elemental sulfur in cobalt sulfide (Co3S4) with the higher metallicity element selenium (Se). This was done to increase catalytic activity and reduce the amount of inactive substances, ultimately leading to an increase in actual energy density. This strategy systematically investigated the electrical conductivity, catalytic activity, and inhibition of the shuttle effect of Co3S2Se2. It was found that cobalt sulfoselenide with a 1:1 ratio of sulfur to selenium exhibited higher catalytic activity than pure cobalt sulfide. Additionally, the hollow structure of cobalt sulfoselenide showed greater performance enhancement than bulk cobalt sulfoselenide. In the assembled lithium-sulfur battery, the initial specific capacity of 1294.7 mAh/g at 0.1C was obtained, and the capacity retention was 77.5 % after 100 cycles. On this basis, the structure–activity relationship between selenium-sulfur ratio and electrochemical properties will provide ideas for the design of microscopic cathode structures.

Modeling of the multi-cycle deep charge and discharge attenuation mechanism of non-aqueous Li–O2 batteries

Due to the high energy density, non-aqueous lithium-oxygen (Li–O2) batteries attract significant attention. However, batteries' high capacity attenuation rate under deep charge and discharge conditions remains a significant challenge. This paper presents a multi-cycle deep charge and discharge model for non-aqueous lithium-oxygen batteries, which predicts the performance of the battery during multiple deep charge and discharge cycles at high and low discharge-specific capacities. The parameter states during different discharge stages in different discharge cycles are investigated by analyzing the battery's cathode porosity, product volume fraction, and oxygen concentration changes. The study shows that as the number of cycles increases, the deposition of a small number of discharge products in the cathode altered the distribution of the newly generated products, thereby affecting the cathode structure and oxygen transport in the subsequent discharge. Moreover, depositing a small amount of discharge products can result in significant capacity attenuation in the battery. This model can accurately evaluate the deep charge and discharge performance attenuation process of non-aqueous Li–O2 batteries, which helps improve the understanding of the deep discharge attenuation mechanism of non-aqueous Li–O2 batteries.

Scalable Precise Nanofilm Coating and Gradient Al Doping Enable Stable Battery Cycling of LiCoO2 at 4.7 V

AbstractThe quest for smart electronics with higher energy densities has intensified the development of high‐voltage LiCoO2 (LCO). Despite their potential, LCO materials operating at 4.7 V faces critical challenges, including interface degradation and structural collapse. Herein, we propose a collective surface architecture through precise nanofilm coating and doping that combines an ultra‐thin LiAlO2 coating layer and gradient doping of Al. This architecture not only mitigates side reactions, but also improves the Li+ migration kinetics on the LCO surface. Meanwhile, gradient doping of Al inhibited the severe lattice distortion caused by the irreversible phase transition of O3−H1−3−O1, thereby enhanced the electrochemical stability of LCO during 4.7 V cycling. DFT calculations further revealed that our approach significantly boosts the electronic conductivity. As a result, the modified LCO exhibited an outstanding reversible capacity of 230 mAh g−1 at 4.7 V, which is approximately 28 % higher than the conventional capacity at 4.5 V. To demonstrate their practical application, our cathode structure shows improved stability in full pouch cell configuration under high operating voltage. LCO exhibited an excellent cycling stability, retaining 82.33 % after 1000 cycles at 4.5 V. This multifunctional surface modification strategy offers a viable pathway for the practical application of LCO materials, setting a new standard for the development of high‐energy‐density and long‐lasting electrode materials.

Scalable Precise Nanofilm Coating and Gradient Al Doping Enable Stable Battery Cycling of LiCoO2 at 4.7 V.

