Cathode Design Research Articles

Doping of group IVB elements for nickel-rich cobalt-free cathodes

Hetero-element doping is a promising strategy to improve the cycling stability of nickel-rich cobalt-free cathodes for the next-generation high energy-density Li ion batteries. To make doping effective, it is important to understand the mechanism of how the dopants regulate the electronic band, lattice parameter adjusting, or hetero-phase formation to achieve high stability. In this study, we investigate LiNi0.9Mn0.1O2 cathodes doped with IVB grouping elements via multiple characterization techniques. By utilizing in situ XRD and TEM methods, we found that the stronger Ti–O bond effectively improves the cathode stability via a dual protection mechanism. Specifically, the bulk lattice of cathode is well-preserved during cycling as a result of the suppressed H2-H3 phase transition, while a in situ formed Ti-rich surface layer can prevent continuous surface degradation. As a result, the 5% Ti doped LiNi0.9Mn0.1O2 cathode exhibits a high capacity retention of 96% after 100 cycles. Whereas, despite IVB group elements Zr and Hf have stronger bonding energy with oxygen, their larger ionic radii actually impede their diffusion into the cathode, thereby they can not improve the cycling stability. Our findings uncover the functional origin of doped elements with their dynamic modification on cathode structure, providing mechanistic insights into the design of nickel-rich cobalt-free cathodes.

Hydrophobic and Homogeneous Conductive Carbon Matrix for High-Rate Non-Alkaline Zinc-Air Batteries.

Non-alkaline zinc-air batteries (ZABs) that use reversible O2 /ZnO2 chemistry exhibit excellent stability and superior reversibility compared to conventional alkaline ZABs. Unlike alkaline ZABs, ZnO2 discharge products are generated on the surface of the air cathodes in non-alkaline ZABs, requiring more gas-liquid-solid three-phase reaction interfaces. However, the kinetics of reported ZABs based on carbon black (CB) is far from satisfactory due to the insufficient reaction areas. The rational structural design of the air cathode is an effective way to increase active surfaces to further enhance the performance of non-alkaline ZABs. In this study, multi-walled carbon nanotubes (MW-CNTs) with unique mesoporous structures and high pore volumes are selected to replace CB in the air cathode preparation. Due to the larger electrochemically active surface area, superior hydrophobicity, and uniform electroconductibility of MW-CNTs-based cathodes, primary ZABs exhibit high specific capacity (704 mAh gZn-1 ) with a Zn utilization ratio of 85.85% at 1.0mA cm-2 , excellent discharge rate performance, and negligible self-discharge. Furthermore, rechargeable ZABs also demonstrate outstanding rate capability and excellent cycling stability at various current densities. This work provides a fundamental understanding of the criteria for the cathode design of non-alkaline ZABs, thus opening a new pathway for more sustainable ZABs.

Molybdenum-optimized electronic structure and micromorphology to boost zinc ions storage properties of vanadium dioxide nanoflowers as an advanced cathode for aqueous zinc-ion batteries

Recently, vanadium dioxide (VO2) has been recognized as one of the most prospective cathodes for aqueous zinc ion batteries (AZIBs) for its high reversible specific capacity; nevertheless, its Zn2+ diffusion kinetics and cycling stability have not yet met expectations. Herein, Mo ions are introduced into VO2 to optimize the intrinsic electronic structure and micromorphology of VO2, achieving significantly enhanced zinc-ion storage. It is found that the substitution of Mo for V narrows the band gap of VO2 and thus enhances the conductivity of the material, while VO2 nanorods are transformed into VO2 nanoflowers which are self-assembled from ultra-thin nanosheets after the introduction of Mo, exposing much more active sites to enhance the migration kinetics of Zn2+. Consequently, the Mo-substituted VO2 (0.5-Mo-VO2) exhibits excellent electrochemical properties, presenting a high initial capacity of 494.5 mAh/g at 0.5 A/g, excellent rate capability of 336 mA h g−1 at 10 A/g and brilliant cycling stability with the capacity retention of 82% over 2000 cycles at 10 A/g. This work provides significant guidance for the design of advanced cathodes for AZIBs by optimizing the electronic structure and tailoring morphology of V-based materials.