The quest for smart electronics with higher energy densities has intensified the development of high-voltage LiCoO2 (LCO). Despite their potential, LCO materials operating at 4.7 V faces critical challenges, including interface degradation and structural collapse. Herein, we propose a collective surface architecture through precise nanofilm coating and doping that combines an ultra-thin LiAlO2 coating layer and gradient doping of Al. This architecture not only mitigates side reactions, but also improves the Li+ migration kinetics on the LCO surface. Meanwhile, gradient doping of Al inhibited the severe lattice distortion caused by the irreversible phase transition of O3-H1-3-O1, thereby enhanced the electrochemical stability of LCO during 4.7 V cycling. DFT calculations further revealed that our approach significantly boosts the electronic conductivity. As a result, the modified LCO exhibited an outstanding reversible capacity of 230 mAh g-1 at 4.7 V, which is approximately 28 % higher than the conventional capacity at 4.5 V. To demonstrate their practical application, our cathode structure shows improved stability in full pouch cell configuration under high operating voltage. LCO exhibited an excellent cycling stability, retaining 82.33 % after 1000 cycles at 4.5 V. This multifunctional surface modification strategy offers a viable pathway for the practical application of LCO materials, setting a new standard for the development of high-energy-density and long-lasting electrode materials.

Electrochemical machining of titanium alloy blades using optimized cathode with built-in insulators

ABSTRACT The passivation characteristics of titanium alloys in electrolytes are often the main reason that impede the electrochemical reaction process. Hence, maintaining uniform electrochemical dissolution is a prerequisite for stable electrochemical machining (ECM) of titanium alloys. In this study, a novel cathode structure with built-in insulator is proposed, whichimproves machining stability of titanium alloys in ECM. Flow dynamics simulation results show that the cathodes with built-in insulator 1 or insulator 3 demonstrate more uniform flow effect. ECM experiments reveal that the optimized cathode can reduce the time of current from transition section to balance section, presenting a optimal transition time of 180 s. Compared with the original cathode, the sample surface machined using the optimized cathode is smooth without defects. Additionally, the optimal width of the non-processing stray corrosion area decreases from 603.47 μm to 214.54 μm, and 1010.47 μm to 349.25 μm. The optimal machining taper angle is 9.85°.

Biomass-Derived Carbon Utilization for Electrochemical Energy Enhancement in Lithium-Ion Batteries.

Cathodes made of LiFePO4 (LFP) offer numerous benefits including being non-toxic, eco-friendly, and affordable. The distinctive olivine structure of LFP cathodes contributes to their electrochemical stability. Nonetheless, this structure is also the cause of their low ionic and electronic conductivity. To enhance these limitations, an uncomplicated approach has been effectively employed. A straightforward solid-state synthesis technique is used to apply a coating of biomass from potato peels to the LFP cathode, boosting its electrochemical capabilities. Potato peels contain pyridinic and pyrrolic nitrogen, which are conducive to ionic and electronic movement and facilitate pathways for lithium-ion and electron transfer, thus elevating electrochemical performance. When coated with nitrogen-doped carbon derived from potato peel biomass (PPNC@LFP), the LFP cathode demonstrates an improved discharge capacity of 150.39 mAh g-1 at a 0.1 C-rate and 112.83 mAh g-1 at a 1.0 C-rate, in contrast to the uncoated LFP which shows capacities of 141.34 mAh g-1 and 97.72 mAh g-1 at the same rates, respectively.

Effects of foam cathode electrode structure on alkaline water electrolysis for hydrogen production

Hydrogen is widely recognized as a clean and sustainable energy source. One of the most promising methods for hydrogen production is alkaline water electrolysis. The efficiency and cost-effectiveness of this process heavily depend on the choice of a suitable porous electrode structure. This paper aims to investigate impact of the porous structure on the performance of alkaline electrolytic water through experiments and multi-physics field simulation. Specifically, the whole cell performance test and hydrogen-evolution reaction (HER) test of nickel foam were conducted in an electrolytic cell using 1 M KOH. Results revealed that various parameters of the electrode structure, such as specific surface area, pore density, thickness, and electronic conductivity, significantly influenced the hydrogen evolution. Increasing the specific surface area or pore density proved to enhance the hydrogen evolution under conventional voltage. Reducing the thickness has a similar effect. Additionally, materials with high conductivities increase the reaction rate. Based on experimental results, the optimal nickel foam cathode structure was 1000 μm thickness and 75 PPI pore density. The results of stability tests and electrolysis voltage efficiency analysis provide further support for the positive effect of this structure on hydrogen evolution. This study provides rational reference for designing efficient and stable porous electrode structures.