Spontaneously dissolved MnO: A better cathode material for rechargeable aqueous zinc-manganese batteries

Manganese-based oxides (MnOx) cathodes, with profuse crystal structures and valence states, have raised extensive research interstate for aqueous zinc-manganese batteries. However, the lack of a clear reaction mechanism and source of capacity presents significant challenges for the design and development of advanced manganese-based oxide cathodes. Herein, by exploring the electrochemical activation processes and reaction mechanisms of MnOx (including MnO2, Mn2O3, Mn3O4 and MnO), MnO is proved to hold superior potential for zinc-ion batteries cathode application compared to other MnOx owing to its exceptional spontaneous dissolution activation activity and the largest proportion of Mn. Further, to ulteriorly enhance the dissolution activation and poor electronic conductivity of MnO, a porous carbon matrix-encapsulated MnO nanocomposite (MnO@PC) is successfully synthesized. Moreover, the porous carbon matrix could facilitate electrolyte infiltration and promote adsorption towards Mn2+ and Zn2+ cations, leading to more Zn4SO4·(OH)6·xH2O (ZSH) deposition and greater stability of the reversible ZSH-assisted deposition/dissolution reaction. Therefore, MnO@PC can display improved capacity of 269 mAh g-1 (0.1 A g-1) with an exceptional capacity retention of 93% after 120 cycles in pure ZnSO4 electrolyte. And at 2.0 A g-1, the capacity could reach 75 mAh g-1 and be well maintained in 2000 cycles.

Design method and experimental study of a cathode tool with an extremely high leveling ratio for electrochemical machining of blisk

To obtain final parts with the desired dimensional accuracy and repeatability via electrochemical machining (ECM), the machining process must enter an ECM balanced state. However, for the ECM processing of blisk, a key component of aerospace engines, the surface of the blade blank often has an uneven allowance distribution due to the narrow passage of the cascade. It is difficult to remedy this issue in subsequent processing steps, which is necessary to ensure the dimensional accuracy and repeatability of the final blade profile. To solve this problem, electrolytic machining must be preceded by electrolytic shaping, which requires cathode tools with large leveling ratios to quickly homogenize the blank surface of the blade. In this study, to obtain a cathode tool with an extremely high leveling ratio, a design method based on the variation in the electrode gap in the non-equilibrium electrolytic state is proposed, and a dissolution model based on the non-equilibrium state is established. In this design method, the allowance on the blank to be machined is first divided into many discrete allowances with the normal direction. The initial machining clearance, feed rate, and total machining time are then calculated using classical ECM equilibrium state theory based on the maximum allowance. Meanwhile, the point coordinates of the cathode tool at maximum allowance can be determined. The non-equilibrium model can then be used to calculate the relative coordinate positions corresponding to the remaining discrete allowances. Finally, the entire cathode tool profile is designed. Simulations, fundamental experiments, and blisk unit workpiece experiments were carried out to validate the design approach. In the simulated processing of the plane workpiece, the leveling ratio of the cathode tool designed by the proposed method (0.77) was 83% higher than that of the cathode tool designed using the traditional method. The simulation results were confirmed by processing experiments. In the machining of blisk unit workpieces with complex curved surfaces, the leveling ratios of the convex and concave parts of the blade machined using the proposed cathode tool respectively reached 0.75 and 0.54, which are 75% and 38% higher than those obtained using the traditional method. This new cathode design method and machining technology can significantly improve the surface allowance distribution of blank before electrolytic finishing. It is helpful for finishing machine to enter electrolytic equilibrium state. Finally, the final blade profile accuracy can be guaranteed and repeated errors can be reduced.