Sustainable electro-Fenton simultaneous reduction of Cr (VI) and degradation of organic pollutants via dual-site porous carbon cathode driving uncoordinated molybdenum sites conversion

Simultaneous removal of heavy metals and organic contaminants remains a substantial challenge in the electro-Fenton (EF) system. Herein, we propose a facile and sustainable “iron-free” EF system capable of simultaneously removing hexavalent chromium (Cr (VI)) and para-chlorophenol (4-CP). The system comprises a nitrogen-doped and carbon-deficient porous carbon (dual-site NPC-D) cathode coupled with a MoS2 nanoarray promoter (MoS2 NA). The NPC-D/MoS2 NA system exhibits exceptional synergistic electrocatalytic activity, with removal rates for Cr (VI) and 4-CP that are 20.3 and 4.4 times faster, respectively, compared to the NPC-D system. Mechanistic studies show that the dual-site structure of NPC-D cathode favors the two-electron oxygen reduction pathway with a selectivity of 81 %. Furthermore, an electric field-driven uncoordinated Mo valence state conversion of MoS2 NA enchances the generation of dynamic singlet oxygen and hydroxyl radicals. Notably, this system shows outstanding recyclability, resilience in real wastewater, and sustainability during a 3 L scale-up operation, while effectively mitigating toxicity. Overall, this study presents an effective approach for treating multiple-component wastewater and highlights the importance of structure-activity correlation in synergistic electrocatalysis.

Tautomeric pillars in vanadyl phosphate cathode to screen the divalent charge on Zn2+ for aqueous Zn batteries

Cathode materials with high redox potential are important for constructing high-energy-density aqueous zinc batteries. The polyanion compound of layered hydrate vanadyl phosphate (H2O-VOP) provides high potential thanks to the inductive effect. However, the sluggish Zn2+ diffusion in the lattice results in large voltage hysteresis, obstructing the capacity release at high voltage. Herein, tautomeric pillars are inserted in the VOPO4 layers (Tau-VOP) by the desulfhydryl reaction of l-cysteine, aiming to suppress voltage hysteresis with their charge screening effect. Specifically, the Lewis alkaline sites on the tautomers capture inserted Zn2+, and the divalent charge is further delocalized over the conjugated structure of pillars. This reduction of effective charge on cations ensures much weakened electrostatic interactions with the lattice and reduced diffusion barrier. As a result, the Tau-VOP cathode achieves 193 mAh g−1 capacity with 1.47 V/1.6 V redox voltage in zinc cells, which are superior to 110 mAh g−1 capacity and 1.1 V average discharge voltage with large voltage hysteresis obtained with H2O-VOP. The rate performance and energy efficiency are also significantly improved with the help of tautomer pillars. This work presents an effective charge screening strategy by suitable pillars to facilitate multivalent cation transport in cathode structures and enhance electrochemical performance.

MnO2 superstructure cathode with boosted zinc ion intercalation for aqueous zinc ion batteries

The simultaneous intercalation of protons and Zn2+ ions in aqueous electrolytes presents a significant obstacle to the widespread adoption of aqueous zinc ion batteries (AZIBs) for large-scale use, a challenge that has yet to be overcome. To address this, we have developed a MnO2/tetramethylammonium (TMA) superstructure with an enlarged interlayer spacing, designed specifically to control H+/Zn2+ co-intercalation in AZIBs. Within this superstructure, the pre-intercalated TMA+ ions work as spacers to stabilize the layered structure of MnO2 cathodes and expand the interlayer spacing substantially by 28 % to 0.92 nm. Evidence from in operando pH measurements, in operando synchrotron X-ray diffraction, and X-ray absorption spectroscopy shows that the enlarged interlayer spacing facilitates the diffusion and intercalation of Zn2+ ions (which have a large ionic radius) into the MnO2 cathodes. This spacing also helps suppress the competing H+ intercalation and the formation of detrimental Zn4(OH)6SO4·5H2O, thereby enhancing the structural stability of MnO2. As a result, enhanced Zn2+ storage properties, including excellent capacity and long cycle stability, are achieved.

Photoelectrochemical Communication Between Cyanobacteria and Electrospun Cellulose‐Acetate–Graphene‐Based Electrodes for Photosynthetic and Respiratorial Photocurrent and Hydrogen Generations via Sustainable Solar Energy

In this article, the potential of biophotovoltaic devices (BPVs) as a sustainable solution for addressing the global energy crisis and combating climate change is explored. BPVs harness renewable electricity from sunlight and water through the photosynthetic activity of microorganisms, such as cyanobacteria and algae, serving as living photocatalysts. The focus is primarily on enhancing photocurrent outputs by developing efficient anode materials. Carbon‐based electrodes, particularly graphene (Gr), emerge as promising candidates due to their cost‐effectiveness, electrical conductivity, and mechanical strength. Despite reduced graphene oxide being commonly used, unoxidized Gr has not been extensively explored until recent research demonstrating its excellent current harvesting capacities. Additionally, 1D‐structured nanomaterials, such as electrospun nanofibers, show potential in promoting electron transport and enhancing charge collection efficiency. An innovative photoanode design is introduced, utilizing cyanobacteria immobilized on a cellulose acetate/Gr electrospun mat, offering a porous structure conducive to cyanobacterial attachment and efficient electron transfer. A complementary cathode structure, employing aniline‐modified Pt nanoparticles, facilitates the reduction of protons to yield hydrogen gas. Overall, in this study, BPVs’ potential is highlighted as a viable clean energy technology and novel approaches to enhance their efficiency and sustainability are presented.

3D printed reticular manganese dioxide cathode with high areal capacity for aqueous zinc ion batteries

The integration of electronic devices has placed increasing demands on the low area occupancy, high areal capacity and safety of energy storage devices. Aqueous zinc ion batteries are expected to be used in highly integrated precision electronics due to their high safety, environmentally friendly and low cost advantages. However, the conventional coating method limits the structure and the areal capacity of electrodes. To address this issue, we design and fabricate a novel 3D printed reticular MnO2 self-supporting cathode. Ascribed to the high mass loading and reticular structure of the reticular MnO2 cathode, the AZIBs deliver a high areal capacity (3.43 mAh cm−2 at 2 mA cm−2). It is demonstrated that the reticular structure facilitates electrolyte storage and rapid diffusion of Zn2+ and reduces charge transfer impedance. Furthermore, the 3D printing technology can realize layer-by-layer printing of electrodes. The areal capacity of the two-layer 3D reticular MnO2 cathode is almost twice as high as that of 3D reticular MnO2. This work indicates the great potential of 3D printing technology in the design and fabrication of high-load electrodes with a high areal capacity and customized shapes.

Chemical short-range disorder in lithium oxide cathodes.

Ordered layered structures serve as essential components in lithium (Li)-ion cathodes1-3. However, on charging, the inherently delicate Li-deficient frameworks become vulnerable to lattice strain and structural and/or chemo-mechanical degradation, resulting in rapid capacity deterioration and thus short battery life2,4. Here we report an approach that addresses these issues using the integration of chemical short-range disorder (CSRD) into oxide cathodes, which involves the localized distribution of elements in a crystalline lattice over spatial dimensions, spanning a few nearest-neighbour spacings. This is guided by fundamental principles of structural chemistry and achieved through an improved ceramic synthesis process. To demonstrate its viability, we showcase how the introduction of CSRD substantially affects the crystal structure of layered Li cobalt oxide cathodes. This is manifested in the transition metal environment and its interactions with oxygen, effectively preventing detrimental sliding of crystal slabs and structural deterioration during Li removal. Meanwhile, it affects the electronic structure, leading to improved electronic conductivity. These attributes are highly beneficial for Li-ion storage capabilities, markedly improving cycle life and rate capability. Moreover, we find that CSRD can be introduced in additional layered oxide materials through improved chemical co-doping, further illustrating its potential to enhance structural and electrochemical stability. These findings open up new avenues for the design of oxide cathodes, offering insights into the effects of CSRD on the crystal and electronic structure of advanced functional materials.