Rational design of a membrane-coated cathode for selective electrochemical hydrogen evolution in chlorate electrolysis

The industrial chlorate process has traditionally used chromium(VI) as an electrolyte additive for high Faraday efficiency. However, due to its recognized toxicity and carcinogenic properties, the EU has regulated its usage, prompting the need for alternative approaches. In this study, we propose the adoption of a polymeric membrane-coated cathode (MCC) as a straightforward yet highly efficient solution to enhance the selectivity of the hydrogen evolution reaction (HER) in chlorate electrolysis. Proof-of-concept MCCs were fabricated by coating roughened titanium substrates with cation and anion exchange membrane layers, which function as selective barriers for anodic hypochlorite species. The study revealed that a thin membrane coating on the electrode surface effectively suppressed the permeation of anodic intermediates, without compromising the current density for HER. By optimizing the coating layer thickness and substrate surface properties of MCC, the chlorate electrolysis cell demonstrated an impressive Faradaic efficiency of up to 95% at a current density of 150 mA/cm², while maintaining exceptional stability. The outcome of this study can potentially advance the feasibility of industrial chlorate production in meeting regulatory requirements and effectively mitigating environmental consequences.

Research on depth control of machining trace in electrochemical trepanning

Electrochemical trepanning (ECTr) is a highly effective and economic manufacturing technology for machining difficult-to-cut metal materials that are often used in aeroengine components. Integral structural components such as blisks, diffusers, etc. are composed of hubs and blades. In continuous ECTr, machining trace stems from on the hub between adjacent blades. The depth of machining trace significantly influences the surface integrity of the integrated components, even causes the scrapping of the workpiece. In order to solve the problem of machining trace in ECTr, a cathode design method based on the relation between cathode profile and electric field distribution is proposed in this study, the edge of the cathode that affects the machining trace is chamfered. A electric field model of ECTr is established and dynamic electric field simulation of ECTr for cathodes with different chamfered edges is performed. The electric field intensity distribution at the cathode edge and the forming profile of the hub are compared. The simulation results show that optimal chamfering parameters can improve the machining trace. Subsequently, a group of cathodes with different chamfered edge is designed, and corresponding ECTr experiments are conducted. The optimal chamfering parameters are determined (α = 5°, b = 2 mm), the depth of the machining trace is reduced from 0.370 mm to 0.122 mm, the surface flatness is significantly improved. Overall, this depth control method of machining trace is verified effectively.

A sulfur cathode design strategy for polysulfide restrictions and kinetic enhancements in Li-S batteries through oxidative chemical vapor deposition

Lithium-sulfur (Li-S) batteries offer a promising solution for achieving high-density and low-cost energy storage devices. However, the practical utilization of Li-S batteries is hindered by the main bottleneck of polysulfides transport from the cathode to the electrolyte and anode, which leads to the detrimental degradation of the electrolyte and non-uniform microstructure evolution on the anode, ultimately resulting in rapid capacity fading. To overcome this limitation, we propose a groundbreaking mitigation strategy that leverages the oxidative chemical vapor deposition (oCVD) technique to limit the shuttling of polysulfides in the cathode. This gas-phase approach is unique in that highly conducting and conformal polymer coating entirely eliminates the use of traditional binders in the cathode while enhancing the kinetic conditions of the sulfur conversion and inhibiting the shuttling of polysulfides during battery operation. Complementary experimental and theoretical investigations identify that polysulfides are physically and chemically confined in the cathode region. The sulfur cathode manufactured using this approach demonstrates high active material loading (90 wt%), a high sulfur utilization ratio of 84.4% (∼1413 mAh g−1 at 0.1 C), and capacity retention of 85% after 300 cycles (∼810 mAh g−1) at 0.5 C. The pouch cell also showcases a high specific energy of up to 202 Wh kg−1 with a low electrolyte/sulfur ratio of 4.55, proving the immense potential for practical applications.

Synthesis of High-capacity and High-rate Intergrown Cathodes for Lithium-ion Batteries

Nowadays, general energy storage and electric vehicles urgently need to develop advanced lithium-ion batteries (LIB) with high specific energy and low cost, and one of the great challenges is to invent cheap cathode materials. Manganese-based cathode materials have been widely studied due to the low prices and high reserves of precursors, such as lithium-rich manganese-based (LMR) and Mn-based disordered rock-salt (DRX) cathodes. Inspired by the concept of layered-layered intergrown structure in LMR, we design a spinel-rock salt intergrown nano-composite. The as-developed cathode (Li1.7Ni0.12Mn1.48O4) shows a partially intergrown structure of spinel- and DRX-phases. Most importantly, the material enables the combination of the structural and electrochemical merits of the individual spinel and rock-salt phases, and it yields ultrahigh-capacity in comparison with the LMR or DRX and displays outstanding rate performance. It is hoped this novel intergrown cathode with low cost can inspire the design of advanced cathode for LIB.

Construction of high-rate performance sulfurized Poly(acrylonitrile) nanofibers cathodes for practical lithium–sulfur batteries via tellurium catalytic regulation

The rapid charge-discharge and wide operating temperature range are of great significance to the research of lithium-sulfur batteries. However, the poor electronic and ionic conductivity of sulfurized polyacrylonitrile limits the high-rate and low-temperature performance of lithium-sulfur batteries. In this work, a tellurium-doped sulfurized polyacrylonitrile nanofibers-based cathode material (Te0.02S0.98FPAN) is successfully fabricated by air-blow spinning for lithium-sulfur batteries. It is found that Te0.02S0.98FPAN maintained a high reversible specific capacity of 742 mAh·g−1composites after 200 cycles at a current density of 0.2 C (0.014% decay per cycle), whereas it provides a reversible specific capacity of 641 mAh·g−1composites after 500 cycles even at a large current density of 1.0 C (0.021% decay per cycle), manifesting its excellent high-rate performance. Moreover, Te0.02S0.98FPAN still maintained a high reversible specific discharge capacity of 586 mAh·g−1composites after 100 cycles at 0.2 C at a low temperature of 5.0 °C, confirming its wide operating temperature range. Both the eutectic accelerator (tellurium) and the one-dimensional nanofibrous structure greatly improve the migration rate and electron transport ability of Li+ ions, enhancing reaction kinetics and providing fast and stable migration channels for ions and electrons. Therefore, Te0.02S0.98FPAN has a higher oxidation-reduction reaction rate and less polarization. This study not only provides new ideas for the cathode design of lithium-sulfur batteries with high rate and wide temperature range, but also paves the way for the development of practical lithium-sulfur batteries. In particular, when tested in practical conditions of high areal loading (Te0.02S0.98: 5.0 mg cm−2) and lean electrolyte (E/Te0.02S0.98: 10 μL mg−1), this cathode delivers high reversible capacities of 725 mAh g−1 composite (0.1 C) and 663 mAh g−1 composite (0.2 C), demonstrating its great potential for future application.

Optimizing the Composite Cathode Microstructure in All‐Solid‐State Batteries by Structure‐Resolved Simulations

AbstractAll‐solid‐state batteries are considered as an enabler for applications requiring high energy and power density. However, they still fall short of their theoretical potential due to various limitations. One issue is poor charge transport kinetics resulting from both material inherit limitations and non‐optimized design. Therefore, a better understanding of the relevant properties of the cathode microstructure is necessary to improve cell performance. In this article, we identify optimization potentials of the composite cathode by structure‐resolved electrochemical 3D‐simulations. In our simulation study, we investigate the influence of cathode active material fraction, density, particle size, and active material properties on cell performance. Special focus is set on the impact of grain boundaries on the cathode design. Based on our simulation results, we can predict target values for cell manufacturing and reveal promising optimization strategies for an improved cathode design.

Design and Optimization of Composite Cathodes for Solid-State Batteries Using Hybrid Carbon Networks with Facile Electronic and Ionic Percolation Pathways.

Solid-state batteries (SSBs) have emerged as a promising alternative to conventional liquid electrolyte batteries due to their potential for higher energy density and improved safety. However, achieving high performance in SSBs is difficult because of inadequate contact and interfacial reactions that generate high interfacial resistance, as well as inadequate solid-solid contact between electrodes. These chronic issues are associated with inhomogeneous ion and electron transport networks owing to imperfect solid-solid interfacial contact. This study developed an optimal interfacial engineering strategy to facilitate an ion-electron transport network by designing an active material (NCM622) uniformly filled with a thin layer of a solid electrolyte (garnet-type Li6.25Ga0.25La3Zr2O12) and conductive additives. The optimal composite electrode architecture enhanced the high capacity, high rate capability, and long-term cycle stability, even at room temperature, owing to the percolating network for facile ionic conduction that assured a homogeneous reaction. In addition to mitigating the mechanical degradation of the cathode electrode, it also reduced the crosstalk effects on the anode-solid electrolyte interface. Effectively optimizing the selection and use of conductive additives in composite electrodes offers a promising approach to addressing key performance-limiting factors in SSBs, including interfacial resistance and solid-solid contact issues. This study underscores the critical importance of cathode architecture design for achieving high-performance SSBs by ensuring that the interfaces are intact with solid electrolytes at both the cathode and anode interfaces while promoting uniform reactions. This study provides valuable insights into the development of SSBs with improved performance, which could have significant implications for a wide range of applications.

LaB6 hollow cathode with a novel graphite heater

In this study, the design and experimental characterization of a LaB6 hollow cathode utilizing a novel heater made of graphite are presented. Hollow cathodes commonly use heaters where a refractory metal wire is wound around a high temperature ceramic insulator with grooves. These heaters have issues related to thermal fatigue and the recrystalization embrittleness of the heater wire at high temperatures causing the cathode to malfunction, leading to short lifetime. Rather than using refractory metals, a heater made of graphite is designed and integrated into an existing hollow cathode. The graphite can be manufactured easily and does not show any embrittlement at high temperatures, which increases its operational life time. Additionally, due to its lower sputtering yield, undesirable operational conditions are eliminated. A zig-zag shape is used to tailor the geometry to reach desired resistance value of the heater. The presented graphite-heater eliminates these problems as long as enough care is taken in its initial manufacturing and assembly stage. Additionally, the design of the graphite-heater can be modified in such a way to provide heating to a targeted area, which help decrease the required heater power as well as increase the heating speed of the cathode insert material. Successful tests of the hollow cathode with the novel graphite heater indicate long lifetime and steady operation performance, making it suitable for use in real space missions.

Rational Design of Nanostructured MnO2 Cathode for High-performance Aqueous Zinc Ion Batteries

Rational Design of Nanostructured MnO2 Cathode for High-performance Aqueous Zinc Ion Batteries

Eliminating Local Electrolyte Failure Induced by Asynchronous Reaction for High‐Loading and Long‐Lifespan All‐Solid‐State Batteries

AbstractThe design of practical cathodes with high areal capacity in polymer‐based all‐solid‐state batteries remains challenged by the absence of an effective guiding principle that prolongs battery life‐span. Unlike liquid batteries, the notorious interface incompatibility between cathodes and electrolytes limited the cycling life of the all‐solid‐state batteries. Herein, this study proposes a dynamically stable cathode design with a fully covered surface, effectively mitigating interface failure and enabling the cyclic time of batteries with a cathode loading of 12.7 mg cm‒2 over 10 000 h. This study unveils the importance of local state of charge in affecting the interfacial properties of particles through local oxidative‐stability of electrolytes on the interface. This study shows that the phenomena can be strongly influenced by the porosity of the cathode through the perspective of discreteness of ion transport. These insights and approach provide a broader promise for solid batteries for long lifetime.

Design of atomic cobalt selenide-doped sulfurized polyacrylonitrile cathode with enhanced electrochemical kinetics for high performance lithium-SPAN batteries

In this work, sulfurized polyacrylonitrile (SPAN) cathodes with atomically dispersed Co and Se active site, namely cobalt selenide doped-sulfide polyacrylonitrile (CoSe2-x@SPAN, x = 6, 10, 15) with different CoSe2 doping concentrations of 6, 10, and 15 wt%, were fabricated by co-heating approach to strengthen the charge conductivity and catalytic activity of SPAN cathode. Atomic scale CoSe2 were doped into the SPAN skeleton to expediating the redox kinetics of lithium storage process, and the catalytic mechanism was made clear by a viewing angle of frontier molecular orbital theory. The DFT calculation results show that CoSe2@SPAN has a more uniform electrostatic potential distribution with a smaller LUMO-HOMO band gap, which is more conducive to electron transport. The Co/Se loaded SPAN polymer constructed by N-Co-S chemical coordination improves the matching degree between the highest occupied molecular orbital (HOMO) of the nucleophile S2− and the lowest unoccupied molecular orbital (LUMO) of the electrophile Li+ during the discharge process, and effectively reduces the bonding orbital σ level of the deposited product Li2S, thereby promoting the lithium storage kinetics of CoSe2@SPAN cathode material and avoiding the shuttle effect. Meanwhile, the larger Gibbs free energy variation during the lithiation process indicates the enhanced reaction kinetics of the CoSe2@SPAN cathode. Ultimately, The Li-SPAN battery with CoSe2-10@SPAN cathode delivers high reversible capacity of 1475 mAh g−1 at 0.2 A/g, superior rate capability and long-term capacity retention of 71.1% after 500 cycles at 1.0 A/g. Accordingly, this study offers insights into the utilization of frontier molecular orbital theory (FMO) to improve the redox kinetics and sulfur utilization of Li-SPAN batteries.

Intrinsic Descriptor Guided Noble Metal Cathode Design for Li-CO2 Battery.

To date, the effect of noble metal (NM) electronic structures on CO2 reaction activity remains unknown, and explicit screening criteria are still lacking for designing highly efficient catalysts in CO2 -breathing batteries. Herein, by preferentially considering the decomposition of key intermediate Li2 CO3 , an intrinsic descriptor constituted of the orbital states and the electronegativity for predicting high-performance cathode material are discovered. As a demonstration, a series of graphene-supported noble metals (NM@G) as cathodes are fabricated via a fast laser scribing technique. Consistent with the preliminary prediction, Pd@G exhibits an ultralow overpotential (0.41V), along with superior cycling performance up to 1400h. Moreover, the overall thermodynamic reaction pathways on NM@G confirm the reliability of the established intrinsic descriptor. This basic finding of the relationship between the electronic properties of noble metal cathodes and the performance of Li-CO2 batteries provides a novel avenue for designing remarkably efficient cathode materials for metal-CO2 batteries.

Design of composite cathodes for sulfide-based all-solid-state batteries

Design of composite cathodes for sulfide-based all-solid-state batteries

MoSe2 hollow nanospheres with expanded selenide interlayers for high-performance aqueous zinc-ion batteries

Transition metal dichalcogenides (TMDs) as materials for aqueous zinc-ion batteries (ZIBs) have received a lot of interest because of their large theoretical capacity and unique layered structure. However, the sluggish kinetics and inferior cyclic stability limit the usefulness of ZIBs. In the present investigation, the interlayer spacing enlarged MoSe2 hollow nanospheres comprised of nanosheets with ultrathin shells have been successfully synthesized through a combined strategy of template assistance and anion-exchange reaction. The hierarchical ultrathin nanosheets and hollow structure effectively suppress the agglomeration of pure nanosheets and ameliorate volume fluctuations induced by ion migration during (dis)charging/charging. The interlayer expansion provides good channels for the transport of Zn2+ ions and speeds up the insertion/extraction of Zn2+. In addition, in-situ carbon modification can significantly improve electronic conductivity. Therefore, the electrode prepared from MoSe2 hollow nanospheres with enlarged interlayer spacing not only exhibits outstanding cycle stability (capacity retention of 94.5% after 1600 cycles) but also exhibits high-rate capability (266.1 mA h g−1 at 0.1 A g−1 and 203.6 mA h g−1 at 3 A g−1). This work could provide new insights into the design of cathode using TMDs of hollow structure for Zn2+ storage.

Examination of the Potential Effect of Corrosion Current Density of Ship Hulls on the Sacrificial Anode Cathodic Protection

In this study, the sacrificial anode cathodic protection system, which is one of the electrical protection methods in the prevention of corrosion in ships, was examined. Within the scope of the study, the potential effects of corrosion current density, which is an important parameter for cathodic protection design, were studied. The study includes cathodic protection calculations for a bulker with a protected hull area of 9406 m2 and a general cargo ship with a protected hull area of 1770 m2. As a result, it was estimated that each 1 mA/m2 change in the electric current density parameter changes the anode usage amount by 64 kg in bulker and 12 kg in general cargo, depending on the reference parameters such as protected hull area, anode type, and design life. It can be stated that the evaluation of the corrosion current density parameter, taking into account the operating conditions of each ship, will be beneficial in terms of optimizing the sacrificial anode consumption.